Etching method using oxygen-containing hydrofluorocarbon
12628589 · 2026-05-12
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Inventors
Cpc classification
International classification
Abstract
An etching method for forming a high aspect ratio aperture by selectively etching one or more silicon-containing films in a substrate using a patterned mask layer deposited on top of the one or more silicon-containing films comprises: mounting the substrate in a processing chamber; introducing an etching gas containing a vapor of an oxygen-containing hydrofluorocarbon into the processing chamber; converting the etching gas to a plasma; and allowing an etching reaction to proceed between the plasma and the one or more silicon-containing films so that the one or more silicon-containing films are selectively etched versus the patterned mask layer to form the high aspect ratio aperture, wherein the oxygen-containing hydrofluorocarbon has a general formula C.sub.xH.sub.yF.sub.zO.sub.n, where 2x13, 1y15, 1z21, 1n3.
Claims
1. An etching method for forming a high aspect ratio aperture by selectively etching one or more silicon-containing films in a substrate using a patterned mask layer deposited on top of the one or more silicon-containing films, the method comprising: mounting the substrate in a processing chamber; introducing an etching gas containing a vapor of an oxygen-containing hydrofluorocarbon into the processing chamber; converting the etching gas to a plasma; and allowing an etching reaction to proceed between the plasma and the one or more silicon-containing films so that the one or more silicon-containing films are selectively etched versus the patterned mask layer to form the high aspect ratio aperture, wherein the oxygen-containing hydrofluorocarbon has a general formula C.sub.xH.sub.yF.sub.zO.sub.n, where 2x13, 1y15, 1z21, 1n3, provided that when x=4, y3, z7, n1, wherein the oxygen-containing hydrofluorocarbon has at least one ether group represented by one of following formulas:
R.sub.1COOCH.sub.2R.sub.1,
R.sub.2CH.sub.2OCH.sub.2R.sub.2 or
R.sub.3CHFOCF.sub.2R.sub.1, wherein R.sub.1 is H, F, C.sub.xH.sub.2x+2-zF.sub.z or C.sub.xF.sub.2x+2; R.sub.2 is H, C.sub.xH.sub.2x+2-zF.sub.z or C.sub.xF.sub.2x+2; R.sub.3 is F, C.sub.xH.sub.2x+2-zF.sub.z or C.sub.xF.sub.2x+2, where 2x3 and 1z3.
2. The method of claim 1, wherein the oxygen-containing hydrofluorocarbon contains at least one oxygen atom in an ether group or in a carbonyl group.
3. The method of claim 1, wherein the oxygen-containing hydrofluorocarbon is selected from C.sub.4H.sub.2F.sub.6O.sub.2, C.sub.3H.sub.2F.sub.6O, C.sub.2H.sub.2F.sub.4O, C.sub.2HF.sub.3O, C.sub.3H.sub.5F.sub.3O, C.sub.2H.sub.4F.sub.2O, C.sub.5H.sub.4F.sub.8O, C.sub.5HF.sub.11O, C.sub.2H.sub.3F.sub.3O, or their isomers.
4. The method of claim 1, wherein the oxygen-containing hydrofluorocarbon is C.sub.4H.sub.2F.sub.6O.sub.2 or its isomers.
5. The method of claim 1, wherein the oxygen-containing hydrofluorocarbon is C.sub.4H.sub.2F.sub.6O.sub.2, CAS No. 407-38-5.
6. The method of claim 1, wherein the etching gas further includes a vapor of a fluorocarbon or hydrofluorocarbon selected from CF.sub.4, C.sub.2F.sub.6, C.sub.3F.sub.6, C.sub.4F.sub.6, C.sub.4F.sub.8, C.sub.5F.sub.8, C.sub.5F.sub.10, C.sub.6F.sub.12, C.sub.7F.sub.14, C.sub.8F.sub.16, CH.sub.2F.sub.2, CH.sub.3F, CHF.sub.3, C.sub.5HF.sub.7, C.sub.3H.sub.2F.sub.6, C.sub.3H.sub.4F.sub.2, C.sub.3F.sub.2H.sub.4, C.sub.4H.sub.2F.sub.6, C.sub.4H.sub.3F.sub.7, C.sub.3HF.sub.4N, CF.sub.3I, C.sub.3F.sub.7I, C.sub.4F.sub.9I, C.sub.4H.sub.9F.sub.3Si, C.sub.5H.sub.9F.sub.5Si or combinations thereof.
7. The method of claim 1, wherein the etching gas further includes an oxidizing gas selected from O.sub.2, O.sub.3, CO, CO.sub.2, SO, SO.sub.2, FNO, N.sub.2, NO, N.sub.2O, NO.sub.2, H.sub.2O, COS or combinations thereof.
8. The method of claim 1, wherein the etching gas further includes an inert gas selected from He, Ar, Xe, Kr or Ne.
9. The method of claim 1, wherein the etching gas further includes an additional gas selected from H.sub.2, SF.sub.6, NF.sub.3, N.sub.2, NH.sub.3, Cl.sub.2, BCl.sub.3, Br.sub.2, F.sub.2, HBr, HCl, PF.sub.3 or combinations thereof.
10. The method of claim 1, wherein an aspect ratio of the high aspect ratio aperture is above 5.
11. The method of claim 1, wherein the one or more silicon-containing films comprise a layer of Si.sub.aO.sub.bH.sub.cC.sub.dN.sub.e, where a>0, b, c, d and e0, selected from silicon oxide, silicon nitride, crystalline Si, poly-silicon, polycrystalline silicon, amorphous silicon, low-k SiCOH, SiOCN, SiC, SiON, or a layer of alternating silicon oxide and silicon nitride (ONON) films or alternating silicon oxide and poly-silicon (OPOP) films.
12. The method of claim 11, wherein a selectivity of the silicon oxide film versus the silicon nitride film in the layer of ONON films ranges from 1:2 to 2:1.
13. An etching method for forming a high aspect ratio aperture by selectively etching a silicon oxide film in a substrate using a patterned mask layer deposited on top of the silicon oxide film, the method comprising: mounting the substrate in a processing chamber; introducing an etching gas containing an oxygen-containing hydrofluorocarbon C.sub.4H.sub.4F.sub.6O or C.sub.4H.sub.2F.sub.6O.sub.2 vapor into the processing chamber; converting the etching gas to a plasma; and allowing an etching reaction to proceed between the plasma and the silicon oxide film so that the silicon oxide film is selectively etched versus the patterned mask layer to form the high aspect ratio aperture.
14. The method of claim 13, wherein the oxygen-containing hydrofluorocarbon is C.sub.4H.sub.2F.sub.6O.sub.2, CAS 407-38-5.
15. The method of claim 13, wherein the etching gas further includes a vapor of a fluorocarbon or hydrofluorocarbon selected from CF.sub.4, C.sub.2F.sub.6, C.sub.3F.sub.6, C.sub.4F.sub.6, C.sub.4F.sub.8, C.sub.5F.sub.8, C.sub.5F.sub.10, C.sub.6F.sub.12, C.sub.7F.sub.14, C.sub.8F.sub.16, CH.sub.2F.sub.2, CH.sub.3F, CHF.sub.3, C.sub.5HF.sub.7, C.sub.3H.sub.2F.sub.6, C.sub.3H.sub.4F.sub.2, C.sub.3F.sub.2H.sub.4, C.sub.4H.sub.2F.sub.6, C.sub.4H.sub.3F.sub.7, C.sub.3HF.sub.4N, CF.sub.3I, C.sub.3F.sub.7I, C.sub.4F.sub.9I, C.sub.4H.sub.9F.sub.3Si, C.sub.5H.sub.9F.sub.5Si or combinations thereof.
16. The method of claim 13, wherein the etching gas further includes an oxidizing gas selected from O.sub.2, O.sub.3, CO, CO.sub.2, SO, SO.sub.2, FNO, N.sub.2, NO, N.sub.2O, NO.sub.2, H.sub.2O, COS or combinations thereof.
17. The method of claim 13, wherein the etching gas further includes an inert gas selected from He, Ar, Xe, Kr or Ne.
18. The method of claim 13, wherein the etching gas further includes an additional gas selected from H.sub.2, SF.sub.6, NF.sub.3, N.sub.2, NH.sub.3, Cl.sub.2, BCl.sub.3, Br.sub.2, F.sub.2, HBr, HCl, PF.sub.3 or combinations thereof.
