Independent control of etching and passivation gas components for highly selective silicon / silicon nitride etching

Abstract

A method for selective plasma etching of silicon oxide relative to silicon nitride is described. The method includes providing a substrate containing a silicon oxide film and a silicon nitride film, and selectively etching the silicon oxide film relative to the silicon nitride film by: a1) exposing the substrate to a plasma-excited passivation gas containing carbon, sulfur, or both carbon and sulfur, wherein the plasma-excited passivation gas is free of fluorine or hydrogen, and b1) exposing the substrate to a plasma-excited etching gas containing a fluorine-containing gas. The method can further include an additional step a2) between a1) and b1): exposing the substrate to a plasma-excited additional passivation gas containing a fluorocarbon gas, a hydrofluorocarbon gas, a hydrochlorocarbon gas, a hydrochlorofluorocarbon gas, or a hydrocarbon gas or a combination thereof.

Description

[0001] Cross-reference to related applications

[0002] This application relates to and claims priority to U.S. Provisional Patent Application Serial No. 62 / 830,223, filed April 5, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the fields of semiconductor manufacturing and semiconductor devices, and more particularly to a method for selectively plasma etching silicon oxide relative to silicon nitride in semiconductor manufacturing. Background Technology

[0004] The development of next-generation semiconductor technologies presents significant challenges due to the need for selective dry etching to remove one material relative to others. Selective etching of silicon oxide relative to silicon nitride has numerous applications, and preferred passivation (mostly carbon-based) has been extensively studied for high etch selectivity when using plasmas containing fluorocarbon (FC) or hydrofluorocarbon (HFC) gases. However, many conventional etching methods have limitations, including a lack of separate control over the etching component (e.g., fluorine or hydrogen) and the passivation component (e.g., carbon) in the plasma-excited process gas. For example, etching gases containing C4F6 / C4F8 gases facilitate passivation, and passivation gases containing H2 / CH2F2 / CH3F / CH4 gases also facilitate etching. Furthermore, many etching methods use only one FC or HFC gas, which is insufficient flexibility for selectively etching silicon oxide relative to silicon nitride for advanced semiconductor devices. Attempts to completely separate the etching and passivation components have not yet provided fully independent control. Summary of the Invention

[0005] Several embodiments disclose a method for selective plasma etching of silicon oxide relative to silicon nitride in semiconductor manufacturing.

[0006] According to one embodiment, the plasma processing method includes providing a substrate containing a silicon oxide film and a silicon nitride film, and selectively etching the silicon oxide film relative to the silicon nitride film by: a1) exposing the substrate to a plasma-excited passivation gas containing carbon, sulfur, or both carbon and sulfur, wherein the passivation gas is free of fluorine or hydrogen, and b1) exposing the substrate to a plasma-excited etching gas containing a fluorine-containing gas.

[0007] According to one embodiment, the plasma processing method includes providing a substrate containing a silicon oxide film and a silicon nitride film, and selectively etching the silicon oxide film relative to the silicon nitride film by: a1) exposing the substrate to a plasma-excited passivation gas, wherein the plasma-excited passivation gas contains CO, COS, CS2, CCl4, C2Cl4, CCl2Br2, SCl2, S2Cl2 or combinations thereof, and wherein the passivation gas is free of fluorine or hydrogen; and b1) exposing the substrate to a plasma-excited etching gas containing F2, XeF2, ClF3, HF or NF3 or combinations thereof.

[0008] According to one embodiment, the plasma processing method includes providing a substrate containing a silicon oxide film and a silicon nitride film, and selectively etching the silicon oxide film relative to the silicon nitride film by: a1) exposing the substrate to a plasma-excited passivation gas, wherein the plasma-excited passivation gas contains CO, COS, CS2, CCl4, C2Cl4, CCl2Br2, SCl2, or S2Cl2 or combinations thereof, and wherein the passivation gas is free of fluorine or hydrogen; a2) exposing the substrate to an additional plasma-excited passivation gas containing fluorocarbon gas, hydrofluorocarbon gas, hydrochlorofluorocarbon gas, hydrochlorofluorocarbon gas, hydrocarbon gas, or combinations thereof; and b1) exposing the substrate to a plasma-excited etching gas containing F2, XeF2, ClF3, HF, NF3, or combinations thereof. Attached Figure Description

[0009] In the attached diagram:

[0010] Figure 1 This is a process flow diagram for selective plasma etching of a silicon oxide film relative to a silicon nitride film according to an embodiment of the present invention;

[0011] Figures 2A to 2F A method for selective plasma etching of a silicon oxide film relative to a silicon nitride film according to an embodiment of the present invention is schematically illustrated by cross-sectional views.

