SYSTEMS AND METHODS FOR STORAGE AND SUPPLY OF F3NO-FREE FNO GASES AND F3NO-FREE FNO GAS MIXTURES FOR SEMICONDUCTOR PROCESSES

Abstract

A method for storage and supply of a F3NO-free FNO-containing gas comprises the steps of storing the F3NO-free FNO-containing gas in a NiP coated steel cylinder with a polished inner surface, releasing the F3NO-free FNO-containing gas from the cylinder to a manifold assembly by activating a cylinder valve in fluid communication with the cylinder and the manifold assembly, de-pressurizing the F3NO-free FNO-containing gas by activating a pressure regulator in the manifold assembly so as to divide the manifold assembly into a first pressure zone upstream of the pressure regulator and a second pressure zone downstream of the pressure regulator, and feeding the de-pressurized F3NO-free FNO-containing gas to a target reactor downstream of the second pressure zone.

Claims

1. A method for storage and supply of a F.sub.3NO-free FNO-containing gas, the method comprising the steps of: storing the F.sub.3NO-free FNO-containing gas in a NiP coated steel cylinder with a polished inner surface; releasing the F.sub.3NO-free FNO-containing gas from the cylinder to a manifold assembly by activating a cylinder valve in fluid communication with the cylinder and the manifold assembly; de-pressurizing the F.sub.3NO-free FNO-containing gas by activating a pressure regulator in the manifold assembly so as to divide the manifold assembly into a first pressure zone upstream of the pressure regulator and a second pressure zone downstream of the pressure regulator; and feeding the de-pressurized F.sub.3NO-free FNO-containing gas to a target reactor downstream of the second pressure zone.

2. The method of claim 1, further comprising the step of producing F.sub.3NO-free FNO contained in the F.sub.3NO-free FNO-containing gas by mixing NO and F.sub.2 gases at a ratio of F.sub.2 gas to NO gas less than or equal to ½ and a purity of NO gas at least 99.9% by volume, wherein the produced F.sub.3NO-free FNO contains less than approximately 1% F.sub.3NO by volume.

3. The method of claim 2, wherein the F.sub.3NO-free FNO-containing gas is a gas mixture of F.sub.3NO-free FNO gas, F.sub.2 and N.sub.2 for etch films produced by the steps of mixing the produced F.sub.3NO-free FNO gas with an additional amount of F.sub.2 to produce the gas mixture of the F.sub.3NO-free FNO gas and F.sub.2; and diluting the gas mixture of the F.sub.3NO-free FNO gas and F.sub.2 in N.sub.2 to form the gas mixture of F.sub.3NO-free FNO gas, F.sub.2 and N.sub.2.

4. The method of claim 1, further comprising the step of passivating the manifold assembly with F.sub.2 or FNO.

5. The method of claim 1, wherein the cylinder valve, the pressure regulator and line components in the first pressure zone are made of nickel containing material having at least 14% nickel by weight.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0209] For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

[0210] FIG. 1, reproduced from Yonemura et al., represents the etch rates as a function of gas concentration for FNO/Ar, F.sub.3NO/Ar, NF.sub.3/Ar and C.sub.2F.sub.6/O.sub.2;

[0211] FIG. 2 is a diagram of an exemplary packaging of F.sub.3NO-free FNO gas and/or F.sub.3NO-free FNO gas mixture from a cylinder to a semiconductor application chamber;

[0212] FIG. 3(a) is an order of mixing F.sub.2, NO and N.sub.2 to produce FNO in N.sub.2;

[0213] FIG. 3(b) is another order of mixing F.sub.2, NO and N.sub.2 to produce FNO in N.sub.2;

[0214] FIG. 3(c) is another order of mixing F.sub.2, NO and N.sub.2 to produce FNO in N.sub.2;

[0215] FIG. 3(d) is another order of mixing F.sub.2, NO and N.sub.2 to produce FNO in N.sub.2;

[0216] FIG. 4 is a comparison of FT-IR spectra of F.sub.3NO impurity in 30% FNO in N.sub.2 produced from on-site synthesis under stoichiometric condition versus 30% FNO in N.sub.2 produced from on-site synthesis under F.sub.2-rich condition;

[0217] FIG. 5(a) is an order of mixing F.sub.2, NO and N.sub.2 to produce a gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2;

[0218] FIG. 5(b) is another order of mixing F.sub.2, NO and N.sub.2 to produce F.sub.3NO-free FNO/F.sub.2/N.sub.2 gas mixture;

[0219] FIG. 5(c) is another order of mixing F.sub.2, NO and N.sub.2 to produce a gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2;

[0220] FIG. 5(d) is another order of mixing F.sub.2, NO and N.sub.2 to produce a gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2;

[0221] FIG. 6 is a data set of F.sub.3NO formations with 1.sup.st F.sub.2 feeding amount (%) versus total amount of F.sub.2;

[0222] FIG. 7 is a data set of F.sub.3NO formations with 1.sup.st N.sub.2 feeding amount (%) versus total amount of N.sub.2.

[0223] FIG. 8 is FTIR signals and etch rates after SiN etched with FNO and F.sub.2 gas mixture with different F.sub.2 mixing orders;

[0224] FIG. 9 is F.sub.3NO formation with different N.sub.2 mixing orders;

[0225] FIG. 10 is FTIR signals and etch rates versus FNO concentrations;

[0226] FIG. 11 is FTIR signals and etch rates versus etch time;

[0227] FIG. 12 is FTIR results of monitoring of different compositions; and

[0228] FIG. 13 is results of monitoring of etching performance.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0229] Disclosed are systems and methods for storing and supplying F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures, such as FNO/F.sub.2, FNO/F.sub.2/N.sub.2, for using as thermal and/or plasma dry etching gases to etch semiconductor structures. Disclosed are also systems and methods for thermally and/or plasma dry etching semiconductor structures using F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures. Furthermore, disclosed are methods for producing F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures for using as thermal etching gases to etch semiconductor structures. The disclosed methods for producing F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures may provide a purity of F.sub.3NO-free FNO gas of 99% or greater, and an impurity of F.sub.3NO less than 1%.

[0230] FNO (nitrosyl fluoride. CAS number: 7789-25-5, boiling point: −72.4° C. (−98.3 F)) and/or a mixture of FNO with other etching gases, such as F.sub.2, HF, cC.sub.4F.sub.8, C.sub.4F.sub.6, CF.sub.4, CHF.sub.3, CF.sub.3H, CH.sub.2F.sub.2, COS, CS.sub.2, CF.sub.3I, C.sub.2F.sub.3I, C.sub.2F.sub.5I, SO.sub.2, and the like, may be used as highly reactive fluorinating thermal etching gases. Applicant discovered that FNO gas used for thermally etching the semiconductor structures should contain less to no F.sub.3NO (trifluoroamine oxide, CAS number: 13847-65-9, boiling point: −87.6° C.) impurity. Thus, the disclosed F.sub.3NO-free FNO gas contains less to no F.sub.3NO impurity, which refers to F.sub.3NO-free FNO gas. F.sub.3NO-free herein refers to a gas having F.sub.3NO impurity less than 1%. F.sub.3NO-free may also refer to F.sub.3NO-less having the same definition as F.sub.3NO-free. In semiconductor applications, FNO may be diluted in an inert gas, such as N.sub.2, Ar, He, Ne, Kr, Xe, or mixtures thereof, to obtain a concertation of FNO as needed. The FNO gas mixture FNO/F.sub.2/N.sub.2 is one of exemplary FNO gas mixtures. When F.sub.3NO-free FNO diluted in the inert gas, the F.sub.3NO impurity in the mixture is even less than 1%. For instance, 15% FNO in a gas mixture of F.sub.3NO-free FNO and N.sub.2 may have F.sub.3NO impurity less than 0.15%.

[0231] In semiconductor applications, FNO gas may be pre-synthesized for use as an etchant or produced in situ or in close proximity to where it is used to etch semiconductor structures. Regarding the pre-synthesized FNO gas, a purity of 99%.sup.+ FNO may be obtained and F.sub.3NO impurity exists in FNO is less than 1% taking into account that other impurities may exist in FNO gas.

[0232] It is known that mixing F.sub.2 and NO in situ produces FNO. However, using F.sub.2 and NO as starting materials to produce FNO may generate other products such as, F.sub.3NO, FNO.sub.2, NF.sub.3, N.sub.2O, NO.sub.2, etc., as byproducts existing in the product FNO. The reactions involved in mixing NO and F.sub.2 may include the following reactions.

2NO+F.sub.2.fwdarw.2FNO

2NO+3F.sub.2.fwdarw.2F.sub.3NO

FNO+F.sub.2.fwdarw.F.sub.3NO

N.sub.2O+2F.sub.2.fwdarw.NF.sub.3+FNO

N.sub.2O and NO.sub.2 may exist in the starting material NO as impurity.

[0233] Thus, when F.sub.2 is mixed with NO forming a gas mixture of F.sub.2 and NO in situ at the time it is used in an etching process, besides forming the desired FNO etching gas, oxyfluorides of nitrogen containing a grouping F—N—O, such as F.sub.3NO, may also be formed as impurity in the gas mixture of F.sub.2 and NO. Applicant found that F.sub.3NO does exist in the mixture of F.sub.2 and NO when producing FNO by mixing F.sub.2 and NO if a ratio of F.sub.2 to NO is very well controlled.

