JPH0661461A - Manufacture of laminated soi wafer - Google Patents

Abstract

PURPOSE:To obtain a manufacturing method wherein, when a laminated SOI wafer is manufactured, the contamination and the scratch of a silicon film layer due to particles by oxide-film chips produced in a cutting operation are not caused, the finish accuracy of a chamfered part is high, the efficiency of an operation is high and an oxide film between layers for the wafer is not damaged. CONSTITUTION:The outer circumferential part of a silicon wafer 11 on one side of a laminated wafer 10 lamina by interposing an oxide film 20 is cut, in the thickness direction from a face opposite to the oxide film 20, up to a part in which a residual thickness (z) is left between the silicon wafer and the oxide film 20. The laminated wafer which has been cut is immersed in an etchant which does not dissolve the oxide film. It is etched until the oxide film is exposed. Then, it is immersed in an etchant which dissolves the oxide film, and the oxide film which has been exposed is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a bonded SOI wafer, and more particularly to a method for chamfering an outer peripheral portion of a bonded wafer when manufacturing a thin film SOI wafer.

[0002]

2. Description of the Related Art Conventionally, SOI (Silicon On Insulator)
As a general method for manufacturing a semiconductor substrate having a structure, at least one flat surface portion of two mirror-finished silicon wafers is oxidized to form an oxide film of SiO ₂ on the surface, and the oxide film is Two wafers are sandwiched and pressure-bonded to each other, one surface of the wafer is ground and polished to form a thin film having a predetermined thickness, and a laminated body including an oxide film and a silicon film layer is sequentially formed on the surface of the supporting wafer. It is known how to do it. Wafers used in this process are shipped in a state where the wafer thinly cut from the ingot is chamfered and mirror-polished on one side.
The outer peripheral portion is generally round-chamfered to have a radius of curvature on both front and back surfaces in order to prevent generation of particles due to conveyance and to prevent damage to the mirror surface and the back surface. Therefore, when bonding two such wafers,
An overhang portion is formed on the outer peripheral portion that cannot be attached to each other. In addition, the outermost peripheral portion of the bonding is often mirror-polished, and unbonded portions often remain.

In the thus bonded wafers (hereinafter referred to as "bonded wafers"), the wafer on the side to be an active layer for forming a thin film device (hereinafter referred to as "active wafer") is subjected to surface grinding and polishing. When a thin film SOI having an active layer thickness of about 1 μm is formed, first, a residual thickness of 2 to 3 μm is left on the oxide film by grinding, but the overhang portion at this time is a sharply pointed thin film. There was a problem that during the next polishing, it was finely crushed and scattered as particles (small pieces), which were attached to the polishing surface and contaminate or scratch the finished surface during the final polishing.

In order to avoid this problem, it is necessary to remove the overhang portion after laminating and bonding the wafers. However, if the peripheral part of the wafer that is not thinned (hereinafter referred to as "supporting wafer") is also chamfered at the same time, including the unbonded part of the bonding surface, the diameter will be reduced and it will not be possible to carry it in subsequent steps. However, it is inconvenient because it becomes difficult to enter the exposure apparatus.

Conventionally, as a method of removing the overhang portion of such a bonded surface (hereinafter referred to as "chamfering"), there is a method of removing the outer peripheral portion of the active wafer by grinding with an NC chamfering machine. The grinding range is, as shown in FIG. 2 (a), a wafer outer peripheral line w in a plan view.
To the chamfer line m set inside the outer peripheral line s of the oxide film 20
From the outer surface of the active wafer 11, the oxide film 20 is crossed to a part of the thickness of the supporting wafer 12 in a vertical sectional view. When chamfering is performed by grinding in this way, the oxide film 20 is originally brittle and harder than silicon. Therefore, when grinding reaches the oxide film layer, the oxide film inside the chamfer line m is generated by the blade pressure or vibration of the cutter when the grinding reaches the oxide film layer. Grinding damage goes deep, and the effect of removing the outer peripheral part by chamfering is lost. In order to remove this grinding damage, deep etching of 10 to 100 μm is performed only on the chamfered portion. However, since an etching solution for a normal silicon wafer only etches silicon and not an oxide film, a thin oxide film having a thickness of several μm is exposed again on the chamfered surface, as shown in FIG. We found that a hard oxide film is damaged during transportation and during final polishing, and becomes particles that scatter to contaminate or scratch the finished surface. This damage also occurs in the subsequent device process, which causes many defective particles.

