JPS5961184A - Thin film transistor and its manufacturing method - Google Patents

Abstract

PURPOSE:To introduce an impurity at a low temperature at a low cost by making indium contain in a source region and a drain region as the impurity and forming these regions to a gate electrode in a self-alignment manner. CONSTITUTION:A semiconductor thin-film 402 is formed on a glass substrate 401, a gate insulating film 403 is deposited, the gate electrode 404 is formed, the gate insulating film 403 except a region coated with the gate electrode 404 is removed, and a thin-film 405 containing indium is deposited on the whole surface. Indium made contain in the thin-film 405 is diffused in the semiconductor thin- film 402 through proper heat treatment. Or indium can be diffused in the semiconductor thin-film 402 in the same manner even when the thin-film 405 is deposited while heating the substrate. Accordingly, the source region 406 and the drain region 407 containing indium as the impurity are formed. The thin-film 405 containing indium is removed, and an inter-layer insulating film 408, a source electrode 409 and a drain electrode 410 are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin film transistor using a semiconductor thin film and a method for manufacturing the same, and more particularly to a structure of a source region and a drain region thereof and a method for manufacturing the same.

In recent years, active research and development has been conducted on thin film transistors using semiconductor thin films, particularly thin film transistors using silicon thin films such as polycrystalline silicon and/or amorphous silicon. Most of these are aimed at constructing active matrix panels using thin film transistors to realize large-area, large-capacity flat displays. In this case, an inexpensive transparent insulating substrate such as glass is often used as the substrate. This is to reduce the cost of the substrate, which accounts for a large proportion of the total cost of an active matrix panel, and to improve the display quality of the display by using a transparent substrate.

To meet these specifications, glass is most commonly used as the substrate. However, glass lacks heat resistance,
It is impossible to use it above 500°C to 600°C. Therefore, all steps in the manufacturing process for thin film transistors formed on glass must be performed at temperatures below this temperature.

For this reason, various problems arise in manufacturing excellent thin film transistors. One of them is the structure of the source region and drain region and the method of forming the same. Hereinafter, the structure and manufacturing method of a conventional thin transistor will be described, and then the problems of the source region and drain region will be described in detail.

FIG. 1 is a drawing showing the general structure of a conventional thin film transistor. 101 is a glass substrate, and 102 is a semiconductor HIi film made of polycrystalline silicon, amorphous silicon, or the like. 1
06 is a source region, and 104 is a drain region, which are doped with appropriate impurities and have P-type or N-type conductivity. 105 is a gate insulating film, 106 is a gate electrode,
107 is an interlayer insulating film. 108 is a source electrode, 10
9 is a drain electrode, and the source region 103,
It is in contact with the drain region 104. As described above, the structure of the thin film transistor is basically the same as a normal MO8 type transistor using single crystal silicon, and the operating mechanism is also very similar.

FIG. 2 is a drawing showing an example of a method for manufacturing a thin film transistor having the structure shown in FIG.

First, a semiconductor thin film 202 is deposited on a glass substrate 201 as in the 21st Te (α). Next, a gate insulating film 203 is formed as shown in FIG. 2(b). Formation methods include chemical vapor deposition (hereinafter referred to as OVD) and plasma OV.
The D method or the sputtering method is used. Then the 21st
A gate electrode 204 is formed as shown in ffi (C).

A semiconductor thin film such as polycrystalline silicon or a metal thin film is used for this purpose. After that, as shown in No. 21'N(d), appropriate impurities are added to the semiconductor thin film 20 by ion implantation.
2, the source region 205 and the drain region 20
form 6. Next, as in No. 21J(e), after depositing an interlayer insulating film 207, a contact hole 208 is opened. Furthermore, as shown in FIG. 2(1), a source electrode 209 and a drain electrode 210 are formed to complete the thin film transistor.

In the above example, when forming the source region and the drain region, ion implantation (ion implantation method) is used; other methods include introducing impurities using thermal diffusion and depositing a semiconductor thin film containing impurities. A method of using this as a source region and a drain region is known.

When forming the source region and drain region of a thin film transistor, the following three points are required for the formation method.

