Method and apparatus for cleaning wafer substrate holding plates

Abstract

To provide a washing method and device of a plate for holding a used wafer substrate which can excellently remove a deposited matter such as natural rubber and colloidal silica that easily remains.SOLUTION: A washing device comprises: an ultrasonic washing tank 10 which stores alkali-based washing liquid; a plate holding part 20 and a rotation bush 30 which are provided in the washing tank; a storage tank 40 which stores the washing liquid discharged from the washing tank; a filter part 50 which is provided between the storage tank and the washing tank; a circulation path 60 and a circulation pump 70 in which the washing liquid in the storage tank is circulated to the washing tank via the filter part; and an ultrasonic wave generation device which is provided in an outer wall part of the washing tank and is not shown in the figure. Since a plate 1 for holding a used wafer substrate input to the washing tank 10 is subjected to ultrasonic washing and brush washing, a deposited matter such as natural rubber that easily remains in a base end side corner part of a columnar protrusion part 1a and on an upper surface of the columnar protrusion part of the plate 1 can be excellently removed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cleaning method and a cleaning apparatus for a wafer substrate holding plate incorporated in a polishing apparatus, and particularly to a cleaning method and a cleaning apparatus for a wafer substrate holding plate in which the processing accuracy related to the flatness of the wafer substrate is improved.

Background Art

[0002] In recent years, due to the development of the mobile communication field such as mobile phones, the demand for surface acoustic wave devices has been increasing. As the substrate for this surface acoustic wave device, piezoelectric oxide single crystal wafer substrates such as lithium tantalate, lithium niobate, lithium tetraborate, quartz, and langasite are used. In addition, with the thinning of mobile phones and the like, the surface acoustic wave device, which is one of the main devices, has been made lower-profile, and the demand for thinning of the piezoelectric oxide single crystal wafer substrate used for this surface acoustic wave device has been increasing year by year.

[0003] The wafer substrate used as the surface acoustic wave device generally has a comb-shaped electrode provided on its main surface side, and a desired surface acoustic wave is generated between the electrodes by applying a voltage signal. Therefore, the electrode formation surface needs to be mirror-polished. Also, if the surface opposite to the surface on which the electrode is formed is also mirror-polished, obstacle waves such as bulk waves passing through the inside of the substrate generated together with the surface acoustic wave will be reflected from the mirror-polished opposite surface, causing spurious abnormalities in the frequency characteristics. For this reason, the wafer substrate used for the surface acoustic wave device needs to have one side mirror-finished and the other side rough-finished, and usually, a method of mirror-polishing only one side of a wafer substrate with both sides roughened is adopted.

[0004] One of the required shape characteristics for piezoelectric oxide single-crystal wafer substrates used in the above-mentioned surface acoustic wave (SWA) elements is the flatness of the wafer surface. In other words, when metal electrodes are patterned on the wafer substrate surface using photochemical exposure technology during the manufacturing process of SWA elements, irregular irregularities on the wafer substrate surface can cause focal misalignment and other problems, such as the metal electrodes not being formed according to the pattern. For this reason, wafer substrates with a surface shape that has little unevenness, i.e., good flatness, are required. In particular, in recent years, with the aim of obtaining as many elements as possible from a single wafer, the demand for high flatness has been increasing year by year, not only in the center of the wafer substrate but also in the processing accuracy near the outermost edge, and even slight surface sagging on the outer edge of the wafer substrate often becomes a problem from the standpoint of yield. Generally, a TTV (Total Thickness Variation) of 3 μm or less and a maximum LTV (Local Thickness Variation: 5 mm square) of less than 0.5 μm are required (see Patent Document 1).

[0005] Incidentally, when polishing only one side of a wafer substrate to a mirror finish, it is necessary to fix and hold the side that is not to be polished. As a means of doing so, methods described in Patent Documents 2 to 3 are known, which use a wafer substrate holding plate 1 having a plurality of cylindrical convex portions 1a on one side [see Figures 4(A) and 4(B)] and a template 2 having a plurality of openings that fit into the cylindrical convex portions 1a (see Figure 5).

[0006] Specifically, as shown in Figure 5, the template 2 consists of a template body 2a having multiple openings and an adhesive portion 2b provided on one side of the template body 2a excluding the openings, which fixes the template body 2a to the wafer substrate holding plate 1. The template body 2a is then attached to the wafer substrate holding plate 1 by the adhesive portion 2b, and a concave wafer housing portion 3 is formed between the upper surface of the cylindrical convex portion 1a of the plate 1 and the inner wall surface of the opening of the template body 2a, as shown in Figure 5.

[0007] Then, when the wafer substrate holding plate 1, which holds the wafer substrate, is incorporated into the polishing apparatus for mirror polishing, the process is carried out as follows.

[0008] First, the back side of the wafer substrate 4, which has both sides roughly polished, is attached to the concave portion forming the wafer housing section 3 via a liquid such as water. The wafer substrate 4 is then held in place by the suction force of the liquid on the upper surface of the cylindrical convex portion 1a of the wafer housing section 3. At this time, the height of the surface of the wafer substrate 4 is slightly higher than the surface height of the template body 2a, as shown in Figure 5, and protrudes outward.

