JPH0766123A - Formation of microcrystal silicon - Google Patents

Abstract

PURPOSE:To eliminate the need of high voltage ion acceleration step by introducing microcrystals selectively into an arbitrary region within an amorphous film while sustaining an amorphous silicon at a low temperature close to room temperature thereby protecting a substrate against softening and the device structure against fracture due to high temperature of the amorphous silicon. CONSTITUTION:An amorphous silicon film 2 is formed on a substrate 1 made of glass or silicon and then it is irradiated with a high luminance X-ray 3 thus forming microcrystals 4 selectively in a desired region thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention introduces microcrystals into amorphous silicon in order to add a new function that conventional amorphous silicon does not have, and a thin film transistor (TFT) for driving a liquid crystal display. The present invention relates to a method for forming microcrystalline silicon used when, for example, polycrystalline thin film silicon used for is formed on a substrate such as glass.

SUMMARY OF THE INVENTION In the present invention, in a technique for producing a polycrystalline thin film semiconductor on an insulating substrate such as glass or a technique for producing a semiconductor material in which amorphous and microcrystalline are mixed, first, CVD (Chemical Vapor) is used. Deposition) deposits an amorphous semiconductor film on the substrate at a low temperature, and then irradiates the amorphous semiconductor film with X-rays, so that the amorphous semiconductor film is finely divided into the amorphous semiconductor film at a low temperature and at a high speed. It forms crystals.

[0003]

2. Description of the Related Art Nano-sized microcrystalline silicon has been attracting attention as having the possibility of exhibiting a quantum size effect. However, when these fine particles are introduced into amorphous silicon, optical bandgap and other optical properties are almost eliminated. It is known to have the unique physical properties of showing high-speed electron mobility close to that of crystals while exhibiting the properties of amorphous silicon, and is expected as a new material in the future.

Usually, such microcrystalline mixed type amorphous silicon is produced under a certain deposition condition in the electron cyclotron resonance plasma CVD method. Recently, a method combining a normal CVD method and hydrogen radical annealing has been attempted.

However, in each of these methods, not only is it impossible to introduce microcrystals in a selective region on the substrate, but also deposition of an amorphous film and introduction of microcrystals are simultaneously performed by plasma, and therefore, amorphous is formed. It is difficult to control the quality performance and the crystallite performance separately.

On the other hand, when a polycrystalline silicon thin film is formed on a low melting point substrate such as glass, the following method is adopted.

First, amorphous silicon is deposited on a substrate by plasma CVD or the like using silane gas (SiH ₄ ) or the like as a raw material, and then annealed at a temperature of 300 to 400 ° C. to be contained in the amorphous silicon. Desorb a large amount of hydrogen.

Then, again at a temperature of 500 to 600 ° C.,
Annealing is performed to polycrystallize the amorphous film.

[0009]

By the way, as an annealing method used in the above-mentioned technique, not only annealing by an electric furnace but also annealing by laser irradiation is carried out. Since crystallization by means of using a temperature of 500 to 600 ° C., there is a problem that the glass or the like which becomes the substrate is softened or the device structure already manufactured is destroyed.

Therefore, in order to solve such a problem,
A method has been attempted in which high-concentration ions of silicon or impurities are implanted into amorphous silicon in advance to crystallize the amorphous film at a low temperature. However, when the amorphous film is thick, high voltage is applied. There is a drawback that acceleration of ions is required.

In view of the above circumstances, the present invention can selectively introduce microcrystals into an arbitrary region in an amorphous film while keeping the amorphous silicon at a low temperature near room temperature. It is an object of the present invention to provide a method for forming microcrystalline silicon that can prevent the softening of the substrate and the destruction of the device structure that occur when the crystalline silicon is heated to a high temperature, and that does not require the acceleration treatment of ions by a high voltage.

[0012]

In order to achieve the above object, the present invention provides a microcrystalline silicon forming method for applying energy to an amorphous silicon film to form microcrystals in the amorphous silicon film. By irradiating the amorphous silicon film with an X-ray beam, microcrystals are selectively formed in a desired region of the amorphous silicon film.

[0013]

In the above structure, by irradiating the amorphous silicon film with an X-ray beam, microcrystals are selectively formed in a desired region of the amorphous silicon film, and the amorphous silicon film is thereby protected. Prevents softening of the substrate and destruction of the device structure caused by raising the temperature of amorphous silicon by selectively introducing microcrystals into an arbitrary region of the amorphous film while maintaining it at a low temperature near room temperature. In addition, the acceleration processing of the ions by the high voltage becomes unnecessary.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the microcrystalline silicon forming method according to the present invention will be described in detail below with reference to the drawings.

