JPS61296741A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To keep the intrusion of the bird's beak short without producing defective crystal by making the thickness of the silicon oxide film buffer layer thinner at the circumference of an active layer smaller than that at the internal section. CONSTITUTION:After the first silicon oxide film buffer layer 2 and the first silicon nitride film 3 are formed on an N-type silicon substrate 1, the first silicon nitride film 3 where a separation oxide film is to be formed is removed, and the silicon oxide film 2 is wet-etched to side-etch the first silicon nitride film, which is left in a insular-shape, from the end to the outside. The surface of the exposed silicon substrate 1 is oxidized again to form the second silicon oxide film buffer layer 4. The second cilicon nitride film 5 is deposited on the whole surface, and then only the second silicon nitride film 5 that is exposed on the flat surface is removed by anisotropy dray etching method. At this time, the silicon oxide film buffer layer is thin around the active layer and thick inside. If a separation oxide film 6 is formed approx. 1mum in this state, the intrusion of the bird's beak can be kept within 5,000Angstrom .

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to highly integrated semiconductor devices using oxide film isolation, particularly bipolar integrated circuit devices in which a relatively thick isolation oxide film of about 1 μm is formed. Relating to a manufacturing method. .

[Conventional technology]

Currently, in bipolar S-product circuits, the oxide film isolation method is widely used as an isolation means because the area required for isolation VC is smaller than that of pn junction isolation, and it is advantageous for higher integration of elements. Conventionally, the method shown in FIG. 2 has been the usual technique for forming this oxide film separation. That is, the second
As shown in FIG. 5, a silicon oxide film buffer layer 2 and a silicon nitride film 3t are formed on the main surface of a silicon substrate 1, and a silicon nitride film is formed in a region where an isolation oxide film is to be formed using a photolithography process. Remove membrane 3. Subsequently, as shown in FIG. 2 (2), oxidation is performed using the silicon nitride film 3 left in an island shape on the active region as a mask to form an isolation oxide film 6. Here, when forming the isolation oxide film 6 with a thickness of 1μ,
The thickness of the silicon nitride film 3 as a mask for oxidation should be about 300 mm thick, but it should be 1000 mm thick to prevent pinholes etc.
Usually, a film thickness of about λ is used. Furthermore, in order to relieve the stress that the silicon nitride film 3 exerts on the silicon substrate 1 during oxidation at high temperatures, the thickness of the silicon oxide film 2 is, for example, 500 mm.
Use λ.

[Problem that the invention seeks to solve]

In the conventional formation method described above, when performing separation oxidation,
It climbs onto the active area called "Bird's Beak". For example, in FIG. 2, the thickness of the silicon oxide buffer layer 2 is 500,
The thickness of the silicon nitride film 3 is 1000, and the isolation region i
When the isolation oxide film 6 is formed to have a thickness of c1μ, a bird's beak is formed from the end of the silicon nitride [3(7) to a distance of about 1μ trench toward the active region side.

The length of this bird's beak digging in depends on the formation temperature of the isolation oxide film, the thickness of the silicon oxide film buffer layer, the film thickness of the silicon nitride film, etc. In particular, the bird's beak can be reduced by making the silicon oxide film buffer layer thinner. It can be made shorter. However, simply making the buffer layer thinner does not alleviate the stress from the silicon nitride film by taking advantage of the fact that the viscosity of the silicon oxide film decreases at high temperatures, which leads to the generation of defects within the silicon substrate. It's not appropriate.

In addition, since the silicon nitride film is thinned at the same time and is defect-free, the silicon nitride film is usually formed by a vapor phase growth method that utilizes thermal decomposition, so there is a concern that pinholes may occur. As described above, it is difficult to shorten the bird's beak and promote high integration without lowering the yield of devices using the conventional method of forming an isolation oxide film.

・[Means for solving the problem] In the method for fabricating a semiconductor device of the present invention, an island-like region of a silicon nitride film selectively provided on a silicon substrate is used as a mask to form a film with a thickness of 0.5 μm or more. When performing complete oxide film insulation isolation, the thickness of the buffer layer of silicon oxide film provided between the silicon nitride film and the silicon substrate is formed so that it is thinner at the periphery of the island region than at the inside. All features.

According to this method VC, since the silicon oxide buffer layer is thinner in the peripheral region, the bird's beak that occurs directly under the edge of the silicon nitride film can be kept short. Also,
In the portion used as the internal active region, the thick silicon oxide film buffer layer sufficiently relieves the stress from the silicon nitride film, so that a thick isolation oxide film can be formed without generating crystal defects.

〔Example〕

Next, one embodiment of the present invention will be described with reference to the drawings.

Figures 1 to 1 are longitudinal sectional views for explaining the steps of an embodiment of the present invention. The main surface of the hexagonal silicon substrate 1 is oxidized to form a first silicon oxide film buffer layer 2 of about 800A, followed by depositing about 1000 layers of silicon nitride film 3 of straw 1, and then an isolation oxide film is formed. The first silicon nitride film 3 in the region is removed (FIG. 1(A)).

Next, perform wet etching of the silicon oxide film 2,
The first silicon nitride film left in the form of an island is side-etched inward from the end by approximately 5,000 steps.

The exposed surface of the silicon substrate 1 is oxidized again to about 100%
The entire second silicon oxide film buffer layer 4 is released, and a second silicon nitride film 5 is deposited to a thickness of about 300 Å over the entire surface. After this, only the second silicon nitride film 5 exposed on the flat surface is removed by anisotropic dry etching (a!1 Figure 0).
. At this time, the silicon oxide film buffer layer is thin (second silicon oxide film 4) around the active region and thick inside (first silicon oxide film 4).
The silicon oxide film 2) is in the state of 2). Therefore, if the separation oxide film 6 is shaped in this state by about 1 μm, the bite of the bird's beak can be suppressed to within 5 mm.

〔Effect of the invention〕

As explained above, in the present invention, when forming an isolation oxide film, the thickness of the non-silicon oxide buffer layer is adjusted between the silicon nitride film that masks the active region and the silicon substrate. RC machining also makes the internal edges thinner at the periphery, which creates crystal defects and has the effect of keeping the bird's beak bite short. According to the method of the present invention, since the area of unnecessary bird's beaks can be reduced, it is possible to realize a semiconductor device with a higher degree of integration using oxide film insulation isolation.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of the main manufacturing steps of an embodiment of the present invention, and FIG. 2 is a vertical cross-sectional view of the main steps of a conventional manufacturing method. DESCRIPTION OF SYMBOLS 1... N-type silicon substrate, 2... (first) silicon oxide film buffer layer, 3... (first) silicon nitride film, 4... . . . second silicon oxide film layer, 5 . . . second silicon nitride film, 6 . . . isolation oxide film. Agent Patent Attorney Susumu Uchihara 1st session

Claims (1)

[Claims] When performing oxide film insulation isolation using an island-like region of a silicon nitride film selectively provided on a silicon substrate as a mask,
Manufacture of a semiconductor device characterized in that a buffer layer of a silicon oxide film provided between a silicon nitride film and a silicon substrate is formed to be thinner at a peripheral part of the island-like region than at an inner part. Method.