[0009] Figure 6 is an explanatory diagram of a polishing apparatus for polishing one side of a wafer substrate 4 held on a wafer substrate holding plate 1. In Figure 6, a polishing cloth 6 is attached to the upper surface of a polishing platen 5 that constitutes the polishing apparatus, and a polishing liquid (not shown) is supplied onto the polishing cloth 6. The polishing platen 5 is rotated at an arbitrary rotational speed by motor control or the like via a drive shaft 7 connected to the platen 5. The wafer substrate holding plate 1 that holds the wafer substrate 4 is set so that the surface of the wafer substrate 4 faces the polishing cloth 6, and by contacting the pressing mechanism 8 with the back side of the plate 1, an arbitrary load can be applied to the wafer substrate 4 via the wafer substrate holding plate 1. The pressing mechanism 8 is connected to a drive shaft 9 and is rotated at an arbitrary rotational speed by motor control or the like, causing the plate 1 to rotate together with the pressing mechanism 8.

[0010] Then, by supplying polishing fluid onto the polishing cloth 6 while rotating the polishing platen 5, and simultaneously rotating the pressing mechanism 8 together with the plate 1 in the opposite direction to the polishing platen 5, the surface of the wafer substrate 4 pressed against the polishing cloth 6 is mirror-polished, and the polishing process ends when a predetermined thickness is reached. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2020-099962 [Patent Document 2] Japanese Patent Publication No. 2005-034926 [Patent Document 3] Japanese Patent Publication No. 2011-206891 [Patent Document 4] Japanese Patent Publication No. 2007-253258 [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] Incidentally, after polishing the wafer substrate 4, the wafer substrate 4 is separated from the wafer substrate holding plate 1. However, since there remains residue of adhesive material 2b made of natural rubber or the like, or residue of polishing liquid made of colloidal silica or the like, on the wafer substrate holding plate 1 from which the wafer substrate 4 has been separated, the used wafer substrate holding plate 1 needs to be cleaned, and after cleaning, the wafer substrate holding plate 1 is reused.

[0013] Conventionally, methods for cleaning wafer substrate holding plates include chemical cleaning, which involves immersing the wafer substrate holding plate in a chemical solution such as caustic soda to chemically remove adhered materials such as natural rubber, and physical cleaning, which involves rubbing a brush against the surface of the wafer substrate holding plate to physically remove adhered materials such as silica. Patent document 4 proposes a cleaning method that combines chemical cleaning and physical cleaning.

[0014] In other words, the method for cleaning a wafer substrate holding plate described in Patent Document 4 involved cleaning the surface of the wafer substrate holding plate by sliding a brush against it, and simultaneously spraying a pressurized cleaning solution (a mixed solution of an alkaline cleaning agent and water) onto the surface of the wafer substrate holding plate to clean the grooves formed on the surface of the wafer substrate holding plate.

[0015] However, when cleaning the wafer substrate holding plate 1 shown in Figure 4(A), which has multiple cylindrical convex portions 1a on one side, using the method described in Patent Document 4, which combines chemical cleaning and physical cleaning, it was difficult to completely remove the silica and other deposits remaining at the base end corners of the cylindrical convex portions 1a and on the upper surface of the cylindrical convex portions 1a.

[0016] Therefore, when the wafer substrate holding plate 1 and template 2 are combined after cleaning to form a concave wafer housing portion 3, the presence of residual deposits at the base end corner of the cylindrical convex portion 1a can cause poor fitting between the cylindrical convex portion 1a of the wafer substrate holding plate 1 and the opening of the template 2. Furthermore, the presence of residual deposits on the upper surface of the cylindrical convex portion 1a can easily cause deformation of the wafer substrate 4. When deformation of the wafer substrate 4 occurs, excessive polishing of the deformed area can form depressions on the surface of the wafer substrate. Similarly, when poor fitting occurs, excessive polishing can also form depressions on the surface of the wafer substrate.

[0017] Furthermore, when depressions form on the surface of the wafer substrate, the flatness of the wafer substrate decreases significantly, making it difficult to meet the TTV and LTV standards related to flatness mentioned above, resulting in a problem where the defect rate is high at approximately 3.2%.