19. The method of claim 13, wherein an aspect ratio of the high aspect ratio aperture is above 5.
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:
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DESCRIPTION OF PREFERRED EMBODIMENTS
(11) Disclosed are plasma etching methods using new oxygen-containing hydrofluorocarbons based plasma etching chemistry as an etchant for anisotropic etching of silicon oxide, silicon nitride, a stack of alternating silicon oxide and silicon nitride films, and other Si-containing films with high etch rates (ERs), high selectivity to a mask material (e.g., amorphous carbon or doped amorphous carbon), and forming patterns with a defined profile in high aspect ratio structures. The disclosed plasma etching methods may be used in high aspect ratio etching processes for fabrication of 3D NAND structures, contact holes, DRAM capacitors etc., but not limited to those applications. The disclosed plasma etching methods are methods of processing a workpiece including one or more target etching processing films (e.g., silicon oxide, silicon nitride or combinations thereof) and non-processing target films (e.g., amorphous carbon, amorphous silicon, doped amorphous carbon, doped amorphous silicon, metals), when a processing gas mixture including at least one oxygen-containing hydrofluorocarbon (e.g., C.sub.4H.sub.4F.sub.6O, C.sub.4H.sub.2F.sub.6O.sub.2), optionally at least one inert gas (e.g., He, Ar, Kr, Xe, Ne), optionally an oxidizing gas (e.g., O.sub.2, O.sub.3, CO, CO.sub.2, SO, SO.sub.2, FNO, NO, NO.sub.2, H.sub.2O), optionally a fluorocarbon and/or hydrofluorocarbon gas (e.g., C.sub.4F.sub.8, C.sub.4F.sub.6, CH.sub.2F.sub.2) and optionally an additional gas (e.g., SF.sub.6, H.sub.2, C.sub.12, F.sub.2, Br.sub.2, HCl, HBr) is used for the formation of reactive species and ions in the plasma. The workpiece could be any type of targets as long as it may be processed by plasma etching.
(12) Herein the term high aspect ratio etching refers to the formation of a pattern with apertures in a target film by plasma etching method when aspect ratio (ratio of height to width) of formed apertures exceeds a value of 5. High anisotropy of the plasma etching process is required to achieve high aspect ratio of the etched structure. In order to achieve anisotropy of the process (directional etch in the vertical direction when lateral etching is minimized), typically formation of a polymer on the sidewall of the etched structure is used. The formation of the polymer preferentially on the sidewall of the etched structure is achieved by competition between etching process (removal of the polymer) and deposition process (formation of the polymer). Presence of directional (in vertical direction) etching by ion bombardment allows removing the polymer on the horizontal surfaces more effectively than on vertical surfaces, resulting in promotion of the formation of the polymer on vertical sidewalls. Furthermore, fine tuning of the balance between etching and deposition processes allows achieving preferential etching of the workpiece in the vertical direction when etching in lateral direction is suppressed, thereby preserving horizontal dimensions of the etched structure.
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(15) To determine etching performances, blanket, trench, hole or aperture pattern wafers have been examined where the layers to be etched are deposited on a Si substrate defining an initial film thickness. The wafers are etched using a plasma composed of a fluorocarbon or hydrofluorocarbon and additional gas based mixture. Etched layers are partially or totally removed to produce a second defined film thickness. The difference between the first and second defined thicknesses reveals the amount of etched material. The ratio of etched material amount in between different layers (e.g., bulk material, mask, sacrificial layer) defines selectivity. Pattern lateral dimensions (e.g., width for trenches or diameter for holes) at different depths (top, neck, bow, and bottom) are also evaluated. The difference in diameter between etched and non-etched patterns, as well as change in circularity, (in the case of hole pattern) define the level of profile quality control.
(16) In some cases, it is possible to achieve so-called infinite selective etching, when the etching target material is etched while the thickness of non-etching materials remains unchanged or increased (polymer deposition preserving them from etching) after the retching process. Typically, the infinite selectivity comes at cost of lower etch rate comparing to processes with lower selectivity.
(17) <Processing Gases>
(18) In the disclosed etching method, selection of process gases and ratio of each gas concentrations in a process gas mixture is required to achieve balance between deposition process for protection of vertical surfaces (hereafter passivation) and etching process for anisotropic removal of the target material. Typically, combinations of process gases are used, where each gas type is playing different role. The process gas mixture include the disclosed oxygen-containing hydrofluorocarbon gas used as etching gas, at least one inert gas (e.g., N.sub.2, He, Ar, Kr, Xe, Ne) for generation of plasma and promotion of ion bombardment, an oxidizing gas (e.g., O.sub.2, CO, CO.sub.2) to promote isotropic etching and surface or gas phase chemical reactions, and at least one fluorocarbon or hydrofluorocarbon gas (e.g., C.sub.4F.sub.8, C.sub.4F.sub.6, CF.sub.4, CH.sub.2F.sub.2) to promote both anisotropic etching process of target film and vertical surface and/or non-target film passivation.
(19) Each gas in the process gas mixture is provided at greater than 95% v/v purity, preferably at greater than 99.99% v/v purity, and more preferably at greater than 99.999% v/v purity. Each gas in the process gas mixture contains less than 5% by volume trace gas impurities, with less than 150 ppm by volume of impurity gases, such as H.sub.2O, contained in said trace gaseous impurities. Preferably, the water content in the plasma etching gas is less than 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 molecular sieve.
(20) <Hydrofluorocarbon and Fluorocarbon Gas>
(21) Examples of hydrofluorocarbon and/or fluorocarbon gases that may be used in the disclosed plasma etching method include but not limited to compounds CF.sub.4, C.sub.2F.sub.6, C.sub.3F.sub.6, C.sub.4F.sub.6, C.sub.4F.sub.8, C.sub.5F.sub.8, C.sub.5F.sub.10, C.sub.6F.sub.12, C.sub.7F.sub.12, C.sub.8F.sub.16, CF.sub.3I, C.sub.3F.sub.7I, C.sub.4F.sub.9I, C.sub.4H.sub.9F.sub.3Si, or C.sub.5H.sub.9F.sub.5Si. Examples of hydrofluorocarbon gases that may be used in the plasma etching process include but not limited to compounds CH.sub.2F.sub.2, CH.sub.3F, CHF.sub.3, C.sub.5HF.sub.7, C.sub.3H.sub.2F.sub.6, C.sub.3F.sub.2H.sub.4, C.sub.4H.sub.2F.sub.6, C.sub.4H.sub.3F.sub.7 and C.sub.3HF.sub.4N. Under the plasma conditions, various reactive species and ions are generated directly by dissociation of these above-mentioned fluorocarbon and hydrofluorocarbon compounds and chemical reactions through interaction between species presented in the gas phase. Plasma etching may be achieved with any of compounds represented by the above-mentioned compounds, when the mentioned compounds are used individually or mixed with each other. Depending on the structure of individual compound, it may promote either etching performance including increase of etching speed of particular target materials, or passivation during high aspect ratio etching process. In particular, a mixture of C.sub.4F.sub.6 and C.sub.4F.sub.8 is one of commonly used mixtures because C.sub.4F.sub.6 is effective to promote passivation and C.sub.4F.sub.8 is effective to increase the etching speed resulting in a high anisotropy of etching processes. Furthermore, hydrofluorocarbon gases, such as CH.sub.2F.sub.2, may be added to increase the etching speed of silicon nitride film and/or further promote polymer deposition if it is desired.
(22) The disclosed hydrofluorocarbon and fluorocarbon gases are provided at greater than 95% v/v purity, preferably at greater than 99.99% v/v purity, and more preferably at greater than 99.999% v/v purity. The disclosed hydrofluorocarbon and fluorocarbon gases contain less than 5% by volume trace gas impurities, with less than 150 ppm by volume of impurity gases, such as N.sub.2 and/or H.sub.2O and/or CO.sub.2, contained in said trace gaseous impurities. Preferably, the water content in the plasma etching gas is less than 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 molecular sieve.
