Plasma processing method

Abstract

In a plasma processing method of a mask pattern including an inorganic resist, a pattern that suppresses thinning of the mask pattern and has low roughness is provided. A plasma processing method for reducing the roughness of a mask pattern containing an inorganic resist of tin oxide exposed by EUV, the plasma processing method including a step of performing plasma processing using a plasma generated using pulse-modulated high-frequency power and generated using BCl3 gas, and a step of performing plasma processing on the mask pattern by using a plasma generated using BCl3 gas, and selectively etching the protruding portions of the side walls of the inorganic resist with respect to the film thickness direction of the inorganic resist. The processing time of the plasma in the step and the duty ratio of the pulse modulation in the step are values specified on the basis of the correlation among the roughness, the processing time of the plasma, and the duty ratio of the pulse modulation acquired in advance. The time during which a sedimentary radical is selectively irradiated to the upper surface of the inorganic resist with respect to ions is set as the turn-off time of the pulse.

Description

Technical Field

[0001] This disclosure relates to a plasma processing method, and more particularly to a plasma processing method that includes a process of precisely controlling the shape of a mask pattern containing an inorganic resist. Background Technology

[0002] Due to the miniaturization of semiconductor device structures, extreme ultraviolet (EUV) lithography has begun to be used in exposure technology. Furthermore, the introduction of high-NAEUV technology to improve the aperture ratio of optical systems has been investigated. Simultaneously, progress has been made in the thin-film production of photoresists. As a photoresist material with high etching resistance, inorganic photoresists (MOR), mainly composed of tin and oxygen, have attracted attention. Therefore, there is a need for processes that ensure etch selectivity for mask patterns containing EUV-exposed inorganic photoresists and reduce line edge roughness (LER) and line width roughness (LWR).

[0003] Patent Document 1 proposes a method for smoothing a metal oxide film containing tin oxide through atomic layer etching (ALE) and selective atomic layer deposition (ALD). ALE in Patent Document 1 is obtained by repeatedly modifying the surface of the metal oxide film using plasma treatment with boron trichloride (BCl3) gas, and then removing the modified surface using plasma treatment with Ar gas. ALD is obtained by selectively depositing metal oxide. When applying the method of Patent Document 1 to a mask pattern containing an inorganic resist, smoothing is achieved by irradiating it with ions generated by Ar plasma from above the wafer. Therefore, ALE suffers from the problem that it can only process the upper surface of the mask pattern and cannot reduce the roughness of the sidewalls. No particularly effective method for reducing LER and LWR is explicitly described.

[0004] Patent Document 2 discloses a method for developing a tin- or titanium-containing metal film with exposed areas using plasma etching with BCl3 gas. Patent Document 2 discloses a method for selectively etching exposed areas of a metal film, where sidewall roughness is primarily caused by unevenness during development. Therefore, in the method of Patent Document 2, the thin-film development of the mask pattern makes it difficult to effectively remove sidewall irregularities, and no suitable etching method is disclosed for improving roughness such as LER and LWR.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: U.S. Patent Application Publication No. 2019 / 0131130

[0008] Patent Document 2: Japanese Patent Application Publication No. 2023-170393 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] As described above, in order to ensure etching selectivity and reduce LER and LWR of a mask pattern containing an inorganic resist for a thin film, techniques for processing sidewalls by suppressing etching of the upper surface of the mask pattern become important. However, in the method of Patent Document 1, the wafer is smoothed by irradiating it with ions generated by Ar plasma from above, so only the upper surface of the mask pattern can be processed in ALE, resulting in the inability to reduce the roughness of the sidewalls. In addition, the method of Patent Document 2 also discloses a method for selectively etching the exposed area containing the metal film, thus making it difficult to effectively remove the unevenness of the sidewalls. Figure 6 A cross-sectional view of the mask pattern during plasma treatment using the BCl3 gas plasma treatment method described in Patent Document 2 is shown. A mask is formed on the lower mask film 32. The shape of the mask before plasma treatment is represented by mask shape 33, and the shape of the mask before plasma treatment is represented by mask 30. Figure 6 As shown, compared to the mask shape 33 before plasma treatment, the shape of the mask 30 after plasma treatment becomes thinner, which cannot effectively reduce LER and LWR. Therefore, it is necessary to etch the protrusions on the sidewalls of the pattern while suppressing the thinning of the mask pattern, thereby reducing LER and LWR.

