JP2023084785A - Washing method and washing device of plate for holding wafer substrate - Google Patents

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

The present invention relates to a cleaning method and cleaning apparatus for a wafer substrate holding plate incorporated in a polishing apparatus, and more particularly to a cleaning method and cleaning apparatus for a wafer substrate holding plate that improves the processing accuracy related to the flatness of a wafer substrate. .

In recent years, the demand for surface acoustic wave devices has been increasing due to the development of the mobile communication field such as mobile phones. and other piezoelectric oxide single crystal wafer substrates. In addition, as mobile phones become thinner, surface acoustic wave devices, which are one of the main devices, are becoming thinner. On the other hand, the demand for thinning is increasing year by year.

A wafer substrate used as the surface acoustic wave element generally has comb-shaped electrodes on its main surface side, and a desired surface acoustic wave is generated between the electrodes by applying a voltage signal. Must be mirror polished. Further, if the surface opposite to the surface on which the electrodes are formed is also mirror-polished, disturbance waves such as bulk waves that pass through the substrate and are generated together with surface acoustic waves are reflected from the mirror-finished opposite surface. resulting in spurious anomalies in the frequency characteristics. For this reason, the wafer substrate used for surface acoustic wave devices must have a mirror surface on one side and a rough surface on the other side. is adopted.

The flatness of the wafer surface is one of the shape characteristics required for the piezoelectric oxide single crystal wafer substrate used for the surface acoustic wave device and the like. That is, in the process of manufacturing a surface acoustic wave device, when patterning a metal electrode on the surface of a wafer substrate by exposure technology using a photochemical reaction, if there are irregular irregularities on the surface of the wafer substrate, it will cause defocus, etc., and the pattern will not match. In this case, a problem such as a failure to form a metal electrode is caused. For this reason, the surface shape of the wafer substrate is required to be less undulating such as unevenness, that is, to have good flatness. In recent years, in particular, with the aim of obtaining as many elements as possible from one wafer, there has been an increasing demand for high flatness not only in the center of the wafer substrate but also in the processing accuracy near the outermost periphery. In many cases, a slight surface sagging or the like on the outer periphery of the wafer substrate becomes a problem from the viewpoint 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).

By the way, when only one side of the wafer substrate is mirror-polished, it is necessary to fix and hold the non-polished side. A) and (B)], and the methods described in Patent Documents 2 and 3 using a template 2 (see FIG. 5) having a plurality of openings that fit into the cylindrical convex portion 1a are known. .

That is, as shown in FIG. 5, the template 2 includes a template body 2a having a plurality of openings, and a portion of the template body 2a excluding the openings on one side of the template body 2a, which is fixed to the wafer substrate holding plate 1. It is composed of an adhesive portion 2b. Then, the template main body 2a is attached to the wafer substrate holding plate 1 by the adhesive portion 2b, and the upper surface of the cylindrical convex portion 1a of the plate 1 and the inner wall surface of the opening of the template main body 2a are as shown in FIG. A recessed wafer accommodating portion 3 is formed.

Then, when the wafer substrate holding plate 1 holding the wafer substrate is installed in a polishing apparatus and mirror-polished, the process is carried out as follows.

First, the back side of the wafer substrate 4 having both surfaces rough-polished is attached to the concave portion forming the wafer accommodating portion 3 via a liquid such as water, whereby the cylindrical convex portion 1a of the wafer accommodating portion 3 is formed. The wafer substrate 4 is held by the adsorption force of the liquid on the upper surface. At this time, the height of the surface of the wafer substrate 4 is slightly higher than the height of the surface of the template body 2a, as shown in FIG.

FIG. 6 is an explanatory diagram of a polishing apparatus for polishing one side of the wafer substrate 4 held by the wafer substrate holding plate 1. As shown in FIG. In FIG. 6, a polishing cloth 6 is attached to the upper surface of a polishing platen 5 constituting a polishing apparatus, and a polishing liquid (not shown) is supplied onto the polishing cloth 6 . Further, 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 polishing platen 5 . The wafer substrate holding plate 1 for holding the wafer substrate 4 is set so that the surface of the wafer substrate 4 faces the polishing cloth 6, and the pressing mechanism portion 8 is brought into contact with the back side of the plate 1. Thus, any 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 driven to rotate at an arbitrary rotational speed by motor control or the like, whereby the plate 1 rotates together with the pressing mechanism 8 .