(23) The hydrofluorocarbon and fluorocarbon gases used herein may contain between 0.01% v/v and 99.99% v/v of its isomers, particularly when the isomer mixture provides improved process parameters or if isolation of the target isomer is too difficult or expensive. The mixture of isomers may also reduce the need for two or more gas lines to the reaction chamber.
(24) <Oxygen-Containing Hydrofluorocarbon Gas>
(25) The disclosed oxygen-containing hydrofluorocarbon gas used in the disclosed methods may have a formula C.sub.xH.sub.yF.sub.zO.sub.n, where 2x10, 1y15, 1z21, 1n3, preferably, at least one oxygen atom is incorporated to the molecule in an ether group or in a carbonyl group.
(26) The disclosed oxygen-containing hydrofluorocarbon gas may contain at least one ether group or in a carbonyl group that may specifically be represented by formula R.sub.1COOCH.sub.2R.sub.1, R.sub.2CH.sub.2OCH.sub.2R.sub.2 or R.sub.3CHFOCF.sub.2R.sub.1, wherein R.sub.1 is H, F, C.sub.xH.sub.2x+2zF.sub.z or C.sub.xF.sub.2x+2; R.sub.2 is H, C.sub.xH.sub.2x+2zF.sub.z or C.sub.xF.sub.2x+2; R.sub.3 is F, C.sub.xH.sub.2x+2zF.sub.z or C.sub.xF.sub.2x+2, where 2x3 and 1z3.
(27) Exemplary disclosed oxygen-containing hydrofluorocarbon gas may include without limitation, C.sub.4H.sub.4F.sub.6O, C.sub.4H.sub.2F.sub.6O.sub.2, C.sub.3H.sub.2F.sub.6O, C.sub.2H.sub.2F.sub.4O, C.sub.2HF.sub.3O, C.sub.3H.sub.5F.sub.3O, C.sub.2H.sub.4F.sub.2O, C.sub.4H.sub.6F.sub.4O, C.sub.5H.sub.4F.sub.8O, C.sub.5HF.sub.11O, C.sub.2H.sub.3F.sub.3O and their isomers.
(28) Examples of C.sub.4H.sub.4F.sub.6O isomers include 1,1,2,3,3,3-Hexafluoropropyl methyl ether (CAS No.: 382-34-3), Bis(2,2,2-trifluoroethyl) Ether (CAS No.: 333-36-8), 2,2,3,4,4,4-Hexafluoro-1-butanol (CAS No.: 382-31-0), 1,1,1,2,3,3-hexafluoroisopropyl methyl ether (CAS No.: 13171-18-1), 1,1,1,3,3,3-Hexafluoro-2-methyl-2-propanol (CAS No.: 1515-14-6), 2,2,3,3-tetrafluoropropyl difluoromethyl ether (CAS No.: 35042-99-0), 1,1,1,2,3,3-hexafluoro-2-methoxypropane (CAS No.: 568550-25-4), hexafluoroisopropyl methyl ether (CAS No.: 27215-56-1), 1-(2,2-Difluoroethoxy)-1,1,2,2-tetrafluoroethane, CAS: 50807-77-7), 2,2,3,3,4,4-Hexafluoro-1-butanol (CAS No.: 60838-59-7), 1,1,2,2,3,3-hexafluoro-1-methoxypropane (CAS No.: 160620-20-2), 1-Propanol, 2-(difluoromethyl)-2,3,3,3-tetrafluoro (CAS No.: 318293-89-9), 1,1,1,4,4,4-hexafluoro-2-butanol (CAS No.: 86884-17-5), 1-hydro-1-methoxyhexafluoropropane (CAS No.: 123202-00-6), 1,1,2,2,3,3-hexafluorobutan-1-ol (CAS No.: 119398-75-3), and 3,3,3-trifluoro-2-(trifluoromethyl)propan-1-ol (CAS No.: 81503-71-1).
(29) Examples of C.sub.4H.sub.2F.sub.6O.sub.2 isomers include 3,3,3-Trifluoro-2-(trifluoromethyl)propanoic acid (CAS No.: 564-10-3), 2,2,2-Trifluoroethyl trifluoroacetate (CAS No.: 407-38-5), 2,2,3,3,4,4-hexafluorobutanoic acid (CAS No.: 679-12-9), 2,2,3,4,4,4-Hexafluorobutanoic acid (CAS No.: 379-90-8), 1,1,1,3,3,3-Hexafluoro-2-propanyl formate (CAS No.: 856766-70-6), Trifluoromethyl 3,3,3-trifluoropropanoate (CAS No.: 93667-89-1), (2E)-1,1,1,4,4,4-Hexafluoro-2-butene-2,3-diol (CAS No.: 856295-72-2), and 1,1,1,4,4,4-Hexafluoro-3-hydroxy-2-butanone (CAS No.: 1683-73-4).
(30) The disclosed oxygen-containing hydrofluorocarbon gases are provided at greater than 95% v/v purity, preferably at greater than 99.99% v/v purity, and more preferably at greater than 99.999% v/v purity. The disclosed oxygen-containing hydrofluorocarbon gases contain less than 5% by volume trace gas impurities, with less than 150 ppm by volume of impurity gases, such as N.sub.2 and/or H.sub.2O and/or CO.sub.2, contained in said trace gaseous impurities. Preferably, the water content in the plasma etching gas is less than 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 molecular sieve.
(31) The disclosed oxygen-containing hydrofluorocarbon gases may contain between 0.01% v/v and 99.99% v/v of its isomers, particularly when the isomer mixture provides improved process parameters or if isolation of the target isomer is too difficult or expensive. The mixture of isomers may also reduce the need for two or more gas lines to the reaction chamber. In case, some of the disclosed oxygen-containing hydrofluorocarbon compounds are non-gaseous compounds at room temperature and atmospheric pressure (i.e., liquid or solid), their gas form may be produced by vaporizing the compounds through a conventional vaporization step, such as direct vaporization or by bubbling with inert gas (such as N.sub.2, Ar, He). The non-gaseous compounds may be fed in liquid state to a vaporizer where it is vaporized before it is introduced into a reactor.
(32) The disclosed oxygen-containing hydrofluorocarbon molecule with at least one ether group or at least one carbonyl group could bring improved uniformity of etched hole's shape by taking advantage of better control of polymer film deposition profile compared to the case when O.sub.2 is used (e.g., increased anisotropy and/or bowing) in the plasma-etching process. Additionally, use of molecule from the disclosed oxygen-containing hydrofluorocarbon molecule allows the etching of Si-containing compounds with higher etch rates while having a lower amorphous carbon etch rate compared to standard fluorocarbon gases (e.g., C.sub.4F.sub.8, CH.sub.2F.sub.2, C.sub.4F.sub.6), resulting in improved selectivity to the mask layer during the etching of high aspect ratio structures. The disclosed oxygen-containing hydrofluorocarbon molecule with at least one ether group or at least one carbonyl group may be beneficial for improvement of high aspect ratio etching process linked to the generation of oxygen-containing hydrofluorocarbon and/or oxygen-containing fluorocarbon fragments by dissociation of the disclosed oxygen-containing hydrofluorocarbon molecule with at least one ether group in the plasma. Commonly O.sub.2 is used in the plasma gas mixture for both control the Si-containing film etch rate and etching profiles by adjusting thickness of the deposited fluorinated polymer film. In contrast, O.sub.2 is also efficient for etching of the amorphous carbon mask layer, leading to reduced selectivity. Furthermore, addition of O.sub.2 promotes isotropic etching and results in removal of fluorinated polymer protection film and amorphous carbon mask, reducing sidewall protection and formation of undesired distortions in pattern's profile (e.g., increase in diameter, bowing). That is, amorphous carbon mask and deposited polymer films are etched faster and more isotropically using O.sub.2. The disclosed oxygen-containing hydrofluorocarbon molecules are capable of providing more anisotropic etching process resulting in better profile control and lower amorphous carbon and fluoropolymer film etch rates. The difference between the disclosed oxygen-containing hydrofluorocarbons and fluorocarbons with addition of molecular oxygen is generated reactive species in plasma. Oxygen-containing fluorocarbon and hydrofluorocarbon fragments produced in the plasma by dissociation of the disclosed oxygen-containing hydrofluorocarbon molecules are less reactive with carbon-based materials compared to oxygen radicals formed from molecular oxygen, therefore, in the case of oxygen-containing hydrofluorocarbon gases, additional ion bombardment is required to react and remove amorphous carbon and fluorinated polymer films, bringing higher anisotropy. Furthermore, it has been verified from Examples that follow that the fluorocarbon-based fragments from the oxygen-containing fluorocarbon and hydrofluorocarbon molecules may preferentially deposit on pattern sidewalls bringing additional protection, while both fluorocarbon and oxygen-containing fluorocarbon fragments allows a high etch rate of Si-containing materials.
