JPS62261142A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To prevent the yield of roughness in a silicon substrate in a process for removing a silicon nitride film, by isolating the frame of the silicon nitride and the silicon substrate by an silicon oxide film, which intrudes into a part beneath the frame of the silicon nitride film. CONSTITUTION:On the surface of a silicon substrate 1, a protecting silicon oxide film 2 and a first silicon nitride film 3 are sequentially laminated. Then a hole 4 for isolating an element region is formed. On the bottom and side surfaces of the hole 4 and the entire surface of the first silicon nitride film 3, a second silicon film 5 is formed. Thereafter, the second silicon nitride film 5 at the bottom surface of the hole 4 is removed. Then, a isolating silicon nitride film 6 is formed on the silicon substrate 1, which is exposed at the bottom surface of the hole 4. Thereafter, the first and second silicon nitride films 3 and 5 are removed. A frame 7 of the silicon nitride film is made to remain around the hole 4. At this time, the final point of plasma etching is detected by the change in intensity of the nitrogen spectrum. Then, a silicon oxide film is added on the entire surface of the silicon substrate by thermal oxidation. An isolating thermal silicon oxide film 8 is made to intrude into a part beneath the frame 7 of the silicon nitride film. Thereafter the frame of the silicon nitride film is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device having an element isolation region.

(Prior Art) Conventionally, the LOCO8 method has been used as an i-element isolation technique in the manufacturing process of semiconductor integrated circuit devices, particularly MO3 type LSIs. However, in the normal LOCO8 method, there is an interlayer in which the tip of the isolation oxide film invades the element region during thermal oxidation, resulting in the element region becoming narrower. As a countermeasure to this problem, improved LOC prevents the intrusion of the isolation oxide film by forming a frame of silicon nitride film around the element area.
The OS method has been proposed.

This improved LOCO8 method will be explained with reference to process cross-sectional views shown in FIGS. 2(a) to 2(c). As shown in FIG. 2(a), first, a protective silicon oxide film 2 and a first silicon nitride film 3 are sequentially laminated on the surface of a silicon substrate 1, and then an opening 4 is formed to separate the device regions. , and further aperture 4
After forming the second silicon nitride film 5 on the bottom and side surfaces of the opening 4 and the entire surface of the first silicon nitride film 3, the second silicon nitride film 5 on the bottom of the opening 4 is removed.

Next, as shown in FIG. 2(b), a silicon oxide film 6 for isolation is applied to the silicon substrate 1 exposed in the opening 4 by thermal oxidation.
form.

Next, as shown in FIG. 2(c), the first and second silicon nitride films 3 and 5 are removed.

(Problems to be Solved by the Invention) However, in the improved LOCO3 method as described above, the second silicon nitride film 5 is in contact with the silicon substrate 1 in the frame of the element region, as shown in FIG. Therefore, after forming the silicon oxide film 6 for isolation, when removing the first and second silicon nitride films 3 and 5, whether hot phosphoric acid solution etching or plasma etching is used, the silicon substrate 1 will be roughened. There was a problem in that this caused a negative effect on the device.

The present invention solves the above problems and provides a method for manufacturing a semiconductor device in which a silicon substrate is not roughened when a silicon nitride film is removed.

(Means for Solving the Problems) In order to solve the above problems, one aspect of the present invention is to remove the first and second silicon nitride films by plasma etching after forming the isolation silicon oxide film. , the end point is detected by the intensity change of the nitrogen spectrum, and a frame of silicon nitride film is left around the device region. This can be controlled with high precision by changing the intensity of the nitrogen spectrum described above.

Next, a silicon oxide film with a thickness of 500 to 2000 thick is additionally formed on the entire surface of the silicon substrate by thermal oxidation, and the tip of the protective and isolation silicon oxide film is penetrated under the frame of the silicon nitride film. A silicon oxide film is formed between the silicon nitride film frame and the silicon substrate. Furthermore, the remaining silicon nitride film frame is removed.

(Function) With the above configuration, the frame of the silicon nitride film and the silicon substrate are isolated by the silicon oxide film that penetrates under the frame of the silicon nitride film, so that the silicon substrate is not roughened during the process of removing the silicon nitride film. does not occur. Furthermore, since the tip of the isolation silicon oxide film can only penetrate under the frame of the silicon nitride film, the area of the element region does not become too small, and the stress applied to the silicon substrate can be almost ignored.

(Example) An example of the present invention will be described with reference to FIGS. 1(a) to e).

As shown in FIG. 1(a), first, a protective silicon oxide film 2 and a first silicon nitride film 3 are sequentially laminated on the surface of a silicon substrate 1, and then apertures 4 are formed to separate device regions. After further forming a second silicon nitride film 5 on the bottom and side surfaces of the opening 4 and the entire surface of the first silicon nitride film 3,
The second silicon nitride film 5 on the bottom of the opening 4 is removed.

Next, as shown in FIG. 1(b), a silicon oxide film 6 for isolation is formed on the silicon substrate 1 exposed at the bottom of the opening 4.

Next, as shown in FIG. 1(c), the first and second silicon nitride films 3 and 5 are removed by plasma etching, leaving a frame 7 of the silicon nitride film around the opening 4. At this time, the end point of plasma etching is detected by the change in intensity of the nitrogen spectrum.

Next, as shown in FIG. 1(d), a silicon oxide film with a thickness of 500 to 2000 layers is added to the entire surface of the silicon substrate 1 by thermal oxidation, and an isolation layer is placed under the frame 7 of the silicon nitride film. A thermally oxidized silicon film 8 is introduced.

Next, as shown in FIG. 1(e), the frame 7 of the silicon nitride film is removed by plasma etching or hot phosphoric acid etching.

(Effects of the Invention) As explained above, according to the present invention, when removing the frame 7 of the silicon nitride film formed around the element region, the silicon substrate 1 is protected by the thermally oxidized silicon film 8 for isolation. Therefore, it is possible to obtain a silicon oxide film for element isolation that does not cause roughness on the silicon substrate and has the same shape as the conventional improved LOGO8 method.

[Brief explanation of drawings]

1(a) to e) are cross-sectional views of a model showing the steps of the method for manufacturing a semiconductor device according to the present invention, and FIGS. 2(a) to c) are cross-sectional views of a model showing the steps of the conventional improved LOCO5 method. It is. DESCRIPTION OF SYMBOLS 1... Silicon substrate, 2... Protective silicon oxide film, 3... First silicon nitride film, 4... Opening hole,
5... Second silicon nitride film, 6... Silicon oxide film for isolation, 7... Frame of silicon nitride film, 8...
・Thermal oxidation silicon film for isolation. Patent applicant: Matsushita Electronics Co., Ltd. Figure 2

Claims (1)

[Claims] A step of sequentially laminating a silicon oxide film and a first silicon nitride film on the surface of a silicon substrate, a step of removing a predetermined region of the silicon oxide film and the first silicon nitride film to form an opening, and a step of forming an opening as described above. After forming a second silicon nitride film on the bottom and side surfaces of the opening and the top surface of the first silicon nitride film, removing the second silicon nitride film on the bottom of the opening;
forming a silicon oxide film for isolation on the silicon substrate exposed at the bottom of the opening; and leaving a frame of the silicon nitride film at the end of the opening of the silicon oxide film and forming the first and second silicon nitride films. A method for manufacturing a semiconductor device, comprising the steps of etching away the film, thermally oxidizing the surface of the silicon substrate, and removing the frame of the silicon nitride film.