Plasma treatment method

Abstract

The present disclosure provides a plasma processing method which is related to a technology for minimizing a footing profile that is observed in a lower layer part of an organic film. Disclosed is a plasma processing method for forming a mask by etching an organic film with use of plasma, the plasma processing method including: a first step for etching an inorganic film that is formed above the organic film; a second step for etching the organic film with use of a sulfur element-containing gas after the first step; a third step for removing a deposited film that is deposited on a film to be etched, which is formed below the organic film, after the second step; and a fourth step for etching the organic film after the third step.

Description

[Technical Field]

[0001] The present disclosure relates to a plasma processing method, and is applicable to a plasma processing method relating to a vertical processing technique for vertically processing an organic film in fine pattern processing. [Background technology]

[0002] With the advancement of high-resolution lithography, extreme ultraviolet (EUV) lithography is being developed as an even finer fabrication technology. Development of a tri-layer organic film patterning technology using EUV patterns is progressing. Among these, there is a need for high-precision processing technology for organic films (ACL: amorphous carbon) that can be used for mandrels in self-aligned double patterning (SADP). In particular, vertical processing of organic film profiles is required, and technology to minimize the difference between the top-CD and bottom-CD values ​​of organic films is required. A vertical processing accuracy of 16 nm or less is required. Here, CD stands for critical dimension.

[0003] Prior art (JP 2021-77843 A) proposes a method for preventing side etching of the upper part of the organic film, but it appears that no consideration has been given to a method for processing the lower part of the organic film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-77843 Summary of the Invention [Problem to be solved by the invention]

[0005] High-precision processing technology for microfabrication with pattern dimensions of 16 nm or less using EUV patterns is required, and the etching process for vertically processing the organic film that is the lower layer of the tri-layer structure sample is important. If the processed shape of the organic film has a tapered shape or a footing shape seen in the lower layer of the organic film, it becomes problematic because it deteriorates the dimensional controllability of the pattern, deteriorating the device performance and reliability of the semiconductor product.

[0006] The present disclosure provides a plasma processing method relating to a technique for suppressing a footing shape observed in the lower layer of an organic film. [Means for solving the problem]

[0007] According to an embodiment of the present disclosure, there is provided a plasma processing method for forming a mask by etching an organic film using plasma, the method comprising: a first step of etching an inorganic film formed above the organic film; a second step of etching the organic film using a sulfur-containing gas after the first step; a third step of removing a deposition film deposited on the film to be etched formed below the organic film after the second step; and a fourth step of etching the organic film after the third step.

[0008] In the fourth step, the organic film is etched using an H-containing gas (gas containing hydrogen element) or a mixed gas of an H-containing gas and Ar gas, thereby processing a skirting shape portion at the bottom of the organic film.

[0009] The sulfur-containing gas is SO2 gas or COS gas. The deposited film is an oxide-based deposited film, for example, a sulfur oxide-based deposited film.

[0010] The pattern formed on the inorganic film may be either a carbon-based or an oxide-based pattern. [Effects of the Invention]

[0011] According to one embodiment of the present disclosure, a third step of removing a deposited film (oxide deposition film) that adheres to an organic film (an amorphous carbon film (ACL: amorphous carbon layer) or a coated organic underlayer (SOC)) after etching the organic film (amorphous carbon film (ACL) or coated organic underlayer (SOC)) using a sulfur-containing gas (SO gas or COS gas) and a fourth step of etching the organic film excluding the deposited film are performed, thereby establishing a vertical processed shape of the organic film and suppressing variations in the processed dimensions of the organic film. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view of a plasma etching apparatus according to the present disclosure. [Figure 2A] 1 is a flow diagram showing a plasma etching method according to the present disclosure, and a cross-sectional view showing the cross-sectional structure of a wafer to be plasma etched. [Figure 2B] 1 is a flow diagram showing a plasma etching method according to the present disclosure, and is a cross-sectional view showing a step of etching an inorganic film. [Figure 2C] 1 is a flow diagram showing a plasma etching method according to the present disclosure, and is a cross-sectional view and a partially enlarged cross-sectional view showing a step of etching an organic film. FIG. [Figure 2D] FIG. 1 is a flow diagram showing a plasma etching method according to the present disclosure, including a cross-sectional view and a partially enlarged cross-sectional view showing a step of removing a deposition film deposited on a film to be etched formed below an organic film. [Figure 2E] 1 is a flow diagram showing a plasma etching method according to the present disclosure, and is a cross-sectional view and a partially enlarged cross-sectional view showing a step of etching a skirting portion of an organic film. FIG. [Figure 3A] FIG. 10 is a diagram showing the components of a deposition film that adheres after an organic film etching process. [Figure 3B] FIG. 10 is a diagram showing the components of an organic film when a deposit film is removed after an organic film etching process. [Figure 4] 1A to 1C are diagrams illustrating an etching flow according to a plasma processing method of the present disclosure. [Figure 5]FIG. 4 is a diagram showing an example of etching conditions in each step according to the plasma processing method of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] Embodiments of the present disclosure will be described below with reference to the drawings. In the following description, the same components are designated by the same reference numerals, and repeated description may be omitted. The drawings may be more schematic than the actual embodiment for clarity of explanation, but they are merely examples and are not intended to limit the interpretation of the present invention. [Example]

