Plasma processing 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

Plasma treatment method

[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.

[0002] With the advancement of high-resolution lithography, extreme ultraviolet lithography (EUV) using extreme ultraviolet (EUV) is being developed as an even finer processing technology, and progress is being made in the development of tri-layer organic film pattern microfabrication technology using EUV patterns. Among these, there is a need for the development of a technology for highly accurate processing of organic films (ACL: amorphous carbon) that can be used for mandrels in SADP (Self-Aligned Double Patterning). In particular, there is a need for vertical processing of organic film profiles, and there is a need for a technology that minimizes the difference between the Top-CD and Bottom-CD values ​​of organic films. Processing accuracy required is vertical processing with a Line-CD value of 16 nm or less. 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 an organic film, but it appears that no consideration has been given to a method for processing the lower part of the organic film.

[0004] Japanese Patent Application Laid-Open No. 2021-77843

[0005] High-precision processing technology for microfabrication using EUV patterns with pattern dimensions of 16 nm or less is required, and etching processing to vertically process the organic film that is the lower layer of a tri-layer structure sample is becoming 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, which deteriorates the device performance and reliability of semiconductor products.

[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.

[0007] According to one embodiment of the present disclosure, a plasma processing method for forming a mask by etching an organic film using plasma includes: 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; 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 an 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.

[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 (an amorphous carbon film (ACL: amorphous carbon layer) or a 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 carried out, thereby establishing a vertical processed shape of the organic film and suppressing variations in the processed dimensions of the organic film.

[0012] FIG. 1 is a schematic cross-sectional view of a plasma etching apparatus according to the present disclosure; FIG. 2 is a flow diagram showing a 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. 3 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; FIG. 4 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. 5 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 removing a deposited film deposited on a film to be etched formed below an organic film; FIG. 6 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 shape portion of an organic film; FIG. 7 is a diagram showing the components of a deposited film adhering after an organic film etching process; FIG. 8 is a diagram showing the components of an organic film when the deposited film is removed after an organic film etching process; FIG. 9 is a diagram showing an etching flow according to the plasma processing method according to the present disclosure; FIG. 10 is a diagram showing an example of etching conditions in each step according to the plasma processing method according to the present disclosure.

[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.

[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] An 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 inside of 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 the sample stage 110. A DC voltage is applied to the sample stage 110 by an electrostatic adsorption power supply 109. This generates an electrostatic adsorption force on the sample stage 110, which causes the wafer 111, serving as 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-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] As shown in FIG. 2A , the wafer 111 has, stacked on a silicon substrate (not shown) in the following order from bottom to top, an inorganic film 201 to be etched, a 65-nm-thick organic film 202, a 10-nm-thick inorganic film 203 that is a SOG (spin-on-glass) film, and a 22-nm-thick chemically amplified photoresist (CAR) 204 that has been patterned in advance 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 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, the inorganic film 203 is patterned by using a mask 204 patterned by EUV exposure. ６ ) gas and fluoroform (CHF ３ ) gas mixture, or the mixed gas containing hydrogen (H ２ ) gas is added. ６ Gas and CHF ３ When a mixture of gases is used, for example, SF ６ The gas flow rate was 15 mL / min, CHF ３ 2B under the etching conditions of a gas flow rate of 100 mL / min, a processing pressure of 0.4 Pa, a microwave power of 1300 W, an RF bias of 50 W, and a processing time of 35 seconds (first step). That is, in the first step, the inorganic film 203 formed above the organic film 202 is etched using a mask 204 exposed to EUV.

[0026] Furthermore, the CD dimension can be controlled by over-etching 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 that has been etched in FIG. 2B as a mask. In etching the organic film 202, the organic film 202 is etched with a sulfur-containing gas, for example, sulfur dioxide (SO ２ A mixture of SO 2 gas and argon (Ar) gas was used. ２The etching conditions are as follows: gas flow rate of 150 mL / min, Ar gas flow rate of 500 mL / min, process pressure of 0.6 Pa, microwave power of 900 W, RF bias of 150 W, and process time of 100 seconds. As a result, the organic film 202 is etched as shown in FIG. 2C (second step). That is, in the second step, after the first step, the organic film 202 is etched using a sulfur-containing gas.

[0028] The sulfur-containing gas used to etch the organic film 202 is a mixture of carbonyl sulfide (COS) gas and oxygen (O ２ ) gas, nitrogen (N ２ ) gas mixtures may also be used.

[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 of 9.72 nm and the bottom CD value (Bottom-CD value) of the organic film of 14.09 nm was 4.37 nm, indicating poor dimensional controllability. Observation of the processed shape of the organic film 202 in which the CD difference occurred using an SEM image revealed 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 over-etching of the organic film 202 was performed as additional etching. However, 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 Fig. 2C. The deposition film 206 can also be called a deposition film.

