Method of etching semiconductor structures with etch gas

Abstract

Disclosed are sulfur-containing compounds for plasma etching channel holes, gate trenches, staircase contacts, capacitor holes, contact holes, etc., in Si-containing layers on a substrate and plasma etching methods of using the same. The plasma etching compounds may provide improved selectivity between the Si-containing layers and mask material, less damage to channel region, a straight vertical profile, and reduced bowing in pattern high aspect ratio structures.

Claims

1. A method for plasma etching a silicon-containing layer on a substrate, the method comprising, introducing a vapor of a compound into a chamber containing the silicon-containing layer on a substrate, the compound selected from the group consisting of: C.sub.2F.sub.4S.sub.2 (CAS 1717-50-6), F.sub.3CSH (CAS 1493-15-8), F.sub.3C—CF.sub.2—SH (CAS 1540-78-9), F.sub.3C—CH.sub.2—SH (CAS 1544-53-2 CHF.sub.2—CF.sub.2—SH 812-10-2 CF.sub.3—CF.sub.2—CH.sub.2—SH (CAS 677-57-6), F.sub.3C—CH(SH)—CF.sub.3 (CAS 1540-06-3), F.sub.3C—S—CF.sub.3 (CAS 371-78-8), F.sub.3C—S—CHF.sub.2 (CAS 371-72-2), F.sub.3C—CF.sub.2—S—CF.sub.2—CF.sub.3 (CAS 155953-22-3), F.sub.3C—CF.sub.2—CF.sub.2—S—CF.sub.2—CF.sub.2—CF.sub.3 (CAS 356-63-8), c(-S—CF.sub.2—CF.sub.2—CHF—CF.sub.2—) (CAS 1035804-79-5), c(-S—CF.sub.2—CHF—CHF—CF.sub.2—) (CAS 30835-84-8), c(-S—CF.sub.2—CF.sub.2—CF.sub.2—CF.sub.2—CF.sub.2—) (CAS 24345-52-6), c(-S—CFH—CF.sub.2—CF.sub.2—CFH—)(2 R, 5 R) (CAS 1507363-75-8), c(-S—CFH—CF.sub.2—CF.sub.2—CFH—)(2 R, 5 S) (CAS 1507363-76-9), and c(-S—CFH—CF.sub.2—CF.sub.2—CH.sub.2—) (CAS 1507363-77-0); introducing an inert gas into the chamber; generating a plasma to produce an activated vapor from the vapor; and removing volatile by-product from the chamber, wherein the activated vapor selectively reacts with the silicon-containing layer to form the volatile by-product.

2. The method of claim 1, wherein the compound is C.sub.2F.sub.4S.sub.2 (CAS 1717-50-6).

3. The method of claim 1, wherein the compound is selected from the group consisting of F.sub.3CSH (CAS 1493-15-8), F.sub.3C—CF.sub.2—SH (CAS 1540-78-9), F.sub.3C—CH.sub.2—SH (CAS 1544-53-2), CHF.sub.2—CF.sub.2—SH (812-10-2), CF.sub.3—CF.sub.2—CH.sub.2—SH (CAS 677-57-6), and F.sub.3C—CH(SH)—CF.sub.3 (CAS 1540-06-3).

4. The method of claim 1, wherein the compound is selected from the group consisting of F.sub.3C—S—CF.sub.3 (CAS 371-78-8), F.sub.3C—S—CHF.sub.2 (CAS 371-72-2), F.sub.3C—CF.sub.2—S—CF.sub.2—CF.sub.3 (CAS 155953-22-3), and F.sub.3C—CF.sub.2—CF.sub.2—S—CF.sub.2—CF.sub.2—CF.sub.3 (CAS 356-63-8).

5. The method of claim 1, wherein the compound is selected from the group consisting of c(-S—CF.sub.2—CF.sub.2—CHF—CF.sub.2—) (CAS 1035804-79-5), c(-S—CF.sub.2—CHF—CHF—CF.sub.2—) (CAS 30835-84-8), c(-S—CF.sub.2—CF.sub.2—CF.sub.2—CF.sub.2—CF.sub.2—) (CAS 24345-52-6), c(-S—CFH—CF.sub.2—CF.sub.2—CFH—)(2 R, 5 R) (CAS 1507363-75-8), c(-S—CFH—CF.sub.2—CF.sub.2—CFH—) (2 R, 5 S) (CAS 1507363-76-9), and c(-S—CFH—CF.sub.2—CF.sub.2—CH.sub.2—) (CAS 1507363-77-0).

6. The method of claim 1, wherein the silicon-containing layer comprises a layer of silicon oxide, silicon nitride, polysilicon, or combinations thereof.

7. The method of claim 1, further comprising introducing an oxidizer into the chamber.

8. The method of claim 7, wherein the oxidizer is selected from the group consisting of O.sub.2, O.sub.3, CO, CO.sub.2, NO, N.sub.2O, NO.sub.2, and combinations thereof.

9. The method of claim 7, wherein the oxidizer is O.sub.2.

10. The method of claim 1, further comprising introducing an etching gas into the chamber, wherein the etching gas is selected from the group consisting of cC.sub.5F.sub.8, cC.sub.4F.sub.8, C.sub.4F.sub.8, C.sub.4F.sub.6, 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; SO.sub.2; trans-1,1,1,4,4,4-hexafluoro-2-butene; cis-1,1,1,4,4,4-hexafluoro-2-butene; hexafluoroisobutene; hexafluorocyclobutane (trans-1,1,2,2,3,4); pentafluorocyclobutane (1,1,2,2,3-); tetrafluorocyclobutane (1,1,2,2-); and hexafluorocyclobutane (cis-1,1,2,2,3,4).

11. The method of claim 1, wherein the compound is F.sub.3C—CH.sub.2—SH (CAS 1544-53-2).

12. The method of claim 1, wherein the silicon-containing layer comprises a combination of silicon oxide and silicon nitride.

