JPS63178559A - Thin-film transistor - Google Patents

Abstract

PURPOSE:To prevent the deterioration, etc., of element characteristics, and to improve heat resistance by adding a substance except a semiconductor thin- film and an electrode material difficult to be ionized to one parts or the whole region of a source region and a drain region in the semiconductor thin-film being in contact with a source electrode and a drain electrode. CONSTITUTION:A gate electrode 12 is formed onto an insulating substrate 11 consisting of glass, etc. A gate insulating film 13 is shaped onto the substrate 11, coating the electrode 12, and non-doped amorphous Si14 is formed onto the gate insulating film 13 as a semiconductor film. A not more than 20 at. % substance except a semiconductor thin film and an electrode material difficult to be ionized is contained onto the film 14, and N<+> layers 15, 16 to which nitrogen is added are shaped according to predetermined patterns as an example, and a source electrode 17 and a drain electrode 18 are formed onto the layers 15, 16. Accordingly, the deterioration of element characteristics and the instability of characteristics are eliminated, thus improving heat resistance.

Description

[Detailed Description of the Invention] The present invention relates to thin film transistors (TFT: Th1n Film Tr) such as amorphous silicon thin film transistors.
The present invention relates to an improvement in the element structure of an-sister.

FIG. 4 shows a conventional structure of a staggered amorphous silicon thin film transistor (hereinafter simply referred to as a thin film transistor or TPT) as an example of a conventional strained thin film transistor. l is an insulating substrate such as glass, 2 is a gate electrode such as Or, 3 is a gate insulating film, 4 is a non-doped silicon film as a semiconductor thin film, 5.6 is an n1 layer formed in a predetermined pattern on the upper surface of the silicon film, 7 8 is a source electrode such as Al, and 8 is a drain electrode, which is made of the same <AN material as the source electrode 7.

In this configuration, the n+ layers 5 and 6 are formed by:
This is to establish ohmic contact between the source and drain regions and the electrodes 7 and 8.

The n' layer is formed by adding phosphorus or the like as an impurity when forming the silicon film 4, or by ion implantation or diffusion after forming a non-doped film. Forming the n1 layer in order to make ohmic contact with the electrode is explained in, for example, ``41st Japan Society of Applied Physics Conference Proceedings, Fall 1980, 2.408.19P-Y-1, ``Heat-resistant gate It is also disclosed in publications such as "A-3iFET Supplies, Pine Wood" with

Furthermore, in addition to forming the above-mentioned n'' layer, as a method of bringing the source region and the drain region into contact with the electrode, there is also known a method of bringing the electrode into direct contact with the i-layer, which becomes the channel.

By the way, if an electrode such as A1 is brought into contact with, for example, an n layer as described above, if the element is kept at a relatively high temperature, the metal that is the electrode material will leak into the source and drain regions. This causes problems such as deterioration of device characteristics and destabilization of characteristics. Additionally, if there is a heat treatment step in the process after electrode formation, problems may arise with heat resistance.
Furthermore, it also brings about changes in TPT characteristics in the temperature test in the reliability test.

In view of these problems, the present invention aims to improve the deterioration of element characteristics, instability of characteristics, and heat resistance.

In order to achieve the above object, the thin film transistor according to the present invention includes a thin film transistor containing a material other than the semiconductor thin film and the electrode material in a part or the entire region of the semiconductor thin film in contact with the source electrode and the drain electrode. It is characterized by the addition of a substance that is difficult to ionize.

When a substance other than the semiconductor thin film and electrode material that is difficult to ionize is added to the semiconductor thin film, this substance has a low tendency to ionize, so it does not combine with other substances in the semiconductor thin film and exists alone. do. Therefore, when the electrode material tries to diffuse into the semiconductor thin film, the substance acts to suppress the diffusion. Since this substance is different from the electrode material, it does not adversely affect the device characteristics or heat resistance. still,
If a large amount of a substance other than the semiconductor thin film and electrode material is added to the semiconductor thin film, it will affect its properties as an active semiconductor, so it is necessary to limit the amount to an appropriate amount.

