JP2863980B2 - Wafer fabrication method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a wafer for forming a wafer having a flat and thin portion on cavities distributed in a plane.

[0002]

2. Description of the Related Art Conventionally, there have been the following two methods for manufacturing a wafer having a thin portion on cavities distributed in a plane. The first method is to bond a thick second wafer onto a first wafer having a cavity, and then reduce the thickness of the second wafer by polishing. The second method is a method of bonding a second wafer having a small thickness in advance on a first wafer having a cavity.

[0003]

However, in the above-described first method, when the polishing progresses and the thickness of the second wafer becomes thinner, the second wafer has a smaller thickness on the cavity of the first wafer. The portion bends into the cavity of the first wafer due to the load on the polishing surface during polishing. For this reason, at the end of polishing, the portion of the second wafer above the cavity of the first wafer has a shape in which the center of the cavity bulges like an abacus ball. Therefore, it has been difficult to form a wafer having a flat and thin portion on the cavity. In addition, there is a method of reducing the thickness of the second wafer by wet etching or the like instead of polishing. However, in this case, there is a problem that the material of the second wafer is limited. Difficult to etch.

In the above-described second method, the bonding surface between the first wafer and the second wafer needs to be clean immediately before bonding in order to obtain good bonding. For this reason, it is necessary to clean both the first wafer and the second wafer individually. However, the second wafer is formed to have a small thickness, and if the second wafer has a large area, the handleability of the second wafer is reduced. For this reason, it has been difficult to manufacture a large-diameter wafer having a thin portion on the cavity.

Accordingly, the present invention has been made to solve the above-mentioned conventional problems, and its object is to
It is an object of the present invention to provide a method of manufacturing a wafer capable of obtaining a large-diameter wafer having a flat and thin portion on a cavity.

[0006]

In order to achieve the above object, a method of manufacturing a wafer according to the present invention comprises the steps of: bonding a dummy wafer to one surface of a first wafer; Polishing the surface to a predetermined thickness;
Forming a cavity on at least one surface of the first wafer, and bonding the first wafer and the second wafer with the other surface of the first wafer facing the one surface of the second wafer And a step of removing the dummy wafer bonded to the first wafer.

[0007]

According to the present invention, a thin first wafer is formed on the surface of a second wafer having a cavity without being affected by polishing.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. (Embodiment 1) FIGS. 1 (a) to 1 (e) are sectional views of respective steps for explaining an embodiment of a method of manufacturing a wafer according to the present invention. In the figure, first, as shown in FIG. 1A, a dummy wafer 1 is prepared, and a first wafer 2 is bonded to a surface on the dummy wafer 1. In this case, for example, the first wafer 2 and the dummy wafer 1 having a diameter of about 4 inches are polished to a surface state suitable for bonding, and thereafter, the first wafer 2 and the dummy wafer 1 are cleaned and an adhesive is applied to the polished surface. Apply and join.

The adhesive used here has such an adhesive strength that the first wafer 2 and the dummy wafer 1 are not peeled off during polishing of the first wafer 2 in a later step, and the adhesive is a solvent or the like. For example, an epoxy-based adhesive or the like that can be completely removed to obtain a clean surface is used. Note that it is extremely preferable to provide a groove or the like on the opposite surface of the dummy wafer 1 to be bonded to the first wafer 2 in order to relieve a stress expected to be generated during a future process.

Next, as shown in FIG. 1B, the surface of the first wafer 2 with the dummy wafer 1 is polished, and the first wafer 2 is polished to a predetermined thickness. In this case, the first wafer 2 is thinned by polishing so as to leave about 10 μm, thereby forming a thin first wafer 2 ′.

Next, as shown in FIG. 1C, a second wafer 3 is prepared, and at least one surface of the second wafer 3, for example, the first wafer 2 'of the second wafer 3 is bonded. The cavity 3a is formed on the surface to be formed. In this case, after depositing metal on the surface of the second wafer 3 that is to be joined to the first wafer 2 ', the metal is patterned into a desired shape by a known engraving technique, and dry etching is performed using the metal as a mask. Then, the second wafer 3 is etched to a depth of about several μm. After that, the mask metal is removed. Thereby, the first wafer 2 ′ of the second wafer 3
A cavity 3a is formed on the surface to be joined.

