JPH0132669B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a bipolar transistor.

A conventional method for manufacturing a bipolar transistor will be explained using an npn type transistor as an example with reference to FIG.

In Figure 1A, 1 is 10 ¹⁹ cm ^-3 , a high concentration of N.
First, a relatively thin concentration of N is applied to the surface of the silicon substrate 1 to serve as a collector.
A mold epitaxial layer 2 is formed to have a thickness of about 15 μm.
After forming a silicon oxide film 3 on the surface of this epitaxial layer 2, the silicon oxide film 3 in the active region (region where a transistor is to be formed) 4 is removed by etching.

Next, by diffusing P-type impurities such as boron from the portion where the silicon oxide film 3 has been removed, a P-type diffusion layer (base) 5 is formed in the epitaxial layer 2 as shown in FIG. 1B. do. In addition,
By performing the diffusion in an oxidizing atmosphere, the surface of the P-type diffusion layer 5 is covered with a silicon oxide film 6.

Next, a portion of the silicon oxide film 6 is removed to form an opening 7 as shown in FIG. 1C.
Then, by diffusing an n-type impurity such as arsenic or phosphorus through the opening 7, an n-type diffusion layer (emitter) 8 is formed in the P-type diffusion layer 5 as shown in FIG. 1C.

Finally, although not shown, the base, emitter, and collector electrodes are formed to complete the npn transistor.

In the conventional method as described above, the depth of the base and the carrier concentration are different from the concentration of the epitaxial layer 2 and p
It depends sensitively on the depth and concentration of the type and n-type diffusion layers 5 and 8. However, p-type and n-type diffusion layers 5, 8
Its depth and concentration are difficult to control accurately. Therefore, it has not been possible to obtain bipolar transistors with stable characteristics using conventional methods.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method for manufacturing a semiconductor device that can manufacture a bipolar transistor with stable characteristics.

Embodiments of the present invention will be described below with reference to FIG. 2, taking an npn type as an example.

In FIG. 2A, 11 is an N-type silicon substrate (semiconductor substrate) doped with impurities at a high concentration. First, the surface of this silicon substrate 11 is coated with a vapor phase epitaxial method, a molecular beam epitaxial method, etc. As a result, an epitaxial layer 12 containing impurities of the same conductivity type as the substrate 11 is formed. In this case, the impurities in the epitaxial layer 12 have a distribution as shown in FIG. 3A, with a high concentration on the surface of the epitaxial layer 12 and a low concentration on the substrate 11 side. This can be easily achieved in particular by molecular beam epitaxy.

Next, a silicon oxide film (first film) 13 is formed on a predetermined region of the surface of the epitaxial layer 12 as shown in FIG. 2B. This silicon oxide film 13
is formed with a sufficient thickness so that the conductivity type of the epitaxial layer 12 under the silicon oxide film 13 does not change in the subsequent ion implantation step. Thereafter, as also shown in FIG. 2B, a silicon oxide film (second film) 1 is formed on the exposed surface of the epitaxial layer 12 except for the emitter formation region 14.
form 5. This silicon oxide film 15 is formed to a thickness such that the concentration of implanted impurities reaches its maximum on the epitaxial layer 12 side slightly from the interface between the silicon oxide film 15 and the epitaxial layer 12 in the subsequent ion implantation step. It is formed with In the above, a relatively thin insulating film (silicon oxide film 15) having an opening is formed on the epitaxial layer 12,
A relatively thick insulating film (silicon oxide film 1
3) is formed.

Next, an impurity of a conductivity type opposite to that of the epitaxial layer 12, such as boron ions, is implanted at a high voltage of about 150 KeV. When this ion implantation is performed, in the emitter formation region 14 corresponding to the opening of the silicon oxide film 15, the impurity of the epitaxial layer 12 and the impurity (B: boron) caused by the ion implantation are mixed as shown in FIG. 3B. Has a concentration profile. Therefore, in the emitter formation region 14, an inversion layer 16 is formed at a predetermined depth within the epitaxial layer 12 as shown in FIG.
(second conductivity type layer) is formed. On the other hand, in the portion having the silicon oxide film 15, due to the presence of the silicon oxide film 15, the concentration of boron is maximum immediately below the silicon oxide film 15. Therefore, in the portion having the silicon oxide film 15, an inversion layer 16 (second conductivity type layer) is formed immediately below the silicon oxide film 15 and continuous with the inversion layer 16 of the predetermined depth. These inversion layers 16 serve as a base.
On the other hand, the conductivity type of the surface portion of the epitaxial layer 12 in the emitter formation region 14 does not change, and this portion (first conductivity type layer) becomes the emitter region 17.

Therefore, by completing the ion implantation, an npn type transistor having the impurity concentration profile shown in FIG. 3C, indicated by the - line in FIG. 2C, has been completed. In Figure 3C,
17' is the emitter region 17, 16' is the base region,
18 is a collector area.

If it is desired to make the surface of the emitter region 17 highly concentrated, arsenic or the like may be ion-implanted under conditions such that the inversion layer 16 under the silicon oxide film 15 is not inverted again after the boron ion implantation.

As is clear from the above embodiments, in the method of the present invention, the epitaxial layer formed on the semiconductor substrate has a predetermined impurity concentration profile, and then a bipolar transistor structure is formed by one-time ion implantation. obtain. According to this method, the depth and carrier concentration of the base (second conductivity type layer) are determined by the impurity distribution of the epitaxial layer and the ion implantation conditions, and these can be accurately controlled. Therefore, stable bipolar
It becomes possible to manufacture transistors. In addition, the thickness and concentration profile of the base (second conductivity type layer) can be freely and precisely controlled by changing the impurity concentration on the substrate side of the epitaxial layer and by changing the thickness of the high concentration area on the surface side. can be controlled.
And it has such an effect. The method of this invention can be used for manufacturing bipolar LSI. In the embodiment, an npn type bipolar transistor is explained as an example, but it goes without saying that a pnp type bipolar transistor can be manufactured in the same manner.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a conventional method for manufacturing a bipolar transistor, FIG. 2 is a sectional view showing an embodiment of the method for manufacturing a semiconductor device of the present invention, and FIG. 3 is a diagram showing an impurity concentration profile. be. DESCRIPTION OF SYMBOLS 11...Silicon substrate, 12...Epitaxial layer, 13...Silicon oxide film, 14...Emitter formation region, 15...Silicon oxide film, 16...
Inversion layer, 17...emitter region.

Claims (1)

[Claims] 1. A step of forming an epitaxial layer of a first conductivity type on a semiconductor substrate, with a low impurity concentration on the substrate side and a high impurity concentration on the surface side, and forming an opening on the epitaxial layer. The steps of forming a relatively thin insulating film having a portion and a relatively thick insulating film surrounding the relatively thin insulating film, and ion-implanting impurities of a second conductivity type from above the insulating film, A second conductivity type layer is provided on the surface of the epitaxial layer under the thin insulating film, a first conductivity type layer is provided in the opening portion up to a certain depth from the surface of the epitaxial layer;
A method for manufacturing a semiconductor device, comprising the step of forming a second conductivity type layer under the conductivity type layer.