JPH02222154A - Manufacture of thin film transistor - Google Patents

Abstract

PURPOSE:To form the above thin film transistors readily in a short time when the thin film transistor elements are alinged and formed on a substrate by projecting selectively condensed laser light on a high-resistance, non-single crystal semiconductor thin film, and aiding the crystallization of the light projected part. CONSTITUTION:An Mo film and a low-resistance N-type non-single crystal semiconductor layer are overlapped on a glass plate 11 having an ITO electrode 19. A source 22, a drain 23 and electrodes 24 and 25 are formed by photolithography technology. Then, an I-type non-single crystal film is overlapped by a plasma CVD method. Condensed laser light is projected, and a part 14 wherein the crystal degree is increased is formed. A gate insulating film 17 comprising Si3N4 is overlapped thereon by the plasma CVD method. Vapor deposition of Mo is performed, and the gate electrode 17 is attached. Thus a substrate on which thin film transistors 10 are aligned is completed. A plurality of the thin film transistors can be aligned and formed on the large substrate for liquid display in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a thin film transistor (hereinafter also referred to as TFT) using a non-single crystal semiconductor thin film and a method for manufacturing the same, and in particular to a liquid crystal display.

The present invention relates to a thin film transistor with high-speed response that can be applied to image sensors and the like.

"Prior Art" Recently, thin film transistors using non-single crystal semiconductor thin films fabricated by chemical vapor deposition or the like have been attracting attention.

Since this thin film transistor is formed on an insulating substrate using a chemical vapor phase method as mentioned above, it can be formed at a low temperature of about 450°C at maximum, and it can be formed using inexpensive soda glass or borosilicate. Glass or the like can be used as the substrate.

This thin film transistor is a field effect type, so-called M
It has the same function as an OSFET, but as mentioned above, it can be formed on an inexpensive insulating substrate at low temperatures, and the maximum area that can be fabricated is limited by the dimensions of the equipment that forms the thin film semiconductor. , which had the advantage of being able to easily fabricate transistors on large-area substrates. Therefore, it is extremely promising as a switching element for matrix-structured liquid crystal displays having a large number of pixels, one-dimensional or two-dimensional image sensors, and the like.

Moreover, photolithography, which is an already established technique, can be applied to fabricate this thin film transistor, and so-called microfabrication is possible, and it is also possible to achieve integration like ICs and the like.

A typical structure of this conventionally known thin film transistor is schematically shown in FIG.

(20) is an insulating substrate made of glass, (21)
are thin film semiconductors made of non-single crystal semiconductors, (22), (2
3) is the source/drain region, (24) and (25) are the source/drain electrodes, (26) is the gate insulating film, and (27)
is the gate electrode.

A thin film transistor configured in this way has a gate electrode (
By applying a voltage to source-drain (27),
It adjusts the current flowing between 2) and (23).

At this time, the response speed of this thin film transistor is given by the following equation.

S-μ ・V/L2 Here, L is the channel length, μ is the carrier mobility, and ■ is the gate voltage.

The non-single-crystal semiconductor layer used in this thin-film I transistor contains a large amount of crystal grain boundaries, etc., and due to these, carrier mobility is extremely low compared to single-crystal semiconductors. As can be seen from the equation, a problem occurred in that the response speed of the transistor was extremely slow. In particular, when an amorphous silicon semiconductor is used, its mobility is approximately 0.1 to 1 (cm2/V-3ec), which is such that it hardly operates as a TPT.

As is clear from the above equation, it is known that the solution to this problem is to shorten the channel length and increase carrier mobility, and various improvements have been made.

In particular, various methods have been used to improve mobility. Typically, a non-single-crystal semiconductor is annealed to make it a single crystal or to increase the size of a polycrystalline semiconductor.

In these conventional methods, an expensive heat-resistant substrate must be used because the annealing is performed at high temperatures, and the semiconductor layer on the entire surface of the substrate is made into a single or polycrystalline material, which takes a long processing time. A problem occurred.

Object of the Invention The present invention solves the above-mentioned problems, and provides a method for easily manufacturing a TPT that operates at high speed in a shorter time than conventionally known TPTs. of,
That is the purpose.

rStructure of the Invention In order to achieve the above object, the present invention provides the following features when a plurality of thin film transistor elements are arranged and formed on a substrate.
It is characterized in that a high resistance non-single crystal semiconductor thin film is selectively irradiated with focused laser light to promote crystallization of the high resistance non-single crystal semiconductor layer in the irradiated portion.

Using the present invention, the part irradiated with laser light is TP
By performing the following steps to make the TPT channel part, the carrier mobility of the TPT is increased and the response speed mentioned above is increased, resulting in applications such as liquid crystal displays, image sensors, etc. that could not be applied in the past. This makes it possible to apply the TPT element to.

In the present invention, a plurality of aligned parts are irradiated with laser light in a straight line or in a dot shape, so compared to conventional methods, when irradiating laser light in a straight line, the crystallization of the straight parts is reduced. Acceleration can be performed simultaneously, and multiple portions of a non-single crystal semiconductor thin film can be crystallized in a short time. In addition, even when irradiating in dots, the program for moving the substrate after irradiating one spot is simple because it irradiates aligned parts, and the process is also easy.
Multiple portions of a non-single crystal semiconductor thin film can be crystallized in a short time.