As another chamfering method, for example, Japanese Patent Laid-Open No. 3-2
Japanese Patent No. 50616 discloses that one of the bonded wafers is surface-ground from the back surface of the bonding portion, and then a masking tape is placed inside the peripheral edge of the wafer while leaving the peripheral edge of the wafer on the surface of the ground wafer. There is described a method of adhering, forming a protective film on the exposed surface of the other wafer, and immersing such a bonded wafer in an etching solution for a predetermined time to etch the peripheral edge of the ground wafer. Further, Japanese Patent Publication No. 10736/1992 discloses a method for surface treatment of a semiconductor wafer in which an entire semiconductor wafer having chamfered portions formed on both outer peripheral edges is immersed in an etching solution to perform an etching treatment. Stacking the above wafers,
A surface treatment method is described in which only the chamfered portion of the wafer is brought into contact with the etching solution. However, even in these methods, since the etching solution for a normal silicon wafer only etches silicon and not the oxide film, it is not possible to prevent the oxide film from being exposed as shown in FIG. It was not possible to prevent particle defects due to scattering of particles. A method of using an etching solution that simultaneously dissolves silicon and an oxide film was also tried, but in this case, the dissolution reaction is radical and non-uniform, and the chamfered surface is depressed or corrugated, so this method cannot be adopted. .

Further, in Japanese Unexamined Patent Publication (Kokai) No. 4-85827, an oxide film is attached only to the supporting wafer side, the mirror surface side of the active wafer is chamfered at a peripheral edge portion of 5 mm and then bonded, and then the chamfered portion is ground and removed. This avoids grinding of the oxide film. However, with this method, not only the irregular bonding portion at the periphery of the bonded portion cannot be removed, but also the exposed oxide film remains on the supporting wafer, and this scatters in a later step, which causes particle defects.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and has a high finishing accuracy in chamfering, an interlayer oxide film of a bonded wafer is not destroyed, and a silicon film layer of particles is formed. It is an object of the present invention to provide a method for producing a bonded SOI wafer which is free from contamination and scratches and has high work efficiency.

[0009]

[Means for Solving the Problems] Such problems are caused by laminating two silicon wafers with an oxide film interposed therebetween.
When manufacturing a bonded SOI wafer in which one silicon wafer is removed while leaving an active layer, the outer peripheral portion of the wafer on the side which becomes the active layer of the bonded SOI wafer, in the thickness direction from the surface opposite to the oxide film, Grind to a portion that leaves a residual thickness with the oxide film, immerse this ground bonded wafer in an etching solution that does not dissolve the oxide film, and etch until the oxide film is exposed. This can be solved by providing a method for manufacturing a bonded SOI wafer, which is characterized in that it is immersed in a liquid to remove the exposed oxide film. In addition, such a problem is that when manufacturing the above bonded SOI wafer, the outer peripheral portion of the wafer on the side to be the active layer of the bonded SOI wafer is an oxide film in the thickness direction from the surface opposite to the oxide film. After grinding to the part where a residual thickness is left between the substrate and the ground wafer, the ground wafer is soaked in an oxide film insoluble etchant and etched until the oxide film is exposed. It can be solved by providing a method for manufacturing a bonded SOI wafer, which is characterized by dipping to remove the exposed oxide film and then dipping in a silicon etching solution. In each of the above manufacturing methods, the remaining thickness between the oxide film and the film during grinding is 3 to 8 μm.
It is preferable that In each of the above-mentioned manufacturing methods, the oxide film-insoluble etching solution is preferably a mixed solution of hydrofluoric acid, nitric acid, and acetic acid. Furthermore, in each of the above manufacturing methods, the oxide film-soluble etching solution has a concentration of 1 to 10% by weight.
The hydrofluoric acid is preferably.

The wafer used in the method of the present invention has two silicon wafers, at least one surface of which has been mirror-finished, provided with an oxide film on at least one mirror surface, and the oxide film is interposed between the two silicon wafers. It is obtained by facing each other and pasting them together. Hereinafter, this is referred to as a bonded wafer. This bonded wafer is a bonded wafer prepared for manufacturing a so-called SOI, in which an oxide film made of SiO ₂ is formed on the mirror surface side of the wafer (active wafer) to be thinned, A CVD polysilicon layer is formed on the mirror surface side of the wafer to be formed (supporting wafer).
It also includes a structure in which the surface of the VD polysilicon layer is laminated. At the periphery of such a bonded wafer, there is an overhang portion that is not bonded to each other, and the wafer outer peripheral line formed by the peripheral edge of each wafer is outside the oxide film outer peripheral line formed by the oxide film when viewed in plan view. Are formed.

