Method for cleaning protective film for plasma treatment equipment

Abstract

A highly reliable method for cleaning a protective film for a plasma processing apparatus is provided. The method includes a protective film formed on the surface of a substrate disposed within a processing chamber of a plasma processing apparatus and comprising a material resistant to plasma. The plasma processing apparatus processes a wafer to be processed, which is placed within a processing chamber disposed within a vacuum vessel, using plasma generated within the processing chamber. The method includes the following steps: (a) preparing a substrate having a film containing yttrium on its surface; and (b) immersing the substrate in a dilute nitric acid solution and cleaning the film by ultrasonically irradiating the film. In step (b), the yttrium elution rate is detected during cleaning. After the yttrium elution rate, from the start of ultrasonic irradiation, undergoes a first decrease, a first increase, and a second decrease, cleaning is stopped before the second increase occurs.

Description

Technical Field

[0001] The present invention relates to a method for cleaning a protective film used in a plasma processing device. Background Art

[0002] Plasma etching is used in microfabrication in the manufacture of electronic devices and magnetic memories. Since the inner walls of the processing chamber of a plasma processing apparatus performing plasma etching are exposed to high-frequency plasma and etching gas during the etching process, a plasma-resistant film forms on the inner wall surface to protect it.

[0003] Patent Document 1 (JP-A-2009-176787) describes a ground coating material for a plasma etching device composed of one or more of Al2O3, YAG, Y2O3, Gd2O3, Yb2O3, or YF3. Furthermore, Patent Document 2 (JP-A-2017-31457) describes a cleaning method in which a substrate having a thermally sprayed coating formed on its surface is immersed in an organic acid.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-176787

[0007] Patent Document 2: Japanese Patent Application Publication No. 2017-31457 Summary of the Invention

[0008] Problems that the invention aims to solve

[0009] The plasma-resistant coating described above requires low surface roughness (Ra) and porosity. Therefore, after the coating is formed, post-processing such as polishing is performed on the surface. However, post-processing releases foreign matter adhering to the surface due to thin areas or electrostatically adsorbed inner wall materials, making it more likely that foreign matter will adhere to the etched object. Therefore, a cleaning method is needed to reduce the generation of foreign matter after post-processing.

[0010] An object of the present invention is to provide a highly reliable method for cleaning a protective film for a plasma processing apparatus.

[0011] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

[0012] Means for solving problems

[0013] Among the embodiments disclosed in this application, the outline of a representative embodiment will be briefly described below.

[0014] A representative embodiment of a method for cleaning a protective film for a plasma processing apparatus includes a protective film formed on a surface of a substrate disposed within a processing chamber of the plasma processing apparatus and comprising a material resistant to plasma. The plasma processing apparatus processes a wafer to be processed, which is placed within the processing chamber and disposed within a vacuum vessel, using plasma formed within the processing chamber. The method for cleaning a protective film for a plasma processing apparatus includes the following steps: (a) preparing a substrate having a film containing yttrium on its surface; and (b) immersing the substrate in a dilute nitric acid solution and cleaning the film by ultrasonically irradiating the film. In step (b), the elution rate of yttrium is detected during cleaning. After the elution rate of yttrium decreases, increases, and decreases in sequence since the start of ultrasonic irradiation, cleaning is stopped before the second increase occurs.

[0015] Effects of the Invention

[0016] According to a representative embodiment, a highly reliable method for cleaning a protective film for a plasma processing apparatus can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a longitudinal sectional view schematically showing the structure of a plasma processing apparatus according to an embodiment of the present invention.

[0018] Figure 2 It is a schematic representation of the composition Figure 1 A schematic perspective view of the structure of the components of the ground electrode is shown.

[0019] Figure 3 This is a flowchart illustrating a process of forming and a process of cleaning a protective film for a plasma processing apparatus according to an embodiment of the present invention.

[0020] Figure 4 This is an enlarged cross-sectional view showing the vicinity of the surface of a protective film for a plasma processing apparatus according to an embodiment of the present invention.

[0021] Figure 5 This is a graph showing the relationship between the elution rate and time in the cleaning step of the protective film for a plasma processing apparatus.

[0022] Figure 6 This is a table showing the number of foreign matter particles when plasma etching was performed in each of the prior art 1 and 2 or the present embodiment. DETAILED DESCRIPTION

[0023] Hereinafter, embodiments of the present invention will be described in detail based on the accompanying drawings. In all figures used to illustrate the embodiments, components having the same functions are denoted by the same reference numerals, and their repeated descriptions are omitted. Furthermore, in the embodiments, descriptions of identical or similar parts will not be repeated in principle unless otherwise required.

