JPS6325700B2 - - 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 diffusion method that does not involve undesired diffusion through an oxide diffusion mask.

In the manufacture of semiconductor devices, a process of selectively diffusing impurities by coating an oxide diffusion mask with a glass film containing impurities to be diffused is often used. Referring to FIG. 1, 1 is a silicon substrate, 2
is a diffusion mask of silicon oxide film, 3 is a glass film containing impurities, and this glass film 3 is
It can be formed by a vapor phase growth method, a spin coating method, etc., and can be applied to a wide range of impurities such as phosphorus, boron, arsenic, and antimony, and is particularly convenient for diffusing antimony and arsenic.

During the diffusion from the glass film containing impurities, a crystallized region generally called a rosette appears, and when this rosette occurs in the diffusion mask 2 outside the diffusion region, a penetration phenomenon occurs and the target It has been found that an undesired diffusion region 5 is formed in addition to the diffusion layer 4.

On the other hand, when this rosette occurs in the diffusion region, it remains as a residue because the etching rate is extremely slow when the glass 3 is removed. Particularly when such a diffusion method is applied to buried diffusion, this rosette causes isolation failure and epitaxial layer defects.

By the way, in diffusion using the glass film 3, as a result of the glass film 3 being relatively thickly attached around the diffusion window, the amount of impurities in this area is larger than in other flat areas, and therefore the diffusion result is It is also known that the diffusion shape shown in FIG. 1 is obtained. This is because the glass film thickness used depends on the specific resistance in the diffusion region, and cannot be avoided in practice.

Therefore, if the diffusion window is large to some extent, the first
The undesirable diffusion shown in the figure will occur, and if the diffusion window is small and the glass film thickness can be considered to be approximately constant, diffusion with a uniform depth can be achieved.

In view of the above problems, the present invention aims, firstly, to provide a diffusion method that prevents undesired diffusion due to rosettes, and secondly, to provide a diffusion method that can make the diffusion depth uniform. The purpose is to provide a method.

Therefore, in the present invention, a glass film whose upper part is covered with the first protective film and which contains impurities inside is provided on the desired diffusion region on the surface of the semiconductor substrate, and the surface of the semiconductor substrate which is not covered with the glass film is This method of manufacturing a semiconductor device includes the step of providing a second protective film containing no impurities only in the first protective film, and performing diffusion after removing the first protective film.

The present invention will be described in detail below with reference to embodiments shown in the drawings.

Figures 2 to 5 are drawings showing the first embodiment, and as shown in Figure 2, the specific resistance is 10 to 20 Ωcm.
An antimony glass film 6 is formed on the surface of a P-type silicon substrate 1 by spin coating. Silicate glass film 6 containing approximately 2000 Å of antimony through annealing treatment
get.

Next, a silicon nitride film 7 with a thickness of 1000 Å is deposited on the surface, and after a photo process, the silicon nitride film is plasma etched to leave it only in the diffusion region, and the glass film 6 is further plasma etched using the silicon nitride film 7 as a mask. (See Figure 3).

In the process shown in FIG. 4, thermal oxidation is carried out to form an oxide film 8 of 1500 Å on the exposed surface of the silicon using water at 900° C. for 45 minutes and water at 100° C. or dry oxygen at 1150° C. for 45 minutes.

In the step shown in FIG. 5, the nitride film 7 is removed using hot phosphoric acid. At this time, the oxide film 8 is etched by about 500 Å. In this state, diffusion is performed at 1250°C for 75 minutes. The diffusion atmosphere has an oxygen partial pressure of 20%. As a result, the antimony diffusion layer 9 has a uniform depth and a surface resistance of 20Ω/□.

Finally, only the glass film 6 needs to be removed. There is no need for subsequent heat treatment, and the diffusion can be completed only with the glass film 6 attached. At the time of this diffusion, if the oxide film 8 has a thickness of 1000 Å or more, it has a practically sufficient masking effect, so the oxide film 8 may substantially have a thickness of 1000 Å or more.

Note that the oxygen partial pressure during diffusion is an important factor in increasing the surface concentration of the diffusion layer 9, and in experiments, the surface resistance obtained when the oxygen partial pressure is 0% is 40Ω/□.
Even if the oxygen partial pressure is 40% or more, the surface resistance can be reduced to 16Ω/□ under the same diffusion conditions, and at 20% oxygen partial pressure, it can be reduced to 20Ω/□. In this sense, it is effective to reduce the surface concentration by making sure that there is no oxygen barrier on the glass film 6, as shown in FIG. 5, during the diffusion.
In the case of the diffusion method shown in this embodiment, rosettes outside the diffusion region can be completely eliminated.

In the above embodiment, the oxide film 8 was formed by thermal oxidation of the silicon substrate;
However, the formation method is not limited to the above-mentioned thermal oxidation. That is, after patterning only the glass film 6, a silicon oxide film containing no impurities is deposited using the same resist used for this pattern and lifted off, thereby covering the exposed surface of the silicon that is not covered with the glass film 6. wear it. In this case, if a silicon oxide film containing no impurities is superimposed on the glass film 6, there is a problem that cracks will occur during the diffusion process due to the difference in coefficient of thermal expansion. The most suitable material for covering the exposed surface of silicon is a silicon oxide film, but the material is not limited to this, and silicon oxynitride, silicon nitride, etc. can also be used.

The embodiment shown in FIGS. 6 and 7 shows a method for manufacturing a semiconductor device that can also prevent rosettes in the diffusion region, and as shown in FIG.
Polycrystalline silicon 10 is grown on the surface to a thickness of about 1000 Å. This may be a single crystal. In this case, the surface can be cleaned and free of impurities that form the core of the rosette.

After that, a glass film 11 containing impurities is formed,
Subsequently, an oxidation-resistant film 7 is formed, and both are etched into a desired pattern.

Here, thermal oxidation is performed to convert exposed polycrystalline silicon 10 into silicon oxide film 8.

Thereafter, the oxidation-resistant film 7 is removed, impurities are diffused into a desired region through the polycrystalline silicon 10, and finally the entire surface of the glass film 11 is removed by etching, and the polycrystalline silicon 10 that appears is removed by oxidation.

In this way rosettes within the diffusion region can also be prevented.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a silicon substrate obtained by a conventional diffusion method, and FIGS. 2 to 5 are cross-sectional views of a silicon substrate showing a semiconductor manufacturing process according to a first embodiment of the present invention. 6 and 7 are cross-sectional views of a silicon substrate showing a semiconductor manufacturing process according to a second embodiment of the present invention. In the figure, 1 is a P-type silicon substrate, 6 and 11 are impurity-containing glass films, 7 is an oxidation-resistant film, 8 is a silicon oxide film, 9 is a diffusion region, and 10 is polycrystalline silicon.

Claims (1)

[Claims] 1. A glass film whose upper part is covered with a first protective film and which contains an impurity is provided on the desired diffusion region on the surface of the semiconductor substrate, and the impurity is contained only on the surface of the semiconductor substrate that is not covered with the glass film. 1. A method of manufacturing a semiconductor device, comprising the steps of: providing a second protective film that does not contain a carbonaceous material; and performing diffusion after removing the first protective film.