Plasma processing method

Abstract

The present disclosure provides a plasma processing method relating to a technique for suppressing a skirt shape observed in a lower layer portion of an organic film. The plasma processing method for forming a mask by etching an organic film using plasma includes: a first step of etching an inorganic film formed over the organic film; a second step of etching the organic film using a sulfur element-containing gas after the first step; a third step in which, after the second step, a deposited film deposited on a film to be etched formed below the organic film is removed; and a fourth step of etching the organic film after the third step.

Description

Technical Field

[0001] The present disclosure relates to a plasma processing method, which can be applied to a plasma processing method related to a vertical processing technique for vertically processing an organic film in micro-pattern processing. Background Art

[0002] With the progress of high-resolution lithography, as a further microfabrication technology, the development of extreme ultraviolet lithography (EUV) using extreme ultraviolet (EUV) is underway, and the development of an organic film pattern microfabrication technology using a Tri-Layer (three-layer) structure with an EUV pattern is being promoted. Among them, a technology for precisely processing an organic film (ACL: amorphous carbon) of a mandrel applicable to SADP (Self-Aligned Double Patterning) is sought. In particular, there is a need for verticalization of the processing shape of the organic film, and a technology for minimizing the difference between the Top-CD value and the Bottom-CD value of the organic film is required. As the processing accuracy, vertical processing with a Line-CD value of 16 nm or less is required. Here, CD is an abbreviation for Critical Dimension.

[0003] The prior art (Japanese Unexamined Patent Application Publication No. 2021-77843) has proposed a method for preventing side etching of the upper part of an organic film. However, it is considered that the situation regarding the processing method of the lower part of the organic film has not been studied.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-77843 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] A high-precision processing technology for microfabrication with a pattern size of 16 nm or less using an EUV pattern is required, and an etching process for vertically processing an organic film corresponding to the lower layer film of a Tri-Layer structure sample becomes important. If the processing shape of the organic film is a tapered shape or a skirt shape observed in the lower layer part of the organic film, the size controllability of the pattern deteriorates, and the device performance and reliability of semiconductor products deteriorate, which thus becomes a problem.

[0009] The present disclosure provides a plasma processing method related to a technology for suppressing a skirt shape observed in the lower layer part of an organic film.

[0010] Means for Solving the Problem

[0011] A plasma processing method for forming a mask by etching an organic film using plasma according to an embodiment of the present disclosure includes:

[0012] A first step of etching an inorganic film formed on the organic film;

[0013] After the first step, a second step of etching the organic film using a sulfur element-containing gas;

[0014] After the second step, a third step of removing a deposited film deposited on an etched film formed under the organic film; and

[0015] A fourth step of etching the organic film after the third step.

[0016] In the fourth step, the organic film is etched using a H-containing gas (hydrogen element-containing gas) or a mixed gas of a H-containing gas and an Ar gas. Thereby, a skirt-shaped portion at the lower part of the organic film is processed.

[0017] The sulfur element-containing gas is SO2 gas or COS gas. The deposited film is an oxidation-based deposited film, for example, a sulfur oxide-based deposited film.

[0018] The pattern formed on the inorganic film can be either carbon-based or oxidation-based.

[0019] Advantageous Effects of the Invention

[0020] According to an embodiment of the present disclosure, by performing a third step of removing an attached deposited film (oxidation deposition film) after an etching process (second step) of an organic film (amorphous carbon film (ACL: amorphous carbon layer), spin-on organic underlayer (SOC)) using a sulfur element-containing gas (SO2 gas or COS gas) and a fourth step of etching the organic film after removing the deposited film, a vertical processing shape of the organic film can be established, and deviation in the processing size of the organic film can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic cross-sectional view of a plasma etching apparatus of the present disclosure.

[0022] Figure 2A is a flowchart showing a plasma etching method of the present disclosure and a cross-sectional view showing a cross-sectional structure of a wafer to be plasma-etched.

[0023] Figure 2B is a flowchart showing a plasma etching method of the present disclosure and a cross-sectional view showing a process of etching an inorganic film.

[0024] Figure 2C is a flowchart showing the plasma etching method of the present disclosure, a cross-sectional view showing the process of etching an organic film, and a partial enlarged cross-sectional view thereof.