[0014] A plasma etching apparatus 100 as a plasma processing apparatus for carrying out the present disclosure will be described with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view of an ECR (Electron Cyclotron Resonance) type microwave plasma etching apparatus that uses microwaves and a magnetic field as plasma generation means.

[0015] Microwaves are generated by a magnetron 101, passed through a waveguide 102, and transmitted through a quartz plate 103 to a vacuum vessel 104. A solenoid coil 105 is provided around the vacuum vessel 104, and the magnetic field generated by the solenoid coil 105 and the microwaves transmitted to the vacuum vessel 104 generate electron cyclotron resonance (hereinafter referred to as ECR).

[0016] Etching gas is supplied from a process gas source 106 and introduced into the vacuum chamber 104 via a shower plate 107. The pressure inside the vacuum chamber 104 is adjusted to a desired pressure by evacuating the vacuum chamber 104 with a turbo molecular pump 108 and a dry pump (not shown) through an exhaust port (not shown) provided below the vacuum chamber 104.

[0017] The wafer 111 is a sample having a film to be etched (inorganic film 201: see FIG. 2A) formed thereon, and is placed on a sample stage 110. A DC voltage is applied to the sample stage 110 by an electrostatic adsorption power supply 109. This causes an electrostatic adsorption force to be generated in the sample stage 110, which causes the wafer 111, which is the sample, to be adsorbed to the sample stage 110. In addition, a high-frequency power (hereinafter referred to as RF (Radio Frequency) bias) is supplied to the sample stage 110 by a high-frequency power supply 112, causing ions in the plasma 5 to be accelerated and incident perpendicularly onto the wafer 111.

[0018] Next, a plasma etching method as a plasma processing method according to the present disclosure will be described with reference to FIGS. 2A to 2E. FIG. 2A is a flow diagram illustrating the plasma etching method according to the present disclosure, and is a cross-sectional view showing the cross-sectional structure of a wafer to be plasma etched. FIG. 2B is a flow diagram illustrating the plasma etching method according to the present disclosure, and is a cross-sectional view showing a step of etching an inorganic film. FIG. 2C is a flow diagram illustrating the plasma etching method according to the present disclosure, and is a cross-sectional view and a partially enlarged cross-sectional view showing a step of etching an organic film. FIG. 2D is a flow diagram illustrating the plasma etching method according to the present disclosure, and is a cross-sectional view and a partially enlarged cross-sectional view showing a step of removing a deposition film deposited on a film to be etched formed below the organic film. FIG. 2E is a flow diagram illustrating the plasma etching method according to the present disclosure, and is a cross-sectional view and a partially enlarged cross-sectional view showing a step of etching a skirting portion of an organic film.

[0019] First, the cross-sectional structure of the wafer 111 to be plasma etched by the plasma processing method of the present disclosure will be described.

[0020] 2A, the wafer 111 is formed by stacking, from bottom to top, an inorganic film 201 (the film to be etched) on a silicon substrate (not shown), a 65-nm-thick organic film 202, a 10-nm-thick inorganic film 203 (a spin-on-glass (SOG) film), and a 22-nm-thick chemically amplified photoresist (CAR) 204 that has been pre-patterned by extreme ultraviolet (EUV) exposure. In this embodiment, the pre-patterned pattern is, for example, a groove pattern. The chemically amplified resist 204 is sometimes referred to as a mask 204 because it is used as a mask.

[0021] The dimensions patterned by EUV exposure include not only dense features but also isolated features.