[0024] <Details of room for improvement>

[0025] Plasma etching is sometimes used in the manufacturing process of electronic devices and other components. The processing chamber of the plasma processing device used in plasma etching is located inside a vacuum vessel and is therefore constructed from metals such as aluminum and stainless steel. During the etching process, the inner walls of the plasma processing device are exposed to high-frequency plasma and etching gases, forming a protective film with excellent plasma resistance on the inner wall surface. Yttrium oxide is a potential candidate for such a protective film.

[0026] Foreign matter in the processing chamber can cause manufacturing defects due to foreign matter adhering to the etching target, leading to reduced yield. Therefore, it is important to suppress foreign matter in the processing chamber. Foreign matter in the processing chamber is correlated with the crystal size and phase ratio of the inner wall material.

[0027] The aforementioned film, made of yttrium oxide, is formed using, for example, atmospheric plasma thermal spraying. In atmospheric plasma thermal spraying, a raw material powder with a size of 10 to 60 μm is introduced into a plasma flame along with a carrier gas. Molten or semi-molten raw material particles are sprayed onto the surface of the substrate, where they adhere to the substrate and form a film. However, this plasma thermal spraying method has the following issues: Large surface irregularities; or the formation of numerous pores within the film. Particles that enter these pores react with the film itself or other components, causing film consumption or corrosion.

[0028] Therefore, the aforementioned films are required to have low surface roughness (Ra) and porosity. Therefore, after the films are formed, post-processing such as polishing is performed. However, this post-processing can sometimes cause foreign matter adhering to the surface, such as thin areas of the film or electrostatic adsorption to the inner wall material of the film, to be released during the initial operation of the plasma etching apparatus. Therefore, cleaning methods to reduce the generation of foreign matter after post-processing and methods to inspect the quality of post-processing are required.

[0029] Atmospheric plasma thermal spraying is a film-making method that can entrain air during film-making or cause cracks due to rapid cooling. Therefore, the surface of the film contains surface irregularities and embedded pores (voids) caused by these. That is, parts with weaker adhesion than the surrounding areas will be produced on the surface of the film. In addition, if the above-mentioned grinding process is performed for the purpose of reducing irregularities, the embedded pores may sometimes be opened to produce thin-walled parts, or the film material removed by grinding may sometimes be attached to the surface again due to static electricity. Therefore, the film will become a surface state that is prone to the production of initial foreign matter caused by these.

[0030] In addition, as one of the methods for inspecting whether the post-processing is good or not, there is the following method: for the film on the surface of the component constituting the inner wall of the processing chamber, the porosity, surface roughness (Ra), crystallite size, phase ratio, etc. of the film after the film is formed or after post-processing are detected, and they are compared with the allowable range of the predetermined specifications for evaluation.

[0031] However, after the film is formed, the above-mentioned inspection method does not evaluate the film's properties, such as porosity, surface roughness (Ra to arithmetic mean roughness), crystallite size, and phase ratio, by comparing them against a given tolerance range. For example, the inspection of the component is limited to an appearance inspection. Furthermore, it does not determine whether the film formed on the surface of the components forming the inner wall possesses the desired characteristics and performance (porosity, surface roughness, residual stress, crystallite size, phase ratio, etc.) in the areas where each component is located. Therefore, it is difficult to improve the reliability of the cleaning process by performing only the above-mentioned inspection.

[0032] Another method for inspecting the quality of post-processing involves cutting out a portion of the component inside the processing chamber for inspection. However, this method requires cleaning the portion after cutting it off from the component being inspected. Consequently, the film on the inspected portion is not formed using the same process as the films on other components of the same type. Furthermore, the cutting process can create foreign matter on the surface of the inspected film, potentially compromising inspection accuracy.

[0033] Another method for checking the quality of post-processing is to form a coating on the surfaces of multiple components of a certain type by thermal spraying. In order to ensure that the coating has properties such as performance or shape that are as similar as possible on one component and the other components, a portion of the component is cut out for inspection, or one of the multiple products is used for inspection. However, with this inspection method, if the component dimensions are large, the unit price of the component increases, and the manufacturing cost of the plasma treatment equipment for the inspection is increased.

[0034] As described above, in the above-mentioned technology, the reliability of the plasma processing apparatus and the processing yield are impaired, and also it causes an increase in manufacturing cost.

[0035] Therefore, there is still room for improvement in the cleaning process of the protective film for plasma processing apparatuses by suppressing the generation of foreign matter after post-processing including the cleaning process to enhance the reliability of the cleaning method.