[0018] This invention was made in view of these problems, and its objective is to provide a cleaning method and apparatus for a wafer substrate holding plate that improves the processing accuracy related to the flatness of the wafer substrate. [Means for solving the problem]

[0019] In other words, the first invention according to the present invention is, A cleaning method for a wafer substrate holding plate having multiple cylindrical convex portions on one side, and being incorporated into a polishing device so that one side of a wafer substrate held on the upper surface of the cylindrical convex portions is polished. And, A template having multiple openings that fit into the cylindrical convex portion is attached to the wafer substrate holding plate, and a concave wafer substrate holding portion is formed between the upper surface of the cylindrical convex portion and the inner wall surface of the openings of the template. In the cleaning method, The used wafer substrate holding plate is put into an ultrasonic cleaning tank containing an alkaline cleaning liquid for ultrasonic cleaning, and the tip of a rotating brush provided on the bottom side in the ultrasonic cleaning tank is brought into sliding contact with the upper surface of the cylindrical convex portion for brush cleaning. At the same time, the used alkaline cleaning liquid discharged from the ultrasonic cleaning tank is stored in a storage tank, and the stored alkaline cleaning liquid is circulated to the ultrasonic cleaning tank through a filtering means for recycling the alkaline cleaning liquid. Let's assume 。

[0020] Further, a second invention according to the present invention is In the cleaning method of the wafer substrate holding plate described in the first invention, the rotating brush is composed of a nylon brush with a wire diameter of 0.5 mm, and the brush cleaning is performed for 10 minutes with the rotation speed of the rotating brush set to 5 rpm. A third invention is In the cleaning method of the wafer substrate holding plate according to any one of the first invention to the second invention, a heating step of heating the alkaline cleaning liquid replenished from the storage tank, a filtering step of filtering the heated alkaline cleaning liquid, a cooling step of cooling the filtered alkaline cleaning liquid, a supply step of supplying the cooled alkaline cleaning liquid to the ultrasonic cleaning tank, and the alkaline cleaning liquid is recycled by these steps. A fourth invention is Third Invention In the cleaning method of the wafer substrate holding plate described in in the above filtering step, the filtering means includes three filters, namely a porous filter, an activated carbon filter, and a membrane filter. A part of the alkaline cleaning liquid during circulation use is periodically sampled to check the degree of contamination of the alkaline cleaning liquid, and depending on the contamination of the alkaline cleaning liquid, any one of the porous filter, the activated carbon filter, or the membrane filter is selected for use. A fifth invention is Third InventionIn the method for cleaning wafer substrate holding plates described above, In the above supply process, The supply means is comprised of a supply pipe body having multiple thin tubes that are positioned to cover the entire open section of the ultrasonic cleaning tank and extend downward, and is characterized by supplying an alkaline cleaning solution from the supply port of each thin tube toward the ultrasonic cleaning tank. The sixth invention is, In a method for cleaning a wafer substrate holding plate according to any of the first to fifth inventions, The above wafer substrate is characterized by being a piezoelectric oxide single crystal substrate, The seventh invention is, In the method for cleaning a wafer substrate holding plate described in the sixth invention, The piezoelectric oxide single crystal described above is characterized by being lithium tantalate or lithium niobate.

[0021] Next, the present invention 8 The invention is A cleaning device for a wafer substrate holding plate having multiple cylindrical convex portions on one side, and which is incorporated into a polishing device to polish one side of a wafer substrate held on the upper surface of the cylindrical convex portions. And, A template having multiple openings that fit into the cylindrical convex portion is attached to the wafer substrate holding plate, and a concave wafer substrate holding portion is formed between the upper surface of the cylindrical convex portion and the inner wall surface of the openings of the template. In a cleaning device, An ultrasonic cleaning tank containing an alkaline cleaning solution, A plate holding means is provided within the ultrasonic cleaning tank, with the cylindrical convex portion facing the bottom surface of the ultrasonic cleaning tank, to hold the wafer substrate holding plate. The brush cleaning means consists of a rotating brush provided on the bottom side of the ultrasonic cleaning tank and a drive motor that rotates the rotating brush, and the tip of the rotating brush is brought into sliding contact with the upper surface of the cylindrical convex part to brush clean the wafer substrate holding plate, The ultrasonic cleaning tank is provided with an ultrasonic generating means that applies ultrasonic vibrations to the alkaline cleaning solution inside the ultrasonic cleaning tank to ultrasonically clean the cylindrical convex portion of the wafer substrate holding plate, and The system is characterized by having a storage tank for storing used alkaline cleaning solution discharged from the ultrasonic cleaning tank, a circulation path provided between the storage tank and the ultrasonic cleaning tank and circulating the alkaline cleaning solution from the storage tank to the ultrasonic cleaning tank by a circulation pump, and a filtration means provided in the circulation path for filtering the used alkaline cleaning solution. Let's assume .

[0022] Furthermore, the ninth invention according to the present invention is, In the cleaning apparatus for wafer substrate holding plates described in the eighth invention, The above brush cleaning means is characterized in that the rotating brush is made of a nylon brush with a wire diameter of 0.5 mm. The tenth invention is, In a cleaning apparatus for a wafer substrate holding plate according to any of the eighth to ninth inventions, A heating means for heating the alkaline cleaning solution supplied from the above-mentioned storage tank, A filtration means for filtering a heated alkaline cleaning solution, A cooling means for cooling the filtered alkaline cleaning solution, A supply means for supplying cooled alkaline cleaning solution to the ultrasonic cleaning tank is provided in the above circulation path, The eleventh invention is, In a cleaning apparatus for a wafer substrate holding plate described in any of the eighth to tenth inventions, The above filtration means comprises a porous filter, an activated carbon filter, and a membrane filter, and is characterized in that a portion of the alkaline cleaning solution is periodically taken during circulation to check the degree of contamination of the alkaline cleaning solution, and one of the porous filter, activated carbon filter, or membrane filter is selected according to the degree of contamination of the alkaline cleaning solution. The twelfth invention is, The 10th Invention In the cleaning apparatus for wafer substrate holding plates described above, The above-mentioned supply means is characterized in that it is composed of a supply tube body having a plurality of thin tubes that are arranged to cover the entire open portion of the ultrasonic cleaning tank and extend downward, and an alkaline cleaning solution is supplied from the supply port of each thin tube toward the ultrasonic cleaning tank. [Effects of the Invention]

