JPH06163589A - Thin film transistor and manufacturing method thereof - Google Patents

Abstract

(57) [Abstract] [Purpose] To increase the crystal grain size of a polysilicon thin film formed by crystallizing an amorphous silicon thin film. A metal layer formed in the three cavity portions 5 on the upper surface of the insulating substrate 1 is etched through an etching hole 4 formed in the insulating film 3 so that a space between the insulating substrate 1 and the insulating film 3 is formed. The three cavities 5 are formed in. Next, a semiconductor thin film (amorphous silicon thin film) is formed on the upper surface of the insulating film 3.
7 is formed, and the semiconductor thin film 7 is annealed by irradiating an excimer laser. In this case, the heat radiation from the semiconductor thin film 7 which has absorbed the laser energy to the insulating substrate 1 can be suppressed by the heat insulating effect of the cavity portion 5, so that the solidification rate of the once melted silicon can be slowed down, and eventually the crystal can be crystallized. The particle size can be increased. Further, the insulating film 3 existing between the three cavities 5 forms the supporting portion 6 for supporting the insulating film 3 existing on the cavities 5, so that the mechanical strength of the insulating film 3 existing on the cavities 5 is increased. I am raising.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor and its manufacturing method.

[0002]

2. Description of the Related Art In the technical field of thin film transistors, an amorphous silicon thin film formed on an insulating substrate made of glass or the like is crystallized into a polysilicon thin film by irradiating a laser to anneal it, or an insulating film made of glass or the like is also used. The polysilicon thin film formed on the substrate may be recrystallized to form a single crystal silicon thin film.

[0003]

However, in such a conventional annealing method, a large amount of heat is radiated from the amorphous silicon thin film or the polysilicon thin film absorbing the laser energy to the insulating substrate, so that the solidification rate of the once melted silicon is large. However, the crystal grain size cannot be increased beyond a certain level. As a result, for example, in the case of a thin film transistor using a polysilicon thin film obtained by crystallizing an amorphous silicon thin film as an active layer, if the crystal grain size of polysilicon is small, the mobility cannot be increased. An object of the present invention is to provide a thin film transistor capable of increasing the crystal grain size and a manufacturing method thereof.

[0004]

According to another aspect of the present invention, there is provided a thin film transistor, wherein a semiconductor thin film serving as an active layer is provided on an insulating film having a heat insulating cavity formed below, and the insulating film is provided in the cavity. A supporting portion for supporting is provided. The method of manufacturing a thin film transistor according to claim 2, wherein a plurality of metal layers having a large wet etching ratio with respect to the insulating film material are formed in the thin film transistor forming region on the insulating substrate,
These metal layers are covered with an insulating film, an etching hole is formed in a part of the insulating film corresponding to the metal layer, and the metal layer is completely removed by wet etching through the etching hole. Thereby, a plurality of heat insulating cavities are formed between the insulating substrate and the insulating film, and the insulating film existing between the cavities supports the insulating film existing on the cavities. A support portion is formed, and a semiconductor thin film made of amorphous silicon, polysilicon, or the like is formed on at least a portion of the insulating film corresponding to a part of the cavity, and the semiconductor thin film is irradiated with a laser to form the semiconductor thin film. It is designed to be annealed.

[0005]

According to the present invention, during laser annealing, the heat radiation from the semiconductor thin film that has absorbed the laser energy to the insulating substrate can be suppressed by the adiabatic action of the cavity, and therefore the solidification rate of the once melted silicon can be reduced. It can be slowed down and the grain size can be increased.
In this case, the reason why the supporting portion for supporting the insulating film is provided in the hollow portion is to increase the mechanical strength of the insulating film on the hollow portion.

[0006]

1 to 6 show respective steps of manufacturing a thin film transistor according to an embodiment of the present invention. Therefore, the structure of the thin film transistor will be described together with its manufacturing method with reference to these drawings in order.

First, as shown in FIGS. 1 (A) and 1 (B),
In the thin film transistor formation region on the upper surface of the insulating substrate 1 made of glass or the like, a plurality of strip-shaped metal layers 2 made of metal having a large wet etching ratio with respect to the insulating film material are formed at intervals in the gate length direction. Form. Next, as shown in FIGS. 2A and 2B, an insulating film 3 is formed on the entire surface, and the insulating film 3 covers the three metal layers 2. Next, as shown in FIGS. 3 (A) and 3 (B),
Etching holes 4 are formed in a portion of the insulating film 3 corresponding to both ends of each of the three metal layers 2 in the gate width direction by photolithography. Next, when wet etching is performed with a metal layer etching solution, all three metal layers 2 are etched and removed through the etching holes 4, and as shown in FIGS. Three cavities 5 are formed between the substrate 1 and the insulating film 3. In this case, since the wet etching ratio of the metal layer 2 to the insulating film 3 is large, when the metal layer 2 made of, for example, aluminum is etched with mixed acid, the cavity 5 can be formed by side etching of 100 μm in about 1 hour.
In addition, the insulating film 3 existing between the three cavities 5 causes
2 for supporting the insulating film 3 existing on the two cavities 5
Although one support part 6 is formed, these support parts 6 will be described in detail later.

