JPH1197354A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form on a glass a crystalline Si film having the stability as in case of the solid phase growth method and the same crystallinity as in case of the laser crystallization, by introducing crystal nuclei in an amorphous Si film to grow crystals from the nuclei. SOLUTION: A manufacturing method comprises steps of forming an amorphous Si film 12 on a substrate 1 by the plasma CVD, treating with hydrofluoric acid to form an oxide film 13, dripping an N-added acetate soln. 14 on the surface of the oxide film 13 of the Si film 12, holding this condition for e.g. 5 min, spin-drying using a spinner 15, heating at e.g. 550 deg.C in a nitrogen- atmosphere in a heating furnace for 1 hr. to obtain an Si film 12 partly having a crystallinity on the substrate 11 wherein crystal nuclei can be introduced, and irradiating several shots of a KrF excimer laser in the nitrogen-atmosphere to perfectly crystallize the Si film 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device using a semiconductor having crystallinity and a method for manufacturing the same.

[0002]

2. Description of the Related Art Thin film transistors (hereinafter referred to as TFTs) using thin film semiconductors are known. This TFT
Is a device in which a thin film semiconductor is formed on a substrate, and the thin film semiconductor is used. This TFT is used for various integrated circuits, and is particularly noted as a switching element provided in each pixel of an electro-optical device, particularly an active matrix type liquid crystal display device, and a driver element formed in a peripheral circuit portion. ing.

[0003] As a thin film semiconductor used for a TFT,
Although it is convenient to use an amorphous silicon film, there is a problem that its electrical characteristics are low. In order to improve the characteristics of the TFT, a silicon thin film having crystallinity may be used. The silicon film having crystallinity is called polycrystalline silicon, polysilicon, microcrystalline silicon, or the like. In order to obtain a silicon film having this crystallinity, an amorphous silicon film is first formed, and then it may be crystallized by heating or irradiation with laser light or the like.

[0004] However, crystallization by heating requires a heating temperature of 600 ° C. or more for a period of 10 hours or more, and there is a problem that it is difficult to use a glass substrate as a substrate. For example, Corning 7059 generally used for an active type liquid crystal display device
Glass has a glass strain point of 593 ° C., and in view of increasing the area of the substrate, heating at 600 ° C. or more poses an industrial problem. The crystallization method using laser is
It is an excellent method that can almost ignore the distortion due to heat of the glass substrate by using a short pulse laser such as an excimer laser, but the variation in forming the element is large, and the sense of the next generation technology is strong . One of the causes of this variation is the lack of stability of the laser beam, and this will be gradually resolved in the future. However, an even more significant factor is the temperature distribution of the laser beam irradiated part. This will be further described.

BACKGROUND OF THE INVENTION The present inventors have developed a method for promoting thermal crystallization and a method for improving the crystallization of laser in order to solve the problems associated with the crystallization of amorphous silicon as described above. Two investigations were made on the method of reducing the noise. Regarding the former, a trace amount of elements such as nickel, palladium, and lead are deposited on the surface of the amorphous silicon film and then heated, so that crystallization can be performed at 550 ° C. for about 4 hours. Make sure that.

[0006] In order to introduce the above trace elements (catalytic elements that promote crystallization), plasma treatment, vapor deposition, and ion implantation may be used. Plasma treatment refers to the use of a material containing a catalyst element as an electrode in a parallel plate type or positive column type plasma CVD apparatus, and generation of plasma in an atmosphere such as nitrogen or hydrogen to form a catalyst element on an amorphous silicon film. This is a method of adding.

However, the presence of a large amount of such elements in semiconductors impairs the reliability and electrical stability of devices using these semiconductors, and is not preferable.

In other words, the above-described elements that promote crystallization such as nickel (the elements that promote crystallization are referred to as catalyst elements in the present specification) are necessary when crystallizing amorphous silicon. It is desirable that the crystallized silicon is not contained as much as possible. In order to achieve this purpose, at the same time as selecting a catalyst element that has a strong tendency to be inactive in crystalline silicon, the amount of the catalyst element required for crystallization is minimized,
Crystallization must be performed in a minimum amount. For that purpose, it is necessary to precisely control the amount of the catalyst element to be introduced.