[0025] Figure 2D is a flowchart showing the plasma etching method of the present disclosure, a cross-sectional view showing the process of removing a deposited film stacked on an etched film formed under an organic film, and a partial enlarged cross-sectional view thereof.

[0026] Figure 2E is a flowchart showing the plasma etching method of the present disclosure, a cross-sectional view showing the process of etching a skirt-shaped portion of an organic film, and a partial enlarged cross-sectional view thereof.

[0027] Figure 3A is a diagram showing the composition of a deposited film attached after organic film etching treatment.

[0028] Figure 3B is a diagram showing the composition of an organic film in the case where a deposited film is removed after organic film etching treatment.

[0029] Figure 4 is a diagram showing an etching process related to the plasma processing method of the present disclosure.

[0030] Figure 5 is a diagram showing an example of etching conditions in each step related to the plasma processing method of the present disclosure. Detailed Embodiments

[0031] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, in the following description, the same reference numerals are assigned to the same components, and redundant descriptions may be omitted. It should be noted that the drawings are sometimes schematically shown for the sake of clarity of explanation, but are merely examples and do not limit the interpretation of the present invention.

[0032] Examples

[0033] Use Figure 1 The plasma etching apparatus 100 as a plasma processing apparatus for implementing the plasma processing of the present disclosure will be described. Figure 1 is a schematic cross-sectional view of a microwave plasma etching apparatus of the ECR (Electron Cyclotron Resonance) type that uses microwaves and a magnetic field as a plasma generation unit.

[0034] Microwaves are oscillated by a magnetron 101 and propagated through a waveguide 102 and a quartz plate 103 to a vacuum chamber 104. A solenoid coil 105 is disposed around the vacuum chamber 104, and electron cyclotron resonance (hereinafter referred to as ECR) is generated by the magnetic field generated by the solenoid coil 105 and the microwaves propagated to the vacuum chamber 104.

[0035] An etching gas is supplied from a process gas 106 and introduced into the vacuum chamber 104 via a showerhead plate 107. The pressure inside the vacuum chamber 104 is adjusted to a desired pressure while exhausting the inside of the vacuum chamber 104 using a turbo molecular pump 108 and a dry pump (not shown) via an exhaust port (not shown) provided below the vacuum chamber 104.

[0036] The wafer 111 is a sample on which an inorganic film 201 to be etched is formed (refer to Figure 2A ), and is placed on a sample stage 110. A DC voltage is applied to the sample stage 110 by an electrostatic chuck power supply 109. Thus, the wafer 111 as a sample is adsorbed to the sample stage 110 by the electrostatic adsorption force generated on the sample stage 110. In addition, 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, so that ions in the plasma 5 are incident while being accelerated vertically with respect to the wafer 111.

[0037] Next, Figures 2A - 2E a plasma etching method as the plasma processing method of the present disclosure will be described. Figure 2A FIG. is a flowchart showing the plasma etching method of the present disclosure, and is a cross-sectional view showing the cross-sectional structure of a wafer to be plasma-etched. Figure 2B FIG. is a flowchart showing the plasma etching method of the present disclosure, and is a cross-sectional view showing a process of etching an inorganic film. Figure 2C FIG. is a flowchart showing the plasma etching method of the present disclosure, and is a cross-sectional view showing a process of etching an organic film and a partial enlarged cross-sectional view thereof. Figure 2D FIG. is a flowchart showing the plasma etching method of the present disclosure, and is a cross-sectional view showing a process of removing a deposited film deposited on an etched film formed under an organic film and a partial enlarged cross-sectional view thereof. Figure 2E FIG. is a flowchart showing the plasma etching method of the present disclosure, and is a cross-sectional view showing a process of etching a skirt-shaped portion of an organic film and a partial enlarged cross-sectional view thereof.

[0038] First, the cross-sectional structure of the wafer 111 subjected to plasma etching by the plasma processing method of the present disclosure will be described.