In the method for forming microcrystalline silicon according to this embodiment, first, as shown in FIG. 1, a substrate 1 on which a material such as glass or silicon crystal is formed in a flat plate shape is prepared, and an amorphous silicon film is formed on the substrate 1. 2 is deposited.

After that, the amorphous silicon film 2 is selectively irradiated with high-intensity X-rays 3 to form microcrystals 4 in a desired region of the amorphous silicon film 2.

Thus, the silicon crystal is used as the substrate 1, the temperature of the substrate at the time of deposition is set to 500 ° C., the amorphous silicon is deposited by the electron cyclotron resonance plasma method, and the amorphous silicon film 2 is formed. Microcrystallization was performed using synchrotron radiation as the luminance X-rays. At this time, the substrate temperature at the time of irradiation was about 50 ° C.

As a result, the irradiation X-ray dose is the product of the storage ring current and the irradiation time, that is, about 100 mAh.
(= 1 × 10 ¹⁷ photons / cm ² · s) is used, and the crystallization peak intensity around 521 cm ⁻¹ in the laser Raman spectrum is normalized and plotted as that of a single crystal as a parameter indicating microcrystallization. The measurement results shown in FIG. 2 could be obtained.

As is clear from this figure, no remarkable crystallization was observed up to a certain value of the irradiation X-ray dose, but a clear crystallization peak was confirmed above a certain value, although the peak intensity was very weak. We were able to. Further, it should be confirmed that this crystallization peak gradually increases with the irradiation time, and that very few crystals (microcrystals 4) are formed in the amorphous silicon film 2 by the irradiation of the high-intensity X-ray. I was able to.

As described above, in the method of forming microcrystalline silicon according to the present embodiment, the amorphous silicon film 2 is irradiated with the high-intensity X-beam 3 while the amorphous silicon film 2 is kept at a low temperature near room temperature, and the amorphous silicon film 2 is arbitrarily formed. Since the microcrystals 4 are selectively introduced into the region of 1., inconveniences such as the softening of the substrate 1 and the destruction of the device structure caused by raising the temperature of the amorphous silicon film 2 and the ion acceleration treatment due to the high voltage. It is possible to prevent such inconvenience.

Further, in this embodiment, the following effects can be obtained.

First, by converging the X-ray beam with which the amorphous silicon film 2 is irradiated by using a diffraction grating or a reflection mirror, it is possible to selectively form the microcrystals 4 in a local region. , X by using the interference effect of crystals
Since the line beam can be focused to atomic scale size, selective microcrystallization can be achieved with nanoscale resolution.

Further, unlike laser light and the like, X-rays have high transparency to semiconductor materials such as silicon, so that microcrystals can be formed even in thick film amorphous.
The electron beam and the like require a vacuum for irradiation, but the X-ray beam can be irradiated under atmospheric pressure, so that the entire apparatus can be simplified and the irradiation process can be simplified.

Further, in the above-mentioned embodiment, the substrate 1
Although the microcrystals 4 are introduced into the upper amorphous silicon film 2, this technique may be applied to form a polycrystalline thin silicon film on the substrate 1.

In this case, after depositing the amorphous silicon film 2 on the substrate 1 made of glass or the like, high brightness X
The amorphous silicon film 2 is selectively irradiated with a line 3 to generate microcrystals 4 in a desired region of the amorphous silicon film 2, and annealed in an electric furnace or the like during or after X-ray irradiation, The amorphous silicon film 2 is crystallized using the fine crystal grains as seeds.

[0026]

As described above, according to the present invention, microcrystals can be selectively introduced into an arbitrary region in an amorphous film while keeping the temperature of the amorphous silicon at a low temperature near room temperature. As a result, the softening of the substrate caused by raising the temperature of the amorphous silicon to high temperature can be prevented, and the ion acceleration treatment by a high voltage can be made unnecessary.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a method for forming microcrystalline silicon according to the present invention.

FIG. 2 is a table for explaining the effect of the microcrystalline silicon forming method shown in FIG.

[Explanation of symbols]

 1 Substrate such as glass substrate 2 Amorphous silicon film 3 High brightness X-ray (X-ray beam) 4 Microcrystal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Norifumi Egami 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside the Japan Broadcasting Corporation Broadcasting Technology Laboratory

Claims (1)

[Claims] 1. A method of forming microcrystalline silicon, wherein energy is applied to an amorphous silicon film to form microcrystals in the amorphous silicon film, wherein the amorphous silicon film is irradiated with an X-ray beam. A method of forming microcrystalline silicon, characterized in that microcrystals are selectively formed in a desired region of the amorphous silicon film.