JP2002341548A - Method of processing wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a yield by ensuring the protection of the wafer surface to be protected in a method of processing the wafer. SOLUTION: In subjecting the one surface of the wafer 3 to prescribed processing, a peelable protective sheet 4 is deposited on one surface to be protected of the wafer 3 and the other surface of the wafer 3 is subjected to the prescribed processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer processing method applied to, for example, manufacturing of electronic devices.

[0002]

2. Description of the Related Art In recent years, research and development of micromachining technology for microfabricating electronic components such as sensors and actuators or electronic device systems configured by combining them with semiconductor process technology or ultra-precision processing technology have been actively conducted. It is expected that sensors and the like will be made smaller and more sophisticated. A so-called optical lithography technique for transferring a pattern by exposure is used as a method for manufacturing these sensors and the like. Optical lithography is a technique for forming a mask pattern on a photoresist film previously formed on a wafer surface by spin coating. For example, when patterning a film on a wafer surface, only a portion of the photoresist film that is desired to be etched is removed, and a resist mask that leaves the photoresist film in a portion that is not desired to be etched is formed on the wafer. By subjecting the wafer in this state to, for example, wet etching, the film can be patterned into a desired shape.

FIGS. 7 to 9 show a process of patterning an insulating film, for example, a silicon oxide film, formed on the surface of a semiconductor wafer, for example, a silicon wafer into a predetermined pattern when the wafer is processed by photolithography. Is shown. First, as shown in FIG. 7A, a silicon semiconductor wafer 19 having a silicon oxide film (SiO ₂ ) 20 deposited and formed on both surfaces is prepared. Next, as shown in FIG. 7B, in a state where the wafer 19 is supported on the stage 23 of the spin coater 22 by vacuum suction, a photoresist, in this example, a positive resist is formed on the silicon oxide film 20 on one surface of the wafer 19. A mold photoresist is dropped and rotated at a high speed via a rotating shaft 24 to form a photoresist film 25. Next, as shown in FIG. 7C, the wafer 19 is placed on a hot plate 26 with the silicon oxide film 20 on the side where the photoresist film 25 is not formed facing down, and the photoresist film 2
5 is performed.

[0004] Next, as shown in FIG. 8D, the wafer 19 is supported on a stage 31 of an exposure apparatus by, for example, vacuum suction, and is irradiated with exposure light L via a photomask 27 to form a photomask on one side. The resist film 25 is selectively exposed to a predetermined pattern. The bonding of the photoresist in the exposed portion (the portion to be removed) in the exposure process is loosened. And
As shown in FIG. 8E, the wafer 19 is immersed in a developing solution 18 for developing. As a result, unnecessary portions of the photoresist film 25 are decomposed and removed. Next, as shown in FIG. 9F, the wafer 19 is immersed in an etching solution 29 of the silicon oxide film 20 and wet-etched,
The exposed silicon oxide film 20 is selectively removed by etching. In this manner, as shown in FIG. 9G, a wafer 19 in which the silicon oxide film 20 is patterned into a predetermined shape by wet etching is obtained. Thereafter, the wafer 19 is subjected to required processing, for example, etching, using the patterned silicon oxide film 20 as a mask.

[0005]

By the way, in the above-mentioned process, for example, in the spin coating process of FIG. 7B, the wafer surface which comes into contact with the stage 23 during the spin coating of the photoresist film 25, that is, the silicon oxide film 20 is damaged. Very likely. Similarly, the silicon oxide film 20 in contact with the hot plate 26 in the drying step of FIG.
Scratches easily. In the exposure step of FIG. 8D,
Since there are many occasions where the wafer 19 rubs against the stage 31, the back surface of the wafer may be damaged. In the case where no countermeasures are taken against the wafer surface as described above, a large number of fine scratches are generated on the silicon oxide film 20 on the wafer surface. When wet etching is performed in this state, there are many portions (so-called pinholes) where the silicon oxide film is missing due to surface scratches other than the silicon exposed portion formed by patterning. The etchant penetrates into the silicon wafer, and the silicon in the part to be protected is etched, resulting in a decrease in yield. As one of measures against such a flaw, for example, the silicon oxide film 2 on the non-patterned side is used.
It is considered to protect the silicon oxide film by forming a photoresist film on the surface of the photoresist. However, in this case, the photoresist film in contact with the stage is scratched. The portion of the silicon oxide film 20 corresponding to the scratches on the photoresist film is etched, thereby lowering the yield.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a method of processing a wafer which ensures the protection of the surface of the wafer to be protected and improves the yield.

