JPH0677484A - Thin-film transistor and its manufacture - Google Patents

Abstract

PURPOSE:To efficiently and surely perform a hydrogenation operation in order to terminate a dangling bond near the interface between an Si film and a gate insulating film. CONSTITUTION:A hydrogen supply source for a hydrogenation operation is installed near the interface between an Si film and a gate insulating film by means of a manufacturing method including a process wherein an Si layer to be used as a channel is formed as a two-layer structure and a lower-layer channel poly-Si film 31 is formed, a process wherein a plasma SiN film 2 containing hydrogen in large quantities is formed by a PCVD method and a process wherein an upper-layer channel poly-Si film 32 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a polycrystalline silicon thin film transistor, and more particularly to manufacturing a polycrystalline silicon thin film transistor on a transparent amorphous insulator substrate such as glass or quartz used for liquid crystal display devices. Regarding the method.

[0002]

2. Description of the Related Art Conventionally, a polycrystalline Si (silicon) thin film transistor (hereinafter, the thin film transistor is abbreviated as TFT)
In the manufacture of liquid crystal display devices, chemical vapor deposition (CV) is performed on a transparent amorphous insulator substrate such as alkali-free glass or quartz.
D) method or the like is used to deposit amorphous Si, and the amorphous Si is deposited by an electric furnace.
Heat anneal at about 00 ° C. for about 1 to 100 hours, or irradiation with a laser beam or a lamp for 10 nsec.
The temperature is raised to about 800 to 1200 ° C. for about several seconds to polycrystallize.

After etching the polycrystalline Si film thus formed into a desired shape and size, an insulating film or polycrystalline Si film is formed.
A film or metal film is formed and patterned. Then, at the end of the normal TFT formation process, dangling bonds (10 ¹⁹ to 10 ¹⁹⁾ existing near the interface between the polycrystalline Si film and the gate insulating film are formed.
Hydrogenation is carried out in which ²² cm ⁻³ ) is filled with hydrogen to be terminated. This hydrogenation improves transistor characteristics such as an increase in field effect mobility and a decrease in threshold voltage.
The maximum process temperature up to hydrogenation is about 600 ° C. or lower, which is lower than the strain point of the glass used as the substrate.

Conventionally, plasma hydrogenation or SiN film hydrogenation has been used as the hydrogenation method. Plasma hydrogenation is performed in a plasma-enhanced chemical vapor deposition (PCVD) apparatus at 200-
This is a method of hydrogenating a TFT exposed to hydrogen plasma at 400 ° C. Hydrogenation by a SiN film forms a SiN film containing a large amount of hydrogen as a passivation film, and hydrogen in the film is 300 to 450. It is a method of hydrogenating by diffusing by heat of about ℃.

[0005]

However, as shown in the sectional view of FIG. 2, the conventional planar type polycrystalline Si TFT is used.
In, the polycrystalline S of the surface and the channel where hydrogen begins to enter
i surface is about 1 μm apart, and the thickness is 200n
Since hydrogen hardly diffuses into the Si gate electrode 5 having a thickness of about m or more, hydrogen reaches the Si-gate insulating film interface from the periphery of the gate electrode through the gate insulating film 4 in the lateral direction through the interlayer insulating film.

In this way, the diffusion distance is long, and in the case of plasma hydrogenation, the hydrogen concentration in the PCVD apparatus is 10 ⁹
Since it is as low as cm ^-3, there is a problem that it takes about several hours until sufficient hydrogenation is completed.

In addition, in hydrogenation using a SiN film,
Since the hydrogen concentration is about 10 ²² cm ^-3 and the density is higher than that of plasma hydrogenation, hydrogenation is performed in a short time of about 30 minutes. However, the passivation SiN film and the polycrystalline Si-gate insulating film interface are still present. Since there is a distance of about 1 μm from each other, a large-sized TFT is less likely to be hydrogenated, and there is a problem that characteristics such as an increase in mobility and a decrease in threshold voltage are not performed.

Further, in any hydrogenation, polycrystalline S
Since hydrogen diffusion in i is slow, hydrogen is diffused from the periphery of the gate electrode only in the lateral direction in the gate insulating film 4, so that hydrogen is diffused in the entire Si-gate insulating film interface of TFTs of any size. However, there is also a problem that the characteristics of the TFT vary.

