JPS62104117A - Manufacture of semiconductor thin film - Google Patents

Abstract

PURPOSE:To contrive the lowering of a process temperature by determining a scanning velocity at a beam spot diameter X 5,000/sec or above when an amorphous semiconductor thin film is irradiated with laser beams such as Cw Ar laser beams by scanning. CONSTITUTION:On a substrate 4 made of soda-lime glass, a silicon oxide film 3 is deposited to 2,000Angstrom at 350 deg.C of substrate temperature by plasma CVD technique using SiH4 and N2O as material gases. Subsequently, an amorphous silicon film 2 is deposited to 3,000Angstrom at the same substrate temperature 350 deg.C by using SiH4 as a material gas. Next,this amorphous silicon film is irradiated with CW Ar laser beams 1 by scanning. The diameter of a beam spot is 100mum and the scanning velocity 1.2m/sec (beam spot diameter X 12,000/sec) and laser power 9W. The diameter of a crystal grain of the obtained polysilicon film 5 is 0.2-3.0mum and the amorphous silicon film which is dark red and almost opaque at that time becomes to show a light yellow color and an almost transparent state by the scanning irradiation with the laser beams.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a semiconductor thin film used for manufacturing thin film transistors and the like on an insulating substrate.

[Prior Art] A thin film transistor (TPT) formed on an insulating substrate such as a glass substrate is seen as a promising active matrix for flat display devices using liquid crystals, electroluminescence, or the like. Conventionally, a method using an amorphous silicon film and a method using a polycrystalline silicon film have been proposed as a semiconductor thin film on an insulating substrate for forming this thin film transistor.

In the method using the first amorphous silicon film, plasma C
By VD method etc., the film deposition temperature is generally 300"O
The low-temperature process, including the overall temperature of the transistor formation process, allows the use of inexpensive glass substrates that do not have high heat resistance, and also allows for the deposition equipment to be easily enlarged, making it possible to use large substrates as active matrices. It is considered to be a promising method because it is easy to implement.

However, since the conductivity of the amorphous silicon film is low, it is necessary to increase the size of the transistor in order to obtain sufficient on-current for the transistor as an active matrix, resulting in a decrease in reliability and the aperture ratio of the pixel. Furthermore, due to low carrier mobility, the operating speed of the transistor is slow, there is a limit to the number of pixels that can be controlled as an active matrix, and the peripheral scanning circuit of an active matrix cannot be formed on the same substrate. are doing. Furthermore, since the amorphous silicon film has high photoconductivity, a photocurrent is generated when the transistor is turned off, and the on/off ratio of the current is significantly reduced under light irradiation.

To address these drawbacks, a method using a second polycrystalline silicon material has been proposed. Polycrystalline silicon films are usually formed by low-pressure CVD, and their physical properties include electrical conductivity and carrier mobility that are more than an order of magnitude higher than that of amorphous silicon films, and their photoconductivity is lower, resulting in higher performance and higher performance. It is possible to form a reliable active matrix and is being actively investigated as a method to solve the drawbacks of using an amorphous silicon film.

[Problems to be Solved by the Invention] Conventionally, a low pressure CVD method or a plasma CVD method has been used to form a polycrystalline silicon film on a glass substrate.

However, with these formation methods, the substrate temperature during formation is 600°C.
℃ or higher, and only an amorphous silicon film can be obtained at lower temperatures. Therefore, the glass substrate used must be an expensive glass substrate material such as quartz glass, which has a higher heat resistance than ordinary soda lime glass. . In addition, film forming equipment using low pressure CVD or plasma CVD in this temperature range is difficult to increase in size compared to plasma CVD equipment for forming amorphous silicon films in a lower temperature range, making it difficult to increase the size of the substrate. It is extremely difficult to respond to Molecular beam evaporation has also been proposed as another polycrystalline silicon film formation method, but it allows for a slightly lower substrate temperature of around 550°C. This method is more difficult and requires more expensive equipment.

As described above, the conventional polycrystalline silicon film forming method has major drawbacks in terms of the formation temperature, the heat resistance temperature of the glass substrate that can be used, and the possibility of adapting to larger substrate sizes.

