JPS6149417A - Forming method of buried layer - Google Patents

Abstract

PURPOSE:To form a buried layer by forming a buried layer pattern of 2-layer structure of an Sb glass and an SiO2, again coating the entire surface with an SiO2 layer, heat treating it and diffusing only Sb from the glass in a semiconductor substrate. CONSTITUTION:Sb glass is rotatably coated on an Si substrate, and a CVD SiO2 layer 8 is superposed at approx. 800-850 deg.C. An Sb diffusion does not occur at this low temperature. A buried layer pattern 9 of 2-layer structure is formed by photoetching, and an SiO2 layer 4 is accumulated by a low temperature CVD method. In this case, since the end of the layer 2 is exposed but is very small area, self-addition to the peripheral region is very small. When it is then diffused at 1,200-1,250 deg.C, Sb is diffused only from the pattern 9 to form an ideal buried layer 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for forming a buried layer that prevents autotope of a dopant from entering the peripheral area.

In the process of forming a bipolar IC, a buried layer is formed in a semiconductor substrate (hereinafter simply referred to as a substrate) in order to reduce the series resistance of the collector of each semiconductor element.

Here, the buried layer consists of a semiconductor region that is of a different conductivity type than the substrate and exhibits high conductivity, and the semiconductor is epitaxially grown on this layer, and then connected to the collector region during the subsequent diffusion or implantation of dopants. is being carried out.

Each element constituting the IC needs to be completely insulated in the semiconductor region inside the substrate, and to achieve this, diffusion junction isolation or dielectric isolation is performed.

However, in the first buried layer formation process, the dopant is autodoped and spread beyond the pattern formation area, and if the buried layer is substantially enlarged as a result, the isolation between elements may not be sufficient. In some cases, a short-circuit condition occurs, which causes a decrease in yield when forming an IC.

Therefore, there is a need for a method for forming a buried layer that does not cause autodoping of dopants.

[Conventional technology]

Various methods have been put into practical use for forming the buried layer.

For example, a silicon dioxide (SI02) layer is formed on a substrate by a chemical vapor deposition method (abbreviated as CVD method) or a thermal oxidation method, and then a window is opened in the buried layer formation region using photolithography. After this process, the aperture is either implanted into the part, or a dopant-containing silicate glass (silicate glass (
There is a method in which a thin film is formed by applying silicate glass (silicate glass), and this is heat-treated to diffuse the dopant contained in the silicate glass.

In addition, we spin-code silicate glass containing dopants directly onto the substrate to create a thin film that serves as a diffusion source, pattern this using photolithography, and then thermally diffuse the impurities in the thin film and embed it. Another method is to create layers.

Comparing these methods, the latter method is the simplest in terms of process, and the method of forming a silicate glass layer on a substrate by spin coding is called the spin-on-glass method and is generally used. There is.

The present invention relates to an improvement in the method of forming a buried layer using this method.

FIGS. 2A to 2D are cross-sectional views showing a conventional buried layer forming process.

That is, after coating a gel-like dopant-added silicate glass (for example, antimony-added silicate glass, hereinafter abbreviated as sb glass) whose viscosity is adjusted using a solvent such as alcohol on the substrate 1 using a spin cord method, The solvent, binder, etc. are evaporated or decomposed by heating at a temperature of about 200°C, and as shown in Figure (A), about 15
An sb glass layer 2 having a thickness of 0.00 mm is formed.

Next, photoetching is performed using a photolithographic technique 1 to form a buried layer pattern 3 made of SB glass, as shown in FIG. 3(B).

Next, a Si02 layer 4 is formed on the entire surface of the substrate 1 on which the buried layer pattern 3 has been formed using the CVD method, and is coated as shown in FIG.
Because the temperature is as high as 850°C, the buried layer pattern 3 is removed during this process.
Antimony oxide (Sb 205', S
b 203 ) evaporates and these oxides are likely to re-deposit around the pattern, so-called autodoping.