[0234] To our knowledge, so far no existing work has been mentioning the presence of F.sub.3NO as impurity in either pre-synthesized FNO gas and/or in the FNO product produced in situ, such as produced by mixing F.sub.2 and NO gas in situ. Since F.sub.3NO has higher reactivity against Si-containing materials than FNO as shown in FIG. 1, for etching semiconductor structures, the produced etching gas FNO should be free of F.sub.3NO. F.sub.3NO existing in FNO etching compositions may have detrimental effects to etching processes such as, particles formed on the substrate and cracks occurring in the substrate, which may be seen in the examples that follow. F.sub.3NO existing in FNO etching compositions may also influence etching performance, such as selectivity and etch rate controllability. Thus, a control of F.sub.3NO formation in producing FNO is required in order to perform a precise etching process in semiconductor industry. To this point, FNO used as an etching compound has to be in high purity, with minimal F.sub.3NO levels.

[0235] In semiconductor applications, oxyfluorides of nitrogen, i.e. compounds containing the grouping F—N—O, such as FNO, FNO.sub.2 and F.sub.3NO, may be corrosive to etching gas containers and pipelines, etching chambers, substrates to be etched, etc., which may lower the semiconductor device performance. In addition, materials made of containers, pipelines and components along the pipelines for storage and delivery of FNO-containing gas to an etching chamber and materials made of the etching chamber have to be compatible with FNO. This means no corrosions and no reactions occur between FNO and the above materials that could cause contaminations to the etching gases and the substrate to be etched. When FNO is produced from the precursors/starting materials (e.g., NO and F.sub.2) at the time it is used as an etching gas, the precursors may also create different storage and handling problems from the product FNO. As a result, when producing FNO, material compatibilities between starting materials (e.g., F.sub.2 and NO) and even FNO itself and a container (e.g., cylinder), valves, manifolds and a reaction chamber along with etching performance degradation thereof with short-term or long-term use have been concerned.

[0236] Material compatibility tests are important to determine if any component of the disclosed F.sub.3NO-free FNO and F.sub.3NO-free FNO gas mixtures will react with materials of the container (e.g., cylinder), valves, manifolds and chamber and if any component of the disclosed F.sub.3NO-free FNO and F.sub.3NO-free FNO gas mixtures will degrade the etching performance thereof with short term or long-term use. Material compatibility refers to a material's resistance to corrosion, rust or stains when it comes in contact with a chemical, such as F.sub.2, NO, FNO, F.sub.3NO, etc. At times the materials made of the container (e.g., cylinder), valves, manifolds and chamber are exposed to these chemicals at high temperatures, for example, higher than 20° C., and high pressures, for example, higher than 1 atm, for thermal etching, which may enhance their degradation.

[0237] The disclosed methods for producing F.sub.3NO-free FNO gas include mixing the starting materials F.sub.2 and NO by controlling mixing ratios of F.sub.2 and NO. In order to obtain various concentrations of F.sub.3NO-free FNO gas, an inert gas, such as N.sub.2, Ar, Kr and Xe, preferably N.sub.2, may be added to dilute the produced F.sub.3NO-free FNO gas to a target concentration of F.sub.3NO-free FNO gas. In addition, adding an inert gas helps reduce F.sub.3NO formation in the process of producing F.sub.3NO-free FNO gas in situ referring to the Examples that follow. With the disclosed mixing methods, the formation of F.sub.3NO during the reaction between F.sub.2 and NO may be restrained. To our knowledge, the disclosed mixing methods (i.e., mixing ratio) have not been found in the prior art for producing FNO with F.sub.2 and NO. It is known a direct reaction between F.sub.2 and NO is disclosed as the simplest method to produce FNO. However, there is no past work mentioning F.sub.3NO as impurity in FNO, while Applicant discovered the presence of F.sub.3NO from the reaction between F.sub.2 and NO is detrimental to the use of FNO gas in various etching processes. Applicant also discovered the mixing methods of F.sub.2 and NO with or without N.sub.2 in order to control F.sub.3NO amount in the mixture to produce F.sub.3NO-free FNO gas. This is beneficial for producing FNO gas with precise F.sub.3NO impurity control.

[0238] The disclosed methods for producing F.sub.3NO-free FNO gas mixtures include mixing the starting materials F.sub.2 and NO by controlling mixing ratios of F.sub.2 and NO and then mixing with an addition gas by controlling mixing order of F.sub.2, NO and the additional gas. The additional gas may be selected from the group consisting of F.sub.2, HF, cC.sub.4F.sub.8, C.sub.4F.sub.8, C.sub.4F.sub.6, C.sub.5F.sub.8, CF.sub.4, CH.sub.3F, CF.sub.3H, CH.sub.2F.sub.2, COS, CS.sub.2, CF.sub.3I, C.sub.2F.sub.3I, C.sub.2F.sub.5I, CFN, SO.sub.2, NO, O.sub.2, CO.sub.2, CO, NO.sub.2, N.sub.2O, O.sub.3, Cl.sub.2, H.sub.2, HBr, and combination thereof. Preferably, the additional gas is F.sub.2. In order to obtain various concentrations of F.sub.3NO-free FNO gas in the F.sub.3NO-free FNO gas mixture, an inert gas, such as N.sub.2, Ar, Kr and Xe, preferably N.sub.2, may be added to dilute the produced F.sub.3NO-free FNO gas mixture to a target concentration of F.sub.3NO-free FNO gas. Similarly, adding an inert gas helps reduce F.sub.3NO formation in the process of producing F.sub.3NO-free FNO gas mixture in situ referring to the Examples that follow. With the disclosed mixing methods, the formation of F.sub.3NO during the reaction between F.sub.2, NO and the additional gas may be restrained. To our knowledge, the disclosed mixing methods (i.e., controlling mixing ratio and controlling mixing order) have not been found in the prior art for producing FNO gas and FNO gas mixture with F.sub.2 and NO. Applicant discovered the mixing methods of F.sub.2, NO and additional gas with or without N.sub.2 in order to control F.sub.3NO amount in the mixture to produce F.sub.3NO-free FNO gas mixture. This is beneficial for producing FNO-containing gas mixture with precise F.sub.3NO impurity control.

[0239] The disclosed mixing methods provide processes to suppress the formation of F.sub.3NO impurity when F.sub.2 is mixed with NO in situ. The disclosed mixing methods for producing F.sub.3NO-free FNO from F.sub.2 and NO include a step of mixing F.sub.2 and NO at a ratio F.sub.2/NO equal to or less than stoichiometric condition (F.sub.2/NO≤½). In this way, the formation of F.sub.3NO impurity in the produced F.sub.3NO-free FNO may be suppressed. The produced F.sub.3NO-free FNO may be further diluted in an inert gas, such as N.sub.2, Ar, Kr and Xe, preferably N.sub.2, to form different concentrations of F.sub.3NO-free FNO in N.sub.2 according to application requirements.

[0240] The disclosed mixing methods for producing F.sub.3NO-free FNO gas mixture (e.g., FNO/F.sub.2) from F.sub.2 and NO include a two-step of F.sub.2 mixing process. In the first step, F.sub.2 and NO are mixed equal to or less than stoichiometric condition (F.sub.2/NO≤½) to produce F.sub.3NO-free FNO gas. In the second step additional F.sub.2 is added to the produced F.sub.3NO-free FNO gas to produce F.sub.3NO-free FNO and F.sub.2 gas mixture. In this way, the formation of F.sub.3NO impurity in the produced F.sub.3NO-free FNO and F.sub.2 gas mixture may be suppressed. The produced F.sub.3NO-free FNO and F.sub.2 gas mixture may be further diluted in an inert gas, such as N.sub.2, Ar, Kr and Xe, preferably N.sub.2, to form different concentrations of F.sub.3NO-free FNO and F.sub.2 in N.sub.2 depending on application requirements.

[0241] NO gas is not stable and may contain a trace gas impurities of nitrogen oxygen compounds, such as NO.sub.2, N.sub.2O, or the like, resulting from instability. Once NO mixed with F.sub.2, the trace gas impurities may react with F.sub.2 to eventually produce F.sub.3NO in the product of FNO, as shown in the following reaction: F.sub.2+NO.sub.2.fwdarw.F.sub.3NO or F.sub.2+N.sub.2O.fwdarw.F.sub.3NO. Therefore, it is highly preferable to use high purity NO designed for low impurities like N.sub.2O and NO.sub.2. In order to suppress the formation of F.sub.3NO, NO gas used herein to produce FNO should be pure as pure as feasible. Preferably, the purity of NO is provided at between approximately 99.9% by volume and approximately 100.0% by volume, more preferably between approximately 99.99% by volume and approximately 100.00% by volume, and even more preferably between approximately 99.999% by volume and approximately 100.000% by volume. In addition, NO gas may contain between approximately 0.0% by volume and approximately 0.1% by volume trace gas impurities with between approximately 0 ppm by volume to approximately 600 ppm by volume of N—O containing gases other than NO gas, such as NO.sub.2, N.sub.2O, or the like, contained in said trace gaseous impurities.

[0242] since the disclosed mixing methods are capable of suppressing the formation of F.sub.3NO, the impurity F.sub.3NO in FNO may not impact the etching performance when using the disclosed F.sub.3NO-free FNO gas as thermal and/or plasma dry etching gas.