When nickel is used as a catalyst element, an amorphous silicon film is formed, nickel is added by a plasma treatment method to produce a crystalline silicon film, and the crystallization process and the like are examined in detail. However, the following matters were found. (1) When nickel is introduced onto an amorphous silicon film by plasma treatment, nickel has already penetrated to a considerable depth in the amorphous silicon film before heat treatment. (2) The initial nucleation of the crystal occurs from the surface into which nickel is introduced. (3) Even when nickel is formed on an amorphous silicon film by a vapor deposition method, crystallization occurs as in the case where plasma processing is performed.

[0010] From the above, it is concluded that all the nickel introduced by the plasma treatment is not functioning effectively. That is, it is considered that some nickel does not function sufficiently even if a large amount of nickel is introduced. From this, it is considered that the point (plane) where nickel and silicon are in contact functions at the time of low-temperature crystallization.
It is concluded that it is necessary for nickel to be dispersed as finely as possible. In other words, it is concluded that "what is necessary is to introduce as low a concentration of nickel as possible in the form of atoms in the vicinity of the surface of the amorphous silicon film in a range where low-temperature crystallization is possible".

A method for introducing a very small amount of nickel only near the surface of the amorphous silicon film, in other words, a method for introducing a very small amount of a catalytic element for promoting crystallization only near the surface of the amorphous silicon film is as follows. , Evaporation method can be mentioned,
The vapor deposition method has a problem that the controllability is poor and it is difficult to strictly control the introduction amount of the catalyst element.

It is necessary that the amount of the catalyst element to be introduced is as small as possible. In this case, however, there is a problem that crystallinity becomes poor, and it is important to control an appropriate amount of the catalyst element.

Next, as for the variation in characteristics during laser crystallization, as a result of the examination, two main points are the difference in crystallinity caused by the temperature distribution in the laser irradiation part and the accidental nucleation. Recognized that it was the cause. To explain the reason in more detail, the laser light intensity distribution generally has a Gaussian distribution, and the temperature of the amorphous silicon film also has a distribution along with this distribution. As a result, in the crystallization process through melting or partial melting, the temperature should be lower than the melting point of the amorphous silicon film from a low temperature or a high heat diffusion, and crystallization should occur.
Crystal nuclei do not always exist in this part, and crystallization is expected to occur explosively when the supercooled liquid contacts the crystal nuclei. Further, it is expected that uniform crystallization is difficult because the crystal nuclei themselves are irregularities at the interface with silicon oxide.

In order to avoid this phenomenon, it is desirable that the portion where the molten portion first drops to a temperature lower than the melting point coincides with the portion where the crystal nucleus exists. For this purpose, the present inventors have tried to introduce a crystal nucleus controlled in advance before laser crystallization and then perform laser crystallization. As a result, when a material having a crystal nucleus having a higher transmittance of laser light than amorphous silicon and having a high thermal conductivity is used, that is, a material whose temperature lowers to the melting point of silicon earlier than amorphous silicon is used. In such a case, it has been found that crystal growth starts therefrom, and that a good crystalline silicon thin film can be obtained. As such a material, many crystalline materials can be cited as candidates. Among them, as a material that can be epitaxially grown, particularly, a fine crystal grain of crystalline silicon, or a crystalline silicon after adding a nickel catalyst to amorphous silicon. It has been found that nickel silicide or the like obtained by heating is particularly desirable.

In the place where the crystal nuclei are introduced, the nuclei are not uniformly introduced into the entire amorphous silicon film, but are introduced at the upper interface with the substrate or near the interface with the base,
Further, it has been found that a crystalline silicon film having the best characteristics can be obtained by irradiating the direction of laser light irradiation from the interface side where the crystal nuclei are introduced. The introduction of crystal nuclei at the interface is considered to be due to the fact that crystal growth is sufficiently possible in the film thickness direction, and is considered to have the effect of increasing one crystal grain. The direction of laser irradiation may be caused by the effect of heating the interface through the crystal nucleus, or the effect of temperature gradient in the film thickness direction, but the mechanism has not been completely elucidated. Absent.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a good crystalline silicon film on glass. Still another object of the present invention is to provide a method for obtaining a material having both the same stability as that obtained by using the solid phase growth method and the same high crystallinity as that obtained by using laser crystallization.

