JPH05166721A - Formation of epitaxial layer - Google Patents

Abstract

PURPOSE:To suppress generation of crystal defects during growth of an epitaxial layer and to prevent autodoping. CONSTITUTION:In a method for forming an epitaxial layer of a predetermined thickness over a semiconductor wafer, an epitaxial layer is grown for example at 1180 deg.C, and then growth of an epitaxial layer is reopened at 1050 deg.C after an elapse of predetermined time; then successively an epitaxial layer is grown at 900 deg.C. High temperature growth prevents crystal defects from being generated in an epitaxial layer, and low temperature growth prevents autodoping from a wafer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an epitaxial layer, and more particularly to a method for forming an epitaxial layer which prevents autodoping and out-diffusion and has a small transition width and a uniform resistance.

[0002]

2. Description of the Related Art Various methods for growing an epitaxial layer on a silicon wafer have been proposed. In this epitaxial growth method, it is necessary to prevent auto-doping and out-diffusion in which impurities in the wafer are redistributed in the epitaxial growth layer during epitaxial growth. As a technique for preventing this autodoping, a method of performing epitaxial growth at a low temperature is known.

[0003]

However, such a conventional method for growing an epitaxial layer at a low temperature has a problem that crystal defects are likely to occur in the epitaxial layer.

Therefore, the inventors of the present invention have found that the crystal defects generated by the low temperature epitaxial growth method are the result of the formation of a natural oxide film on the surface of the wafer. To grow a thin epitaxial layer once, and then grow the epitaxial layer at a low temperature to suppress the occurrence of crystal defects, and
It is proposed to obtain a method for forming an epitaxial layer that prevents autodoping.

[0005]

According to a first aspect of the invention, in a method of forming an epitaxial layer having a predetermined thickness on a semiconductor wafer, a step of growing the epitaxial layer at a first temperature, Then, an epitaxial step including a step of growing the epitaxial layer at a second temperature lower than the first temperature and a step of growing the epitaxial layer at a third temperature lower than the second temperature. It is a method of forming a layer. That is, the epitaxial growth at a high temperature is not suddenly performed at a low temperature, but the epitaxial growth is performed at a temperature in between, and then the epitaxial temperature is changed to that at a low temperature.

[0006]

According to the method of growing an epitaxial layer according to the present invention, the epitaxial layer is grown to a predetermined thickness at a high temperature and then further grown to a lower temperature. Then, epitaxial growth is performed at a lower temperature. Therefore, crystal defects are less likely to occur in the epitaxial layer due to high temperature growth, and autodoping from the wafer can be prevented by low temperature growth. In particular, by growing the epitaxial layer at these intermediate temperatures, it is possible to grow an epitaxial layer with fewer defects.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a graph showing a time change of temperature in epitaxial growth according to an embodiment of the present invention. Figure 2
Is a graph showing the value of the specific resistance with respect to the depth of the wafer on which the epitaxial layer is formed in this case.

In this example, a boron high-concentration wafer having a large auto-doping effect was used as a wafer, and a cylinder type epitaxial furnace was used. Gas was supplied at 200 l / min. It is assumed that the back surface of this silicon wafer is covered with a SiO ₂ film. Then, in FIG. 1, epitaxial growth was performed with the temperature histories of (A), (B), and (C). (A) is H at 1180 ° C
This is a case where epitaxial growth was performed at 900 ° C. after Cl etching. The growth rate of this epitaxial growth is 0.1 μm / min. As a result, stacking faults occurred in the epitaxial layer. Further, (B) shows that after etching, epitaxial growth was performed at 1180 ° C., then gas supply was stopped, and gas supply was restarted at 900 ° C. In this case, a stacking fault has occurred in the epitaxial layer. Here, under the temperature condition shown in (C), 1
After etching at 180 ° C., gas is supplied to perform epitaxial growth at high temperature. Then, the gas supply is once stopped to lower the wafer temperature, and the gas supply is restarted at 1050 ° C. The temperature is further lowered for 2 minutes from the restart 900
To ℃. Epitaxial growth is performed at 900 ° C. for 9 minutes, for example. As a result, a thin low resistance epitaxial layer can be grown on a silicon wafer.
The epitaxial growth rate at this time is 0.3 μm / min. The epitaxial layer thus obtained is
As shown in FIG. 2, the transition width is 0.70 μm, which is about 1/3 of the conventional manufacturing method.

[0009]

According to the present invention, auto-doping of the epitaxial layer from the wafer is prevented and the generation of crystal defects is suppressed. That is, the impurity concentration can be highly controlled, and an epitaxial layer with few defects can be formed.

[Brief description of drawings]

FIG. 1 is a graph showing a temporal change in temperature during epitaxial growth according to an example of the present invention.

FIG. 2 is a graph showing the value of specific resistance with respect to the depth of a wafer on which an epitaxial layer according to an embodiment of the present invention is formed.

Claims (1)

[Claims] 1. A method of forming an epitaxial layer having a predetermined thickness on a semiconductor wafer, comprising: a step of growing the epitaxial layer at a first temperature; and a second step lower than the first temperature. A method of forming an epitaxial layer, comprising: a step of growing the epitaxial layer at a temperature; and a step of growing the epitaxial layer at a third temperature lower than the second temperature.