[0243] The disclosed systems and methods also include systems and methods for storage and delivery of F.sub.3NO-free FNO gas and/or F.sub.3NO-free FNO gas mixture through using compatible materials between FNO and containers, manifolds, pipelines, etching chambers, etc.

[0244] The disclosed method for storage and delivery of F.sub.3NO-free FNO and/or F.sub.3NO-free FNO diluted in an inert gas, such as N.sub.2, Ar, Kr and Xe, preferably N.sub.2, include storing a corrosive gas F.sub.3NO-free FNO or F.sub.3NO-free FNO/N.sub.2 mixture in a steel cylinder made of alloy 4130X with NiP coated inner surface, and delivering the corrosive gas F.sub.3NO-free FNO or F.sub.3NO-free FNO/N.sub.2 mixture to an application reactor through a manifold assembly. An internal surface of the steel cylinder made of alloy 4130X is coated with nickel plating, and the inner surface of the nickel plating is polished so as to have smooth surface resulting in low moisture content. Hereinafter, the steel cylinder made of alloy 4130X with an inner surface coating of nickel plating with polished inner surface of the nickel plating refers to the NiP coated steel cylinder.

[0245] A cylinder valve in fluidly communication with the cylinder and the manifold assembly is made of nickel or nickel alloy. Due to a pressure difference between the cylinder and the application reactor, the manifold assembly is divided into a high-pressure zone in fluidly communication with the cylinder valve and a low-pressure zone in fluidly communication with the application chamber by a pressure regulator or a pressure reducing device. The manifold assembly is not limited to be divided into two pressure zones. The manifold assembly may be divided into multiple pressure zones each having different reduced pressures. Thus, with the multiple pressure zones, the manifold assembly is able to deliver the gas to different reaction chambers each requiring a different reduced pressure.

[0246] The pressure of the corrosive gas F.sub.3NO-free FNO or F.sub.3NO-free FNO/N.sub.2 mixture is reduced by the pressure regulator before entering the low-pressure zone. Line components in the high-pressure zone may be composed of high nickel content material. Line components in the low-pressure zone may be composed of low nickel content material, metal or metal alloy. The line components in the high and low-pressure zones include gas filters, pressure sensors, gas valves, mass flow controllers (MFCs), pipes, etc. The high nickel content material refers to nickel alloys that contains at least 14% nickel by weight. For example, MONEL®, INCONEL® or HASTELLOY® C-22® alloy. The low nickel content material refers to a material contains less than 14% nickel by weight or contains no nickel. For example, stainless steel. In this way, F.sub.3NO impurity and degradation of the equipment may be reduced. The NiP coated steel cylinder may be, but is not limited to, in a size ranging from 0.5 L to 49L NiP coated steel cylinder. The cylinder valve may be a Ceodeux D306 Ni body Ni diaphragm. The cylinder valve may be made of HASTELLOY® C-22® alloy, MONEL®, INCONEL®, pure nickel, or any other high nickel content materials.

[0247] The high-pressure zone of the manifold assembly may have a pressure ranging from approximately 0.8 MPa to approximately 10 MPa, more preferably, approximately 0.8 to approximately 3.5 MPa. The low-pressure zone of the manifold assembly may have a pressure ranging from approximately 0.1 MPa to approximately 0.8 MPa. The manifold assembly includes the following line components: the pressure regulator, pressure sensors, valves, gas filters, piping, etc. in the two pressure zones. The line components in the high-pressure zone may be composed of high nickel content materials, such as, MONEL®, INCONEL® or HASTELLOY® C-22® alloy. The high nickel content material may contains at least 14% nickel. Typically, any material that contains 14% or higher nickel may be used to make of the line components in the high-pressure zone, however, Fe-containing alloy, such as stainless steel (SS), may not be used. Whereas, in the low-pressure zone the line components may be composed of low nickel content material that contains less than 14% nickel by weight or contains no nickel. The line components in the low-pressure zone may also be made of any metal or any mental alloy, including high nickel content materials. The line components in the low-pressure zone may be made of stainless steel.

[0248] The following are exemplary embodiments of the disclosed storage and delivery systems for delivery of the disclosed F.sub.3NO-free FNO gas and/or F.sub.3NO-free FNO gas mixture into a target application reactor (e.g., an etching chamber for etching or a deposition chamber for cleaning) in which material compatibilities are considered.

[0249] In one embodiment, a packaging of F.sub.3NO-free FNO gas from a cylinder to a semiconductor application, e.g., an etching chamber, is shown in FIG. 2. The packaging includes a manifold 101 that contains two pressure zones, one is a high-pressure zone 102, the other is a low-pressure zone 104. The pressure in the pressure zone 102 is higher than that in the pressure zone 104. The pressure range in the pressure zone 102 is approximately from 0.8 MPa to 10 MPa. The pressure range in the pressure zone 104 is approximately from 0.1 MPa to 0.8 MPa. In one exemplary embodiment, the pressure in the pressure zone 102 is 0.99 MPa; the pressure in the pressure zone 104 is 0.5 MPa. A cylinder 106 that contains a pressurized etching gas F.sub.3NO-free FNO (e.g., from 0.8 MPa to 3.5 MPa) is fluidly connected to the pressure zone 102 through a cylinder valve 108. The F.sub.3NO-free FNO gas stored in cylinder 106 may be synthesized using F.sub.2 and NO as starting materials or may be a pre-synthesized FNO. The F.sub.3NO-free FNO gas stored in the cylinder 106 has a purity of 99%. Alternatively, the F.sub.3NO-free FNO gas stored in the cylinder 106 may be diluted in an inert gas (N.sub.2, Ar, Kr and Xe), for example, diluted in N.sub.2 gas, forming a mixture of F.sub.3NO-free FNO and N.sub.2. The cylinder 106 is a carbon steel cylinder made of alloy 4130X with an internal surface coating of nickel plating and a polished coating surface (i.e., NiP coated steel cylinder). The internal surface of coated nickel plating is important because a smooth surface may reduce contamination of moisture from air. A cylinder valve 108 controls the etching gas F.sub.3NO-free FNO to be delivered from the pressure zone 102 to the pressure zone 104 through a pipeline 110, where a valve 112, a pressure sensor 114 and a pressure regulator 116 are fluidly connected to the pipeline 110. The pressure sensor 114 reads the pressure in the pressure zone 102. An inert gas (e.g., N.sub.2) may be added to the F.sub.3NO-free FNO gas in the pressure zone 102 to produce a diluted F.sub.3NO-free FNO gas. For example, N.sub.2 gas is added to the flow of F.sub.3NO-free FNO gas through a valve 118 in the pressure zone 102 forming a mixture of F.sub.3NO-free FNO with N.sub.2 therein. If the cylinder 106 contains already diluted F.sub.3NO-free FNO gas (e.g., 50% FNO in N.sub.2), N.sub.2 gas added to the flow of the already diluted F.sub.3NO-free FNO gas through a valve 118 in the pressure zone 102 will have the already diluted F.sub.3NO-free FNO gas further diluted. In this way, the concentration of F.sub.3NO-free FNO gas may be adjusted depending on application requirements. The pressure regulator 116 reduces the pressure of the gas mixture of F.sub.3NO-free FNO and N.sub.2 before the gas mixture of F.sub.3NO-free FNO with N.sub.2 enters the pressure zone 104. A pressure sensor 120 reads the pressure in the pressure zone 104. The gas mixture of F.sub.3NO-free FNO and N.sub.2 from the pressure zone 102 is then de-pressurized and forwarded to a mass flow controller 126 in the pressure zone 104 through a pipeline 130. The mass flow controller 126 controls a flow rate of the gas mixture of F.sub.3NO-free FNO and N.sub.2 fed to an etching chamber 128 for an etching process. Valves 122 and 124 may be installed downstream and upstream of the mass flow controller 126.

[0250] Key materials involved in the cylinder, valves, manifolds, the chamber etc., shown in FIG. 2, include high nickel content materials including NiP coated steel, nickel, nickel alloys, and low nickel content materials including stainless steel. The F.sub.3NO-free FNO gas was filled in the cylinder 106 within a pressure range between approximately 0.8 to approximately 10 MPa. The cylinder 106 may be a vessel, cylinder or any pressure container (pressure range 0.1 MPa to 10 MPa). The cylinder 106 with high nickel content valve 108 is in fluidly communication with the manifold 101 including delivery line components, such as, pressure regulator, pressure sensors, valves, gas filters piping, etc., which are fluidly connected to the etching chamber 128. The cylinder 106 contains FNO gas having a purity of 99%. The cylinder 106 made of NiP coated steel. The cylinder 106 is a carbon steel cylinder made of alloy 4130X with an internal surface coating of nickel plating and the internal surface of the nickel plating is polished.

[0251] The cylinder valve 108 may be an alloy having nickel content >14%, preferably the cylinder valve 108 is HASTELLOY® or other nickel alloys. In one exemplary embodiment, the cylinder valve 108 may specifically use HASTELLOY® materials, in which metal impurities (such as Fe, Ni, Cr, Mn) are less than 1 ng/mL. High pressure FNO or FNO/N.sub.2 mixture is more corrosive than low-pressure one. Thus, the high pressure FNO/N.sub.2 mixture in a special package is designed to have a NiP coated steel cylinder 106 communicate with a nickel alloy manifold 101 up to the pressure regulator 116, where the pressure regulator 116 is applied to reduce the pressure. In this way, the depressurized FNO/N.sub.2 mixture is less corrosive down the low-pressure zone 104 and the etching chamber 128. With this setup, the cylinder valve 108 composed of nickel was found to have less corrosion/powder formation. The cylinder 106 composed of NiP coated steel has very smooth surface and lower moisture.