[0022] The organic film 202 is a carbon-based material such as an amorphous carbon (ACL) film, a coating type organic underlayer (SOC) film, etc. Furthermore, the material of the mask 204 patterned by EUV exposure may be a metal oxide (MOR: Metal Oxide Resist).

[0023] A wafer 111 shown in FIG. 2A is placed on a sample stage 110 of a plasma etching apparatus 100, and the plasma processing described below is carried out.

[0024] Next, a plasma etching method for the organic film 202 will be described.

[0025] First, using a mask 204 patterned by EUV exposure, the inorganic film 203 is etched using a mixed gas of sulfur hexafluoride (SF) gas and fluoroform (CHF) gas, or a mixed gas obtained by adding hydrogen (H) gas to the mixed gas. When using a mixed gas of SF and CHF, the inorganic film 203 is etched under the following etching conditions (first step), as shown in FIG. 2B: SF gas flow rate 15 mL / min, CHF gas flow rate 100 mL / min, process pressure 0.4 Pa, microwave power 1300 W, RF bias 50 W, and process time 35 seconds. That is, in the first step, the inorganic film 203 formed above the organic film 202 is etched using the mask 204 exposed to EUV.

[0026] Furthermore, the CD dimension can be controlled by overetching 5% to 50% relative to the film thickness of the inorganic film 203. Here, CD is an abbreviation for Critical Dimension.

[0027] Next, the organic film 202 is etched using the inorganic film 203 etched in FIG. 2B as a mask. The organic film 202 is etched using a sulfur-containing gas, such as a mixture of sulfur dioxide (SO2) and argon (Ar) gas, under the following etching conditions: SO2 gas flow rate 150 mL / min, Ar gas flow rate 500 mL / min, processing pressure 0.6 Pa, microwave power 900 W, RF bias 150 W, and processing time 100 seconds. This results in the etching of the organic film 202 (second step) as shown in FIG. 2C. That is, in the second step, after the first step, the organic film 202 is etched using a sulfur-containing gas.

[0028] Furthermore, the sulfur-containing gas for etching the organic film 202 may be a mixed gas of carbonyl sulfide (COS) gas, oxygen (O2) gas, and nitrogen (N2) gas.

[0029] When the CD dimensions of the processed shape of the organic film 202 after etching were measured, the difference (CD difference) between the top CD value (Top-CD value) of the organic film 202 = 9.72 nm and the bottom CD value (Bottom-CD value) of the organic film = 14.09 nm was 4.37 nm, indicating poor dimensional controllability. When the processed shape of the organic film 202 having the CD difference was observed using an SEM image, it was found that the organic film 202 was trailing at the lower layer 2021 of the organic film 202. In other words, the organic film 202 has a trailing shape portion 205 in the lower layer 2021.

[0030] To improve the CD difference, the etching conditions for the organic film 202 were used to remove the skirting portion 205 of the organic film 202, and additional etching was performed by overetching the organic film 202, but it was found that the CD difference was 3.57 nm, and no significant improvement was observed.

[0031] In order to obtain detailed information about the shape of the organic film 202 after etching, the processed shape was observed using a TEM, and it was found that a deposition film 206 had been deposited, as shown in Figure 2C. The deposition film 206 can also be called a deposition film.

[0032] The components of the deposited film 206 were analyzed using an XPS analyzer, and as shown in FIG. 3A, sulfur oxide (SO4 2- It can be seen that carbon dioxide (CO₂) 301 and organic sulfate (SC) 302 are deposited. This result shows that, during etching of the organic film 202, the carbon film is etched with SO₂ gas, so that the deposition film 206 is not formed and the etching of the organic film 202 proceeds. However, when the organic film 202 is etched down to the surface 2011 of the lower film 201 (inorganic film 201) and the organic film 202 is gone, the deposition film 206 is deposited on the surface 2011 of the lower film 201. Furthermore, since the deposition film 206 also adheres to the sidewalls 2022 of the organic film 202, side etching of the organic film 202 is suppressed, and the organic film 202 can be processed into an anisotropic shape.

[0033] This shows that because the deposit film 206 adheres to the organic film 202 and the underlying film 201, over-etching using the etching conditions for the organic film 202 does not proceed, and therefore the skirting portion 205 of the organic film 202 cannot be removed, and a vertical shape cannot be obtained. It is believed that the CD difference increases as a result of the above, deteriorating dimensional controllability.