[0039] As Figure 2AAs shown, on the silicon substrate (not shown), the wafer 111 is successively stacked from the bottom with an inorganic film 201 as an etched film, an organic film 202 with a thickness of 65 nm, an inorganic film 203 which is a SOG (spin-on-glass) film with a thickness of 10 nm, and a chemically amplified photoresist (CAR) 204 with a thickness of 22 nm that is pre-patterned by extreme ultraviolet (EUV) exposure. It should be noted that the pre-patterned pattern in this embodiment is, for example, a trench pattern. Since the chemically amplified photoresist 204 is used as a mask, it is sometimes referred to as the mask 204.

[0040] The dimensions patterned by EUV exposure include not only dense patterns but also isolated patterns.

[0041] The organic film 202 is a carbon-based material such as an amorphous carbon (ACL) film or a spin-on organic underlayer (SOC) film. In addition, the material of the mask 204 patterned by EUV exposure can be a metal oxide resist (MOR).

[0042] Figure 2A The shown wafer 111 is placed on the specimen stage 110 of the plasma etching apparatus 100, and the plasma treatment described below is performed.

[0043] Next, a plasma etching treatment method for the organic film 202 will be described.

[0044] First, initially, the mask 204 patterned by EUV exposure is used, and for the inorganic film 203, a mixed gas of sulfur hexafluoride (SF6) gas and trifluoromethane (CHF3) gas, or a mixed gas in which hydrogen (H2) gas is added to the said mixed gas is used. In the case of using the mixed gas of SF6 gas and CHF3 gas, for example, under the etching conditions where the gas flow rate of SF6 gas is 15 mL / min, the gas flow rate of CHF3 gas is 100 mL / min, the processing pressure is 0.4 Pa, the microwave power is 1300 W, the RF bias is 50 W, and the processing time is 35 sec, as Figure 2B shown, the inorganic film 203 is etched (first step). That is, in the first step, the inorganic film 203 formed on the organic film 202 is etched using the mask 204 after EUV exposure.

[0045] In addition, the CD size can be controlled by over-etching 5% to 50% with respect to the film thickness of the inorganic film 203. Here, CD is the abbreviation of Critical Dimension.

[0046] Next,Figure 2B The inorganic film 203 that has been etched in is used as a mask to etch the organic film 202. In the etching of the organic film 202, the following etching conditions are set for the organic film 202: a mixed gas of a sulfur element-containing gas, such as sulfur dioxide (SO2) gas and argon (Ar) gas, is used, the gas flow rate of the SO2 gas is 150 mL / min, the gas flow rate of the Ar gas is 500 mL / min, the processing pressure is 0.6 Pa, the microwave power is 900 W, the RF bias is 150 W, and the processing time is 100 sec. Thus, as Figure 2C shown, the organic film 202 is etched (second step). That is, in the second step, after the first step, the organic film 202 is etched using a sulfur element-containing gas.

[0047] In addition, as the sulfur element-containing gas for etching the organic film 202, a mixed gas of carbonyl sulfide (COS) gas, oxygen (O2) gas, and nitrogen (N2) gas can also be used.

[0048] When measuring the CD size of the processed shape of the organic film 202 after the etching treatment, it is known that the upper CD value (Top-CD value) of the organic film 202 = 9.72 nm, and the difference (CD difference) from the lower CD value (Bottom-CD value) of the organic film = 14.09 nm is 4.37 nm. There is a CD difference, and the controllability of the size is poor. Observing the processed shape of the organic film 202 with the CD difference by SEM image, it is found that in the lower layer part 2021 of the organic film 202, the organic film 202 has a rim. That is, the organic film 202 has a skirt-shaped part 205 in the lower layer part 2021.

[0049] As an improvement of the CD difference, in order to remove the skirt-shaped part 205 of the organic film 202, using the etching treatment conditions of the organic film 202, over-etching of the organic film 202 is performed as additional etching, but the CD difference is 3.57 nm, and no significant improvement is found.

[0050] In order to obtain detailed information on the processed shape of the organic film 202 after etching, the processed shape is observed using TEM, and as Figure 2C shown, it is determined that the deposited film 206 accumulates. The deposited film 206 can also be called an accumulated film.

