JPS63153840A - Selective oxidation isolating method - Google Patents

Abstract

PURPOSE:To prevent the narrowing of the effective channel width of an MOS transistor even when the width of an active region is 1mum or less by a method wherein, after the side face of a groove and an active region have been coated with a silicon nitride film, a polycrystalline silicon layer is buried contacting to the exposed surface of a substrate on the bottom part of the groove, and said layer is oxidized. CONSTITUTION:A thermally oxided film 12 and the first silicon nitride film 13 are grown on a substrate 11, the region which becomes a field region is etched, a groove is formed in the substrate 11, and the impurities having the conductive type same as the substrate 11 are ion-implanted. Then, after the second silicon nitride film has been grown on the substrate 11, the second silicon nitride film 15 is left on the side face only of the groove by performing anisotropic etching, a polycrystalline film 16 is grown on the substrate 11, and photoresist 17 is thickly coated thereon. Then, the photoresist 17 and the polycrystalline silicon film 16 are anisotropically etched, and a flat polycrystalline silicon film 16' is left in the groove only of the substrate 11. Then, the whole surface of the substrate 11 is thermally oxided, and the polycrystalline silicon film 16' in the groove is oxided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a silicon integrated circuit, and particularly to a method for isolating elements.

[Conventional technology]

As a device isolation method in LSI manufacturing technology, the LOCO8 method is generally used, which uses a thick oxide film formed by selective oxidation using a silicon nitride film as a mask. But L
When a field region is formed using the OCO8 method, the bird's beak protrudes into the active region, which has the disadvantage that the area of the active region becomes small. It is being done. This improved LOCO8 method involves forming a thin oxide film and a first silicon nitride film on a silicon substrate, and then etching the film leaving a predetermined active region.
Furthermore, a second silicon nitride film is formed on the side surface of this remaining film to form a mask for thermal oxidation, and the intended field area is selectively oxidized.

This method will be explained below using three figures. As shown in FIG. 3(a), a silicon substrate (hereinafter simply referred to as a substrate) 3
An oxide film 32 of about 50 OA and a first silicon nitride film 32 of about 2000 OA are grown on the first silicon nitride film.

Next, as shown in FIG. 3(b), the oxide film 32. After the first silicon nitride film 33 is etched to expose the surface of the substrate 310, impurity ions having the same conductivity type as the substrate 31 are implanted. After that, the board 31
After growing a second silicon nitride film of about 50 OA on top, anisotropic etching is performed to remove the oxide film 32 in the area to be activated.
! , a second silicon nitride film is left on the side surface of the first silicon nitride film.

Since the thermal oxidation mask is formed in the area to be activated as described above, the entire surface of the substrate 31 is thermally oxidized to form a thick field oxide film (approximately 800 OA) 36 and a channel stopper layer 37 as shown in FIG. 3(e). form. The advantage of this method is that both the top and side surfaces of the thermal oxidation mask are covered with a silicon nitride film, which prevents oxidizing air from entering the active region during thermal oxidation, and prevents the bird's beak from elongating. The goal is to suppress the

Next, as shown in FIG. 3(d) K, after removing the first and second silicon nitride films 3γ and A, the thin oxide film 32' is removed to expose the substrate surface in the active region. In the case of a MOS transistor, a gate oxide film is formed.

By the way, although the above-mentioned improved LOCO8 method suppresses the extension of the bird's beak, as shown in FIG. 3 (cl), the field oxide film partially extends below the active region.

Similarly, the channel stopper layer 37 formed by the diffusion of ion-implanted impurities also invades the active region.

[Problem that the invention seeks to solve]

In the improved LOCO8 method described above, the extension of the bird's beak into the active layer region is small at approximately α3 to α4 μm;
This is often completely negligible, but as semiconductor devices become smaller, it has become a problem.
It is not applicable to semiconductor devices having a width of less than μm.

In addition, the channel stopper layer and brim layer also invade the active region, and in the case of a MOS transistor, a diffusion layer of impurities of the opposite conductivity type to the semiconductor substrate is formed in the active region, so the diffusion layer and the channel stopper layer are A large capacitance is formed between them, which prevents high-speed operation of the semiconductor device.

In addition, the second silicon nitride film of the thermal oxidation mask relies on direct contact with the semiconductor substrate to prevent the birth beak from growing large. A large stress is generated in the vicinity of the 2-silicon nitride film, which is disadvantageous in that crystal defects and breakdown voltage defects in the diffusion layer are likely to occur.

An object of the present invention is to provide a new selective oxidation separation method that eliminates the above-mentioned drawbacks.

[Means for solving problems]

The selective oxidation separation method of the present invention includes the steps of sequentially forming an oxide film and a first silicon nitride film on a silicon substrate, and etching the oxide film, the first silicon nitride film, and the substrate in a region where a field is to be formed to a predetermined depth. a step of forming a groove, a step of ion-implanting the same conductive impurity as the substrate into the substrate at the bottom of the trench, and a step of forming a sidewall made of a second silicon nitride film on the side surface of the trench; forming a polycrystalline silicon film to a predetermined depth within the groove; thermally oxidizing the entire surface of the substrate to change the polycrystalline silicon film into a field oxide film; The method includes a step of removing the second silicon nitride film, and a step of filling the void around the active region caused by the removal of the second silicon nitride film with an insulator. In general, this method involves forming a trench in a substrate in a region where a field is planned, covering the sides of the trench and the active region with a silicon nitride film, and then layering a polycrystalline silicon layer in contact with the exposed surface of the substrate at the bottom of the trench. A field oxide film is formed by burying the polycrystalline silicon layer and oxidizing the polycrystalline silicon layer.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1(a), a thin thermal oxide film (approximately 5.0 OA) 12 and a relatively thin first silicon nitride film (approximately 150 OA) 13 are grown on a substrate 11. As shown in FIG. 1st
As shown in FIG.
Form a groove of 0 μm. Thereafter, impurity ions having the same conductivity type as the substrate 11 are implanted. At this time, silicon nitride film 11 and oxide film 12 on the active region! is a mask9
, the impurity is not ion-implanted.