[0252] The packaging shown in FIG. 2 may also be used to store and deliver F.sub.3NO-free FNO gas mixture formed by mixing F.sub.3NO-free FNO gas with an additional etching gas, such as F.sub.2. In this case, the F.sub.3NO-free FNO gas mixture is F.sub.3NO-free FNO and F.sub.2.

[0253] The disclosed systems for storage and delivery of F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixture (e.g., a gas mixture of F.sub.3NO-free FNO and F.sub.2) include a passivation process with the cylinder 106, the cylinder valve 108, the low-pressure zone 104 of manifold assembly 101 to reduce metal impurities delivery into the etching chamber 128. The passivation process may be done with FNO gas or F.sub.2 gas. In the high-pressure zone 102, a passivation process for the line components may or may not work due to the high pressure. Thus, high nickel content materials are applicable for making of the line components in the high-pressure zone. In the low-pressure zone 104, a passivation process may apply.

[0254] The disclosed systems and methods also include systems and methods of etching semiconductor structures using the disclosed F.sub.3NO-free FNO gas and/or F.sub.3NO-free FNO gas mixtures. The disclosed etching systems and methods include thermal etching, plasma dry etching including ALE (atomic layer etching), or the like. The disclosed F.sub.3NO-free FNO gas and/or F.sub.3NO-free FNO gas mixtures are applied to thermal and plasma dry etching processes. The disclosed F.sub.3NO-free FNO gas may be used as etching gas alone (pure) or diluted in an inert gas, for example, N.sub.2, Ar, He, Xe, etc. The concentration of the diluted F.sub.3NO-free FNO may be less than 15%, preferably less than 10%, more preferably less than 5%, even more preferably less than 1%. In one embodiment, the concentration of the diluted F.sub.3NO-free FNO may be diluted to 0.01%. The disclosed F.sub.3NO-free FNO gas may also be used as etching gas mixed with an additional etching gas, such as, F.sub.2, HF, cC.sub.4F.sub.8, C.sub.4F.sub.6, C.sub.4F.sub.8, C.sub.5F.sub.8, CF.sub.4, CH.sub.3F, CF.sub.3H, CH.sub.2F.sub.2, COS, CS.sub.2, CF.sub.3I, C.sub.2F.sub.3I, C.sub.2F.sub.5I, CFN, SO.sub.2, NO, O.sub.2, CO.sub.2, CO, NO.sub.2, N.sub.2O, O.sub.3, Cl.sub.2, H.sub.2, HBr, and combination thereof. Preferably, the disclosed F.sub.3NO-free FNO gas is used as etching gas mixed with F.sub.2.

[0255] Exemplary other gases include, without limitation, oxidizers such as O.sub.2, O.sub.3, CO, CO.sub.2, COS, NO, N.sub.2O, NO.sub.2, SO.sub.2, and combinations thereof. The disclosed etching gases and the oxidizer may be mixed together prior to introduction into the reaction chamber or the etching chamber.

[0256] Alternatively, the oxidizer may be introduced continuously into the reaction chamber and the etching gas introduced into the reaction chamber in pulses. Alternatively, both the oxidizer and the etching gas may be introduced continuously into the reaction chamber. The oxidizer may comprise between approximately 0.01% by volume to approximately 99.99% by volume of the mixture introduced into the chamber (with 99.99% by volume representing introduction of almost pure oxidizer for the continuous introduction alternative).

[0257] In one embodiment, the disclosed F.sub.3NO-free FNO gas diluted in N.sub.2 (i.e., FNO/N.sub.2) and mixed with an additional etching gas F.sub.2 (i.e., FNO/N.sub.2/F.sub.2 mixture). The disclosed F.sub.3NO-free FNO gas mixtures FNO/N.sub.2/F.sub.2 may comprise greater than 10% by volume of FNO, preferably greater than 15% by volume FNO.

[0258] The disclosed F.sub.3NO-free FNO etching gas and the additional gas (e.g., F.sub.2) may be mixed prior to introduction to the reaction chamber. The additional etching gas may comprise between approximately 0.01% by volume to approximately 99.99% by volume of the mixture introduced into the chamber.

[0259] The disclosed F.sub.3NO-free FNO gas are provided at equal to or greater than 99% v/v by volume purity, preferably at greater than 99.99% v/v by volume purity, and more preferably at greater than 99.999% v/v by volume purity. The disclosed F.sub.3NO-free FNO gas contain equal to or less than 1% by volume trace gas impurities, with less than 150 ppm by volume of impurity gases, such as H.sub.2O, NO.sub.2, N.sub.2O and/or CO.sub.2, contained in said trace gas impurities. Preferably, the water content in the disclosed F.sub.3NO-free FNO gas is less than 20 ppm by weight.

[0260] The disclosed F.sub.3NO-free FNO gas contains less than 1% by volume, preferably less than 0.1% by volume, more preferably less than 0.01% by volume of F.sub.3NO, which may provide precise etching performance and better process repeatability.

[0261] The disclosed F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures may be used to thermal etch or plasma dry etch silicon-containing films, such as SiN film, capped on top of a semiconductor structure, such as, a 3D NAND flash memory or a DRAM memory. The disclosed F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures may also be used to thermal etch or plasma dry etch silicon-containing films on a substrate, such as, SiN layer. The disclosed thermal etching or plasma dry etching method may be useful in the manufacture of semiconductor devices such as NAND or 3D NAND gates or Flash or DRAM memory or transistors such as fin-shaped field-effect transistor (FinFET), Lateral Gate-All-Around (LGAA) devices and Vertical Gate-All-Around (VGAA) devices, Bulk complementary metal-oxide-semiconductor (Bulk CMOS), fully depleted silicon-on-insulator (FD-SOI) structures, Monolithich 3D (M3D). The disclosed F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures may be used in other areas of applications, such as different front end of the line (FEOL) and back end of the line (BEOL) etch applications and low k applications as well. Additionally, the disclosed F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures may also be used for etching Si in 3D through silicon aperture (TSV) etch applications for interconnecting memory to logic on a substrate. The disclosed F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures may be used to remove a layer of deposits or a film formed on the inner surface of a deposition chamber after a deposition process. Such a process refers to a cleaning process after deposition.

[0262] The disclosed etching method includes providing a reaction chamber having a substrate having a film disposed thereon or deposits (or film) on the internal surface of the chamber wall. The reaction chamber may be any enclosure or chamber within a device in which etching methods take place such as, and without limitation, any chambers or enclosures used for plasma etching, such as, reactive ion etching (RIE), capacitively coupled plasma (CCP) with single or multiple frequency RF sources, inductively coupled plasma (ICP), Electron Cyclotron Resonance (ECR) or microwave plasma reactors, or other types of etching systems capable of selectively removing a portion of the silicon-containing film. The chamber can be also a chamber for deposition process with one or more gas inlet for different precursors. The chamber for deposition usually has controllable temperature on the substrate holder and maybe a buffer chamber between reaction chamber and gas inlet. The pressure of chamber is controlled by pump system. Suitable pre-synthesized reaction chambers include but are not limited to the Applied Materials magnetically enhanced reactive ion etcher sold at the trademark eMAX™, the Lam Research CCP reactive ion etcher dielectric etch product family sold at the trademark 2300® Flex™ or Tokyo Electron deposition systems sold at the trademarks INDY™, INDY PLUS™ and NT333™. The reaction chamber may be heated to a temperature ranging from room temperature to approximately 1000° C. Preferably from room temperature to 600° C., more preferably from 100 to 300° C. Depending on application targets, the temperature may be approximately 100° C., 500° C. or 600° C. This kind of thermal etcher can introduce molecules by different ways such as flow through, shower head, or other design. There will be a gas outlet connecting to a pumping system that controls the pressure of the chamber.

[0263] The disclosed F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures are suitable for etching semiconductor structures including thermal etching and plasma dry etching, such as, channel holes, gate trenches, staircase contacts, capacitor holes, contact holes, etc., in the silicon-containing films. For thermal etching, the disclosed F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures may be applied for isotropic etching purpose in a thermal reactor. For plasma etching, the disclosed F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures are not only compatible with currently available mask materials but also compatible with the future generations of mask materials because the disclosed F.sub.3NO-free FNO gas and mixtures induce little to no damage on the mask along with good profile of high aspect ratio structures. In other words, the disclosed F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures may produce vertical etched patterns having minimal pattern collapse or roughness. Preferably, the disclosed F.sub.3NO-free FNO gas and F.sub.3NO-free FNO gas mixtures etching compositions are suitably stable during the etching process for delivery into the reactor/chamber.

[0264] The reaction chamber may contain one or more than one substrate. The substrates may be any suitable substrates used in semiconductor, photovoltaic, flat panel or LCD-TFT device manufacturing. Examples of suitable substrates include wafers, such as silicon, silica, glass, or GaAs wafers. The wafer will have multiple films or layers on it from previous manufacturing steps, including silicon-containing films or layers. The layers may or may not be patterned.