[0036] (Implementation Method)

[0037] use Figure 1 as well as Figure 2 The structure of a plasma processing apparatus according to an embodiment of the present invention will be described. Figure 1 This is a longitudinal cross-sectional view schematically illustrating the structure of a plasma processing apparatus according to an embodiment of the present invention. The plasma processing apparatus shown in this figure is a plasma etching apparatus that generates plasma within a processing chamber within a vacuum vessel and uses the plasma to etch a film structure having a mask layer pre-formed on the surface of a sample, such as a semiconductor wafer, disposed within the processing chamber, and a film layer to be processed thereunder.

[0038] Figure 1 The plasma processing apparatus 100 of the illustrated embodiment includes a partially cylindrical metal vacuum vessel 1. Furthermore, the plasma processing apparatus 100 includes a plasma generating unit, which includes a generator disposed above the vacuum vessel 1 and generates an electric field or magnetic field for forming plasma in the depressurized interior of the vacuum vessel 1. The generated electric field or magnetic field is then supplied to the interior. Furthermore, the plasma processing apparatus 100 includes an exhaust unit disposed below the vacuum vessel 1 and includes a vacuum pump connected to the vacuum vessel 1 to exhaust and depressurize the interior of the vacuum vessel 1. The outer sidewall of the vacuum vessel 1 is connected to a transport container, which is another vacuum vessel 1. Wafers, serving as sample processing targets, are transported within the depressurized interior transport space. A gate is provided in the sidewall of the vacuum vessel 1. This gate extends horizontally through the sidewall, serving as a passage connecting the interior of the vacuum vessel 1 to the outside, allowing wafers to be transported through the interior. The transport container is connected to the side wall of the vacuum container 1 surrounding the outer periphery of the opening of the shutter so that the space inside the vacuum container 1 and the space inside the transport container can communicate with each other.

[0039] The vacuum container 1 has a processing chamber 7 as a space in which a sample to be processed is arranged and a plasma is formed. The processing chamber 7 has a discharge portion arranged at the top and having a cylindrical shape and forming a plasma 15. A cylindrical sample stage, i.e., a carrier 6, is arranged in a space at the bottom that is connected to the discharge portion. The carrier 6 has a circular upper surface as a surface on which a wafer 4 serving as a substrate to be processed is placed. In addition, the carrier 6 has a heater for heating the wafer 4 and a refrigerant flow path for cooling the wafer 4, and is provided with a pipeline for supplying helium (He) gas as a heat transfer gas between the circular upper surface of the carrier 6 and the back surface of the wafer 4 placed on the upper surface.

[0040] Furthermore, a metal electrode is disposed within stage 6 and is electrically connected to a high-frequency power supply 14 via an impedance matching box 13. This high-frequency power supply 14 supplies the electrode with high-frequency power for forming a potential on wafer 4 during the processing of wafer 4 using plasma 15. The potential difference between the bias potential formed on wafer 4 by the high-frequency power during the formation of plasma 15 and the plasma is utilized to induce charged particles such as ions within wafer 4 to the surface of wafer 4, thereby promoting the etching process.

[0041] The wafer 4 is placed on the tip of an arm of a transport device (not shown) such as a robot arm disposed in a transport space within the transport container and transported to the processing chamber 7, where it is then placed on the stage 6. The wafer 4 placed on the stage 6 is attracted and held on the upper surface of the dielectric film by electrostatic force generated by applying a DC voltage to an electrode for electrostatic attraction.

[0042] A circular shower plate 2 and a window member 3 are placed above the upper end of the cylindrical sidewall member surrounding the discharge section of the vacuum vessel 1, sandwiching an annular member. The window member 3, together with the sidewall member 41 surrounding the outer periphery of the discharge section, constitute the vacuum vessel 1. A sealing member such as an O-ring is interposed between the lower surface of the outer periphery of the window member 3, the upper surface of the sidewall member's upper end, and the annular member disposed therebetween, connecting these components. This creates an airtight separation between the processing chamber 7 within the vacuum vessel 1 and the atmospheric pressure atmosphere outside.

[0043] As will be described later, the window member 3 is a disc-shaped member made of ceramic (quartz in this embodiment) through which the electric field of the microwaves used to form the plasma 15 is transmitted. A gap 8 of a given size is left below it, and a shower plate 2 having a plurality of through holes 9 in the center is arranged. The shower plate 2 faces the interior of the processing chamber 7 to form its top surface. The processing gas, whose flow rate is adjusted to a given value by a gas flow control unit (not shown), is introduced into the gap 8. After diffusing in the gap 8, the gas passes through the through holes and is introduced into the processing chamber 7 from above. In addition, the valve 51 arranged on the processing gas supply pipe 50 connected to the annular member is opened to introduce the processing gas into the gap 8.