[0017]

SUMMARY OF THE INVENTION The present invention comprises a step of forming an amorphous silicon film, a step of introducing a crystal nucleus into the amorphous silicon film, and a step of growing crystals from the crystal nucleus. And a step of obtaining a basic configuration.

In order to introduce crystal nuclei into the amorphous silicon film, an element which promotes crystallization, such as nickel, is introduced into the surface of the amorphous silicon film and then heated or irradiated with light (irradiation of infrared rays). This is done by supplying energy.

In order to grow a crystal from this crystal nucleus, it is sufficient to irradiate a laser beam with strong light from the side where the crystal nucleus is formed.

According to the present invention, there is provided an amorphous silicon film in which a single catalyst element represented by nickel or a compound containing the catalyst element, which promotes crystallization of the amorphous silicon film, is retained. In the state where the catalyst element alone or the compound containing the catalyst element is in contact with the film, a heat treatment is performed at a low temperature that does not affect the glass substrate, and the amorphous silicon film is partially crystallized, and crystal nuclei are formed. Is the first feature. Then, a crystal having good crystallinity is obtained by performing pseudo-epitaxial crystal growth with crystal nuclei of fine crystalline silicon formed in advance by performing crystallization by irradiating laser light or strong light. The second feature is to obtain a conductive silicon thin film.

As a method for introducing a catalytic element for promoting crystallization, a method in which a solution containing the catalytic element is applied to the surface of the amorphous silicon film is useful.

In particular, the present invention is characterized in that the catalytic element is introduced in contact with the surface of the amorphous silicon film. This is extremely important in controlling the amount of the catalytic element.

The catalyst element may be introduced on the upper surface or the lower surface of the amorphous silicon film. If the catalytic element is introduced on the upper surface of the amorphous silicon film, a solution containing the catalytic element may be applied onto the amorphous silicon film after the amorphous silicon film is formed. If the catalyst element is introduced into the lower surface of the silicon film, a solution containing the catalyst element is applied to the base surface before forming the amorphous silicon film, and the catalyst element is held in contact with the base surface. I just need.

In a semiconductor device using the present invention, it is effective to use a crystallized silicon semiconductor film to form an active region having at least one PN, PI, NI, or other electrical junction. As the semiconductor device, a thin film transistor (TFT), a diode, or an optical sensor can be used.

By adopting the configuration of the present invention, the following basic significance can be obtained. (A) The concentration of the catalyst element in the solution can be strictly controlled in advance to increase the crystallinity and reduce the amount of the element. (B) If the solution is in contact with the surface of the amorphous silicon film,
The amount of the catalyst element introduced into the amorphous silicon is determined by the concentration of the catalyst element in the solution. (C) Since the catalytic element adsorbed on the surface of the amorphous silicon film mainly contributes to the crystallization, the catalytic element can be introduced at a minimum necessary concentration. (D) A crystalline silicon film having good crystallinity can be obtained without requiring a high-temperature process.

As a method of applying a solution containing an element that promotes crystallization on the amorphous silicon film, an aqueous solution, an organic solvent solution, or the like can be used as the solution. Here, “containing” includes both the meaning of being included as a compound and the meaning of being included simply by being dispersed.

As the solvent containing the catalyst element, a solvent selected from polar solvents such as water, alcohol, acid and ammonia can be used.

When nickel is used as a catalyst and this nickel is contained in a polar solvent, nickel is introduced as a nickel compound. Typical examples of the nickel compound include nickel bromide, nickel acetate, nickel oxalate, nickel carbonate, nickel chloride, nickel iodide, nickel nitrate, nickel sulfate, nickel formate, nickel acetylacetonate, and 4-cyclohexylbutyric acid. A material selected from nickel, nickel oxide, and nickel hydroxide is used.

As the solvent containing the catalyst element, non-polar solvents such as benzene, toluene, xylene, carbon tetrachloride,
Chloroform and ether can be used.

In this case, nickel is introduced as a nickel compound. As the nickel compound, typically, a compound selected from nickel acetylacetonate and nickel 2-ethylhexanoate can be used.