Further, in the present invention, even during etching, the portions irradiated with laser light are less likely to be etched than the portions not irradiated, so the yield during etching can be increased and costs can be reduced.

The present invention will be explained in detail below using Examples.

"Example 1" In this example, the production of a thin film transistor for use in a liquid crystal display will be described.

FIG. 1 schematically shows the manufacturing process of a thin film transistor corresponding to this example.

First, a 300 mm substrate (11) having an ITO electrode (pixel electrode) patterned as a transparent conductive film was used.
This substrate (1
1) Fabricate a molybdenum film on top. Then, a non-single-crystal silicon film having an N-type conductivity type is formed as a low-resistance non-single-crystal semiconductor by a known plasma CVD method. The manufacturing conditions at this time were as follows.

Substrate temperature 250°C Reaction pressure 0.05 Torr 11f power (13,56 MIIz) 150 W Gas used SiH, +PH3 film thickness
2000 people This N-type non-single-crystal silicon film may be formed by introducing a large amount of H2 gas during its formation, increasing the Rf power, and microcrystallizing the film to lower its electrical resistance.

Next, using known photolithography technology, the non-single-crystal silicon film is masked in a predetermined external pattern of the source and drain regions (22), (23) and their extraction electrodes, and dry etching is performed using CF and + gas. and
The state shown in FIG. 1(a) was obtained.

Next, an I-type non-single-crystal silicon film (13) is formed as a high-resistance semiconductor layer by the same plasma CVD method as described above. The manufacturing conditions were almost the same as those for the N-type non-single crystal silicon film, except that only 5il14 gas was used and the film thickness was 6000mm.

Next, the non-single crystal silicon film (13) is
Eximer laser light (15) with a wavelength of 248.7 nm, which is focused by an optical system, is irradiated with a rectangular cross section of 10 μm in mm as shown in FIG. 1(b),
The crystallinity of the area irradiated with light was increased. Normally, laser light is strong at the center and weak at the edges, exhibiting a Gaussian distribution of intensity. Therefore, if the light is irradiated in this state, crystallization will proceed only in the center of the light, so in this example, an optical system was used to uniformize the intensity of the light and perform the irradiation.

Then, the state shown in FIG. 1(C) was obtained. However, in Figure 1 (c
), laser light is irradiated in a straight line to show only the areas with increased crystallinity.

The laser beam irradiation conditions in this example are a power density of 0.5 J/cm 2 and a pulse duration of 15.17 sec.

In this example, three pulses of this laser light were applied.

The number of irradiations and laser conditions vary depending on the workpiece, and in this example, preliminary experiments were conducted to determine the conditions described above, and those conditions were used.

Next, 100 silicon nitride films (16) were formed on this ■-shaped silicon film (13) by plasma CVD to form a gate insulating film.

After patterning these into a predetermined pattern, a molybdenum film is deposited using a known sputtering method to form a gate electrode (17), and thin film transistors (10) are aligned as shown in FIG. 1(d). The board was completed. (FIG. 1(e)) After forming an insulating film, a liquid crystal cell was completed through an alignment film coating process, a spacer dispersion process, a bonding process, and a liquid crystal injection process.

As described above, the crystallization of non-single-crystal silicon films corresponding to multiple thin film transistors can be simultaneously promoted using a laser beam with a linear cross section using an optical system, which can be used in liquid crystal displays. This method is particularly effective when fabricating a plurality of TPTs aligned on such a large substrate, as it can be processed in a short time.

Example 2J In this example, similar to Example 1, a case where the present invention is used in manufacturing a liquid crystal display will be described.

First, a molybdenum film is formed on the same substrate as used in Example 1 in the same manner as in Example 1, and then a non-single crystal silicon film having N type conductivity is formed.

Next, using a known photolithography technique, the non-single crystal silicon film was masked into a predetermined external pattern of the source and drain regions and their extraction electrodes in the same manner as in Example 1, and dry etching was performed using CF and gas. I do.

Next, as in Example I, an I-type non-single crystal silicon film is formed as a high-resistance semiconductor layer.

Next, for this non-single crystal silicon film, a 1110 μm length 5
As shown in Figure 3, YAG laser light with a wavelength of 1.06 μm, which is focused by the optical system so as to have a rectangular irradiation cross section of μm, is irradiated point-wise, and the substrate is
, or moved by a certain length in the Y direction and irradiated the next location. In this way, the crystallinity of the area irradiated with light was increased.

The laser beam irradiation conditions at this time are a power density of 0°6J/
cm2, and the repetition frequency is 10 kHz. In this example, this laser light was applied for 1.5 seconds.

The number of irradiations and laser conditions vary depending on the workpiece, and in this example, preliminary experiments were conducted to determine the conditions described above, and those conditions were used.

In this example, as in Example 1, an optical system was used to make the laser beam uniform.

Next, 100 silicon nitride films were formed on this I-type silicon film by a plasma CVD method to form a gate insulating film.