[0023] According to the method for cleaning wafer substrate holding plates according to the present invention, Used wafer substrate holding plates are placed in an ultrasonic cleaning tank containing an alkaline cleaning solution and ultrasonically cleaned. The tip of a rotating brush provided on the bottom side of the ultrasonic cleaning tank is brought into contact with the upper surface of the cylindrical convex part for brush cleaning. The used alkaline cleaning solution discharged from the ultrasonic cleaning tank is stored in a storage tank, and the stored alkaline cleaning solution is circulated back into the ultrasonic cleaning tank via a filtration means for reuse. This method effectively removes organic deposits such as natural rubber and inorganic deposits such as silica that tend to remain on the base corners and upper surface of cylindrical convex sections, and also reduces cleaning costs through the circulation of alkaline cleaning solutions.

[0024] Furthermore, when a wafer substrate holding plate cleaned using the method of the present invention is reused to polish the wafer substrate surface, the occurrence of depressions on the wafer substrate surface caused by the above-mentioned adhering substances is suppressed, improving the flatness of the wafer substrate. This has the effect of reducing the rate of defective products compared to when a wafer substrate holding plate cleaned using a conventional method is reused. [Brief explanation of the drawing]

[0025] [Figure 1] An explanatory diagram of a cleaning apparatus for a wafer substrate holding plate according to the first embodiment. [Figure 2] An explanatory diagram of a cleaning apparatus for a wafer substrate holding plate according to the second embodiment. [Figure 3] A diagram illustrating the configuration of the filter section in a cleaning apparatus for wafer substrate holding plates according to the second embodiment. [Figure 4]Figure 4(A) is a plan view of the wafer substrate holding plate, and Figure 4(B) is a side view of the wafer substrate holding plate. [Figure 5] This diagram illustrates a state in which a template having multiple openings that fit into a cylindrical convex portion is attached to a wafer substrate holding plate, and a concave wafer substrate holding portion is formed by the upper surface of the cylindrical convex portion and the inner wall surface of the openings in the template. [Figure 6] An explanatory diagram of a polishing apparatus that polishes one side of a wafer substrate held in a wafer substrate holding plate. [Modes for carrying out the invention]

[0026] Embodiments of the present invention will be described in detail below.

[0027] [First Embodiment] The cleaning apparatus according to the first embodiment, as shown in Figure 1, mainly consists of an ultrasonic cleaning tank 10 for containing an alkaline cleaning solution, a plate holding section 20 and a rotating brush 30 provided inside the ultrasonic cleaning tank 10, and an ultrasonic generating device (not shown) provided on the outer wall of the ultrasonic cleaning tank 10. Furthermore, it is equipped with a means for circulating the alkaline cleaning solution, which consists of a storage tank 40 for storing the used alkaline cleaning solution discharged from the ultrasonic cleaning tank 10, a circulation path 60 provided between the storage tank 40 and the ultrasonic cleaning tank 10 and circulating the alkaline cleaning solution from the storage tank 40 to the ultrasonic cleaning tank 10 by a circulation pump 70, and a filter section 50 (porous filter, etc.) provided in the circulation path 60 for filtering the used alkaline cleaning solution. Also, in Figure 1, reference numeral 61 indicates the supply port of the supply pipe body 100 located on the open side of the ultrasonic cleaning tank 10.

[0028] First, the plate holding portion 20 consists of a ring-shaped holding portion body 21 attached to the inner wall surface of the ultrasonic cleaning tank 10 and a ring-shaped locking portion 22 provided on the inner circumferential surface of the holding portion body 21, and is configured to hold the wafer substrate holding plate 1 with the cylindrical convex portion 1a side of the wafer substrate holding plate 1 facing the bottom surface of the ultrasonic cleaning tank 10.

[0029] Furthermore, the rotating brush 30 consists of a disc-shaped rotating brush body 31, a group of brushes 32 provided on the upper surface of the rotating brush body 31, and a variable-speed drive motor 33 attached to the back side of the rotating brush body 31. The tips of the brush group 32 slide against the upper surface of the cylindrical convex portion 1a of the wafer substrate holding plate 1, thereby cleaning the wafer substrate holding plate 1 with the brushes. The variable-speed drive motor 33 is equipped with a rotation speed control means (not shown) for controlling the rotation speed of the motor, and the rotation speed of the rotating brush 30 is controlled by this rotation speed control means.

