JPH0521344A - Thin film transistor and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a thin film transistor useful for a TFT active matrix, etc., in which an amorphous or polycrystalline semiconductor layer partly recrystallized with high crystallinity is formed on an insulating board. CONSTITUTION:A thin film transistor comprising a heat sink layer 4 having a high the conductivity is provided corresponding to a recrystallized region between an insulating board 1 and a partly recrystallized polycrystalline or amorphous semiconductor layer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to S constituting a thin film transistor.
The present invention relates to a method for recrystallizing a polycrystalline or amorphous semiconductor layer of a thin film having an OI structure.

[0002]

2. Description of the Related Art At least a part of a semiconductor film formed by dividing a polycrystalline or amorphous semiconductor layer into a plurality of regions on an insulating substrate such as glass is heated to a recrystallization temperature or higher by a local heating means. Then, after recrystallizing the semiconductor film, a thin film transistor is formed on each of the semiconductor films in the plurality of regions, and a method of manufacturing a semiconductor device is known (Japanese Patent Laid-Open No. 64-45162). . Then, according to the method, by separating the semiconductor film that is recrystallized and the semiconductor film that is not recrystallized, recrystallization can be performed in a state where there is little thermal influence on the semiconductor film that is not recrystallized. .

However, according to the above method, since the semiconductor layer is directly formed on the insulating substrate, a substrate having no heat resistance cannot be used. Further, when a laser beam that is usually used as a heating means for recrystallizing a polycrystalline or amorphous semiconductor layer is used, a bimodal laser beam that is known as a method capable of controlling the position of crystal defects is used. Even if it is used, when a substrate having poor thermal conductivity such as glass is used, there is a problem that the temperature distribution of the semiconductor layer becomes as shown in FIG. 4 and a film with good crystallinity cannot be obtained.

[0004]

[Object] The present invention relates to a thin film transistor in which an amorphous or polycrystalline semiconductor layer partially recrystallized with good crystallinity is formed on an insulating substrate.

[0005]

According to the present invention, in a thin film transistor formed on an insulating substrate, a heat sink having good thermal conductivity corresponding to a recrystallized region between the insulating substrate and a partially recrystallized polycrystalline or amorphous semiconductor layer. The present invention relates to a thin film transistor having a layer. However, it is not necessary to recrystallize the semiconductor on the heat sink layer over the entire surface. For example, when only the transistor formation portion driven at high speed is recrystallized, the area of the recrystallized region is smaller than that of the heat sink layer.

Next, the structure of the thin film transistor of the present invention and the manufacturing method thereof will be specifically described with reference to the drawings. First, on the insulating substrate 1, a heat sink layer 4 made of a high melting point metal film of Ta, W, Cr, Mo or the like and having good thermal conductivity is formed. The heat sink layer 4 is provided corresponding to a region of the polycrystalline or amorphous semiconductor layer 5 provided with the insulating layer 3 recrystallized. This heat sink layer 4
The thickness of 1 depends on the semiconductor film to be recrystallized and the laser irradiation conditions, but may be 1 to several μm. The means for forming the heat sink layer 4 may be one that is usually adopted for forming a metal film, but a mask sputtering method or a mask vapor deposition method is particularly preferable. Even if the film thickness is several μm,
Since the inclination of the end of the heat sink layer is gentle, there is an advantage that the coverage of the film formed on the upper portion is improved.

The thermal barrier layer 2 may be previously formed on the insulating substrate before the heat sink layer is formed. Especially when a substrate having no heat resistance is used, it is preferable to provide such a film. For example, the SiO ₂ layer 2 is formed to a thickness of 2000 to 5000 Å by a CVD method or the like to form a thermal barrier layer.

After forming the heat sink layer 4, the insulating layer 3, the polycrystalline or amorphous Si layer 5, and the insulating film 6 are sequentially formed by a conventional method. SiO ₂ as the insulating films 3 and 6
Alternatively, a Si ₃ N ₄ film is used. The insulating film 6 is formed for the purpose of suppressing the reflection of the laser light applied to crystallize the a-Si film 4 and preventing hydrogen from being released from the a-Si layer when the laser light is applied.

The polycrystalline or amorphous Si layer 5
Is melted and recrystallized from above the insulating film by using a laser beam 7. This laser recrystallization is performed only on the semiconductor region on the heat sink layer 2. When crystallization is performed using the laser beam 7, the power distribution in the laser beam 7 usually has a Gaussian distribution. Therefore, if irradiation is performed as it is, crystal growth proceeds from the periphery of the irradiation region to the center,
Due to the large number of nucleation, each growth surface meets and it is not possible to obtain a large single crystal. Therefore, the temperature distribution of the polycrystalline or amorphous layer 5 is periodically changed, or a bimodal type is used for crystal growth.

Also in the present invention, it is preferable to use a bimodal beam for laser beam irradiation. The method of Souhou Beam is
In the present invention, although not particularly limited, for example, 1
A method of circularly polarizing the laser light of a book using a quarter-wave plate and making it into two bimodal beams by a crystal birefringent plate can be mentioned.