[0007]

According to a method of processing a wafer according to the present invention, when a predetermined process is performed on one surface of a wafer, a peelable protection sheet is attached to one surface of the wafer to be protected. The predetermined processing is performed on the other surface of the wafer.

In the method of processing a wafer according to the present invention, a releasable protection sheet is applied to one surface of the wafer to be protected and a predetermined process is performed on the other surface. The wafer surface (the one surface) on the side contacting the wafer mounting table is protected by the protective sheet, and defects such as scratches on the wafer surface can be significantly reduced. Therefore, the yield of the subsequent required processing is improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for processing a wafer according to the present invention will be described with reference to the drawings.

FIGS. 1 to 5 show an embodiment in which the processing method of the present invention is applied to patterning of a semiconductor wafer including a surface film. In the present embodiment, first,
As shown in FIG. 1A, an insulating film 2 [2A, 2
B] is prepared. In this example, a silicon single crystal wafer having a thickness of 0.3 mm, a diameter of 4 inches, and a (100) crystal plane on the surface is used as the semiconductor wafer 1, and an insulating film 2 [2A, 2B] is formed on both front and back surfaces thereof. A 30 nm thick silicon oxide film (Si
O ₂ film). Reference numeral 3 denotes a sample wafer in which silicon oxide films 2A and 2B are formed on both surfaces of the semiconductor wafer 1. It is to be noted that the silicon single crystal wafer 1 is formed before the silicon oxide film 2 is formed by thermal oxidation.
Is subjected to a mirror surface treatment so that the surface roughness Ra falls within a range of, for example, 2 to 10 nm. In addition, the sample wafer 3 is subjected to processing such as ultrasonic cleaning using acetone and pure water cleaning using a jet water flow in advance, and it is confirmed that there is no dust or stain on the resist coat surface to be coated with the next resist. .

Next, as shown in FIG. 1B, the surface of the sample wafer 3, that is, the surface of the silicon oxide film 2 A, which is a so-called stage contact surface, that is, a wafer surface that contacts a stage of a spin coater as a resist coating device. A protective sheet (a generic name including a sheet-like body, a tape-like body, a film-like body, etc.) 4 is attached via an adhesive 6. Protective sheet 4
Is drawn out from a so-called sheet roll 40 in which the sheet is wound in a roll shape, and is attached to the surface of the sample wafer 3. The protection sheet 4 of this example is formed from a base material sheet 5 and an adhesive layer 6 provided on one surface thereof. Protective sheet 4
Has a property that it does not peel at room temperature (about 20 to 25 ° C.) and peels without thermal deformation at a subsequent drying temperature of the resist (for example, about 100 ° C.) or a peeling treatment temperature (for example, about 100 ° C.) . For this reason, the heat-resistant temperature of the pressure-sensitive adhesive layer 6 needs to be equal to or higher than room temperature and lower than 100 ° C., for example, 40 ° C. to 95 ° C., and the heat-resistant temperature of the sheet base material 5 of the protective sheet 4. It is safe to greatly exceed 100 ° C. As the protective sheet 4, for example, a fluororesin adhesive film (manufactured by Tokyo Glass Co., Ltd .: trade name VF-81, heat-resistant temperature 93 ° C.) can be used.

In order to improve the adhesive strength of the resist before the application of the resist, it is preferable to form a resist adhesive strength enhancing film. For example, O 2 is formed on the surface of the silicon oxide film 2B.
AP film (hexamethyldisilazane, manufactured by Tokyo Ohka Kogyo Co., Ltd.)
Is formed. OAP film thickness is 50 nm to several hundred nm
After the film formation, the OAP film is baked. Note that this OAP film can be applied to a wafer made of a material other than metal such as silicon and glass as a wafer.

