Plasma processing method

Abstract

Provided is a plasma processing method for a mask pattern that includes an inorganic resist, the plasma processing method making it possible to achieve a low roughness while suppressing thinning of the mask pattern. According to the present invention, a plasma processing method for reducing the roughness of a mask pattern that includes an EUV-exposed tin oxide inorganic resist includes a step for selectively etching protrusions at a side wall of the inorganic resist in the film thickness direction of the inorganic resist using plasma generated using pulse-modulated high-frequency power and BCl3 gas. The duration of the plasma processing and the duty ratio of the pulse modulation are determined on the basis of the roughness as acquired in advance and the correlation between the duration of the plasma processing and the duty ratio of the pulse modulation. The off duration of the pulse is set to the duration that an upper surface of the inorganic resist is to be selectively irradiated with depositable radicals with respect to ions.

Description

Plasma treatment method

[0001] The present disclosure relates to a plasma processing method, and more particularly to a plasma processing method including a step of precisely controlling the shape of a mask pattern containing an inorganic resist.

[0002] Due to the miniaturization of semiconductor device structures, exposure technology has begun to adopt extreme ultraviolet (EUV) exposure technology, and the introduction of high-NA EUV technology, which increases the numerical aperture of optical systems, is also being considered. As a result, resists have become thinner, and inorganic resists (metal oxide resists, MORs) composed mainly of tin and oxygen have attracted attention as resist materials with high etching resistance. Therefore, a process is needed to reduce the line edge roughness (LER) and line width roughness (LWR) of a mask pattern containing an inorganic resist exposed by EUV while ensuring etching selectivity.

[0003] Patent Document 1 proposes a method for smoothing a metal oxide film containing tin oxide by atomic layer etching (ALE) and selective atomic layer deposition (ALD). The ALE in Patent Document 1 is a method for smoothing a metal oxide film containing tin oxide by using boron trichloride (BCl ３ ALD involves repeating a process of modifying the surface of a metal oxide film by plasma treatment using Ar gas and a process of removing the surface modified by plasma treatment using Ar gas, while ALD involves a process of selectively depositing metal oxide. When the technique of Patent Document 1 is applied to a mask pattern containing an inorganic resist, smoothing is performed by irradiating the wafer from above with ions generated by Ar plasma, so ALE can only process the top surface of the mask pattern and cannot reduce sidewall roughness, and there is a problem that no technique is specified that is particularly effective for reducing LER and LWR.

[0004] In Patent Document 2, a method for developing a metal-containing film containing tin or titanium having an exposed region is described, in which BCl ３ Plasma etching using a gas has been proposed. Patent Document 2 discloses a method for selectively etching exposed regions of a metal-containing film, and sidewall roughness is mainly caused by unevenness during development. Therefore, with the method of Patent Document 2, the mask pattern becomes thinner, making it difficult to effectively remove sidewall irregularities, and Patent Document 2 does not disclose an appropriate etching method for improving roughness such as LER and LWR.

[0005] US Patent Application Publication No. 2019 / 0131130 JP 2023-170393 A

[0006] As described above, in order to reduce LER and LWR while ensuring etching selectivity for a mask pattern containing a thin inorganic resist, it is important to have a technique for processing the sidewalls by suppressing etching of the upper surface of the mask pattern. However, in the method of Patent Document 1, smoothing is performed by irradiating ions generated by Ar plasma from above the wafer, so there is a problem that ALE can only process the upper surface of the mask pattern and cannot reduce the roughness of the sidewalls. Furthermore, the method of Patent Document 2 also has a problem in that it is difficult to effectively remove unevenness on the sidewalls because it discloses a method for selectively etching exposed regions of a metal-containing film. ３ 6 shows a cross-sectional view of the mask pattern when plasma-treated by a plasma treatment method using a gas. A mask is formed on a mask underlayer film 32, and the shape of the mask before plasma treatment is shown as mask shape 33, and the shape of the mask before plasma treatment is shown as mask 30. As shown in FIG. 6, the shape of the mask 30 after plasma treatment is thinner than the mask shape 33 before plasma treatment, and LER and LWR cannot be effectively reduced. Therefore, it is necessary to reduce LER and LWR by etching the convex portions of the pattern sidewalls while suppressing the thinning of the mask pattern.

[0007] An object of the present disclosure is to provide a pattern with low roughness while suppressing thinning of the mask pattern in a plasma processing method for a mask pattern containing an inorganic resist. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

[0008] A brief summary of representative aspects of this disclosure is as follows.

