JPH0645314A - Wafer etching method - Google Patents

Abstract

(57) [Summary] [Structure] The first etching tank 3 is filled with an etching solution having a diffusion-controlled chemical composition, and the second etching tank 4 is filled with an etching solution having a stirring-controlled chemical composition. The etching jig 1 in which a large number of wafers are set is rotated and can be moved between these tanks by a transportation means which is full and is not shown. [Effect] Not only the amount of heat generated by a chemical reaction during etching can be reduced, but also the surface fine structure created by the etching treatment can be improved in terms of micro and macro.

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 for maintaining flatness (TTV) of a wafer such as silicon by etching the wafer with a mixed acid (hydrofluoric acid, nitric acid, acetic acid, water) solution. .

[0002]

2. Description of the Related Art A silicon wafer is produced by laminating, etching and polishing a thin disk obtained by cutting a silicon single crystal in this order.

When the above-mentioned polishing step is carried out by so-called mechanical chemical polishing, submicron silica sol dispersed in an alkaline aqueous solution is used as an abrasive to soften the wafer in a wet state in order to reduce processing scratches on the finished mirror surface as much as possible. Since the porous urethane foam is polished with a light load, for example, 50 to 100 g / cm ² (wafer), if the shape accuracy of the wafer surface before the polishing step is poor, expect a higher mirror surface shape accuracy. I can't. Therefore, for highly integrated wafers, it is strongly desired to improve the surface shape accuracy in the etching process.

In this etching step, etching is usually carried out in a dilute mixed aqueous solution of hydrofluoric acid, nitric acid, water or acetic acid. Generally, when the nitric acid concentration is high, the diffusion rate is controlled, and when the hydrofluoric acid concentration is high, surface reaction is performed. It is rate limiting and both water and acetic acid are believed to act as diluents. Further, under the above diffusion rate-controlled condition, the macroscopic shape accuracy is maintained, but the microscopic shape accuracy is inferior, and conversely, under the surface reaction rate-controlled condition, the microscopic shape accuracy is improved, but the macroscopic shape accuracy deteriorates. It is estimated.

[0005]

However, conventionally, in etching a wafer such as silicon, a carrier containing a large number of wafers is rotated in a mixed acid solution having a predetermined chemical composition filled in one etching tank. After that, the substrate was dipped in the washing tank to be etched and then washed in the washing tank. Therefore, in the above method, the microstructure formed on the wafer surface is uniquely determined by the treatment with one kind of mixed acid solution. The reality is that the etching conditions are selected at the expense of shape accuracy. For this reason, there has been a complaint that the shape accuracy cannot be satisfied for both macro and micro.

Further, in the above etching method, there is a possibility that the flatness (TTV) of the wafer may be deteriorated due to the reaction heat generated by the increase of the diameter of the wafer.

[0007]

Therefore, the inventors of the present invention have conducted extensive research to solve the above-mentioned problems, and as a result, to solve the problems, the etching process is divided into several steps by etching in multiple tanks. Found to be effective.

For this reason, the inventors of the present invention can maintain the flatness (TTV) with a smaller circulating amount of the solution because the multi-bath etching process can disperse the reaction heat generated by the chemical reaction. It is estimated that this is possible.

That is, the method of etching a wafer according to the present invention is characterized in that the wafer is etched by successively immersing the wafer in an etching solution filled in two or more etching tanks.

In this case, the above two or more etching baths are divided into two types, one of which is filled with an etching solution having a diffusion-controlled chemical composition, and the other is filled with an etching solution having a stirring-controlled chemical composition. First, immerse the wafer in an etching tank filled with an etching solution having a diffusion-controlled chemical composition, and then immerse the wafer in an etching tank filled with an etching solution having a stirring-controlled chemical composition. It is preferred to etch the wafer.