[0011] The purpose of this disclosure is to provide a pattern that suppresses thinning of the mask pattern and has low roughness in a plasma processing method for mask patterns containing inorganic resists. Other issues and new features will become apparent from the description and drawings in this specification.

[0012] Methods for solving problems

[0013] If we were to briefly describe the outline of a representative scheme in this disclosure, it would be as follows.

[0014] According to one embodiment, a plasma processing method forms a mask containing an inorganic photoresist over a metal oxide film exposed by extreme ultraviolet (EUV) lithography, wherein...

[0015] The plasma processing method includes the following steps: using plasma generated by pulse-modulated high-frequency power and BCl3 gas, selectively etching the sidewalls of the inorganic resist relative to the film thickness direction of the inorganic resist.

[0016] More specifically, in a plasma processing method for reducing the roughness of a mask pattern containing inorganic resist in tin oxide exposed by EUV, an etching step is included: selectively etching the protrusions of the sidewalls of the inorganic resist relative to the film thickness direction using plasma generated by pulse-modulated high-frequency electricity and BCl3 gas. The plasma processing time and the duty cycle of the pulse modulation in the etching step are values ​​specified based on a pre-observed correlation between the roughness, the plasma processing time, and the pulse modulation duty cycle. Furthermore, the pulse off-time is defined as the time during which deposited free radicals selectively irradiate the upper surface of the inorganic resist relative to ions.

[0017] Invention Effects

[0018] According to this disclosure, a mask pattern that suppresses thinning and has low roughness can be provided. This is because BCl3 gas can be used to form a deposited film on the upper surface of the mask pattern instead of on the sidewalls, thus suppressing the reduction of the film thickness of the mask pattern containing the inorganic resist and etching the protrusions on the sidewalls. As a result, the LER and LWR of the mask pattern can be reduced, as well as the LER and LWR of the underlying layer after etching of the mask pattern. Attached Figure Description

[0019] Figure 1 This is an example of an apparatus for implementing the plasma processing method of this disclosure.

[0020] Figure 2 This is an example of the process flow of the plasma processing method disclosed herein.

[0021] Figure 3 This is an example of a cross-sectional view of the mask pattern before plasma processing in this embodiment.

[0022] Figure 4 This is an example of a cross-sectional view of the mask pattern used in the plasma processing of this embodiment.

[0023] Figure 5 This is an example of a cross-sectional view of the mask pattern after plasma processing in this embodiment.

[0024] Figure 6 This is an example of a cross-sectional view of the mask pattern used to illustrate a subject of an existing method.

[0025] Figure 7This is an explanatory diagram of microwaves using standing waves in the plasma processing of this embodiment.

[0026] Figure 8 This is an explanatory diagram showing the use of pulse-modulated microwaves in the plasma processing of this embodiment.

[0027] Figure 9 This is an illustrative diagram illustrating an example of a method for specifying plasma processing time and the duty cycle of pulse modulation. Detailed Implementation

[0028] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings. It should be noted that in all the drawings, parts with the same function are labeled with the same reference numerals, and repeated descriptions are omitted.

[0029] [Example]

[0030] The etching apparatus of this embodiment is an apparatus that selectively etches the sidewall protrusions of a mask pattern containing an inorganic resist formed on a wafer to reduce roughness.

[0031] Figure 1 The following is an example of the overall structure of the plasma processing apparatus of this embodiment. The etching apparatus 100, which is part of the plasma processing apparatus, includes a processing chamber 101, a gas source 102, a gas flow 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 storage unit 119. Each functional block constituting the apparatus control unit 114 can be implemented by a personal computer (PC).

[0032] Gas supplied from gas source 102 to processing chamber 101 via gas flow controller 103 and gas supply unit 104 is decomposed into plasma 108 within processing chamber 101 by electron cyclotron resonance generated by microwaves applied from microwave power supply 105 controlled by microwave control unit 118 and magnetic field generated by coil 107. Furthermore, the pressure within processing chamber 101 is maintained constant while a predetermined flow rate of processing gas is maintained by gas flow controller 103 and vacuum pump 113 connected to processing chamber 101. Free radicals generated from plasma 108 within processing chamber 101 diffuse within processing chamber 101 and irradiate the surface of wafer 109. Ions generated from plasma 108 are accelerated by a bias voltage applied to wafer stage 110 from bias power supply 111 controlled by bias control unit 117 and irradiate the surface of wafer 109.

[0033] As an example of the plasma processing method in this embodiment, a method for selectively etching the protrusions on the sidewalls of a mask pattern containing an inorganic resist relative to a metal oxide film exposed by EUV within a processing chamber 101 will be described.

