JPH0541376A - Formation of semiconductor interelement isolation - Google Patents

Abstract

(57) [Abstract] [Purpose] When the isolation between semiconductor elements is formed, the stress applied to the substrate is relaxed so that crystal defects do not occur in the substrate. [Structure] After a silicon oxide film 12, a polycrystalline silicon film 13, and a silicon nitride film 14 are formed in a stacked state on a silicon substrate 11, a part of each film is removed to remove the upper surface 11a of the silicon substrate 11. In the exposed state, a formation space 15 for element isolation is provided. After that, a sidewall 18 is formed on the sidewall 17 of each film in the space 15 for forming the element isolation, and then the sidewall 18 and the upper layer of the silicon substrate 11 are oxidized to form an element isolation region 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming isolation between semiconductor devices.

[0002]

2. Description of the Related Art In order to form isolation between semiconductor elements, it is usually formed by a LOCOS method or a so-called improved LOCOS method which suppresses the occurrence of bird's beaks. Especially improved L
Since the OCOS method can reduce the width of element isolation by suppressing the occurrence of bird's beak, it is used for element isolation of a semiconductor device that requires high integration.

Next, the improved LOCOS method will be described with reference to FIG. As shown in FIG. 1A, a silicon oxide film 32 is formed on the upper surface of the silicon substrate 31 by, for example, a thermal oxidation method. Then, a silicon nitride film 33 is formed by a chemical vapor deposition method. Then, as shown in FIG. 2B, a part of the silicon nitride film 33 and the silicon oxide film 32 is removed so that a part 31a of the upper surface of the silicon substrate 31 is exposed, and a space 34 for forming an element isolation is formed. To provide. Subsequently, as shown in FIG. 3C, a polycrystalline silicon film (hereinafter referred to as po) is formed in the formation space 34 for element isolation and on the upper surface of the silicon nitride film 33.
35) is formed. Then poly-
Etch back the portion indicated by the chain double-dashed line of the Si film 35,
A sidewall 37 is formed on the sidewall 36. After that, as shown in FIG. 4D, so-called field oxidation is performed to oxidize the side wall 37 (portion indicated by a chain double-dashed line) and a part of the upper layer of the silicon substrate 31 (portion shown by a one-dot chain line), and the element The inter-separation region 38 is formed.

[0004]

However, when the element isolation region is formed by the above method, the silicon nitride film is peeled off from the silicon oxide film during field oxidation. This is because tensile stress acts on the sidewall when the sidewall is oxidized. This tensile stress acts as a stress for peeling the silicon nitride film in contact with the upper side of the sidewall from the silicon oxide film. Therefore, the silicon nitride film is peeled off from the silicon oxide film. As a result, when the silicon nitride film is peeled off, tensile stress is applied to the substrate through the silicon oxide film, so that crystal defects occur in the substrate.

It is an object of the present invention to provide a method for forming isolation between semiconductor devices which does not generate crystal defects.

[0006]

SUMMARY OF THE INVENTION The present invention is a method for forming isolation between semiconductor devices, which has been made to achieve the above object. That is, in the first step, a silicon oxide film, a polycrystalline silicon film, and a silicon nitride film are formed in a stacked state on a silicon substrate. Then, in a second step, a part of each of the films is removed to form a space for element isolation in a state where a part of the upper surface of the silicon substrate is exposed. Next, in a third step, sidewalls are formed on the side walls of each film in the space for forming the element isolation. Then in the fourth step,
The sidewall and a part of the upper layer of the silicon substrate are oxidized to form an element isolation region in a state of filling the formation space of the element isolation.

[0007]

In the above-described method for forming the semiconductor element isolation, the polycrystalline silicon film is formed between the silicon oxide film and the silicon nitride film, so that when the element isolation region is generated by oxidation, the sidewall is formed. The generated tensile stress tends to peel off the silicon nitride film. At this time, the stress applied to the substrate is relaxed by the polycrystalline silicon film.