[0009] According to one embodiment, a plasma processing method for forming a mask including an inorganic resist of a metal oxide film exposed by Extreme Ultra Violet (EUV) includes the steps of: ３ The method includes a step of selectively etching the sidewall of the inorganic resist with plasma generated using a gas relative to etching in the thickness direction of the inorganic resist.

[0010] More specifically, in a plasma processing method for reducing the roughness of a mask pattern including an inorganic resist of tin oxide exposed to EUV, a plasma is generated using pulse-modulated high frequency power and BCl ３ The method includes an etching process in which protrusions on the sidewalls of the inorganic resist are selectively etched in the film thickness direction of the inorganic resist using plasma generated using a gas. The plasma processing time and the pulse modulation duty ratio of the etching process are values ​​specified based on the correlation between the roughness obtained in advance and the plasma processing time and the pulse modulation duty ratio. The time during which depositional radicals are selectively irradiated onto the upper surface of the inorganic resist relative to ions is defined as the pulse off time.

[0011] According to the present disclosure, it is possible to provide a mask pattern with small roughness while suppressing thinning. ３Since the gas can be used to form a deposition film on the top surface of the mask pattern without forming a deposition film on the sidewalls of the mask pattern, it is possible to etch the protrusions on the sidewalls while suppressing a decrease in the film thickness of the mask pattern containing the inorganic resist, thereby reducing LER and LWR of the mask pattern and reducing LER and LWR after etching the lower layer of the mask pattern.

[0012] FIG. 1 is an example of an apparatus for implementing the plasma processing method of the present disclosure; FIG. 2 is an example of a process flow of the plasma processing method of the present disclosure; FIG. 3 is an example of a cross-sectional view of the mask pattern before plasma processing in this embodiment; FIG. 4 is an example of a cross-sectional view of the mask pattern during plasma processing in this embodiment; FIG. 5 is an example of a cross-sectional view of the mask pattern after plasma processing in this embodiment;

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In all drawings, components having the same functions are denoted by the same reference numerals, and repeated description thereof will be omitted.

[0014] The etching apparatus according to this embodiment selectively etches the sidewall convex portions of a mask pattern containing an inorganic resist formed on a wafer, thereby reducing roughness.

[0015] 1 shows an overall configuration of an example of a plasma processing apparatus according to this embodiment. The plasma processing apparatus, an etching apparatus 100, includes a processing chamber 101, a gas source 102, a gas flow rate controller 103, a gas supply unit 104, a microwave power supply 105, a waveguide 106, a coil 107, a wafer stage 110, a bias power supply 111, an exhaust port 112, a vacuum pump 113, and an apparatus control unit 114. The apparatus control unit 114 includes functional blocks such as an exhaust system control unit 115, a gas control unit 116, a bias control unit 117, a microwave control unit 118, and a memory unit 119. Each of the functional blocks constituting the apparatus control unit 114 can be implemented by a single personal computer (PC).

[0016] A gas supplied from a gas source 102 to the processing chamber 101 via a gas flow rate controller 103 and a gas supply unit 104 generates electron cyclotron resonance (ECR) due to microwaves applied from a microwave power supply 105 controlled by a microwave control unit 118 and a magnetic field generated by a coil 107, causing the gas to be decomposed into plasma 108 within the processing chamber 101. The pressure within the processing chamber 101 can be kept constant by flowing a predetermined flow rate of processing gas using the gas flow rate controller 103 and a vacuum pump 113 connected to the processing chamber 101. Radicals generated by decomposition into plasma 108 within the processing chamber 101 diffuse within the processing chamber 101 and are irradiated onto the surface of a wafer 109. Ions generated in the plasma 108 are accelerated by a bias voltage applied to a wafer stage 110 from a bias power supply 111 controlled by a bias control unit 117 and are irradiated onto the surface of the wafer 109.

[0017] As an example of the plasma processing method in this embodiment, a method of selectively etching the convex portions on the sidewalls of a mask pattern including an inorganic resist of a metal oxide film exposed to EUV in the processing chamber 101 will be described.

[0018] The etching apparatus 100 according to the present embodiment uses boron trichloride (BCl ３A deposition film is formed on the upper surface of the mask pattern using plasma containing a ) gas, and the protrusions on the sidewalls of the mask pattern are etched away.