[0044] Furthermore, a passage is provided at the bottom of the vacuum vessel 1, connecting the interior of the processing chamber 7 with the exterior, allowing the plasma 15 within the processing chamber 7, products generated during wafer 4 processing, and particles of the processing gas to be exhausted. This passage's circular opening inside the processing chamber 7 serves as an exhaust port and is located directly below the stage 6 positioned above, at a position where their central axes are aligned when viewed from above. Connected to the bottom of the vacuum vessel 1 are a turbomolecular pump 12, which serves as a vacuum pump for the exhaust section, and a dry pump 11, located downstream of the turbomolecular pump 12. Furthermore, the inlet of the turbomolecular pump 12 is connected to the exhaust port via exhaust piping.

[0045] A valve 18 is disposed on the exhaust piping connecting the turbomolecular pump 12 and the dry pump 11. The exhaust piping between the valve 18 and the dry pump 11 is connected to another exhaust piping 10 connected to the bottom surface of the vacuum vessel 1 and communicating with the bottom of the processing chamber 7. This other exhaust piping 10 is connected so that it branches into two pipes midway and then merges back into a single pipe. Valves 17 and 19 are disposed at each branch. Of these, valve 17 is a slow exhaust valve used to gradually evacuate the processing chamber 7 from atmospheric pressure to a vacuum state using the dry pump 11, while valve 19 is a main exhaust valve used for high-speed exhaust using the dry pump 11.

[0046] The processing chamber 7 is equipped with a pressure sensor 75 for detecting the pressure within it. A circular pressure adjustment plate 16 is located in the lower portion of the processing chamber 7, above the exhaust port and between the bottom surface of the stage 6 in this embodiment. This pressure adjustment plate 16 moves vertically within this space to open and close the exhaust port, and adjusts the exhaust flow rate or speed by increasing or decreasing the opening area of ​​the exhaust port. The pressure within the processing chamber 7 increases or decreases based on the balance between the process gas or other gas introduced into the processing chamber 7 through the gas inlet port, which serves as the through hole of the shower plate 2, and the exhaust flow rate or speed from the exhaust port. For example, while gas is introduced into the processing chamber 7 from the shower plate 2 at a given flow rate or speed corresponding to the processing conditions of the wafer 4, the exhaust flow rate or speed is adjusted by adjusting the vertical position of the pressure adjustment plate 16 to achieve a pressure in the processing chamber 7 corresponding to the processing conditions.

[0047] A plasma generating unit is disposed on the metal sidewalls surrounding the outer periphery of the discharge portion of the processing chamber 7 at the top of the vacuum vessel 1, and above and around the window member 3. The plasma generating unit includes a magnetron oscillator 20 that outputs the electric field of microwaves used to form plasma 15, and a waveguide 21 that propagates the microwaves into the processing chamber 7. The waveguide 21 includes a square portion extending horizontally (left-right in the figure) and having a rectangular or square cross-section, and a circular portion connected to one end of the square portion and extending vertically and having a cylindrical shape. The magnetron oscillator 20 is disposed at the other end of the square portion.

[0048] The lower end of the circular portion is connected to the upper end of a cylindrical hollow portion, which is located above window member 3 and has a diameter approximately equal to that of window member 3, but larger than the diameter of the circular portion. Furthermore, annular solenoid coils 22 and 23 are provided above the hollow portion and on the outer periphery of the sidewall of vacuum vessel 1 surrounding the outer periphery of the hollow portion and the discharge portion, respectively, to generate a magnetic field by supplying DC power.

[0049] The inner wall surface of the sidewall member 41 of the processing chamber 7 is exposed to the plasma 15 formed within the discharge section. However, in order to stabilize the potential of the plasma 15, a component serving as a ground is required within the processing chamber 7. In this embodiment, a ring-shaped ground electrode 40, which serves as a ground within the discharge section, is disposed above the stage 6, surrounding the upper surface of the stage 6. The ground electrode 40 is constructed from a metal member such as a stainless steel alloy or an aluminum alloy. Because the ground electrode 40 is exposed to the plasma 15, it is subject to interaction with the highly reactive or corrosive particles within the plasma 15, potentially causing corrosion, metal contamination, or foreign matter generation due to generated products.