13. The method of claim 12, wherein the compound is F.sub.3C—CH.sub.2—SH (CAS 1544-53-2).

14. The method of claim 12, wherein the compound is C.sub.2F.sub.4S.sub.2 (CAS 1717-50-6).

15. A method for plasma etching a silicon-containing layer, the method comprising, introducing F.sub.3C—CH.sub.2—SH (CAS 1544-53-2) gas into a chamber containing the silicon-containing layer on a substrate, wherein the silicon-containing layer comprises a combination of silicon oxide and silicon nitride; introducing an inert gas into the chamber; plasma activating F.sub.3C—CH.sub.2—SH (CAS 1544-53-2) gas; and removing volatile by-product from the chamber, wherein the plasma activated F.sub.3C—CH.sub.2—SH (CAS 1544-53-2) gas selectively reacts with the silicon-containing layer to form the volatile by-product.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIG. 1 is a diagram showing exemplary layers in a NAND stack;

(3) FIG. 1a is a diagram showing polymer deposited on the sidewall during etching in a NAND stack;

(4) FIG. 2 is a diagram showing exemplary layers in a DRAM stack;

(5) FIG. 3 is a mass spectrometry (MS) graph plotting the volume of species fractions produced by C.sub.2H.sub.3F.sub.3S (in Torr) versus energy (in eV);

(6) FIG. 4 is a MS graph plotting the volume of species fractions produced by C.sub.2F.sub.4S.sub.2 (in Torr) versus energy (in eV);

(7) FIG. 5 is a comparative MS graph plotting the volume of species fractions produced by C.sub.2F.sub.6S.sub.2 (in Torr) versus energy (in eV);

(8) FIG. 6 is a schematic drawing of the etcher used in the examples that follow;

(9) FIG. 7 is a X-ray photoelectron spectroscopy (XPS) graph of the atoms in a polymer deposited from C.sub.2H.sub.3F.sub.3S;

(10) FIG. 8A is a Scanning Electron Microscope (SEM) picture of the polymer film deposited by C.sub.2H.sub.3F.sub.3S;

(11) FIG. 8B is the same SEM picture of the polymer film deposited by C.sub.2H.sub.3F.sub.3S with the addition of lines to better mark the boundaries of each layer;

(12) FIG. 9 is a XPS graph of the atoms in the Si coupon on which an attempt was made to deposit a polymer from C.sub.2F.sub.6S.sub.2;

(13) FIG. 10 is a graph of the etch rates of C.sub.2H.sub.3F.sub.3S on SiO.sub.2, SiN, p-Si and a-C plotted as a function of oxygen flow rate;

(14) FIG. 11 is a graph of the etch rates of the combination of C.sub.2H.sub.3F.sub.3S with CF.sub.4 on SiO.sub.2, SiN, p-Si and a-C plotted as a function of CF.sub.4 flow rate;

(15) FIG. 12 is a graph of the etch rates of C.sub.2F.sub.4S.sub.2 on SiO.sub.2, SiN, p-Si and a-C plotted as a function of oxygen flow rate;

(16) FIG. 13 is a graph of the etch rates of cC.sub.4F.sub.8 on SiO.sub.2, SiN, p-Si and a-C plotted as a function of oxygen flow rate;

(17) FIG. 14 is a graph of the etch rates of C.sub.4F.sub.6 on SiO.sub.2, SiN, p-Si and a-C plotted as a function of oxygen flow rate; and

(18) FIG. 15 is a graph of the etch rates of the combination of cC.sub.4F.sub.8 with CF.sub.4 on SiO.sub.2, SiN, p-Si and a-C plotted as a function of CF.sub.4 flow rate.

DESCRIPTION OF PREFERRED EMBODIMENTS

(19) Disclosed are sulfur-containing compounds for plasma etching channel holes, gate trenches, staircase contacts, capacitor holes, contact holes, etc., in silicon-containing layers. The disclosed etching compounds may provide higher selectivity to mask layers and no profile distortion in high aspect ratio structures.

(20) The plasma etching compounds may provide improved selectivity between the Si-containing layers and mask materials, less damage to channel region, and reduced bowing in pattern high aspect ratio structures. The plasma etching compounds may also etch through alternating layers of polySi, SiO, and/or SiN, resulting in a vertical etch profile.

(21) The disclosed sulfur-containing compounds have one of the following formulae:
R.sup.1—SH
R.sup.2—S—R.sup.3
C.sub.2F.sub.4S.sub.2 (CAS 1717-50-6)
wherein R.sup.1, R.sup.2, and R.sup.3 is each independently a saturated C1 to C4 alkyl or fluoroalkyl group and R.sup.2 and R.sup.3 may be joined to form a 5 or 6 member S-containing ring.

(22) In one alternative, the sulfur-containing compound is C.sub.2F.sub.4S.sub.2 (CAS 1717-50-6). This compound is commercially available. Applicants believe that the cyclic structure of this compound will produce fragments during the plasma process that are suitable for both anisotropically etching the Si-containing layer and depositing a S-containing polymer passivation layer on the sidewalls of the structure being etched (see FIG. 1a).

(23) In another alternative, the compound has the formula R.sup.1—SH, wherein R.sup.1 is a saturated C1 to C4 alkyl or fluoroalkyl group. These compounds may be commercially available or synthesized in one-step method by reduction of the corresponding sulfenyl chlorides by an excess of hydrogen sulfide in an autoclave at room temperature (see, e.g., Bekker et al., Phosphorus, Sulfur, and Silicon and the Related Elements (1996) 119, 161-68). Alternatively, R.sup.1—S—Cl and Cl.sub.2—P—O—CH.sub.3 may be reacted in a 2-step process with PSCl.sub.3 followed by H.sub.2O (see, e.g., Haas and Kortmann, Zeitschrift fuer Anorganische and Allgemeine Chemie, 501, 79-88, 1983).