Next, as shown in FIG. 1D, the surface of the second wafer 3 to be bonded to the first wafer 2 'and the second wafer 3' of the first wafer 2 'with the dummy wafer 1 are bonded to the second wafer 3. The surface condition is previously finished to a surface roughness suitable for bonding before forming the cavity 3a, and is cleaned after forming the cavity 3a, and the bonding surface of the second wafer 3 and the first wafer 2 'with the dummy wafer 1 are provided. Is joined with an adhesive.
In this case, the adhesive used here is, for example, a ceramic-based adhesive having such an adhesive strength that the bonding portion between the first wafer 2 ′ and the second wafer 3 is not peeled when the dummy wafer 1 is peeled in a later step. Use an adhesive or the like.

Next, only the dummy wafer 1 is removed, and FIG.
As shown in (e), the first wafer having a small thickness is formed on the second wafer 3.
The wafer 2 'with the cavity is bonded to the wafer 2'. In this case, in a state where the first wafer 2 ′ with the dummy wafer 1 and the second wafer 3 are bonded, the bonding between the dummy wafer 1 and the first wafer 2 ′ is performed by the epoxy-based adhesive, and Wafer 3 and first wafer 2 '
Is bonded with ceramics, the entire wafer bonded body is immersed in an organic solvent to reduce the bonding strength of the epoxy-based adhesive, and the dummy wafer 1 is removed.

According to such a method, the cavity 3a
Flat and thin first surface on the surface of the second wafer 3 having
Large-diameter cavity-containing wafer 4 having wafer 2 '
Can be manufactured.

As a use of the cavity built-in wafer 4 incorporating the cavity 3a manufactured here, a substrate wafer for producing a sensor element using a thin portion on the cavity 3a as a diaphragm can be considered. The requirements for these substrate wafers include that the thickness of the diaphragm portion can be arbitrarily designed, that the diaphragm portion is flat, and that the diameter of the wafer is somewhat large.

On the other hand, according to the manufacturing method of Embodiment 1, when the thickness of the diaphragm is reduced by polishing,
There is a flat dummy wafer that is uniformly in close contact under the wafer constituting the diaphragm, and a flat diaphragm can be easily manufactured. Further, since a wafer to be polished is provided with a dummy wafer having a certain thickness, there is no need to worry about handling properties, and a large-diameter wafer can be formed thin.

(Embodiment 2) Next, another embodiment of the method of manufacturing a wafer according to the present invention will be described. In the first embodiment, the bonding interface between the first wafer 2 and the dummy wafer 1 is adhered and adhered by an intervening substance such as an adhesive, but the intervening substance can be unnecessary and adhered. For example, a case where the first wafer 2 and the second wafer 3 are sapphire wafers and the dummy wafer 1 is a glass wafer will be described. Generally, a glass wafer polished to a mirror surface is easily brought into close contact at room temperature when the partner is a mirror surface and there is no intervening foreign matter on the contact surfaces. Therefore, the first wafer 2
Then, the dummy wafer 1 is polished to a mirror surface, then cleaned, and the first wafer 2 and the dummy wafer 1 are superimposed so as to come into contact from one point, thereby bringing the first wafer 2 and the dummy wafer 1 into close contact with each other.

In the case where the dummy wafer 1 and the first wafer 2 are easily available, if the wafers have substantially the same dimensions, the wafers tend to have the same thickness.
In this case, after the two are brought into close contact with each other, the first wafer 2 (sapphire) with the dummy wafer 1 (glass wafer) is immersed in hydrofluoric acid, for example, when the thickness of the dummy wafer 1 (glass) is reduced to half. It is possible to reduce the stress in the first wafer 2 that is expected to occur in the heat treatment step.

According to such a manufacturing method, the first wafer 2 can be easily and uniformly polished in a later step without unevenness in thickness of an inclusion such as an adhesive. Further, it is not necessary to know the thickness of the adhesive (there is no adhesive layer), and it is easy to form the first wafer 2 to a desired thickness. In addition, it is possible to prevent the bonding interface from becoming a contamination source during the post-process (the width of a solution that can be used when cleaning or etching is performed in the post-process increases).

When the first wafer 2 is a sapphire wafer and the dummy wafer 1 is a glass wafer, the first wafer 2 with the dummy wafer 1 is subjected to a heat treatment so that the dummy wafer 1 and the first wafer 2 are heated. Can be increased as long as it can withstand the polishing step of the first wafer 2. In this case, the heat treatment temperature is 200 to 300 ° C.
By increasing and decreasing the temperature with a substantially constant temperature gradient, it is possible to obtain a bonding strength that can withstand polishing.