(1) Low temperature within the range that guarantees the heat resistance of glass (5
Impurities can be introduced at temperatures below 00 to 600°C.

(2) Be formed in a self-aligned manner with respect to the gate electrode.

(8) It can be formed at low cost.

(1) is a limitation caused by the use of a glass substrate as described above. The main objective of (2) is to reduce parasitic capacitance, and this is particularly strongly required when realizing a large-area active matrix panel or when realizing a thin film transistor that operates at high speed. (3) is
This is to reduce the cost of the active matrix channel, and if the process cost becomes expensive, it becomes pointless to manufacture thin film transistors at low temperatures using inexpensive glass substrates.

The ion implantation method satisfies items (1)e and (2), but the equipment is very expensive and does not satisfy item (3). In addition, the thermal diffusion method satisfies (2) and (1), but generally has a
It requires a temperature of 0°C or higher and does not satisfy (1). Furthermore, methods of depositing a semiconductor thin film containing impurities and using this as a source region and a drain region are (1), (
Although item 3) is satisfied, item (3) cannot be satisfied because it is difficult to form it in a self-aligned manner with respect to the gate electrode. That is, no matter which conventional method is used, the above three items cannot be satisfied.

The present invention aims to eliminate such drawbacks, and its purpose is to provide a novel method for forming a source/drain region that can be formed inexpensively at low temperatures and in a self-aligned manner, and a structure of a thin film transistor using the same. be. Specifically, the source region and the drain region contain indium as an impurity, and the gate 141 . A thin film transistor characterized in that it is formed in a self-aligned manner with respect to a pole, and a step of forming a gate insulating film on a semiconductor thin film, a step of forming a gate electrode on the gate insulating film, and a step of forming a gate electrode on the gate electrode. A thin) thin transistor comprising the steps of: removing the gate insulating film in areas other than the covered region; depositing a thin film containing indium; and diffusing the indium into the semiconductor thin film. Hereinafter, the present invention will be described in detail based on embodiments, which provide a manufacturing method. FIG. 3 is a drawing that does not show an example of the structure of a thin film transistor according to the present invention. 301 is a glass substrate, 302
is a semiconductor thin film such as polycrystalline silicon or amorphous silicon. 303 is a source region, and 304 is a drain region, to which indium is added as an impurity. Since indium is a trivalent element, it acts as an acceptor in the semiconductor thin film, forming the source region 303 and the drain region 3.
04 has P-type conductivity. Furthermore, source area 3
03 and the drain region 304 are formed in a self-aligned manner with respect to the gate electrode 506. - 305 is a gate insulating film, and 307 is an interlayer insulating film. 30B is a source electrode,
3o9 is a drain electrode, and each source region 3o
3. It is in contact with drain region 304.

As can be seen from this, the thin film transistor according to the present invention is characterized in that the source region 303 and the drain region 504 contain indium as an impurity and are formed in a self-aligned manner with respect to the gate electrode 8ii305.

FIG. 4 is a drawing showing an example of a method for manufacturing a thin film transistor according to the present invention. First, as shown in FIG. 4(a), after forming a semiconductor thin film 402 on a glass substrate 401, a gate insulating film 403 is deposited, and then a gate electrode 404 is deposited.
form. The manufacturing method up to this point is the same as the conventional one.

Next, as shown in FIG. 4 (Ch), the gate insulating film 403 except the area covered by the gate electrode 404 is removed. At this time, the electrode 404 can be used as a mask. Next, as shown in FIG. 4(C), a thin film 405 containing indium is deposited over the entire surface.