(24) Applicants believe that the terminal SH of R.sup.1—SH provides lighter S-containing fragments in the plasma, permitting the S-containing polymer to deposit the passivation layer on the sidewalls of the structure being etched (see FIG. 1a) more effectively during the etch process, thereby protecting the integrity of the hardmask profile and leading to an etch profile that is desired. The presence of H in the S-containing polymer passivation layer may also strengthen the polymer, making it more resistant to damage from the etching environment than layers containing less H. Exemplary compounds having the formula R.sup.1—SH include F.sub.3CSH (CAS 1493-15-8), F.sub.3C—CF.sub.2—SH (CAS 1540-78-9), F.sub.3C—CH.sub.2—SH (CAS 1544-53-2), CHF.sub.2—CF.sub.2—SH (CAS 812-10-2), CF.sub.3—CF.sub.2—CH.sub.2—SH (CAS 677-57-6), and F.sub.3C—CH(SH)—CF.sub.3 (CAS 1540-06-3).

(25) In another alternative, the compound has the formula R.sup.2—S—R.sup.3, wherein R.sup.2 and R.sup.3 is each independently a saturated C1 to C4 alkyl or fluoroalkyl group and R.sup.2 and R.sup.3 may be joined to form a 5 or 6 member S-containing ring. Applicants believe that S being in its +2 oxidation state in these molecules provides a better ability to produce fragments suitable for formation of the sidewall polymer passivation layer than those produced from compounds having S in higher oxidation states. The combination of one sulfur atom with two or more carbon atoms in the R2-S—R3 molecule may also produce a carbon rich S-containing polymer passivation layer that may better protect the sidewall from damage during the etch process.

(26) Exemplary linear molecules having the formula R.sup.2—S—R.sup.3 include

(27) F.sub.3C—S—CF.sub.3 (CAS 371-78-8), F.sub.3C—S—CHF.sub.2 (CAS 371-72-2), F.sub.3C—CF.sub.2—S—CF.sub.2—CF.sub.3 (CAS 155953-22-3), and F.sub.3C—CF.sub.2—CF.sub.2—S—CF.sub.2—CF.sub.2—CF.sub.3 (CAS 356-63-8). These compounds may be commercially available or synthesized by reacting Hg(SCF.sub.3).sub.2 with MeI (see, e.g., Yu et al., Inorganic Chemistry (1974), 13(2), 484-6). Alternatively, the compound may be synthesized by photolysis of CF.sub.3SOC(O)Me (see, id.).

(28) Exemplary cyclic molecules having the formula R.sup.2—S—R.sup.3 include

(29) c(—S—CF.sub.2—CF.sub.2—CHF—CF.sub.2—) (CAS 1035804-79-5), c(—S—CF.sub.2—CHF—CHF—CF.sub.2—) (CAS 30835-84-8), c(—S—CF.sub.2—CF.sub.2—CF.sub.2—CF.sub.2—CF.sub.2—) (CAS 24345-52-6), c(—S—CFH—CF.sub.2—CF.sub.2—CFH—)(2 R, 5 R) (CAS 1507363-75-8), c(—S—CFH—CF.sub.2—CF.sub.2—CFH—)(2 R, 5 S) (CAS 1507363-76-9), and c(—S—CFH—CF.sub.2—CF.sub.2—CH.sub.2—) (CAS 1507363-77-0). These compounds may be synthesized by fluorinating the analogous unsaturated S-containing ring structure with potassium tetrafluorocobaltate (III) (see, e.g., Coe, e-EROS Encyclopedia of Reagents for Organic Synthesis, No pp. given; 2001). Alternatively, these compounds may be synthesized by vacuum pyrolysis of copolymers of unit structures —(CF.sub.2).sub.mS(CF.sub.2).sub.nS—. The —(CF.sub.2).sub.mS(CF.sub.2).sub.nS— copolymers may be produced by reacting F.sub.2C:CF.sub.2 with CSF.sub.2 or tetrafluorothiirane. (see, e.g., James and Rowsell, Journal of the Chemical Society [Section] D: Chemical Communications (1969)(21), 1274-5).

(30) The disclosed sulfur-containing plasma etch compounds are provided at between approximately 99.9% v/v and approximately 100.0% v/v purity, preferably between approximately 99.99% v/v and approximately 100.00% v/v purity, and more preferably between approximately 99.999% v/v and approximately 100.000% v/v purity. The disclosed etch compounds 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 150 ppm by volume of nitrogen-containing and oxygen-containing gases, such as N.sub.2 and/or H.sub.2O and/or HF and/or H.sub.2S and/or CO.sub.2 and/or CO, and/or SO.sub.2 contained in said trace gaseous impurities. Preferably, the water content in the plasma etch compound is between approximately 0 ppm by weight and approximately 20 ppm by weight. The purified product may be produced by distillation and/or passing the gas or liquid through a suitable adsorbent, such as a 4 A molecular sieve.

(31) In one alternative the disclosed plasma etch compounds contains between approximately 0% v/v and approximately 5% v/v, preferably between approximately 0% v/v and approximately 1% v/v, more preferably between approximately 0.0% v/v and approximately 0.1% v/v, and even more preferably between approximately 0.00% v.v. and approximately 0.01% v/v of any of its isomers. This alternative may provide better process repeatability. This alternative may be produced by distillation of the gas or liquid. Alternatively, the disclosed plasma etch compounds may contain between approximately 5% v/v and approximately 50% v/v of one or more of its isomers, particularly when the isomer mixture provides improved process parameters or isolation of the target isomer is too difficult or expensive. For example, a mixture of isomers may reduce the need for two or more gas lines to the plasma reactor. One exemplary mixture may combine 50% v/v F.sub.3C—CF.sub.2—SH (CAS 1540-78-9) with 50% v/v F.sub.3C—S—CHF.sub.2 (CAS 371-72-2) or 90% c(—S—CFH—CF.sub.2—CF.sub.2—CFH—) (2 R, 5 R) (CAS 1507363-75-8) with 10% c(—S—CFH—CF.sub.2—CF.sub.2—CFH—)(2 R, 5 S) (CAS 1507363-76-9).