When Si is melted and recrystallized by using a bimodal beam as a laser beam, crystallization starts from the center point of irradiation of the bimodal beam, that is, a portion having a low temperature, and the crystal grows to the outside. It is easy to obtain a high mobility film having a large particle size. However, if the temperature distribution is not optimized, many crystal defects such as cracks will occur even if a bimodal beam is used.
You can't get a good film. For example, when a substrate having poor thermal conductivity such as glass is used, the difference in temperature between the beam center point and other portions becomes too large as shown in FIG. 4, so that a good film can be obtained. Absent. However, by providing the heat sink layer, even in such a case, the inclination of the temperature distribution becomes gentle and a crystal grain having a large grain size can be obtained.

The type of the laser beam 7 used in the present invention is not particularly limited, and examples thereof include an excimer laser and an argon laser.

In the present invention, the semiconductor layer crystallized by the laser beam is not limited to the above-mentioned polycrystal or amorphous Si layer, and silicon will be described in detail as the semiconductor thin film of the present invention. Not limited to silicon, it can be applied to all materials having a periodic rate of IV, III-V, II-VI, or a compound semiconductor, the crystal structure of which is a diamond structure or a zinc blend structure. , Specifically, in addition to Si,
Ge, SiC, BN, BP, BAs, AlP, AlS
b, GaP, GaAs, GaSb, InP, InAs,
InSb, ZnS, ZnSe, ZnTe, CdS, Cd
Se, CdTe, CdHg, etc.

Further, the heating source for recrystallizing the polycrystalline or amorphous semiconductor is not limited to the laser beam such as the excimer laser or the argon laser described above, and other lasers or electron beams may be used. Good.

After melting and recrystallization by the laser as described above, the peripheral circuit is formed in the recrystallized region, that is, in the upper portion of the heat sink layer, and the TFT of the pixel portion is provided in the non-recrystallized region 3.
By forming a matrix, it is possible to obtain a TFT active matrix that has high-performance peripheral circuits built therein and has no variation in display characteristics.

[0016]

[Effects] (1) Since the heat sink layer having good thermal conductivity is formed only on the transparent insulating substrate under the semiconductor film in the region to be recrystallized, it is possible to form an inexpensive heat-resistant substrate such as glass. Can form a TFT that can operate at high speed. Further, since the portion where the heat sink layer is not formed is transparent, it becomes possible to form pixels such as a liquid crystal display or a light receiving element of an image sensor. That is, it is possible to configure not only the pixel switching elements of the liquid crystal display but also peripheral circuits such as a scanning circuit for displaying an image with TFTs on the same substrate. Furthermore, since the heat generated by laser irradiation escapes through the heat sink layer, the thermal effect on the polycrystalline or amorphous semiconductor layer not irradiated with laser is small. (2) Not only can the heat sink layer be formed at a predetermined position on the heat sink layer by adopting the mask sputtering method or the mask vapor deposition method as the heat sink layer forming method, but also the heat sink layer can be thickened to a thickness of several μm to heat it. In order to improve the absorption of the heat sink layer, the inclination of the end portion of the heat sink layer becomes gentle, so that the coverage of the film formed on the upper portion is improved and the disconnection of the signal wiring or the like does not occur. (3) By adopting a laser beam having a bimodal energy distribution as a local heating means, an appropriate bimodal temperature distribution can be obtained even when a substrate having a poor heat conductor such as glass is used. A Si film having a large diameter can be obtained.

[Brief description of drawings]

FIG. 1 shows a cross-sectional view of an insulating substrate provided with a thermal barrier layer (SiO ₂ ), a heat sink layer and an insulating film used for manufacturing the thin film transistor of the present invention.

FIG. 2 is a sectional view of a thin film transistor having an amorphous or polycrystalline semiconductor layer provided on the insulating substrate of FIG.

FIG. 3 is a plan view of an insulating substrate partially provided with a heat sink layer used for manufacturing the thin film transistor of the present invention.

FIG. 4 shows a temperature distribution of a semiconductor layer of a thin film transistor. X: A curve showing the temperature distribution of the semiconductor layer on the glass substrate provided with the heat sink layer which is a constituent of the present invention. Y: A curve showing the temperature distribution of the semiconductor layer when only the glass substrate is used.

[Explanation of symbols]

1 Insulating Substrate 2 Thermal Barrier Layer (SiO ₂ ) 3 Insulating Layer 4 Heat Sink Layer 5 Polycrystalline or Amorphous Semiconductor Layer 6 Insulating Layer 7 Laser Beam

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

Claims (3)

[Claims] 1. In a thin film transistor formed on an insulating substrate, a heat sink layer having good thermal conductivity corresponding to the recrystallized region is provided between the insulating substrate and the partially recrystallized polycrystalline or amorphous semiconductor layer. A thin film transistor which is provided. 2. A heat sink layer is partially provided on an insulating substrate, and then a polycrystalline or amorphous semiconductor layer is formed, and then only the semiconductor layer region on the heat sink layer is partially recrystallized. The method of manufacturing a thin film transistor according to claim 1, wherein. 3. A polycrystalline or amorphous semiconductor film is recrystallized by using a laser beam having a bimodal energy distribution, and a heat sink layer having good thermal conductivity is formed by a mask sputtering method or a mask evaporation method. The method for producing a thin film transistor according to claim 2, wherein the method is performed using the thin film transistor.