As another hydrogenation method, the channel S
A SiN film is deposited on the entire lower layer of the i film, and a hydrogen supply source and S
There is a method of shortening the distance to the i-SiO ₂ interface, but this is because of the large internal stress of the plasma silicon nitride film itself and the rapid temperature change caused by heat treatment.
After heat treatment with a laser or a lamp, a crack occurs in the film, which causes a problem that the TFT does not operate.

In addition to this, it is possible to use a SiN film as the gate insulating film instead of the SiO ₂ film to eliminate the need for hydrogenation. However, since the SiN film itself tends to deviate from stoichiometry, the resistivity is 10%. ^As low as ⁹ Ωcm,
If the film thickness is as thin as about 100 nm, it is easy to leak between the gate and the source or between the gate and the drain due to conduction of the insulating film, pinholes, etc.
The film thickness must be thicker than about m. If the film thickness is increased, the mutual conductance of the TFT becomes small even if the field effect mobility is high, and high-speed operation becomes impossible,
This means that the purpose of the polycrystalline SiTFT, in which the driver circuit is also formed on the transparent glass substrate, cannot be achieved.

Therefore, an object of the present invention is to provide a dangling at the interface between the polycrystalline Si and the gate insulating film in a planar type polycrystalline Si TFT in which amorphous Si is polycrystallized by annealing with a laser beam or a lamp, regardless of the size of the TFT. Hydrogenation for terminating the bonds is to be carried out efficiently and surely, and electric characteristics such as field effect mobility and threshold voltage of the SiTFT are uniformly improved.

[0012]

In the polycrystalline silicon thin film transistor of the present invention, the polysilicon film of the channel portion is formed by two layers.
The problem is solved by forming a layer and enclosing a layer made of plasma silicon nitride containing a large amount of hydrogen between the layers. Further, in the present invention, a step of depositing a lower layer channel polysilicon on a substrate, a step of depositing a plasma silicon nitride containing a large amount of hydrogen by a plasma chemical vapor deposition method, and an unnecessary portion of the plasma silicon nitride. A polycrystalline silicon thin film transistor can be manufactured by a method including a step of etching and a step of depositing an upper layer channel polysilicon.

[0013]

According to the present invention, in the manufacturing process of the polycrystalline SiTFT, the polySi film of the channel portion has a two-layer structure, and the plasma silicon nitride film containing a large amount of hydrogen is confined between the layers, thereby making The plasma silicon nitride film may be used as a hydrogen source for hydrogenating dangling bonds at the Si-gate insulating film interface.

As a result, the distance from the dangling bond that requires hydrogen to the hydrogen supply source becomes very short,
The thermal annealing process time for hydrogenation can be shortened. Further, since hydrogen is uniformly supplied to the channel portion, pixel TFTs and driver TFs on the same substrate.
Polycrystalline Si TFTs having different shapes and sizes such as T are also uniformly hydrogenated.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1 shows a poly-Si TFT of the present invention with a channel poly S.
FIG. 3 is a cross-sectional view of a structure having two i films and a plasma silicon nitride film containing a large amount of hydrogen sandwiched between the i films. This plasma silicon nitride film is deposited by a parallel plate type plasma vapor deposition (PCVD) apparatus. An example of the deposition conditions is that the flow rate of the raw material is SiH ₄ ; 30SCCM, N
H ₃ ; 100 SCCM, pressure 0.6 Torr, RF power 0.16 W / cm ² , temperature 300 ° C.

The hydrogen in the plasma silicon nitride film does not escape by the heat applied by a lamp, a laser or the like for a short time, and the hydrogen remains in the plasma silicon nitride film even after the formation of the protective film after the TFT process is completed. Is about 10 ²² cm ^-3, which is a sufficient amount, and can serve as a hydrogenation supply source. Also, since the Si film is as thin as about 200 nm or less,
Hydrogen can also diffuse in the vertical direction of the film.

