JPH0338035A - Manufacture of diffusion wafer - Google Patents

Abstract

PURPOSE:To manufacture a diffusion wafer at a low cost by reducing the thickness of silicon ingot which is sued to obtain one diffusion wafer. CONSTITUTION:By cutting and polishing silicon ingot, a lapped wafer 1 is obtained, whose thickness is about twice the conventional lapped wafer, and finally, two diffusion wafers 3 are manufactured from the one lapped wafer 1. When the lapped wafer 1 is obtained from the silicon ingot, the same cutting margin and lapping margin are prepared for one lapped wafer 1. In this case, the total of the cutting margin and the lapping margin for obtaining total lapped wafers may be one half as compared with the conventional method. As a result, the total of the cutting margin and the lapping margin required for obtaining the final diffusion wafer 3 from the initial silicon ingot is reduced. Thereby the diffusion wafer 3 can be manufactured at a low cost.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method of manufacturing a diffusion wafer.

[Conventional technology]

Some silicon wafers are shipped to users with impurity diffusion applied to one side by the manufacturer, and these are generally called diffusion wafers. This diffusion wafer is mainly used as a substrate for triple diffusion type transistors because accurate diffusion concentration and diffusion depth are ensured.

Conventionally, diffusion wafers have been manufactured by the method shown in FIGS. 2(a) to 2(d). First, for example, an N-type silicon ingot is sliced and wrapped to obtain an N-type wrapped wafer 1 (as shown in FIG. 2(a)).

For example, an N-type impurity is diffused on both sides of this lap wafer 1 to form an N0-type diffusion layer 2 (diffusion depth 70 to 250t1M) (as shown in FIG. 3B). Here, the conductivity type of the lap wafer and the diffusion layer may be either N type or P type depending on the application. The diffusion layer on one side of the wafer 1, which has been subjected to double-sided diffusion, is polished and removed (as shown in FIG. 2C). after that,
After cleaning, a diffusion wafer 3 as shown in FIG. 2(d) is prepared.
is obtained.

Note that there is also a method of diffusing impurities only on one side of the wafer in the step shown in FIG. 2(b), but in this case also, in the step corresponding to FIG. Polishing is performed.

[Problem to be solved by the invention]

However, in the conventional method, there was a problem in that the cost increased because the cutting margin and wrapping margin of one diffusion sear n3 was large until manufacturing the diffusion wafer from the silicon ingot through the lapped wafer. .

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a method of manufacturing a diffusion wafer at low cost.

[Means to solve the problem]

The method for manufacturing a diffusion wafer of the present invention includes a step of diffusing impurities on both sides of a plurality of silicon wafers, a step of bonding a plurality of silicon wafers that have been diffused on both sides with an adhesive to prepare an ingot, and forming an ingot. This method is characterized by comprising a step of cutting the central portion of each silicon wafer that has been diffused on both sides, and a step of removing the adhesive to obtain a diffusion wafer that has been diffused on one side.

In the present invention, as in the prior art, the conductivity type of the lap wafer and the diffusion layer may be either N type or P type, and is determined depending on the application.

In the present invention, the adhesive is not particularly limited, but it is preferably one that does not allow impurities to adhere to the wafer and can be easily removed. Such adhesives include, for example, paraffin. Paraffin is easy to purify and can be easily removed using an organic solvent. Since the amount of adhesive varies depending on the diameter of the wafer, it cannot be limited to -ta, but if the amount of adhesive is too small, the bonding will be difficult. If it is too large, the bonding will be uneven, making it impossible to bond uniformly.

In the present invention, in order to cut (slice) the central part of each silicon wafer constituting an ingot made by bonding a plurality of double-sided diffused silicon wafers with an adhesive, an ingot pulled by the C2 method is used. A method similar to that used for slicing is used. That is, the ingot is adhered to a carbon base, the carbon base and the carbon base are set in a cutting machine, and the ingot and the carbon base are sliced with a blade.

