JPH04336447A - Fabrication of semiconductor device - Google Patents

Abstract

PURPOSE:To form a fine transistor without preparing excessive selective oxidation film by performing concurrent selective oxidation of a semiconductor substrate and a poly-Si film in a trench through a common antioxydant Si3N4 film thereby reducing the number of steps in the formation of selective oxidation film. CONSTITUTION:A first insulating film 2 and an antioxydant film 3 are applied sequentially on a semiconductor substrate 1. The antioxydant film 3 is then patterned with a first resist film 4 as a mask, followed by formation of a trench 5 in the semiconductor substrate 1 with the antioxydant film 3 as a mask. A second insulating film 6 is then formed on the inner wall of the trench 5 and a poly-Si film 7 is filled therein. The antioxydant film 3 is then patterned with the second resist film 8 as a mask and removed from an element isolation film forming region through etching. The Si films 7 on the semiconductor substrate 1 and in the trench 5 are then selected concurrently with the antioxydant film 3 as a mask thus forming an element isolation film 9 on the semiconductor substrate 1 and on the surface of the trench 5.

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 element insulating isolation films, etc., by selective oxidation of semiconductor substrates, such as bipolar transistors.

[0002] In recent years, there has been a demand for higher integration and miniaturization of elements in semiconductor devices. For this reason, the proportion of element insulation isolation films on the surface of conventional semiconductor devices is large.
It is necessary to develop a technology to reduce the size of these element isolation films.

0003

2. Description of the Related Art FIG. 4 is an explanatory diagram of a conventional example. In the figure, 28 is a Si substrate, 29 is a first SiO2 film, and 30
is the first Si3N4 film, 31 is the element insulation isolation SiO2
32 is a second Si3N4 film, 33 is a resist film,
34 is a trench, 35 is a second SiO2 film, 36 is a poly-Si film, and 37 is a third SiO2 film.

In a conventional semiconductor device, for example, a bipolar transistor, an element insulating isolation film is formed by a process shown in FIG. That is, as shown in FIG. 4(a), after thinly oxidizing the surface of a silicon (Si) substrate 28 to form a first silicon dioxide (SiO2) film 29, a first silicon nitride (Si3N4) film is formed thereon. membrane 30
was grown, and using a resist film (not shown) as a mask, the first
The Si3N4 film 30 is patterned.

Next, as shown in FIG. 4(b), the LO
The Si substrate 28 is oxidized by COS (selective oxidation method) to form an element insulation isolation SiO2 film 31. Figure 4 (
As shown in c), the second Si3N4 film 32 is coated and the resist film 33 is used as a mask.
pattern.

As shown in FIG. 4(d), the second Si3
Using the N4 film 32 as a mask, the element insulation isolation SiO2 film 3 is etched by anisotropic dry etching using the RIE method.
1 and the Si substrate 28, the Si substrate 28 is etched.
A trench 34 is formed therein.

As shown in FIG. 4(e), the inner wall of the trench 34 is oxidized to form a second SiO2 film, and then a polycrystalline silicon (poly-Si) film 36 is formed in the trench 34 by CVD. Embed.

As shown in FIG. 4(f), the second Si3
Using the N4 film 32 as a mask, the surface of the poly-Si film 36 is oxidized by selective oxidation to form a third SiO2 film 37.
S by the element insulation isolation SiO2 film 31 and the trench 34
Element isolation of the bipolar transistors on the i-substrate 28 is completed.

This method includes two selective oxidation steps: selective oxidation of the Si substrate 28 and selective oxidation of the surface of the poly-Si film 36 in the trench 34, and the steps up to the completion of the formation of the element insulation isolation film. becomes longer.

[0010] Furthermore, a certain amount of margin is required for the distance from the bird's beak portion of the selective oxide film to the trench, which has the disadvantage that the ratio occupied by the element insulating isolation film (field SiO2 film) becomes large.

[0011]

[Problems to be Solved by the Invention] Therefore, it has become difficult to miniaturize elements and the throughput is also poor. The present invention
It is an object of the present invention to provide a method of reducing the process of forming a selective oxide film and forming a fine transistor without forming an extra selective oxide film.

0012

[Means for Solving the Problems] FIG. 1 is a diagram illustrating the principle of the present invention. In the figure, 1 is a semiconductor substrate, 2 is a first insulating film, 3 is an oxidation-resistant film, 4 is a first resist film, 5 is a trench, 6 is a second insulating film, 7 is a poly-Si film, and 8 is the second
The resist film 9 is an element isolation insulating film.

[0013] In order to solve the above problems, the conventional method of LOCOS of the semiconductor substrate and the poly-S in the trench are required.
Oxidation-resistant Si3 used in both LOCOS and i-film
This can be achieved by using the N4 film and forming LOCOS at the same time.

That is, the object of the present invention is to sequentially coat a semiconductor substrate 1 with a first insulating film 2 and an oxidation-resistant film 3, and then coat a first resist film 4 as shown in FIG. 1(a). A step of patterning the oxidation-resistant film 3 as a mask, and a step of patterning the oxidation-resistant film 3 as a mask.
As shown in (b), using the oxidation-resistant film 3 as a mask,
Steps of forming trenches 5 in the semiconductor substrate 1 and FIG.
As shown in FIG. 1(c), a second insulating film 6 is formed on the inner wall of the trench 5, and a poly-Si film 7 is embedded in the trench 5. As shown in FIG. 1(d), a second insulating film 6 is formed on the inner wall of the trench 5. The oxidation-resistant film 3 is patterned using the resist film 8 as a mask, and the oxidation-resistant film 3 in the element isolation film formation region is etched away as shown in FIG. 1(e). f)
As shown in FIG. 2, this is accomplished by including the steps of oxidizing the semiconductor substrate 1 by selective oxidation to form an element isolation insulating film 9 on the semiconductor substrate 1.