As described above, the manufacturing method of the present invention comprises grinding the active wafer as the first step, etching the outer peripheral portion of the active wafer as the second step, and etching the oxide film as the third step. In another embodiment, the step of etching the chamfered portion of the supporting wafer is added as the fourth step.

Next, each step will be described in detail. In the first step of the present invention, the outer peripheral portion of the wafer to be the active layer of the bonded wafer (active wafer), the thickness direction from the surface opposite to the oxide film, the residual thickness between the oxide film Grind to the part to be left. Here, the outer peripheral portion is set to the inner side beyond the outer peripheral line formed by the oxide film (oxide film outer peripheral line) from the wafer outer peripheral line formed by the active wafer when the bonded wafer is viewed in plan view. It is up to the boundary. This boundary line is called a chamfer line. In addition, this grinding is performed in the thickness direction from the surface opposite to the oxide film, that is, the outer surface of the active wafer, when the bonded wafer is viewed in a vertical sectional view.
The area up to the portion where a residual thickness is left between the oxide film and the oxide film. In this way, the grinding does not reach the oxide film and leaves the remaining thickness of the wafer on the oxide film, so that the oxide film inside the chamfered line may be damaged by cracking or peeling due to cutter blade pressure or vibration. It is prevented from receiving.

Here, the above-mentioned residual thickness is preferably 3 to 8 μm. If the residual thickness is less than this, the possibility of the oxide film cracking or peeling off due to the blade pressure or vibration of the cutter increases, and if the residual thickness is greater than this, it will take more time than necessary for the subsequent etching process. Efficiency is reduced. Such grinding can be performed using a normal grinding tool such as a diamond wheel.

The second step of the present invention is peripheral etching of the active wafer. This process aims to expose the oxide film outside the chamfer line by chemically removing the residual thickness left on the outer periphery of the active wafer by grinding by immersing it in an etchant that does not dissolve the oxide film. I am trying.
In this process, prior to etching, a plurality of ground bonded wafers are laminated in a cylindrical shape with their central axes aligned in the same direction, and sandwiched by vinyl chloride plates on both sides to form a wafer aggregate. It is preferable.
This protects parts other than the chamfered part of the bonded wafer from etching without complicated steps such as masking,
At the same time, it helps improve the productivity of etching. Immersing such a wafer assembly in an oxide film insoluble etching solution,
Etching is performed while rotating around the central axis of the wafer.

The oxide film insoluble etching solution used here is an etching solution which dissolves silicon but does not substantially dissolve an oxide film. As such an oxide film insoluble etching solution, an aqueous solution of an alkali metal hydroxide or a mixed solution of hydrofluoric acid and nitric acid can be used, but it is particularly preferable to use a mixed solution of hydrofluoric acid, nitric acid and acetic acid. .
This mixed solution can dissolve the remaining thickness of the silicon wafer and expose the oxide film in a short time. Further, the mixing ratio of hydrofluoric acid, nitric acid and acetic acid is preferably set to 1: 6: 3. This mixing ratio improves the selectivity of dissolving silicon and not dissolving the oxide film. By adopting this step, it is possible to avoid damage to the bonded wafers caused by the grinding reaching the oxide film.

The third step of the present invention is to remove the exposed oxide film by immersing it in an oxide film-soluble etching solution. Immersing the wafer assembly that has been subjected to the process of the second step in the oxide film etching solution as it is (without disassembling),
It is preferable to perform oxide film etching.

The oxide film-soluble etchant is an etchant capable of dissolving silicon oxide, and such an oxide film-soluble etchant is an aqueous solution of an alkali metal hydroxide having a specific concentration. Although a mixed solution of hydrofluoric acid and nitric acid can be used, it is particularly preferable to use hydrofluoric acid having a concentration of 1 to 10% by weight. Hydrofluoric acid in this concentration range selectively dissolves silicon oxide and does not dissolve silicon. The immersion time may be 15 to 60 seconds, depending on the grinding surface width and the oxide film thickness. Since the assembly is completed in such a short time, it is not necessary to rotate the aggregate in the liquid. As a result, the oxide film is completely removed. By adopting this step, the oxide film exposed in the previous step is completely removed, and the oxide film inside the chamfered line and the exposed wafer surface are not damaged.