[Effect]

In the method of the present invention, a silicon ingot is cut and polished to obtain a lapped wafer approximately twice as thick as a conventional lapped wafer, and finally two diffusion wafers are produced per lapped wafer. That is, if conventionally A lapped wafers were obtained from a silicon ingot, in the method of the present invention, it is only necessary to obtain A/2 lapped wafers from a silicon ingot. Therefore, when obtaining lapped wafers from silicon ingots, if the same cutting allowance and wrapping allowance are expected for each lapped wafer, the total cutting allowance and wrapping allowance to obtain all lapped wafers is calculated using the method of the present invention. It only requires 1/2 of the conventional method. Also, when obtaining a diffusion wafer from a lap wafer,
The lapping allowance for polishing the diffusion layer on one side using the conventional method and the cutting allowance for cutting the central portion of each silicon wafer using the method of the present invention may be approximately the same. Therefore, in the method of the present invention, the overall cutting and lapping allowances from the initial silicon ingot to the final diffusion wafer can be significantly reduced compared to the conventional methods, so diffusion wafers can be manufactured at low cost. .

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1(a) to 1(d). In addition, in the following examples, the total thickness is 2
A case will be described in which a diffusion wafer with a diffusion layer depth of 150 μs and a diffusion layer depth of 150 μs is manufactured.

First, an N-type silicon ingot was sliced and wrapped to a thickness of 900 mm. N-type impurities are diffused on both sides of a 5-inch diameter N-type lapped wafer 1 to a diffusion depth of 15.
A 0μ N+ type dispersed layer 2 was formed (as shown in Figure 1(a)).
. Next, prepare a plurality of wafers 1 with this double-sided diffusion,
An ingot was prepared by dropping 1 to 5 g of paraffin 4 heated to 50 to 150° C. and bonding them one after another by applying pressure (as shown in FIG. 13(b)). After bonding this ingot to a carbon base and setting it in a cutting machine (not shown), the central part of each wafer 1 comprising the ingot, which had been diffused on both sides, was cut until the carbon base was separated. Furthermore, the carbon base was removed by alkali washing, and paraffin 4 was removed by washing with a solvent. Thereafter, a final cleaning was performed, and finally a mirror finish was performed (as shown in FIG. 4(c)).

Thus, the thickness is 20 On and the diffusion depth is 150. A diffusion wafer 3 was obtained (as shown in FIG. 3(d)).

Here, the thickness is 200B and the diffusion depth is 15B by the conventional method.
In order to obtain a 0 n diffusion wafer, a lapped wafer with a thickness of 450 μm is required, allowing for a lap allowance of 250 μm. In order to obtain a wrapped wafer having a thickness of 450 nm, a silicon ingot having a thickness of 860 nm per lapped wafer is used, with a cutting allowance and a wrapping allowance of 410 tan. That is, conventionally the thickness was 200p.
A silicon ingot with a thickness of 860μ is used to obtain a diffusion wafer of .

On the other hand, in the above example, in order to obtain a diffusion wafer with a thickness of 20 On and a diffusion depth of 150 M, the cutting allowance for each wafer was 25 On, and the total thickness of the two wafers was 500 nm.
Two diffusion wafers are obtained from a 00μ lapped wafer. In order to obtain a lapped wafer having a thickness of 900 tan, a silicon ingot having a thickness of 1310B is used for one lapped wafer, with a cutting allowance and a wrapping allowance of 410°. That is, in the above example, in order to obtain two diffusion sheets with a thickness of 200μ, a thickness of 13
A 10μ silicon ingot is used, and the thickness of the silicon ingot per diffusion sea urchin is 855n.

As described above, in this embodiment, the thickness of the silicon ingot used to obtain one diffusion wafer can be reduced by 205 m (24%) compared to the conventional method. Accordingly, in this embodiment, the material cost can be reduced by 24% compared to the conventional method.

〔Effect of the invention〕

As described in detail above, the method of the present invention allows diffusion wafers to be manufactured at low cost, and its industrial value is extremely large.

[Brief explanation of drawings]

Figures 1 (a) to (d) are cross-sectional views showing the method for manufacturing a diffusion wafer in an embodiment of the present invention, and Figures 2 (a) to (d)
1 is a cross-sectional view showing a conventional method for manufacturing a diffusion wafer. 1... Silicon wafer, 2... Diffusion layer, 3... Diffusion wafer, 4... Paraffin (adhesive)

Claims (1)

[Claims] A process of diffusing impurities onto both sides of multiple silicon wafers, a process of bonding multiple silicon wafers that have been diffused on both sides with an adhesive to create an ingot, and a central part of each silicon wafer that has been diffused on both sides that make up the ingot. 1. A method for manufacturing a diffusion wafer, comprising the steps of: cutting the wafer; and removing an adhesive to obtain a diffusion wafer with diffusion on one side.