JPS6224616A - Epitaxial growth method - Google Patents

Abstract

PURPOSE:To prevent deterioration in element characteristics and reduction in yield, by removing an impurity diffusion layer on the back surface side of a semiconductor substrate and then performing epitaxial growth. CONSTITUTION:SiO2 films 2 and 3 are formed on a Si substrate 1, and then the back surface of a wafer, in which embedded diffusion layers 5 are formed by a thermal diffusion method with diffusion windows 4 formed on the SiO2 film 2, is mechanically polished, to remove the back surface diffusion layer 6 and uniformize the wafer thickness. Thereafter, with a washing process fully performed, the SiO2 film 2 formed as the surface protecting film and diffusion mask is removed and epitaxial growth is performed by an ordinary method. Without excessive thermal processes after forming the embedded diffusion layers 5, deterioration in characteristics can be avoided, and on account of no covering layer with dissimilar thermal expansion coefficiency during the epitaxial growth, a bend of wafer does not occur. Besides, because the back surface is covered with the protection film while polishing the back surface, damage and contamination can be avoided.

Description

[Detailed Description of the Invention] [Summary] A method for manufacturing an epitaxial wafer having a buried diffusion layer, in which an impurity diffusion layer on the back side of a semiconductor substrate is removed, epitaxial growth is performed, and autodoping from the back side is performed. To prevent.

[Industrial application field]

The present invention relates to a method for manufacturing an epitaxial wafer having a buried diffusion layer as a low resistance layer for reducing the collector resistance of bipolar ICs, an etching stop layer for devices such as pressure sensors that require three-dimensional processing, and the like.

[Conventional technology]

FIGS. 2A to 2E show a conventional epitaxial growth method that prevents autodoping.

In Figure A (initial oxidation), a SiO2 film 2,
3 is formed, and the back surface is polished to a predetermined thickness in Figure B (photoetching), a diffusion window 4 is formed in the SiO2 film 2, and heat treatment is performed in Figure C (debo, diffusion). A buried diffusion layer 5 is formed by diffusion, and at that time, a back diffusion layer 6 is formed.
In Figure D (mask removal, backside coating), PSG (phosphorus silicate glass), N5C (silicate glass), Si3N4. A backside coating layer 7 of Po1ySi or the like is formed, the SiO2 film 2 serving as a diffusion mask is removed, and epitaxial growth is performed as shown in FIG.

[Problem that the invention seeks to solve]

However, the above conventional method has the following drawbacks.

(2) Since the back side is processed (photoetching, CVD, etc.) after the buried diffusion layer is formed, it is necessary to hold it on the front side, which causes scratches and contamination on the surface and reduces yield.

(2) After the buried diffusion layer is formed, an extra thermal process is required to form the backside coating layer, which makes it difficult to control the impurity profile of the buried diffusion layer, resulting in deterioration of device characteristics.

■A backside coating process is required, increasing the number of processes.

(2) Warpage occurs in the wafer during the epitaxial growth process because the wafer has coating layers with different coefficients of thermal expansion.

[Means for solving problems]

In order to solve the above problems, in the present invention, after forming a diffusion mask on one main surface side of a semiconductor substrate and forming a buried diffusion layer by selective diffusion, the surface on one main surface side of the semiconductor substrate is formed. Cover with a protective film, remove the impurity diffusion layer on the back side of the semiconductor substrate, remove the protective film and diffusion mask on the one main surface side, and then form an epitaxial growth layer on the vaginal surface.

[Effect]

According to the above, since there is no extra heat step after forming the buried diffusion layer, there is no risk of deterioration of characteristics, and since there is no covering layer with a different coefficient of thermal expansion during epitaxial growth, no warping of the wafer occurs.

Furthermore, even if there is variation in the initial thickness of the wafers (between wafers or within a wafer), it can be made uniform by polishing when removing the impurity diffusion layer on the back side.

〔Example〕

FIG. 1 shows a manufacturing process diagram of an embodiment of the present invention, which will be explained below.

FIGS. A to C are the same as the conventional FIG. 2, and the reference numerals are the same.

In the drawing, the back surface of the urchin/'% on which the buried diffusion layer is formed is mechanically polished to remove the back surface diffusion layer 6.

At the same time, the thickness of the wafer is made uniform.

During this backside polishing, in order to protect the surface, it is covered with a protective film (not shown), such as wax or film (manufactured by Nitto Denko, Elepcover). Thereafter, thorough cleaning is performed to remove the surface protective film and the SiO2 film 2 of the diffusion mask.

In Figure E, epitaxial growth is performed by a conventional method.

〔Effect of the invention〕

As is clear from the above, according to the present invention, the following effects can be obtained.

■Deterioration of device characteristics 1 No decrease in yield.

This is because in the present invention, the surface is covered with a protective film during backside polishing, so there is no damage or contamination, and there is no extra heat process required in the conventional method after forming the buried diffusion layer. based on.

■Wafer does not warp.

Because there is no coating with a different coefficient of thermal expansion during epitaxial growth.

■The thickness of the wafer can be made uniform.

Even if there are variations in the initial values both within a wafer and between wafers, they can be made uniform by the polishing process when removing the backside diffusion layer.

In particular, in the manufacture of pressure sensors and the like, there is an advantage that the wafer thickness adjustment for uniform diaphragm formation can be performed simultaneously during the polishing process for removing the back diffusion layer.

[Brief explanation of drawings]

Figure 1 A-E is a process diagram of an embodiment of the present invention, Figure 2 A-E
is a manufacturing process diagram of a conventional example. Main code 1: Si substrate 2: Si02 film 3: 5i02 film 4: Diffusion window 5: Buried diffusion layer 6: Back diffusion layer 7: Back surface wave RIT layer 8: Epitaxial growth layer

Claims (1)

[Claims] A step of forming a diffusion mask on one main surface side of a semiconductor substrate and forming a buried diffusion layer by selective diffusion, a step of covering the one main surface side of the semiconductor substrate with a protective film. The method includes the following steps: removing an impurity diffusion layer on the back side of the semiconductor substrate, removing a protective film and a diffusion mask on the one main surface, and forming an epitaxial growth layer on the one main surface. Characteristic epitaxial growth method.