(32) The disclosed compounds are suitable for plasma etching channel holes, gate trenches, staircase contacts, capacitor holes, contact holes, etc., in one or more Si-containing layers and compatible with the current and future generation of mask materials because they induce little to no damage on the mask along with good profile of high aspect ratio structures. In order to achieve those properties, the S atoms contained in the disclosed compounds may deposit an etch-resistant polymer layer during etching and help reduce the direct impact of the oxygen and fluorine radicals during the etching process. The disclosed compounds may also reduce damage to poly-Si channel structure during etching (see US 2011/0180941). Preferably, the S-containing compound is both suitably volatile and stable during the etching process for delivery into the reactor/chamber.

(33) Material compatibility tests are important to determine if any of the S-containing compounds will react with the chamber materials and degrade its performance with short term or long term use. Key materials involved in parts of chamber, valves, etc. include Stainless Steel, Aluminum, Nickel, PCTFE, PVDF, PTFE and other metals and polymers. At times these materials are exposed to higher temperatures and pressures which may enhance their degradation. The metrology methods may include visual inspection, weight measurement, measuring nanometer scale changes in SEM, tensile strength, hardness, etc.

(34) The disclosed sulfur-containing compounds may be used to plasma etch silicon-containing layers on a substrate. The disclosed plasma etching method may be useful in the manufacture of semiconductor devices such as NAND or 3D NAND gates or Flash or DRAM memory. The other areas of applications include its use in different front end of the line (FEOL) and back end of the line (BEOL) etch applications. Additionally, it may also include etching Si for 3D TSV (Through Silicon Via) etch applications for interconnecting memory substrates on logic substrates.

(35) The plasma etching method includes providing a reactor having a substrate disposed therein. The reactor may be any enclosure or chamber within a device in which etching methods take place such as, and without limitation, Reactive Ion Etching (RIE), Dual Capacitively Coupled Plasma with single or multiple frequency RF sources, Inductively Coupled Plasma (ICP), or Microwave Plasma reactors, or other types of etching systems capable of selectively removing a portion of the Si containing layer or generating active species. One of ordinary skill in the art will recognize that the different reactor designs provide different electron temperature control. Suitable commercially available reactors include but are not limited to the Applied Materials magnetically enhanced reactive ion etcher sold under the trademark eMAX™ or the Lam Research Dual CCP reactive ion etcher Dielectric etch product family sold under the trademark 2300® Flex™.

(36) The reactor may contain one or more than one substrate. For example, the reactor may contain from 1 to 200 silicon wafers having from 25.4 mm to 450 mm diameters. Alternatively, the S-containing compounds may be used to remove Si-containing substrates from the reactor walls. A substrate is generally defined as the material on which a process is conducted. The substrates may be any suitable substrate used in semiconductor, photovoltaic, flat panel or LCD-TFT device manufacturing. Typically the substrate will be a patterned substrate having multiple layers thereon. Examples of suitable layers include without limitation silicon (such as amorphous silicon, polysilicon, crystalline silicon, any of which may further be p-doped or n-doped), silica, silicon nitride, silicon oxide, silicon oxynitride, tungsten, titanium nitride, tantalum nitride, mask materials such as amorphous carbon, antireflective coatings, photoresist materials, or combinations thereof. Additionally, layers comprising tungsten or noble metals (e.g. platinum, palladium, rhodium or gold) may be used.

(37) The substrate may include a stack of multiple layers thereon similar to those shown in FIG. 1. In FIG. 1, a stack of seven SiO/SiN layers is located on top of a silicon wafer substrate (i.e., ONON or TCAT technology). One of ordinary skill in the art will recognize that some technologies replace the SiN layers with polySi layers (i.e., SiO/polySi or P-BIOS technology). An amorphous carbon mask layer is located on top of the seven SiO/SiN layers. An antireflective coating layer is located on top of the amorphous carbon mask. A pattern photoresist layer is located on top of the antireflective coating. The stack of layers in FIG. 1 reflects layers similar to those used to produce a 3D NAND gate. One of ordinary skill in the art will recognize that the stack of layers in FIG. 1 is provided for exemplary purposes only and that the disclosed sulfur-containing compounds may be used to etch other stacks of layers. Furthermore, one of ordinary skill in the art will recognize that the number SiO/SiN or SiO/poly-Si layers in the stack may vary (i.e., may include more or less than the seven SiO/SiN layers depicted)

(38) Alternatively, the substrate may include a stack of multiple layers thereon similar to those shown in FIG. 2. In FIG. 2, a stack of four layers is located on top of a silicon wafer substrate. An amorphous carbon mask layer is located on top of a large SiO layer. An antireflective coating layer is located on top of the amorphous carbon mask. A pattern photoresist layer is located on top of the antireflective coating. The stack of layers in FIG. 2 reflects layers similar to those used to produce a DRAM memory. One of ordinary skill in the art will recognize that the stack of layers in FIG. 2 is provided for exemplary purposes only and that the disclosed sulfur-containing compounds may be used to etch other stacks of layers. Furthermore, one of ordinary skill in the art will recognize that the number of layers in the stack may vary (i.e., may include more or less than the four layers depicted).

(39) The vapor of the disclosed sulfur-containing compound is introduced into the chamber containing the substrate and silicon-containing layers. The vapor may be introduced to the chamber at a flow rate ranging from approximately 0.1 sccm to approximately 1 slm. For example, for a 200 mm wafer size, the vapor may be introduced to the chamber at a flow rate ranging from approximately 5 sccm to approximately 50 sccm. Alternatively, for a 450 mm wafer size, the vapor may be introduced to the chamber at a flow rate ranging from approximately 25 sccm to approximately 250 sccm. One of ordinary skill in the art will recognize that the flow rate will vary from tool to tool.