Next, as shown in FIG. 1C, a stage (so-called wafer 3) in which a sample wafer 3 having a protective sheet 4 adhered to one surface is rotated at high speed by a rotating shaft 9 of a resist spin coater 7 as a resist coating apparatus. The protective sheet 4 is placed on the mounting table 8 so as to be in contact with the stage 8, and is fixed, for example, by vacuum suction. Then, a photoresist is dropped on the silicon oxide film 2B on the other surface of the wafer 3, and the stage 8 is rotated at a high speed to form a photoresist film 10. In this example, a positive photoresist is used as the photoresist film 10. However, regarding the photoresist, any photoresist that is resistant to an etching solution (for example, HF solution) for etching the silicon oxide film 2 in the next step, whether it is a positive type or a negative type, can be used. The thickness of the film 10 does not matter.
When the sample wafer 3 is placed and fixed on the stage 8,
Since the silicon oxide film 2A on the back surface is protected by the protection sheet 4, the silicon oxide film 2A is not damaged.

Next, as shown in FIG. 2D, the sample wafer 3 on which the photoresist has been formed is placed on, for example, a hot plate 11 as a drying means so that the protective sheet 4 is in contact with the hot plate surface. After placing and fixing, 100 ° C
Is performed, and the photoresist film 10 is dried. In this baking treatment, the solvent in the photoresist film 10 is volatilized and dried, and the pressure-sensitive adhesive 6 of the protective sheet 4 loses adhesive strength because it exceeds a heat-resistant temperature. It is peeled from the wafer 3. Even during the drying process using the hot plate 11, the silicon oxide film 2A on the back surface of the sample wafer 3 is protected by the protection sheet 4 and is not damaged.

Next, after confirming that the photoresist film 10 is completely cured, as shown in FIG. 2E, a protective sheet is formed on the surface of the photoresist film 10 opposite to the sample wafer 3 in the same manner as described above. Paste 4

Next, as shown in FIG.
After the sample wafer 3 is placed and fixed on the resist spin coater 7 with the side contacting the stage 8, a photoresist film 10 '(the same film as the photoresist film 10) is formed on the silicon oxide film 2A. Also at this time, since the photoresist film 10 on the stage 8 side is protected by the protective sheet 4, there is no damage.

Next, as shown in FIG. 3G, the sample wafer 3 is again placed on the hot plate 11 by the photoresist film 1.
The photoresist film 1 is placed and fixed with 0 'facing upward.
A drying process of 0 'is performed. Also at this time, the photoresist film 10 on the back surface is protected by the protective sheet 4 and is not damaged. Then, as shown in FIG. 3H, the protection sheet 4 is peeled off at the same time when the drying is completed as described above.

Next, as shown in FIG. 3I, the photoresist film on the side not subjected to the exposure processing before the exposure step (that is, the photoresist film on the side mounted on the stage of the exposure apparatus) 1
The protective sheet 4 is stuck on the surface of 0 '. Next, FIG. 4J
As shown in the figure, the sample wafer 3 is placed on the stage 1
3 is mounted and fixed, and the photoresist film 10 is irradiated with exposure light L via a photomask 12 to selectively expose the photoresist film 10. Also in this exposure step, the photoresist film 10 'on the side contacting the stage 13 is protected by the protective sheet 4 and is not damaged.

Next, as shown in FIG. 4K, the protective sheet 4 can be peeled off by, for example, a post-baking process at 100 ° C. performed after the selective exposure. Thereafter, as shown in FIG. 4L, the sample wafer 3 is immersed in a developing solution 14, the exposed portions of the photoresist film 10 are removed, and a resist mask (that is, an etching resistant mask) 1 having a predetermined pattern shape is formed.
5 is formed. In the case of a positive photoresist, it is not necessary to expose the photoresist film 10 'on the back side, but in the case of a negative photoresist, the photoresist film 1' on the back side is not required.
0 'needs to be entirely exposed. In addition, it is also possible to immerse the sample wafer 3 in the developing solution 14 in a state where the protective sheet 4 is not peeled off, perform a developing process, and peel off and remove the protective sheet 4 after the development. Further, the protective sheet 4 can be peeled off with a solvent (for example, acetone) in addition to the peeling off by heat treatment.