[0050] Therefore, in order to suppress such problems, Figure 1 As schematically shown in the enlarged cross-sectional view of the lower left portion of FIG, in this embodiment, a film 42 made of a material with high plasma resistance is disposed on the surface of the ground electrode 40 to cover the surface of the ground electrode 40. Covering the surface with the film 42 allows the ground electrode 40 to maintain its function as a ground while suppressing damage such as corrosion to the ground electrode 40 caused by plasma. The film 42 may be a laminated film.

[0051] Meanwhile, the sidewall member 41 surrounding the discharge section of the vacuum vessel 1 in this embodiment is made of a metal base material such as a stainless steel alloy or an aluminum alloy, but does not function as a ground. To prevent corrosion, metal contamination, and foreign matter from being generated by exposure of the sidewall member 41 to the plasma 15, the inner surface of the sidewall member 41 is subjected to a surface treatment such as passivation, thermal spraying, PVD, or CVD. Furthermore, to prevent the base material of the sidewall member 41 from being directly exposed to the plasma 15, a ceramic component may be formed as follows. Specifically, an annular or cylindrical ceramic component, such as yttrium oxide or quartz, may be positioned between the inner sidewall surface of the cylindrical sidewall member 41 and the discharge section of the processing chamber 7, covering the inner sidewall surface with respect to the plasma 15. This component between the sidewall member 41 and the plasma 15 prevents contact between the sidewall member 41 and the plasma 15, thereby suppressing wear of the sidewall member 41 after the surface treatment by the plasma 15.

[0052] Figure 2 It is a schematic representation of the composition Figure 1 A schematic perspective view of the structure of the components of the ground electrode is shown. Figure 2 In the figure, the image is viewed from the lower side toward the upper side. Figure 1 The diagram shows a case where the ground electrode 40 has an annular or cylindrical shape.

[0053] As shown in this figure, the ground electrode 40 has an overall cylindrical shape of a given thickness, with an inner sidewall and an outer sidewall having the same inner diameter around the vertical center axis. Furthermore, the ground electrode 40 comprises a cylindrical main sidewall portion and an annular electrode portion positioned above the upper end of the main sidewall portion. The outer circumferential surface of the electrode portion has a smaller radius from the vertical center axis than the main sidewall portion below. A rectangular opening 43, forming a through-hole for the gate 49, is located in the vertical middle portion of the cylindrical main sidewall portion.

[0054] When ground electrode 40 is installed inside processing chamber 7, it is positioned between the inner sidewall and processing chamber 7. The lower portion of ground electrode 40 is located on the outer periphery of stage 6, covering the inner wall surface of sidewall member 41 of vacuum vessel 1 surrounding plasma 15. The upper portion of ground electrode 40 is positioned inside sidewall member 41 surrounding the discharge portion, and has a length in the vertical direction sufficient to cover the inner wall surface of sidewall member 41 relative to plasma 15. This shape protects sidewall member 41 from the effects of interaction with plasma 15.

[0055] <Method for Forming and Cleaning a Protective Film for a Plasma Processing Device>

[0056] Next, regarding this embodiment, use Figures 3 to 5 The steps from film formation (thermal spray film) to post-processing after film formation will be described.

[0057] exist Figure 3 The flowchart shows the procedure for performing the following processing: a process for forming a plasma-resistant film for protecting a ground electrode for a plasma processing device (prior art 1); a first post-processing performed after the formation of the film (prior art 2); and a second post-processing (an example of this embodiment).

[0058] Here, first, a ground electrode is prepared and a degreasing treatment is performed on the surface of the ground electrode (step S1). Figure 1 The single electrode before the plasma processing device 100.

[0059] Next, the surface of the ground electrode is sandblasted as a pretreatment for film formation (step S2). Here, abrasive (particles) are blasted onto the ground electrode. This cleans and roughens the surface of the ground electrode, improving the adhesion of the film to be formed later. Next, the surface of the ground electrode is degreased (step S3).

[0060] Next, a film is formed on the surface of the ground electrode by atmospheric plasma spraying (APS: Atmospheric Plasma Spraying) (step S4). Here, a film composed of YF3 (yttrium fluoride) is formed. In addition, the material of the film can also be YOF (yttrium oxyfluoride), Y2O3 (yttrium oxide) or YAG (Yttrium Aluminum Garnet). The atmospheric plasma thermal spraying method is a method of forming a film on the surface of an object by thermal spraying in an atmosphere set to atmospheric pressure. The plasma formed in the atmosphere is used to melt the raw material powder and the molten or semi-molten raw material is sprayed onto the surface of the object and stacked to form a film. The process of steps S1 to S4 so far is set as the existing technology 1.