[0015]

[Operation] In the present invention, the Si3N4 film is first used as a mask material for trench etching, then left as is, and then only the portions of the Si substrate and the poly-Si film in the trench where the selective oxide film is to be formed are etched. The film is patterned and etched and selectively oxidized.

[0016] As a result, the Si3N
The process of growing 4 films, selective oxidation, and removing the Si3N4 film is required only once, and the device isolation insulating film between the trench and the device forming area can be eliminated, reducing the area occupied by the device isolation region. can.

[0017]

Embodiment FIGS. 2 and 3 are schematic sectional views in order of steps of an embodiment of the present invention. In the figure, 10 is a Si substrate, 11 is a buried diffusion layer, 12 is an epitaxial layer, and 13 is a first layer.
, 14 is the Si3N4 film, 15 is the first resist film, 16 is the trench, and 17 is the second SiO2 film.
18 is a poly-Si film, 19 is a third SiO2 film, 2
0 is the second resist film, 21 is the element isolation SiO2 film,
22 is a collector contact diffusion layer, 23 is a base diffusion layer, 24 is an emitter diffusion layer, 25 is an emitter electrode,
26 is a base electrode, and 27 is a collector electrode.

An embodiment in which the present invention is applied to forming an element isolation region of a bipolar transistor will be described. As shown in FIG. 2(a), n+
A type buried diffusion layer 11 is formed, and an n-type epitaxial layer 12 is further grown.

As shown in FIG. 2(b), the surface of the Si substrate 10 is oxidized using a hydrochloric acid oxidation method, and a first S layer is deposited to a thickness of 200 Å.
An iO2 film 13 is formed, and then a Si3N4 film 14 is grown to a thickness of 1,000 Å by CVD.

Then, the Si3N4 film 14 is patterned using the 1 μm thick first resist film 15 as a mask, and then the first resist film 15 is removed. As shown in FIG. 2(c), using the Si3N4 film 15 as a mask, the first SiO2 film 14 is
, epitaxial layer 12 and buried diffusion layer 11 in sequence,
Anisotropic dry etching is performed to form a trench 16 that reaches the Si substrate 10.

As shown in FIG. 2(d), a second SiO2 film 17 is formed on the inner wall of the trench 16, and then CV
A poly-Si film 18 is grown by the D method, and by polishing with caustic potash, the poly-Si film 18 is grown only in the trench 16.
The i-film 18 is embedded.

Subsequently, as shown in FIG. 3(e), the surface of the poly-Si film 18 is selectively oxidized to form a third SiO2 film 19 with a thickness of 1,000 Å, and then a second resist film 19 is formed. Using the film 20 as a mask, as shown in FIG. 3(f),
The Si3N4 film 14 in the element isolation SiO2 film forming region is removed by etching.

As shown in FIG. 3(g), using the Si3N4 film 14 as a mask, the Si substrate 10 and the poly-Si film 18 in the trench 16 are selectively oxidized at the same time, so that the Si substrate 10 and the surface of the trench 16 are oxidized. Element isolation SiO
2 film 21 is formed to a thickness of 6,000 Å.

Next, a bipolar transistor as shown in FIG. 3(h) is formed by a conventional method through steps such as impurity diffusion, various film formation, patterning, and etching.

[0025]

[Effects of the Invention] As explained above, according to the present invention, processes such as growth and removal of the Si3N4 film, selective oxidation method, etc. can be halved, and the element isolation insulating film between the trench and the element forming part can be eliminated. This greatly contributes to reducing chip size and improving reliability.

[Brief explanation of drawings]

[Figure 1] Diagram explaining the principle of the present invention

[Fig. 2] Schematic sectional view of the process order of one embodiment of the present invention (Part 1)

[Fig. 3] Schematic sectional view of the process order of one embodiment of the present invention (Part 2)

[Figure 4] Explanatory diagram of conventional example

[Explanation of symbols]

1 Semiconductor substrate 2 First insulating film 3 Oxidation-resistant film 4 First resist film 5 Trench 6 Second insulating film 7 Poly-Si film 8 Second resist film 9 Element isolation insulating film 10 Si substrate 11 Buried diffusion layer 12 Epitaxial layer 13 First SiO2 film 14 Si3N4 film 15 First resist film 16 Trench 17 Second SiO2 film 18 Poly-Si film 19 Third SiO2 film 20 Second resist film 21 Element isolation SiO2 film 22 Collector contact diffusion layer 23 Base diffusion layer 24 Emitter diffusion layer 25 Emitter electrode 26 Base electrode 27 Collector electrode

Claims (1)

[Claims] Claim 1: A first insulating film (2) and an oxidation-resistant film (3) are sequentially coated on a semiconductor substrate (1), and the oxidation-resistant film is coated using the first resist film (4) as a mask. (
3) The step of patterning the oxidation-resistant film (3)
forming a trench (5) in the semiconductor substrate (1) using as a mask, forming a second insulating film (6) on the inner wall of the trench (5);
The step of embedding a polycrystalline silicon film (7) inside the
Using the resist film (8) as a mask, the oxidation-resistant film (3
) and etching away the oxidation-resistant film (3) in the element isolation film formation region, and oxidizing the semiconductor substrate (1) by a selective oxidation method to form a layer on the semiconductor substrate (1). A method for manufacturing a semiconductor device, comprising the step of forming an element isolation insulating film (9).