Next, as shown in FIG. 5M, the sample wafer 3 is immersed in an etching solution, for example, a 10% HF (hydrofluoric acid) solution 16, to expose a portion exposed without being covered with the resist mask 15. The silicon oxide film 2B is removed by etching. After confirming that the exposed portion of the silicon oxide film 2B was completely removed, a positive resist mask 1 was formed.
5 is removed in, for example, acetone to obtain a sample wafer 3 on which a silicon oxide film 10 on one side is patterned as shown in FIG. 5N. In the subsequent steps, the silicon wafer 1 is selectively etched away using, for example, an etching solution of TMAH (aqueous solution of 4-methylammonium hydroxide) using the silicon oxide film 2B as an etching resistant mask. Alternatively, a desired impurity can be selectively introduced into the silicon wafer 1 by the ion implantation method or the diffusion method using the silicon oxide film 2B as an impurity introduction mask. Note that the protective sheet 4 is attached to the silicon oxide film 2B until the selective etching of the silicon oxide film 2B.
When removing 0 'with acetone, the protective sheet 4
Can also be peeled off.

As the silicon wafer 1, the crystal plane is (1).
Although the wafer having the (00) plane is used, a wafer having another plane orientation may be used. For example, a (110) plane wafer can be used. A silicon single crystal has a diamond structure, exhibits strong anisotropy chemically, and exhibits a special three-dimensional shape as an etching shape. Therefore, it is preferable as a target to be etched by wet etching. Chemical anisotropic etching using the anisotropy of the workpiece itself,
Since the equipment required for processing is inexpensive, it can be used to produce much more practical devices than dry etching. In order to perform three-dimensional etching, an etchant material to be used is important. In this example, TMAH (4-methylammonium hydroxide aqueous solution) was used as an etchant for a silicon single crystal wafer. Silicon oxide film 2 [2 formed on the surface of silicon wafer 1 by thermal oxidation
A, 2B] has extremely high resistance to TMAH as an etchant, and can be used as an etching resistant mask for silicon. Considering the surface properties of the silicon wafer 1 after etching, the silicon wafer 1
Is preferably smooth, and it is preferable that the front and back surfaces of the silicon wafer 1 are mirror-finished in advance as described above.

In the present invention, various electronic devices can be manufactured using the above-described wafer processing method.

FIG. 6 shows a pressure sensor manufactured using the above-described wafer processing method. This pressure sensor 21
A piezoelectric element 27 is formed in a concave portion 25 formed on one surface of a glass substrate 25, and a silicon substrate 22 in which a portion corresponding to the piezoelectric element 27 is formed as a thin diaphragm portion 24 on the glass substrate 25 is bonded. Is done. Piezoelectric element 2
Reference numeral 7 denotes electrodes 26A and 26B formed on both surfaces, respectively, extending along the upper surface of the glass substrate 25 and connected to conductive terminals 30A and 30B penetrating the glass substrate 25. The diaphragm portion 24 is formed by selectively etching a part of a silicon substrate having an insulating film, for example, silicon oxide films 23A and 23B on both surfaces, to form a concave portion 28, and to make the concave portion 28 thinner. Here, if the silicon oxide film 23A that separates the silicon substrate 22 from the electrodes 26A and 26B of the piezoelectric element 27 is damaged, the silicon substrate 22 and the electrode 2
6A and 26B may be damaged, and the relationship between the pressure and the voltage may be lost. Therefore, when the concave portion 28 is formed in the silicon substrate 22 to form the diaphragm portion 24, the wafer processing method of the above-described embodiment can be applied to prevent the silicon oxide film 23A from being damaged. In the piezoelectric sensor 21, when a pressure F indicated by an arrow is received through the concave portion 28, the silicon diaphragm portion 24 bends, and the displacement thereof is detected by the piezoelectric element 27.