[0030] Furthermore, the storage tank 40 stores the alkaline cleaning solution discharged from the ultrasonic cleaning tank 10 via a circulation path 60 provided at the bottom of the ultrasonic cleaning tank 10, and the stored alkaline cleaning solution is circulated back to the ultrasonic cleaning tank 10 via a filter section 50 using the circulation path 60 and circulation pump 70 connecting the storage tank 40 and the ultrasonic cleaning tank 10.

[0031] Furthermore, when using the cleaning apparatus according to this embodiment, in addition to the brush cleaning described above, ultrasonic vibrations are applied to the alkaline cleaning solution in the ultrasonic cleaning tank 10, so that the cylindrical convex portion 1a side of the wafer substrate holding plate 1 is ultrasonically cleaned. This makes it possible to reliably remove organic deposits such as natural rubber and inorganic deposits such as silica that tend to remain in the base end corners and upper surface of the cylindrical convex portion 1a. For this reason, when the wafer substrate holding plate 1 cleaned using the cleaning apparatus according to the first embodiment is reused to polish the wafer substrate, the occurrence of depressions on the wafer substrate surface caused by deposits such as natural rubber and silica is suppressed. This has the remarkable effect of reducing the rate of defective products compared to when a wafer substrate holding plate cleaned by a conventional method is reused.

[0032] Furthermore, since the alkaline cleaning solution is circulated and reused by the attached circulation mechanism, it also has the effect of reducing the cost required for cleaning.

[0033] [Second Embodiment] In the cleaning apparatus according to the first embodiment, which uses a porous filter or the like as a filtration means, inorganic suspended matter such as silica contained in the used alkaline cleaning solution is efficiently removed, but organic suspended matter such as natural rubber is difficult to remove, which can make it difficult to recycle the alkaline cleaning solution over a long period of time. The cleaning apparatus according to the second embodiment enables the recycled use of the alkaline cleaning solution over a long period of time.

[0034] In other words, the cleaning apparatus according to the second embodiment, as shown in Figure 2, consists mainly of an ultrasonic cleaning tank 10 that contains an alkaline cleaning solution, a plate holding section 20 and a rotating brush 30 provided inside the ultrasonic cleaning tank 10, and an ultrasonic generating device (not shown) provided on the outer wall of the ultrasonic cleaning tank 10. The configuration of the main parts is the same as that of the cleaning apparatus according to the first embodiment.

[0035] However, as shown in Figure 2, a heating means 80 is provided in the circulation path 60 upstream of the filter section 50; as shown in Figure 3, the configuration of the filter section 50 differs from that of the first embodiment; as shown in Figure 2, a cooling means 90 such as a chiller is provided in the circulation path 60 downstream of the filter section 50; and as shown in Figure 2, the configuration of the supply pipe body 100 differs from that of the first embodiment, thus the configuration differs from that of the cleaning device according to the first embodiment.

[0036] Furthermore, the heating means 80 provided in the circulation path 60 upstream of the filter section 50 heats the alkaline cleaning solution supplied from the storage tank 40 to control the viscosity of the alkaline cleaning solution and adjust its viscosity to conditions suitable for filtration.

[0037] Furthermore, as shown in Figure 3, the filter section 50 of the second embodiment includes a porous filter 51, an activated carbon filter 52, and a membrane filter 53, and is configured so that the porous filter 51, activated carbon filter 52, or membrane filter 53 is appropriately selected depending on the contamination of the alkaline cleaning solution. By periodically taking a portion of the alkaline cleaning solution during circulation and analyzing the collected alkaline cleaning solution, the degree of contamination of the cleaning solution can be confirmed, and the appropriate filter corresponding to the contamination of the alkaline cleaning solution, namely the porous filter 51, activated carbon filter 52, or membrane filter 53, can be selected, making it possible to reliably remove organic suspended matter such as natural rubber, and as a result, the lifespan of the alkaline cleaning solution can be extended. Note that in Figure 3, reference numeral 55 indicates a valve.

[0038] Furthermore, the cooling means 90, such as a chiller, provided in the circulation path 60 downstream of the filter section 50, adjusts the alkaline cleaning solution heated by the heating means 80 to a temperature suitable for cleaning the wafer substrate holding plate 1 (for example, room temperature).

[0039] Furthermore, as shown in Figure 2, the supply pipe body 100 of the second embodiment is arranged to cover the entire open portion of the ultrasonic cleaning tank 10 and has a plurality of thin tubes 200 extending downward. Since the alkaline cleaning solution is supplied to the ultrasonic cleaning tank 10 from the supply port 62 of each thin tube 200 with a high (strong) liquid flow, the alkaline cleaning solution can be supplied evenly into the ultrasonic cleaning tank 10, and contaminants floating on the surface of the alkaline cleaning solution in the ultrasonic cleaning tank 10 can be submerged in the alkaline cleaning solution and removed to the storage tank 40 at an early stage.