(40) The disclosed sulfur-containing compounds may be supplied either in neat form or in a blend with a suitable solvent, such as ethyl benzene, xylenes, mesitylene, decane, or dodecane. The disclosed sulfur-containing compounds may be present in varying concentrations in the solvent. The vapor form of the sulfur-containing compounds may be produced by vaporizing the neat or blended sulfur-containing compounds solution through a conventional vaporization step such as direct vaporization or by bubbling. The neat or blended S-containing compounds may be fed in liquid state to a vaporizer where it is vaporized before it is introduced into the reactor. Alternatively, the neat or blended S-containing compounds may be vaporized by passing a carrier gas into a container containing the disclosed S-containing compounds or by bubbling the carrier gas into the disclosed S-containing compounds. The carrier gas may include, but is not limited to, Ar, He, N.sub.2, and mixtures thereof. Bubbling with a carrier gas may also remove any dissolved oxygen present in the neat or blended S-containing compounds solution. The carrier gas and disclosed S-containing compounds are then introduced into the reactor as a vapor.

(41) If necessary, the container containing the disclosed S-containing compounds may be heated to a temperature that permits the S-containing compounds to be in liquid phase and to have a sufficient vapor pressure. The container may be maintained at temperatures in the range of, for example, approximately 0° C. to approximately 150° C. Those skilled in the art recognize that the temperature of the container may be adjusted in a known manner to control the amount of S-containing compound vaporized.

(42) The vapor of the disclosed S-containing compounds is activated by plasma to produce an activated vapor. The plasma decomposes the S-containing compound into radical form (i.e., the activated S-containing compound). The plasma may be generated by applying RF or DC power. The plasma may be generated with a RF power ranging from about 25 W to about 10,000 W. The plasma may be generated or present within the reactor itself. The plasma may be generated in Dual CCP or ICP mode with RF applied at both electrodes. RF frequency of plasma may range from 200 KHz to 1 GHz. Different RF sources at different frequency can be coupled and applied at same electrode. Plasma RF pulsing may be further used to control molecule fragmentation and reaction at substrate. One of skill in the art will recognize methods and apparatus suitable for such plasma treatment.

(43) An inert gas is also introduced into the reactor in order to sustain the plasma. The inert gas may be He, Ar, Xe, Kr, Ne, or combinations thereof. The vapor of the S-containing compound and the inert gas may be mixed prior to introduction to the chamber, with the inert gas comprising between approximately 50% v/v and approximately 95% v/v of the resulting mixture. Alternatively, the inert gas may be introduced to the chamber continuously while the vapor of the S-containing compound is introduced to the chamber in pulses.

(44) Quadropole mass spectrometer, optical emission spectrometer, FTIR, or other radical/ion measurement tools may measure the activated vapor to determine the types and numbers of species produced. If necessary, the flow rate of the vapor and/or the inert gas may be adjusted to increase or decrease the number of radical species produced.

(45) The disclosed S-containing compounds 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. In another alternative, the vapor of the S-containing compound may be introduced into the chamber independently of the other gases such as when two or more of the gases react.

(46) Exemplary gases include, without limitation, oxidizers such as O.sub.2, O.sub.3, CO, CO.sub.2, NO, N.sub.2O, NO.sub.2, and combinations thereof. The vapor of the S-containing compound and the oxidizer may be mixed together prior to introduction into the chamber. Alternatively, the oxidizer may be introduced continuously into the chamber and the vapor of the S-containing compound introduced into the chamber in pulses. The oxidizer may comprise between approximately 5% v/v to approximately 100% v/v of the mixture introduced into the chamber (with 100% v/v representing introduction of pure oxidizer for the continuous introduction alternative).

(47) Other exemplary gases with which the vapors of the S-containing compounds may be mixed include additional etching gases, such as cC.sub.4F.sub.8, C.sub.4F.sub.8, C.sub.4F.sub.6, 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; SO.sub.2; trans-1,1,1,4,4,4-hexafluoro-2-butene; cis-1,1,1,4,4,4-hexafluoro-2-butene; hexafluoroisobutene; hexafluorocyclobutane (trans-1,1,2,2,3,4); pentafluorocyclobutane (1,1,2,2,3-); tetrafluorocyclobutane (1,1,2,2-); or hexafluorocyclobutane (cis-1,1,2,2,3,4). The vapor of the S-containing compound and the etching gas may be mixed prior to introduction to the chamber. The etching gas may comprise between approximately 1% v/v to approximately 99.9% v/v of the mixture introduced into the chamber.

(48) The Si-containing layers and the activated vapor react to form volatile species that are removed from the reactor. The amorphous carbon mask, antireflective coating, and photoresist layer may be less reactive with the vapor of the disclosed sulfur-containing compound.

(49) The temperature and the pressure within the reactor are held at conditions suitable for the silicon-containing layer to react with the activated S-containing gas. For instance, the pressure in the reactor may be held between approximately 0.1 mTorr and approximately 1000 Torr, preferably between approximately 1 mTorr and approximately 10 Torr, more preferably between approximately 10 mTorr and approximately 1 Torr, and more preferably between approximately 10 mTorr and approximately 100 mTorr, as required per the etching parameters. Likewise, the substrate temperature in the reactor may range between about approximately −196° C. to approximately 500° C., preferably between −120° C. to approximately 300° C., and more preferably between −10° C. to approximately 40° C. Chamber wall temperatures may range from approximately −196° C. to approximately 300° C. depending on the process requirements.