[0265] The disclosed F.sub.3NO-free FNO etching gas is introduced into the reaction chamber containing the substrate. The gas may be introduced to the chamber at a flow rate ranging from approximately 0.1 sccm to approximately 30 slm. One of ordinary skill in the art will recognize that the flow rate may vary from tool to tool and application to application.

[0266] The disclosed F.sub.3NO-free FNO etching gas may be supplied either in neat form or in a blend with an inert gas, such as N.sub.2, Ar, He, Xe, etc. The disclosed F.sub.3NO-free FNO etching gas may be present in varying concentrations in the blend.

[0267] FTIR, microscope analyses, pressure monitoring (pressure sensor), ellipsometer, Energy-dispersive X-ray spectroscopy (EDX), Inductively coupled plasma mass spectrometry (ICP-MS), analytical electron microscopy (AEM), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscope (SEM), Transmission electron microscopy (TEM) or other measurement tools may be used to monitor changes of compositions and etching performance using the disclosed F.sub.3NO-free FNO etching gas to etch the semiconductor structures, and also monitor the thermally activated etching gas from the chamber exhaust to determine the degradation of materials of the cylinder, the cylinder valve and the line components in the manifold assembly.

[0268] The disclosed F.sub.3NO-free FNO etching gas may be mixed with other gases either prior to introduction into the reaction chamber or inside the reaction chamber. Preferably, the gases may be mixed prior to introduction to the chamber in order to provide a uniform concentration of the entering gas.

[0269] In another alternative, the disclosed F.sub.3NO-free FNO etching gas may be introduced into the chamber independently of the other gases such as when two or more of the gases react.

[0270] In another alternative, the disclosed F.sub.3NO-free FNO etching gas and the inert gas are the only two gases that are used during the etching process.

[0271] The temperature and the pressure within the reaction chamber are held at conditions suitable for the film on the substrate to react with the etching gas. For instance, the pressure in the chamber may be held between approximately 0.1 mTorr and approximately 1000 Torr, preferably between approximately 1 Torr and approximately 400 Torr, as required by the etching parameters. Likewise, the substrate temperature in the chamber may range between approximately room temperature to approximately 1000° C. depending on the process requirements. Preferably from room temperature to 600° C., more preferably from 100 to 300° C. Depending on application targets, the temperature may be approximately 100° C., 500° C. or 600° C.

EXAMPLES

[0272] The following non-limiting examples are provided to further illustrate embodiments of the invention. However, the examples are not intended to be all inclusive and are not intended to limit the scope of the inventions described herein.

[0273] In the following examples, FTIR spectra were collected with Thermo NICOLET6700 with cell length: 6.4 mm; cell temperature: 40° C.; cell pressure: 10 Torr; scan: 10 times and 2 cm.sup.−1 resolution. In the following examples, the etching gas was selected from F.sub.3NO-free FNO-only and/or F.sub.3NO-free FNO/F.sub.2/N.sub.2 gas mixture. The F.sub.3NO-free FNO/F.sub.2/N.sub.2 gas mixture contained about 15% F.sub.3NO-free FNO and about 10% F.sub.2 in N.sub.2.

Example 1 Pre-Synthesized F.SUB.3.NO-Free FNO

[0274] The pre-synthesized F.sub.3NO-free FNO gas has a purity of 99% FNO. Impurities in the pre-synthesized F.sub.3NO-free FNO gas may include F.sub.3NO, NO.sub.2, N.sub.2O, etc. NO.sub.2 and N.sub.2O may come from NO cylinder aging. F.sub.3NO impurity is less than 1%. From the example that follows, FNO diluted in an inert gas, for example, N.sub.2 gas, may suppress F.sub.3NO formation when producing FNO in situ with F.sub.2 and NO. Furthermore, depending on semiconductor applications, FNO gas either mixed with one or more addition etching gases or diluted in an inert gas. Thus, the FNO-containing etching gas formed by the pre-synthesized F.sub.3NO-free FNO will contain even less F.sub.3NO impurity. For example, if a FNO-containing etching gas formed by the pre-synthesized F.sub.3NO-free FNO contains 15% pre-synthesized F.sub.3NO-free FNO, the F.sub.3NO impurity will be less than 0.15%. Thus, the FNO-containing etching gas formed by the pre-synthesized F.sub.3NO-free FNO will contains less to no F.sub.3NO.

Example 2 F.SUB.3.NO-Free FNO Produced In Situ

[0275] Besides the pre-synthesized F.sub.3NO-free FNO, F.sub.3NO-free FNO may be produced in situ with starting materials F.sub.2 and NO through the reaction of F.sub.2+2NO.fwdarw.2FNO. In order to suppress the formation of F.sub.3NO impurity in the product FNO, the reaction of F.sub.2 and NO is at stoichiometry condition, that is, the ratio of the reactants F.sub.2 and NO is equals to approximately ½. To ensure less to no F.sub.3NO formed, the ratio of the reactants F.sub.2 and NO may be less than approximately ½.

[0276] The produced F.sub.3NO-free FNO gas may be diluted in an inert gas for using as etching gas in semiconductor applications. The inert gas may be N.sub.2, Ar, He, Ne, Kr, Xe. In one embodiment, F.sub.3NO-free FNO gas may be diluted with N.sub.2, forming F.sub.3NO-free FNO and N.sub.2 gas mixture. The F.sub.3NO-free FNO and N.sub.2 gas mixture may be produced by mixing F.sub.2, NO and N.sub.2 at a molar ratio of F.sub.2/NO≤½ with required N.sub.2 amount depending on application requirements of FNO concentration. The orders of mixing F.sub.2, NO and N.sub.2 to form the F.sub.3NO-free FNO and N.sub.2 gas mixture are shown in FIG. 3(a) to FIG. 3(d). The key point for the mixing orders is the ratio of F.sub.2 to NO is at stoichiometry condition, that is, equals to approximately ½, or less than approximately ½. FIG. 3(a) shows the three components F.sub.2, NO and N.sub.2 are mixed in a reactor simultaneously and then excess N.sub.2 is added to the reactor. This is equivalent to the reactants F.sub.2 and NO are initially diluted in N.sub.2 to produce a product FNO in N.sub.2 and the produced FNO is then further diluted in N.sub.2. The reaction equation is 2NO+F.sub.2.fwdarw.2FNO. With equal to or less than equivalent of F.sub.2 in the reactants, FNO is produced and the formation of F.sub.3NO may be controlled. For example, feeding a mixture of F.sub.2, NO and N.sub.2, formed with 7.5 sccm F.sub.2, 15 sccm NO and 75 sccm N.sub.2, to a reactor, where the reaction between F.sub.2 and NO occurs to form the product FNO diluted in N.sub.2. Since the ratio of F.sub.2 to NO is =½, all F.sub.2 will be consumed to produce FNO and no F.sub.2 remains to generate F.sub.3NO. In this way, F.sub.3NO formation may be restrained and the produced FNO is F.sub.3NO-free FNO. More N.sub.2 (10 sccm) is then added to the reactor resulting in the F.sub.3NO-free FNO diluted in N.sub.2, thereby forming a gas mixture of 15% F.sub.3NO-free FNO in N.sub.2.

[0277] Alternatively, the gas mixture of F.sub.3NO-free FNO and N.sub.2 may be produced by mixing F.sub.2/N.sub.2 and NO at a molar ration of F.sub.2/NO≤½. The order of mixing F.sub.2, N.sub.2 and NO is shown in FIG. 3(b). A mixture of F.sub.2 and N.sub.2 is formed first and then NO is added into the mixture, in which the reaction of F.sub.2 and NO occurs to produce FNO in N.sub.2. Additional N.sub.2 is then added to the product FNO forming FNO diluted in N.sub.2. The reaction equation is 2NO+F.sub.2.fwdarw.2FNO. With equal to or less than equivalent of F.sub.2 in the reactants, the formation of F.sub.3NO may be controlled. For example, a mixture of F.sub.2 and N.sub.2 is formed with 7.5 sccm F.sub.2 and 75 sccm N.sub.2 fed to a reactor. The mixture is then mixed with 15 sccm NO in the reactor where the reaction between F.sub.2 and NO occurs to form the product F.sub.3NO-free FNO. The product F.sub.3NO-free FNO is then diluted in N.sub.2 with 10 sccm N.sub.2 forming a gas mixture of 15% FNO diluted in N.sub.2.

[0278] Alternatively, the gas mixture of F.sub.3NO-free FNO and N.sub.2 may be produced by mixing F.sub.2 and NO/N.sub.2 at a molar ratio of F.sub.2/NO≤½. The order of mixing F.sub.2, N.sub.2 and NO is shown in FIG. 3(c). A mixture of NO and N.sub.2 is formed first and then F.sub.2 is added into the mixture, in which the reaction of F.sub.2 and NO occurs to produce FNO in N.sub.2. Additional N.sub.2 is then added to the product FNO forming FNO further diluted in N.sub.2. The reaction equation is 2NO+F.sub.2.fwdarw.2FNO. With equal or less equivalent of F.sub.2 in the reactants, the product FNO is produced and the formation of F.sub.3NO may be controlled.