[0061] Next, the ground electrode, with the film formed on it, is immersed in pure water for ultrasonic cleaning (step S5). Next, the ground electrode is treated with a chemical solution (step S6), after which it is immersed in pure water again for ultrasonic cleaning (step S7). Next, the ground electrode is polished (step S8), after which it is immersed in pure water again for ultrasonic cleaning (step S9). The steps S5 to S9 (first post-processing) up to this point constitute Conventional Technology 2.

[0062] Next, the ground electrode with the film is immersed in dilute nitric acid and ultrasonically irradiated (step S10). Next, the ground electrode is cleaned with pure water (step S11). The steps S10 and S11 (second post-processing) up to this point are considered as examples of this embodiment. The film formation and post-processing (first post-processing and second post-processing) are completed as described above. After that, the ground electrode 40 is assembled to Figure 1 The plasma processing apparatus 100 is shown.

[0063] In addition to the conventional film formation step (steps S1 to S4) and the first post-treatment (steps S5 to S9), this embodiment primarily features ultrasonic cleaning in dilute nitric acid (step S10) performed under the conditions described below. Specifically, this embodiment primarily features cleaning in dilute nitric acid by ultrasonic irradiation, thereby removing portions that are weakly bonded to their surroundings through acid dissolution and ultrasonic vibration.

[0064] like Figure 4As shown, after the first post-processing is completed (just after step S9), the surface of the film 42 becomes a state with unevenness, pores and foreign matter attached to the surface. As the foreign matter attached to the surface, specifically, there is a water adsorbent 43a adsorbed between the film 42 and the surface due to water on the surface of the film 42. In addition, as the foreign matter attached to the surface, there is an electrostatic adsorbent 43b that is electrostatically adsorbed relative to the surface of the film 42. In addition, as the foreign matter attached to the surface, there is a stress-fixed object 43c that is stress-fixed by utilizing the unevenness of the surface of the film 42. Most of these foreign matter attached to the surface are foreign matter separated from the film 42 during the grinding process of the first post-processing, and the materials of these foreign matter are the same as the material of the film 42.

[0065] Furthermore, the weak portion 42a is a portion of the membrane 42, and due to its thin thickness, it is weakly bonded to the surrounding area. Breaking or dissolving the weak portion 42a can produce surface foreign matter. The ultrasonic cleaning in dilute nitric acid (step S10) of this embodiment removes this surface-attached foreign matter and the weak portion 42a, thereby preventing the generation of foreign matter due to the membrane's surface condition after post-processing.

[0066] However, if ultrasonic cleaning in dilute nitric acid is performed for a long time, the internal pores 42c that were not exposed on the surface at the beginning of cleaning will open due to the cleaning, thereby increasing the surface area. In other words, a large number of pores 42c are formed in the membrane 42 near the surface of the membrane 42. Between the pores 42c that are particularly close to the surface of the membrane 42 and the surface, there is a thin portion 42b that is a small thickness as part of the membrane 42. If this thin portion 42b is dissolved by prolonged ultrasonic cleaning in dilute nitric acid, the area where the thin portion 42b was formed will become an opening, releasing the pores 42c. As a result, the surface area of ​​the membrane 42 will increase.

[0067] The time of ultrasonic cleaning with dilute nitric acid and the elution rate of yttrium are as follows: Figure 5 The elution rate here refers to the amount (weight) of yttrium eluted per unit time from the measurement point (mark) before the corresponding time to the corresponding time. Figure 5 Among the graphs shown, the example of this embodiment is a graph consisting of black square plots, and this graph will be described here. Figure 5 Each graph shown is obtained by averaging a plurality of plots at a given time.

[0068] like Figure 5 As shown in FIG. 1 , when ultrasonic cleaning with dilute nitric acid is started, first, as the first stage 1A, the elution rate of yttrium is greatly reduced. In this first stage 1A, Figure 4 The water adsorbent 43 a and the electrostatic adsorbent 43 b shown are eluted and separated from the surface of the film 42 . By removing these, the elution rate of yttrium is greatly reduced.

[0069] In the second stage 1B, about 10 minutes after the start of ultrasonic cleaning with dilute nitric acid, the elution rate of the reduced yttrium temporarily increases and then decreases. Figure 4 The remaining electrostatically attracted substances 43b and stress-fixed substances 43c shown in the figure elute and separate. Furthermore, in the second stage 1B, the narrow weak portion 42a elutes, and with this, the distal end portion connected to the narrow weak portion 42a separates from the membrane 42 and elutes. Therefore, in the second stage 1B, the elution rate of the reduced yttrium temporarily increases. Thereafter, the elution rate decreases due to reductions caused by foreign matter adhering to the surface and the elution of the narrow weak portion 42a.