[0012] Figure 3 This is a process flow diagram for selective plasma etching of a silicon oxide film relative to a silicon nitride film according to another embodiment of the present invention; and

[0013] Figures 4A to 4H A method for selective plasma etching of a silicon oxide film relative to a silicon nitride film, according to another embodiment of the present invention, is schematically illustrated by a cross-sectional view. Detailed Implementation

[0014] A method for selective plasma etching of silicon oxide relative to silicon nitride is described. This method utilizes independent control of the etching and passivation gas compositions to achieve highly selective silicon oxide / silicon nitride etching.

[0015] The fundamental difference between the present invention and conventional silicon oxide or silicon nitride etching methods, as described in the embodiments of the present invention, lies in the plasma containing fluorocarbon (FC) or hydrofluorocarbon (HFC) gas. In the method of the present invention, the passivation gas does not contain fluorine or hydrogen substances that contribute to etching, but the passivation gas contains a passivation component (carbon, sulfur, or both) that exhibits a sufficiently different volatility on silicon oxide compared to on silicon nitride. The higher volatility of the passivation component on the silicon oxide surface is considered to be due to the "closed-shell" nature (no unpaired electrons) of carbon byproducts on the silicon oxide surface compared to the "open-shell" nature (unpaired electrons) of carbon byproducts on the silicon nitride surface. Furthermore, sulfur-containing etching byproducts are considered volatile on the silicon oxide surface but non-volatile as polymers on the silicon nitride surface.

[0016] The etching component is provided using a fluorinated gas. According to one embodiment, the fluorinated gas does not contain fluorocarbons or hydrofluorocarbons. This complete separation of the passivation and etching components greatly enhances the processing window and the etching selectivity between silicon oxide and silicon nitride.

[0017] Figure 1 This is a process flow diagram for selective plasma etching of a silicon oxide film relative to a silicon nitride film according to an embodiment of the present invention, and Figures 2A to 2F A method for selective plasma etching of a silicon oxide film relative to a silicon nitride film according to an embodiment of the present invention is illustrated schematically by means of a cross-sectional view.

[0018] Now for reference Figure 1 and Figure 2A The plasma processing method 10 includes providing a substrate 2 containing a silicon oxide film 200 (e.g., SiO2) and a silicon nitride film 220 (e.g., Si3N4) in 12. Figure 2AIn the example shown, silicon oxide film 200 and silicon nitride film 220 are in the same horizontal plane, but embodiments of the invention can also be applied to films that are not in the same horizontal plane but are vertically offset. Si3N4 is the most thermodynamically stable silicon nitride and therefore the most commercially important silicon nitride. However, embodiments of the invention can be applied to other silicon nitrides containing Si and N as main components, wherein the silicon nitride can have a wide range of Si and N compositions. Similarly, SiO2 is the most thermodynamically stable silicon oxide and therefore the most commercially important silicon oxide. However, embodiments of the invention can be applied to other silicon oxides containing Si and O as main components, wherein the silicon oxide can have a wide range of Si and O compositions.

[0019] The method further includes exposing the substrate 2 in step 14 to a plasma-excited passivation gas 201 containing carbon, sulfur, or both carbon and sulfur, wherein the plasma-excited passivation gas 201 is free of fluorine or hydrogen. This in Figure 2B The diagram is schematically shown. In one example, the plasma-excited passivation gas 201 may contain CO, COS, CS2, CCl4, C2Cl4, CCl2Br2, SCl2, or S2Cl2 or combinations thereof. Exposure to the plasma-excited passivation gas 201 forms a passivation layer 222 on the substrate 2, as shown. Figure 2C As shown, the passivation layer 222 is thicker on the silicon nitride film 220 than on the silicon oxide film 200 because the byproducts of the plasma-excited passivation gas 201 are more volatile on the silicon oxide film 200 than on the silicon nitride film 220.