Then, the polishing surface plate 5 is rotated while supplying the polishing liquid onto the polishing cloth 6 , and the pressing mechanism 8 is rotated together with the plate 1 in the opposite direction to the polishing surface plate 5 , thereby pressing the polishing cloth 6 . The polished surface of the wafer substrate 4 is mirror-polished, and the polishing process ends when the wafer substrate 4 reaches a predetermined thickness.

JP 2020-099962 A JP 2005-034926 A JP 2011-206891 A JP 2007-253258 A

By the way, after the wafer substrate 4 is polished, the wafer substrate 4 is separated from the wafer substrate holding plate 1. On the wafer substrate holding plate 1 from which the wafer substrate 4 is separated, the adhesive portion 2b made of natural rubber or the like is attached. Since adherents or adherents of polishing liquid made of colloidal silica or the like remain, it is necessary to wash the used wafer substrate holding plate 1. After washing, the wafer substrate holding plate 1 is reused.

Conventionally, as a method for cleaning the wafer substrate holding plate, there is a chemical cleaning method in which the wafer substrate holding plate is immersed in a chemical solution such as caustic soda to chemically remove solid substances such as natural rubber. A physical cleaning method or the like is adopted in which solid matter such as silica is physically removed by bringing a brush into sliding contact with the plate surface. Proposed.

That is, in the method for cleaning a wafer substrate holding plate described in Patent Document 4, a brush is brought into sliding contact with the surface of the wafer substrate holding plate to perform brush cleaning, and a pressurized cleaning liquid (a mixture of alkaline cleaning agent and water) is used. solution) is sprayed onto the surface of the wafer substrate holding plate to clean the inside of the grooves formed on the surface of the wafer substrate holding plate.

However, the wafer substrate holding plate 1 shown in FIG. 4(A), which has a plurality of cylindrical convex portions 1a on one side, is washed by the method described in Patent Document 4, which combines chemical cleaning and physical cleaning. When washed, it was difficult to completely remove adherents such as silica remaining on the base end side corners of the cylindrical convex portion 1a and on the upper surface of the cylindrical convex portion 1a.

For this reason, when the wafer substrate holding plate 1 and the template 2 after cleaning are combined to form the recessed wafer accommodating portion 3, the sticking matter remaining on the base end side corners of the cylindrical convex portion 1a may cause The cylindrical convex portion 1a of the wafer substrate holding plate 1 and the opening portion of the template 2 are not properly fitted, and furthermore, the wafer substrate 4 is deformed due to the influence of the solid matter remaining on the upper surface of the cylindrical convex portion 1a. Easy to happen. When the wafer substrate 4 is deformed, a depression is formed on the surface of the wafer substrate due to excessive polishing of the portion raised by the deformation. was sometimes formed.

When the recess is formed on the surface of the wafer substrate, the flatness of the wafer substrate is remarkably lowered, making it difficult to meet the above-described TTV and LTV standards relating to flatness, and the rate of occurrence of defective products is about 3.5. There was a problem of as high as 2%.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and its object is to provide a cleaning method and a cleaning apparatus for a wafer substrate holding plate that improve the processing accuracy related to the flatness of the wafer substrate. to do.

That is, the first invention according to the present invention is
A method for cleaning a wafer substrate holding plate which has a plurality of cylindrical convex portions on one side thereof and is incorporated in a polishing apparatus and held on the upper surfaces of the cylindrical convex portions, wherein one side of the wafer substrate is polished. ,
A used wafer substrate holding plate is put into an ultrasonic cleaning tank containing an alkaline cleaning liquid and ultrasonically cleaned. Brush cleaning is carried out by slidingly contacting the upper surface of the cylindrical convex portion, and the used alkaline cleaning liquid discharged from the ultrasonic cleaning tank is stored in a storage tank, and the stored alkaline cleaning liquid is filtered through the filtering means. It is characterized by circulating the alkaline cleaning liquid by circulating to the ultrasonic cleaning tank,
The second invention is
In the method for cleaning a wafer substrate holding plate according to the first invention,
A template having a plurality of openings to be fitted into the cylindrical convex portions of the wafer substrate holding plate is attached to the wafer substrate holding plate so that the upper surface of the cylindrical convex portions and the inner wall surface of the opening of the template form a concave shape. A shaped wafer substrate holding portion is formed.