[0279] Alternatively, the gas mixture of F.sub.3NO-free FNO and N.sub.2 may be produced by mixing F.sub.2/N.sub.2 and NO/N.sub.2 at condition of F.sub.2/NO≤½, in which F.sub.2 and NO are diluted in N.sub.2, respectively. The order of mixing F.sub.2, N.sub.2 and NO is shown in FIG. 3(d). A mixture of F.sub.2 and N.sub.2 is formed first and then a mixture of NO and N.sub.2 is added into the mixture of F.sub.2 and N.sub.2, in which the reaction of F.sub.2 and NO occurs to produce FNO in N.sub.2. Additional N.sub.2 is then added to the product FNO in N.sub.2 forming a different concentration of FNO in N.sub.2. The reaction equation is 2NO+F.sub.2.fwdarw.2FNO. With equal to or less than equivalent of F.sub.2 in the reactants, the product FNO is produced and the formation of F.sub.3NO may be controlled.

Example 3 Stoichiometric Condition Versus F.SUB.2.-Rich Condition

[0280] The resulting products from Example 2 were analyzed by FT-IR and identified less to no trace of F.sub.3NO in the product, since the ratio of F.sub.2 to NO is ≤½, all F.sub.2 will be consumed to produce FNO and no F.sub.2 remains for generating F.sub.3NO. FIG. 4 is a comparison of FTIR spectra of 30% FNO in N.sub.2 produced at stoichiometric condition and at F.sub.2-rich condition, respectively. The upper spectrum is 30% FNO produced at stoichiometric condition; the lower spectrum is 30% FNO produced at F.sub.2-rich condition. No F.sub.3NO peaks were detected if FNO is manufactured under stoichiometric condition.

Example 4 Manufacturing Gas Mixture of F.SUB.3.NO-Free FNO and F.SUB.2 .in N.SUB.2 .In Situ (I)

[0281] The F.sub.3NO-free FNO gas produced in situ may be mixed with an additional etching gas, such as, F.sub.2, for using as etching gas in semiconductor applications. In order to suppress the formation of F.sub.3NO in the process of producing the gas mixture of FNO/F.sub.2/N.sub.2, the mixing procedure was conducted with controlling F.sub.2 mixing order.

[0282] The gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2 may be produced by different mixing orders of F.sub.2, NO and N.sub.2. FIG. 5(a) shows F.sub.2, NO and N.sub.2 are mixed together first and then additional N.sub.2 is added. In order to get target F.sub.2 composition in the gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2, F.sub.2/NO ratio has to be larger than ½. Alternatively, the gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2 may be produced by mixing F.sub.2 and N.sub.2 first, then adding NO at condition of F.sub.2/NO≤½ to produce FNO and then adding additional F.sub.2, and additional N.sub.2, as shown in FIG. 5(b). In this case, the mixing order of N.sub.2 and NO may be interchangeable. That is, mixing F.sub.2 and NO first and then adding N.sub.2 (see parentheses). Alternatively, the gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2 may be produced by mixing NO and N.sub.2 first, then adding F.sub.2 and then adding additional N.sub.2, as shown in FIG. 5(c). In this case, F.sub.2/NO ratio has also to be larger than % A to reach the target F.sub.2 composition the gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2. Alternatively, the gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2 may be produced by mixing F.sub.2 and N.sub.2 first, then adding a mixture of NO and N.sub.2 at condition of F.sub.2/NO=½ and then adding additional N.sub.2, as shown in FIG. 5(d). Similarly, in this case, F.sub.2/NO ratio has also to be larger than ½ to reach the target F.sub.2 composition the gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2.

[0283] The mixing orders shown in FIG. 5(a), FIG. 5(c) and FIG. 5(d) are all one step F.sub.2 mixing procedures at F.sub.2-rich condition. As shown in FIG. 4, under F.sub.2-rich condition, F.sub.3NO was produced and may not be suppressed. Mixing excess F.sub.2 with NO in the one-step F.sub.2 mixing procedure produces more F.sub.3NO than mixing F.sub.2 and NO in the two-step F.sub.2 mixing procedure. The mixing order shown in FIG. 5(b) is a two-step F.sub.2 mixing procedure, which includes a post feeding F.sub.2 or F.sub.2/N.sub.2 to target a final F.sub.2 composition in the gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2. Since in the first step F.sub.2/NO≤½ and F.sub.3NO is suppressed, adding additional amount of F.sub.2 would not produce F.sub.3NO. Thus, only the mixing procedure shown in FIG. 5(b) provides less to no F.sub.3NO generation in the gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2.

[0284] In the processes of synthesizing the gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2, it is discovered F.sub.3NO generation depending on F.sub.2 and NO feeding molar ratio and F.sub.2 mixing procedure/order. Feeding F.sub.2 amount as needed (i.e., stoichiometry condition) for FNO formation produces least F.sub.3NO impurity. For producing a gas mixture of FNO/F.sub.2/N.sub.2, the two-step F.sub.2 mixing procedure is applicable. The two-step F.sub.2 mixing procedure is i) forming a mixture of F.sub.2 and pure NO (at least 99.9% purity) by mixing chemical equivalent F.sub.2 and NO first with or without dilution in N.sub.2 and then ii) adding extra F.sub.2 gas into the mixture with or without dilution in N.sub.2. By the two-step F.sub.2 mixing procedure, less to no F.sub.3NO was detected through FT-IR measurements in the formation of the gas mixture of FNO/F.sub.2/N.sub.2.

[0285] An example, a gas mixture of 15%-FNO and 10%-F.sub.2 in N.sub.2 balanced gas, was prepared by the two-step F.sub.2 mixing procedures as shown in FIG. 5(b) and described in Table 1. N.sub.2 and NO feedings were fixed at 10 mol and 2 mol, respectively. The ratio of 1.sup.st F.sub.2 feeding to 2.sup.nd F.sub.2 feeding (1.sup.st F.sub.2/2.sup.nd F.sub.2) was varied but a total flow rate of F.sub.2 was fixed at 2.3 mol in order to target the same final composition of the FNO/F.sub.2/N.sub.2 gas mixture. F.sub.3NO amount in the FNO/F.sub.2/N.sub.2 gas mixture was monitored with FTIR to check the effect of F.sub.2 mixing order, as shown in FIG. 6.

TABLE-US-00001 TABLE 1 Mixing procedures of F.sub.2, NO and N.sub.2 with a fixed amount of F.sub.2 1.sup.st F.sub.2.sub.—% 1.sup.st F.sub.2 1.sup.st N.sub.2 NO 2.sup.nd F.sub.2 2.sup.nd N.sub.2 (1.sup.st F.sub.2/total F.sub.2) (mol) (mol) (mol) 1.sup.st F.sub.2/NO (mol) (mol) 43% 1 10 2 0.5 1.3 0 66% 1.5 10 2 0.75 0.8 0 83% 1.9 10 2 0.95 0.4 0 100%  2.3 10 2 1.15 0 0

[0286] In the first step, a ratio of 1.sup.st F.sub.2/total F.sub.2 feedings is 43% and a ratio of F.sub.2 to NO needed for FNO formation is F.sub.2/NO=0.5. In the second step, a post feeding of 2.sup.nd F.sub.2 is fed to the mixture of F.sub.2 and NO to target the final F.sub.2 composition (in this case, 10% F.sub.2) in the FNO/F.sub.2/N.sub.2 gas mixture. FIG. 6 shows that F.sub.3NO formation changes (FTIR signals) with F.sub.2 feeding amount (1.sup.st F.sub.2_%). With 43% 1.sup.st F.sub.2/total F.sub.2 feed, no F.sub.3NO was formed, because F.sub.2/NO is at stoichiometry condition. Others, 66%, 83% and 100% of 1.sup.st F.sub.2/total F.sub.2 feed, all generate F.sub.3NO.

Example 5 Manufacturing Gas Mixture of F.SUB.3.NO-Free FNO and F.SUB.2 .in N.SUB.2 .In Situ (II)

[0287] A gas mixture of 3.42%-FNO and 2.31%-F.sub.2 in N.sub.2 balanced gas (F.sub.3NO-free FNO/F.sub.2/N.sub.2) was prepared by 2 step feedings of F.sub.2, as shown in FIG. 5(b) with various mixing amounts of 1.sup.st F.sub.2 and 2.sup.nd F.sub.2, as described in Table 2. 1.sup.st F.sub.2, NO and 2.sup.nd F.sub.2 feedings were fixed at 1 mol, 2 mol, and 1.35 mol, respectively. The ratio of 1.sup.st N.sub.2/2.sup.nd N.sub.2 was varied while a total flow of N.sub.2 was fixed at 55.13 mol to target same final composition of the gas mixture. F.sub.3NO amount was monitored with FTIR to check the effect of N.sub.2 mixing order as shown in FIG. 5(b), where N.sub.2 was split into two feedings, 1.sup.st N.sub.2 and 2.sup.nd N.sub.2. The gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2 may be obtained by the reaction between premixed F.sub.2/N.sub.2 and NO with F.sub.2/NO ratio at ½.