Next, as shown in FIG. 1(e), about 200
After growing a thin second silicon nitride film of ~400A,
The second silicon nitride film 15 is left only on the side surfaces of the groove by anisotropic etching. At this time, the convex portion forming the active region is completely covered with the silicon nitride film by the second silicon nitride film 13' and the first silicon nitride film 13' on the active region, and the bottom surface of the trench is exposed. The state will be as follows. After that, a polycrystalline silicon film 16 with a thickness of 4000 to 5000
^ grown, and a thick layer of photoresist 17 is applied thereon.

Next, as shown in FIG. 1(d), the photoresist 17 and the polycrystalline silicon film 16 are anisotropically etched. At this time, etching is performed so that the etching rates of the photoresist 17 and the polycrystalline silicon film 16 are the same, so that a flat polycrystalline silicon j#16't- is left only in the groove of the substrate 11.

Next, as shown in FIG. 1(e), by thermally oxidizing the entire surface of the substrate 11, the polycrystalline silicon film 1σ in the trench is turned into an oxide film, and at the same time, a part of the bottom surface of the trench is also oxidized. At this time, a polycrystalline silicon film 16 with a thickness of 4000 to 5000 A is formed.
′ becomes an oxide film, the groove is filled with the oxide film. Since the second silicon nitride film 15 exists on the side surfaces of the trench, it is obvious that the thermal oxide film will largely invade into the active region. Further, through this heat treatment, a channel stopper layer 19 having the same conductivity type as the substrate 11 is formed.

Next, as shown in Fig. 1(f), hot phosphoric acid was added.
After the first and second silicon nitride films 13' and 15 are removed by etching, heat is applied again to fill the narrow at area created by removing the second silicon nitride film 15, as shown in Figure 1 (pupil). Depending on the oxidation process, the surface of the substrate on the side surfaces of the groove is formed into a thermal oxide film, and the groove is filled by the volume expansion. Since oxidation separation is performed above, in the case of a MOS transistor, the first
As shown in Figure (h), the thin thermal oxide film 2o on the active region is removed using buffered hydrofluoric acid, and a new gate oxide film 21 is formed.

In the above embodiment, as shown in FIG. 1(g), the defects created by removing the second silicon nitride 1115 on the side surfaces of the active region are filled by thermal oxidation. However, it may be filled in another way. Next, another method will be explained with reference to FIG.

After the process of FIG. 1 (fl) is completed, as shown in FIG. 2 (al), a 7Lica film n is applied and formed on the surface of the substrate 11, and the second silicon nitride film 15 is removed. The resulting narrow grooves are filled and heat treated to solidify.Next, as shown in Figure 2 (bl), the silica film A22 and thin silver oxide film on the active area are removed using buffered hydrofluoric acid. Then, a new gate oxide film 21 is formed.

〔Effect of the invention〕

As explained above, when a field region on a semiconductor substrate is formed by the method of the present invention,
Since the field oxide film does not invade into the active region, the effective channel width of a MOS transistor, for example, will not be narrowed even when the width of the active region is 1 μm or less.

In the case of a MOS transistor, the channel stopper layer exists in a region approximately 1 μm deeper than the surface of the semiconductor substrate where the diffusion layer is formed, so it does not come into direct contact with the diffusion layer. Therefore, the capacitance of the diffusion layer is reduced, which is advantageous for high-speed operation of the semiconductor device.

Further, whether the field region has a large area or a small area, it is possible to bury the oxide film into the groove of the field region using the same method. Furthermore, by oxidizing the polycrystalline silicon film in the trench, there is less stress on the field oxide film, the first and second silicon nitride films for oxidation prevention, and crystal defects and breakdown voltage failures of the diffusion layer can occur. It has the effect of being difficult.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing embodiments of the present invention in the order of steps;
FIG. 3 is a diagram showing a conventional example in the order of steps. 11...Silicon substrate, 12.12! ···Oxide film,
13, 13'...first silicon nitride film, 14...
Ion implantation impurity, 15... Second silicon nitride film, 16, 16'... Polycrystalline silicon film, 17... Photoresist, 18... Field oxide layer, 19...
Channel stopper layer, additive... oxide film, 21... gate oxide film, n... silica film film.

Claims (1)

[Claims] a step of sequentially forming an oxide film and a first silicon nitride film on a silicon substrate; a step of etching the oxide film, the first silicon nitride film and the substrate in the intended field area to a predetermined depth to form a groove; A step of ion-implanting an impurity of the same conductivity type as that of the substrate into the substrate at the bottom of the trench, a step of forming a sidewall made of a second silicon nitride film on the side surface of the trench, and a step of ion-implanting an impurity of the same conductivity type as the substrate into the substrate at a predetermined depth within the trench. a step of forming a crystalline silicon film; a step of thermally oxidizing the entire surface of the substrate to change the polycrystalline silicon film into a field oxide film; a step of removing the first and second silicon nitride films; 1. A selective oxidation isolation method for a semiconductor device, comprising the step of filling in defects around an active region caused by removing a nitride film with an insulator.