Further, since the dummy wafer 1 and the first wafer 2 are joined without any intervening substance such as an adhesive, a wedge-shaped jig (for example, a blade portion of a cutter knife) is inserted into the joining interface. Thereby, the dummy wafer 1 and the first wafer 2 ′ can be separated.

(Embodiment 3) In the first and second embodiments, an intervening substance such as an adhesive is interposed at the bonding interface between the first wafer 2 'and the second wafer 3, and the first wafer 2' and the second wafer 3 are brought into close contact by bonding. However, the inclusions can be made unnecessary and can be closely attached.
For example, when the first wafer 2 and the second wafer 3 are sapphire wafers and the dummy wafer 1 is a glass wafer, the first wafer 2 and the dummy wafer 1 are closely adhered to each other without any inclusion such as an adhesive. The case where they are joined will be described.

A cavity 3a is formed in one of the two surfaces of the second wafer 3 which are to be bonded to the first wafer 2 'and the surface to be bonded to the first wafer 2' with the dummy wafer 1. The mirror surface is polished beforehand, the surface is cleaned after the cavity 3a is formed, and the bonding surface between the first wafer 2 'and the second wafer 3 is overlapped. Thereafter, by performing a heat treatment under substantially the same condition as the heat treatment previously performed for firmly bonding the first wafer 2 ′ and the dummy wafer 1, close contact bonding becomes possible.

In a step of removing the dummy wafer 1, a wafer bonded body in which the dummy wafer 1, the first wafer 2 ', and the second wafer 3 are integrated is immersed in hydrofluoric acid, and the glass wafer as the dummy wafer 1 is removed. It may be completely dissolved and removed.

Also, the first wafer 2 'and the second wafer 3
And the cavity built-in wafer 4 bonded to
The first wafer 2 'and the second wafer 3 are heat-treated at a high temperature of about
Can be further strengthened.

According to such a method, the dummy wafer 1
The peeling can be performed without applying any mechanical load when removing the wafer, and there is no fear of damaging the second wafer 3 and the first wafer 2 ′ which are finally required parts, and there is no need to worry about damage on the cavity 3a. A large-diameter wafer having a flat and thin portion can be manufactured satisfactorily and easily.

In the embodiment described above, the case where the first wafer 2 and the second wafer 3 are sapphire and the dummy wafer 1 is glass has been described.
The present invention is not limited to this, and the same effects as described above can be obtained regardless of whether the wafer is silicon or quartz.

[0028]

As described above, according to the present invention,
An extremely excellent effect is obtained that a large-diameter wafer having a flat and thin first wafer can be easily formed on the surface of the second wafer having a cavity.
Further, by forming the first wafer and the second wafer with the same constituent material and forming the dummy wafer with a glass substrate, a large-diameter wafer having a flat and thin first wafer can be formed easily and easily. An extremely excellent effect of being able to form is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of each step for explaining one embodiment of a wafer manufacturing method according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 dummy wafer 2 first wafer 3 second wafer 3a cavity 4 wafer with built-in cavity

Claims (6)

(57) [Claims] 1. a step of bonding a dummy wafer to one side of a first wafer; a step of polishing the other side of the first wafer to a predetermined thickness; and at least one side of a second wafer Forming a cavity in the first wafer, bonding the first wafer and the second wafer with the other surface of the first wafer facing one surface of the second wafer, Removing the dummy wafer bonded to the wafer. 2. The wafer according to claim 1, wherein the bonding of the first wafer and the dummy wafer is brought into direct contact with the bonding interface between the first wafer and the dummy wafer without any intervening object. Production method. 3. The method of manufacturing a wafer according to claim 2, wherein the first wafer and the dummy wafer are directly adhered to each other by performing a heat treatment when joining the first wafer and the dummy wafer. 4. The method according to claim 1, wherein the first wafer and the second wafer are directly bonded to each other at a bonding interface between the first wafer and the second wafer without any intervening material. A method for producing a wafer, comprising: 5. The wafer manufacturing method according to claim 4, wherein the first wafer and the second wafer are brought into direct contact with each other by performing a heat treatment at the time of bonding. 6. The method of manufacturing a wafer according to claim 1, wherein the dummy wafer is a glass substrate.