(33) The disclosed oxygen-containing hydrofluorocarbon gases are capable of improving etch rate, etched structure profile control and selectivity by producing oxygen-containing fluorocarbon or hydrofluorocarbons reactive species together with fluorocarbon and hydrofluorocarbon fragments when molecular O.sub.2 flow rate in the etching gas mixture is reduced or eliminated.
(34) The disclosed oxygen-containing hydrofluorocarbon molecules also bring higher etch rates than molecules having the same composition but without oxygen.
(35) Additionally, achieving higher etch rate and improved control of the etching profile, the disclosed oxygen-containing hydrofluorocarbon molecules are typically having lower global warming potential compared to standard gases.
(36) The higher etch rate may be achieved as follows. First, effective oxygen-containing fluorocarbon and/or hydrofluorocarbon fragments may reach the bottom of high aspect ratio structures more easily due to their potentially low sticking coefficients. Secondly, thanks to the oxygen in the fragments, fluorine and oxygen atoms are delivered to the etched surface simultaneously so that it is easier to control the reactivity and the thickness of the polymer and mixed layer at the bottom of high aspect ratio structures. Thus, the disclosed oxygen-containing hydrofluorocarbon molecules are effective for anisotropic etching and there may be two mechanisms responsible for that. First, generation of F- and O-rich thin polymer on the bottom of the high aspect ratio structures, by providing high density of F- and O-containing radicals and ions from plasma (F- and O-containing radicals and ions are reactive and providing isotropic etching). Next, hydrofluorocarbon and fluorocarbon fragments without oxygen are also generated in the disclosed etching process and able to deposit a protection polymer film on sidewalls and protect amorphous carbon mask together with the sidewalls. The protection polymer film is formed mainly by carbon-containing fragments without oxygen as explained above.
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(38) On the other hand, in case of C.sub.4H.sub.2F.sub.6+O.sub.2 gas mixture, strong signal from C.sub.4H.sub.2F.sub.6 parent molecule was recorded, indicating low rate of dissociation. In contrast, no signal of oxygen-containing hydrofluorocarbon, C.sub.4H.sub.2F.sub.6O.sub.2, is recorded in the case of C.sub.4H.sub.2F.sub.6O.sub.2, indicating that it is easier to dissociate C.sub.4H.sub.2F.sub.6O.sub.2 molecule by electron impact to ionize it. High rate of dissociation of C.sub.4H.sub.2F.sub.6O.sub.2 molecule may be explained by weak bound in ether group resulting in easy break of those bounds by electron impact and dissociation of molecule. Therefore, it is preferable to use oxygen-containing hydrofluorocarbons with at least one oxygen atom incorporated into ether group or carbonyl group to promote dissociation of molecule in plasma, thereby, enhancing generation of reactive species and increasing etch rate.
(39) In addition, in case of C.sub.4H.sub.2F.sub.6O.sub.2, more CF.sub.3 fragments were produced comparing to C.sub.4H.sub.2F.sub.6+O.sub.2 gas mixture under identical conditions shown in
(40) <Other Process Gasses>
(41) Another gas such as inert gas and/or oxidizing gas may be added to the process gas mixture. The inert gas may be one or more gases selected from N.sub.2, He, Ar, Kr, Xe, Ne. Use of a noble gas increases ion bombardments during the etching process depending on gas ratio in the process gas mixture. The use of the noble gas promotes or suppresses dissociation of other gases in the process gas mixture, which causes direct impact on etching speed and anisotropy of the etching process. Furthermore, addition of oxidizing gas (such as O.sub.2, O.sub.3, CO, CO.sub.2, COS, SO, SO.sub.2, FNO, NO, NO.sub.2, H.sub.2O) allows increasing the etching speed, depending on the process gas mixture and type of target and non-target materials isotropy and selectivity of the etching process.
(42) Further additional gas from the list of H.sub.2, SF.sub.6, NF.sub.3, N.sub.2, NH.sub.3, Cl.sub.2, F.sub.2, Br.sub.2, BCl.sub.3, HBr, HCl, HBr, PF.sub.3, CF.sub.3I, C.sub.3F.sub.7I, C.sub.4F.sub.9I, C.sub.4H.sub.9F.sub.3Si, C.sub.5H.sub.9F.sub.5Si may be added to the etching gas mixture in order to improve control of the process or increase etch rate.
(43) <Flow of Plasma-Etching Method>
(44) Most of semiconductor devices are formed using processes of formation of thin films on the top of a substrate and patterning of those thin films to receive desired structures and devices. Patterning includes lithography step, which allows defining a formed pattern and etching steps that are used to remove unnecessary materials or films from the substrate through the formed pattern. One of commonly used etching processes is a plasma dry etching when the substrate is exposed to plasma or reactive species formed in the inside of a process chamber. Combination of physical (e.g., sputtering by ion bombardment) and chemical (e.g., surface interactions with reactive species) mechanisms in plasma etching allows achieving preferential etching of a particular material selectively to other materials depending on used chemistry and process conditions, in which volatile by-products is formed and will be removed.
(45) Detailed explanation of flow of the disclosed plasma etching method is as follows. In the first step, a workpiece containing one or more target etching films and optionally containing non-target plasma etching film that may be patterned (having some pattern such as openings in the film) is brought to a plasma-etching chamber. The workpiece may be any types of targets as long as it could be processed by plasma etching. For example, monocrystalline Si wafer including at least one Si-containing film, organic film or metal containing film or plural films part of which may be patterned.
(46) Example of workpiece having target etching film and non-target etching film with pattern is shown on
(47) The disclosed plasma etch methods for forming a high aspect ratio structure by selectively etching one or more silicon-containing films in a substrate using a patterned mask layer deposited on the top of the one or more silicon-containing films comprises the steps of: mounting the substrate in a processing chamber; introducing an etching gas containing a vapor of an oxygen-containing hydrofluorocarbon into the processing chamber; converting the etching gas to a plasma; and allowing an etching reaction to proceed between the plasma and the one or more silicon-containing films so that the one or more silicon-containing films are selectively etched versus the patterned mask layer to form the high aspect ratio structure.
(48) The one or more processing films may be silicon-containing films including Si.sub.aO.sub.bC.sub.cN.sub.dH.sub.e where a, b, c, d, e range from 0.1 to 6 and b, c, d, e each may be independently 0. The one or more processing films may also include dopants, such as B, C, P, As Ga, In, Sn, Sb, Bi and/or Ge. The non-etching films may be patterned hardmask layers, e.g., amorphous carbon, amorphous silicon, doped amorphous carbon, doped amorphous silicon, metals, etc.
(49) In the disclosed plasma etching method, the plasma etching chamber is equipped with parallel plate electrodes plasma generators where a high frequency electromagnetic field of 60 MHz is applied to the upper electrode and a 2 MHz one is applied to the lower electrode, when the gap between the electrodes is kept in a range between 10 and 35 mm. Combination of these electric fields allows applying power to the upper electrode within a range of 0-2000 W and to the lower electrode within the range of 1500-7000 W. Pressure in the etching chamber during the plasma-etching process is maintained between 15 and 30 mTorr with introduced the process gas mixture.
(50) If necessary, a container containing the disclosed oxygen-containing hydrofluorocarbon etching compounds may be heated to a temperature that permits the oxygen-containing hydrofluorocarbon etching compounds to be gas phase or in liquid phase having a sufficient vapor pressure for delivery into a plasma-etching chamber or a reaction chamber. The container may be maintained at temperatures in the range of, for example, approximately 0 C. to approximately 150 C., preferably from approximately room temperature to approximately 100 C., more preferably from approximately room temperature to approximately 50 C. More preferably, the container is maintained at room temperature in order to avoid heating lines to the plasma-etching chamber. Those skilled in the art recognize that the temperature of the container may be adjusted in a known manner to control the amount of the oxygen-containing hydrofluorocarbon etching compounds vaporized.