[0034] The etching apparatus 100 of this embodiment is an apparatus that uses plasma containing boron trichloride (BCl3) gas to form a deposition film on the upper surface of the mask pattern, etch and remove the protrusions of the sidewalls of the mask pattern.

[0035] Figure 2 This is a diagram illustrating an example of the process flow of the plasma treatment method in this embodiment. Additionally, Figure 3 This is an example of a cross-sectional view of the mask pattern before plasma processing in this embodiment. Regarding... Figure 3 The cross-sectional shape of the mask shown can also be identified by receding or protruding portions 31 on the sidewalls of the mask pattern 30 formed on the lower mask film 32. In this embodiment, based on Figure 2 The process for, for example Figure 3 The method of selectively etching the protrusions 31 on the sidewalls of the mask pattern 30 will be described.

[0036] In this embodiment, as an example, the material of the mask pattern 30 containing an inorganic resist, which is a metal oxide film exposed by EUV, is described as tin oxide. Alternatively, the mask pattern 30 may also be a pattern developed by EUV exposure. Furthermore, as the material of the lower film 32 of the mask pattern 30, spin-coated glass (SOG) is described, but it may also be a film composed of other materials with low reactivity with BCl3 plasma, such as silicon-containing films, carbon-containing films such as amorphous carbon layers (ACL), or metals such as titanium (Ti).

[0037] First, the wafer 109 is placed onto the stage 110 within the processing chamber 101, and the process of etching the sidewalls of the mask pattern 30 formed on the wafer 109 begins (S3). This process S3 can be described as follows: using plasma generated with pulse-modulated high-frequency power and BCl3 gas, the sidewalls of the inorganic resist, which serves as the mask pattern 30, are selectively etched relative to the film thickness direction of the inorganic resist. Based on a control signal from the device control unit 114, etching gas 102 is supplied to the processing chamber 101 at a predetermined flow rate. The supplied etching gas generates electron cyclotron resonance through microwaves applied from the microwave power supply 105 controlled by the device control unit 114 and a magnetic field generated by the coil 107, becoming plasma 108 within the processing chamber 101, generating free radicals and ions. The free radicals and ions generated by the plasma 108 reach the surface of the wafer 109 and begin... Figure 3 Plasma treatment of the mask pattern 30 shown.

[0038] As the etching gas 102, for example, a mixture of BCl3 gas with argon (Ar) gas, chlorine (Cl2) gas, nitrogen (N2) gas, etc., a mixture of BCl3 gas with Ar gas, a mixture of BCl3 gas with Cl2 gas, a mixture of BCl3 gas with Cl2 gas and Ar gas, a mixture of BCl3 gas with N2 gas, etc.

[0039] In the plasma treatment of step S3, in order to suppress the etching of the upper surface of the mask pattern 30 and selectively perform sidewall etching, it is necessary to use the microwave control unit 116 to control the microwave in step S3 to pulse it. Here, the correlation between etching parameters and roughness, such as plasma treatment conditions, microwave power (high-frequency power), RF (high-frequency) bias power, gas flow rate, pressure, stage temperature, microwave modulation frequency and duty cycle, and plasma treatment time, is obtained in advance. It is particularly preferable to obtain the correlation between these parameters and roughness in advance. Figure 9 The correlation between plasma processing time, pulse modulation duty cycle, and roughness is shown in (a).

[0040] The frequency of the microwave pulse modulation is in the range of 100Hz to 1000Hz.

[0041] Alternatively, based on a pre-established correlation between roughness and plasma treatment conditions, before step S3, a roughness reduction target amount can be set according to the roughness before plasma treatment, and step S2 can be added specifying the plasma treatment conditions to achieve the roughness reduction target amount. In step S2, in particular, it is also possible to base... Figure 9The relationship between the roughness obtained as shown in (a), the plasma processing time, and the duty cycle of pulse modulation are determined before step S3. Based on the roughness 70 before plasma processing, a roughness reduction target value 71 is set, and the plasma processing time and pulse modulation duty cycle for achieving the roughness reduction target value 71 are specified.

[0042] The roughness can be determined by taking a top view of the mask pattern 30 using an electron microscope 120, such as a scanning electron microscope (SEM), and calculating it using analytical software based on the captured top view. The roughness value can be expressed using LER (representing the roughness at the pattern ends) and LWR (representing the roughness across the pattern width). LER can be calculated as three times the standard deviation (3σ) of the pattern end position, and LWR can be calculated as three times the standard deviation of the pattern width.

