JPH06291039A - Amorphous-semiconductor formation substrate and manufacture of polycrystalline-semiconductor formation substrate using it - Google Patents

Abstract

PURPOSE:To provide an amorphous semiconductor formation substrate whose film thickness is comparatively thick so as not to thermally damage a low- melting-point glass substrate and which is provided with a buffet layer not increasing an internal stress due to the thick film thickness. CONSTITUTION:An amorphous semiconductor formation substrate is formed in such a way that an a-Si film 5 is formed on a low-melting-point glass substrate 1 via a buffer layer 4 for impurity-diffusion prevention. In the formation substrate, the buffer layer 4 is formed of a film in which tensile films 2a to 2c composed of SiO2 and compressive films 3a to 3c composed of SiO2 in the same manner have been laminated alternately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amorphous semiconductor forming substrate formed by forming an amorphous semiconductor film on a glass substrate through a buffer layer, and a polycrystalline semiconductor formed from this amorphous semiconductor forming substrate. The present invention relates to a method for manufacturing a formed substrate.

[0002]

2. Description of the Related Art Devices such as liquid crystal displays and contact type line sensors are manufactured by using thin film transistors (T) on a glass substrate.
It is formed by forming a large number of FTs, and a material of the thin film transistor is amorphous silicon (hereinafter, a-
Si) and polycrystalline silicon (hereinafter poly-).
(Abbreviated as Si) is used. The above a-Si film is
Its electron mobility is as low as 1 cm ² / Vs, and it is not suitable for improving the quality of the device. Therefore, pol, which has a relatively high electron mobility, is required for high functionality and high integration of the device.
The use of y-Si films is increasing.

As a method for forming the poly-Si film, a method for directly forming the poly-Si film by a low temperature CVD method or the like, or a solid phase growth method for recrystallizing by annealing the a-Si film for a long time Alternatively, recrystallization methods using various lasers are known. Among them, the laser recrystallization method using an excimer laser has little thermal effect on the substrate, high throughput can be expected, and higher mobility is easier than other methods. It is considered promising because it can be annealed.

In the laser recrystallization method, the substrate temperature is heated to about 400 ° C. during laser irradiation in order to increase the grain size and mobility of the recrystallized poly-Si film. It has been reported that (Jan.
J.Appl.Phys.30 (12), P3700 (1991)), when the laser is irradiated on the substrate at a temperature of about 400 ° C., as shown in FIG. The heat from the a-Si film 22 that has conducted the heat is also applied to the low melting point glass substrate 20.
In addition, the low melting point glass substrate 20 may be thermally damaged. Therefore, it is necessary to form the buffer layer 21 between the low melting point glass substrate 20 and the a-Si film 22 in a relatively thick film (about 1 μm or more).

[0005]

However, if the film thickness of the buffer layer 21 is increased, the buffer layer 21
When the buffer layer 21 is formed, the internal stress increases during the formation of the buffer layer 21. When the buffer layer 21 is formed, cracks easily occur in the buffer layer 21 and peeling occurs, which lowers the yield particularly in a large-sized substrate. When the a-Si film 22 is recrystallized in the cracked state, mobile ions such as Na ⁺ in the glass substrate 20 diffuse into the a-Si film 22 to deteriorate the device quality. Let

In view of the above circumstances, the present invention comprises a buffer layer having a relatively large film thickness that does not cause thermal damage to the glass substrate, but does not increase internal stress due to the large film thickness. It is an object of the present invention to provide a substrate for forming an amorphous semiconductor, and a method for manufacturing a substrate for forming a polycrystalline semiconductor with high quality and high mobility using the substrate for forming an amorphous semiconductor.

[0007]

In order to solve the above problems, an amorphous semiconductor forming substrate according to the present invention is formed by forming an amorphous semiconductor film on a glass substrate with a buffer layer interposed therebetween. The crystalline semiconductor forming substrate is characterized in that the buffer layer is composed of a laminated film of a tensil film and a compressive film.

Further, at least one of the plurality of films constituting the above buffer layer is made of WO having a high impurity diffusion blocking effect.
It is characterized by being composed of a ₃ or MoO ₃ film.

In the method for manufacturing a polycrystalline semiconductor forming substrate according to the present invention, the amorphous semiconductor film is irradiated with a high energy beam in a state where the amorphous semiconductor forming substrate is heated to form the polycrystalline semiconductor film. It is characterized by forming.

[0010]

According to the above-mentioned substrate for forming an amorphous semiconductor, the total internal stress in the buffer layer can be reduced due to the stresses in the opposite directions of the tensile film and the compressive film forming the buffer layer. Even if the layer is formed thick, cracks are not generated during the formation.