[0019] FIG. 2 is a diagram showing an example of a process flow of the plasma processing method in this embodiment. FIG. 3 is an example of a cross-sectional view of the mask pattern before plasma processing in this embodiment. Regarding the cross-sectional shape of the mask shown in FIG. 3, recesses or protrusions 31 may be observed on the sidewalls of the mask pattern 30 formed on the mask underlayer film 32. In this embodiment, a method of selectively etching the protrusions 31 on the sidewalls of the mask pattern 30 as shown in FIG. 3 will be described based on the flow in FIG. 2.

[0020] In this embodiment, as an example, tin oxide is used as the material for the mask pattern 30, which includes an inorganic resist of a metal oxide film exposed by EUV. The mask pattern 30 may also be a pattern exposed by EUV and developed. Although the material for the underlying film 32 of the mask pattern 30 is Spin On Glass (SOG), other materials may also be used, such as silicon-containing films, carbon-containing films such as amorphous carbon layer (ACL), metals such as titanium (Ti), and BCl. ３ A film made of other material that is less reactive with plasma may also be used.

[0021] First, the wafer 109 is placed on the stage 110 in the processing chamber 101, and a process for etching the sidewalls of the mask pattern 30 formed on the wafer 109 is started (S3). This process S3 is performed by using pulse-modulated high frequency power and BCl ３This can be rephrased as a process of selectively etching the sidewalls of the inorganic resist serving as the mask pattern 30 with plasma generated using a gas, relative to etching in the film thickness direction of the inorganic resist. Based on a control signal from the apparatus control unit 114, an etching gas 102 is supplied to the processing chamber 101 at a predetermined flow rate. The supplied etching gas generates electron cyclotron resonance due to microwaves applied from a microwave power supply 105 controlled by the apparatus control unit 114 and a magnetic field generated by a coil 107, turning into plasma 108 within the processing chamber 101 and generating radicals and ions. The radicals and ions generated by the plasma 108 reach the surface of the wafer 109, initiating plasma processing of the mask pattern 30 as shown in FIG. 3 .

[0022] The etching gas 102 is, for example, BCl ３ Gases including argon (Ar) gas and chlorine (Cl ２ ) gas, nitrogen (N ２ ) gas mixture, BCl ３ A mixture of BCl and Ar gas ３ Gas and Cl ２ Gas mixture, BCl ３ Gas and Cl ２ A mixture of BCl and Ar gas ３ Gas and N ２ Mixtures of gases, such as mixtures of gases, can be used.

[0023] In the plasma processing in step S3, in order to suppress etching of the upper surface of the mask pattern 30 and selectively proceed with etching of the sidewalls, the microwave in step S3 must be pulsed under control of the microwave control unit 116. Here, the relationship between the roughness and the plasma processing conditions, such as microwave power (radio frequency power), RF (radio frequency) bias power, gas flow rate, pressure, stage temperature, microwave modulation frequency, and etching parameters such as duty ratio and plasma processing time, is acquired in advance. In particular, it is desirable to acquire in advance the correlation between the plasma processing time, the duty ratio of pulse modulation, and roughness, as shown in FIG. 9( a).

[0024] The frequency of the pulse modulation of the microwave is within the range of 100 Hz to 1000 Hz.

[0025] Step S2 may be included before step S3, in which a target amount of roughness reduction from the roughness before plasma processing is set based on the correlation between the roughness obtained in advance and the plasma processing conditions, and plasma processing conditions are specified so as to achieve the target amount of roughness reduction. Step S2 may include, before step S3, setting a target value of roughness reduction 71 from the roughness 70 before plasma processing based on the correlation between the obtained roughness and the plasma processing time and the duty ratio of pulse modulation, as shown in particular in FIG. 9( a).

[0026] The roughness may be calculated by capturing a top view of the mask pattern 30 using an electron microscope 120 such as a scanning electron microscope (SEM) and using analysis software from the captured top view. The roughness value may be LER, which indicates the roughness of a pattern edge, or LWR, which indicates the roughness of a pattern width. For LER, three times the standard deviation (3 sigma) of the pattern edge position may be used, and for LWR, three times the standard deviation of the pattern width may be used.