Furthermore, as a method for solving the above-mentioned drawbacks, a method has been proposed in which an amorphous silicon film formed on an insulating film is irradiated with a CW Ar laser beam to form a polycrystalline silicon film. (Applied Physics Letters,
vol. 38 (1981), No. 8. pp 81
3-fl15) Even in this case, the formation temperature of the amorphous silicon film needs to be 500° C. or higher, and the process temperature has to be 500° C. or higher, which is a major drawback.

[Means for Solving the Problem] The present invention has been made to solve the aforementioned problems of the conventional method of forming a polycrystalline semiconductor thin film on an insulating substrate. In a method for manufacturing a semiconductor thin film in which a semiconductor thin film is formed and a laser beam is scanned and irradiated to convert the amorphous semiconductor thin film into a polycrystalline semiconductor film, the scanning speed of the laser beam is adjusted to the beam spot diameter x 5.
000/sec or more to crystallize without reaching a complete molten state.

In the configuration of the present invention, first, a plasma CVD method or a photo CVD method is applied to an insulating substrate such as a glass substrate or a ceramic substrate.
An amorphous semiconductor thin film typified by an amorphous silicon film is deposited by a method such as the D method, low pressure CVD method, or electron beam evaporation method. The thickness of the deposited film at this time is preferably 4000 to 100. Generally, Sih, Si2H
When forming an amorphous semiconductor thin film by plasma CVD or photoCVD using a hydride such as 6 as a raw material gas, when the substrate temperature is low, a significantly large amount of hydrogen is incorporated into the amorphous semiconductor thin film. When the amorphous semiconductor thin film is crystallized by beam irradiation, this hydrogen gasifies and blows out, preventing stable crystallization, so the substrate temperature is kept at 300℃.
350℃ after forming an amorphous silicon film instead of
Dehydrogenation treatment may be carried out by maintaining the material at a temperature of approximately .degree. C. in an inert gas atmosphere or in vacuum.

At this time, the reason why it is preferable to set the deposited film thickness of the amorphous semiconductor thin film such as the amorphous silicon film to 4000 Å or less will be explained. When the film is thicker than 4,000 people, the effect of the gaseous ejection of hydrogen contained in the film during the subsequent laser beam irradiation is strong.

Since cracks, voids, and peeling are likely to occur in the obtained polycrystalline semiconductor thin film, it is necessary to prevent this by setting the deposition temperature to 500"C or higher.
00 Å or less, the deposition temperature does not need to be higher than 500"C, and the laser power tolerance range becomes wider. Note that this amorphous semiconductor thin film is difficult to convert into a TFT by less than 100 people. It is preferable to use a thick film of 100 or more.

Therefore, it is preferable that the thickness of the amorphous semiconductor thin film is appropriately determined to be 4000 Å or less, but it is usually about 2000 to 3000 people.

Further, when forming the amorphous semiconductor thin film, an insulating film such as a silicon oxide film or a silicon nitride film may be deposited on the insulating substrate in advance.

The amorphous semiconductor thin film may be patterned in advance into an island shape.Then, the amorphous semiconductor S film is scanned and irradiated with a laser beam.

The spot diameter of the laser beam can be determined as appropriate, but
It is preferable to make it sufficiently larger than the short side dimension of the transistor to be formed later, but as the size increases, the power of the laser light source required also increases.2 Usually, it is 30 to 20G.
4 ta is selected.

In the present invention, the scanning speed of the laser beam is selected to be less than or equal to the beam spot diameter x 5000/sec, so that the amorphous semiconductor thin film is crystallized without reaching a completely melted state.
It can be a polycrystalline semiconductor thin film.

The laser beam used in the present invention is a continuous wave laser with a wavelength of about 20,000 to 1,000 wavelengths, such as YAG laser, He-Me laser, alexandrite laser, At laser, Kr laser and their high frequency lasers, dyes, etc. Lasers, excimer lasers, etc. can be used. Among these, lasers in the visible light range to the ultraviolet range are preferred.