Moreover, the third invention according to the present invention is
In the method for cleaning a wafer substrate holding plate according to the first invention or the second invention,
The rotating brush is composed of a nylon brush with a wire diameter of 0.5 mm, and the rotation speed of the rotating brush is set to 5 rpm and the brush is washed for 10 minutes,
The fourth invention is
In the method for cleaning a wafer substrate holding plate according to any one of the first to third inventions,
a heating step of heating the alkaline cleaning liquid supplied from the storage tank;
a filtration 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 solution to the ultrasonic cleaning tank;
characterized in that the alkaline cleaning solution is circulated and used,
The fifth invention is
In the method for cleaning a wafer substrate holding plate according to any one of the first invention to the fourth invention,
In the filtering step,
Characterized by selecting and using a porous filter, an activated carbon filter, or a membrane filter according to the dirtiness of the alkaline cleaning liquid,
The sixth invention is
In the method for cleaning a wafer substrate holding plate according to any one of the first to fifth inventions,
In the above supply process,
A supply means is constituted by a supply pipe body having a plurality of thin tubes arranged so as to cover the entire opening of the ultrasonic cleaning tank and extending downward. characterized by supplying an alkaline cleaning liquid,
The seventh invention is
In the method for cleaning a wafer substrate holding plate according to any one of the first invention to the sixth invention,
characterized in that the wafer substrate is a piezoelectric oxide single crystal substrate,
The eighth invention is
In the method for cleaning a wafer substrate holding plate according to the seventh invention,
The piezoelectric oxide single crystal is lithium tantalate or lithium niobate.

Next, the ninth invention according to the present invention is
A cleaning apparatus for a wafer substrate holding plate, which has a plurality of cylindrical convex portions on one side thereof, and is incorporated in a polishing apparatus to polish one side of a wafer substrate held on the upper surface of the cylindrical convex portions. ,
an ultrasonic cleaning tank containing an alkaline cleaning liquid;
a plate holding means provided in the ultrasonic cleaning tank for holding the wafer substrate holding plate with the cylindrical convex part side facing the bottom side of the ultrasonic cleaning tank;
It is composed of a rotating brush provided on the bottom side of the ultrasonic cleaning tank and a drive motor for rotating the rotating brush, and the tip of the rotating brush is brought into sliding contact with the upper surface of the cylindrical convex portion to hold the wafer substrate. a brush cleaning means for brush cleaning the plate;
ultrasonic wave generating means provided on the outer wall of the ultrasonic cleaning tank and applying ultrasonic vibrations to the alkaline cleaning liquid in the ultrasonic cleaning tank to ultrasonically clean the cylindrical convex portion side of the wafer substrate holding plate; and
a storage tank for storing the used alkaline cleaning liquid discharged from the ultrasonic cleaning tank; and a circulation pump provided between the storage tank and the ultrasonic cleaning tank for ultrasonically cleaning the alkaline cleaning liquid in the storage tank. The alkaline cleaning liquid circulation means is provided with a circulation path for circulating to the tank and a filtering means provided in the circulation path for filtering the used alkaline cleaning liquid,
A tenth invention is
In the wafer substrate holding plate cleaning apparatus according to the ninth invention,
A template having a plurality of openings to be fitted into the cylindrical convex portions of the wafer substrate holding plate is attached to the wafer substrate holding plate so that the upper surface of the cylindrical convex portions and the inner wall surface of the opening of the template form a concave shape. A shaped wafer substrate holding portion is formed.

Moreover, the eleventh invention according to the present invention is
In the wafer substrate holding plate cleaning apparatus according to the ninth or tenth invention,
The rotating brush of the brush cleaning means is composed of a nylon brush with a wire diameter of 0.5 mm,
A twelfth invention is
In the wafer substrate holding plate cleaning apparatus according to any one of the ninth to eleventh inventions,
heating means for heating the alkaline cleaning liquid supplied from the storage tank;
filtering means for filtering the heated alkaline cleaning liquid;
cooling means for cooling the filtered alkaline cleaning liquid;
A supply means for supplying the cooled alkaline cleaning solution to the ultrasonic cleaning tank is provided in the circulation path,
A thirteenth invention is
In the wafer substrate holding plate cleaning apparatus according to any one of the ninth to twelfth inventions,
The filtering means comprises a porous filter, an activated carbon filter, or a membrane filter, and the porous filter, the activated carbon filter, or the membrane filter is selected according to the contamination of the alkaline cleaning liquid,
A fourteenth invention is
In the wafer substrate holding plate cleaning apparatus according to any one of the ninth to thirteenth inventions,
The supply means is composed of a supply pipe body having a plurality of thin tubes arranged so as to cover the entire opening of the ultrasonic cleaning tank and extending downward, and directed from the supply port of each thin tube to the ultrasonic cleaning tank. It is characterized in that the alkaline cleaning liquid is supplied to the