[0040] Therefore, it is possible to further improve the cleaning effect of the wafer substrate holding plate 1 compared to the cleaning apparatus according to the first embodiment. [Examples]

[0041] The following describes specific embodiments of the present invention.

[0042] [Example 1] 1. Cleaning of wafer substrate holding plate The used ceramic wafer substrate holding plate 1 shown in Figures 4(A) and 4(B) was cleaned using the cleaning apparatus shown in Figure 1.

[0043] The wafer substrate holding plate 1 to be cleaned has a plate body with a diameter of 485 mm and five cylindrical convex portions 1a with a diameter of 150.1 mm and a height of 0.50 mm on one side. The total height of the plate body and the cylindrical convex portions 1a is 17 mm.

[0044] Furthermore, as the alkaline cleaning solution to be introduced into the ultrasonic cleaning tank 10 of the cleaning device, we used "PK-LCG23" (dilution ratio 10%), a product of Parker Corporation.

[0045] Furthermore, the alkaline cleaning solution in the storage tank 40 is circulated to the ultrasonic cleaning tank 10 via a 0.5 μm porous filter to maintain the cleanliness of the cleaning solution.

[0046] Then, the rotation speed of the rotating brush 30, which consists of nylon bristles with a wire diameter of 0.5 mm, was set to 5 rpm, and brush cleaning and ultrasonic cleaning were performed on the wafer substrate holding plate 1, which was held in the plate holding section 20 of the ultrasonic cleaning tank 10, for 10 minutes.

[0047] 2. Mirror polishing of wafer substrates The cleaned ceramic wafer substrate holding plate 1 was reused, and the wafer substrate was mirror-polished using the polishing apparatus shown in Figure 6.

[0048] (1) Wafer substrate The substrate to be polished was a lithium tantalate (hereinafter abbreviated as LT) single crystal substrate (plane-ground substrate) with a substrate diameter of 6 inches (150 mm) and rough-surface polished on both sides.

[0049] The substrate thickness before polishing was 0.215 mm to 0.515 mm, and the amount of polishing was set to 12 μm or more from the surface grinding surface. The target of polishing was a 0.25 mm thick LT single crystal substrate (surface-ground substrate) with both sides roughened.

[0050] (2) Concave wafer substrate holding part A washed ceramic wafer substrate holding plate 1 and a 0.55 mm thick template 2 made of epoxy glass were combined to form a concave wafer substrate holding section.

[0051] Furthermore, the thickness of the adhesive portion 2b, made of natural rubber, that fixes the template 2 to the wafer substrate holding plate 1 was 0.10 mm.

[0052] As a result, the 0.25mm thick LT single crystal substrate, with both sides roughened, is held in the concave wafer substrate holder with a protrusion of 0.10mm [(0.50mm + 0.25mm = 0.75mm) - (0.55mm + 0.10mm = 0.65mm) = 0.10mm] from the template surface.

[0053] (3) Mirror polishing using a polishing device An LT single crystal substrate (plane-ground substrate) was placed in a concave wafer substrate holder formed by combining a wafer substrate holder plate 1 and a template 2, and then assembled into the polishing apparatus shown in Figure 6.

[0054] Then, colloidal silica polishing solution [Yamaguchi Seiken Co., Ltd. product name "CL-110S", liquid temperature: 25℃, polishing solution particle size: 45nm, polishing solution specific gravity: 1.140g / cm³] is applied to the polishing cloth 6 attached to the polishing platen 5. 3 ~1,150 g / cm³ 3 While supplying [amount of material], the polishing platen 5 and the pressing mechanism 8 are slowly rotated upward, and the pressing mechanism 8 is gradually pressurized in conjunction with this rotation at a predetermined rotation speed and pressure (500 g / cm²). 2 After reaching this state, the LT single crystal substrate (plane-ground substrate) was polished to a mirror finish on one side by maintaining this state for a certain period of time (30 to 70 minutes depending on the type of substrate).

[0055] (4) Flatness evaluation Then, the flatness of 20 LT single-crystal substrates that had undergone mirror finishing was measured using an optical flatness measuring instrument (NIDEK FT-900).

[0056] As a result, 1.1% of the LT single crystal substrates exhibited depressions of 0.5 μm or more at a maximum LTV (Local Thickness Variation: 5 mm square).

[0057] In other words, based on the average values ​​of 20 LT single crystal substrates, the TTV (Total Thickness Variation) was 1.65 μm, and the occurrence rate of maximum LTV (5 mm square) exceeding 0.5 μm was 1.1%.

[0058] Furthermore, the passing criteria for flatness are a TTV of 3.0 μm or less and a maximum LTV (5 mm square) of less than 0.5 μm.

[0059] [Example 2] The used ceramic wafer substrate holding plate 1 shown in Figures 4(A) and 4(B) was cleaned using the cleaning apparatus shown in Figure 2.