TABLE-US-00002 TABLE 2 Mixing procedures of F.sub.2, N.sub.2 and NO with a fixed amount of N.sub.2 1.sup.st N.sub.2.sub.—% 1.sup.st F.sub.2 1.sup.st N.sub.2 NO 2.sup.nd F.sub.2 2.sup.nd N.sub.2 (1.sup.st N.sub.2/total N.sub.2) (mol) (mol) (mol) 1.sup.st F.sub.2/NO (mol) (mol)  0% 1 0 2 0.5 1.35 55.13 11% 1 5.85 2 0.5 1.35 49.28 42% 1 23.39 2 0.5 1.35 31.74 100%  1 55.13 2 0.5 1.35 0

[0288] FIG. 7 shows F.sub.3NO formation changes (FTIR signals) with N.sub.2 feedings and N.sub.2 feeding amount (1.sup.st N.sub.2_%). Without N.sub.2 feeding, F.sub.3NO was generated. With the increase of the ratio of 1.sup.st N.sub.2 feeding to total N.sub.2 feeding, F.sub.3NO formation was getting less and less and almost nil when 1.sup.st N.sub.2 feeding reached 100%. Thus, adding N.sub.2 is beneficial for reducing F.sub.3NO formation.

Example 6 Etching Effects with On-Site Mixing Produced F.SUB.3.NO-Free FNO

[0289] The etching effects were done on SiN films using on-site mixing produced F.sub.3NO-free FNO as etching gas.

Etching Effect of 1.sup.st F.sub.2 Feeding

[0290] F.sub.2 was fed by two-steps, as shown in FIG. 5(b). Ratios of 1.sup.st F.sub.2 to 2.sup.nd F.sub.2 varied in order to produce FNO and various mixtures of FNO and F.sub.2 for etching SiN films. Etching conditions are as follows. Pressure was 20 Torr; Temperature was 70° C.; Etching time was 2 min; Total flow rate was 1 slm fixed; Etching composition concentrations: FNO/F.sub.2=1.48; FNO was 3.42% fixed, F.sub.2 was 2.31% fixed; total F.sub.2 was 40.2 sccm. Four SiN samples (1, 2, 3 and 4) were etched with different 1.sup.st F.sub.2 feeding amounts. A total of seven SiN films, listed in Table 3 were used for various etching tests.

TABLE-US-00003 TABLE 3 SiN film samples Sample 1.sup.st F.sub.2/total F.sub.2 Total F.sub.2 (sccm) FNO (%) Etch time (min) 1 43% 40.2 3.42 2 2 57% 40.2 3.42 2 3 72% 40.2 3.42 2 4 100%  40.2 3.42 2 5 43% 115.2 9.80 2 6 43% 40.2 3.42 5 7 100%  40.2 3.42 5

[0291] FIG. 8 are FTIR signals and etch rates after SiN etched with FNO and F.sub.2 gas mixture with different 1.sup.st F.sub.2 feeding amounts. Clearly, more F.sub.3NO generated by more 1.sup.st F.sub.2 feeding leads to higher SiN etch rates, but not uniform etching results on SiN film surface (not shown). Sample 1, with 43% 1.sup.st F.sub.2 feeding, had the lowest amount of F.sub.3NO; Samples 2 and 3, with 57% and 72% 1.sup.st F.sub.2 feedings, had F.sub.3NO gradually increasing. Sample 4 with 100% 1.sup.st F.sub.2 feeding, which had no 2.sup.nd F.sub.2 feeding meaning one step of F.sub.2 mixing process, has the highest amount of F.sub.3NO. For the four samples, etch rates were increased with the increase of F.sub.3NO. Sample 1 has the lowest F.sub.3NO formation and good etching surface (not shown) comparing to the other three samples and the original SiN film. Thus, less to no F.sub.3NO impurity in FNO or less to no F.sub.3NO impurity in the gas mixture of FNO and F.sub.2 benefits etching performance.

Etching Effect of N.SUB.2 .Feeding

[0292] Etching conditions are as follows. Pressure was 20 Torr; Temperature was 70° C.; Etching time was 2 min; Total flow rate was 1 slm fixed; Etching composition concentrations: FNO/F.sub.2=1.48; FNO was 3.42% fixed, F.sub.2 was 2.31% fixed; total N.sub.2 was 942.7 sccm. N.sub.2 was fed by 2 steps, as shown in FIG. 5(a) and FIG. 5(c). Ratios of 1.sup.st to 2.sup.nd N.sub.2 varied to produce FNO and a mixture of FNO and F.sub.2 to etch SiN films. As shown in FIG. 9, without N.sub.2 dilution, F.sub.3NO formed. Thus, N.sub.2 dilution for F.sub.2/NO reaction reduces F.sub.3NO formation.

Etching Effect of FNO and F.SUB.2 .Concentrations

[0293] Etching composition contained FNO and F.sub.2. FNO concentration was varied from 3.42% to 9.80%. F.sub.2 concentration was varied from 2.31% to 6.62%. Etching conditions are as follows. Pressure was 20 Torr Temperature was 70° C.; Etching time was 2 min; Total flow rate was 1 slm fixed; Etching composition concentrations: FNO/F.sub.2=1.48 with 1.sup.st F.sub.2 feeding amounts of 43% of total F.sub.2.

[0294] As shown in FIG. 10, increasing FNO concentration does not increase F.sub.3NO amount referring to Samples 1 and 5 in Table 3. The increase of SiN etch rate for Sample 5 is due to higher concentration of FNO than that of Sample 1. The etching surface colour for Sample 5 is quite different from Sample 1 (not shown), meaning low concentration of FNO and F.sub.2 benefits the etching performance.

Effect of Etch Time

[0295] Etching conditions are as follows. Pressure was 20 Torr; Temperature was 70° C.; Total flow rate was 1 slm fixed; Etching composition concentrations: FNO/F.sub.2=1.48; FNO was 3.42% fixed, F.sub.2 was 2.31% fixed; total F.sub.2 was 40.2 sccm. Etch time varied from 2 to 5 mins. Two steps F.sub.2 mixing method, as shown in FIG. 5(b), was applied to form gas mixture of FNO/F.sub.2/N.sub.2.

[0296] Referring to FIG. 11 and Table 3, samples 1 and 6 with 43% 1st F.sub.2 had low F.sub.3NO; samples 4 and 7 with 100% 1st F.sub.2 had high F.sub.3NO. As shown, no effect of etch time within 5 mins on the FNO and F.sub.3NO concentrations.

Example 7 Material Compatibility for Cylinder to Store FNO and for Line Components at High Pressure

[0297] Material compatibility tests included testing the material compatibility between etching gas mixture FNO/F.sub.2/N.sub.2 with the storage cylinder 106 and the components in high-pressure zone 102 shown in FIG. 2, e.g., cylinder valve 108, pipeline 110, valve 112, pressure sensor 114 and pressure regulator 116.

[0298] The tested samples were HASTELLOY® C-22®, NiP, stainless steel gasket (such as stainless steel 316L (SS316L)) and Ni gasket at pressure 0.99 MPa.

[0299] XPS results show F-penetration up to 12000 Å in a vessel made of SS316L material. Thus, SS316L material may not be compatible with the etching gas mixture FNO/F.sub.2/N.sub.2.

[0300] XPS results show F-penetration up to approximately 6000 Å in a vessel made of HASTELLOY® C-22® material. Material HASTELLOY® C-22® is better than SS316L.

[0301] XPS results show F-penetration less than approximately 50 Å in a vessel made of NiP coated steel material. Thus, NiP coated steel material is compatible with the etching gas mixture FNO/F.sub.2/N.sub.2.

[0302] XPS results show F-penetration less than approximately 800 Å in a vessel made of nickel material. Although nickel material is not as good as NiP coated steel material, nickel material is somewhat compatible with the etching gas mixture FNO/F.sub.2/N.sub.2.

[0303] In summary, in the high-pressure zone (e.g., 0.99 MPa), NiP coated steel is good for making cylinder body. Pure nickel or nickel alloys may be used for cylinder valve. It may be preferred that other line components (e.g., pressure regulator, valves, gas filter, piping) in high-pressure zone may use nickel alloys, such as, HASTELLOY® C-22®⋅MONEL® or INCONEL®, which contain high Ni content. Passivation process with F.sub.2 or FNO may be applied in the high-pressure zone. The passivation process includes a process that elevates pressure gradually.

Example 8 Material Compatibility Tests for Line Components at Low-Pressure

[0304] Material compatibility tests also included testing the material compatibility between etching gas mixture FNO/F.sub.2/N.sub.2 and the components in low-pressure zone 104 shown in FIG. 2, e.g., pressure sensor 120, pipeline 130, valves 122 and 124.

SS316L & Ni Material Compatibility

[0305] The vessels used herein were Ni vessels each containing a Ni gasket sample and one or two SS gasket (i.e., SS316L gasket) samples. The samples were tested at 0.50 MPa with the etching gas F.sub.3NO-free FNO/F.sub.2/N.sub.2 in periods of 17 days and 21 days.

[0306] SS samples were covered with particles and corrosion was observed when exposed to F.sub.3NO free FNO/F.sub.2/N.sub.2. Thus, SS sample is not compatible with F.sub.3NO-free FNO/F.sub.2/N.sub.2 even at low-pressure. No corrosion was observed on the nickel samples.

[0307] For FNO-only, SS sample was found compatible with FNO-only at low-pressure with no observed corrosion however for F.sub.3NO-free FNO/F.sub.2/N.sub.2 it was found not as compatible in the low pressure zone. However, after passivation using F.sub.2 or FNO, SS sample may be compatible with the etching gas F.sub.3NO-free FNO/F.sub.2/N.sub.2 in the low-pressure zone. Alternatively, if the etching gas does not contains F.sub.2, SS is suitable for making the line components in the low-pressure zone.