[0043] In process S2, the relationship between the pre-obtained roughness, plasma processing time, and pulse modulation duty cycle is considered. Figure 9 (a) illustrates an example of a method for specifying the plasma processing time and pulse modulation duty cycle in step S3. Figure 9 . Figure 9 (a) shows an example of the correlation between the roughness before and after plasma treatment, the plasma treatment time, and the duty cycle of pulse modulation. Figure 9 (b) illustrates an example of the correlation between film thickness changes before and after plasma treatment, plasma treatment time, and pulse modulation duty cycle. To obtain... Figure 9 (a) The plasma processing time and pulse modulation duty cycle dependence of the roughness change before and after plasma treatment are obtained in advance. Next, a roughness reduction target value of 71 is set, based on... Figure 9 The graph shown in (a) specifies the plasma treatment time 72 and pulse modulation duty cycle 73 in process S3, which are required to achieve the target roughness reduction value 71. When the target value can be achieved under several conditions, it can be obtained by... Figure 9 (a) The same method was used to obtain a prior correlation between film thickness, plasma processing time, and pulse modulation duty cycle. Figure 9 In (b), the condition with minimal change in film thickness before and after treatment is taken as the optimal condition.

[0044] Alternatively, a system may be provided that stores the correlation between pre-obtained roughness and plasma treatment conditions in a storage unit 119, and obtains the pattern roughness using an electron microscope 120 before plasma treatment, determining the plasma treatment conditions based on the measured roughness, the pre-obtained roughness, and the correlation between the plasma treatment conditions. Alternatively, this system may be used to automatically obtain the optimal plasma treatment conditions for process S3 based on the correlation, using the roughness measurement value before plasma treatment in process S3, and perform plasma treatment under the obtained conditions.

[0045] One embodiment of the etching process in this example is characterized by the following conditions: with Ar gas added to BCl3 gas, the BCl3 flow rate is 15 mL / min, the Ar flow rate is 85 mL / min, the pressure is 1.0 Pa, the stage temperature is 40 °C, the microwave power is 800 W, the microwave modulation frequency is 100 Hz, the duty cycle is 25%, and the plasma treatment time is 5 s.

[0046] An example of a cross-sectional view of the pattern during the etching process in step S3 is shown below. Figure 4 (a) and (b). Figure 4 (a) shows a patterned cross-sectional view of the pulsed microwave off time. Figure 4 (b) shows an example of a patterned cross-sectional view of the time 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 duty cycle of the pulsed microwaves specified in step S2, as... Figure 4 As shown in (a), a deposition film 34 is formed on the upper surface of the mask pattern 30. This deposition film 34 may contain low-dissociation free radicals BCl3 from the plasma generated from BCl3 gas. x 35. By forming a deposition film 34 on the upper surface of the pattern, etching of the upper surface of the pattern is suppressed, preventing the mask pattern from becoming thin film, and etching through the protrusions of the pattern sidewalls, thereby reducing roughness.

[0047] 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 relative to a specified value of the duty cycle of pulse modulation. In addition, the pulsed microwave off time (pulse turn-off time) can be said to be the time of time for deposited free radicals to selectively irradiate the upper surface of the inorganic resist 30 with respect to ions.

[0048] An example of a cross-sectional view of the pattern after the plasma treatment in step S3 is shown. Figure 5When plasma treatment of step S3 is performed under plasma treatment conditions such as the plasma treatment time specified by step S2 and the duty cycle of the pulsed microwave, etching of the upper surface of the pattern can be suppressed, the sidewall protrusions of the pattern can be selectively etched, and roughness such as LER and LWR can be reduced.

[0049] If the highly dissociated ions 37 of boron (B) and chlorine (Cl) and free radicals 36 from the plasma generated from the BCl3-containing gas used in the plasma processing of this embodiment irradiate the mask pattern 30 of the inorganic resist composed of tin oxide, a highly volatile product is generated, and etching is performed. The highly volatile product may include tin chloride (SnCl4), BClO (Boron chloride oxide), etc. (see reference) Figure 4 (b)

[0050] In this embodiment, microwave pulsed plasma generation is used. The plasma processing time dependence of microwave power, ion density, and free radical density when the microwave is set as a standing wave is shown in the figure. Figure 7 (a), (b), and (c). When the microwave is set as a standing wave, such as... Figure 7 As shown in (a), the microwave is always enabled, and after a certain period of time, as Figure 7 As shown in (b) and (c), BCl3 gas is always decomposed into plasma, generating highly dissociated B and Cl ions 37 and free radicals 36. When the highly dissociated ions 37 and free radicals 36 irradiate the mask pattern 30 of an inorganic resist composed of tin oxide, highly volatile products such as SnCl4 and BClO are generated, and etching is performed.