[0070] Here, if the dilute nitric acid ultrasonic cleaning is continued, about 60 minutes after the start of the dilute nitric acid ultrasonic cleaning, the elution rate of yttrium will enter the third stage 1C, where the elution rate of yttrium increases significantly. In the third stage 1C, the elution rate of yttrium increases by more than 1.5 times compared to the stage immediately before. This is because Figure 4 The thin portion 42b shown is eluted, releasing pores 42c, thereby increasing the surface area of ​​the membrane 42. With the surface area of ​​the membrane 42 thus increased, the pure water cleaning in step S11 is performed, and the ground electrode assembled into the plasma processing apparatus is in a state where foreign matter can be easily released from the membrane 42. In other words, if the dilute nitric acid ultrasonic cleaning time is not specified and prolonged, it is believed that even after-treatment, the generation of foreign matter cannot be effectively suppressed. Therefore, the dilute nitric acid ultrasonic cleaning needs to be stopped before the elution rate in the third stage 1C begins to increase.

[0071] Therefore, as a key feature of the method of this embodiment, in the dilute nitric acid ultrasonic cleaning process in step S10, the ground electrode to be cleaned is immersed in the dilute nitric acid solution, ultrasonic irradiation is initiated, and cleaning is stopped after the yttrium elution rate (elution amount) decreases (first stage 1A), increases again, and decreases again (second stage 1B), and before it increases again (third stage 1C). In other words, in this cleaning process, the yttrium elution rate is detected during cleaning, and cleaning is stopped before the second increase occurs after the yttrium elution rate has sequentially decreased, increased, and decreased since the start of ultrasonic irradiation. For example, in this embodiment, cleaning is stopped after 10 or 20 minutes have passed and before 60 minutes have passed since the start of ultrasonic irradiation.

[0072] This removes foreign matter sources from the inner wall material surface that may be generated during post-processing after film formation, and allows post-processing to be completed while suppressing the exposure of pores 42c. Specifically, since the surface area of ​​film 42 is prevented from increasing excessively, the generation of foreign matter due to the surface condition of film 42 after the ground electrode is assembled in the plasma processing apparatus can be suppressed. Consequently, the reliability of the cleaning method for the protective film for plasma processing apparatus can be improved.

[0073] Furthermore, by determining the elution rate (elution amount) of yttrium in each of the first stage 1A and the second stage 1B and setting it as an indicator of attached foreign matter, it can be used as an inspection indicator for cleaning. In other words, these elution rates serve as a basis for determining whether cleaning has ended at the desired timing or when cleaning should end. This allows for managing the quality of the film 42. By using a ground electrode that has undergone such cleaning, the generation of foreign matter within the processing chamber of the plasma processing device can be suppressed, thereby improving the yield rate of wafer processing. Based on the above, the aforementioned room for improvement can be addressed.

[0074] Here we explain the concentration of dilute nitric acid used in the above-mentioned dilute nitric acid ultrasonic cleaning. Figure 5 , the examples of this embodiment are shown by the black square plots. Here, the concentration of dilute nitric acid is set to a medium level (more than 0.001 mol / liter and less than 0.05 mol / liter). In addition, the graph consisting of the black circle plots is a graph of a comparative example in which the concentration of dilute nitric acid is set to be higher than 0.05 mol / liter. In addition, the graph consisting of the black triangle plots is a graph of a comparative example in which the concentration of dilute nitric acid is set to be lower than 0.001 mol / liter. In addition, the graph consisting of the white circle plots is a graph of a comparative example in which the object is not immersed in dilute nitric acid but immersed in pure water and ultrasonic cleaning is carried out.

[0075] As shown in the ultrasonic cleaning (chart of white circle) in pure water, even if do not use dilute nitric acid, elution rate also can significantly reduce in the 1st stage 1A, and in the 3rd stage 1C, pore 42c is exposed because of physical destruction, so the elution rate of yttrium increases.In addition, under the situation that dilute nitric acid concentration is high (chart of black circle), owing to the increase of the elution rate confirmed in the 2nd stage 1B of the embodiment of present embodiment produces under the timing close to the 1st stage 1A side, therefore be difficult to confirm the increase of initial elution rate.In this case, be difficult to carry out after the increase of initial elution rate and before increasing again, stop cleaning the dilute nitric acid ultrasonic cleaning of such present embodiment.Therefore, in order that the 1st stage 1A and the 2nd stage 1B are separated, dilute nitric acid concentration need be below 0.05mol / liter.