After that, by applying an appropriate heat treatment at around 300°C, the indium contained in the thin film 405 is removed from the semiconductor thin film 405.
Diffusion into 02. Alternatively, indium can be similarly diffused into the semiconductor thin film 402 by depositing the thin film 405 while heating the substrate to a temperature of around 300°C. Unlike phosphorus, arsenic, boron, etc., indium has the property of diffusing and activating at low temperatures. Therefore, it is possible to diffuse indium at a temperature of around 300° C. and make it work as an acceptor. In this way, a source region 406 and a drain region 407 containing indium as an impurity are formed. Note that the thin film 405 may be made of any material as long as it contains indium and can be diffused into the semiconductor thin film 402, but a typical material is indium oxide (
Examples thereof include indium tin oxide (N, O8) and indium tin oxide (T0). Next, the thin film 405 containing indium is removed as shown in FIG. 4 (Cd), and finally, the interlayer insulating film 408, source electrode 409, and drain electrode 410 are formed as shown in FIG. 4 (i). As described above, the method for manufacturing a thin film transistor according to the present invention includes a step of forming a gate insulating film on a semiconductor thin film, a step of forming a gate electrode on the gate insulating film, and a step of forming a gate insulating film on the semiconductor thin film, a step of forming a gate electrode on the gate insulating film, and a step of forming a gate insulating film on the semiconductor thin film. According to the present invention, which is characterized by comprising the steps of removing a gate insulating film, depositing a thin film containing indium, and diffusing the indium into the semiconductor thin film, the above-mentioned source It is possible to satisfy all three requirements when forming a region and a drain region, that is, 30
It is now possible to introduce impurities at a low temperature of around 0℃,
It becomes possible to form the source/drain regions in a self-aligned manner with respect to the gate electrode, and furthermore, it becomes possible to form them at low cost without using expensive equipment such as ion implantation. As described above, the present invention has excellent effects that could not be achieved with conventional techniques.

FIG. 5 is a drawing showing another embodiment of the thin film transistor and method of manufacturing the same according to the present invention. First, Figure 5 (σ)
After forming a semiconductor thin film 502 on a glass substrate 501, a gate insulating film 503 is deposited IL11, and a gate electrode 504 is further formed. Next, Fig. 5Cb)
The gate insulating film 503 except the area covered by the gate tit electrode 504 is removed as shown in FIG. Next, Figure 5 (C1
), a thin film 505 containing indium is deposited. By applying appropriate heating during deposition or after deposition, the indium in the M film 505 is converted into the semiconductor thin film 50.
2, the source region 506 and the drain region 5
07 is formed. The manufacturing method up to this point is the same as that of the previous embodiment shown in FIG. Thereafter, as shown in FIG. 5Cd), the thin film 505 is patterned to form a source electrode 508 and a drain N-pole 509. In the previous example shown in FIG. 4, the thin film containing indium was removed and new source and drain electrodes were formed, but in this example shown in FIG. 5, the thin film containing indium was removed. Instead, they are used as source and drain electrodes as they are.

Thin films containing indium, such as To, are usually used as transparent conductive films, and if they can be used as source or drain electrodes, they are very convenient for active matrix panel configurations and can shorten the process. It also leads to Of course, it is also possible to further form an interlayer insulating film and add a wiring layer. A feature of the present invention is that the source region and the drain region can be formed in self-alignment with the gate electrode using indium as an impurity, and there are no restrictions on other parts.

As described above, the present invention provides a film transistor on a glass substrate in which a source region and a drain region can be formed in a self-aligned manner with respect to a gate electrode, and impurities can be introduced at low temperature and at low cost. It has extremely excellent effects in forming.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of a conventional thin film transistor. FIG. 2 is a diagram showing a method of manufacturing the conventional thin film transistor shown in FIG. 1. FIG. 6 is a diagram showing the structure of a thin film transistor according to the present invention. FIG. 4 is a diagram showing a method of manufacturing the thin film transistor according to the present invention shown in FIG. 3. FIG. 5 is a diagram showing a second embodiment of the method for manufacturing a thin film transistor according to the present invention. Applicant: Kaiho Seikosha Co., Ltd. Agent Patent Attorney

Claims (2)

[Claims] (1) In a thin film transistor using a semiconductor thin film and having a source electrode, a drain electrode, and a gate electrode, a source region in contact with the source electrode and a drain region in contact with the drain electrode contain indium as an impurity, and the A thin film transistor characterized in that it is formed in a self-aligned manner with respect to a gate electrode. (2) forming a gate insulating film on a semiconductor thin film; forming a gate electrode on the gate insulating film; and removing the gate insulating film other than the region covered by the gate electrode. A method for manufacturing a thin film transistor, comprising the steps of: depositing a thin film containing indium; and diffusing the indium into the semiconductor thin film.