As mentioned above, the scanning speed of this laser beam is set to be less than the beam spot diameter x 5,000/second, and usually at the maximum it is less than the beam spot diameter x 5,000,007 seconds. In addition, specifically, it is preferable to set it as 40 m/sec or less,
Thereby, the amorphous semiconductor thin film can be crystallized without reaching a completely molten state, and can be made into a polycrystalline semiconductor thin film.

The reason for this will be explained below from the relationship between changes in the amorphous semiconductor thin film when scanned and irradiated with a laser beam and the laser power at that time. First, when the irradiation laser power is increased from a sufficiently low value at a scanning speed of 1, a first laser power threshold appears where the amorphous semiconductor thin film begins to show crystallization and becomes a polycrystalline semiconductor thin film. Crystallization without going through a completely molten state will be explained in detail later. When the laser power is further increased, the semiconductor thin film finally reaches a molten state and a second laser power threshold is found. In order to stably form a polycrystalline semiconductor thin film, it is necessary to select the irradiation laser power between the first and second laser power vA values. However, when the scanning speed is slow, the interval between the two laser power thresholds becomes smaller, and when the scanning speed is made even slower, there is finally a laser power setting margin suitable for stably forming a polycrystalline semiconductor thin film between the two idle values. cease to exist. On the other hand, when the scanning speed is fast, the dark value of the laser power both increases and at the same time the interval widens, as compared to when the scanning speed is slow, and the setting margin for the laser power increases. Here, the reason why a desirable range of scanning speed exists in relation to the beam spot diameter is that when looking at an irradiated area that is sufficiently smaller than the beam spot diameter, the irradiation time is proportional to the beam spot diameter at a scanning speed of This is because the irradiation energy is proportional to the irradiation time.For the above reasons, the scanning speed is set to the beam spot diameter x 5000/sec.

This allows the amorphous semiconductor thin film to crystallize without reaching a completely molten state and becomes a polycrystalline semiconductor thin film in a very short time, making it possible to use inexpensive glass substrates with low heat resistance. Moreover, it is possible to easily cope with an increase in the substrate size (F=f).

Note that when scanning and irradiating an amorphous silicon film with a laser beam, an insulating film such as a silicon oxide film or a silicon nitride film is formed on the amorphous semiconductor film in advance to prevent the reflection of the laser beam or the surface. It may also be used as a protective film.

In the present invention, the amorphous semiconductor thin film means not only one having a completely amorphous structure but also one having a grain size of 50 nm.
The most suitable amorphous semiconductor thin film of the present invention is an amorphous silicon film, but other films such as amorphous germanium etc. It can also be applied to amorphous semiconductor thin films. Also, what is the beam spot diameter referred to in the present invention?

Refers to the diameter that contains approximately 87% or more of the laser power on the irradiated surface.

A description will be given of how the amorphous semiconductor thin film described above crystallizes without going through a complete melting state.

Generally, when energy is applied to cause crystallization or crystal grain growth, a method is used in which the material is melted and then re-solidified, or it is held at a high temperature below the melting point for a very long time. In the former case, the re-solidification speed is generally limited to 10 cm/sec or less at best, and requires a high temperature above the melting point.

The latter method requires very long processing times, for example over 100 hours, as the holding temperature falls below the melting point.

On the other hand, when an amorphous semiconductor thin film is irradiated with laser light, phenomena such as light 1-induced structural change, crystallization in the solid phase, and generation of crystallization heat, which are unique to amorphous semiconductor thin films, occur. As a result, high-speed crystallization is possible without going through a completely molten state, and the present invention utilizes this phenomenon to enable low-temperature, high-speed crystallization.

[Operation] The present invention achieves a complete melting state by scanning and irradiating a laser beam such as a CWAr laser beam onto an amorphous semiconductor thin film such as an amorphous silicon film formed on an insulating substrate such as a GalaYL substrate. It is possible to form a polycrystalline semiconductor thin film such as a high-quality silicon film without undergoing any process, and the temperature of the insulating substrate at that time hardly increases on average, and even partially and instantaneously increases the melting temperature of the semiconductor material. much lower than
Furthermore, since the temperature remains sufficiently lower than the so-called crystallization temperature of an amorphous semiconductor thin film defined as a physical property value, an insulating substrate with low heat resistance can be used.