(50) The reactions between the Si-containing layer and the plasma activated S-containing compound results in removal of the Si-containing layer from the substrate. Atoms of nitrogen, oxygen, and/or carbon may also be present in the Si-containing layer. The removal is due to a physical sputtering of Si-containing layer from plasma ions (accelerated by the plasma) and/or by chemical reaction of plasma species to convert Si to volatile species, such as SiF.sub.x, wherein x ranges from 1-4.

(51) The plasma activated vapor of the S-containing compound preferably exhibits high selectivity toward the mask and etches through the alternating layers of SiO and SiN resulting in a vertical etch profile with no bowing, which is important for 3D NAND applications. For other applications, such as DRAM and 2D NAND, for example, the plasma activated vapor of the S-containing compound may selectively etch SiO from SiN. The plasma activated vapor of the S-containing compound preferably selectively etches SiO and/or SiN from mask layers, such as amorphous carbon, photoresist, polysilicon, or silicon carbide; or from metal contact layers, such as Cu; or from channel regions consisting of SiGe or polysilicon regions.

(52) The disclosed etch processes using the disclosed S-containing compounds produce channel holes, gate trenches, staircase contacts, capacitor holes, contact holes, etc., in the Si-containing layers. The resulting aperture may have an aspect ratio ranging from approximately 10:1 and approximately 100:1 and a diameter ranging from approximately 40 nm to approximately 50 nm. For example, one of ordinary skill in the art will recognize that a channel hole etch produces apertures in the Si-containing layers having an aspect ratio greater than 60:1.

(53) In one non-limiting exemplary plasma etch process, the vapor of C.sub.2F.sub.3H.sub.3S is introduced into a 200 mm Dual CCP plasma etch tool using a controlled gas flow device. The device may be a mass flow controller or a bubbler design with inert gas flow to deliver the vapor of the desired molecule. In case of high boiling point molecules, special low pressure drop mass flow controller from Brooks Automation (No. GF120XSD), MKS Instruments, etc., may be used. The pressure of the plasma etch tool is set at approximately 30 mTorr. No gas source heating is necessary, as the vapor pressure of this compound is approximately 400 torr at room temperature. The distance between the two CCP electrodes is kept at 1.35 cm and the top electrode RF power is fixed at 750 W. The bottom electrode RF power is varied to analyze the performance of the molecule. The plasma etch tool includes a chamber containing a substrate having Si-containing layers thereon. Argon is independently introduced into the chamber at a 250 sccm flow rate. C.sub.2H.sub.3F.sub.3S is independently introduced into the chamber at 15 sccm. O.sub.2 is independently introduced into the chamber at 0-20 sccm to determine optimum etching conditions.

EXAMPLES

(54) 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.

Example 1

(55) Analysis of C.sub.2H.sub.3F.sub.3S (2,2,2-trifluoroethanethiol or F.sub.3C—CH.sub.2—SH) purchased from Sigma Aldrich was performed by mass spectrometry (MS) to study the electron impact ionization. The C.sub.2H.sub.3F.sub.3S etchant flowed through a mass spectrometer chamber and a quadrupole mass spectrometer (Hiden Analytical Inc.) detector studied the fragments from the etch gas as a function of electron energy. The resulting MS graph plotting the volume of plasma species fractions (Torr) versus energy (eV) is shown in FIG. 3. FIG. 3 shows that the major fragments for C.sub.2H.sub.3F.sub.3S are CH.sub.3S and CHS. These fragments lack fluorine and are therefore readily polymerize upon reaching the substrate.

(56) Materials compatibility tests were also performed on C.sub.2H.sub.3F.sub.3S. Vapor of C.sub.2H.sub.3F.sub.3S was introduced into and isolated in an evacuated stainless steel container having samples of stainless steel, nickel, aluminum, PCTFE (polychlorotrifluoroethylene), PVDF (polyvinylidine fluoride), and PTFE (polytetrafluoroethylene) therein. The pressure in the container after isolation was therefore approximately the vapor pressure of C.sub.2H.sub.3F.sub.3S (0.55 bar at 20° C.). The container was maintained at this pressure and room temperature for one month. No degradation of the samples was observed.

Example 2

(57) Analysis of C.sub.2F.sub.4S.sub.2 (2,2,4,4-tetrafluoro-1,3-dithietane) purchased from SynQuest was performed by mass spectrometry (MS) to study the electron impact ionization. The C.sub.2F.sub.4S.sub.2 etchant flowed through the same mass spectrometer chamber and quadrupole mass spectrometer detector used in Example 1 to study the fragments from the etch gas as a function of electron energy. The resulting MS graph plotting the volume of plasma species fractions (Torr) versus energy (eV) is shown in FIG. 4. FIG. 4 shows that the major fragments for C.sub.2F.sub.4S.sub.2 are CFS and CF.sub.2S. These fragments have sulfur in the fragment and may therefore polymerize upon reaching the substrate.

Comparative Example 1

(58) MS analysis of C.sub.2F.sub.6S.sub.2 (bis(trifluoromethyl)disulfide) purchased from Synquest was performed to study the electron impact ionization. The C.sub.2F.sub.6S.sub.2 etchant flowed through the same mass spectrometer chamber and quadrupole mass spectrometer (Hiden Analytical Inc.) detector used in Examples 1 and 2 to study the fragments from the etch gas as a function of electron energy. The resulting MS graph plotting the volume of plasma species fractions (Torr) versus energy (eV) is shown in FIG. 5.

(59) Comparing FIGS. 3 and 4 to FIG. 5, a larger abundance of sulfur containing fragments was generated by C.sub.2H.sub.3F.sub.3S and C.sub.2F.sub.4S.sub.2 than by C.sub.2F.sub.6S.sub.2. This means that C.sub.2H.sub.3F.sub.3S and C.sub.2F.sub.4S.sub.2 will provide more sulfur containing plasma species with improved passivation film on the planar and vertical layers during plasma etch process. The sulfur film being more etch resistant to etch may lead to a better etch profile and allow high aspect ratio etching.

