JPS6129538B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for forming a buried layer of a semiconductor device.

Hereinafter, a method for forming a buried layer of a bipolar integrated circuit will be described as an example.

FIGS. 1a to 1c are cross-sectional views showing each formation step of a conventional method for forming a buried layer.

First, an insulating film 2 is formed on the main surface of a P-type silicon substrate 1.
form. Next, the insulating film 2 is selectively etched to form an impurity diffusion window 3. Next, on the insulating film 2 including the main surface of the P-type silicon substrate 1 exposed in the window 3, an antimony compound mainly composed of a silicon compound is suspended in an organic solvent using a centrifugal rotary coater. A coating film 4 is formed by applying a solution [such as OCD solution manufactured by Tokyo Ohka Kogyo Co., Ltd.] [FIG. 1a]. Thereafter, when the P-type silicon substrate 1 is subjected to high-temperature heat treatment, ^an N-type diffusion layer 5 is formed on the main surface of the P-type silicon substrate 1 within the window 3 [FIG. 1b]. Next, after removing the insulating film 2 and coating film 4 from the main surface of the P-type silicon ^substrate 1,
When the N type semiconductor layer 6 is formed on the P type diffusion layer 5 and the main surface of the P type silicon substrate 1, the N ⁺ type diffusion layer 5 is formed.
A buried layer 7 consisting of the following is formed (FIG. 1c).

By the way, in the method for forming the buried layer 7 described above, since the adhesion between the coating film 4 and the main surface of the P-type silicon substrate 1 is poor, a layer is formed uniformly on the main surface of the P-type silicon substrate 1 within the window 3. It was not easy to form a coating film 4 that adhered to the surface. For this reason, there was a drawback that the thickness of the buried layer 7 could not be formed uniformly. In order to solve this drawback, a method is used in which an oxide film having good adhesion to the coating film 4 is previously formed on the main surface of the P-type silicon substrate 1 exposed within the window 3.

FIGS. 2a to 2c are cross-sectional views showing each formation step of the method for forming a buried layer according to this prior art.

First, an oxide film 8 having a thickness of, for example, about 0.03 microns is formed on the main surface of the P-type silicon substrate 1 exposed within the window 3 of the insulating film 2 formed on the main surface of the P-type silicon substrate 1. [Figure 2a]. Next, after forming the coating film 4 on the insulating film 2 including on the oxide film 8, the P-type silicon substrate 1 is subjected to high-temperature heat treatment. ⁺
A shaped diffusion layer 5a is formed (FIG. 2b). Thereafter, the insulating film 2, coating film 4, and oxide film 8 are removed from the main surface of the P-type silicon substrate 1 and the N ⁺ type diffusion layer 5a, and the main surface of the P-type silicon substrate 1 is removed. An N type semiconductor layer 6 is formed on top and on the N ⁺ type diffusion layer 5a. A buried layer 7a consisting of an N ⁺ type diffusion layer 5a is formed [FIG. 2c].

In such a method of forming the buried layer 7a according to the prior art, since the adhesion between the coating film 4 and the oxide film 8 is good, the coating film 4 can be formed on the oxide film 8 in uniform adhesion thereto. For this reason, it becomes possible to form the buried layer 7a with a uniform layer thickness, but it is also possible to form the buried layer ^7a with a uniform layer thickness. At the stage shown in FIG. 1B, the N-type impurities in the coating film 4 diffuse into the main surface of the P-type silicon substrate 1 through the oxide film 8, so that the sheet resistance of the buried layer 7a is reduced by the conventional method shown in FIG. There was a new drawback that the sheet resistance was approximately 30% higher than the sheet resistance of the formed buried layer 7, and its function as a buried layer was inhibited.

This invention was made in view of the above-mentioned drawbacks, and in order to improve the adhesion with a coating film containing impurities, ions are implanted into an oxide film formed on the main surface of a semiconductor substrate. A substrate of impurities for forming the buried layer is formed by forming the coating film thereon and heat-treating these to diffuse the impurity through the oxide film to the main surface of the semiconductor substrate to form a buried layer. It is an object of the present invention to provide a method for forming a buried layer of a semiconductor device, which can facilitate diffusion into the semiconductor device and obtain a buried layer having a uniform layer thickness and low sheet resistance.

3a to 3c are cross-sectional views showing each formation step of a method for forming a buried layer according to an embodiment of the present invention.

First, as in the step shown in FIG. 2A, an oxide film 8 having a thickness of about 0.03 microns is formed on the main surface of the P-type silicon substrate 1 within the window 3 of the insulating film 2. Next, N-type impurity ions such as arsenic ions and antimony ions are implanted into the oxide film 8 from the direction of arrow I in the figure (FIG. 3a). At this time, the implantation energy of the N-type impurity ions is set to about 50 Kev or more, and the implantation amount is set to about 2×10 ¹⁴ ions/cm ³ .