When the bonded wafer used is, for example, a patterned thin film SOI, a CVD polysilicon layer is further interposed between the supporting wafer and the oxide film. In this case, it is preferable to dissolve and remove the CVD polysilicon layer outside the chamfered line (outer peripheral portion). Therefore, in the fourth step in one aspect of the present invention, the chamfered portion of the supporting wafer is etched. It also removes the irregularities originally generated on the oxide film side surface of the supporting wafer and floats in the etching solution as it is undissolved in the previous oxide film removal process It also helps prevent redeposition of oxide particles that had adhered to the. Also in this step, it is preferable that the wafer assembly is continuously moved (without being disassembled) into a silicon etching solution and rotated to perform etching.

The silicon etching liquid used here is
It is an etching solution that substantially dissolves silicon. As such an etching solution, the same etching solution as the oxide film-insoluble etching solution used in the second step can be used. That is, an alkali metal hydroxide aqueous solution or a mixed solution of hydrofluoric acid and nitric acid can be used, but it is particularly preferable to use a mixed solution of hydrofluoric acid, nitric acid and acetic acid. This mixed solution can uniformly dissolve a constant thickness of the outer peripheral portion of the supporting wafer in a short time.

In particular, since CVD polysilicon has a higher etching rate than single crystal silicon, it is necessary to strictly control the etching time and be careful not to etch off the deep part of the CVD polysilicon layer. By such a fourth step of the present invention, the outer peripheral portion of the CVD polysilicon layer can be effectively removed, and the damaged layer on the entire chamfered surface can be removed to improve the finishing accuracy.

The structure and operation of the present invention are as described above. This will be described in more detail with reference to FIG.

EXAMPLE A bonded wafer 10 shown in FIG.
Is prepared for manufacturing a so-called SOI, and the oxide film 20 made of SiO _{2 is formed} on the mirror surface side of the active wafer 11 to be thinned on the mirror surface side of the supporting wafer 12 on the base side. A CVD polysilicon layer 30 is formed, and the oxide film 20 and the CVD polysilicon layer 30 are formed.
The surfaces of and are pasted together. The active wafer 11 has an overhang portion 14 at its periphery,
Outside the oxide film outer peripheral line s formed by the surface of the oxide film 20,
A wafer outer peripheral line w formed by the tip of the wafer is formed.

In the first step (chamfer grinding step), as shown in FIG.
As shown in (b), the outer peripheral portion of the active wafer 11 is ground from the surface opposite to the oxide film, leaving a residual thickness z in the thickness direction. A diamond wheel is used for grinding. The grinding range at this time is, from a plan view, a range from the wafer outer peripheral line w to the chamfered line m set inside the oxide film outer peripheral line s. Since the oxide film outer peripheral line s is irregular and the oxide film in the vicinity thereof is unstable in physical properties and morphology, the chamfer line m is, for example, at least 3 mm from the oxide film outer peripheral line s.
Set on the inner side apart from the above. However, it should be avoided to set it inward more than necessary because it reduces the effective area of the substrate.

The grinding range in the thickness direction in this step is from the outer surface of the active wafer 11 toward the oxide film 20, parallel to the oxide film, and part of the thickness of the active wafer 11,
That is, the remaining thickness z is left. This residual thickness z is, for example, 3
~ 8 μm.

In the second step, first, as shown in FIG. 1C, a plurality of ground bonded wafers 10 obtained in the first step are aligned in the same direction with their central axes aligned in the same direction to form a cylindrical shape. And the both sides are sandwiched by vinyl chloride plates 40 to form a wafer integrated body. This integrated body is immersed in a bath of an etching solution in which hydrofluoric acid, nitric acid and acetic acid are mixed in a weight ratio of 1: 6: 3, and etching is performed while rotating around the central axis of the wafer integrated body. The etching temperature in this case is 40 ° C. Although the dipping time needs to be adjusted depending on the remaining thickness z, it is about 30 seconds to 1 minute. When the oxide film on the outer peripheral portion of the wafer is exposed, the etching end point is set (see FIG. 1D), and the bonded wafer assembly is pulled out from the etching solution.

In the third step, the aggregate after the treatment in the second step is immersed in a hydrofluoric acid bath containing 1 to 10% by weight to dissolve and remove the oxide film. In this case, rotation is unnecessary. In this embodiment, when 5% hydrofluoric acid is used as the oxide film etching solution, the immersion time is about 30 seconds to 1 minute at room temperature.

In the fourth step, the integrated body from which the oxide film has been removed with hydrofluoric acid is again etched using the same etching solution as in the second step to etch off the portion including the CVD polysilicon layer below the oxide film (FIG. 1). (See (e)). The etching temperature at this time is 40 ° C. Immersion time is 15 to 3
It is about 0 seconds.