(60) Additionally, a F:C ratio of ranging from 0.1:1 to 3:1 is desired for enhanced polymer formation on the sidewalls of the structure being etched (see FIG. 1a). The mass spectrometer species for both C.sub.2H.sub.3F.sub.3S and C.sub.2F.sub.4S.sub.2 shows a lower F:C ratio in comparison with the species for C.sub.2F.sub.6S.sub.2. As a result, these two molecules may favor stronger polymer characteristics.

(61) Materials compatibility tests were also performed on C.sub.2F.sub.6S.sub.2. Vapor of C.sub.2F.sub.6S.sub.2 was introduced into and isolated in an evacuated stainless steel container having samples of stainless steel, nickel, aluminum, PCTFE (polychlorotrifluoroethylene), PVDF (polyvinylidine fluoride), and PTFE (polytetrafluoroethylene) therein. The pressure in the container after isolation was therefore approximately the vapor pressure of C.sub.2F.sub.6S.sub.2 (0.6 bar at 20° C.). The container was maintained at this pressure and room temperature for one month. No degradation of the samples was observed.

Example 3

(62) Plasma vapor deposition testing was performed with C.sub.2H.sub.3F.sub.3S on 1×1 cm.sup.2 Si coupons. The testing was performed in a commercial LAM 4520 XLE etcher, schematically shown in FIG. 6. The etcher is a dual frequency capacitively coupled plasma reactor equipped with two 8 inch electrodes that allows independent control of number density and ion energy. The upper electrode was connected to a 27 MHz power supply (source power), that allows independent control of number density. The Si coupon was placed on the temperature controlled bottom electrode connected to a 2 MHz power supply (bias power) that allows independent control of ion energy. A 8 inch silicon showerhead on the upper electrode allowed a uniform distribution of the feed gas during plasma processes.

(63) 15 sccm C.sub.2H.sub.3F.sub.3S via 250 sccm of Ar gas was introduced through the showerhead for 60 seconds into the etcher having 750 W/0 W bias, 30 mTorr pressure, and a 1.35 cm gap between the top surface of the electrostatic chuck and the bottom surface of the showerhead. A 90 nm polymer film was deposited on the Si coupon (measured at 3 points by Scanning Electron Microscope (SEM)). As a result, the deposition rate was approximately 90 nm/minute. The sample was sent for X-ray photoelectron spectroscopy (XPS) analysis. The resulting XPS graph plotting an atom's electron binding energy on the X axis versus the count (number of electrons detected) on the Y axis is shown in FIG. 7. The wide scan elemental analysis of FIG. 7 shows the presence of C, F, O, and S peaks, and more particularly a S 2s peak at approximately 228 ev and a S 2p peak at approximately 164 eV.

(64) Some portion of the deposited film included a powdery material (see FIGS. 8A and 8B). The uniform film deposited can be seen below the powder particle in FIGS. 8A and 8B. Even when bias power of 1500 W is applied, when no oxygen is added, powdery material was observed on the Si wafer. One of ordinary skill in the art will recognize that the polymer and powder formation may be controlled by changing process parameters, such as bias power and/or oxygen flow rate.

Example 4

(65) Plasma vapor deposition testing was performed with C.sub.2F.sub.4S.sub.2 on 1×1 cm.sup.2 Si coupons. The testing was performed in the same commercial LAM 4520 XLE etcher used in Example 3 and schematically shown in FIG. 6. The upper electrode was connected to a 27 MHz power supply (source power), that allows independent control of number density. The Si coupon was placed on the temperature controlled bottom electrode connected to a 2 MHz power supply (bias power) that allows independent control of ion energy. A 8 inch silicon showerhead on the upper electrode allowed a uniform distribution of the feed gas during plasma processes.

(66) 15 sccm C.sub.2F.sub.4S.sub.2 via 250 sccm of Ar gas was introduced through the showerhead for 60 seconds into the etcher having 750 W/0 W bias, 30 mTorr pressure, and a 1.35 cm gap between the top surface of the electrostatic chuck and the bottom surface of the shower head. A 75 nm polymer film was deposited on the Si coupon (measured at 3 points by SEM). As a result, the deposition rate was approximately 75 nm/minute.

Comparative Example 2

(67) Plasma vapor deposition testing was performed with C.sub.2F.sub.6S.sub.2 on 1×1 cm.sup.2 Si coupons. 15 sccm C.sub.2F.sub.6S.sub.2 via 250 sccm of Ar gas was introduced for 60 seconds into the etcher of FIG. 6 having 750 W/0 W bias, 30 mTorr pressure, and a 1.35 cm gap. No film was deposited. The sample was sent for XPS analysis. The resulting XPS graph is shown in FIG. 9, showing only Si and O peaks, and more particularly a Si 2s peak at approximately 156 ev and a Si 2p peak at approximately 105 eV. No evidence of either C or S in FIG. 9 indicates that no protective polymer was formed. The lack of deposition will not provide sufficient passivation during the plasma etch process and therefore may lead to high bowing in the etched structures. As a result, the C.sub.2F.sub.6S.sub.2 etchant will not be useful for applications that require profile control or sidewall passivation.

Example 5

(68) Etching experiments were performed with C.sub.2H.sub.3F.sub.3S on four 1×1 cm.sup.2 coupons that were glued to the 200 mm Si carrier wafer using double sided carbon tape. The four substrate materials investigated were Silicon oxide (SiO.sub.2), Silicon Nitride (SiN), polysilicon (p-Si), and amorphous carbon (a-C). The etching tests were performed in the etcher of FIG. 6 set at a pressure of 30 mTorr, source power of 750 W (27 MHz), and bias power of 1500 W (2 MHz). The feed mixture contained 250 sccm of Ar and 15 sccm of C.sub.2H.sub.3F.sub.3S. The oxygen (O.sub.2) flow rate varied from 0 to 15 sccm. The etch rates were measured using an ellipsometer and the deposition rates were measured by SEM by measuring the change in film thickness as a function of process time.