(51) Temperature and pressure within the plasma-etching chamber are held at conditions suitable for the processing films to react with the activated 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 mTorr and approximately 10 Torr, more preferably between approximately 10 mTorr and approximately 1 Torr, even more preferably between approximately 10 mTorr and approximately 100 mTorr, as required by etching parameters. Likewise, substrate temperature in the plasma-etching chamber may range from approximately 196 C. to approximately 500 C., preferably from approximately 120 C. to approximately 300 C., more preferably from approximately 100 C. to approximately 50 C.; and more preferably from approximately 70 C. to approximately 40 C. Chamber wall temperature may range from approximately 196 C. to approximately 300 C. depending on process requirements.
(52) Typical materials that need to be etched may be SiO or SiN. An etch stop layer may be silicon oxygen nitride (SiON), poly silicon, metal or metal nitride (e.g., W or TiN). A mask material used may be a-C, doped a-C, amorphous silicon (a-Si), doped a-Si or p-Si, selected from B-doped a-C, W-doped a-C, B-doped a-Si, or photo resist materials.
(53) The disclosed plasma etch methods using the disclosed oxygen-containing hydrofluorocarbon compounds as etching gas produce apertures, such as channel holes, gate trenches, staircase contacts, capacitor holes, contact holes, contact etch, slit etch, self-aligned contact, self-aligned vias, super vias etc., in silicon-containing films. The resulting apertures may have an aspect ratio ranging from approximately 5:1 to approximately 500:1, preferably from approximately 20:1 to approximately 400:1; and a diameter ranging from approximately 5 nm to approximately 500 nm, preferably less than 100 nm. The resulting apertures may have an aspect ratio above 5, preferably above 10, more preferably above 20. For example, one of ordinary skill in the art will recognize that a channel hole etch produces apertures in the silicon-containing films having an aspect ratio greater than 50. The silicon-containing film comprises a layer of Si.sub.aO.sub.bH.sub.cC.sub.dN.sub.e, where a>0, b, c, d and e0, selected from silicon oxide, silicon nitride, crystalline Si, poly-silicon, polycrystalline silicon, amorphous silicon, low-k SiCOH, SiOCN, SiC, SiON, or a stack of alternating silicon oxide and silicon nitride (ONON) films or alternating silicon oxide and poly-silicon (OPOP) films.
(54) However, the disclosed plasma etching method is not limited to the above stated experimental conditions in any way, types of plasma etching tool (e.g., capacity coupled or inductively coupled plasma), process conditions (e.g., pressure, power, temperature, duration of process), process gas mixture, combination and proportion of gases in the process gas mixture, gas flow, workpiece and plasma etching chamber itself may be altered for each process and during the process.
(55) In summary, the disclosed plasma etching methods provide new chemistries able to enhance control of the deposition profile of the polymer film, as well as to etch silicon oxide and silicon nitride or combination thereof with high etch rates and selectivity. Additionally, the disclosed oxygen-containing hydrofluorocarbon compounds have lower global warming potentials compared to commonly used ones (e.g., SF.sub.6, C.sub.4F.sub.6 and C.sub.4F.sub.8), enabling more eco-friendly processes.
(56) Furthermore, the disclosed plasma etching methods provide use of an oxygen-containing hydrofluorocarbon compound or gas as an etching gas, preferably an oxygen-containing hydrofluorocarbon compound or gas with oxygen included into an ether group. The disclosed oxygen-containing hydrofluorocarbon compounds are effective for control of polymer film deposition to keep defined etching profile, while also etching Si-containing materials (e.g., SiO.sub.2, Si.sub.3N.sub.4, or a stack of alternating SiO.sub.2 and Si.sub.3N.sub.4 layers) with high etch rates and high selectivity to a mask layer (e.g., amorphous carbon, amorphous silicon). The disclosed plasma etching method may apply to etching of high aspect ratio structures, such as, contact holes, channels, high aspect ratio capacitors, required for fabrication of semiconductor devices such as 3D NAND and DRAM.
(57) There are advantages of adding oxygen-containing hydrofluorocarbon to an etching gas mixture. When a vapor of the disclosed oxygen-containing hydrofluorocarbon is added to an etching gas mixture, observed improvements in performance is attributed to generation of specific reactive species in plasma by dissociation, compared to commonly used fluorocarbons and hydrofluorocarbons, e.g., C.sub.4F.sub.8, C.sub.4F.sub.6, CH.sub.2F.sub.2, and use less to no molecular O.sub.2 in the gas mixture. Formation of oxygen-containing reactive fluorocarbon and hydrofluorocarbon species by direct dissociation of the disclosed oxygen-containing hydrofluorocarbon in the plasma allows delivering reactive oxygen and fluorine to the surface of target etching material simultaneously, resulting in the formation of volatile by-products, such as, fluorides and/or oxyfluorides of etching target material. This increases etch rate compared to commonly used mixture of fluorocarbon or hydrofluorocarbons with molecular O.sub.2 where delivery of reactive oxygen and fluorine to surface of target etching materials happens independently, which may result in an etch rate reduction. On the other hand, the presence of oxygen in the disclosed oxygen-containing hydrofluorocarbon allows reducing or even excluding use of molecular O.sub.2 in the etching gas mixture, which results in reduced isotropy of the etching process and lower damage of sidewalls (lateral etch) of the etched structure and mask. Moreover, the generation of fluorocarbon and hydrofluorocarbon fragments by dissociation of the disclosed oxygen-containing hydrofluorocarbons with potentially lower sticking coefficient compared to counterparts in the plasma allows depositing more conformal polymer on the sidewall of the etched structure and mask, thereby further improving control of the etched structure profile and selectivity to the mask. Here the etched structure may be an aperture, via, hole, or trench. Use of molecular O.sub.2 gas leads to the generation of oxygen reactive species (e.g., atoms, radicals and ions) that promotes isotropic etching leading to damage of the amorphous carbon mask layer and sidewall protective polymer film. In contrast, use of vapor of the disclosed oxygen-containing hydrofluorocarbons (preferentially containing an ether group) as an etching gas provides a better control over the polymer film deposition on sidewall and mask, resulting in preferentially anisotropic etching of the targeted material and an improved control of shape of the etched structure. This helps keep the protective film on the sidewalls during etching process and etch high aspect ratio structures with a thin and straight profile by preventing lateral etching and profile distortions. In addition, the vapor of the disclosed oxygen-containing hydrofluorocarbons is also effective for anisotropic etching SiO.sub.2 and Si.sub.3N.sub.4 with a high etch rate compared to commonly used etching chemistry (e.g., C.sub.4F.sub.8, C.sub.4F.sub.6, O.sub.2) and also effective for a selectivity of SiO.sub.2 versus SiN. The selectivity of SiO.sub.2 versus SiN using the disclosed oxygen-containing hydrofluorocarbons may range from approximately 1:20 to 20:1; preferably from 1:10 to 10:1, more preferably from 1:5 to 5:1, even more preferably from 1:2 to 2:1. The selectivity of SiO.sub.2 versus SiN using the disclosed oxygen-containing hydrofluorocarbons may be close to approximately 1. Decreased sticking coefficient of hydrofluorocarbons disclosed in US 20210193475 to Ishino et al. is also beneficial for improvement of polymer uniformity during etching process resulting better profile control of the etched structure. The disclosed oxygen-containing hydrofluorocarbons may provide higher selectivity by depositing more conformal hydrofluorocarbon polymer to protect the mask layer (e.g., a-C mask) and sidewall and reduced use of molecular O.sub.2 in the etching gas mixture, resulting in reduced isotropy of the etching process.
(58) According to the present disclosure, it is possible to provide a plasma etching method that may increase the selectivity to the mask and sufficiently inhibit the lateral dimension expansion of the etched structure during a high aspect ratio etching process while keeping high etch rate by use of a vapor of oxygen-containing hydrofluorocarbon compound.
