JP2563798B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to an element isolation method.

[Conventional technology]

A conventional element isolation method for a semiconductor device is shown in FIG.
This will be described with reference to (f). First, as shown in FIG. 2A, an oxide film 2 is formed on a semiconductor substrate of the first conductivity type, and then a nitride film 3 is formed. Next, as shown in FIG. 2B, unnecessary portions of the nitride film 3 are removed by photolithography. Next, as shown in FIG. 2C, the same conductivity type impurities as those of the semiconductor substrate are ion-implanted. After that, thermal oxidation is performed, and as shown in FIG. 2D, the element isolation oxide film 4 is formed on the portion where the nitride film is removed.
To form. At this time, the oxide film 4 of the semiconductor substrate 1
The impurity concentration near the interface with and becomes higher than the substrate impurity concentration of the semiconductor substrate 1. This portion becomes a so-called channel stopper. Next, FIG. 2 (e)
As described above, the oxide film 2 and the nitride film 3 are removed. Next, an oxide film 6 is formed by thermal oxidation, and then a polycrystalline silicon film 7 is formed. Then, an unnecessary polycrystalline silicon film is removed by photolithography to remove the mos transistor as shown in FIG. 2 (f). To form.

[Problems to be solved by the invention]

However, when the element isolation oxide film 4 is formed in the above-mentioned conventional technique, since the oxidation is performed at a high temperature for a long time, impurities in the channel stopper region 5 are mo as shown in FIG.
There is a problem in that the so-called narrow channel effect occurs that the threshold voltage of the mos type transistor is changed by diffusing to the vicinity of the surface of the active region of the s type transistor.

Therefore, the present invention solves such a problem,
The purpose is to prevent impurities in the channel stopper region from diffusing to the vicinity of the surface of the active region of the mos transistor even if the channel stopper is formed.

[Means for solving problems]

The method of manufacturing a semiconductor device according to the present invention includes (a) a step of implanting an impurity of the same conductivity type as that of the substrate into the semiconductor substrate, (b)
Forming a first oxide film on the semiconductor substrate,
(C) a step of forming a silicon nitride film on the first oxide film, (d) a step of removing a part of the silicon nitride film, and (e) a part for element isolation in the part where the silicon nitride film is removed. A step of forming a silicon oxide film, (f) a step of removing the silicon nitride film not removed in the step (d) and the step of removing the first oxide film, and (g) a mos on the active region.
A method of manufacturing a semiconductor device, comprising the step of forming a transistor, wherein in the step (a) of implanting the impurities, the impurities are separated into a silicon oxide film for element isolation and the semiconductor substrate in an element isolation region. It is characterized in that it is carried out under a predetermined condition of being located at the interface and at a depth where it does not diffuse to the vicinity of the surface of the active region in the active region.

〔Example〕

An embodiment according to the present invention will be described in detail with reference to FIGS. First, as shown in FIG. 1A, an impurity of the same conductivity type as the semiconductor substrate, for example, boron is ion-implanted into a semiconductor substrate of the first conductivity type, for example, a P-type silicon substrate, by ion implantation to reach 1 × 10 ¹¹ cm ⁻² to 1 ×. Implanting is performed with energy so that the impurity peak is 0.2 μm to 1 μm at a dose amount of 10 ¹⁴ cm ⁻² . Then, annealing is performed at a temperature of 800 ° C. to 1000 ° C. to activate the ion-implanted boron. Next, as shown in FIG. 1 (b), the silicon oxide film 2 is removed by thermal oxidation.
After forming 0Å to 1000Å, the silicon nitride film 3 is formed to 50 by CVD method.
0Å ~ 2000Å form. Next, as shown in FIG. 1C, the unnecessary portion of the silicon nitride film 3 is removed by photolithography. Next, thermal oxidation is performed to form a device isolation silicon oxide film 4 at 5000Å to 20000Å in the portion where the silicon nitride film is removed as shown in FIG. 1 (d). After that, Fig. 1 (e)
Like the silicon oxide film 2 and the silicon nitride film 3
Is removed. Next, as shown in Fig. 1 (f), 10
A silicon oxide film 6 of 0Å to 1000Å is formed, and then a polycrystalline silicon film 7 of 1000Å to 5000Å is formed by a CVD method, and then an unnecessary polycrystalline silicon film is removed by a photolithography method. A mos transistor is formed as in f).

〔The invention's effect〕

As described above, according to the present invention, the portion having a high impurity concentration that serves as a channel stopper is near the interface between the element isolation oxide film and the semiconductor substrate in the element isolation region, and deep in the semiconductor substrate in the active region of the mos transistor. This impurity does not diffuse up to near the surface of the active region. Therefore, the narrow channel effect of the mos transistor does not occur while having the effect of the conventional channel stopper.

[Brief description of drawings]

1 (a) to 1 (f) are sectional views of a semiconductor device according to an embodiment of the present invention, and FIG. 2 (a) to 2 (f) are sectional views of a semiconductor device according to a conventional method. 1 ... Semiconductor substrate 2 ... Oxide film 3 ... Nitride film 4 ... Element isolation oxide film 5 ... Channel stopper region 6 ... Gate oxide film 7 ... Gate electrode

Claims (1)

(57) [Claims] 1. A process of implanting an impurity of the same conductivity type as that of a substrate into a semiconductor substrate, a process of forming a first oxide film on the semiconductor substrate, and a process of forming the first oxide film. A step of forming a silicon nitride film on the film, (d) a step of removing a part of the silicon nitride film, (e) a step of forming a silicon oxide film for element isolation in the part where the silicon nitride film is removed, (F) a silicon nitride film not removed in the step (d) and a step of removing the first oxide film; (g) a step of forming a mos transistor on the active region; In the step (a) of implanting the impurities, the impurities are located at the interface between the silicon oxide film for element isolation and the semiconductor substrate in the element isolation region, and in the active region the active region. Spread near the surface Method of manufacturing a semiconductor device characterized in that it is carried out under predetermined conditions to be located at a depth that does not.