JPS62120051A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To improve the flatness and to prevent the characteristics of a semiconductor device from deteriorating by removing a silicon oxide film once formed by a mask of a silicon nitride film to form a recess on a silicon substrate to reduce a step between the final silicon oxide film surface and the substrate surface. CONSTITUTION:An Si3N4 film 2 is formed on a silicon substrate 1, and a window is opened on a portion 5 to form an SiO2 film 3. The exposed surface is then selectively oxidized, and the film 3 is grown. An SiO2 film 4 is so grown as to bury a recess 6 by selective oxidation with the film 2 as a mask. Thereafter, the film 2 used as the mask is removed. The SiO2 film formed as above is removed, and element separating deep SiO2 film 4 having less step with the substrate 1 surface can be formed by selectively oxidizing again and the characteristics of a semiconductor element are not damaged.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to a method for manufacturing a semiconductor device in which a thick silicon oxide film for isolation between elements is formed using a silicon nitride film as a mask.

[Prior art and its problems]

Conventionally, in order to selectively generate a silicon oxide film on a silicon substrate for isolation between elements, a window opening in a silicon nitride film provided on the silicon substrate is selectively formed on the surface of the silicon substrate. The method of removing the silicon nitride film after forming a silicon oxide film by oxidizing the silicon nitride film was through a tube. However, in this method of producing a silicon oxide film, the surface of the silicon oxide film produced is considerably raised from the original silicon substrate surface, so there is a step difference between the unoxidized silicon substrate surface and the silicon oxide film surface. arise. That is, in this method, as shown in FIG.
By opening a window and selectively oxidizing the exposed surface of the
When the film 3 is grown, the silicon substrate 1 and the Si3Ng film 2 are grown.
The 5tot film 3 enters between the For example, when the SiJ film 3 is formed 1-, a considerable step difference occurs between the surface of the silicon substrate 1 and
It rises by about 0.6 μ and increases by about 0.4 p in the depth direction.
m grow. Therefore, a step difference d of about 0.6- is generated between the surface of the substrate 1 and the surface of the Stow film 3. When such a large step difference occurs, there is a drawback that a step break occurs in the metal wiring such as M formed on the silicon substrate. In addition, the PSG film covering the surface of the substrate is also reflowed to planarize it, but this has the disadvantage that the loose wiring in the PSG is eroded. As a method to prevent such level differences, for example, the Institute of Electronics and Communication Engineers, published in 1978, Opening [rLS [Technology] 125 and 1
As described on page 26, there is a method in which a nitride film is patterned, the silicon substrate is etched, and then the silicon substrate is oxidized. However, it has been found that in this case, etching damages the silicon substrate and impairs the characteristics of the semiconductor device.

Purpose of the Invention The present invention solves the above-mentioned problems and reduces the level difference between the surface of a silicon oxide film formed on a silicon substrate and the surface of an unoxidized silicon substrate without damaging the silicon substrate. The purpose is to improve surface flatness. Summary of the Invention In the present invention, after a silicon nitride film is formed on a silicon substrate, the window opening is oxidized through the portion, the generated silicon oxide film is removed, and the surface of the recess is oxidized again. The formation of the silicon oxide film causes less damage to the silicon substrate, and the formation of the silicon oxide film in the recesses reduces the level difference between the oxide film surface and the substrate surface, thereby achieving the above object.

[Embodiments of the invention]

Figure 1+a+~(C1 shows one embodiment of the present invention;
In FIG. 181, a 5isN4 film 2 is provided on the surface of a silicon substrate 1, and a window is opened in a portion 5 where a film 3 is to be formed. Next, the exposed surface was selectively oxidized to grow the Stow film 3, as shown in Fig. 1 (see Fig. 1). The process up to this point is the same as the conventional method described above. 181 shows a state in which the Sing film 3 has been removed and a recess 6 has been formed on the surface of the silicon substrate 1. Then, as shown in FIG. 1 181, the St, Na film 2 is used again as a mask. By selective oxidation, 5iOtll! 4 is grown to fill the recess 6. After that, the 5lsNa film 2 used as a mask
181 in FIG. 1 shows the state after removing SiO! produced by the conventional method. By removing the film and selectively oxidizing it again, it is possible to produce a deep S10° film 4 for element isolation with few steps from the surface of the silicon substrate 1.

【Effect of the invention】

According to the present invention, before forming a silicon oxide film for element isolation using a silicon nitride film as a mask, the silicon oxide film produced using the same mask is removed to form a depression in the silicon substrate. The level difference between the final silicon oxide film surface and the silicon substrate surface is also reduced, and flatness is improved. Moreover, unlike etching, it does not damage the silicon substrate, so the device characteristics are not impaired, and the improved flatness eliminates the disconnection of metal wiring, and there is no risk of corrosion of the U62 wire due to PSG glue flow. The effects obtained are extremely large.

[Brief explanation of drawings]

FIG. 1 is a sectional view sequentially showing the procedure of an embodiment of the present invention, and FIG. 2 is a sectional view sequentially showing the procedure of a conventional method. 1: Silicon substrate, 2: 5iJa film, 3, 4: SiO
! ? ! Si listening 1? 2Si3
Ntll'J, 2 6 concave, 2 2. 45+02 prefecture 2 Figure 1

Claims (1)

[Claims] 1) When forming a thick silicon oxide film for element isolation using a silicon nitride film as a mask, the silicon nitride film is formed on a silicon substrate and then oxidized through the window opening of the film, and the formed silicon oxide film is 1. A method for manufacturing a semiconductor device, which comprises removing the recess and oxidizing the surface of the recess again.