[0076] In addition, when the dilute nitric acid concentration is low (black triangle chart), the increase in the third stage 1C occurs before the increase in the elution rate confirmed in the second stage 1B of the example of the present embodiment occurs. That is to say, the third stage 1C (irradiation upper limit) is reached only by the physical destruction caused by the ultrasonic wave. Therefore, it is difficult to stop cleaning the dilute nitric acid ultrasonic cleaning of the present embodiment after the initial increase in the elution rate and before the increase. Further, since the narrow and weak portion 42a and the stress fixture 43c in the second stage 1B cannot be removed, sufficient cleaning cannot be carried out. Therefore, the dilute nitric acid concentration needs to be set to more than 0.001 mol / liter.

[0077] exist Figure 6 The results of the experiments conducted by the present inventors are shown in the table. Figure 6 The table shows the use of Figure 1 The number of foreign matter that falls on the surface of the wafer when the plasma processing device 100 shown in FIG. 1 performs plasma etching. In the case of prior art 1 (no post-processing), that is, Figure 3 In the case where the preparation process of the ground electrode and the film is completed in step S4 and the first post-processing and the second post-processing are not performed, the amount of foreign matter exceeds 100. In addition, in the case of the prior art 2 in which the first post-processing is performed, that is, in Figure 3 When the processing of step S9 is completed, the amount of foreign matter is 5.67.

[0078] On the other hand, in the case of the example of this embodiment in which the second post-processing is performed following the first post-processing, that is, Figure 3 After the post-processing in step S11 is completed, the amount of foreign matter is 3.76. Thus, in this embodiment, by starting ultrasonic irradiation in dilute nitric acid, stopping cleaning after the yttrium elution rate decreases, then increases again, then decreases again, and then increases again before the elution rate stops, the source of foreign matter can be effectively removed.

[0079] As mentioned above, the invention completed by the inventors of the present invention has been specifically described based on the embodiments. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

[0080] Industrial Availability

[0081] The present invention can be widely utilized in a method for cleaning a protective film for a plasma processing apparatus.

[0082] Description of Reference Signs

[0083] 1 Vacuum container

[0084] 4 chips

[0085] 15 Plasma

[0086] 40 Grounding Electrode

[0087] 41 side wall components

[0088] 42 membrane

[0089] 42a Narrow and weak part

[0090] 42b thin part

[0091] 42c pores

[0092] 43a Water adsorbate

[0093] 43b Electrostatic adsorption

[0094] 43c Stress fixings

[0095] 100 Plasma treatment device

Claims

1. A method for cleaning a protective film for a plasma processing apparatus, wherein the protective film is formed on a surface of a substrate disposed in a processing chamber of the plasma processing apparatus and comprises a material having resistance to plasma, wherein: The plasma processing apparatus processes a wafer to be processed placed in a processing chamber disposed within a vacuum container using the plasma formed in the processing chamber. The method for cleaning a protective film for a plasma processing device is characterized by comprising the following steps: (a) preparing the substrate having a protective film for a plasma processing device containing yttrium on its surface; and (b) immersing the substrate in a dilute nitric acid solution and cleaning the protective film of the plasma treatment device by ultrasonic irradiation, In the step (b), after the elution rate of yttrium from the start of the ultrasonic irradiation has sequentially undergone a first decrease, a first increase, and a second decrease, cleaning is stopped before the second increase occurs.

2. The method for cleaning a protective film for a plasma processing apparatus according to claim 1, wherein: The dilute nitric acid concentration of the dilute nitric acid solution is below 0.05 mol / liter.

3. The method for cleaning a protective film for a plasma processing apparatus according to claim 1, wherein: The dilute nitric acid concentration of the dilute nitric acid solution is greater than 0.001 mol / liter.

4. The method for cleaning a protective film for a plasma processing apparatus according to claim 1, wherein: The dilute nitric acid solution has a dilute nitric acid concentration of 0.001 mol / liter or more and 0.05 mol / liter or less.

5. The method for cleaning a protective film for a plasma processing apparatus according to claim 1, wherein: In the step (b), washing was stopped before 60 minutes had passed from the start of the ultrasonic irradiation.

6. The method for cleaning a protective film for a plasma processing apparatus according to claim 5, wherein: In the step (b), cleaning was stopped after 10 minutes had passed from the start of the ultrasonic irradiation.

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