(69) The resulting etch rates of SiO.sub.2, SiN, p-Si and a-C using C.sub.2H.sub.3F.sub.3S are plotted as a function of oxygen flow rate in sccm and are presented in FIG. 10. The positive y-axis represents etch rates while the negative y-axis represents deposition rates. The x-axis is O.sub.2 flow in sccm. As oxygen is added, the SiO.sub.2:a-C selectivity drops drastically and there is a condition where a-C etch rates are higher than those for the SiO.sub.2 and SiN films.

(70) As illustrated in FIG. 10, when no oxygen is added (0 sccm O.sub.2 condition), the etch rates of SiO.sub.2 and SiN are close to one another (with Selectivity ˜1:1, and etch rate of ˜300 nm/min), while uniform deposition (no powder) is seen on the p-Si and a-C substrates. As a result, this compound may be suitable for the 3D NAND process, which requires the etch rates of SiO.sub.2 and SiN to be similar and the etch rates of p-Si and a-C to be low. The similar etch rates for SiO.sub.2 and SiN may result in less bowing and faceting. The low etch rates for p-Si and a-C may help to preserve the mask material. However, the etch rates of SiO.sub.2 and SiN are lower than those for the standard cC.sub.4F.sub.8 gas (above 550 nm/min). Additional etch gases, such as CF.sub.4, may be added to increase the etch rate (see Example 6).

Comparative Example 3

(71) Etching experiments were performed with cC.sub.4F.sub.8 as a function of O.sub.2 flowrate, under similar process conditions described in Example 5. The results are shown in FIG. 13. As illustrated in FIG. 13, the selectivity of SiO.sub.2 and SiN with respect to p-Si and a-C is lower than C.sub.2H.sub.3F.sub.3S when no oxygen is added.

Comparative Example 4

(72) Etching experiments were performed with C.sub.4F.sub.6 as a function of O.sub.2 flowrate, under similar process conditions described in Example 5. The results are shown in FIG. 14. As illustrated in FIG. 14, the selectivity of SiO.sub.2 and SiN with respect to p-Si and a-C is higher for C.sub.4F.sub.6 than it is for C.sub.2H.sub.3F.sub.3S. However, the SiO.sub.2:SiN selectivity of C.sub.4F.sub.6 is higher than it is in Example 5, making C.sub.4F.sub.6 less suitable for some applications. The C.sub.2H.sub.3F.sub.3S molecule, on the other hand, gives similar etch rates for SiO.sub.2 and SiN, when no oxygen is added, as shown in FIG. 10.

Example 6

(73) In order to improve the C.sub.2H.sub.3F.sub.3S etch rates of the SiO.sub.2/SiN films to be comparable to the performance of cC.sub.4F.sub.8, CF.sub.4 was added to the etch gas mixture of 250 sccm Ar and 15 sccm C.sub.2H.sub.3F.sub.3S. The CF.sub.4 addition varied from 0 to 15 sccm. As illustrated in FIG. 11, adding CF.sub.4 to the process gas mixture increases the etch rates of SiO.sub.2/SiN to 400 nm/min and above, while maintaining the selectivity to p-Si and a-C, making this an excellent molecule for 3D NAND application.

Comparative Example 5

(74) Etching experiments were also performed where CF.sub.4 was added to the etch gas mixture of 250 sccm Ar and 15 sccm cC.sub.4F.sub.8 and results are shown in FIG. 15. As illustrated in FIG. 15, the etch rates of all the four substrates increased and as a result no improvement in selectivity is obtained. On the other hand, using C.sub.2H.sub.3F.sub.3S, the etch rates of SiO.sub.2 and SiN are increased thus increasing selectivity to p-Si and a-C.

Example 7

(75) Etching experiments were performed with C.sub.2F.sub.4S.sub.2 on four 1×1 cm.sup.2 coupons that were glued to the 200 mm Si carrier wafer using double sided carbon tape. The four substrate materials investigated were Silicon oxide (SiO.sub.2), Silicon Nitride (SiN), polysilicon (p-Si), and amorphous carbon (a-C). The etching tests were performed in the etcher of FIG. 6 set at a pressure of 30 mTorr, source power of 750 W (27 MHz), and bias power of 1500 W (2 MHz). The feed mixture contained 250 sccm of Ar and 15 sccm of C.sub.2F.sub.4S.sub.2. The oxygen (O.sub.2) flow rate varied from 0 to 15 sccm. The etch rates were measured using an ellipsometer and the deposition rates were measured using SEM by measuring the change in film thickness as a function of process time.

(76) The resulting etch rates of SiO.sub.2, SiN, p-Si and a-C using C.sub.2F.sub.4S.sub.2 are plotted as a function of oxygen flow rate in sccm and are presented in FIG. 12. The positive y-axis represents etch rates while the negative y-axis represents deposition rates. The x-axis is O.sub.2 flow in sccm. As the oxygen flow rate increases, the etch rate of SiO.sub.2 decreases while the etch rates for p-Si and a-C increases. As a result, the selectivity of SiO.sub.2 to a-C and p-Si decreases with increased oxygen flow rates.

(77) As illustrated in FIG. 12, the etch rates for SiO.sub.2, SiN and p-Si are approximately the same at a 15 sccm O.sub.2 flow rate. This may indicate that C.sub.2F.sub.4S.sub.2 generates free fluorine as the dominant etchant at this flow rate, making C.sub.2F.sub.4S.sub.2 a good additive to highly polymerizing gases, such as C.sub.4F.sub.6 and C.sub.5F.sub.8.

(78) While embodiments of this invention have been shown and described, modifications thereof can 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.