[0060] Furthermore, the cleaning apparatus shown in Figure 2 is substantially the same configuration as the cleaning apparatus shown in Figure 1, except that a heating means 80 is provided in the circulation path 60 upstream of the filter section 50, the filter section 50 comprises a porous filter 51, an activated carbon filter 52, and a membrane filter 53, and is configured so that the porous filter 51, the activated carbon filter 52, or the membrane filter 53 is appropriately selected depending on the contamination of the alkaline cleaning solution, a cooling means 90 such as a chiller is provided in the circulation path 60 downstream of the filter section 50, and the supply pipe body 100 is arranged to cover the entire open section of the ultrasonic cleaning tank 10 and has a plurality of thin tubes 200 extending downward.

[0061] Furthermore, using the cleaning device shown in Figure 2, the lifespan of the alkaline cleaning solution can be extended, making it possible to reduce the frequency of cleaning solution replacement from three times / week to once / week compared to using the cleaning device shown in Figure 1, thus reducing the cost required for cleaning.

[0062] Furthermore, the flatness evaluation described above was substantially the same as in Example 1.

[0063] [Comparative Example] 1. Cleaning of wafer substrate holding plate Using the cleaning apparatus shown in Figure 1, the ultrasonic generator (not shown) provided on the outer wall of the ultrasonic cleaning tank 10 was turned OFF, and only brush cleaning was performed on the used wafer substrate holding plate 1 held by the plate holding section 20 for 10 minutes.

[0064] 2. Mirror polishing of wafer substrates Similar to Example 1, the cleaned ceramic wafer substrate holding plate 1 was reused, and the wafer substrate was mirror-polished using the polishing apparatus shown in Figure 6.

[0065] Furthermore, the object to be polished, the template 2 to be combined with the cleaned ceramic wafer substrate holding plate 1, and the polishing conditions were the same as in Example 1.

[0066] [Flatness evaluation] Similar to Example 1, the flatness of 20 mirror-finished LT single-crystal substrates was measured using an optical flatness measuring instrument (NIDEK FT-900).

[0067] As a result, the average value of 20 LT single crystal substrates showed a TTV (Total Thickness Variation) of 3.83 μm, and the incidence rate of maximum LTV (5 mm square) exceeding 0.5 μm was 3.2%.

[0068] [confirmation] Using the cleaning apparatus shown in Figures 1 and 2, brush cleaning and ultrasonic cleaning are performed on the used wafer substrate holding plate for 10 minutes, confirming that deposits such as natural rubber and silica that tend to remain on the base end corners and upper surface of the cylindrical convex portion are effectively removed.

[0069] Therefore, when the wafer substrate holding plates according to Examples 1 and 2 are reused after cleaning to polish the wafer substrate surface, the occurrence of depressions on the wafer substrate surface caused by the above-mentioned adhering substances is suppressed. As a result, it has been confirmed that the rate of defective products can be reduced from 3.2% to 1.1% compared to when the wafer substrate holding plates according to the comparative example, which were cleaned by the conventional method, are reused. [Industrial applicability]

[0070] When a wafer substrate holding plate cleaned using the method of the present invention is reused to polish the wafer substrate surface, the occurrence of depressions on the wafer substrate surface caused by adhering materials is suppressed, improving the flatness of the wafer substrate. Therefore, it has industrial applicability as a single-sided mirror-finish substrate that can meet the demand for thinner wafers due to the recent trend towards lower-profile devices. [Explanation of Symbols]

[0071] 1. Wafer substrate holding plate 1a Cylindrical convex part 2 Templates 2a Template body 2b Adhesive part 3. Wafer housing section 4 wafer substrates 5. Polishing surface plate 6 Polishing cloth 7 Drive shaft 8. Pressing mechanism 9 Drive shaft 10. Ultrasonic cleaning tank 20 Plate holding section 21 Ring-shaped holding part body 22 Ring-shaped locking part 30 Rotating Brushes 31 Rotating brush body 32 brush groups 33 Variable speed drive motor 40 Storage tanks 50 Filter section 51 Porous Filter 52 Activated carbon filter 53 Membrane Filter 55 valves 60 Circulation path 61 Supply port 62 supply ports 70 Circulation pump 80 Heating means 90 Cooling means 100 Supply pipe body 200 tubular

Claims

1. A method for cleaning a wafer substrate holding plate having a plurality of cylindrical convex portions on one side, and being incorporated into a polishing device to polish one side of a wafer substrate held on the upper surface of the cylindrical convex portions, In a method for cleaning a wafer substrate holding plate, a template having multiple openings that fit into the cylindrical convex portion is attached to the wafer substrate holding plate, and a concave wafer substrate holding portion is formed between the upper surface of the cylindrical convex portion and the inner wall surface of the openings of the template, A method for cleaning a wafer substrate holding plate, characterized by: placing a used wafer substrate holding plate into an ultrasonic cleaning tank containing an alkaline cleaning solution and cleaning it ultrasonically; sliding the tip of a rotating brush provided on the bottom side of the ultrasonic cleaning tank against the upper surface of the cylindrical convex part to clean it with a brush; storing the used alkaline cleaning solution discharged from the ultrasonic cleaning tank in a storage tank; and circulating the stored alkaline cleaning solution back into the ultrasonic cleaning tank via a filtration means to reuse the alkaline cleaning solution.

