JP2718074B2 - Method of forming thin film semiconductor layer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a thin film semiconductor layer.

[Summary of the Invention]

According to the present invention, in a method for forming a thin film semiconductor layer, a non-single-crystal thin film semiconductor layer is formed on an insulating substrate, and an oxidation-resistant film is selectively formed on the semiconductor layer. Then, the exposed semiconductor layer is oxidized by irradiating the entire surface thereof with an energy beam in an oxidizing atmosphere, and the semiconductor layer under the oxidation-resistant film is subjected to a heat treatment, so that solid-phase growth of the semiconductor layer to be an active layer is achieved. At the same time, a selective oxidation (LOCOS) layer serving as an element isolation region can be formed, and a selective oxidation layer without a bird's beak can be formed.

[Conventional technology]

Generally, when a semiconductor device, particularly a thin film semiconductor device, is formed, an Si ₃ N ₄ film is used as a gate insulator, as a capacitor, or as an oxidation-resistant mask at the time of element isolation. This Si ₃ N ₄ film has a large dielectric constant and excellent oxidation resistance and chemical resistance, and is suitable for the above-mentioned applications. In addition, when a gate insulator is used as a capacitor, the Si ₃ N ₄ film is not used alone and is often in a sandwich structure of SiO ₂ —Si ₃ N ₄ —SiO ₂ .

As a dimension of element isolation in a semiconductor integrated circuit, a so-called LOCOS method (selective oxidation method) in which an SiO ₂ —Si ₃ N ₄ layer is used as an oxidation-resistant mask and thermal oxidation is performed on portions other than the element portion has become mainstream.

As a method of improving the crystal quality of an active layer made of polycrystalline silicon such as a thin film semiconductor device, a method of irradiating an excimer laser to grow a crystal is also known.

[Problems to be solved by the invention]

Incidentally, in the semiconductor device, when using the the Si ₃ N ₄ film as a gate insulating film, a capacitor, SiO ₂ -Si ₃ as described above
Although it has a sandwich structure of N ₄ -SiO ₂ , S
The iO ₂ film is formed by thermally oxidizing the surface of the Si ₃ N ₄ film at about 1100 ° C. Since this thermal oxidation treatment is usually performed in an electric furnace, there are inconveniences such as defects occurring in the single-crystal silicon substrate as an active layer and diffusion of impurities during the thermal oxidation.

On the other hand, in element isolation by the LOCOS method, there is a problem of so-called bird's beak, and formation of a selective oxidation layer without bird's beak is desired.

For crystal growth of the active layer by excimer laser irradiation, it is necessary to cap the polycrystalline silicon of the active layer with an SiO ₂ film or the like at the time of irradiation.

The present invention has been made in view of the above points, and aims to simplify the process by simultaneously performing crystal growth of an active layer and formation of a selective oxidation layer for element isolation. It is an object of the present invention to provide a method of forming a thin film semiconductor layer that enables formation of a selective oxidation layer without bird's beak.

[Means for solving the problem]

According to the method of forming a thin film semiconductor layer of the present invention, a polycrystalline or amorphous non-single-crystal thin film semiconductor layer (2) is formed on an insulating substrate (1), and selectively formed on the semiconductor layer (2). Si ₃ N ₄
An oxidation resistant film (4) is formed. Thereafter, the exposed semiconductor layer (2) is selectively oxidized by irradiating the entire surface thereof with an energy beam such as an excimer laser in an oxidizing atmosphere, and the semiconductor layer (2) below the oxidation-resistant film (4) is heat-treated. It is like that.

[Action]

According to the above-described forming method of the present invention, since the energy beam is irradiated at a high temperature for a short time in an oxidizing atmosphere, the oxidation-resistant film (4) of the non-single-crystal thin-film semiconductor layer (2) as the active layer is not formed. The region is selectively oxidized to form a selective oxidation layer (6) serving as an element isolation region, and a non-single-crystal thin-film semiconductor layer (2) serving as an active layer below the oxidation-resistant film (4) is formed at the same time. Perform solid phase growth. During the solid phase growth, the step of forming the capping layer is omitted because the oxidation resistant film (4) acts as a capping layer.

Further, since the energy beam is irradiated in a straight line and only the irradiated portion is oxidized, the bird's beak phenomenon is controlled, and the selective oxidation layer (6) without the bird's beak is formed.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a process chart showing a method for forming a thin film semiconductor device according to the present embodiment. Hereinafter, the steps will be described step by step.

Although this embodiment describes a P-channel thin film transistor, it can be applied to an N-channel thin film transistor.

First, as shown in FIG. 1A, a P-type polycrystalline silicon thin film (2) is grown on an insulator (1) made of SiO ₂ by, for example, a CVD method.

Next, as shown in FIG. 2B, thermal oxidation is performed on the surface of the polycrystalline silicon thin film (2) to form a SiO ₂ oxide film (3) for a gate. Thereafter, a gate Si ₃ N ₄ thin film (4) is similarly grown on the SiO ₂ oxide film (3) by a CVD method or the like.

Then, because of the isolation, as shown in FIG. C, Si ₃ N ₄
A part of the thin film (4) and a part of the SiO ₂ oxide film (3) are removed by etching using a photolithography technique to expose a part (2A) of the polycrystalline silicon thin film (2) existing in the lower layer.