Large Group One Spot [Example 1] FIG. 1 shows the structure of a staggered amorphous silicon thin film transistor as an example of the present invention. 1) is an insulating substrate made of glass or ceramics, on which a gate electrode 12 is formed in a predetermined pattern. A gate insulating film 13 is formed on the insulating substrate 1) covering the gate electrode 12, and a non-doped amorphous silicon 14, for example, is formed thereon as a semiconductor film. On the silicon film 14, n' layers 15 and 16 doped with nitrogen, which is an example of a substance other than the semiconductor thin film and electrode material that is difficult to ionize, are formed in a predetermined pattern.
A source electrode 17 and a drain electrode 18 are formed on the electrodes 5 and 16.

The gate electrode 12 is formed by depositing, for example, chromium or gold/chromium by electron beam evaporation and patterning. The gate insulating film 13 is formed, for example, by growing a silicon nitride film using a plasma CVD method. The non-doped amorphous silicon film 14 is also formed by the plasma CVD method. n" layer 15,1
6 is first formed on the entire surface of the silicon film 14 by the plasma CVD method, and then patterned together with the electrodes 17 and 18 by etching to form a predetermined pattern. n3
When forming layers 15 and 16 by plasma CVD, 1 to 2% phosphine (PH3) is added to silane gas as a reactive gas.
, mixed with 1 to 20% ammonia (NHs) is used. The source electrode 17 and the drain electrode 18 are formed on the entire surface of the unpatterned N1 layer 15.
It is formed by depositing the I material by a resistance heating deposition method and then patterning it. Patterning is performed on the n''' layer 15.
This will be done in conjunction with 16. That is, first, the upper layer, AI!
, the film, and then the n'' layer. The n'' layer is etched until the non-doped layer is exposed. Incidentally, the etching can be performed by either dry etching or wet etching.

The table below lists typical materials, film thicknesses, and manufacturing methods for each layer and region of the thin film transistor.

Below c, blank space] The typical size of the channel portion between the source region and drain region of the fabricated TPT is a channel width of 50 μm,
The channel length is 20 μm.

FIG. 2 shows the concentration distribution of the electrode material (AI) in the source region or drain region. The solid line is an example of the present invention, and the broken line is a conventional example. From the figure, it can be seen that in the case of the present invention, diffusion of electrode material into the source and drain regions is significantly suppressed.

FIG. 3 shows the temporal change in the OFF current when the TPT manufactured in the above example was left in an atmosphere at 150°C.

As can be seen from the figure, in the conventional TPT without nitrogen added to the n'' layer, the OFF current changes from 10-'' (A) to 10-1° (A) over time, but as in this example, the OFF current changes from 10-'' (A) to 10-1° (A). In the case where nitrogen is added to the n'' layer, the OFF current is 10-''
There was almost no change from (A). From this,
It can be said that adding nitrogen to the n'' layer can improve reliability such as heat resistance.

In the above embodiment, the gate insulating film 13, the non-doped amorphous silicon layer 14, and the n' layers 15 and 16 are exposed to plasma C.
Although the VD method is used for manufacturing, it goes without saying that other methods such as sputtering may be used. Further, although ammonia is mixed in as a method of adding nitrogen, it can also be carried out using nitrogen gas. Furthermore, ion implantation technology can be used as a method for adding nitrogen.

In addition, the higher the concentration of nitrogen in the n layer, the greater the effect of suppressing the diffusion of the electrode material;
This will affect the properties of the active semiconductor, so the upper limit of the concentration will be determined automatically. Experiments have confirmed that the nitrogen concentration should be kept below 20 at%.

[Example 2] In Example 1, the concentration of nitrogen added to the n' layer is gradually increased as it approaches the source and drain electrodes. This can be achieved by gradually increasing the ammonia concentration during the fabrication of the n+ layer. In this way, by creating a gradient in the nitrogen concentration so that the concentration is highest near the electrode where the electrode material diffuses greatly, the diffusion of the electrode material can be suppressed very effectively.