The reason why the buried layer pattern 3 is covered with the SiOz layer 4 is that in the next dopant diffusion step, it is desired to limit the diffusion of the dopant sb only to the turn region of the buried layer.

However, as explained earlier, there is s around the buried layer pattern 3.
When b is present, in the diffusion treatment performed at 1200 to 1250°C, not only is an sb diffusion layer 6 formed in the substrate 1 where the buried layer pattern 3 is present, as shown in FIG. This also occurs in the peripheral area 7, and this causes IC failures such as insulation failure or conduction even if elements are isolated later.

[Problem that the invention seeks to solve]

As explained above, in the process of forming a buried layer on a substrate using the spin-on-glass method, an auto-doping phenomenon occurs in which dopants diffuse to the periphery of the buried layer pattern, thereby ensuring sufficient isolation between IC elements. The problem is that it is not achieved.

[Failure to solve the problem]

The above problem can be solved by sequentially forming the SB glass layer and the 5402 layer on the semiconductor substrate, performing selective processing and notching to form a two-layer buried layer pattern, and then covering the entire surface with the St 02 layer again. This problem can be solved by using a method of forming a buried layer in which the sb in the sb glass is diffused onto the semiconductor substrate by heat treatment.

[Effect]

In the present invention, dopant diffusion to the periphery of the buried layer pattern is achieved during the CVD process of coating the Si02 layer on top of the dopant.
This is caused by autodoping from the B glass layer, but we focused on the fact that the diffusion of dopants from the buried layer pattern to the substrate is negligible at this CVD processing temperature, and the Sb glass layer is on top of Si
By providing the 02 layer thinly, autodoping of the donomant is suppressed from occurring during the CVD process.

〔Example〕

FIGS. 1A to 1D are cross-sectional views showing processing steps according to the present invention.

That is, as shown in the same figure (A), approximately 15 sb glass layer 2 is deposited on the substrate 1 by the spin-on-glass method as in the conventional method.
After forming the SiO2 layer 8 to a thickness of approximately 1000 nm, a SiO2 layer 8 is subsequently formed thereon to a thickness of approximately 1000 nm using the C, VD method.

Here, the CVD processing temperature is 800 to 850°C, but at this temperature, dopant does not diffuse from the sb glass layer 2 to the substrate 1.

Next, as shown in FIG. 2B, a buried layer pattern 9 having a two-layer structure is formed using photolithography.

Since almost no heat is applied in this step, no dopant adheres to the surface of the substrate 1.

Next, as in the conventional method, a CVD method is used to form a Si 02 layer 4 as shown in FIG. 2(C).

Here, the end face of the sb glass layer 2 is exposed, but since the exposed area is minute, autodoping to the peripheral region is much less than in the past.

Next, as shown in the same figure (D), 1200 to 1
When the diffusion treatment is performed at 250° C., the dopant sb is diffused only from the buried layer pattern 9 where the sb glass layer 2 is located, and an ideal buried layer 10 can be formed.

〔Effect of the invention〕

As described above, by implementing the present invention, the buried layer pattern can be
It is possible to suppress contamination of the peripheral area due to dopants during the step of covering with the St 02 layer using the D method, and therefore it is possible to improve the yield in the buried layer forming process.

[Brief explanation of drawings]

FIGS. 1(A) to (D) are cross-sectional views showing the process of forming a buried layer according to the present invention; FIGS. 2(A) to (D) are cross-sectional views showing the process of forming a buried layer using a conventional method; It is. In the figure - 1 is the substrate, 2 is the sb glass layer, 3.9
is a buried layer pattern, 4, 8 is a SiOz layer, 5 is a s
b, 6 is the sb expansion layer, 7 is the peripheral area,
10 is a buried layer.

Claims (1)

[Claims] After sequentially forming an antimony glass layer and a silicon dioxide layer on a semiconductor substrate, selective etching is performed to form a two-layer structure diffusion source pattern, and after that, the entire surface is covered with a silicon dioxide layer, and then heat treatment is performed. A method for forming a buried layer, which comprises forming a buried layer by diffusing antimony in antimony glass into a semiconductor substrate.