Furthermore, by setting the thickness of the amorphous semiconductor thin film to 4000 Å or less, defects such as cracks, voids, and peeling occur due to the gaseous ejection of hydrogen during laser beam irradiation even if the deposition temperature is less than 500°C. can be easily prevented.

Furthermore, the crystallization rate of the amorphous semiconductor thin film in the present invention is
Scanning laser beam irradiation is much faster than solidification and recrystallization from a molten state, which is generally seen in the method called laser annealing method. Crystallization occurs even when the scanning speed is set to beam spot diameter x 50007 seconds or more. It can be crystallized at low temperatures and at high speeds. Furthermore, at such a scanning speed, there is also the advantage that there is a sufficiently wide setting margin for the laser power that can be used to stably form a multilingual conductor thin film.

Although the present invention is most suitable for application to an amorphous silicon film as an amorphous semiconductor thin film, it is of course applicable to other amorphous semiconductor thin films such as an amorphous germanium film.

[Example] Example 1 Sih and 82
2,000 silicon oxide films (SiOz) were deposited by the plasma CVD method at a substrate temperature of 350°C using a raw material gas of 0.0°C, and then an amorphous silicon oxide film (SiOz) was deposited using SiHm gas as a raw material at a substrate temperature of 350°C. Siligo 7p4 3 (1
After 00A deposited, C-
A laser beam is scanned and irradiated. The beam spot diameter was 100 gm, the scanning speed was 1.2 m/sec (beam spot diameter x 12.000/sec), and the laser power was 9 W.

The crystal grain size of the obtained polycrystalline silicon film is 0.2 to 3.
It was 0 bowls. At this time, the dark red and nearly opaque amorphous silicon film became pale yellow and nearly transparent due to the scanning irradiation of the laser beam.

FIG. 1 is a cross-sectional view showing this scanning state, and 1 is a CWA
r laser beam, 2 is an amorphous silicon film, 3 is an insulating film, and 4 is a glass substrate; by scanning in the front and back direction of the figure, the amorphous silicon film portion becomes a polycrystalline silicon film 5. It shows crystallization.

Comparative Examples 1 to 7 On the other hand, when the laser power was increased to lIW (
In Comparative Example 1), the amorphous silicon film was nearly transparent after irradiation, but showed an agglomerated state and was rough on the glass substrate, and did not exhibit a homogeneous film shape. This indicates that a molten state has been reached.

Furthermore, when the laser power was 7W (Comparative Example 2), the amorphous silicon film had only a slight decrease in light transmittance after irradiation compared to before irradiation, and did not become a polycrystalline silicon film. .

Each amorphous silicon 11 formed in the same manner as in Example 1, -
The CWAr laser beam was
As a comparative example, when scanning irradiation is carried out at a scanning speed of 0.20 m/sec (beam spot diameter 2000 times/sec), when the laser power is 2.8 W (Comparative Example 3), the amorphous silicon film becomes smaller than before irradiation. When the laser power was 3.1 W (
In Comparative Example 4), the irradiated surface was deformed into aggregates and became rough.
It changed to almost transparent, indicating that it had reached a molten state, and the second
As shown in the figure, the surface of the glass substrate was also deformed in an uneven manner, and microcranks 6 were also observed to occur in some areas.

When the thickness of the amorphous silicon film is 5000, C
When irradiated with a WAr laser beam under the same conditions as in Example 1 (beam spot flilo Os Peng, scanning speed 1.2 m/sec, Ray 4j'-Hower 9W) (Comparative Example 5),
As shown in Figure 3, there are many voids 7 in the polycrystalline silicon film.
The occurrence of cracks that seemed to connect voids was also observed. At this time.

When the laser power was set to 7 W (Comparative Example 6), the same change as in Comparative Example 2 was observed, such as a decrease in light transmittance, but no polycrystalline silicon film was formed, and when the laser power was set to 11 W (Comparative Example 7) In addition to being rough in the same agglomerated state as in Comparative Example 1, scattering of the film was also observed in one part.