FNO and F.sub.2 with Low Level of F.sub.3NO or F.sub.3NO-Free

[0308] Two SS samples were installed in each of three vessels, respectively, at 0.5 MPa for 20 days. One vessel was fed with FNO-only, the other two were fed with the gas mixture of 15% F.sub.3NO-free FNO and 10% F.sub.2 in N.sub.2 and half concentration of the gas mixture of 15% F.sub.3NO-free FNO and 10% F.sub.2 in N.sub.2, for comparison. Even with F.sub.3NO-free, the gas mixture of 15% F.sub.3NO-free FNO and 10% F.sub.2 in N.sub.2 resulted in corrosion on SS316L at 0.5 MPa, but no corrosion with FNO only on SS316L surface. SS316L is not compatible with the gas mixture of 15% F.sub.3NO-free FNO and 10% F.sub.2 in N.sub.2. Thus, F.sub.2 or FNO passivation in low-pressure zone for F.sub.3NO-free F.sub.2/FNO/N.sub.2 is needed. SS316L may be compatible with the etching gas F.sub.3NO-free FNO/F.sub.2/N.sub.2 after F.sub.2 or FNO passivation. SS316L may be compatible with the gas mixture of FNO and N.sub.2 without F.sub.2.

Example 9 Material Compatibility Summary

[0309] The material compatibility test conditions and results for both high pressure and low-pressure zones are listed in Table 4. In summary, high content nickel materials including NiP coated steel, pure nickel or nickel alloys, may be compatible with high-pressure zone. SS316L is compatible with FNO and N.sub.2 gas mixture in the low-pressure zone. However, with F.sub.2 or FNO passivation, SS316L may be compatible with FNO/F.sub.2/N.sub.2 gas mixture in the low-pressure zone. Furthermore, metals, metal alloys without nickel content or metal alloys with high nickel content or low nickel content may compatible with the low-pressure zone.

TABLE-US-00004 TABLE 4 Material compatibility summary F.sub.2 (%) 10.5 10.5 10.5 5.3 10.5 5.3 0  FNO (%) 14.5 14.5 14.5 7.3 14.5 7.3 14.5 F.sub.3NO Exist Exist Exist Exist free free free Pressure (MPa)  0.99  0.99  0.50  0.50  0.50  0.50  0.50 Total duration (days) 7  21   21   43   20   20   20   Non-coated steel C C — — — — — SS316L — C C  C  C  C  A  NiP coated steel — A A* A* A* A* A* Nickel — B B  B* B* B* B* HASTELLOY ® C-22 ® — B B* B* B* B* B*

[0310] Note in Table 4, “A” means excellent compatibility or good to use; “A*” means excellent compatibility or good to use but actual tests were not done; “B” means acceptable with limitations or limited; “B*” means acceptable with limitations or limited but actual tests were not done; “C” means poor or not compatible; “-” means no actual tests. The non-coated steel may be any type of steel without a NiP coating on the surface, such as Mn-steel. The SS316L contains up to 14% nickel.

Example 10 Stability (Shelf Life) Test

[0311] A 10 L size NiP coated steel cylinder and a Ceodeux D306 Ni body Ni diaphragm cylinder valve were used for stability test. The cylinder was pre-treated with vacuum baking first and then passivated with F.sub.2. 15% FNO/N.sub.2 by mixing F.sub.2, NO and N.sub.2 as described in Example 3 was filled to the 10 L size NiP coated steel cylinder at 0.99 MPa(G). The shelf life test was done by monitoring FNO and impurities (NO.sub.2, HF, F.sub.3NO) with FT-IR for 6 months. The etching performance test was done by periodically checking SiN etch rate for 6 months and the stability of the product was confirmed up to 6 months in terms of composition and SiN etching performance.

[0312] FIG. 12 is the results of monitoring of different composition by FT-IR. FIG. 13 is the results of monitoring of etching performance over time. The etching performance was done with the etching gas of 20% F.sub.2 and 1% FNO at temperature 100° C., pressure 20 Torr. The etching time was 1 min. The results from FIG. 12 and FIG. 13 show no significant concentration changes on FNO and impurities and no significant etching performance changes, meaning that 6-month stability is solid and long-term stability is promising.

Example 11 Storage and Supply Packaging for F.SUB.3.NO-Free FNO-Containing Gas

[0313] Referring to FIG. 2, a packaging for storage and supply of F.sub.3NO-free FNO-containing gas for thermal and plasma dry etching applications or the like in semiconductor industry may include a NiP coated steel cylinder for storage of F.sub.3NO-free FNO-containing gas. The NiP coated steel cylinder may be a carbon steel cylinder made of alloy 4130X with an internal surface coating of nickel plating (NiP) and a polished surface of NiP coating. The supply packaging further include a nickel cylinder valve for controlling delivery of the F.sub.3NO-free FNO-containing gas from the NiP coated steel cylinder to a manifold assembly that has a high-pressure zone and a low-pressure zone divided by a pressure regulator. Line components in the high-pressure zone are made of high nickel content material/alloy having at least 14% nickel by weight. The line components in the high-pressure zone include pressure regulator, valves, gas filter, piping, pressure sensors, or the like. The high nickel content alloy may be MONEL®, INCONEL®, HASTELLOY® C-22® or the like. The high-pressure zone may be passivated with F.sub.2 or FNO with gradually increasing the pressure. Line components in the low-pressure zone may be made of any metal or any metal alloy including high nickel content material/alloy, low nickel content material/alloy or no nickel content material/alloy, for example, stainless steel. The low-pressure zone may be passivated with F.sub.2 or FNO.

[0314] With pre-synthesized F.sub.3NO-free FNO (F.sub.3NO impurity is less than 1%) on-site, FNO and N.sub.2 may be mixed in situ to produce F.sub.3NO-free FNO/N.sub.2 gas mixture with various concentrations of FNO in N.sub.2. Thus, F.sub.3NO-free FNO gas may be diluted in N.sub.2 and stored in the NiP coated steel cylinder. The concentration of FNO in the mixture of F.sub.3NO-free FNO/N.sub.2 may range from approximately 0.01% to approximately 80%. Preferably, the concentration of FNO in the mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2 may range from approximately 0.01% to approximately 30%. In one embodiment, the concentration of FNO in the mixture of F.sub.3NO-free FNO/N.sub.2 is approximately 3%. In another embodiment, the concentration of FNO in the mixture of F.sub.3NO-free FNO/N.sub.2 is approximately 15%.

[0315] With pre-synthesized F.sub.3NO-free FNO (F.sub.3NO impurity is less than 1%) on-site, FNO and F.sub.2 may be mixed in situ to produce F.sub.3NO-free FNO/F.sub.2/N.sub.2 gas mixture with various concentrations of FNO and F.sub.2 in N.sub.2. The concentration of FNO in the mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2 may range from approximately 0.01% to approximately 80% and the concentration of F.sub.2 in the mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2 may range from approximately 0% (no F.sub.2) to approximately 80%. Preferably, the concentration of FNO in the mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2 may range from approximately 0.01% to approximately 30% and the concentration of F.sub.2 in the mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2 may range from approximately 0% to approximately 20%.

[0316] In one embodiment, the concentration of FNO in the mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2 is approximately 15% and the concentration of F.sub.2 in the mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2 is approximately 10%. F.sub.3NO-free FNO gas may be diluted in N.sub.2 and stored in the NiP coated steel cylinder first. Then either pure F.sub.2 or diluted F.sub.2 in N.sub.2 is mixed with the diluted F.sub.3NO-free FNO producing F.sub.3NO-free approximately 15% FNO and approximately 10% F.sub.2 in N.sub.2 gas mixture for use as etching gas in semiconductor applications. The produced F.sub.3NO-free approximately 15% FNO and approximately 10% F.sub.2 in N.sub.2 gas mixture may be stored in the NiP coated steel cylinder. The advantages of supplying pre-synthesized F.sub.3NO-free FNO for producing the gas mixture of F.sub.3NO-free FNO/F.sub.2/N.sub.2 are i) no exothermic reaction by mixing FNO and F.sub.2; ii) less to no impurity F.sub.3NO generated; iii) better reproducibility of etching performance shown in the above examples.

[0317] Alternatively, the F.sub.3NO-free FNO/F.sub.2/N.sub.2 gas mixture may be produced in situ by mixing NO (purity at least 99.9%) and F.sub.2 gases with two-step F.sub.2 mixing method as described above in Example 3. The produced F.sub.3NO-free FNO/F.sub.2/N.sub.2 gas mixture may be stored in a NiP coated steel cylinder for use as etching gas or other purposes in semiconductor applications. The advantages of producing F.sub.3NO-free FNO/F.sub.2/N.sub.2 gas mixture by mixing NO and F.sub.2 is the concentration of FNO in the F.sub.3NO-free FNO/F.sub.2/N.sub.2 gas mixture may be adjustable depending on requirements of etching applications.

[0318] It will be understood that many additional changes in the details, materials, steps, and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above and/or the attached drawings.

[0319] While embodiments of this invention have been shown and described, modifications thereof may be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and not limiting. Many variations and modifications of the composition and method are possible and within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims which follow, the scope of which shall include all equivalents of the subject matter of the claims.