[0051] The plasma treatment time dependence of microwave power, ion density, and free radical density during microwave pulsed processing is shown in the figure. Figure 8 (a), (b), and (c). In the case of microwave pulsedness, such as... Figure 8 As shown in (a), the microwave activation time 50 and deactivation time 51 alternate. Plasma dissociation occurs during the microwave activation time 50, as... Figure 8 As shown in (b) and (c), highly dissociated ions 37 (B, Cl) and free radicals 36 are generated. However, no ions or free radicals are generated during the microwave off-time 51, while low-dissociation free radicals generated during the on-time irradiate the mask pattern. Therefore, in pulsed plasma, low-dissociation free radicals are generated, and more BCl can be generated compared to continuous plasma. xFree radical 35. Moreover, since ions 37 are mainly generated during the microwave power activation time, the flux of ions irradiated from pulsed plasma is less than that from continuous plasma irradiation. Therefore, by pulsed microwaves, the reduction in pattern film thickness can be suppressed.

[0052] Low dissociation BCl x Free radical 35 has a high adhesion probability to the surface of the etched material, thus enabling selective formation of a deposited film on the patterned surface. On the other hand, on the sidewalls where no deposited film has formed, the highly dissociated B and Cl free radicals 36, which are highly reactive on the surface of the etched material, can react to reduce the roughness of the sidewalls.

[0053] The above description, based on specific embodiments, illustrates the disclosure made by the present discloser. However, this disclosure is not limited to the described embodiments, and various modifications can be made without departing from its spirit. For example, the above embodiments are examples described in detail for the purpose of easily understanding and illustrating this disclosure, and are not necessarily limited to having all the described structures. Furthermore, regarding a part of the structure of each embodiment, other structures can be added, deleted, or replaced.

[0054] Explanation of reference numerals in the attached figures:

[0055] 100: Etching apparatus; 101: Processing chamber; 102: Gas source; 103: Gas flow 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: Device control unit; 115: Exhaust system control unit; 116: Gas control unit; 117: Bias control unit; 118: Microwave control unit; 119: Storage unit; 120: Electron microscope; 30: Mask pattern; 31: Unevenness of mask pattern sidewalls; 32: Underlying film of mask pattern; 33: Pattern shape before plasma treatment; 34: Deposited film; 35: Low-dissociation BCl. x Free radical, 36: Highly dissociated free radical, 37: Highly dissociated ion, 50: Time to activate pulsed microwave, 51: Time to deactivate pulsed microwave, 70: Roughness before plasma treatment, 71: Target value for roughness reduction, 72: Plasma treatment time to achieve the target value for roughness reduction, 73: Duty cycle to achieve the target value for roughness reduction.

Claims

1. A plasma processing method for forming a mask containing an inorganic resist after exposure to extreme ultraviolet (EUV) lithography on a metal oxide film, characterized in that, The plasma processing method includes the following steps: using plasma generated by pulse-modulated high-frequency power and BCl3 gas, selectively etching the sidewalls of the inorganic resist relative to the film thickness direction of the inorganic resist.

2. The plasma treatment method according to claim 1, characterized in that, The metal oxide film is tin oxide.

3. The plasma treatment method according to claim 1, characterized in that, 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 specified value of the duty cycle of the pulse modulation.

4. The plasma treatment method according to claim 1, characterized in that, The pulse-modulated high-frequency power has the pulse off-time and the pulse on-time of the high-frequency power. The pulse off time is the time it takes for deposited free radicals to selectively irradiate the upper surface of the inorganic resist relative to ions.

5. The plasma treatment method according to claim 1, characterized in that, The plasma is generated using a mixture of BCl3 gas and Ar gas, a mixture of BCl3 gas and Cl2 gas, or a mixture of BCl3 gas and N2 gas.

6. The plasma treatment method according to claim 1, characterized in that, The frequency of the pulse modulation is within the range of 100Hz to 1000Hz.

7. The plasma treatment method according to claim 1, characterized in that, The lower layer of the inorganic resist is either spin-coated glass (SOG) or an amorphous carbon layer (ACL).

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