Example 2 At this time, the substrate temperature of the amorphous silicon was raised to 500°C, the film thickness was similarly set to 5000° C., and the At laser beam was heated to a beam spot diameter of 1004° C. under the same conditions as described in L.
When irradiated at a scanning speed of 1.2 m/sec, when the laser power was 9W, a polycrystalline silicon film equivalent to the 9W thermal irradiation in Example 1 was obtained, but when the laser power was 8W, as in Comparative Example 2, a polycrystalline silicon film was obtained. When the change is limited to a decrease in optical properties, and IOW occurs, as shown in Figure 3, a large number of voids and cracks connecting the voids are observed in the polycrystalline silicon film, and as a result, a polycrystalline silicon film is obtained. However, compared to the case shown in Example 1, the margin for setting the laser power was smaller and the temperature also needed to be higher.

[Effects of the Invention] As described above, the present invention improves the scanning speed when scanning and irradiating a laser beam such as a GWAr laser beam onto an amorphous semiconductor thin film such as an amorphous silicon film of an insulating substrate E such as a glass substrate. By setting the beam spot diameter X to 5000/sec or more, the amorphous semiconductor thin film is crystallized without reaching a completely molten state and stably becomes a polycrystalline semiconductor thin film; By setting the deposited film thickness of the amorphous semiconductor thin film to 4000 F or more, the deposition temperature of the usable amorphous semiconductor thin film can be lowered to less than 500°C, so that the substrate temperature on which the polycrystalline semiconductor thin film is formed can be lowered. As a result, the process temperature can be lowered to less than 500℃ compared to the conventional method, and a normal glass substrate can be used as the insulating substrate material.
In addition, the present invention can sufficiently cope with an increase in substrate size, and is extremely superior and useful as a method for manufacturing an active matrix for a flat display device over a conventional method for forming a polycrystalline semiconductor thin film.

Furthermore, according to the method of the present invention, it is possible to selectively form only a specific portion of an amorphous semiconductor thin film on an insulating substrate into a polycrystalline semiconductor thin film, and to It becomes possible to easily manufacture a portion to be used as a thin film and a portion to be used as a polycrystalline semiconductor thin film without adding a separate film forming process and a patterning process by photolithography.

Furthermore, the method according to the present invention can also be applied to the manufacture of multilayered semiconductor devices, and can be applied to an amorphous semiconductor thin film formed at low temperature on an insulating film on a semiconductor device on which elements and circuits have already been formed. Forming polycrystalline semiconductor thin films without causing thermal damage to underlying elements and circuits,
It becomes possible to make it into an element.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing that an amorphous silicon film stably becomes a polycrystalline silicon film in an example of the present invention. Figures 2 and 3 show polycrystalline silicon 11 in a comparative example.
FIG. 1---- CW Ar laser beam 2--1--Amorphous silicon film 3--M-Insulating film 4--1 Glass substrate 5---1 Polycrystalline silicon film 6----Micro crack 7 -----Poid

Claims (6)

[Claims] (1) In a method for manufacturing a semiconductor thin film in which an amorphous semiconductor thin film is formed on an insulating substrate and a laser beam is scanned and irradiated to form the amorphous semiconductor thin film into a polycrystalline semiconductor film, the scanning speed of the laser beam is Beam spot diameter x 5000/
1. A method for producing a semiconductor thin film, characterized in that crystallization is carried out without reaching a complete molten state for more than a second. (2) The method for manufacturing a semiconductor thin film according to claim 1, wherein the amorphous semiconductor thin film is an amorphous silicon thin film. (3) The method for manufacturing a semiconductor thin film according to claim 1 or 2, wherein the thickness of the amorphous semiconductor thin film is 4000 Å or less. (4) Laser beam wavelength is 20,000 to 1,000 Å
A method for manufacturing a semiconductor thin film according to claim 1 or 2. (5) The semiconductor thin film manufacturing method according to claim 4, wherein the laser beam is a CWAr laser. (6) The semiconductor thin film manufacturing method according to claim 1, wherein the insulating substrate is a glass substrate.