As a result, first, the action of the diffusion-controlling type etching solution improves the macroscopic shape accuracy of the wafer, that is, the surface roughness, and then the action of the stirring-controlling type etching solution causes the surface reaction rate-controlling. As a result, the microscopic shape accuracy is improved, and it is possible not only to reduce the amount of heat generated as described above, but also to improve the surface fine structure created by the etching process.

Here, the etching solution having the above diffusion-controlled chemical composition has a volume% of hydrofluoric acid: nitric acid: acetic acid:
Water is preferably 1: 5 to 20: 2 to 12: 1 to 12, and as an etching solution having a chemical composition of stirring-controlled type, the volume ratio of hydrofluoric acid: nitric acid: acetic acid = 1: 1 to 4: 1 to
3 is desirable.

Further, in the wafer etching method of the present invention, the above-mentioned two or more etching tanks are filled with an etching solution having the same chemical composition, and the wafers are successively immersed in these etching tanks to carry out the etching treatment a plurality of times. It may be divided into two steps. In this case, it is preferable that the total etching time in each etching tank is the same as the etching processing time performed in one ordinary processing. In this case as well, the amount of heat generated can be reduced in the same manner as described above, and the flatness (TTV) of the wafer can be maintained.

Further, the etching liquid is 50 L / min.
The wafer may be etched by immersing the wafer in the etching bath constituted by the circulation system that is circulated as described above. By setting the circulation speed to 50 L / min, the reaction heat caused by the increase in the diameter of the wafer is quickly diffused, and the possibility of deteriorating the flatness (TTV) of the wafer is reduced.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The wafer etching method of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a perspective view showing an example of an etching apparatus used in the wafer etching method of the present invention.

In this etching processing apparatus, a cube-shaped first etching tank 3 and a cube-shaped second etching tank 4 are provided with a central washing bath 2 interposed therebetween, and a large number of wafers are set by a transporting means (not shown). The etching jig 1 is configured to move between these tanks while rotating.

The first etching bath 3 and the second etching bath 4 are respectively connected to an etching liquid exchange bath (not shown) by two connecting pipes 5, and the first etching bath 3 and the second etching bath 4 are connected to each other.
The etching solutions filled in the etching tank and the second etching tank can be circulated.

Further, in this embodiment, the first etching bath 3
, The composition is% by volume, and hydrofluoric acid: nitric acid: acetic acid: water =
An etching solution having a diffusion-controlled composition, which is 1: 6: 6: 2, is filled. On the other hand, the second etching tank 4
In, the composition is a hydrofluoric acid: nitric acid: acetic acid = 1: 3: 2 and is filled with an etching solution having a stirring rate-controlling composition.

The etching process of a silicon wafer using this apparatus is performed as follows.

First, the etching solution filled in the first etching tank 3 and the etching solution filled in the second etching tank 4 are moved at a speed of 50 L / min, respectively.
The etching jig 1 having a large number of wafers is rotated at 20 times / minute while being circulated in the above step, and is immersed in the washing tank 2.

Then, the etching jig 1 is immersed in the first etching bath 3 for a predetermined time by a transporting means (not shown) to etch the wafer.

Further, after being immersed in the water washing tank 2 and washed with water, the etching jig 1 is immersed in the second etching tank 4 and etched for a predetermined time.

Finally, the etching jig 1 is washed again with the washing tank 2
Then, it is soaked in water and washed with water to end the etching.

By carrying out the etching treatment in this way, first, the macroscopic shape accuracy, that is, the surface roughness is improved by the action of the diffusion-controlled etching liquid, and then by the action of the stirring-controlled etching liquid. The surface reaction is rate-determining, the microscopic shape accuracy of the wafer is improved, and the surface fine structure created by the etching process can be improved. Further, the etching process is performed separately in the first etching tank and the second etching tank, and the etching liquid is moved at a speed of 50 L.
Since it is circulated at a speed of 1 / min, the reaction heat generated by the chemical reaction can be dispersed, and the flatness (TTV)
Can be easily maintained without deteriorating.