After patterning these into a predetermined pattern, a molybdenum film was deposited and patterned using a known sputtering method to form a gate electrode and complete a thin film transistor.

After forming an insulating film, a liquid crystal cell was completed through a liquid crystal alignment film coating process, a spacer spraying process, a bonding process, and a liquid crystal injection process.

In this way, by irradiating laser light only on the part corresponding to the channel part of the non-single crystal silicon film of the plurality of thin film transistors formed in an array and promoting crystallization, thin film transistors with high response speed can be formed. In addition, because the laser beam is irradiated partially, crystallization can be achieved in a shorter time than with the conventional method of irradiating the entire surface.

In this example, since only the necessary parts are irradiated compared to Example 1, even if a slight residue remains during etching of a non-single crystal silicon film, unnecessary parts will not be crystallized. Since the leakage current is not advanced, the leakage current can be reduced.

Example 3J In this example, a case where the present invention is used in manufacturing an image sensor will be described.

First, a molybdenum film is formed on a glass substrate in the same manner as in Example 1, and then a non-single crystal silicon film having N-type conductivity is formed.

Next, using a known photolithography technique, the non-single crystal silicon film was masked into a predetermined external pattern of the source and drain regions and their extraction electrodes in the same manner as in Example 1, and dry etching was performed using CF and gas. I do.

Next, as in Example 1, an I-type non-single crystal silicon film is formed as a high-resistance semiconductor layer.

Next, a medium 10 μm length 23
The wavelength 24 is focused by the optical system so that the irradiation cross section is approximately linear at 0 mm (corresponding to the length of the substrate).
8.7 nm excimer laser light was irradiated to increase the crystallinity of the irradiated portion.

The laser light irradiation conditions at this time are a power density of 0°5J/
cm2, 12 μsec during pulse. In this example, three pulses of this laser light were applied. The number of irradiations and laser conditions vary depending on the workpiece, and in this example, preliminary experiments were conducted to determine the conditions described above, and those conditions were used.

In this example, as in Example 1, an optical system is used to make the laser beam uniform.

Next, 100 silicon nitride films were formed on this ■-type silicon film by the plasma CVD method to form a gate insulating film.

After patterning these into a predetermined pattern, a molybdenum film was deposited and patterned using a known sputtering method to form a gate electrode, and then an insulating film was formed to complete a thin film transistor.

In this way, by irradiating laser light only on the portion corresponding to the channel portion of the non-single crystal silicon film of the plurality of thin film transistors formed in a straight line, and promoting crystallization, response is achieved. A thin film can be produced at a high speed, and since the laser beam is irradiated partially, crystallization can be achieved in a shorter time than in the conventional method of irradiating the entire surface.

r Effect j According to the configuration of the present invention, it was possible to increase crystal dust in the channel portion of thin film transistors formed in alignment.

This has made it possible to use TPTs using non-single crystal semiconductors, which conventionally could not be used as switching elements in display devices, image sensors, etc. due to low carrier mobility.

In addition, since we used laser processing technology to increase crystal dust in the channel area, there is no problem with processing accuracy even when the area is increased, and it is possible to form a large number of thin film transistors with good characteristics on a large area substrate. has become very easy.

Furthermore, since laser processing is performed only on necessary parts such as straight lines and driver shapes, processing time can be shortened, the yield during etching can be increased, and leakage current can be reduced. did it.

Furthermore, in this example, the fabrication of a staggered thin film transistor was described, but from the technical idea of the present invention,
It is clear that other inverted staggered, coplanar, and inverted coplanar thin film transistors can also be used.

In this embodiment, only N-type is described as a low-resistance non-single-crystal semiconductor, but it is clear from the technical idea of the present invention that the present invention can be applied to P-type as well.

[Brief explanation of the drawing]

FIGS. 1(a) to (e) and FIG. 3 are schematic diagrams showing the manufacturing process of a thin film transistor according to an embodiment of the present invention. FIG. 2 shows a cross-sectional structure of a conventional TPT. 10・ ・ ・ 11.20・ 13.21・ 14・ ・ ・ 15・ ・ 16.26・ 17.27・ 18・ ・ 19・ ・ 20・ ・ 22.23・ 24.25 ! J I helangistor...Substrate...High resistance non-single crystal semiconductor layer Partial area with increased crystal dust Laser light...Gate insulating film...Gate electrode Thin film transistor Pixel electrode Substrate Source, drain region...Source, drain electrode

Claims (1)

[Claims] 1. A process of forming a low-resistance non-single-crystal semiconductor having N or P type conductivity to serve as source and drain regions on a substrate having an insulating surface when forming a plurality of thin film transistor elements in alignment. , a step of forming a high resistance non-single crystal semiconductor layer, a step of forming a gate insulating film, and a step of forming a gate electrode, and selectively applying a laser to the high resistance non-single crystal semiconductor layer. A method for manufacturing a thin film transistor element, characterized by irradiating the device with light to promote crystallization of a portion irradiated with laser light, and manufacturing the device so that the portion becomes a channel portion of a plurality of thin film transistors.