[0020] The method further includes exposing the substrate in step 16 to a plasma-excited etching gas 203 containing a fluorine-containing gas. This in Figure 2D The diagram is schematically illustrated. In one example, the plasma-excited etching gas 203 comprises F2, XeF2, ClF3, HF, NF3, or combinations thereof. The plasma-excited etching gas may optionally further comprise Ar, He, or combinations thereof. According to one embodiment, the fluorine-containing gas does not contain fluorocarbon or hydrofluorocarbon gases. Exposure to the plasma-excited etching gas 203 selectively etches the silicon oxide film 200 relative to the silicon nitride film 220 because the passivation layer 222 on the silicon nitride film 220 is thicker than that on the silicon oxide film 200. Selective etching occurs in... Figure 2E The diagram schematically shows that the passivation layer 222 is removed from the silicon oxide film 200 and the silicon oxide film 200 is etched, while the passivation layer 222 on the silicon nitride film 220 becomes thinner, but protects the silicon nitride film 220 from etching.

[0021] According to one embodiment, exposure steps 14 and 16 can be performed alternately and sequentially. Furthermore, as indicated by process arrow 18, exposure steps 14 and 16 can be repeated at least once to further selectively etch the silicon oxide film 200. According to one embodiment, exposure steps 14 and 16 can at least partially overlap in time.

[0022] This method can further include removing the passivation layer 222 from the substrate 2 using an ashing process after the etching process. This is in Figure 2F It is shown schematically in the diagram.

[0023] Figure 3 This is a process flow diagram for selective plasma etching of a silicon oxide film relative to a silicon nitride film according to an embodiment of the present invention, and Figures 4A to 4H A method for selective plasma etching of a silicon oxide film relative to a silicon nitride film, according to another embodiment of the present invention, is schematically illustrated by a cross-sectional view.

[0024] Now for reference Figure 3 and Figure 4A The plasma processing method 30 includes providing a substrate 4 containing a silicon oxide film 400 and a silicon nitride film 420 in 32. Figure 4A In the example shown, the silicon oxide film 400 and the Si3N4 film 420 are in the same horizontal plane, but embodiments of the present invention can also be applied to films that are not in the same horizontal plane but are vertically offset.

[0025] The method further includes exposing the substrate 4 in step 34 to a plasma-excited passivation gas 401 containing carbon, sulfur, or both carbon and sulfur, wherein the passivation gas is free of fluorine or hydrogen. This is in Figure 4B The diagram is schematically shown. In one example, the plasma-excited passivation gas 401 may comprise CO, COS, CS2, CCl4, C2Cl4, CCl2Br2, SCl2, S2Cl2, or combinations thereof. Exposure to the plasma-excited passivation gas 401 forms a passivation layer 422 on the substrate 4, as shown. Figure 4C As shown, the passivation layer 422 is thicker on the silicon nitride film 420 than on the silicon oxide film 400 because the byproducts of the plasma-excited passivation gas 401 are more volatile on the silicon oxide film 400 than on the silicon nitride film 420.

[0026] The method further includes exposing the substrate 4 at step 36 to a plasma-excited additional passivation gas 423 containing a fluorocarbon gas, a hydrofluorocarbon gas, a hydrochlorofluorocarbon gas, a hydrochlorofluorocarbon gas, a hydrocarbon gas, or a combination thereof. In one example, the plasma-excited additional passivation gas may contain CF2Cl2, CH2F2, CH4, CH3F, CHF3, C4H6, C2H4, C3H6, CH2Cl2, CH3Cl, CH3Cl, CH2ClF, CHCl2F, or a combination thereof. Exposure to the plasma-excited additional passivation gas 423 forms an enhanced passivation layer 424 on the substrate 4, such as... Figure 4E As shown. Additional passivation gas 423, exposed to plasma-excited conditions, is used to modify and strengthen the passivation layer 422 without damaging the underlying silicon nitride film 420, since the passivation layer 422 protects the underlying silicon nitride film 420 during plasma exposure. In one example, the additional passivation gas 423 exposed to plasma-excited conditions can be performed using a low or zero substrate bias to prevent damage to the silicon nitride film 420 by fluorine or hydrogen ions and / or free radicals in the plasma.