Further, according to the method for manufacturing a polycrystalline semiconductor forming substrate, recrystallization can be performed by using the amorphous semiconductor forming substrate having a relatively thick buffer layer in which cracks are not generated. Therefore, heat damage to the glass substrate due to heating and irradiation of a high energy beam is reduced, and diffusion of impurities such as Na ⁺ ions from the glass substrate into the semiconductor film is prevented.

Further, WO ₃ or M having a high impurity diffusion blocking effect is provided in at least one of the films constituting the buffer layer.
By forming oO ₃ , the effect of preventing impurity diffusion into the polycrystalline semiconductor film after irradiation with a high energy beam is further improved, and the quality of the polycrystalline semiconductor formation substrate can be further improved.

[0013]

【Example】

(Embodiment 1) The present invention will be described below with reference to the drawings showing the embodiment. FIG. 1 is a sectional view of an amorphous semiconductor formation substrate according to the present invention. This substrate for forming an amorphous semiconductor includes a low melting point glass substrate 1, a first tensile film 2a, a first compressive film 3a, a second tensile film 2b, which are sequentially formed on the low melting point glass substrate 1. The buffer layer 4 including the second compressive film 3b, the third tensil film 2c, and the third compressive film 3c, and the amorphous silicon (hereinafter referred to as a-Si) formed on the buffer layer 4. (Abbreviated) membrane 5 and. Here, the above-mentioned tencil films 2a to 2c are made of, for example, SiO ₂ and
It is formed by the CVD method. On the other hand, the compressive films 3a to 3c are made of, for example, SiO ₂ and are formed by the RF sputtering method.

Next, a method for manufacturing the above-mentioned amorphous semiconductor forming substrate and a method for manufacturing a thin film transistor by obtaining a polycrystalline semiconductor forming substrate from this amorphous semiconductor forming substrate will be described with reference to FIG. First, as shown in FIG.
A low-melting-point glass substrate 1 is prepared, and then, as shown in FIG.
First tensile film 2a made of ₂ film, a first compressive layer 3a, a second tensile film 2b, a second compressive layer 3b, a third tensile film 2c, and a third compressive film 3c Formed sequentially and the total thickness is 1.5 μm
To obtain the buffer layer 4.

Tensile films 2a to 2a consisting of the above SiO ₂ film
2c is formed by, for example, the APCVD method. The formation conditions are as follows: flow rate of silane gas (SiH ₄ ) is 0.9 liter / min, flow rate of oxygen (O ₂ ) is 1.5 liter / m.
in, glass substrate temperature 430 ° C., film formation rate 10
It is set to 00Å / min. The internal stress of the tensile films 2a to 2c thus formed is +1.5 to 3.5 × 1.
It becomes 0 ⁹ dyn / cm ² .

On the other hand, the compressive films 3a to 3c made of SiO ₂ film are formed by, for example, the RF sputtering method. The formation conditions are RF power of 200 W, glass substrate temperature of 200 ° C., and chamber pressure of 5 mTorr.
r, the amount of argon (Ar) gas injected is 10 sccm, and the film forming rate is 30 Å / min. The internal stress of the compressive film thus formed is -1.2 to -1.8.
It becomes × 10 ⁹ dyn / cm ² .

The tensile films 2a to 2c and the compressive films 3a to 3c are formed to have a film thickness of about 7,000 Å or less so that their internal stresses do not become too large.

Next, as shown in FIG.
The film 5 is formed with a film thickness of 500Å by the plasma CVD method. As a result, an amorphous semiconductor formation substrate is obtained.

Next, as shown in FIG. 3D, the above amorphous semiconductor formation substrate is heated to 400 ° C. by the heater 6, and in this state, as shown in FIG. -An excimer laser of 300 mJ / c is applied to the Si film 5.
Irradiation is performed under the conditions of m ² and 8 shots. As a result, a poly-Si film 5'having a grain size of 5000 Å or more can be obtained without cracks in the buffer layer. Above poly-S
When the i film 5'is obtained, as shown in FIG.
The ly-Si film 5'is patterned, and further, the source contact region and the drain contact region are formed by impurity doping, and the oxide insulating film 7, the gate electrode 8, the source electrode 9, the drain electrode 10 and the like are formed. A TFT (thin film transistor) is formed. In this TFT, the field effect mobility is 200 cm ² / V · s
Is achieved.

As described above, in the amorphous semiconductor forming substrate according to the present invention, the buffer layer 4 of the substrate is a tensil film 2a to 2c.
And the compressive films 3a to 3c are laminated, the total stress in the buffer layer 4 is reduced by internal stress in the opposite directions of the tensile films 2a to 2c and the compressive films 3a to 3c. Getting smaller,
Generation of cracks is prevented. Then, by using the above-mentioned amorphous semiconductor formation substrate having the buffer layer 4 of a relatively thick film in which no crack is generated, the low melting point glass substrate 1 by heating for recrystallization and irradiation of excimer laser 1 Heat damage to the semiconductor film is reduced, and diffusion of impurities from the low melting point glass substrate 1 to the semiconductor film is prevented. Therefore, the high mobility poly-Si film can be stably formed on an inexpensive glass substrate.