It is also useful to add a surfactant to the solution containing the catalyst element. This is to increase the adhesion to the surface to be coated and control the adsorption. This surfactant may be applied in advance on the surface to be coated.

When nickel alone is used as the catalyst element, it must be dissolved in an acid to form a solution.

The above is an example in which a solution in which nickel as a catalytic element is completely dissolved is used. Even if nickel is not completely dissolved, a powder composed of nickel alone or a nickel compound is dispersed in a dispersion medium. A material such as an emulsion which is uniformly dispersed in the emulsion may be used. Alternatively, a solution for forming an oxide film may be used. As such a solution, OCD (Ohka Diffusion) of Tokyo Ohka Kogyo Co., Ltd.
Source) can be used. With the use of this OCD solution, a silicon oxide film can be easily formed by applying it on the surface to be formed and baking it at about 200 ° C. Further, since it is free to add impurities, it can be used in the present invention.

The same applies to the case where a material other than nickel is used as the catalyst element.

When nickel is used as a catalyst element for promoting crystallization and a polar solvent such as water is used as a solution solvent for containing the nickel, when these solutions are directly applied to the amorphous silicon film, the solution becomes elastic. It may be lost. In this case, a thin oxide film having a thickness of 100 ° or less is first formed, and a solution containing a catalyst element is applied thereon, whereby the solution can be applied uniformly. It is also effective to improve the wetting by adding a material such as a surfactant to the solution.

Further, by using a non-polar solvent such as a toluene solution of nickel 2-ethylhexanoate as a solution, it can be directly applied to the surface of the amorphous silicon film. In this case, it is effective to apply a material such as an adhesive used in applying the resist in advance. However, care must be taken when the amount of coating is too large, since this would hinder the addition of the catalytic element to the amorphous silicon.

The amount of the catalyst element contained in the solution depends on the type of the solution, but the general tendency is that the amount of nickel is 200 ppm to 1 ppm, preferably 50 ppm to 1 ppm (in terms of weight) based on the solution. It is desirable. This is a value determined in view of the nickel concentration in the film after crystallization is completed.

The amorphous silicon film to which the catalytic element is added is subjected to a heat treatment to form a crystal nucleus, and then irradiated with a laser beam, so that the entire surface of the amorphous silicon film is uniformly transformed into a crystalline silicon film. It can be crystallized. In the crystallization process using this laser, a very specific phenomenon has been observed. In the case where no crystal nucleus is introduced, the same crystallization can be performed with a considerably small laser power as compared with the laser power required for performing the entire crystallization. Generally, in order to crystallize a microcrystallized amorphous film,
It is said that higher laser power is required (because the absorbed laser power is small due to different transmittance) than crystallizing a film that does not contain a crystal component, but the opposite trend is true. This is one of the great advantages of the present invention. Here, by adjusting the amount of the catalyst element to be introduced, the amount of the region that is crystallized and becomes a crystal nucleus can be controlled. This state can be regarded as a state in which a component having crystallinity and an amorphous component are mixed as a whole. Here, by irradiating a laser beam, crystal growth can be performed from a crystal nucleus existing in the component having crystallinity, and a silicon film with high crystallinity can be obtained. That is, small crystal grains can be grown into large crystal grains. Therefore, the crystal growth distance, the size of the crystal grains accompanying the crystal growth, the number of crystal grains, and the like can be controlled by appropriately setting the amount of the catalyst element to be initially introduced and the laser power.

Instead of laser light irradiation, a method of irradiating strong light, particularly infrared light, may be employed. Since infrared light is hardly absorbed by glass and easily absorbed by a silicon thin film, it is useful because the silicon thin film formed on the glass substrate can be selectively heated. This method using infrared light is called rapid thermal annealing (RTA) or rapid thermal process (RTP).

In the present invention, the most remarkable effect can be obtained when nickel is used as the catalyst element. However, other usable types of catalyst elements are preferably Ni, Pt, Cu, Ag, Au, and Au. In, Sn, P
d, P, As, and Sb can be used. Also VI
One or more elements selected from Group II elements, IIIb, IVb, and Vb elements can also be used.

The method of introducing the catalytic element is not limited to the use of an aqueous solution or a solution such as alcohol, but a wide range of substances containing the catalytic element can be used.
For example, a metal compound or oxide containing a catalyst element can be used.