After that, on the insulating film 2 including the oxide film 8,
Using a centrifugal rotary coating machine, a coating film 4 similar to that described in the step of FIG. 1a is formed. Next, when the P-type silicon substrate 1 is subjected to high-temperature heat treatment, an N ⁺ type diffusion layer 5 is formed on the main surface of the P-type silicon substrate 1 within the window 3.
b is formed [Fig. 3b]. Next, the insulating film 2, coating film 4, and oxide film 8 on the main surface of the P-type silicon substrate 1 and the N ⁺ type diffusion layer 5b are removed, and the main surface of the P-type silicon substrate 1 is removed. When the N type semiconductor layer 6 is formed on the N ⁺ type diffusion layer 5b, a buried layer 7b made of the N ⁺ type diffusion layer 5b is formed.
is formed [Fig. 3c].

In this way, in the method for forming the buried layer 7b of this embodiment, the adhesion between the coating film 4 and the oxide film 8 is good, so that the coating film 4 is formed on the oxide film 8 in uniform contact with the oxide film 8.
, and the thickness of the buried layer 7b can be made uniform. Moreover, the oxide film 8
By implanting impurity ions into the silicon substrate 1, the N ^- type impurities contained in the coating film 4 are implanted into the main layer of the P-type silicon substrate 1 through the oxide film 8 at the stage of forming the N + type diffusion layer 5b in FIG. 3b. Since it becomes easier to diffuse to the surface, the sheet resistance of the buried layer 7b is approximately equal to the sheet resistance of the buried layer 7 shown in FIG. It can be made to the same extent. In addition, this ion implantation is not performed by directly implanting N-type impurity ions such as arsenic ions and antimony ions to form a buried layer on the main surface of the P-type silicon substrate, but by implanting them through the oxide film 8 as described above. The implanted ions may be ions of boron, argon, etc., since the purpose is to facilitate the diffusion of
The amount of implantation is about 10 ¹⁴ ions/cm ³ , and the time required for implanting the impurity ions is short, making it easy to form a buried layer with a high concentration of antimony, which has been difficult to form in the past. can be formed into

In the above embodiments, a P-type silicon substrate has been described, but the present invention can also be applied to an N-type silicon substrate.

Further, although the method for forming a buried layer of a bipolar integrated circuit device has been described so far, the present invention is not limited to this, and can be applied to methods of forming a buried layer of other semiconductor devices.

As described above in detail, according to the method of the present invention, the semiconductor substrate exposed within the window of the insulating film formed on the main surface of the first conductivity type semiconductor substrate and having an impurity diffusion window. After forming an oxide film on the main surface and implanting ions into this oxide film, a coating film containing impurities of the second conductivity type is formed on the insulating film including on the oxide film, and Since the buried layer is formed by thermal diffusion of impurities contained in the film to the main surface of the semiconductor substrate through the oxide film, the adhesion between the coating film and the oxide film is good. By implanting ions into the oxide film, it is possible to form the coating film on the oxide film, which is in uniform contact with the oxide film, and to make the thickness of the buried layer uniform. Since thermal diffusion of impurities contained in the coating film to the main surface of the semiconductor substrate through the oxide film becomes easy, the sheet resistance of the buried layer can be lowered.

[Brief explanation of the drawing]

Figures 1a to 1c are cross-sectional views showing each formation step of a conventional method for forming a buried layer, and Figures 2a to 2c are
3A to 3C are cross-sectional views showing each formation step of a buried layer formation method according to the prior art, and FIGS. 3A to 3C are cross-sectional views showing each formation step of a buried layer formation method according to an embodiment of the present invention. In the figure, 1 is a P-type (first conductivity type) silicon substrate, 2 is an insulating film, 3 is an impurity diffusion window, 4 is a coating film, and 5, 5a, and 5b are N-type (second conductivity type) diffusion layers, respectively. , 6 are N-type semiconductor layers, 7 and 7b are buried layers, and 8 is an oxide film. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A first step of forming an insulating film having an impurity diffusion window on the main surface of a semiconductor substrate of a first conductivity type, forming an oxide film on the main surface of the semiconductor substrate exposed in the impurity diffusion window. a second step of implanting ions into the oxide film, and a third step of forming a coating film containing an impurity of a second conductivity type on the insulating film including on the oxide film; After completing the process, the semiconductor substrate is subjected to high temperature heat treatment to diffuse impurities contained in the coating film through the oxide film to the main surface of the semiconductor substrate within the window to form a second conductivity type diffusion layer. a fourth step of removing the insulating film, the coating film, and the oxide film from the main surface of the semiconductor substrate and the diffusion layer; A method for forming a buried layer of a semiconductor device, comprising a fifth step of forming a second conductivity type semiconductor layer thereon.