[0027] FIG. 9 shows an example of a method for determining the plasma processing time and pulse modulation duty ratio in step S3 based on FIG. 9( a), which shows the correlation between the roughness, plasma processing time, and pulse modulation duty ratio previously acquired in step S2. FIG. 9( a) shows an example of the correlation between the roughness before and after plasma processing, the plasma processing time, and the pulse modulation duty ratio. FIG. 9( b) shows an example of the correlation between the film thickness change before and after plasma processing, the plasma processing time, and the pulse modulation duty ratio. To obtain FIG. 9( a), the dependence of the roughness change before and after plasma processing on the plasma processing time and the pulse modulation duty ratio is obtained. Next, a roughness reduction target value 71 is set, and a plasma processing time 72 and a pulse modulation duty ratio 73 in step S3 are determined based on the graph shown in FIG. 9( a) so that the roughness reduction target value 71 can be reached. If the target value can be achieved under several conditions, the optimum conditions may be selected from those that result in the least change in film thickness before and after processing, based on FIG. 9(b), which shows the correlation between film thickness, plasma processing time, and pulse modulation duty ratio, obtained in advance using a method similar to that of FIG. 9(a).

[0028] Furthermore, a system may be provided in which the correlation between the roughness and the plasma processing conditions obtained in advance is stored in the storage unit 119, and further the roughness of the pattern is obtained by the electron microscope 120 before the plasma processing, and the plasma processing conditions are determined based on the correlation between the measured roughness and the plasma processing conditions obtained in advance. Using the system, optimal plasma processing conditions for step S3 may be automatically obtained based on the correlation from the roughness measurement value before the plasma processing in step S3, and plasma processing may be performed under the obtained conditions.

[0029] In this example, the etching conditions are as follows: ３ When Ar gas is added to the gas, BCl ３ The flow rate was 15 mL / min, the Ar flow rate was 85 mL / min, the pressure was 1.0 Pa, the stage temperature was 40°C, the microwave power was 800 W, the microwave modulation frequency was 100 Hz, the duty ratio was 25%, and the plasma treatment time was 5 s.

[0030] 4(a) and (b) show examples of cross-sectional views of the pattern during etching in step S3. FIG. 4(a) shows an example of a cross-sectional view of the pattern when the pulsed microwave is off, and FIG. 4(b) shows an example of a cross-sectional view of the pattern when the pulsed microwave is on. When plasma processing is performed using pulsed microwaves under plasma processing conditions such as the plasma processing time and the duty ratio of the pulsed microwaves specified in step S2, a deposition film 34 is formed on the upper surface of the mask pattern 30 as shown in FIG. 4(a). This deposition film 34 is made of BCl ３ Low-dissociation radical BCl in gas-generated plasma ｘ The deposition film 34 formed on the upper surface of the pattern suppresses etching of the upper surface of the pattern, preventing the mask pattern from becoming thin, and etching the convex portions on the sidewalls of the pattern reduces roughness.

[0031] That is, in the plasma treatment of step S3, the time of step S3 can be said to be a value specified based on the correlation between the roughness of the inorganic resist 30 and the time of step S3, with respect to a predetermined value of the duty ratio of the pulse modulation. Also, the time when the pulsed microwave is off (pulse off time) can be said to be the time during which the top surface of the inorganic resist 30 is irradiated with depositing radicals selectively with respect to ions.

[0032] 5 shows an example of a cross-sectional view of the pattern after completion of the plasma treatment in step S3. When the plasma treatment in step S3 is performed under the plasma treatment conditions, such as the plasma treatment time and the duty ratio of the pulsed microwaves, specified in step S2, etching of the top surface of the pattern is suppressed, and convex portions on the sidewalls of the pattern are selectively etched, thereby making it possible to reduce roughness such as LER and LWR.

[0033] BCl used in the plasma treatment of this example ３When the highly dissociated ions 37 and radicals 36 of boron (B) and chlorine (Cl) in the plasma generated from the gas containing boron (B) and chlorine (Cl) are irradiated onto the inorganic resist mask pattern 30 made of tin oxide or the like, highly volatile products are generated and etching proceeds. The highly volatile products are tin chloride (SnCl ４ ), BC1O (Boron chloride oxide), etc. (see FIG. 4B).

[0034] In this example, the microwaves that generate plasma are pulsed. The plasma processing time dependence of microwave power, ion density, and radical density when the microwaves are standing waves is shown in Figures 7(a), (b), and (c). When the microwaves are standing waves, the microwaves are always on as shown in Figure 7(a), and after a certain time, the microwaves are always on as shown in Figures 7(b) and (c). ３ The gas is decomposed into plasma to generate highly dissociated ions 37 of B and Cl and radicals 36. When the highly dissociated ions 37 and radicals 36 are irradiated onto an inorganic resist mask pattern 30 made of tin oxide or the like, they dissociate into SnCl ４ Highly volatile products such as BC1O are produced, and etching progresses.

