JPS598349A - Fabrication of semiconductor device - Google Patents

Abstract

PURPOSE:To realize element isolation without bird beak by leaving a second silicon nitride film under the penthouse consisting of a first silicon nitride film and then oxidating it. CONSTITUTION:An SiO2 film 202 and an Si3N4 film 203 are formed on an Si substrate 201 and a window is opened thereon. At this time, a penthouse part is formed on the Si3N4 film by over-etching the SiO2 film 202. A second Si3N4 film 204 is formed on the entire surface of substrate by the plasma vapor growth method. Thereafter, a part 205 of the second Si3N4 film is left only at the area under the penthouse part of the first Si3N4 film 203 by etching the entire part of second Si3N4 film through the etching method having directivity. Then, a field oxide film 206 is formed under the ordinary steam ambient. Thereby, generation of bird beak can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention e relates to a method of manufacturing a semiconductor device, and in particular relates to an element isolation method for completely isolating the elements in a semiconductor substrate. In order to keep all the active elements electrically independent, it is necessary to provide isolation regions between the elements. For example, M using a silicon substrate
In the OS type integrated circuit device W, isolation between the active elements is achieved by providing a silicon oxide film with a thickness of about 1μ between the active elements. Conventionally, this thick silicon oxide film 11! j! In order to selectively form VC between elements, a silicon nitride film is selectively left on the silicon substrate, and the silicon nitride film is used as a mask to completely oxidize the silicon substrate, forming a thick but open field oxide film between the elements. was. At this time, in order to form a thick field oxide film, thermal oxidation is required at a high temperature of around 1000°C for a long time, so if the silicon nitride film is directly deposited on the silicon substrate, the silicon Due to differences in thermal expansion coefficients of the nitride films, strain is introduced into the silicon substrate, deteriorating the characteristics of elements to be formed later. In order to avoid this phenomenon, a method is generally used in which a thin silicon oxide film of several hundred to 1000 Å is interposed between the silicon substrate and the silicon nitride film to alleviate the strain.

This method certainly makes it possible to reduce distortion during thermal oxidation and to minimize the deterioration of device characteristics. As the particles diffuse through the silicon oxide film, a so-called bird's beak problem arises in which the edge of the field oxide film for isolation between particles gets under the silicon nitride film. When this bird's beak occurs, the width of the field conversion film becomes wider by the width thereof, which has been a major obstacle to improving the #1 degree in which the area in which the element is formed is narrow.

Conventionally, in order to suppress the occurrence of bird's beaks, a thin silicon oxide film or silicon nitride film was first selectively formed, and therefore a silicon nitride film was formed over the entire surface, and then a directional dry etching method such as reactive ion etching was used. The entire surface is etched, and at the end of the thin silicon oxide film and silicon nitride film that were originally formed, there is a newly formed silicon nitride film step. There is a method of suppressing the occurrence of bird's beak using this remaining silicon nitride film.

However, in this conventional method, it is very difficult to set the conditions for etching the entire surface, and it is extremely difficult to suppress bird's beak with good reproducibility.Therefore, the object of the present invention is to eliminate the above-mentioned problems in the generation of bird's beak. The object of the present invention is to provide a method for isolating elements without any problems.

In the present invention, in the thin silicon oxide film and silicon nitride film that are selectively formed, the silicon nitride film extends outward from the lower thin silicon oxide film in a canopy state, and the next silicon nitride film is grown. Based on the knowledge that by performing plasma vapor phase epitaxy or low pressure vapor phase epitaxy, it is possible to reproducibly leave a second silicon nitride film under the eaves of the selectively formed silicon nitride film. <.
1. According to the method of the present invention, the second silicon nitride film crawls under the eaves of the first silicon nitride film.
Even if over-etched during etching, the thin silicon oxide film and the edge of the first silicon nitride film are formed selectively, remaining reliably because they penetrate under the silicon nitride film of skin 1 and with good reproducibility. Therefore, there is a great advantage that the occurrence of bird's beak can be suppressed with good reproducibility.

Next, in order to better understand the present invention, the present invention will be explained using drawings.