According to the method for cleaning a wafer substrate holding plate according to the present invention,
A used wafer substrate holding plate is put into an ultrasonic cleaning tank containing an alkaline cleaning liquid and ultrasonically cleaned, and the tip of a rotating brush provided on the bottom side of the ultrasonic cleaning tank is turned into the cylindrical projection. The upper surface of the mold is slidably contacted with a brush for cleaning, and the used alkaline cleaning liquid discharged from the ultrasonic cleaning tank is stored in a storage tank, and the stored alkaline cleaning liquid is filtered to the ultrasonic cleaning tank In order to circulate and use the alkaline cleaning liquid,
It is possible to sufficiently remove organic adherents such as natural rubber and inorganic adherents such as silica that tend to remain on the base end side corners of the cylindrical convex part and on the upper surface of the cylindrical convex part, and to circulate the alkaline cleaning liquid. It is possible to reduce the cleaning cost by using it.

Then, when the wafer substrate surface is polished by reusing the wafer substrate holding plate cleaned by the method of the present invention, the generation of depressions on the wafer substrate surface caused by the adhered matter is suppressed, and the wafer substrate is flattened. Therefore, compared with the case where the wafer substrate holding plate cleaned by the conventional method is reused, the rate of occurrence of defective products can be reduced.

FIG. 4 is an explanatory diagram of a cleaning apparatus for a wafer substrate holding plate according to the first embodiment; FIG. 4 is an explanatory diagram of a cleaning apparatus for a wafer substrate holding plate according to a second embodiment; FIG. 10 is an explanatory diagram of the configuration of a filter unit in the wafer substrate holding plate cleaning apparatus according to the second embodiment; 4A is a plan view of the wafer substrate holding plate, and FIG. 4B is a side view of the wafer substrate holding plate. A template having a plurality of openings to be fitted into the cylindrical convex portions is attached to the wafer substrate holding plate, and a recessed wafer substrate holding portion is formed between the upper surface of the cylindrical convex portions and the inner wall surface of the opening of the template. Explanatory drawing which shows the formed state. FIG. 2 is an explanatory diagram of a polishing apparatus for polishing one side of a wafer substrate held by a wafer substrate holding plate;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail.

[First embodiment]
The cleaning apparatus according to the first embodiment, as shown in FIG. An ultrasonic generator (not shown) provided on the outer wall of the ultrasonic cleaning bath 10 constitutes a main part thereof, and furthermore, the used alkaline cleaning liquid discharged from the ultrasonic cleaning bath 10 is stored. a storage tank 40, a circulation path 60 provided between the storage tank 40 and the ultrasonic cleaning tank 10 for circulating the alkaline cleaning liquid in the storage tank 40 to the ultrasonic cleaning tank 10 by means of a circulation pump 70; and a filter unit 50 (porous filter or the like) for filtering the used alkaline cleaning liquid. 1, reference numeral 61 denotes a supply port of the supply pipe body 100 arranged on the open side of the ultrasonic cleaning tank 10. As shown in FIG.

First, the plate holding portion 20 is composed of a ring-shaped holding portion main 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 peripheral surface of the holding portion main body 21. The wafer substrate holding plate 1 is held so that the cylindrical convex portion 1a side of the wafer substrate holding plate 1 faces the bottom surface side of the ultrasonic cleaning bath 10 .

The rotating brush 30 includes a disk-shaped rotating brush main body 31, a brush group 32 provided on the upper surface side of the rotating brush main body 31, and a variable speed drive motor attached to the rear side of the rotating brush main body 31. 33, and the tip of the brush group 32 is brought into sliding contact with the upper surface of the cylindrical convex portion 1a of the wafer substrate holding plate 1 to clean the wafer substrate holding plate 1 with the brush. The variable speed drive motor 33 is provided with a rotation speed control means (not shown) for controlling the rotation speed of the motor, and the rotation speed of the rotary brush 30 is controlled by the rotation speed control means. It's becoming

Further, the storage tank 40 stores the alkaline cleaning liquid discharged through a circulation path 60 provided on the bottom surface of the ultrasonic cleaning tank 10, and a circulation path connecting the storage tank 40 and the ultrasonic cleaning tank 10. 60 and a circulation pump 70 are used to circulate the stored alkaline cleaning liquid to the ultrasonic cleaning tank 10 via the filter section 50 .