Next, as shown in FIGS. 5 (A) and 5 (B),
A semiconductor thin film 7 made of amorphous silicon, polysilicon or the like is patterned on a predetermined portion of the upper surface of the insulating film 3 including a portion corresponding to a part of the cavity 5. Then, the semiconductor thin film 7 is irradiated with an excimer laser to anneal the semiconductor thin film 7. In this case, the heat radiation from the semiconductor thin film 7 which has absorbed the laser energy to the insulating substrate 1 can be suppressed by the heat insulating effect of the cavity portion 5, so that the solidification rate of the once melted silicon can be slowed down, and eventually the crystal can be crystallized. The particle size can be increased. As a result, for example, in the case of a thin film transistor having a polysilicon thin film obtained by crystallizing an amorphous silicon thin film as an active layer, the crystal grain size of polysilicon can be increased, so that the mobility can be increased.

In the following, as shown in FIG.
As shown in (B) and (C), the semiconductor thin film 7 is separated into elements, then the gate insulating film 8 is patterned, then the gate electrode 9 is patterned, and then the semiconductor thin film 8 is formed using the gate electrode 9 as a mask. Injecting impurities to activate
Next, contact holes 10 are formed in the gate insulating film 8 and then source / drain electrodes 11 are patterned to complete a thin film transistor. If the impurities injected into the semiconductor thin film 7 are activated by irradiating the excimer laser, the heat radiation from the semiconductor thin film 7 which has absorbed the laser energy to the insulating substrate 1 is also caused by the heat insulating action of the cavity portion 5 in this case. Can be suppressed.

Now, the supporting portion 6 for supporting the insulating film 3 existing on the cavity 5 will be described. For example, the height of the cavity 5 is set to 6000Å and the insulating film 3 is filled with plasma C
A 4000 N thick silicon nitride film deposited by VD and a film thickness of 1 deposited by sputtering on this silicon nitride film.
In the case of a 000 Å silicon oxide film, if the width of the cavity 5 in the gate length direction is about 20 μm, it can withstand a pressure of about 100 kg / cm ² . Therefore, by the support portion 6 provided in the cavity portion 5,
The mechanical strength of the insulating film 3 on the cavity 5 can be increased. As a result, especially in the case of a thin film transistor having a large size, it is possible to prevent the mechanical strength from being lowered even if the cavity 5 is provided.

In the above embodiment, a thin film transistor having a single layer structure has been described, but the present invention is not limited to this, and can be applied to a thin film transistor having a multilayer structure. For example, in the case of a thin film transistor having a two-layer structure, an interlayer insulating film is provided on the entire surface of the first layer thin film transistor shown in FIG. 6, and the insulating substrate 1 of the thin film transistor shown in FIG. A second layer thin film transistor corresponding to the removed portion may be provided.

[0012]

As described above, according to the present invention, the heat radiation from the semiconductor thin film which has absorbed the laser energy to the insulating substrate can be suppressed by the adiabatic action of the cavity, so that the once melted silicon is solidified. The speed can be slowed down, and the grain size can be increased. As a result, for example, in the case of a thin film transistor having a polysilicon thin film obtained by crystallizing an amorphous silicon thin film as an active layer, the crystal grain size of polysilicon can be increased, so that the mobility can be increased. Moreover, the mechanical strength of the insulating film on the cavity can be increased by the support provided in the cavity.

[Brief description of drawings]

1A is a plan view showing a state in which a metal layer is formed on an upper surface of an insulating substrate in manufacturing a thin film transistor according to an embodiment of the present invention, and FIG. 1B is a sectional view taken along line XX thereof.

FIG. 2A is a plan view showing a state in which an insulating film is formed in manufacturing the same thin film transistor, and FIG. 2B is a sectional view taken along line XX thereof.

FIG. 3A is a plan view showing a state in which an etching hole is formed in manufacturing the same thin film transistor, and FIG.
-A sectional view taken along the line X.

FIG. 4A is a plan view showing a state in which a metal layer is removed to form a cavity portion and a support portion at the time of manufacturing the thin film transistor, and FIG. 4B is a sectional view taken along line XX thereof.

FIG. 5A is a plan view showing a state in which a semiconductor thin film is formed in manufacturing the same thin film transistor, and FIG. 5B is its XX line.
Sectional drawing which follows the line.

6A is a plan view showing a completed state of the thin film transistor, FIG. 6B is a sectional view taken along the line XX, and FIG. 6C is a sectional view taken along the line YY.

[Explanation of symbols]

 1 Insulating Substrate 2 Metal Layer 3 Insulating Film 4 Hole for Etching 5 Cavity 6 Support 7 Semiconductor Thin Film

Claims (2)

[Claims] 1. A semiconductor thin film serving as an active layer is provided on an insulating film in which a heat insulating cavity is formed below, and a supporting portion for supporting the insulating film is provided in the cavity. Thin film transistor. 2. A plurality of metal layers having a large wet etching ratio with respect to an insulating film material are formed in a thin film transistor formation region on an insulating substrate, and these metal layers are covered with an insulating film, and the metal layer of the insulating film is formed. An etching hole is provided in a part of the corresponding portion, and the metal layer is completely removed by wet etching through the etching hole, whereby a plurality of heat insulating layers are provided between the insulating substrate and the insulating film. And forming a support part for supporting the insulating film existing on the cavity part by the insulating film existing between the cavity parts, and at least a part corresponding to a part of the cavity part. A semiconductor thin film made of amorphous silicon or polysilicon is formed on the insulating film, and the semiconductor thin film is irradiated with a laser to anneal the semiconductor thin film. And a method of manufacturing a thin film transistor.