EXAMPLES
(59) A more detailed description of the disclosed methods through examples is provided as follows. However, the disclosed methods is not limited to presented examples in any way and process conditions, process gas mixture, combination and proportion of gases in the gas mixture, workpiece and plasma etching chamber itself may be altered.
(60) Plasma etching conditions, plasma etching chamber and workpiece together with results of plasma etching process are described in the examples below.
(61) <Plasma Etching Device>
(62) In the disclosed methods, a parallel plate (capacity coupled plasma) plasma generator was used as the plasma etching device. The parallel plate configuration included upper electrode and lower electrode, on which the workpiece was placed (lower electrode was used as sample holder with temperature regulation capability). The separation between the electrodes was 20 mm. The upper electrode was connected to 60 MHz generator while the lower electrode was connected to 2 MHz generator.
(63) <Plasma Etching Condition>
(64) During the plasma etching process power supplied to the upper electrode was varied in range from 500 to 2000 W, while power applied to the lower electrode was varied in range from 750 to 7000 W. Pressure has been maintained constant during the process at values selected in range between 15 and 30 mTorr. The plasma etching time was set at value between 30 and 300 seconds. Etch rate has been estimated in nanometers per minute. Plasma process gas mixture included at least one of gases from the list: Ar, O.sub.2, C.sub.4H.sub.2F.sub.6 as a hydrofluorocarbon gas and C.sub.4H.sub.2F.sub.6O.sub.2 or C.sub.4H.sub.4F.sub.6O as oxygen-containing hydrofluorocarbon gas.
(65) <Workpieces>
(66) In Examples 1-5 and 11-17, a workpiece shown in
(67) In Examples 6-10, a workpiece of monocrystalline silicon plane wafer with target etching SiO.sub.2 film having a thickness of 2000 nm deposited on top of the monocrystalline silicon plane wafer was used for silicon oxide etching; a workpiece of monocrystalline silicon plane wafer with target etching Si.sub.3N.sub.4 film having a thickness of 2000 nm deposited on top of the monocrystalline silicon plane wafer was used for silicon nitride etching.
(68) <Plasma Etching Profile and Selectivity>
(69) For comparison of high aspect ratio etching performances of the disclosed plasma etching processes and the reference plasma etching processes using molecules with the same amount of C, H, and F atoms excluding O, referring to
(70) During comparison, higher value of selectivity was targeted, when top CD (numeral 9 in
Example 1
(71) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. A process gas mixture including following flows of gases was introduced to the plasma-etching chamber: 150 sccm of Ar and 65 sccm of C.sub.4H.sub.2F.sub.6O.sub.2. Plasma etching process was carried out for 1 minute. Resulting the structure of cross-section of the workpiece after the etching process observed by SEM (not shown), comparison results are summarized in Table 1.
Example 2
(72) Plasma etching was performed in the same way as in Example 1, with exception that process gas mixture was replaced by the following: 150 sccm of Ar, 65 sccm of O.sub.2 and 65 sccm of C.sub.4H.sub.2F.sub.6. Resulting the structure of cross-section of the workpiece after the etching process observed by SEM (not shown), comparison results are summarized in Table 1.
Example 3
(73) Plasma etching was performed in the same way as in Example 1, with exception that process gas mixture was replaced by the following: 150 sccm of Ar, 19.5 sccm of O.sub.2 and 65 sccm of C.sub.4H.sub.2F.sub.6O.sub.2. Resulting the structure of cross-section of the workpiece after the etching process observed by SEM (not shown), comparison results are summarized in Table 1.
Example 4
(74) Plasma etching was performed in the same way as in Example 1, with exception that process gas mixture was replaced by the following: 150 sccm of Ar, 84.5 sccm of O.sub.2 and 65 sccm of C.sub.4H.sub.2F.sub.6. Resulting structure of cross-section of workpiece after the etching process observed by SEM (not shown), comparison results are summarized in Table 1.
(75) TABLE-US-00001 TABLE 1 Summary of compared values for Examples 1-4 Main SiO.sub.2 ER a-C ER Selectivity Neck CD TOP CD Example etching gas (nm/min) (nm/min) (SiO.sub.2/a-C) (nm) (nm) 1 C.sub.4H.sub.2F.sub.6O.sub.2 336 152 100 49 2 C.sub.4H.sub.2F.sub.6 + O.sub.2 510 112 00 127 126 3 C.sub.4H.sub.2F.sub.6O.sub.2 + O.sub.2 601 100 00 115 121 4 C.sub.4H.sub.2F.sub.6 + O.sub.2 528 47 00 163 155
Example 5
(76) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. One of the following gas mixtures with defined gas flows was introduced to the plasma-etching chamber: 150 sccm of Ar and, 13 sccm of O.sub.2, 65 sccm of C.sub.4H.sub.2F.sub.6O.sub.2 or 150 sccm of Ar and, 78 sccm of O.sub.2, 65 sccm of C.sub.4H.sub.2F.sub.6. Plasma etching process was carried out for 1, 3.5 or 6.5 minutes. Resulting etch rates as a function of aspect ratio of the etched structure is summarized in
(77) The results observed in Table 1 indicates that the deposited polymer film on a-C mask and sidewall of the etched structure was etched anisotropically by oxygen-containing hydrofluorocarbon reactive species generated from C.sub.4H.sub.2F.sub.6O.sub.2 and directional ion bombardment (in vertical direction), leading to absence of lateral etching and development of the polymer film on the sidewall of mask and etched structure in Example 1. On contrary, in the case of C.sub.4H.sub.2F.sub.6 and O.sub.2 gas mixture in Example 2 more isotropic etching process was observed due to generation of reactive oxygen species from O.sub.2, resulting in the presence of lateral etch, CD expansion and less to no polymer deposition on sidewalls. Since the process conditions in both Examples 1 and 2 were chosen to achieve the same number of C, H, F, O and Ar atoms in the gas mixture and all other parameters were the same when only the way of supplying oxygen was different (in C.sub.4H.sub.2F.sub.6O.sub.2 or in O.sub.2), it clearly shows the difference between bringing oxygen in the hydrofluorocarbon molecule and in the O.sub.2 molecule. This means that the observed difference in results was originated only from the way of supplying the oxygen from either C.sub.4H.sub.2F.sub.6O.sub.2 or O.sub.2. It may be concluded that supplying oxygen by using oxygen-containing hydrofluorocarbon as an etching gas brings improved selectivity and etched structure profile control by improved polymer deposition and higher anisotropy compared to use of molecular O.sub.2.
(78) The initial workpiece with patterned mask, SiO.sub.2 hole etched using conditions from Example 1 with C.sub.4H.sub.2F.sub.6O.sub.2/Ar etching gas mixture and SiO.sub.2 hole etched using conditions from Example 2 with C.sub.4H.sub.2F.sub.6/O.sub.2/Ar gas mixture measured by SEM (not shown), comparison results are summarized in Table 1.
(79) As it may be observed in Table 1, addition of small amount of O.sub.2 to Ar/C.sub.4H.sub.2F.sub.6O.sub.2 etching gas mixture in Example 3 results in significant increase of etch rate compared to the case without O.sub.2 in Example 1. Moreover, it may be observed that in case of Experiment 4 when oxygen was supplied only in O.sub.2 molecule, etching speed is lower and lateral etching is much faster compared to results from Experiment 3 where oxygen was mainly supplied from C.sub.4H.sub.2F.sub.6O.sub.2. Faster etch rate, reduced lateral etch and improved control of the etched structure profile demonstrated in Example 3 clearly shows that use of oxygen-containing hydrofluorocarbon is essential for etching of high aspect ratio structures. Considering that number of C, F, H and O atoms in the gas mixtures in Examples 3 and 4 was the same, it may be concluded that incorporation of oxygen into hydrofluorocarbon molecule in the case of C.sub.4H.sub.2F.sub.6O.sub.2 is beneficial for increase of etch rate and increase of anisotropy compared to use of C.sub.4H.sub.2F.sub.6/O.sub.2 gas mixture. Suggested mechanism is that oxygen-containing fluorocarbon and hydrofluorocarbon fragments generated by dissociation of C.sub.4H.sub.2F.sub.6O.sub.2 may have lower sticky coefficient compared to fragments generated from commonly used fluorocarbon or hydrofluorocarbon gases therefore, the oxygen-containing fluorocarbon and hydrofluorocarbon fragments could easily reach the bottom of the etched structure and deliver F and O simultaneously to produce a F- and O-rich thin polymer film on the bottom promoting formation of volatile byproducts and increasing etching speed.