[0034] Next, a method for removing the deposition film 206 will be described. Fig. 3A is a diagram showing the components of the deposition film that adheres after an organic film etching process. Fig. 3B is a diagram showing the components of the organic film when the deposition film is removed after the organic film etching process.

[0035] The deposition film 206, which is a deposited film, is considered to be an oxide (oxidation-based deposit) based on the measurement results (horizontal axis: bond (binding) energy, vertical axis: count number) of the X-ray photoelectron spectroscopy (XPS) analyzer in FIG. 3A, and is etched using, for example, the etching conditions for the inorganic film 203. That is, the etching conditions for the inorganic film 203 are a mixed gas of SF6 gas and CHF3 gas, with a gas flow rate of 15 mL / min for SF6 gas and 100 mL / min for CHF3 gas, a processing pressure of 0.4 Pa, a microwave power of 1300 W, an RF bias of 0 W, and a processing time of 10 seconds. Here, considering damage to the inorganic film 203, which serves as a mask for the organic film 202, the RF bias is set to 0 W without application of the RF bias, and the deposition film 206 is removed (third step). That is, in the third step, the deposition film 206 deposited on the etching target film 201 formed below the organic film 202 after the second step is removed. The third step S3 is performed by placing the sample 111 on which the etching target film 201 has been formed on the sample stage 110 of the plasma etching apparatus 100, and setting the high frequency power supplied to the sample stage 110 to 0 W.

[0036] As shown in FIG. 2D, it was confirmed by TEM observation that the deposit film 206 could be removed. In addition, the measurement results of the X-ray photoelectron spectroscopy (XPS) analyzer shown in FIG. 3B (horizontal axis: bond (binding) energy, vertical axis: count number) also showed that sulfur oxide (SO4 2-) 301 has returned to its initial state, which indicates that the deposition film 206 has been successfully removed.

[0037] Next, the etching process (fourth step) of the skirting portion 205 of the organic film 202 will be described. That is, in the fourth step, the organic film 202 after the third step is etched. Specifically, in the fourth step, the skirting portion 205 of the organic film 202 is etched.

[0038] As described above, the deposit film 206 adhering to the surface 2011 of the film to be etched 201 and the sidewall 2022 of the organic film 202 is removed, the skirting portion 205 of the organic film 202 is etched, the processed shape of the organic film 202 becomes vertical, and the etched shape of the organic film 202 shown in FIG. 2E is obtained, and it can be seen that the Top-CD value and Bottom-CD value can be improved.

[0039] However, since the deposition film 206 attached to the sidewall 2022 of the organic film 202 was also removed, if the conditions used for etching the organic film 202 are used, side etching will occur on the sidewall 2022, resulting in a problem of a thinner CD value.

[0040] Considering this damage to the sidewall 2022 of the organic film 202, it is necessary to consider the process conditions for sputter etching using ions. The etching gas used in sputter etching is a mixture of Ar gas, a rare gas, and hydrogen gas (H gas), a hydrogen-containing gas (H-containing gas). Alternatively, hydrogen bromide (HBr) or methane (CH) gas, which are H-containing gases, may be used for etching. For example, when using a mixture of Ar gas and H gas, the skirting portion 205 of the organic film 202 is etched under the following etching conditions: Ar gas flow rate 100 mL / min, H gas flow rate 100 mL / min, process pressure 0.4 Pa, microwave power 900 W, RF bias 200 W, and process time 20 seconds.

[0041] Furthermore, since Ar gas alone does not react with carbon, a C—H bond reaction is required, making a gas containing H necessary.

[0042] FIG. 4 shows an etching flow according to the plasma processing method of the present disclosure. FIG. 5 shows an example of etching conditions for each step of the plasma processing method of the present disclosure. The vertical axis of FIG. 5 shows the etching conditions for the inorganic film 203 in the first step S1, the etching conditions for the organic film 202 in the second step S2, the etching conditions for removing the deposited film 206 in the third step S3, and the etching conditions for the organic film 202 in the fourth step S4. The horizontal axis of FIG. 5 shows parameters such as the gas flow rate (mL / min) of the gas used, the processing pressure (unit: Pa) of the vacuum chamber 104, the microwave power (M power) value (unit: W), the RF bias (B-RF) value (unit: W), and the processing time (time) (unit: sec).

[0043] The etching flow according to the plasma processing method of the present disclosure will be described with reference to FIGS. 4 and 5, but for a detailed description, please refer to the descriptions of FIGS. 2A to 2D and 3A and 3B.