[0051] As the composition analysis of the deposited film 206, analysis is performed using an XPS analyzer, and as Figure 3A shown, it is known that sulfur oxide (SO4 2-)(301) and organic sulfur compounds (S-C) (302) are stacked. According to this result, during the etching process of the organic film (202), the carbon film is etched using SO2 gas, so the deposition film (206) is not formed, and the etching of the organic film (202) progresses. However, when the organic film (202) is etched to the surface (2011) of the underlying film (201) (inorganic film (201)) and the organic film (202) disappears, the deposition film (206) accumulates on the surface (2011) of the underlying film (201). In addition, by depositing the film (206) on the sidewall (2022) of the organic film (202) as well, the side etching of the organic film (202) is suppressed, and an anisotropic shape can be processed.

[0052] It can be seen from this that the deposition film (206) adheres to the organic film (202) and the underlying film (201). Therefore, even if over-etching is performed under the etching conditions of the organic film (202), the etching does not progress. As a result, the skirt-shaped portion (205) of the organic film (202) cannot be removed, and a vertical shape cannot be obtained. It is considered that due to the influence of the above results, the CD difference becomes larger and the dimensional controllability deteriorates.

[0053] Next, a method for removing the deposition film (206) will be described. Figure 3A It is a diagram showing the composition of the deposition film attached after the organic film etching process. Figure 3B It is a diagram showing the composition of the organic film in the case where the deposition film is removed after the organic film etching process.

[0054] The deposition film (206) as the deposited film is considered to be an oxide (oxidized deposit) according to the measurement results of the X-ray photoelectron spectroscopy (XPS) analyzer of Figure 3A (the horizontal axis: binding (bonding) energy, the vertical axis: count). For example, etching treatment is performed using the etching conditions of the inorganic film (203). That is, a mixed gas of SF6 gas and CHF3 gas, which is the etching condition of the inorganic film (203), is used. The gas flow rate of SF6 gas is 15 mL / min, the gas flow rate of CHF3 gas is 100 mL / min, the processing pressure is 0.4 Pa, the microwave power is 1300 W, the RF bias is 0 W, and the processing time is 10 sec. Here, regarding the RF bias, considering the damage of the inorganic film (203) as the mask of the organic film (202), the RF bias is not applied, and the etching condition set to 0 W is used to remove the deposition film (206) (the third step). That is, in the third step, after the second step, the deposition film (206) accumulated on the etched film (201) formed under the organic film (202) is removed. The sample (111) on which the etched film (201) is formed is placed on the sample stage (110) of the plasma etching apparatus (100), and the third step (S3) is performed by setting the high-frequency power supplied to the sample stage (110) to 0 W.

[0055] As Figure 2D shown, it was confirmed by TEM observation that the deposition film (206) can be removed. In addition, inFigure 3B In the measurement results of the X-ray photoelectron spectroscopy (XPS) analyzer (horizontal axis: binding (trapping) energy, vertical axis: count), sulfur trioxide (SO4 2- ) 301 also returns to the initial state, from which it can be seen that the deposited film 206 can be removed.

[0056] Next, the etching process (fourth step) of the skirt-shaped 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 skirt-shaped portion 205 of the organic film 202 is etched.

[0057] As described above, the deposited film 206 attached to the surface 2011 of the film 201 to be etched and the side wall 2022 of the organic film 202 can be removed, the skirt-shaped portion 205 of the organic film 202 is etched, and the processed shape of the organic film 202 becomes vertical, obtaining Figure 2E the etching shape of the organic film 202 shown, and it can be seen that the Top-CD value and the Bottom-CD value can be improved.

[0058] However, since the deposited film 206 attached to the side wall 2022 of the organic film 202 is also removed, if the conditions used in the etching of the organic film 202 are adopted, side etching will occur on the side wall 2022, resulting in the problem of a decrease in the CD value.

[0059] Considering such damage to the side wall 2022 of the organic film 202, it can be seen that it is necessary to study the process conditions of the ion-based sputter etching main body. The etching gas used in sputter etching is a mixed gas of Ar gas as a noble gas and hydrogen gas (H gas) as a hydrogen element-containing gas (H-containing gas). In addition, as the H-containing gas, hydrogen bromide (HBr) gas or methane (CH4) gas can also be used for etching. For example, in the case of using a mixed gas of Ar gas and H2 gas, under the etching conditions of setting the gas flow rate of Ar gas to 100 mL / min, the gas flow rate of H2 gas to 100 mL / min, the processing pressure to 0.4 Pa, the microwave power to 900 W, the RF bias to 200 W, and the processing time to 20 sec, the skirt-shaped portion 205 of the organic film 202 is etched.