Further, since the first etching tank 3 and the second etching tank 4 are formed in a cubic shape, when the etching solution circulates, four-sided overflow occurs and the flow of the etching solution becomes good.

2 (a) and 2 (b) show a wafer obtained by the etching method of this embodiment and a conventional wafer, respectively.
3 shows changes in the wafer cross-sectional shape before and after etching with a wafer obtained by an etching method using a mixed acid solution of various types, by a capacitance type sensor ADE7200.

From these results, the wafer obtained by the conventional etching method has a large amount of the central portion etched, whereas the wafer obtained by the etching method of the present embodiment has the etching along the shape of the lapping wafer. It was confirmed that the surface shape was smoother and was superior to the conventional example.

[0029]

As described above, in the method for etching a wafer according to the first aspect of the present invention, the wafer is etched by sequentially immersing the wafer in the etching solution filled in each of the two or more etching tanks. Since the heat of reaction generated by can be dispersed, the flatness (TTV) can be maintained with a smaller circulating amount of the solution.

Therefore, according to the wafer etching method of the first aspect, the flatness of the wafer (TT
V) can be maintained and improved.

In the method of etching a wafer according to the present invention, the wafer is immersed in an etching bath filled with an etching solution having a diffusion-controlled chemical composition and then filled with an etching solution having a stirring-controlled chemical composition. Since the wafer is etched by immersing the wafer in the etching tank, the heat generated by the chemical reaction during etching can be reduced and the surface microstructure created by the etching process is improved from the micro and macro points. It becomes possible to do.

Further, there is an effect that etching can be performed according to the physical properties of the wafer, and the surface fine structure can be arbitrarily manipulated by the etching amount ratio of the first liquid and the second liquid.

Further, in the method for etching a wafer according to the third aspect, the wafers are successively immersed in an etching solution having the same chemical composition and filled in two or more etching tanks, and the etching treatment is performed in plural times. So
Similarly, the amount of heat generated by a chemical reaction during etching can be reduced, and the flatness (TTV) of the wafer can be reduced.
It is possible to maintain.

In the method for etching a wafer according to claim 4, since the wafer is etched by immersing the wafer in an etching bath constituted by a circulation system in which an etching solution is circulated at 50 L / min or more, the wafer diameter is increased. The reaction heat generated by the diffusion is rapidly diffused, and the risk of degrading the flatness (TTV) of the wafer is reduced.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an apparatus used in the wafer etching method of the present invention.

FIG. 2 is a sectional view showing a sectional structure of a wafer,
(A) is sectional drawing before and after the processing method of this invention, (b) is sectional drawing before and behind the conventional processing method.

[Explanation of symbols]

 1 Etching jig 2 Washing tank 3 First etching tank 4 Second etching tank

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazunari Takaishi 3-8-16 Iwamotocho, Chiyoda-ku, Tokyo Sanryo Material Silicon Co., Ltd. (72) Inventor Tadashi Okada 3-chome, Iwamotocho, Chiyoda-ku, Tokyo No. 16 Sanritsu Material Silicon Co., Ltd. (72) Inventor Satoshi Shimizu 3-8-16 Iwamotocho, Chiyoda-ku, Tokyo Sanritsu Material Silicon Co., Ltd.

Claims (4)

[Claims] 1. A method for etching a wafer, which comprises sequentially immersing the wafer in an etching solution filled in two or more etching tanks to etch the wafer. 2. A wafer is dipped in an etching tank filled with an etching solution having a diffusion-controlled chemical composition, and then immersed in an etching tank filled with an etching solution having a stirring-controlled chemical composition. The method of etching a wafer according to claim 1, wherein the wafer is etched by etching. 3. The wafer according to claim 1, wherein the wafers are successively immersed in an etching solution having the same chemical composition, which is filled in two or more etching tanks, and the etching treatment is performed in plural times. Etching method. 4. The wafer according to claim 1, wherein the wafer is etched by immersing the wafer in an etching bath constituted by a circulation system in which an etching solution is circulated at 50 L / min or more. Etching method.