JPH02234422A - Method of suppressing auto doping - Google Patents

Abstract

PURPOSE:To reduce auto doping to an epitaxial layer by a method wherein antimony is included in an imbedded layer containing arsenic as impurities to grow an epitaxial layer on the imbedded layer. CONSTITUTION:Arsenic (As) being n-type impurity is doped on a silicon substrate 1 to form an imbedded layer 2, and then by ion implanting antimony (Sb) on the surface of the imbedded layer 2 an antimony implantation layer 2a is formed over the imbedded layer 2. Then with annealing performed antimony is activated as well as crystals are restored to grow an epitaxial layer 3 with low impurities concentration on the imbedded layer 2 formed with the antimony implantation layer 2a. The epitaxial layer 3 thus formed is a layer having low impurities concentration but arsenic does not mix into the underlying imbedded layer 2 thereby suppressing auto doping.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for suppressing autodoping in epitaxy technology, and more specifically to autodoping when an epitaxial layer is formed on a buried layer containing impurities. This relates to a suppression method.

[Summary of the Invention] The present invention provides a method for suppressing arsenic (
By incorporating antimony (Sb) in the upper part of the buried layer containing As, ) as an impurity and growing an epitaxial layer on the buried layer, evaporation and elution of impurities in the buried layer are suppressed and auto-doping to the epitaxial layer is achieved. It is designed to prevent this.

[Prior art] In silicon epitaxy technology, when an epitaxial layer with a low impurity concentration is formed on a substrate with a high impurity concentration (for example, arsenic concentration of 0.18 to 10" cm), impurities are separated from the substrate with a high impurity concentration. and drift near the substrate surface.
Autodoping, in which impurities are incorporated into the formed epitaxial layer, has become a problem.

Therefore, the following methods are conventionally known as methods for suppressing autodoping.

stomach. The pressure is lowered to facilitate the flow of impurities from the highly impurity-concentrated substrate using a purge gas (for example, Ht) and to thin the stagnation layer on the surface of the substrate.

The evaporation of impurities from a highly impurity-concentrated substrate is reduced by lowering the temperature.

C. Before performing epitaxial growth on a high impurity concentration substrate, thin capping epitaxial growth is performed on the substrate to suppress evaporation of impurities from the substrate, and then normal epitaxial growth is performed (two-step epitaxial growth).

[Problems to be Solved by the Invention] However, the above-mentioned method A has a problem in that there is a limit to how low the pressure can be reduced.

Furthermore, the above-mentioned method has the problem that the crystal deteriorates as the temperature decreases.

Furthermore, although method C is a simple method that has been put into practical use, there is a problem in that the doping suppression effect decreases as the thickness of the epitaxial layer decreases.

Furthermore, in methods A, C, and C, increasing the flow rate of the carrier gas efficiently replaces impurities and reduces autodoping, but as the amount of purge gas increases, the susceptor temperature decreases and the susceptor There were problems such as non-uniform temperature distribution and a decrease in the maximum temperature (insufficient RF output), and non-uniform film thickness distribution.

The present invention has been devised by focusing on such conventional problems, and even when the thickness of the epitaxial layer is reduced, doping of impurities can be sufficiently suppressed.
Moreover, it is an object of the present invention to provide a method for suppressing doping without impairing crystallinity.

[Means for Solving the Problems] Therefore, the present invention includes a method of including antimony (Sb) in the upper part of a buried layer containing arsenic (As) as an impurity and growing an epitaxial layer on the buried layer. It is used as a solution.

[Function] At the top of the buried layer, there is a layer with a small diffusion coefficient and low vapor pressure.
Moreover, by containing antimony having a large atomic radius, antimony prevents evaporation and elution of arsenic in the buried layer.

[Example] Hereinafter, details of the autodoping suppression method according to the present invention will be explained based on an example shown in the drawings.

FIG. 1A to FIG. 1C are cross-sectional views showing the steps of this embodiment.

First, as shown in FIG. 1A, a silicon substrate 1 is doped with arsenic (As), which is an n-type impurity, to form a buried layer (n'' layer) 2 used, for example, in a bibolar device.

Next, antimony (Sb) is added to the surface of the buried layer 2 by
An antimony implantation layer 2a is formed on the top of the buried layer 2 by ion implantation at a dose of 10"cm-3 or more (Figure IB).The depth of antimony implantation depends on the characteristics of the device. The depth is set to a level that does not affect the antimony.Next, annealing is performed at, for example, about 1000°C to activate the antimony and recover the crystal.The annealing method is halogen lamp annealing. It is possible to use methods such as laser annealing and laser annealing.

Next, as shown in FIG.
An epitaxial layer (n layer) 3 with a low impurity concentration is grown on the buried layer 2 in which the .

Although the epitaxial layer 3 thus formed is a low impurity concentration layer, arsenic in the underlying buried layer 2 is not mixed in, and autodoping is suppressed.

Figure 2 is a graph of the impurity concentrations of the epitaxial layer 3 and buried layer 2 viewed in the depth direction.As can be seen from the graph, there is a steep concentration profile at the depth beyond the shrimp interface and reaching the buried layer 2 side. It has become. Therefore, it is confirmed that doping of the impurity As in the buried layer 2 toward the epitaxial layer 3 during epitaxial growth is suppressed.

Here, antimony in the antimony implantation layer 2a above the buried layer 2 is an n-type impurity like AS, but its atomic radius is large and its diffusion coefficient is small. Since both vapor pressures are small, it is difficult to evaporate from the silicon substrate 1 during the formation of the epitaxial layer 3, and arsenic in the buried WJ 2 is prevented from evaporating. Therefore, autodoping of arsenic into the epitaxial layer 3 can be prevented.

Although the embodiments have been described above, the present invention can be modified in various ways in accordance with the gist of the above-described configuration. For example, the amount of antimony ions implanted can be changed as appropriate.

Furthermore, it goes without saying that the present invention is applicable to semiconductor device manufacturing processes other than bipolar device processes.

This has the effect of making improvements possible.

[Brief explanation of the drawing]

Figures 1A to 1C are cross-sectional views showing examples of the autodoping suppression method according to the present invention, and Figure 2 is a graph showing impurity concentrations in the depth direction of the epitaxial layer, antimony implantation layer, and buried layer. be. DESCRIPTION OF SYMBOLS 1... Silicon substrate, 2... Buried layer, 2a... Antimony implantation layer, 3... Epitaxial layer. [Effects of the Invention] As is clear from the above explanation, according to the method for suppressing doping according to the present invention, autodoping to the epitaxial layer can be sufficiently reduced, and a steep impurity concentration profile can be obtained at the shrimp interface. becomes possible. This has the effect of making it possible to manufacture devices with good characteristics. In addition, it can be easily introduced into the current process by simply adding an antimony ion implantation process and an annealing process to the conventional process. B. Work surface: 5i texture profile Figure 2

Claims (1)

[Claims] (1) A method for suppressing autodoping, characterized by including antimony (Sb) in the upper part of a buried layer containing arsenic (As) as an impurity, and growing an epitaxial layer on the buried layer.