JPH01196849A - Formation of isolation region of semiconductor device - Google Patents

Abstract

PURPOSE:To shorten a dispersion time for connection by forming a trench from the surface of an epitaxial layer toward the circumference end of a buried layer, and forming the other conductivity type layer, dispersing impurities from the sidewall and the bottom part of the trench. CONSTITUTION:A trench 6 is formed which is deep enough to nearly reach an N<+> buried layer 2 from the surface of a P-type epitaxial layer 3 on a P-type substrate 1. A mask for forming the trench 6 is utilized again, impurities are introduced into the sidewall and the bottom part of the trench 6 by ion- implantation to make them of N-type, and an N<+> dispersion layer 7 is formed by drive dispersion. A P-type region 5 isolated by the N<+>-type buried layer, the trench part 6 and the dispersion layer 7 are formed in the epitaxial layer 3. Consequently, the dispersion time for the connection is shortened.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a buried layer of a different conductivity type existing at the interface with the substrate in an epitaxial layer deposited on a semiconductor substrate, and a buried layer from the surface of the epitaxial layer. The present invention relates to a method of forming a semiconductor element isolation region of one conductivity type by surrounding it with a diffusion layer of a different conductivity type that reaches the layer.

(Prior Art) As an isolation region in an epitaxial layer, a structure as shown in FIG. 2 is conventionally known.

Such a structure is constructed by, for example, forming an island-shaped buried diffusion N2 on a P-type silicon substrate 1, depositing a P-type silicon epitaxial layer 3, and then depositing an island-shaped buried diffusion N2 from the surface of the epitaxial layer 3. By forming the N0 diffusion layer 4 that reaches the diffusion 11i2, a separation region 5 surrounded by the N2 diffusion layer is formed in the P-type substrate.

[Problem to be solved by the invention]

However, like a power device, the separation layer 4 shown as D in FIG.
If a relatively deep depth is required, there is a drawback that it becomes difficult to form a diffusion layer that reaches the buried layer. The reason for this difficulty is that it requires a long diffusion time, and furthermore, as the diffusion takes a long time, outward diffusion from the buried layer 2 and the separation diffusion layer 4 increases, making it difficult to achieve effective separation.
The problem was that the volume of M region 5 became smaller.

The object of the present invention is to eliminate the above-mentioned drawbacks, eliminate factors that degrade device characteristics such as crystal defects that occur with high-temperature and long-time diffusion processing, and easily form semiconductor device isolation regions with arbitrary depths. The object of the present invention is to provide a forming method.

[Means to solve the problem]

In order to solve the above-mentioned problems, the method of the present invention is to form an -it type epitaxial layer on a substrate of one conductivity type having a buried layer of another conductivity type, and then to form a -it type epitaxial layer from the surface of the epitaxial layer to the periphery of the buried layer. A trench is dug toward the buried layer, and impurities are diffused from the sidewalls and bottom of the trench to form a layer of a different conductivity type that connects to the buried layer.

[Effect]

The diffusion time required to connect the impurity diffusion layer from the sidewalls and bottom of the trench dug from the epitaxial layer surface to the buried layer is significantly longer than the conventional impurity diffusion time from the epitaxial layer surface to the buried layer. It only takes a short time.

〔Example〕

FIG. 1 shows a portion M 9 formed according to an embodiment of the present invention.
This is a cross-sectional view including the M region, and as is clear from FIG. 0, in which parts common to those in FIG. A groove 6 deep enough to reach the layer 2 is formed. This groove 6 can also be formed by wet etching, but if the groove is narrow and deep, it is advantageous to form it by dry etching. Using the same mask used to form the trench 6, impurities for making the trench N-type are introduced into the side walls and bottom of the trench by ion implantation, and the N4 diffusion layer 7 is formed by drive diffusion. This diffusion layer 7
can be connected to the buried layer 2 even if it is shallow, and a P shadow region 5 can be formed in the epitaxial layer 3, separated from the N type buried layer 2 by the trench 6 and the N expansion diffusion layer 7. If it is desired that the surface of the epitaxial layer be flat, the grooves 6 may be filled with the same insulating material as the semiconductor surface protective film, but since the insulation properties or the bubble rate are not particularly important, they may be filled with other materials. good.

〔Effect of the invention〕

According to the present invention, - when forming in an epitaxial layer of a conductivity type a region separated by a pn junction from a buried layer of a different conductivity type and a diffusion layer of a different conductivity type reaching from the surface of the epitaxial layer to the buried layer, By digging a trench from the surface of the epitaxial layer to the vicinity of the buried layer and connecting it to the buried layer through a shallow diffusion layer from the sidewalls and bottom of the trench, a long diffusion time for the separation layer is no longer required.
This method is extremely effective for device separation when a drive heat treatment at a relatively high temperature and for a long period of time is undesirable in order to obtain a large-volume separation region, such as in the production of power devices or MO3 devices that require deep separation layers.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an element isolation region obtained according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of a conventional element isolation region.

Claims (1)

[Claims] 1) Forming an epitaxial layer of one conductivity type on a substrate of one conductivity type having a buried layer of another conductivity type, and then digging a groove from the surface of the epitaxial layer toward the periphery of the buried layer,
A method for forming a semiconductor element isolation region, characterized in that a layer of a different conductivity type connected to the buried layer is formed by diffusing impurities from the sidewalls and bottom of the trench.