[0060] In addition, since there is no reaction with carbon only with Ar gas, a C-H bond reaction is required, and a hydrogen-containing gas is required.

[0061] Figure 4 The etching process related to the plasma processing method of the present disclosure is shown. In addition, Figure 5 An example of the etching conditions in each step related to the plasma processing method of the present disclosure is shown. Figure 5The vertical direction shows the etching conditions of the inorganic film 203 in the first step S1, the etching conditions of 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 of the organic film 202 in the fourth step S4. Figure 5 The horizontal direction shows the gas flow rate (mL / min) of the gas used, the processing pressure of the vacuum chamber 104 (unit: Pa), the value of the microwave power (M power) (unit: W), the value of the RF bias (B-RF) (unit: W), and the processing time (Time) (unit: sec) as parameters.

[0062] Use Figure 4 and Figure 5 to illustrate the etching process involved in the plasma processing method of the present disclosure. For detailed descriptions, reference can be made to Figures 2A - 2D and Figure 3A , Figure 3B for the description.

[0063] The first step S1 is a process of etching the inorganic film 203 formed on top of the organic film 202. The etching conditions of the inorganic film 203 are described in the Figure 5 section of "Inorganic Film Etching". The inorganic film 203 is etched using a mask 204 exposed by 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 (ACL) film or a film of a coating-type organic underlayer (SOC) material.

[0064] The second step S2 is a process of etching the organic film 202 using a sulfur element-containing gas after the first step S1. The etching conditions of the organic film 202 are described in the Figure 5 section of "Organic Film Etching". The sulfur element-containing gas is, for example, SO2 gas or COS gas.

[0065] The third step S3 is a process of removing the deposited film 206 that has accumulated on the etched film 201 formed under the organic film 202 after the second step S2. The etching conditions for removing the deposited film 206 are described in the section of "Deposition Removal Step". The deposited film 206 is an oxide-based deposited film. The third step S3 is performed with the high-frequency power supplied to the sample stage 110 on which the sample 111 having the etched film 201 formed thereon is placed set to 0 W.

[0066] The fourth step S4 is a process of etching the organic film 202 (specifically, the skirt-shaped portion 205 of the organic film 202) after the third step S3. The etching conditions of the skirt-shaped portion 205 of the organic film 202 are described in the section of "Edge Removal Step". The fourth step S4 uses a hydrogen element-containing gas to etch the organic film 202 after the third step S3. The hydrogen element-containing gas is, for example, hydrogen gas.

[0067] As described above, the present disclosure has been specifically described based on the embodiments, but the present disclosure is not limited to the above embodiments, and various modifications can of course be made.

[0068] Explanation of reference numerals:

[0069] 100: Plasma etching apparatus, 101: Magnetron, 102: Waveguide, 103: Quartz plate, 104: Vacuum chamber, 105: Solenoid coil, 106: Etching gas, 107: Jet plate, 108: Turbomolecular pump, 109: Electrostatic chuck power supply, 110: Specimen stage, 111: Wafer (specimen), 112: High-frequency power supply, 201: Material to be etched, 202: Organic film, 203: Inorganic film, 204: Resist, 205: Organic film skirt-shaped portion, 206: Deposited film, 301: Sulfur oxide (SO4 2- ), 302: Organic sulfur oxide compound (S-C).

Claims

1. A plasma processing method for forming a mask by etching an organic film using plasma, characterized in that, the plasma processing method includes: a first step of etching an inorganic film formed on the organic film; a second step of etching the organic film using a sulfur element-containing gas after the first step; a third step of removing a stacked film deposited on an etched film formed under the organic film after the second step; and a fourth step of etching the organic film after the third step.

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

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

4. The plasma processing method according to claim 1, characterized in that, the sulfur element-containing gas is SO2 gas or COS gas.

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

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

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

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

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

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

11. The plasma processing method according to claim 10, characterized in that, the sulfur element-containing gas is SO2 gas or COS gas.

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

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