An example of the film thickness and film type of the TFT having this structure is as follows. Plasma silicon nitride film 2 is 200 nm
Is. The channel Si films 31 and 32 have a thickness of about 100 nm. In this, an amorphous Si film is formed by the PCVD method or the like and is polycrystallized by a lamp or laser light. Gate insulating film 4
Forms a SiO ₂ film of 100 to 200 nm by a thermal CVD method or the like. The gate electrode 5 is poly-Si formed by a thermal CVD method or the like.
The film is 200-400 nm thick. The interlayer insulating film 6 is a SiO ₂ film formed by the thermal CVD method to a thickness of 300 to 700 nm. The electrode 7 is formed of a metal such as Al formed by a sputtering method to a thickness of 300 to 1000 nm. The transparent electrode 8 is made of ITO (indium tin oxide) formed by a sputtering method or the like.
de) film with a thickness of 50 to 300 nm. The passivation film 9 is a SiN film or the like formed by the PCVD method, etc.
00 nm is formed. For the diffusion of hydrogen, after forming up to the structure of FIG. 1, thermal annealing is performed at 300 to 450 ° C. in an electric furnace.

FIG. 3 is a diagram showing an example of a process of forming a structure for confining a plasma silicon nitride film with two layers of channel poly Si. If the Si film is formed by the chemical vapor deposition method, the step portion can be covered and the plasma SiN film can be sealed. An example of the process will be described below. Figure 3
In (a), the lower layer channel poly Si31 is first deposited. The plasma SiN film 2 sandwiched in FIG.
After depositing, the SiN film is patterned in FIG. Next, in FIG. 3D, the upper layer channel poly Si 32 is deposited. Then, in FIG. 3E, the channel portion poly-Si film is patterned at a time. The subsequent process is the same as the conventional method.

In the TFT structure of this embodiment, the silicon nitride film has a sufficiently higher resistance than Si, so that
Leakage between drains does not occur, and since the silicon nitride film is patterned, the internal stress of the silicon nitride film itself is relaxed in the vicinity of the transistor, and cracks do not occur in the film. TFT having this structure
In the process, polycrystallization of the amorphous Si film and activation of the source / drain regions are preferably performed by laser or lamp annealing that can be performed in a short time, and it is more preferable to activate the source / drain by laser or lamp.

[0020]

As described above, in the present invention, in the manufacturing process of the polycrystalline Si TFT, the poly-Si film of the channel portion has a two-layer structure, and the plasma silicon nitride film containing a large amount of hydrogen is confined between the layers. As a result, a hydrogen supply source for hydrogenation that terminates the dangling bond at the Si-gate insulating film interface in the final step of SiTFT production is provided near the interface, and the thermal annealing time for hydrogenation is shortened, resulting in a production efficiency. Has the effect of increasing.

In addition, polycrystalline SiTF of any shape and size such as pixel TFTs and driver TFTs on the same substrate.
T is also hydrogenated uniformly, and there is an effect that electric characteristics such as field effect mobility and threshold voltage can be improved uniformly.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a polycrystalline SiTFT of the present invention.

FIG. 2 is a conventional planar type polycrystalline SiTF.
It is sectional drawing of T.

FIG. 3 is a cross-sectional view showing an example of a process of forming a structure for confining a plasma silicon nitride film with two layers of channel poly Si.

[Explanation of symbols]

 1 transparent glass substrate such as non-alkali glass or quartz 2 plasma silicon nitride film 3 channel part polycrystalline Si film 4 gate insulating film 5 gate electrode 6 interlayer insulating film 7 source / drain electrode 8 transparent electrode film 9 passivation film 31 lower layer channel part Polycrystalline Si film 32 Upper channel Polycrystalline Si film

Front page continuation (72) Inventor Shuhei Tsuchimoto 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (2)

[Claims] 1. A polycrystalline silicon thin film transistor, comprising a polysilicon film of a channel portion having two layers, and enclosing a layer made of plasma silicon nitride containing a large amount of hydrogen between the layers. 2. A method of manufacturing a polycrystalline silicon thin film transistor, the step of depositing an underlying channel polysilicon on a substrate, the step of depositing plasma silicon nitride containing a large amount of hydrogen by a plasma chemical vapor deposition method, and A method of manufacturing a polycrystalline silicon thin film transistor, comprising: a step of etching an unnecessary portion of plasma silicon nitride; and a step of depositing an upper layer channel polysilicon.