Figures 1(a) and 1(b) are cross-sectional views for explaining a conventional device isolation method called selective oxidation method.
As shown in FIG. 1(a) VC, a thin silicon oxide film 102 and a silicon nitride film 101 are formed on a silicon substrate 101. Next, as shown in FIG. 1(b), the silicon oxide film 1
01. Using the silicon nitride film 102' as a mask, the silicon substrate is oxidized for a long time at a high temperature of around 1000° C., usually in a steam nitrogen atmosphere, to form a field silicon oxide film 101 with a thickness of 1 μm.0 In this conventional method, In this case, hydroxide and oxygen, which are oxidizing factors of the field oxide film 104, cause the edge IW1 of the silicon oxide film 102 and the silicon nitride film 103 to
05 into the silicon oxide film 102, the field oxide film 104 spreads laterally from the edge 105 of the silicon oxide film 102 and the silicon nitride film 103, and the field oxide film 104 spreads by this amount into the silicon nitride film 103. A big problem arises in that the area covered by the silicon nitride film 103Vc becomes smaller and the element is formed in the area covered by the silicon nitride film 103Vc, resulting in no improvement in the degree of integration. As the rules for setting up ICs become more and more minute, it has become an extremely important issue.

FIGS. 2(a) to 2(d) are cross-sectional views for explaining the device isolation method of the present invention. First, as shown in Figure 2(a),
A thin silicon oxide film 202 and a first silicon nitride film 203tl- are selectively formed on a silicon substrate 201. At this time, the silicon oxide film 202 is replaced by the silicon nitride film 20.
3 as a mask, and by slightly over-etching the silicon oxide film 202, the edge of the silicon nitride film 203 is set back so that the entire silicon nitride film 203 overhangs.

Typically, if the silicon oxide film 202 is 100 OA and the silicon oxide film 203 is 15 UUA, the length of this overhang portion may be around 0.2 μ. This 0.2 μm workability is achieved by etching a silicone film using an etching solution containing hydrofluoric acid, which is a well-known technique, and is a result of good precision.

Thereafter, as shown in FIG. 2(b)K, a second silicon nitride film 204 is formed on the entire surface of the silicon substrate by plasma vapor deposition or U reduced pressure vapor deposition. This second
When the silicon nitride film 204 is grown by low-pressure vapor phase growth or plasma vapor phase growth, it wraps well under the first silicon nitride film. As shown in Figure 2 (c) K,
When the entire surface of the second silicon nitride film 204 is etched using a directional etching method such as reactive ion etching, the overhead W, 2 exposed to the flying etching gas is etched.
When conditions are set such that the silicon nitride film 204 is etched away, the second silicon nitride film 204 is etched only under the overhang of the first silicon nitride film 203.
A portion 205 of the first silicon magnetized film 20 is left behind.
It is very easy to leave a part 205 of the second silicon nitride film under 4 because the first silicon nitride film 204 serves as an etching mask.
Even if sufficient consideration is given to etching only the unnecessary portion of the silicon nitride film 204, the silicon nitride film 205 is left stably and with good reproducibility. Then (d) in Figure 2
A field oxide film 206 having a thickness of about 1 μm is formed at a temperature of about 1000° C. in a normal steam atmosphere. At this time, a portion 20 of the second silicon nitride film is placed between the field oxide film 206 and the thin silicon oxide M2O2.
5 exists, the oxidizing factor does not diffuse into the silicon oxide film 202 during the oxidation for forming the field oxide film 206, and therefore the field oxide film 206 stops at the silicon nitride film 205 at the end. Bird's beak rarely occurs.

The uninvented element isolation method has the advantage that the degree of integration can be greatly improved because bird's beak hardly occurs. Furthermore, according to the method of the present invention, the silicon nitride film 205
Since Vi has entered the eaves of the silicon nitride film 203, even if the silicon nitride film 204 is etched over the entire surface using a directional etching method such as a reactive etching method, it will not remain with good reproducibility. C,
It also has the great advantage of very little variation between samples.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are cross-sectional views for explaining a conventional semiconductor device manufacturing method step by step, and FIGS.
1) is a cross-sectional view for explaining the semiconductor device and manufacturing method of the present invention. In the figure, 101.201... silicon substrate, 102, 104, 202, 206... oxide film, 103.203, 204, 205 silicon nitride film, 105 silicon This is the edge of the nitride film. (3) ~ /θ5 (α) Key diagram

Claims (1)

[Claims] A step of forming the entire silicon oxide film on the silicon substrate, a step of forming a first silicon nitride film on the silicon oxide film, and a step of forming the first silicon nitride film and the silicon oxide film in the same pattern. a step of etching the silicon oxide film overly;
Next, a step of growing a second silicon nitride film, a step of etching the entire second silicon nitride film by a directional etching method, and selectively oxidizing the silicon substrate by thermal oxidation after the etching step. With the process? Method 0 of manufacturing a semiconductor device characterized by including