Next, as shown in FIG.
The entire surface including the Si ₃ N ₄ thin film (4) and the exposed polycrystalline silicon portion (2A) is irradiated with an excimer laser (5) in an O ₂ or O ₃ atmosphere and subjected to a high-temperature and short-time heat treatment. The crystalline silicon portion (2A) is thermally oxidized to change to a SiO ₂ field insulating layer (6) reaching the insulator (1), and the surface of the Si ₃ N ₄ thin film (4) is simultaneously thermally oxidized to SiO
_{2 An} oxide film (7) is formed. This field insulating layer (6) becomes an element isolation region. Simultaneously with the irradiation of the excimer laser (5), a polycrystalline silicon thin film (2) to be an active layer under the Si ₃ N ₄ thin film (4) grows. In this case, the Si ₃ N ₄ thin film (4) has a kind of capping effect on the irradiation of the active layer (2) with the excimer laser (5).

On the other hand, in the field insulating layer (6), only the irradiated polycrystalline silicon portion (2A) is thermally oxidized by the straight irradiation and short-time irradiation of the excimer laser (5), and the active layer (2)
Since the thermal oxidation does not proceed to the side, a so-called bird's beak phenomenon does not occur.

Next, as shown in FIG. E, a polycrystalline silicon layer (8) doped with an impurity (eg, an n-type impurity) serving as a gate electrode on the entire surface is grown by a CVD method or the like, and then as shown in FIG. , Polycrystalline silicon layer (8), SiO ₂ oxide film (7),
The Si ₃ N ₄ thin film (4) and the SiO ₂ oxide film (3) are sequentially etched selectively to form a gate electrode (9) comprising a polycrystalline silicon layer (8) and the SiO ₂ oxide film (3) and the Si ₃ N ₄ thin film. (4) and SiO ₂
A gate insulating film (10) made of an oxide film (7) is formed, and a part of the surface of the active layer (2) other than the gate part is exposed.

Thereafter, as shown in FIG. 9G, a P-type impurity (13) is ion-implanted into the active layer (2) by using the field insulating layer (6) and the gate electrode (9) as a mask to form a source region (11) and a drain. A region (12) is formed to form a P-channel thin film transistor.

In the above embodiment, the active layer (2) is formed of polycrystalline silicon, but may be formed of other amorphous silicon.

In the above example, the SiO ₂ oxide film (3), the Si ₃ N ₄ film (4) and the S
The gate insulating film (10) was composed of the iO ₂ oxide film (7). In addition, after the step of FIG. 1D, these films (3) and (4)
By removing (7), it is also possible to form a gate insulating film of SiO ₂ again.

According to the above-described method of forming a thin film transistor, after selectively forming a Si ₃ N ₄ thin film (4) on a polycrystalline silicon thin film (2) via an SiO ₂ oxide film (3), heat treatment by excimer laser irradiation. By this, the selective oxidation for forming the field insulating layer (6) and the crystallization of the polycrystalline silicon layer (2) to be the active layer under the Si ₃ N ₄ thin film (4) are performed simultaneously. In this case, the Si ₃ N ₄ thin film (4), which serves as an oxidation-resistant mask at the time of selective oxidation, also serves as a capping layer during crystal growth of the polycrystalline silicon thin film (2).
There is no need to add a new capping step.

Further, the surface of the Si ₃ N ₄ thin film (4) is thermally oxidized by irradiation with the excimer laser (5) to form the SiO ₂ oxide film (7), and the gate insulating film (10) (or another capacitor) is formed. dielectric material) as a SiO ₂ -Si ₃ N ₄ sandwich -SiO ₂ for configuring it can be formed at the same time. Therefore,
The manufacturing process of the thin film transistor can be simplified.

On the other hand, when the field insulating layer (6) is formed by selective oxidation, unlike the conventional thermal oxidation at 1100 ° C. for a long time, it is performed by a high-temperature and short-time heat treatment by excimer laser irradiation. 5) is irradiated in a straight line, and only the irradiated portion (2A) is thermally oxidized, thereby suppressing the occurrence of bird's beak. Thus, a field insulating layer (6) without bird's beak can be formed, and the height of the element can be reduced. Density can be increased.

〔The invention's effect〕

In the method for forming a thin film semiconductor device according to the present invention, a non-single-crystal thin film semiconductor layer is formed on an insulating substrate, and an oxidation resistant film is selectively formed on the semiconductor layer. Thereafter, the exposed semiconductor layer is oxidized by irradiating the entire surface thereof with an energy beam in an oxidizing atmosphere, and the semiconductor layer under the oxidation-resistant film is heat-treated. The formation and the crystal improvement of the semiconductor layer serving as the active layer under the oxidation-resistant film can be simultaneously performed. Can be omitted. Therefore, the manufacturing process can be simplified, and high integration of the semiconductor element can be achieved.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method for forming a thin film semiconductor device according to the present embodiment. (1) SiO ₂ insulator, (2) polycrystalline silicon layer (active layer), (3) SiO ₂ oxide film, (4) Si ₃ N ₄ thin film,
(5) is an excimer laser, (6) is a field insulating layer,
(7) is a SiO ₂ oxide film, (8) a polycrystalline silicon layer, (9)
Is a gate electrode, (10) is a gate insulating film, (11) is a source region, and (12) is a drain region.

Claims (1)

(57) [Claims] A step of forming a non-single-crystal thin-film semiconductor layer on an insulating substrate, a step of selectively forming an oxidation-resistant film on the semiconductor layer, and irradiating the entire surface with an energy beam in an oxidizing atmosphere. Oxidizing the exposed semiconductor layer and heat-treating the semiconductor layer under the oxidation-resistant film.