(80) Results summarized in the Table 1 confirms the above statements. It may be noted that when O.sub.2 is not added to the C.sub.4H.sub.2F.sub.6O.sub.2 in Example 1, the process features rich deposition resulting in development of polymer film, shrinking of both top and neck CD and reduced etch rate when compared to C.sub.4H.sub.2F.sub.6/O.sub.2 gas mixture in Example 2. However, in Example 3 when small amount of O.sub.2 was added to C.sub.4H.sub.2F.sub.6O.sub.2 top and neck CD were almost identical to initial values, when it was significantly expanded due to lateral etch in Example 4 where C.sub.4H.sub.2F.sub.6/O.sub.2 mixture was used to match C, H, F and O atoms number to Example 3. Moreover, in Example 3 infinite selectivity to the mask with higher etch rate compared to Example 4 was achieved in addition to good preservation of top and neck CD. Observed results demonstrate that it is possible to improve all of comparison results (etch rate, top CD and neck CD) while maintaining infinite or high value of selectivity if oxygen is introduced into an etching gas mixture using a vapor of oxygen-containing hydrofluorocarbon instead of molecular O.sub.2 or introduced using combination of molecular O.sub.2 and a vapor of oxygen-containing hydrofluorocarbon. Capability of keeping top and neck CDs close to initial value after etching in Example 3 demonstrates exceptional control of shape of etched structure when oxygen-containing hydrofluorocarbon is added to etching gas mixture or used as a main etchant.
(81) Results in
Example 6
(82) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. Following a gas mixture with defined gas flows was introduced to the plasma-etching chamber: 150 sccm of Ar, 65 sccm of C.sub.4H.sub.2F.sub.6O.sub.2 and a flow of O.sub.2 varied ranging between 0 and 40 sccm. Plasma etching process was carried out for 2 minutes. Resulting etch rates of SiO.sub.2 and Si.sub.3N.sub.4 and selectivity of SiO.sub.2/Si.sub.3N.sub.4 as a function of O.sub.2 flow are presented in
Example 7
(83) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. Following a gas mixture with defined gas flows was introduced to the plasma etching chamber: 150 sccm of Ar, 65 sccm of C.sub.4H.sub.2F.sub.6 and flow of O.sub.2 varied ranging between 0 and 40 sccm. Plasma etching process was carried out for 2 minutes. Resulting etch rates of SiO.sub.2 and Si.sub.3N.sub.4 and selectivity of SiO.sub.2/Si.sub.3N.sub.4 as a function of O.sub.2 flow are presented in
Example 8
(84) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. Following a gas mixture with defined gas flows was introduced to the plasma-etching chamber: 150 sccm of Ar, 65 sccm of C.sub.4F.sub.8 and flow of O.sub.2 varied ranging between 0 and 40 sccm. Plasma etching process was carried out for 2 minutes. Resulting etch rate of SiO.sub.2 and Si.sub.3N.sub.4 and selectivity of SiO.sub.2/Si.sub.3N.sub.4 as a function of O.sub.2 flow are presented in
Example 9
(85) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. Following a gas mixture with defined gas flows was introduced to the plasma etching chamber: 150 sccm of Ar and, 65 sccm of C.sub.4H.sub.4F.sub.6O (Bis(2,2,2-trifluoroethyl) Ether, CAS: 333-36-8) and flow of O.sub.2 varied in range between 52 and 91 sccm. Plasma etching process was carried out for 2 minutes. Resulting etch rates of SiO.sub.2 and Si.sub.3N.sub.4 and selectivity of SiO.sub.2/SiN as a function of O.sub.2 flow are presented in
Example 10
(86) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. Following a gas mixture with defined gas flows was introduced to the plasma etching chamber: 150 sccm of Ar and, 65 sccm of C.sub.4H.sub.4F.sub.6O (1,1,2,3,3,3-Hexafluoropropyl methyl ether, CAS: 382-34-3) and flow of O.sub.2 varied in range between 26 and 78 sccm. Plasma etching process was carried out for 2 minutes. Resulting etch rates of SiO.sub.2 and Si.sub.3N.sub.4 and selectivity of SiO.sub.2/SiN as a function of O.sub.2 flow are presented in
(87) It may be observed from
(88) On the other hand, it may be observed from
(89) Another important observation from
(90) From summarizing observations in Examples 1-5 it may be concluded that addition of oxygen-containing hydrofluorocarbon, preferably with at least one oxygen atom incorporated in ether group, and more preferably C.sub.4H.sub.4F.sub.6O or C.sub.4H.sub.2F.sub.6O.sub.2 to the Then a gas mixture allows to improve selectivity and preserve lateral dimensions of the structure during high aspect ratio etching, while also improving etch rate compared to mixture of hydrofluorocarbon and molecular O.sub.2 gas. Additionally, it was confirmed that observed improvement of etch rate remains with increase of aspect ratio, which is essential for high aspect ratio etching process. O.sub.n the other hand, from summarizing observations in Examples 6-8 it may be concluded that use of oxygen-containing fluorocarbon in an etching gas mixture allows more effective etching of Si.sub.3N.sub.4 comparing to commonly used fluorocarbon or hydrofluorocarbon gases under identical conditions. Moreover, it is possible to control selectivity of etching of SiO.sub.2 to Si.sub.3N.sub.4 by changing O.sub.2 flowrate when oxygen-containing hydrofluorocarbon used as an etching gas. It is observed in
Example 11
(91) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. Then a gas mixture including following flows of gases was introduced to the plasma etching chamber: 150 sccm of Ar, 71 sccm of O.sub.2 and 65 sccm of C.sub.4H.sub.4F.sub.6O (Bis(2,2,2-trifluoroethyl) Ether, CAS: 333-36-8). Plasma etching process was carried out for 1 minute. Resulting structure of cross-section of workpiece after the etching process observed by SEM (not shown), comparison results are summarized in Table 2.
Example 12
(92) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. Then, a gas mixture including following flows of gases was introduced to the plasma-etching chamber: 150 sccm of Ar, 104 sccm of O.sub.2 and 65 sccm of C.sub.4H.sub.2F.sub.6. Plasma etching process was carried out for 1 minute. Resulting structure of cross-section of the workpiece after the etching process observed by SEM (not shown), comparison criteria are summarized in Table 2.
(93) Data summarized in the Table 2 demonstrates comparison between C.sub.4H.sub.4F.sub.6O and C.sub.4H.sub.2F.sub.6+O.sub.2 gases to verify difference between addition of O.sub.2 to the gas mixture and containing oxygen in the molecule, when the total flow of O.sub.2 is the same. It may be clearly observed from Table 2 that incorporation of oxygen into molecule allows significant improvement in preservation of lateral dimensions of the structure. It may be explained by a decrease of isotropic etch rate caused by free oxygen radicals in the case of C.sub.4H.sub.4F.sub.6O due to lower O.sub.2 rate. This correlates well with results observed in Table 1 for C.sub.4H.sub.2F.sub.6O.sub.2. Observed data demonstrates that it is possible to improve most of etched structure profile parameters (bow CD, top CD and neck CD) while maintaining infinite or high value of selectivity if oxygen is introduced into an etching gas mixture using oxygen-containing hydrofluorocarbon gas instead of molecular O.sub.2 or introduced using combination of molecular O.sub.2 and oxygen-containing hydrofluorocarbon gas.
Example 13
(94) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. Then a gas mixture including following flows of gases was introduced to the plasma-etching chamber: 150 sccm of Ar, 71 sccm of O.sub.2, 20 sccm of C.sub.4F.sub.6 and 45 sccm of C.sub.4H.sub.4F.sub.6O (Bis(2,2,2-trifluoroethyl) Ether, CAS: 333-36-8). Plasma etching process was carried out for 3 minutes. Resulting structure of cross-section of the workpiece after the etching process observed by SEM (not shown), comparison criteria are summarized in Table 2.