[Other possible examples]

The substance added to the n+ layer is not limited to nitrogen, but any substance other than semiconductor thin film materials and electrode materials that is difficult to ionize can be used. Such substances belong to group III of the periodic table,
It can be selected from Group IV, Group V, and Group VI, and is particularly preferably selected from carbon, boron, and oxygen. Furthermore, the substance is
Not limited to one type among carbon, boron, oxygen and nitrogen, but two
You can select and use more than one type.

Further, the above substance may be added to the entire source region and drain region, or may be added to only a part of the region. In that case, it is preferable to add it so that it exists at a high concentration as close to the electrode as possible.

All of the above embodiments are examples of application to amorphous silicon TPT, but in addition to amorphous silicon TPT, it is also possible to apply to other currently known types of TPT such as polycrystalline silicon TPT. It goes without saying that there is. In addition, the structure of TPT is not limited to the staggered structure shown in the example, but also coplanar (
The application of the present invention is not hindered even in the case of a coplarnar type.

As explained above, according to the TPT according to the present invention, diffusion of the electrode material can be suppressed by adding an appropriate amount of a substance that is difficult to ionize, such as nitrogen, to part or all of the source region and drain region. Therefore, it is possible to stabilize the OFF current and improve heat resistance. TPT is used as a drive circuit for EL display devices and liquid crystal display devices, so
Considering that a large ON10 F F current ratio is required and a wide storage temperature and operating temperature are required, the T of the present invention
PT brings about great effects such as being able to be used outdoors and applied to devices that require high reliability.

In addition, since diffusion of the electrode material is suppressed by the present invention, an inexpensive material such as AA material can be used as the electrode, and the cost of devices such as EL display devices incorporating a large number of TPTs can be reduced. .

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of a staggered amorphous silicon TPT as an example of the present invention, FIG. 2 is a diagram showing the concentration distribution of electrode material (AA) in the source and drain regions, and FIG. FIG. 4 is a diagram showing the temporal change in the OFF current of a TPT left at 150° C., and FIG. 4 is a diagram showing the structure of a conventional amorphous silicon TPT. 1)...Insulating substrate, 12...Gate electrode, 13...
・Gate insulating film, 14... Non-doped amorphous silicon film, 15.16... n layer, 17... Source electrode,
18...Drain electrode. Patent Applicant: Sanyo Electric Co., Ltd. Agent: Patent Attorney Shiro Nakajima Figure 1 Figure 2 Sauce Or Ikui Drain Kinryo\'s AQ Takumoto-kara no Itosa Figure 3 Chorus Figure 4

Claims (1)

[Claims] (1) A substance other than the semiconductor thin film and electrode material that is difficult to ionize is added to a part or the entire region of the source region and drain region of the semiconductor thin film in contact with the source electrode and drain electrode. A thin film transistor characterized by: (2) The thin film transistor according to claim (1), wherein the semiconductor thin film is an amorphous silicon thin film. (3) Substances other than the semiconductor thin film and electrode materials that are difficult to ionize are contained in the source region at a concentration of 20 at% or less.
Claim (1) or (2) characterized in that the compound is added to a part or the entire region of the drain region.
) The thin film transistor according to any one of the items. (4) Claims (1) to (3) characterized in that the source electrode and the drain electrode are formed of an Al material.
2. The thin film transistor according to any one of paragraphs. (5) The substance other than the semiconductor thin film and electrode material that is difficult to ionize is selected from at least one of Group III, Group IV, Group V, and Group VI of the periodic table. The thin film transistor according to any one of ranges (1) to (4). (6) At least one of boron, carbon, nitrogen, and oxygen is selected as the substance other than the semiconductor thin film and electrode material that is difficult to ionize. The thin film transistor according to any one of (4). (7) At least one substance other than the semiconductor thin film and the electrode material that is difficult to ionize increases as it approaches the electrode.
The thin film transistor according to any one of items 1) to (6).