According to the above-described embodiment, the scratches generated on the surface of the sample wafer 3 by the contact of the processing apparatus in each step, that is, the resist spin coater which is a resist coating apparatus, the drying apparatus using a hot plate, the stage of an exposure apparatus, and the like. However, defects such as damage to the silicon oxide film 2A on the surface of the sample wafer can be significantly reduced. Since no defect is generated in the silicon oxide film 2A, when the silicon wafer is selectively etched by wet etching with TMAH (etching solution) using the silicon oxide film 2A as an etching resistant mask, the silicon oxide film 2A penetrates the silicon oxide film 2A and the silicon in the other part is No part is etched. Therefore, the yield of device manufacturing is improved. By setting the heat-resistant temperature of the base material sheet of the adhesive protection sheet 4 to 100 ° C. or higher, and setting the heat-resistant upper limit temperature of the adhesive 6 to less than 100 ° C., for example, 40 to 95 ° C.,
The protection sheet 4 can be easily separated from the sample wafer 3 by heat. That is, since the protection sheet 4 that is weak to heat is used, the protection sheet 4 can be simultaneously peeled off in, for example, a baking treatment step for drying the photoresist films 10 and 10 ′. And not.

Table 1 shows the number of scratches generated per silicon wafer of 4 inches when processed by the conventional wafer processing method and the wafer processing method of the present invention. Here, the scratches are generated from the resist spin coating process to the exposure process, and the average number of scratches generated on any five sheets is shown. According to Table 1, the number of scratches generated is significantly reduced in the wafer processing method of the present invention as compared with the conventional wafer processing method.

[0026]

[Table 1]

In the above example, the protection sheet 4 is used in all the steps of patterning the photoresist film 10 and the silicon oxide film 2.
Is performed while the protective sheet 4 is adhered. Alternatively, the protective sheet 4 may be adhered in some steps. In the above example, the present invention is applied to processing on a semiconductor wafer. However, the present invention can be applied to other wafer processing, for example, processing on a glass wafer, a ceramic wafer, and other wafers.

[0028]

According to the present invention, scratches on the wafer surface due to contact with the stage of the processing apparatus in each process are avoided by the protective sheet, and defects such as scratches on the wafer surface, for example, the wafer surface coating, are greatly reduced. Can be reduced. Therefore, subsequent processing on the wafer,
For example, at the time of selective etching, other parts are not etched. Therefore, the production yield of various devices such as electronic devices can be improved.

[Brief description of the drawings]

1A to 1C are process diagrams (part 1) showing one embodiment of a wafer processing method according to the present invention;

FIG. 2 is a process diagram (part 2) showing an embodiment of the wafer processing method of the present invention.

FIG. 3 is a process diagram (part 3) showing one embodiment of the wafer processing method of the present invention.

FIG. 4 is a process chart (No. 4) showing one embodiment of the wafer processing method of the present invention.

5A to 5N are process diagrams (part 5) showing one embodiment of the wafer processing method of the present invention.

FIG. 6A is a schematic perspective view of a pressure sensor that can be manufactured by using the wafer processing method of the present invention. B is a sectional view thereof.

7A to 7C are process diagrams (part 1) showing a conventional wafer processing method.

FIG. 8 is a process diagram (part 2) showing a conventional wafer processing method.

9A to 9G are process diagrams (part 3) showing a conventional wafer processing method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor wafer, 2 [2A, 2B] ... Silicon oxide film, 3 ... Sample wafer, 4 ... Protection sheet, 5 ... Base material sheet, 6 ... Adhesive, 7 ... Resist spin coater, 8 ... Stage, 10, 10 '
... photoresist film, 11 ... hot plate,
13: exposure apparatus stage, 14: developer, 1
5 ... resist mask, 16 ... etching solution, 2
1 pressure sensor, 22 silicon substrate, 24
..Diaphragm part, 25 ... Glass substrate, 27 ...
・ Piezoelectric element, 30 [30A, 30B] ... conductive terminal,
40 ... Sheet roll.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H025 AA00 AB17 EA04 FA01 5F043 AA02 AA40 BB01 CC20 GG10 5F046 AA28

Claims (3)

[Claims] When performing a predetermined process on one surface of a wafer, a peelable protection sheet is applied on one surface of the wafer to be protected, and a predetermined process is performed on the other surface of the wafer. A method for processing a wafer, comprising: 2. The wafer processing method according to claim 1, wherein the predetermined processing is a photoresist coating, a selective exposure, or a development processing in a patterning step. 3. The wafer processing method according to claim 1, wherein the predetermined processing is performed in a state where one surface of the wafer is in contact with a wafer mounting table of a processing apparatus via the protection sheet. .