When the cleaning apparatus according to the present embodiment is used, in addition to the brush cleaning described above, ultrasonic vibration is applied to the alkaline cleaning liquid in the ultrasonic cleaning tank 10 to clean the cylindrical convex portion of the wafer substrate holding plate 1 . Since the 1a side is ultrasonically cleaned, organic adherents such as natural rubber and inorganic adherents such as silica that tend to remain on the base end side corners of the cylindrical convex portion 1a and on the upper surface of the cylindrical convex portion 1a are removed. It can be removed with certainty. 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 wafer substrate may be damaged due to solid matter such as natural rubber and silica. Since the occurrence of dents on the surface is suppressed, there is a significant effect of reducing the rate of occurrence of defective products compared to the case where wafer substrate holding plates cleaned by the conventional method are reused.

In addition, since the alkaline cleaning liquid is circulated by the attached circulating means, it has the effect of reducing the cost required for cleaning.

[Second embodiment]
In the cleaning apparatus according to the first embodiment, which uses a porous filter or the like as a filtering means, inorganic suspended matter such as silica contained in the used alkaline cleaning liquid is efficiently removed, but organic suspended matter such as natural rubber is removed efficiently. Since the suspended matter is difficult to remove, it may become difficult to recycle the alkaline cleaning liquid over a long period of time. The cleaning apparatus according to the second embodiment enables long-term cyclical use of the alkaline cleaning liquid.

That is, as shown in FIG. 2, the cleaning apparatus according to the second embodiment includes an ultrasonic cleaning tank 10 containing an alkaline cleaning liquid, a plate holder 20 provided in the ultrasonic cleaning tank 10, and a rotating brush 30. , and an ultrasonic wave generator (not shown) provided on the outer wall of the ultrasonic cleaning tank 10, and the configuration of the main part is the same as that of the cleaning apparatus according to the first embodiment.

However, as shown in FIG. 2, a heating means 80 is provided in the circulation path 60 on the upstream side of the filter section 50, and as shown in FIG. As shown in FIG. 2, a cooling means 90 such as a chiller is provided in the circulation path 60 on the downstream side of the filter section 50. Further, as shown in FIG. The configuration is different from that of the cleaning device according to one embodiment.

The heating means 80 provided in the circulation path 60 on the upstream side of the filter unit 50 heats the alkaline cleaning liquid supplied from the storage tank 40 to control the viscosity of the alkaline cleaning liquid, thereby adjusting the alkaline cleaning liquid to conditions suitable for filtration. It adjusts the viscosity of the system cleaning liquid.

In addition, as shown in FIG. 3, the filter unit 50 of the second embodiment includes a porous filter 51, an activated carbon filter 52, and a membrane filter 53, and the porous filter 51, Activated carbon filter 52 or membrane filter 53 is configured to be selected as appropriate. A portion of the alkaline cleaning solution is periodically sampled during circulating use, and the sampled alkaline cleaning solution is analyzed to check the degree of contamination of the cleaning solution. Since the filter, ie, the porous filter 51, the activated carbon filter 52, or the membrane filter 53 can be selected, it is possible to reliably remove organic suspended matter such as natural rubber, and as a result, the life of the alkaline cleaning liquid is extended. can be achieved. In addition, the code|symbol 55 has shown the valve|bulb in FIG.

The cooling means 90 such as a chiller provided in the circulation path 60 on the downstream side of the filter section 50 maintains the alkaline cleaning liquid heated by the heating means 80 at a temperature suitable for cleaning the wafer substrate holding plate 1 (for example, room temperature). ).

Furthermore, the supply pipe main body 100 of the second embodiment has a plurality of thin tubes 200 arranged so as to cover the entire opening of the ultrasonic cleaning tank 10 and extending downward as shown in FIG. Since the structure is such that the alkaline cleaning liquid is supplied from the supply port 62 of the capillary tube 200 to the ultrasonic cleaning tank 10 with a high (strong) liquid flow, the alkaline cleaning liquid can be uniformly supplied into the ultrasonic cleaning tank 10. At the same time, contaminants and the like floating on the surface of the alkaline cleaning liquid in the ultrasonic cleaning bath 10 can be submerged in the alkaline cleaning liquid and quickly removed to the storage tank 40 side.

Therefore, it is possible to improve the cleaning effect of the wafer substrate holding plate 1 as compared with the cleaning apparatus according to the first embodiment.

Examples of the present invention will be specifically described below.

[Example 1]
1. Cleaning of wafer substrate holding plate
Using the cleaning apparatus shown in FIG. 1, the used ceramic wafer substrate holding plate 1 shown in FIGS. 4A and 4B was cleaned.

A wafer substrate holding plate 1 to be cleaned has a plate body with a diameter of 485 mm and five cylindrical projections 1a with a diameter of 150.1 mm and a height of 0.50 mm provided on one side of the plate body. The total height of the plate body and the cylindrical convex portion 1a was 17 mm.