[0035] 8(a), (b), and (c) show the plasma processing time dependence of microwave power, ion density, and radical density when the microwave is pulsed. When the microwave is pulsed, as shown in FIG. 8(a), microwave on-time 50 and off-time 51 alternate. During the microwave on-time 50, plasma dissociation progresses, and highly dissociated ions 37 and radicals 36 of elements such as B and Cl are generated, as shown in FIGS. 8(b) and 8(c). However, during the microwave off-time 51, no ions or radicals are generated, and only the weakly dissociated radicals generated during the on-time are irradiated onto the mask pattern. Therefore, in the pulsed plasma, weakly dissociated radicals are generated, and more BCl radicals are generated than in the case of continuous plasma. ｘRadicals 35 can be generated. Furthermore, since ions 37 are mainly generated while the microwave power is on, the flux of ions irradiated from pulsed plasma is less than that from continuous plasma, and therefore, pulsing the microwave can suppress a decrease in the pattern film thickness.

[0036] Low dissociation of BCl ｘ The radicals 35 have a high adhesion probability to the etching material surface, and therefore can selectively form a deposited film on the upper surface of the pattern. On the other hand, on the sidewalls where no deposited film is formed, highly dissociated B and Cl radicals 36, which are highly reactive with the etching material surface, react with each other, thereby reducing the roughness of the sidewalls.

[0037] The disclosure made by the present inventor has been specifically described above based on examples, but it goes without saying that the present disclosure is not limited to the above examples and can be modified in various ways without departing from the spirit of the present disclosure. For example, the above examples have been described in detail to clearly explain the present disclosure, and are not necessarily limited to those having all of the described configurations. Furthermore, it is possible to add, delete, or replace part of the configuration of each example with other configurations.

[0038] 100: Etching apparatus, 101: Processing chamber, 102: Gas source, 103: Gas flow rate system, 104: Gas supply unit, 105: Microwave power supply, 106: Waveguide, 107: Coil, 108: Plasma, 109: Wafer, 110: Wafer stage, 111: Bias power supply, 112: Exhaust port, 113: Vacuum pump, 114: Apparatus control unit, 115: Exhaust system control unit, 116: Gas control unit, 117: Bias control unit, 118: Microwave control unit, 119: Memory unit, 120: Electron microscope, 30: Mask pattern, 31: Unevenness of mask pattern sidewall, 32: Mask pattern underlayer film, 33: Pattern shape before plasma processing, 34: Deposited film, 35: Low-dissociation BCl ｘRadicals, 36: highly dissociated radicals, 37: highly dissociated ions, 50: on-time of pulsed microwaves, 51: off-time of pulsed microwaves, 70: roughness before plasma treatment, 71: roughness reduction target value, 72: plasma treatment time to achieve the roughness reduction target value, 73: duty ratio to achieve the roughness reduction target value.

Claims

1. A plasma processing method for forming a mask containing an inorganic resist of a metal oxide film exposed to Extreme Ultra Violet (EUV), comprising: ３ A plasma processing method comprising the step of selectively etching a sidewall of the inorganic resist with plasma generated using a gas relative to etching in a thickness direction of the inorganic resist.

2. The plasma processing method according to claim 1, wherein the metal oxide film is tin oxide.

3. A plasma processing method according to claim 1, wherein the time of the process is a value specified based on the correlation between the roughness of the inorganic resist and the time of the process, relative to a predetermined value of the duty ratio of the pulse modulation.

4. A plasma processing method according to claim 1, wherein the pulse-modulated high frequency power has an off-time of the pulse of the high frequency power and an on-time of the pulse of the high frequency power, and the off-time of the pulse is a time during which deposition radicals are selectively irradiated onto the upper surface of the inorganic resist relative to ions.

5. The plasma processing method according to claim 1, wherein the plasma is BCl ３ A mixture of BCl and Ar gas ３ Gas and Cl ２ Gas mixture or BCl ３ Gas and N ２ 1. A method for treating plasma, characterized in that the plasma is generated using a mixture of gases.

6. A plasma processing method according to claim 1, wherein the frequency of the pulse modulation is within the range of 100 Hz to 1000 Hz.

7. The plasma processing method according to claim 1, wherein the underlying film of the inorganic resist is Spin On Glass (SOG) or Amorphous Carbon Layer (ACL).

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