[0032] The components of the deposition film 206 were analyzed using an XPS analyzer, and as shown in FIG. 3A, sulfur oxide (SO ４ ２－From this result, it can be seen that SO 301 and organic sulfuric acid compound (SC) 302 are deposited during etching of the organic film 202. ２ Because the carbon film is etched with gas, the deposition film 206 is not formed, and 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 accumulates on the surface 2011 of the lower film 201. Furthermore, the deposition film 206 also adheres to the sidewalls 2022 of the organic film 202, suppressing side etching of the organic film 202 and allowing it to 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 progress, 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 the 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 deposition film, is considered to be an oxide (oxide-based deposit) based on the measurement results of the X-ray photoelectron spectroscopy (XPS) analyzer shown in FIG. 3A (horizontal axis: bond (binding) energy, vertical axis: count number), and is etched using, for example, the etching conditions for the inorganic film 203. That is, the etching conditions for the inorganic film 203, SF ６ Gas and CHF ３ Gas mixture, SF ６ The gas flow rate was 15 mL / min, CHF ３The etching conditions are a gas flow rate of 100 mL / min, a process pressure of 0.4 Pa, a microwave power of 1300 W, an RF bias of 0 W, and a process time of 10 seconds. Here, the RF bias is set to 0 W without applying RF bias, taking into consideration damage to the inorganic film 203 that serves as a mask for the organic film 202, and the deposition film 206 is removed (third step). That is, in the third step, the deposition film 206 deposited on the film to be etched 201 formed below the organic film 202 after the second step is removed. In the third step S3, the sample 111 on which the film to be etched 201 is formed is placed on the sample stage 110 of the plasma etching apparatus 100, and the high-frequency power supplied to the sample stage 110 is set to 0 W.

[0036] As shown in FIG. 2D, it was confirmed by TEM observation that the deposition 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 (SO ４ 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 can be removed, the skirting shape portion 205 of the organic film 202 is etched, the processed shape of the organic film 202 becomes vertical, 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 deposit film 206 adhering to the sidewall 2022 of the organic film 202 was also removed, if the conditions used for etching the organic film 202 were used, side etching would occur on the sidewall 2022, resulting in a problem of a thinner CD value.

[0040] Considering such damage to the sidewall 2022 of the organic film 202, it is necessary to consider the process conditions mainly for sputter etching using ions. The etching gas used in sputter etching is a mixed gas of Ar gas, which is a rare gas, and hydrogen gas (H gas) as a hydrogen element-containing gas (H-containing gas). The H gas can be hydrogen bromide (HBr) gas, methane (CH ４ For example, etching may be performed using Ar gas and H ２ When using a mixed gas of gases, the flow rate of Ar gas is 100 mL / min, H ２ The skirting portion 205 of the organic film 202 is etched under the following etching conditions: gas flow rate 100 mL / min, processing pressure 0.4 Pa, microwave power 900 W, RF bias 200 W, and processing time 20 seconds.

[0041] Furthermore, since Ar gas alone does not react with carbon, a C--H bond reaction is required, making an H-containing gas 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 according to 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 (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 FIGS. 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 coating-type 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 FIG. 5. The sulfur-containing gas is, for example, SO ２ gas or COS gas.

[0046] The third step S3 is a process of 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 be placed to 0 W.

[0047] The fourth step S4 is a step 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.

[0049] 100: plasma etching apparatus, 101: magnetron, 102: waveguide, 103: quartz plate, 104: vacuum vessel, 105: solenoid coil, 106: etching gas, 107: shower plate, 108: turbomolecular 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 (SO ４ ２－ ), 302: Organic sulfuric acid compound (SC).

Claims

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; and a fourth step of etching the organic film after the third step.

2. A plasma processing method according to claim 1, wherein the fourth step etches the organic film after the third step using a hydrogen-containing gas.

3. The plasma processing method according to claim 1, wherein the deposition film is an oxide-based deposition film.

4. In the plasma processing method according to claim 1, the sulfur-containing gas is SO ２ 4. A plasma processing method, comprising the steps of:

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

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

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

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

9. A plasma processing method according to claim 1, characterized in that the third step is performed with the high frequency power supplied to a sample stage on which the sample having the etched film formed thereon is placed being set to 0 W.

10. The plasma processing method according to claim 8, wherein the fourth step etches the organic film after the third step using a hydrogen element-containing gas.

11. The plasma processing method according to claim 10, wherein the sulfur-containing gas is SO ２ 4. A plasma processing method, comprising the steps of:

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

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