[0027] The method further includes exposing the substrate 4 in step 38 to a plasma-excited etching gas 403 containing a fluorine-containing gas. This in Figure 4F The diagram is schematically illustrated. In one example, the plasma-excited etching gas 403 comprises F2, XeF2, ClF3, HF, NF3, or combinations thereof. The plasma-excited etching gas may optionally further comprise Ar, He, or combinations thereof. According to one embodiment, the fluorine-containing gas does not contain fluorocarbon or hydrofluorocarbon gases. Exposure to the plasma-excited etching gas 403 selectively etches the silicon oxide film 400 relative to the silicon nitride film 420, as... Figure 4G As shown.

[0028] Exposure to plasma-excited etching gas 403 selectively etches the silicon oxide film 400 relative to the silicon nitride film 420 because the enhanced passivation layer 424 on the silicon nitride film 420 is thicker than that on the silicon oxide film 400. Selective etching occurs in… Figure 4G The diagram schematically shows that the reinforcing passivation layer 424 is removed from the silicon oxide film 400 and the silicon oxide film 400 is etched, while the passivation layer 424 on the silicon nitride film 420 becomes thinner, but protects the silicon nitride film 420 from etching.

[0029] According to one embodiment, exposure steps 34-38 can be performed alternately and sequentially. In one example, exposure steps 34-38 can be performed alternately and sequentially in the following order: 34, followed by 36, and then 38. Furthermore, as indicated by process arrow 40, exposure steps 34-38 can be repeated at least once to further selectively etch the silicon oxide film 400. According to one embodiment, one or more of exposure steps 34-38 can at least partially overlap in time.

[0030] This method can further include removing the enhanced passivation layer 424 from the substrate 4 using an ashing process after the etching process. This is in Figure 4H It is shown schematically in the diagram.

[0031] The method of selective plasma etching of silicon oxide films relative to silicon nitride films can be performed in conventional commercial plasma processing systems, including inductively coupled plasma (ICP) systems, capacitively coupled plasma (CCP) systems, microwave plasma systems, remote plasma systems that generate plasma excitation material from upstream of the substrate, electron cyclotron resonance (ECR) systems, and other systems.

[0032] Selective silicon oxide / silicon nitride etching can be performed at substrate temperatures, gas flow rates, gas flow ratios, and gas pressures that optimize the etch selectivity between silicon oxide and silicon nitride. Examples include substrate temperatures between approximately -200°C and approximately 200°C, between approximately -100°C and approximately 25°C, between approximately 0°C and approximately 100°C, between approximately 0°C and approximately 200°C, between approximately -30°C and approximately 25°C, or between approximately 0°C and approximately 25°C. Gas pressures in the plasma etching chamber can be between approximately 5 mTorr and approximately 1000 mTorr, between approximately 10 mTorr and approximately 500 mTorr, or between approximately 20 mTorr and approximately 100 mTorr. Examples of gas flow rates range from 0.1 sccm to 500 sccm, and any gas flow ratio ranges from 0% to 100%.

[0033] Several embodiments of a method for selective plasma etching of silicon oxide relative to silicon nitride in semiconductor manufacturing have been described. For illustrative and descriptive purposes, the foregoing description of embodiments of the invention has been presented. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. This specification and the appended claims include terms used for descriptive purposes only and should not be construed as limiting. Those skilled in the art will understand that many modifications and variations are possible in light of the above teachings. Those skilled in the art will recognize various equivalent combinations and substitutions of the various components shown in the drawings. Therefore, it is intended that the scope of the invention is not limited by this specific embodiment, but rather by the claims appended thereto.

Claims

1. A plasma treatment method, comprising: A substrate containing a silicon oxide film and a silicon nitride film is provided; as well as The silicon oxide film is selectively etched relative to the silicon nitride film in the following manner: a1) Expose the substrate to a plasma-excited passivation gas containing carbon and no fluorine, containing sulfur and no fluorine, containing both carbon and sulfur and no fluorine, containing sulfur and no hydrogen, or containing both carbon and sulfur and no hydrogen. b1) After a passivation layer is formed on the substrate by the passivation gas, the substrate is exposed to an etching gas excited by a plasma containing fluorine gas.

2. The method as described in claim 1, wherein, Step a1) Forming a passivation layer on the silicon nitride film that is thicker than that on the silicon oxide film.