Also, as the alkaline cleaning liquid to be introduced into the ultrasonic cleaning tank 10 of the cleaning apparatus, the product name "PK-LCG23" (dilution ratio 10%) manufactured by Parker Corporation was used.

Further, the alkaline cleaning liquid in the storage tank 40 is circulated to the ultrasonic cleaning tank 10 through a porous filter of 0.5 μm to maintain the cleanness of the cleaning liquid.

Then, the rotating brush 30 made of a nylon brush with a wire diameter of 0.5 mm was set at 5 rpm, and the wafer substrate holding plate 1 held by the plate holding part 20 of the ultrasonic cleaning tank 10 was brushed for 10 minutes. Cleaning and ultrasonic cleaning were performed.

2. Mirror Polishing of Wafer Substrate The cleaned ceramic wafer substrate holding plate 1 was reused, and the wafer substrate was mirror polished by the polishing apparatus shown in FIG.

(1) Wafer Substrate A lithium tantalate (hereinafter abbreviated as LT) single crystal substrate (flat ground substrate) having a substrate diameter of 6 inches (150 mm in diameter) and both surfaces of which were rough-polished was used as a polishing object.

The thickness of the substrate before polishing is 0.215 mm to 0.515 mm, the amount of polishing is 12 μm or more from the surface ground surface, and the LT single crystal substrate (surface ground substrate) having a thickness of 0.25 mm with both sides rough-polished is used as the polishing object. bottom.

(2) Recessed Wafer Substrate Holding Portion A recessed wafer substrate retaining portion was formed by combining a cleaned ceramic wafer substrate holding plate 1 and a template 2 made of epoxy glass and having a thickness of 0.55 mm.

The thickness of the adhesive portion 2b made of natural rubber for fixing the template 2 to the wafer substrate holding plate 1 was 0.10 mm.

As a result, the LT single crystal substrate with a thickness of 0.25 mm, which was rough-polished on both sides, was 0.10 mm [(0.50 mm + 0.25 mm = 0.75 mm) - (0.55 mm + 0.10 mm = 0.65 mm) from the template surface. )=0.10 mm].

(3) Mirror Polishing by Polishing Apparatus An LT single crystal substrate (flat surface ground substrate) is accommodated in a recessed wafer substrate holding portion formed by combining a wafer substrate holding plate 1 and a template 2. After that, as shown in FIG. It was installed in the polishing apparatus shown.

Then, a colloidal silica polishing liquid [manufactured by Yamaguchi Seiken Co., Ltd., trade name “CL-110S”, liquid temperature: 25° C., polishing liquid particle diameter: 45 nm, polishing liquid specific gravity : 1.140 g/cm ³ to 1.150 g/cm ³ ], the polishing surface plate 5 and the pressing mechanism portion 8 are slowly rotated and raised, and the pressing mechanism portion 8 is gradually pressurized in accordance with this to a predetermined amount. After reaching the rotational speed and pressure (500 g/cm ² ) of , this state is maintained for a certain period of time (30 to 70 minutes depending on the type of substrate) to obtain a single-sided mirror surface of the LT single crystal substrate (surface ground substrate). Polished.

(4) Flatness Evaluation The flatness of the 20 mirror-finished LT single crystal substrates was measured using an optical flatness measuring machine (FT-900 manufactured by Nidek).

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

That is, the average TTV (Total Thickness Variation) of 20 LT single crystal substrates was 1.65 μm, and the rate of occurrence of a maximum LTV (5 mm square) of 0.5 μm or more was 1.1%.

Acceptance criteria for the flatness are a TTV of 3.0 μm or less and a maximum LTV (5 mm square) of less than 0.5 μm.

[Example 2]
Using the cleaning apparatus shown in FIG. 2, the used ceramic wafer substrate holding plate 1 shown in FIGS. 4A and 4B was cleaned.

2, the heating means 80 is provided in the circulation path 60 on the upstream side of the filter section 50, and the filter section 50 includes a porous filter 51, an activated carbon filter 52, and a membrane filter 53. , the porous filter 51, the activated carbon filter 52, or the membrane filter 53 is configured to be appropriately selected according to the contamination of the alkaline cleaning liquid, and the circulation path 60 on the downstream side of the filter unit 50 does not include a chiller or the like. Except that the cooling means 90 is provided, and that the supply pipe main body 100 is arranged so as to cover the entire opening of the ultrasonic cleaning tank 10 and has a plurality of thin tubes 200 extending downward, The configuration is substantially the same as that of the cleaning apparatus shown in FIG.