[0044] The first step S1 is a process of etching the inorganic film 203 formed above the organic film 202. The etching conditions for the inorganic film 203 are described in the "Inorganic Film Etching" section of FIG. 5. The inorganic film 203 is etched using a mask 204 exposed to EUV. The material of the mask 204 is, for example, a chemically amplified resist (CAR) or a metal oxide resist (MOR). The organic film 202 is, for example, an amorphous carbon layer (ACL) film or a film of a coated organic underlayer (SOC) material.

[0045] The second step S2 is a process of etching the organic film 202 using a sulfur-containing gas after the first step S1. The etching conditions for the organic film 202 are described in the "Organic Film Etching" section of Figure 5. The sulfur-containing gas is, for example, SO2 gas or COS gas.

[0046] The third step S3 is a process for removing the deposition film 206 deposited on the etching target film 201 formed below the organic film 202 after the second step S2. The etching conditions for removing the deposition film 206 are described in the "deposit removal step" section. The deposition film 206 is an oxide-based deposition film. The third step S3 is performed by setting the high-frequency power supplied to the sample stage 110, on which the sample 111 on which the etching target film 201 is formed, to 0 W.

[0047] The fourth step S4 is a process of etching the organic film 202 (specifically, the skirted portion 205 of the organic film 202) after the third step S3. The etching conditions for the skirted portion 205 of the organic film 202 are described in the "skirt removal step" section. The fourth step S4 etches the organic film 202 after the third step S3 using a hydrogen-element-containing gas. The hydrogen-element-containing gas is, for example, hydrogen gas.

[0048] Although the present disclosure has been specifically described above based on the examples, it goes without saying that the present disclosure is not limited to the above examples and can be modified in various ways. [Explanation of symbols]

[0049] 100: plasma etching device, 101: magnetron, 102: waveguide, 103: quartz plate, 104: vacuum chamber, 105: solenoid coil, 106: etching gas, 107: shower plate, 108: turbo molecular pump, 109: electrostatic adsorption power supply, 110: sample stage, 111: wafer (sample), 112: high frequency power supply, 201: material to be etched, 202: organic film, 203: inorganic film, 204: resist, 205: organic film skirting shape portion, 206: deposition film, 301: sulfur oxide (SO4 2- ), 302: Organic sulfate compounds (SC).

Claims

1. 1. A plasma processing method for forming a mask by etching an organic film using plasma, comprising: a first step of etching an inorganic film formed above the organic film; a second step of etching the organic film using a sulfur-containing gas after the first step; a third step of removing a deposition film deposited on a film to be etched formed below the organic film after the second step; a fourth step of etching the organic film after the third step.

2. 2. The plasma processing method according to claim 1, The plasma processing method is characterized in that the fourth step etches the organic film after the third step using a hydrogen-containing gas.

3. 2. The plasma processing method according to claim 1, The plasma processing method is characterized in that the deposited film is an oxide-based deposited film.

4. 2. The plasma processing method according to claim 1, The sulfur-containing gas is SO ２ A plasma processing method characterized in that the gas is a nitrogen gas or a COS gas.

5. 2. The plasma processing method according to claim 1, The plasma processing method is characterized in that the inorganic film is etched using a mask exposed to EUV.

6. 6. The plasma processing method according to claim 5, The plasma processing method is characterized in that the mask material is a chemically amplified resist (CAR) or a metal oxide resist (MOR).

7. 2. The plasma processing method according to claim 1, The plasma processing method is characterized in that the organic film is an amorphous carbon layer (ACL) film or a film of a coating type organic underlayer (SOC) material.

8. 7. The plasma processing method according to claim 6, The plasma processing method is characterized in that the organic film is an amorphous carbon layer (ACL) film or a film of a coating type organic underlayer (SOC) material.

9. 2. The plasma processing method according to claim 1, The plasma processing method is characterized in that the third step is performed by setting the high frequency power supplied to a sample stage on which the sample having the etching target film formed thereon is placed to 0 W.

10. 9. The plasma processing method according to claim 8, The plasma processing method is characterized in that the fourth step etches the organic film after the third step using a hydrogen-containing gas.

11. 11. The plasma processing method according to claim 10, The sulfur-containing gas is SO ２ A plasma processing method characterized in that the gas is a nitrogen gas or a COS gas.

12. 12. The plasma processing method according to claim 11, The plasma processing method is characterized in that the hydrogen element-containing gas is hydrogen gas.

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