In this embodiment, the tensile films 2a ...
Although 2c and the compressive films 3a to 3c are formed of SiO ₂ films, they may be formed of SiN _x film or the like. When forming a tensile film of SiN _x film, for example, a Si-rich film is formed by a plasma CVD method. On the other hand, when forming a compressive film, for example, a stoichiometry film is formed by a plasma CVD method.

It does not matter whether the uppermost film of the buffer layer 4 is a tensil or a compressive film. However, when the uppermost film is a tensil, po
The ly-Si film 5'is subject to compressive strain, the average effective mass of electrons increases, and the electron mobility slightly decreases. On the other hand, when the uppermost film is made compressive, poly-Si is used.
The film 5'is subjected to tensile stress, the average effective mass of electrons is reduced, and the electron mobility is slightly increased. Therefore, if possible, it is preferable that the uppermost film is a compressive film.

(Embodiment 2) Next, another embodiment of the present invention will be described with reference to FIG. The substrate for forming an amorphous semiconductor of the present embodiment includes a low melting point glass substrate 1, a Tensile film 2a to 2c including a Na ⁺ killer layer 12, and a compressive film 3.
The buffer layer 4 made of a to 3c is formed, and the a-Si film 5 is formed on the buffer layer 4. The Na ⁺ killer layer 12 is made of WO ₃ or MoO ₃ and is formed by a vapor deposition method or a sputtering method to have a film thickness of several hundred Å.
The stress of the Na ⁺ killer layer 12 is + 0.5 × 10 ⁹
It is dyn / cm ² .

According to the above structure, the Na ⁺ killer layer 12 is included in one of the films constituting the buffer layer 4 while reducing the total internal stress in the buffer layer 4, so that the Na ⁺ The effect of preventing impurity diffusion into the poly-Si film 5'is further improved, and the quality of the polycrystalline semiconductor formation substrate can be further improved. Therefore, when a TFT is formed using this film, stable characteristics can be obtained without being affected by mobile ions such as Na ⁺ ions.

[0025]

As described above, according to the present invention, the total internal stress in the buffer layer is reduced due to the stress in the opposite directions of the tensile film and the compressive film, and the cracks in the buffer layer are reduced. Occurrence is prevented.
In addition, by using the above-mentioned amorphous semiconductor formation substrate having a relatively thick buffer layer in which cracks are not generated, heat for recrystallization and thermal damage to the glass substrate due to irradiation of a high energy beam After the recrystallization, the high quality polycrystalline film can be stably obtained with high yield, and the diffusion of impurities from the glass substrate to the semiconductor film can be prevented, and the polycrystalline film can be stabilized. Play together.

Further, WO ₃ or MoO _{3 is} added to the buffer layer.
By forming the film, the effect of preventing the diffusion of impurities into the polycrystalline semiconductor film after the high energy beam irradiation is further improved, and the quality of the polycrystalline semiconductor formation substrate can be further improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an amorphous semiconductor formation substrate of the present invention.

FIG. 2 is a vertical cross-sectional view showing a method of manufacturing an amorphous semiconductor formation substrate of the present invention, a method of manufacturing a polycrystalline semiconductor formation substrate using the amorphous semiconductor formation substrate, and a method of manufacturing a thin film transistor in the order of steps. It is a figure.

FIG. 3 is a cross-sectional view of an amorphous semiconductor formation substrate having a Na ⁺ killer layer as a buffer layer of the present invention.

FIG. 4 is a vertical sectional view of a conventional amorphous semiconductor formation substrate.

[Explanation of symbols]

1 Low melting point glass substrate 2a-2c Tensile film 3a-3c Compressive film 4 Buffer layer 5a-Si film 5'poly-Si film 6 Heater 12 Na ⁺ killer layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 29/784 21/336

Claims (3)

[Claims] 1. An amorphous semiconductor forming substrate formed by forming an amorphous semiconductor film on a glass substrate via a buffer layer, wherein the buffer layer comprises a laminated film of a tensil film and a compressive film. An amorphous semiconductor formation substrate characterized by: 2. The amorphous semiconductor according to claim 1, wherein at least one of the plurality of films forming the buffer layer is made of a WO ₃ or MoO ₃ film having a high impurity diffusion blocking effect. Forming substrate. 3. A polycrystalline semiconductor film is formed by irradiating the amorphous semiconductor film with a high energy beam in a state where the amorphous semiconductor formation substrate according to claim 1 or 2 is heated. A method for manufacturing a crystalline semiconductor formation substrate.