[0042]

【Example】

Example 1 In this example, a catalytic element for promoting crystallization was contained in an aqueous solution, applied on an amorphous silicon film, and then crystallized by heating, and then crystallized by irradiation with laser light. This is an example of increasing

With reference to FIG. 1, the process up to the point of introducing a catalytic element (here, nickel is used) will be described. In this embodiment, Corning 7059 glass is used as the substrate. The size is 100 mm × 100 mm.

First, an amorphous silicon film was formed by plasma CVD or LPCVD.
It is formed at a temperature of 00 to 1500 °. Here, plasma CVD
An amorphous silicon film 12 is formed to a thickness of 1000.degree. (Fig. 1 (A))

Then, a hydrofluoric acid treatment is performed to remove dirt and a natural oxide film.
Å is formed. If the contamination can be ignored, the oxide film 13
Instead, a natural oxide film may be used as it is.

Although the exact thickness of the oxide film 13 is unknown because it is extremely thin, it is considered to be about 20 °.
Here, the oxide film 1 is irradiated with UV light in an oxygen atmosphere.
3 is formed. Film formation conditions are UV in oxygen atmosphere.
For 5 minutes. This oxide film 1
As the film forming method of No. 3, a thermal oxidation method may be used.
Further, a treatment by hydrogen peroxide may be used.

The oxide film 13 is used for spreading the acetate solution over the entire surface of the amorphous silicon film in the subsequent step of applying a nickel-containing acetate solution, that is, for improving the wettability. It is. For example, when an acetate solution is directly applied to the surface of an amorphous silicon film, nickel cannot be introduced into the entire surface of the amorphous silicon film because the amorphous silicon repels the acetate solution. That is, uniform crystallization cannot be performed.

Next, an acetate solution is prepared by adding nickel to the acetate solution. The concentration of nickel is 25 ppm. Then, 2 ml of this acetate solution is dropped on the surface of the oxide film 13 on the amorphous silicon film 12, and this state is maintained for 5 minutes. And spin dry using a spinner (2000r
pm, 60 seconds). (Fig. 1 (C), (D))

The concentration of nickel in the acetic acid solution is 1
If it is at least 10 ppm, preferably at least 10 ppm, it will be practical. When a nonpolar solvent such as a toluene solution of nickel 2-ethylhexanoate is used as the solution, the oxide film 1
3 is unnecessary, and a catalytic element can be directly introduced on the amorphous silicon film.

By performing this step of applying the nickel solution once to a plurality of times, a layer containing nickel having an average film thickness of several to several hundreds of mm is formed on the surface of the amorphous silicon film 12 after spin drying. Can be formed. In this case, nickel in this layer diffuses into the amorphous silicon film in the subsequent heating step and acts as a catalyst for promoting crystallization. Note that this layer is not necessarily a complete film.

After the application of the solution, the state is maintained for one minute. Although the concentration of nickel contained in the silicon film 12 can be finally controlled by the holding time, the largest controlling factor is the concentration of the solution.

Then, in a heating furnace, heat treatment is performed at 550 ° C. for one hour in a nitrogen atmosphere. As a result,
Partially crystalline silicon thin film 1 formed on substrate 11
2 can be obtained. That is, crystal nuclei can be introduced in this step. FIG. 2 schematically shows this state.
It is shown in (A). FIG. 2A shows a state where crystal nuclei 21 formed by the introduction of nickel are formed on the surface of amorphous silicon film 12 formed on glass substrate 11.

The above-mentioned heat treatment can be performed at a temperature of 450 ° C. or higher. However, if the temperature is low, the heating time must be extended, and the production efficiency decreases. Further, if the temperature is 550 degrees or more, the problem of heat resistance of a glass substrate used as a substrate will surface.

In this embodiment, the method of introducing a catalytic element on the amorphous silicon film has been described, but a method of introducing a catalytic element below the amorphous silicon film may be employed. in this case,
Before forming the amorphous silicon film, the catalyst element may be introduced onto the base film using a solution containing the catalyst element.