[0008]

EXAMPLE An example of the present invention will be described with reference to the process chart shown in FIG. As shown in the figure, in the first step, the upper layer of the silicon substrate 11 is oxidized by a thermal oxidation method to form a silicon oxide film 12 having a thickness of, for example, about 10 nm. Then, the silicon oxide film 1 is formed by, for example, a chemical vapor deposition method.
A polycrystalline silicon (hereinafter referred to as poly-Si) film 13 is formed on the upper surface of 2 to a thickness of, for example, 30 nm to 40 nm. Then, the silicon nitride film 14 is formed on the upper surface of the poly-Si film 13 by, for example, a low pressure chemical vapor deposition method.
Is formed to a thickness of 150 nm, for example.

Then, in a second step, a portion of the silicon nitride film 14, the poly-Si film 13 and the silicon oxide film 12 is removed by ordinary photolithography and etching to expose a portion 11a of the silicon substrate 11. In this state, the space 15 for forming the element isolation is provided. After that, an etching mask (not shown) formed by photolithography is removed by, for example, an asher process.

Then, in a third step, a sidewall forming film 16 made of polycrystalline silicon is formed in the formation space 15 for element isolation and on the upper surface of the silicon nitride film 14 by, for example, low pressure chemical vapor deposition. For example, it is formed to have a thickness of about 100 nm. After that, by etching back, the portion indicated by the chain double-dashed line of the side wall forming film 16 is removed, and the side wall 18 is formed on the side wall 17 of the silicon nitride film 14, the poly-Si film 13, and the silicon oxide film 12.

Then, in the fourth step, by the thermal oxidation method,
The side wall 18 (the part indicated by the two-dot chain line) and a part of the upper layer of the silicon substrate 11 (the part indicated by the one-dot chain line) are oxidized to form the element isolation region 19.

As described above, since the poly-Si film 13 is formed between the silicon oxide film 12 and the silicon nitride film 14, the poly-Si film 13 is formed during the thermal oxidation in the fourth step.
The Si film 13 relaxes the stress generated in the silicon nitride film 14 and makes it difficult to transmit this stress to the silicon substrate 11.
Therefore, crystal defects do not occur in the silicon substrate 11 due to the stress generated in the silicon nitride film 14.

A method of forming the element isolation region 19 deeper in the above method to enhance the element isolation performance will be described with reference to FIG. As shown in (1) of FIG. 2, the upper layer of the silicon substrate 11 is overetched by, for example, reactive ion etching at the time of etch back for forming the sidewall 18 in the third step described in FIG. (The portion indicated by the chain double-dashed line) is removed. In this way, when the upper layer of the silicon substrate 11 is removed, (2) in FIG.
As shown in FIG. 1, the element isolation region 19 is formed deeper than in the case described in FIG. 1 during the thermal oxidation in the fourth step described in FIG. Therefore, the isolation performance between elements is further improved.

[0014]

As described above, according to the present invention,
A polycrystalline silicon film was formed between the silicon oxide film and the silicon nitride film. Therefore, in the fourth step, the stress applied to the substrate is relaxed by the polycrystalline silicon film when the silicon nitride film is about to be peeled off, so that no crystal defect occurs in the substrate.

[Brief description of drawings]

FIG. 1 is a process drawing of an example.

FIG. 2 is a process drawing of another embodiment.

FIG. 3 is a diagram illustrating a forming process of a conventional example.

[Explanation of symbols]

 11 Silicon Substrate 12 Silicon Oxide Film 13 Polycrystalline Silicon (Poly-Si) Film 14 Silicon Nitride Film 15 Space for Element Isolation 17 Sidewall 18 Sidewall 19 Element Isolation Region

Claims (1)

[Claims] 1. A first step of depositing a silicon oxide film, a polycrystalline silicon film, and a silicon nitride film on a silicon substrate in a stacked state, the silicon nitride film, the polycrystalline silicon film, and the silicon oxide film. And a part of the upper surface of the silicon substrate is exposed to form a formation space for element isolation, and a side wall of each film in the element isolation formation space. Third step of forming a side wall and fourth step of oxidizing the side wall and a part of the upper layer of the silicon substrate to form an element isolation region in a state of filling the formation space of the element isolation. A method for forming an isolation between semiconductor elements, comprising: