JPS6315468A - Manufacture of thin film transistor - Google Patents

Abstract

PURPOSE:To enable the manufacture of a thin film transistor having excellent characteristics even by a low-temperature process, by applying an oxygen plasma to a gate insulation film. CONSTITUTION:A polycrystalline silicon thin film 2 is evaporated on the upper surface of a glass substrate 1, an active layer element is formed by patterning, a silicon oxide film 3 to be a gate insulation film is deposited then, annealing is applied in the atmosphere of nitrogen, and an oxygen plasma is applied onto the whole surface. After a polycrystalline silicon film 4 and AlSi film 5 are deposited subsequently, a gate 12 is formed on the silicon oxide film 3 by photolithography. By this method, the characteristics of a thin film transistor are improved.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a method for manufacturing thin film transistors that are applied to active matrix liquid crystal displays that constitute large screens. The present invention relates to a method for manufacturing a III-based transistor that can improve the performance of a thin film transistor formed by a low-temperature process.

(b) Conventional technology In recent years, as liquid crystal displays have become larger and have higher resolution, their drive methods have changed from time-division to simple matrix,
In addition, there has been a shift to an active matrix method, making it possible to display large amounts of information. The active matrix method allows a liquid crystal display to have more than one pixel, and a switching transistor is formed for each pixel.

In addition, transparent substrates such as glass and quartz are used as substrates for various liquid crystal displays because of their high display performance, the ability to use twisted nematic modes, and the possibility of transmissive displays for color display. There is.

Particularly when enlarging the display screen, it is economically advantageous to use inexpensive glass for the display substrate. Therefore, in order to take advantage of this economical efficiency, there has been a desire for a technology that can form thin film transistors for operating active matrix liquid crystal displays on the above-mentioned glass substrate with stable performance.

Amorphous silicon or polycrystalline silicon is usually used as the active layer of a thin film transistor, but polycrystalline silicon, which has a high operating speed, is seen as promising when attempting to form a thin film transistor with a drive circuit integrated. In addition, the gate of polycrystalline silicon thin film transistors is closed! Conventionally, the film used is a thermal oxide film that is formed at around 1000 degrees Celsius, so fused silica, which has excellent heat resistance, has been used as the substrate material.

(c) Problems to be solved by the invention However, as the screens of liquid crystal displays become larger, even if it is desired to use a cheaper glass substrate instead of fused silica, the strain point temperature of the glass is 550 to 600 degrees Celsius, and the thermal oxide film Conventional thermal oxidation methods could not be used because the temperature was lower than the temperature required to form . Therefore, although atmospheric pressure CVD, low pressure CVD, plasma CVD, and photoCVD methods, which can form insulating films at lower temperatures, have been used, at present, the insulating films and their interfaces formed by the above methods have been used. Its characteristics are inferior to those of the PjA oxide film, and it has been difficult to form a transistor with excellent operating characteristics. Furthermore, it is known that heat treatment at 900 to 1000'C is effective in improving the properties of these insulating films formed at low temperatures, but of course, such high temperature heat treatment is effective at improving the properties of these insulating films formed at low temperatures. It could not be used to form thin film transistors on glass substrates.

Therefore, it has been expected to develop a low-temperature treatment method that can provide effects equal to or greater than high-temperature heat treatment.

This invention was made in view of the above circumstances, and its purpose is to provide a method for forming high-performance thin film transistors using a low-temperature process on a glass substrate that can easily be made into a large screen. MI with active layer
The object of the present invention is to form an interface having good characteristics in an S-type field effect transistor.

(d) Means for Solving the Problems This invention provides a method for manufacturing a 1119 transistor in which an active layer is formed on one side of a substrate whose surface is at least made of an insulating material, and an MIS field effect transistor is formed on this active layer. Before the gate of the MIS field effect transistor is deposited on the gate insulating film of the transistor, at least a portion of the gate insulating film where the gate is deposited is irradiated with oxygen plasma. This is a method for manufacturing a thin film transistor.

<Effects> The present invention enables the gate insulating film to be improved even at a low temperature below the strain point temperature of glass by irradiating the gate insulating film with oxygen plasma.

(f) Examples Examples of this invention will be described in detail below with reference to the drawings, but the invention is not limited to the following examples.

FIGS. 1a to 1f are cross-sectional views showing the manufacturing process of a polycrystalline silicon thin film transistor forming an MIS field effect transistor.

The substrate 1 is made of Pyrex glass, which is an insulating material. First, a polycrystalline silicon oxide film 2 is deposited by vacuum deposition on the top surface of a Pyrex glass substrate 1 which has been organically and acid-cleaned. The polycrystalline silicon thin film 2 was formed at a substrate temperature of 500°C, a degree of vacuum of 3×10'pa, and a deposition rate of 1.
Conducted under human/SeC conditions, the film thickness formed was 100
There are 0 people. This polycrystalline silicon thin film 2 is patterned to form an active layer portion (see FIG. 1A). Next, a silicon oxide film 3, which will become a gate insulating film, is deposited at 420° C. by the normal pressure CVI method until its i thickness becomes 500 μm, and annealed in a nitrogen atmosphere. Next, the substrate temperature was 400°C.
Then, the entire surface of the silicon oxide film 3 is irradiated with oxygen plasma for 30 minutes. The output of oxygen plasma at this time is 150mW
/ crj. (See Figure 1). Polycrystalline silicon film 4 is deposited by vacuum evaporation method under the same conditions as
is deposited until the film thickness reaches 500 layers. Subsequently, an At51 film 5 is formed on the upper surface by sputtering to a thickness of 5.
000, silicon oxide B! is deposited by photolithography. A gate 12 is formed on 3 (see FIG. 1C). Next, to prevent contamination during ion implantation, the silicon oxide film 6 is grown to a thickness of 5.
After depositing up to 000 atoms, boron ions (B÷) are implanted at 3×10 2 /d at 70 keV (see FIG. 1C). The surface of the silicon oxide film 6 has a thickness of 200 mm.
After etching to form a silicon oxide layer, a silicon oxide film 7, which will become an interlayer insulating film, is deposited by atmospheric pressure CVD until the film thickness reaches 5000 Å, and then etched in a nitrogen atmosphere for boron activation.
Annealing is performed at 00°C for 1 hour. Then pressure 100p
Hydrogenation is performed in a hydrogen plasma atmosphere at 350° C. for 30 minutes. Next, the contact holes 8 and 9 in the source and drain portions are opened (see FIG. 1C) using a sputtering method.
After depositing tSi to a film thickness of 5000 nm, the source electrode 1o and the drain electrode 1 are formed by patterning.
1 (see Figure 1C). Finally, in a hydrogen atmosphere 4
Annealing is performed at 40° C. for 30 minutes to complete the thin film transistor.

Note that the oxygen plasma irradiation may be applied only to a portion of the silicon oxide film 3 where the gate 12 is deposited.

FIG. 2 shows the gate voltage-source current characteristics of a thin film transistor (channel length: 15 μm, channel width: 20 μm) manufactured in an example of the present invention. A is the one that was irradiated with oxygen plasma after the gate insulating film was formed, and B is the one that was not irradiated. Further, at this time, the voltage of the drain with respect to the source is -2V.

From FIG. 2, it can be seen that the characteristics of the thin film transistor are improved by irradiating the gate insulating film with oxygen plasma.

As described above, by employing oxygen plasma irradiation in the process of polycrystalline silicon thin film transistors, thin film transistors with good characteristics can be formed even in a low temperature process performed on a glass substrate.

In this example, the formability of the gate insulating film is as follows:
Although the atmospheric pressure CVD method is used, the present invention is not limited thereto, and may also be used in combination with a low pressure CVD method, a plasma CVD method, a photo CVD method, or a combination of these methods. In addition, in this example, the output of the irradiated plasma was set to 150 mW/oj, but if it exceeds 20,061 W/oj, the oxide film and interface may be damaged, and the characteristics may deteriorate, so the output is 20,061 W/oj.
It is desirable to keep it below 00mW/oj.

In addition, in order to clarify the effects of this invention, a MOS capacitor was manufactured on a single crystal silicon substrate by the following steps,
As shown in Table 1, the characteristics were measured with and without oxygen plasma irradiation.

In all points in Table 1, improvements in properties were observed by oxygen plasma irradiation. Furthermore, even in measurements after two months, the deterioration of the characteristics of the sample irradiated with oxygen plasma was very slight compared to the sample that was not irradiated.

This is because the film quality (density, composition, interatomic distance, bond angle, etc.) of the silicon oxide film becomes close to that of a thermal oxide film due to oxygen plasma irradiation. By applying this method, it is possible to manufacture transistors with very good characteristics even in a low-humidity process.

Note that the MOS capacitor is manufactured as follows.

First, a 500-layer silicon oxide film is deposited at 420° C. by atmospheric pressure CVD on a P-type single-crystal silicon substrate that has been subjected to RCA cleaning. Then, in a nitrogen atmosphere at 550°C for 1
Annealing is performed for a period of time, and oxygen plasma with an output of 150 mW/cm is irradiated for 30 minutes at a substrate temperature of 400°C. Next, an A1 electrode with a thickness of 500 mm was placed on this silicon oxide film.
0 person evaporates, and further 5000 people evaporates A1 on the back side of the substrate. With the above steps, the MOS capacitor is completed.

(G) Effects of the Invention According to this invention, when forming a thin film transistor on a substrate whose surface is an insulating material, by irradiating the gate insulating film with oxygen plasma, a thin film transistor with good characteristics can be manufactured even in a low temperature process. can. This allows active matrix and
This makes it possible to manufacture panels and can be applied to large-area thin displays.

[Brief explanation of the drawing]

Figures 1a to 1f are cross-sectional views of a polycrystalline silicon thin film transistor manufactured in each process, showing an embodiment of the present invention. FIG. 2 is a comparison diagram comparing characteristics of thin film transistors. 1...Substrate (glass substrate), 2...Active layer (polycrystalline silicon thin film), 12.
...Gate, 3...Gate insulating film (silicon oxide film).雜

Claims (1)

[Claims] 1. A method for manufacturing a thin film transistor, in which an active layer is formed on one side of a substrate whose surface is made of an insulating material, and an MIS field effect transistor is formed on the active layer, comprising: 1. A method for manufacturing a thin film transistor, comprising: irradiating oxygen plasma to at least a portion of the gate insulating film where the gate is deposited before the gate is deposited on the gate insulating film of the transistor.