Then, after immersing in an ultrapure water bath to stop the progress of etching, the integrated body is disassembled, washed with ultrapure water or RCA, and finished ground and polished to form an active layer having a predetermined thickness. A thin film SOI having is obtained.

SO formed by such an embodiment
Since no particles are attached to the I semiconductor substrate during the final polishing, contamination and scratches do not occur.

[0029]

[Effect] The method for manufacturing the bonded SOI wafer of the present invention is
When manufacturing two bonded SOI wafers in which two silicon wafers are bonded together with an oxide film interposed therebetween and one of the silicon wafers is removed while leaving the active layer, the outer peripheral portion of the wafer to be the active layer of the bonded SOI wafer is , Grind from the surface opposite to the oxide film in the thickness direction to a portion where a residual thickness remains with the oxide film, and dip this ground bonded wafer in an oxide film insoluble etching solution. Since the exposed oxide film is removed by immersing it in an oxide film-soluble etchant after the etching until the oxide film is exposed, there is no contamination scratch of the silicon film layer due to particles, and damage to the unexposed part of the oxide film is prevented. In addition, the finishing accuracy of the chamfered portion is high and the working efficiency is high. Further, according to the method of claim 2 of the present invention, since the exposed oxide film is removed and then immersed in a silicon etching solution, the outer peripheral portion of the CVD polysilicon layer under the oxide film can be effectively removed and the entire chamfered surface can be removed. The damaged layer can be removed and the finishing accuracy can be further improved. According to the method of claim 3 of the present invention, since the residual thickness between the oxide film and the oxide film during grinding is set to 3 to 8 μm, the oxide film is not damaged and the working efficiency can be further enhanced. According to the method of claim 4 of the present invention, since the etching solution insoluble in the oxide film is a mixed solution of hydrofluoric acid, nitric acid and acetic acid, the working efficiency can be further enhanced while maintaining the finishing accuracy. In the method of claim 5 of the present invention, since the oxide film-soluble etching solution is hydrofluoric acid having a concentration of 1 to 10% by weight, the oxide film exposed in the previous step is completely removed, and the wafer surface is damaged. Never give.

[Brief description of drawings]

1A to 1E sequentially show a bonding S of the present invention.
It is a fragmentary sectional view showing a processing step of a bonded wafer in one example of a manufacturing method of an OI wafer.

FIG. 2 (a) shows a pasting S by a conventional grinding method.
It is a partial elevation sectional view which shows the bonded wafer in the manufacturing method example of an OI wafer, and (b) is a partial vertical sectional view which shows the bonded wafer in the manufacturing method example which performs etching after the conventional grinding.

[Explanation of symbols]

10 ... Bonded wafer, 11 ... Active wafer, 12
... Support wafer, 20 ... Oxide film, z ... Remaining thickness. m ... Chamfer line.

Claims (5)

[Claims] 1. When manufacturing a bonded SOI wafer in which two silicon wafers are bonded together with an oxide film interposed therebetween, and one silicon wafer is removed while leaving an active layer, the side of the bonded SOI wafer to be an active layer is manufactured. The outer peripheral portion of the wafer is ground from the surface opposite to the oxide film in the thickness direction to a portion where a residual thickness is left between the wafer and the oxide film,
The bonded wafers that have been ground are soaked in an oxide film-insoluble etching solution until the oxide film is exposed, and then immersed in an oxide film-soluble etching solution to remove the exposed oxide film. SO pasted together
I wafer manufacturing method. 2. When manufacturing the bonded SOI wafer according to claim 1, the outer peripheral portion of the wafer on the side which becomes the active layer of the bonded SOI wafer is an oxide film in a thickness direction from a surface opposite to the oxide film. After grinding to the part where a residual thickness is left between the substrate and the ground wafer, the ground wafer is soaked in an oxide film insoluble etchant and etched until the oxide film is exposed. Bonding SO characterized by immersing to remove the exposed oxide film and then immersing in a silicon etching solution
I wafer manufacturing method. 3. The method for manufacturing a bonded SOI wafer according to claim 1, wherein the remaining thickness between the oxide film and the oxide film during grinding is 3 to 8 μm. 4. The method for producing a bonded SOI wafer according to claim 1, wherein the oxide film-insoluble etching solution is a mixed solution of hydrofluoric acid, nitric acid and acetic acid. 5. The method for manufacturing a bonded SOI wafer according to claim 5, wherein the oxide film-soluble etching solution is hydrofluoric acid having a concentration of 1 to 10% by weight.