When the cleaning apparatus shown in FIG. 2 is used, the lifetime of the alkaline cleaning liquid can be extended. Therefore, compared to the case of using the cleaning apparatus shown in FIG. It has become possible to reduce the number of times per week, and the cost required for cleaning has been reduced.

The flatness evaluation was substantially the same as in Example 1.

[Comparative example]
1. Cleaning of wafer substrate holding plate
Using the cleaning apparatus shown in FIG. 1, an ultrasonic wave generator (not shown) provided on the outer wall of the ultrasonic cleaning bath 10 is turned off, and the used wafer substrate held by the plate holding portion 20 is held. Plate 1 was only brush washed for 10 minutes.

2. Mirror Polishing of Wafer Substrate As in Example 1, the cleaned ceramic wafer substrate holding plate 1 was reused, and the wafer substrate was mirror polished by the polishing apparatus shown in FIG.

The object to be polished, the template 2 combined with the cleaned ceramic wafer substrate holding plate 1, the polishing conditions, etc. were the same as in the first embodiment.

[Flatness evaluation]
As in Example 1, the flatness of 20 mirror-finished LT single crystal substrates was measured using an optical flatness measuring machine (FT-900 manufactured by Nidek Co., Ltd.).

As a result, the average TTV (Total Thickness Variation) of 20 LT single crystal substrates was 3.83 μm, and the maximum LTV (5 mm square) of 0.5 μm or more was 3.2%.

[confirmation]
Using the cleaning apparatus shown in FIGS. 1 and 2, the used wafer substrate holding plate was subjected to brush cleaning and ultrasonic cleaning for 10 minutes, thereby removing the base end side corners of the cylindrical convex portion and the cylindrical shape. It is confirmed that adherent substances such as natural rubber and silica which tend to remain on the upper surface of the convex portion are removed satisfactorily.

Therefore, when the wafer substrate holding plate according to Examples 1 and 2 after cleaning is reused to polish the surface of the wafer substrate, the generation of depressions on the surface of the wafer substrate due to the adhered matter is suppressed. As a result, it is confirmed that the rate of occurrence of defective products can be reduced from 3.2% to 1.1% as compared with the case of reusing the wafer substrate holding plate according to the comparative example cleaned by the conventional method.

When the wafer substrate surface is polished by reusing the wafer substrate holding plate cleaned by the method of the present invention, the flatness of the wafer substrate is improved by suppressing the occurrence of dents on the wafer substrate surface caused by adhered matter. Therefore, it has industrial applicability as a single-sided mirror surface substrate that meets the demand for thinner wafers accompanying the recent reduction in device profile.

REFERENCE SIGNS LIST 1 wafer substrate holding plate 1a cylindrical convex portion 2 template 2a template body 2b adhesive portion 3 wafer housing portion 4 wafer substrate 5 polishing surface plate 6 polishing cloth 7 drive shaft 8 pressing mechanism portion 9 drive shaft 10 ultrasonic cleaning tank 20 Plate holding portion 21 Ring-shaped holding portion main body 22 Ring-shaped locking portion 30 Rotating brush 31 Rotating brush main body 32 Brush group 33 Variable speed drive motor 40 Storage tank 50 Filter unit 51 Porous filter 52 Activated carbon filter 53 Membrane filter 55 Valve 60 Circulation Path 61 Supply port 62 Supply port 70 Circulation pump 80 Heating means 90 Cooling means 100 Supply pipe body 200 Capillary tube

Claims (14)