Example 14
(95) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. Then a gas mixture including following flows of gases was introduced to the plasma-etching chamber: 150 sccm of Ar, 104 sccm of O.sub.2, 20 sccm of C.sub.4F.sub.6 and 45 sccm of C.sub.4F.sub.8. Plasma etching process was carried out for 3 minutes. Resulting structure of cross-section of the workpiece after the etching process observed by SEM (not shown), comparison criteria are summarized in Table 2.
(96) Data summarized in Table 2 demonstrates comparison between C.sub.4H.sub.4F.sub.6O and C.sub.4F.sub.8 gases as a main etchant in Ar+O.sub.2+C.sub.4F.sub.6 etching recipe. It may be clearly observed that C.sub.4H.sub.4F.sub.6O brings dramatic improvement in selectivity and structure profile control comparing to C.sub.4F.sub.8. Considering that total flow of O atoms to the chamber was the same in both examples, it indicates that bonding O into molecule allows improving selectivity and profile control by reduction of required molecular O.sub.2 flow, which is correlating well with results observed in Examples 1 to 10.
Example 15
(97) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. Then a gas mixture including following flows of gases was introduced to the plasma-etching chamber: 150 sccm of Ar, 30 sccm of O.sub.2 and 60 sccm of C.sub.4F.sub.8. Plasma etching process was carried out for 2 minutes. Resulting structure of cross-section of workpiece after the etching process observed by SEM (not shown), comparison criteria are summarized in Table 2.
Example 16
(98) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. Then a gas mixture including following flows of gases was introduced to the plasma-etching chamber: 150 sccm of Ar, 30 sccm of O.sub.2 and 60 sccm of C.sub.4F.sub.8 and 10 sccm of C.sub.4H.sub.4F.sub.6O (1,1,2,3,3,3-Hexafluoropropyl methyl ether, CAS: 382-34-3). The difference between Example 14 and Example 15 is, in Example 15, an addition of C.sub.4H.sub.4F.sub.6O was added to the gas mixture of Example 14 in which C.sub.4H.sub.4F.sub.6O acted as an additive gas. Plasma etching process was carried out for 2 minutes. Resulting structure of cross-section of workpiece after the etching process observed by SEM (not shown), comparison criteria are summarized in Table 2.
Example 17
(99) Plasma etching was performed in a plasma etching chamber where power of 1400 W was applied to the top electrode at frequency of 60 MHz, power of 7000 W was applied to the bottom electrode at a frequency of the 2 MHz, power applied to both top and bottom electrode was pulsed at 500 Hz with duty cycle of 60%. Pressure in the chamber was maintained at 25 mTorr and gap between the electrodes was set at 20 mm. Then a gas mixture including following flows of gases was introduced to the plasma-etching chamber: 150 sccm of Ar, 30 sccm of O.sub.2 and 50 sccm of C.sub.4F.sub.8 and 10 sccm of C.sub.4H.sub.4F.sub.6O (1,1,2,3,3,3-Hexafluoropropyl methyl ether, CAS: 382-34-3). The difference between Example 14 and Example 16 is, in Example 16, C.sub.4F.sub.8 in the gas mixture used in Example 14 was partially replaced with the addition of C.sub.4H.sub.4F.sub.6O, since the flow of C.sub.4F.sub.8 was reduced from 60 sccm to 50 sccm. Plasma etching process was carried out for 2 minutes. Resulting structure of cross-section of workpiece after the etching process observed by SEM (not shown), comparison criteria are summarized in Table 2.
(100) As shown in Table 2, either addition of C.sub.4H.sub.4F.sub.6O to the gas mixture (Example 15) or partial replacement of C.sub.4F.sub.8 in the gas mixture by C.sub.4H.sub.4F.sub.6O (Example 16) comparing to Example 14 allows significant improvement of etched structure profile comparing to baseline recipe with Ar+O.sub.2+C.sub.4F.sub.8 gas mixture (Example 14). From more detailed measurements presented in Table 2, it may be concluded that use of C.sub.4H.sub.4F.sub.6O as additive or partial replacement gas allows preservation of lateral dimensions and improvement in selectivity. As discussed aboveimprovement in selectivity may be attributed to generation of unique fragments by dissociation C.sub.4H.sub.4F.sub.6O comparing to standard chemistry (Ar+O.sub.2+C.sub.4F.sub.8) and to production of larger number of reactive species due to easy etcher group dissociation, which allows deposition of polymer on the top of the mask and increase of selectivity. O.sub.n the other hand, preservation of lateral dimension and reduction of bowing may be attributed to potentially lower sticking coefficient of fragments generated from C.sub.4H.sub.4F.sub.6O which allows more conformal polymer deposition and preservation of the sidewall.
(101) TABLE-US-00002 TABLE 2 Summary of compared values for Examples 11 to17 Main SiO.sub.2 ER a-C ER Selectivity Neck CD Top CD Bow CD Example etching gas (nm/min) (nm/min) (SiO.sub.2/a-C) (nm) (nm) (nm) 11 Ar + O.sub.2 + C.sub.4H.sub.4F.sub.6O.sub.2 405 89 153 144 144 12 Ar + O.sub.2 + C.sub.4H.sub.2F.sub.6 507 25 20 127 126 126 13 Ar + O.sub.2 + C.sub.4H.sub.4F.sub.6O + C.sub.4F.sub.6 411 25 17 128 145 152 14 Ar + O.sub.2 + C.sub.4F.sub.8 + C.sub.4F.sub.6 626 256 2 190 200 222 15 Ar + O.sub.2 + C.sub.4F.sub.8 695 94 7.3 115 140 145 16 Ar + O.sub.2 + C.sub.4F.sub.8 + C.sub.4H.sub.4F.sub.6O 612 18 34 97 125 125 (C.sub.4H.sub.4F.sub.6O added to gas mixture of Example 15) 17 Ar + O.sub.2 + C.sub.4F.sub.8 + C.sub.4H.sub.4F.sub.6O 620 42 26 115 135 135 (C.sub.4H.sub.4F.sub.6O partially replacing C.sub.4F.sub.8 in gas mixture of Example 15)
(102) From summarizing observations in Examples 1-5 and 11-17 it may be concluded that addition of oxygen-containing hydrofluorocarbon, preferably with at least one oxygen atom incorporated in ether group, and more preferably C.sub.4H.sub.4F.sub.6O or C.sub.4H.sub.2F.sub.6O.sub.2 to a process gas mixture allows to improve selectivity and preserve lateral dimensions of the structure during high aspect ratio etching, while also improving etch rate compared to mixture of hydrofluorocarbon and molecular O.sub.2 gas. Additionally, it is confirmed that observed improvement of etch rate remains with increase of aspect ratio, which is essential for high aspect ratio etching process. Positive effect is verified in various gas mixtures such as Ar/O.sub.2/C.sub.4F.sub.6, Ar/O.sub.2/C.sub.4F.sub.8 or Ar/O.sub.2 when oxygen containing hydrofluorocarbon gas was used as either main etchant, additive or replacement gas. On the other hand, from summarizing observations in Examples 6 to 9 it may be concluded that use of oxygen-containing hydrofluorocarbon in an etching gas mixture allows more effective etching of Si.sub.3N.sub.4 comparing to commonly used fluorocarbon or hydrofluorocarbon gases under identical conditions, which may be explained by easy dissociation of molecule on the ether group resulting in generation of large number of reactive species. Moreover, it is possible to control selectivity of etching of SiO.sub.2 to Si.sub.3N.sub.4 by changing O.sub.2 flowrate when the oxygen-containing hydrofluorocarbon used as an etching gas. Therefore, vapor of oxygen-containing hydrofluorocarbon compounds looks promising as an etching gas or additive to an etching gas for high aspect ratio etching of Si-containing films (e.g., SiO.sub.2, Si.sub.3N.sub.4 and ONON stack) in fabrication of semiconductor devices, such as 3D NAND and DRAM, due to exceptional capabilities of etching profile control, high etch rate and selectivity and fine control over SiO.sub.2 and Si.sub.3N.sub.4 etch rate.
(103) Although the subject matter described herein may be described in the context of illustrative implementations to process one or more computing application features/operations for a computing application having user-interactive components the subject matter is not limited to these particular embodiments. Rather, the techniques described herein may be applied to any suitable type of user-interactive component execution management methods, systems, platforms, and/or apparatus.
(104) 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.