3. The method as described in claim 1, wherein, Exposure steps a1) and b1) are performed alternately and sequentially.

4. The method of claim 3, further comprising: Repeat exposure steps a1) and b1) at least once to further selectively etch the silicon oxide film.

5. The method of claim 1, wherein, The plasma-excited etching gas contains F2, XeF2, ClF3, HF, NF3, or combinations thereof.

6. The method of claim 1, wherein, The etching gas excited by this plasma does not contain fluorocarbon or hydrofluorocarbon gases.

7. The method of claim 1, wherein, The passivation gas excited by the plasma includes CO, COS, CS2, CCl4, C2Cl4, CCl2Br2, SCl2, S2Cl2, or combinations thereof.

8. The method of claim 1, wherein, The silicon oxide film contains SiO2 and the silicon nitride film contains Si3N4.

9. The method of claim 1, further comprising: a2) Expose the substrate to an additional passivation gas excited by a plasma containing fluorocarbon gas, hydrofluorocarbon gas, hydrochlorocarbon gas, hydrochlorofluorocarbon gas, hydrocarbon gas, or a combination thereof.

10. The method of claim 9, wherein, The additional passivation gas excited by the plasma contains CF2Cl2, CH2F2, CH4, CH3F, CHF3, C4H6, C2H4, C3H6, CH2Cl2, CH3Cl, CH3Cl, CH2ClF, CHCl2F, or combinations thereof.

11. The method of claim 9, wherein, The exposure steps a1), a2), and b1) are performed alternately and sequentially in the order of a1), then a2), and then b1).

12. The method of claim 9, further comprising: The exposure steps a1), a2), and b1) are repeated alternately and sequentially at least once to further selectively etch the silicon oxide film.

13. The method of claim 9, wherein, Exposure steps a2) and b1) overlap at least partially in time, or exposure steps a1) and a2) overlap at least partially in time.

14. A plasma treatment method, comprising: A substrate containing a silicon oxide film and a silicon nitride film is provided; as well as The silicon oxide film is selectively etched relative to the silicon nitride film in the following manner: a1) Exposing the substrate to a plasma-excited passivation gas, wherein the plasma-excited passivation gas comprises CO, COS, CS2, CCl4, C2Cl4, CCl2Br2, SCl2, S2Cl2, or combinations thereof, and wherein the passivation gas is free of fluorine or hydrogen. b1) After a passivation layer is formed on the substrate by the passivation gas, the substrate is exposed to an etching gas excited by plasma containing F2, XeF2, ClF3, HF, NF3 or a combination thereof.

15. The method of claim 14, wherein, The etching gas excited by this plasma does not contain fluorocarbon or hydrofluorocarbon gases.

16. A plasma processing method, comprising: A substrate containing a silicon oxide film and a silicon nitride film is provided; as well as The silicon oxide film is selectively etched relative to the silicon nitride film in the following manner: a1) Exposing the substrate to a plasma-excited passivation gas, wherein the plasma-excited passivation gas comprises CO, COS, CS2, CCl4, C2Cl4, CCl2Br2, SCl2, or S2Cl2 or combinations thereof, and wherein the passivation gas is free of fluorine or hydrogen. a2) Expose the substrate to an additional passivation gas excited by a plasma containing fluorocarbon gas, hydrofluorocarbon gas, hydrochlorocarbon gas, hydrochlorofluorocarbon gas, hydrocarbon gas, or a combination thereof, and b1) After a passivation layer is formed on the substrate by the passivation gas and the additional passivation gas, the substrate is exposed to a plasma-excited etching gas containing F2, XeF2, ClF3, HF, NF3 or a combination thereof.

17. The method of claim 16, wherein, The additional passivation gas excited by the plasma contains CF2Cl2, CH2F2, CH4, CH3F, CHF3, C4H6, C2H4, C3H6, CH2Cl2, CH3Cl, CH3Cl, CH2ClF, CHCl2F, or combinations thereof.

18. The method of claim 16, wherein, The etching gas excited by this plasma does not contain fluorocarbon or hydrofluorocarbon gases.

19. The method of claim 16, wherein, The exposure steps a1), a2), and b1) are performed alternately and sequentially in the order of a1), then a2), and then b1).

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