A method for cleaning a wafer substrate holding plate which has a plurality of cylindrical convex portions on one side thereof and is incorporated in a polishing apparatus and held on the upper surfaces of the cylindrical convex portions, wherein one side of the wafer substrate is polished. ,
A used wafer substrate holding plate is put into an ultrasonic cleaning tank containing an alkaline cleaning liquid and ultrasonically cleaned. Brush cleaning is carried out by slidingly contacting the upper surface of the cylindrical convex portion, and the used alkaline cleaning liquid discharged from the ultrasonic cleaning tank is stored in a storage tank, and the stored alkaline cleaning liquid is filtered through the filtering means. A method for cleaning a wafer substrate holding plate, comprising circulating an alkaline cleaning liquid in an ultrasonic cleaning tank. A template having a plurality of openings to be fitted into the cylindrical convex portions of the wafer substrate holding plate is attached to the wafer substrate holding plate so that the upper surface of the cylindrical convex portions and the inner wall surface of the opening of the template form a concave shape. 2. The method of cleaning a wafer substrate holding plate according to claim 1, wherein a shaped wafer substrate holding portion is formed. 3. The cleaning of the wafer substrate holding plate according to claim 1, wherein said rotating brush is composed of a nylon brush having a wire diameter of 0.5 mm, and the rotation speed of said rotating brush is set to 5 rpm, and said brush cleaning is performed for 10 minutes. Method. a heating step of heating the alkaline cleaning liquid supplied from the storage tank;
a filtration 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 solution to the ultrasonic cleaning tank;
4. The method for cleaning a wafer substrate holding plate according to any one of claims 1 to 3, wherein the alkaline cleaning liquid is circulated between and. In the filtering step,
5. The method for cleaning a wafer substrate holding plate according to any one of claims 1 to 4, wherein a porous filter, an activated carbon filter, or a membrane filter is selected and used according to contamination of the alkaline cleaning liquid. In the above supply process,
A supply means is constituted by a supply pipe body having a plurality of thin tubes arranged so as to cover the entire opening of the ultrasonic cleaning tank and extending downward. 6. The method for cleaning a wafer substrate holding plate according to claim 1, wherein an alkaline cleaning liquid is supplied. 7. The method for cleaning a wafer substrate holding plate according to claim 1, wherein said wafer substrate is a piezoelectric oxide single crystal substrate. 8. The method of cleaning a wafer substrate holding plate according to claim 7, wherein the piezoelectric oxide single crystal is lithium tantalate or lithium niobate. A cleaning apparatus for a wafer substrate holding plate, which has a plurality of cylindrical convex portions on one side thereof, and is incorporated in a polishing apparatus to polish one side of a wafer substrate held on the upper surface of the cylindrical convex portions. ,
an ultrasonic cleaning tank containing an alkaline cleaning liquid;
a plate holding means provided in the ultrasonic cleaning tank for holding the wafer substrate holding plate with the cylindrical convex part side facing the bottom side of the ultrasonic cleaning tank;
It is composed of a rotating brush provided on the bottom side of the ultrasonic cleaning tank and a drive motor for rotating the rotating brush, and the tip of the rotating brush is brought into sliding contact with the upper surface of the cylindrical convex portion to hold the wafer substrate. a brush cleaning means for brush cleaning the plate;
ultrasonic wave generating means provided on the outer wall of the ultrasonic cleaning tank and applying ultrasonic vibrations to the alkaline cleaning liquid in the ultrasonic cleaning tank to ultrasonically clean the cylindrical convex portion side of the wafer substrate holding plate; and
a storage tank for storing the used alkaline cleaning liquid discharged from the ultrasonic cleaning tank; and a circulation pump provided between the storage tank and the ultrasonic cleaning tank for ultrasonically cleaning the alkaline cleaning liquid in the storage tank. A wafer substrate characterized in that it is provided with an alkaline cleaning liquid circulation means comprising a circulation path for circulating the bath and a filtering means provided in the circulation path for filtering the used alkaline cleaning liquid. Device for cleaning holding plates. A template having a plurality of openings to be fitted into the cylindrical convex portions of the wafer substrate holding plate is attached to the wafer substrate holding plate so that the upper surface of the cylindrical convex portions and the inner wall surface of the opening of the template form a concave shape. 10. The apparatus for cleaning a wafer substrate holding plate according to claim 9, wherein a shaped wafer substrate holding portion is formed. 11. A cleaning apparatus for a wafer substrate holding plate as set forth in claim 9, wherein said rotating brush of said brush cleaning means is composed of a nylon brush having a wire diameter of 0.5 mm. heating means for heating the alkaline cleaning liquid supplied from the storage tank;
filtering means for filtering the heated alkaline cleaning liquid;
cooling means for cooling the filtered alkaline cleaning liquid;
12. The apparatus for cleaning a wafer substrate holding plate according to claim 9, wherein supply means for supplying the cooled alkaline cleaning liquid to the ultrasonic cleaning tank is provided in the circulation path. The filtering means comprises a porous filter, an activated carbon filter, and a membrane filter, and the porous filter, the activated carbon filter, or the membrane filter is selected according to the contamination of the alkaline cleaning liquid. A cleaning apparatus for a wafer substrate holding plate according to any one of claims 9 to 12. The supply means is composed of a supply pipe body having a plurality of thin tubes arranged so as to cover the entire opening of the ultrasonic cleaning tank and extending downward, and directed from the supply port of each thin tube to the ultrasonic cleaning tank. 14. The apparatus for cleaning a wafer substrate holding plate according to any one of claims 9 to 13, wherein an alkaline cleaning liquid is supplied to said wafer substrate holding plate.

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