2. The method for cleaning a wafer substrate holding plate according to claim 1, characterized in that the rotating brush is made of a nylon brush with a wire diameter of 0.5 mm, and the rotating brush is rotated at 5 rpm for 10 minutes.

3. A heating step in which the alkaline cleaning solution supplied from the above-mentioned storage tank is heated, A filtration process in which the heated alkaline cleaning solution is filtered, A cooling process to cool the filtered alkaline cleaning solution, A supply process in which cooled alkaline cleaning solution is supplied to an ultrasonic cleaning tank. A method for cleaning a wafer substrate holding plate according to any one of claims 1 to 2, characterized in that an alkaline cleaning solution is circulated and reused.

4. In the above filtration process, The cleaning method for a wafer substrate holding plate according to claim 3, characterized in that the filtration means comprises three filters: a porous filter, an activated carbon filter, and a membrane filter, and a portion of the alkaline cleaning solution is periodically taken during circulating use to check the degree of contamination of the alkaline cleaning solution, and one of the porous filter, activated carbon filter, or membrane filter is selected and used according to the contamination of the alkaline cleaning solution.

5. In the above supply process, The method for cleaning a wafer substrate holding plate according to claim 3, wherein the supply means is configured with a supply tube body having a plurality of thin tubes that are arranged to cover the entire open portion of the ultrasonic cleaning tank and extend downward, and an alkaline cleaning solution is supplied from the supply port of each thin tube toward the ultrasonic cleaning tank.

6. A method for cleaning a wafer substrate holding plate according to any one of claims 1 to 5, characterized in that the wafer substrate is a piezoelectric oxide single crystal substrate.

7. The method for cleaning a wafer substrate holding plate according to claim 6, characterized in that the piezoelectric oxide single crystal is lithium tantalate or lithium niobate.

8. A cleaning apparatus for a wafer substrate holding plate having a plurality of cylindrical convex portions on one side, and which is incorporated into a polishing apparatus and polishes one side of a wafer substrate held on the upper surface of the cylindrical convex portions, In a cleaning apparatus for a wafer substrate holding plate, a template having multiple openings that fit into the cylindrical convex portion is attached to the wafer substrate holding plate, and a concave wafer substrate holding portion is formed between the upper surface of the cylindrical convex portion and the inner wall surface of the openings of the template, An ultrasonic cleaning tank containing an alkaline cleaning solution, A plate holding means is provided within the ultrasonic cleaning tank, with the cylindrical convex portion facing the bottom surface of the ultrasonic cleaning tank, to hold the wafer substrate holding plate, The brush cleaning means consists of a rotating brush provided on the bottom side of the ultrasonic cleaning tank and a drive motor that rotates the rotating brush, and the tip of the rotating brush is brought into sliding contact with the upper surface of the cylindrical convex part to brush clean the wafer substrate holding plate, The ultrasonic cleaning tank is provided with an ultrasonic generating means that applies ultrasonic vibrations to the alkaline cleaning solution inside the ultrasonic cleaning tank to ultrasonically clean the cylindrical convex portion of the wafer substrate holding plate, and A cleaning apparatus for wafer substrate holding plates, characterized in that it is equipped with an alkaline cleaning solution circulation means comprising: a storage tank for storing used alkaline cleaning solution discharged from the ultrasonic cleaning tank; a circulation path provided between the storage tank and the ultrasonic cleaning tank and circulating the alkaline cleaning solution from the storage tank to the ultrasonic cleaning tank by a circulation pump; and a filtration means provided in the circulation path for filtering the used alkaline cleaning solution.

9. The cleaning apparatus for wafer substrate holding plates according to claim 8, characterized in that the rotating brush of the brush cleaning means is made of a nylon brush with a wire diameter of 0.5 mm.

10. A heating means for heating the alkaline cleaning solution supplied from the above-mentioned storage tank, A filtration means for filtering a heated alkaline cleaning solution, A cooling means for cooling the filtered alkaline cleaning solution, A cleaning apparatus for wafer substrate holding plates according to any one of 8 to 9, characterized in that a supply means for supplying cooled alkaline cleaning solution to an ultrasonic cleaning tank is provided in the circulation path.

11. The cleaning apparatus for wafer substrate holding plates according to any one of 8 to 10, characterized in that the above-mentioned filtration means comprises a porous filter, an activated carbon filter, and a membrane filter, and a portion of the alkaline cleaning solution is periodically taken during circulating use to check the degree of contamination of the alkaline cleaning solution, and one of the porous filter, activated carbon filter, or membrane filter is selected according to the degree of contamination of the alkaline cleaning solution.

12. The cleaning apparatus for wafer substrate holding plates according to claim 10, characterized in that the supply means is composed of a supply tube body having a plurality of thin tubes that are arranged to cover the entire open portion of the ultrasonic cleaning tank and extend downward, and an alkaline cleaning solution is supplied from the supply port of each thin tube toward the ultrasonic cleaning tank.

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