After the silicon film 12 having partial crystallinity is obtained by the heat treatment, a KrF excimer laser (wavelength 24
The silicon film 12 is completely crystallized by irradiating several shots at a power density of 200 to 350 mJ / cm ^{2 in} a nitrogen atmosphere with a pulse width of 8 nm and a pulse width of 30 nsec. This step may be performed by the above-mentioned irradiation with infrared light. In this step, it is important to perform laser light from the upper surface side of the silicon film 12 in which the catalyst element is introduced and the crystal nucleus is formed.
FIGS. 2A and 2B show a state where the crystal growth is performed as indicated by 22 from the crystal nucleus indicated by 21 when the laser beam 20 is irradiated. The crystallization grows around the crystal nucleus 21 as shown by the arrow in FIG. As the crystallization proceeds, a polycrystalline structure as shown by 23 can be obtained. FIG. 6 shows a cross-sectional photograph of the silicon thin film corresponding to the schematic diagram shown in FIG. FIG. 6 shows a state in which a crystal nucleus is formed on the surface of an amorphous silicon film formed on a glass substrate by introducing nickel, and the crystal nucleus grows slightly. In FIG. 5, this slightly grown crystal component is indicated by a black square. Although a silicon oxide film is formed on the surface of the glass substrate, it cannot be distinguished from the glass substrate in the photograph shown in FIG.

[Embodiment 2] In this embodiment, the concentration of a nickel salt as a catalyst element in the embodiment 1 is set to 10 ppm. All other processes are the same as in the first embodiment. As a result of observing the thin film after the heat treatment under a microscope, the sample in which the concentration was reduced in this manner had more amorphous silicon portions than the sample of Example 1, and the number of crystal nuclei composed of crystalline silicon was reduced to about half. Had declined. Next, the sample after laser crystallization was observed by SEM after secco etching. As a result, it was found that the size of one crystal grain can be made larger than that in Example 1 by reducing the solution concentration as in the present case.

[Embodiment 3] In this embodiment, a TFT is obtained by using a crystalline silicon film manufactured by using the method of the present invention. The TFT of this embodiment can be used for a driver circuit or a pixel portion of an active matrix type liquid crystal display device. It is needless to say that TFTs can be applied not only to liquid crystal display devices but also to thin film integrated circuits generally referred to.

The present embodiment utilizes a technique of introducing a crystal nucleus on the surface side of an amorphous silicon film and thereafter irradiating a laser beam from the side where the crystal nucleus is introduced to obtain a crystalline silicon film. The present invention relates to a method for manufacturing a TFT. According to the findings of the present inventors, it has been found that when such a configuration is employed, the roughness of the surface of the crystalline silicon film can be made very small as compared with the case where crystallization is performed by laser light alone. doing. This is because the surface side of the silicon thin film contains a large amount of crystalline silicon components, so that the portion absorbs a small amount of laser light and is hardly melted, and as a result, the surface roughness is almost the same as in the case of solid phase growth alone. It is thought to be due to Since the surface roughness has an adverse effect on TFTs such as carrier scattering, it is extremely useful to adopt a configuration as in this embodiment.

FIG. 3 shows an outline of the manufacturing process of this embodiment.
First, an underlying silicon oxide film (not shown) is formed on a glass substrate by two steps.
A film is formed to a thickness of 000 mm. This silicon oxide film is provided to prevent diffusion of impurities from the glass substrate.

Then, an amorphous silicon film is formed to a thickness of 500 ° in the same manner as in the first embodiment. After the hydrofluoric acid treatment for removing the natural oxide film, a thin oxide film is
The film is formed to a thickness of about a degree by irradiation with UV light in an oxygen atmosphere. The thin oxide film may be formed by a method using a water treatment or thermal oxidation.

Then, an acetate solution containing 10 ppm of nickel is applied, held for 5 minutes, and spin-dried using a spinner. Thereafter, the silicon oxide films 20 and 21 are removed with buffered hydrofluoric acid, and the silicon film is partially crystallized by heating at 550 ° C. for one hour. The partially crystallized portion functions as a crystal nucleus in a subsequent laser crystallization step. By performing this heat treatment, a silicon film in which an amorphous component and a crystalline component are mixed can be obtained.

Then, a crystalline silicon film is obtained by irradiating a KrF excimer laser beam from the surface side at 200 to 300 mJ. In the laser light irradiation step,
The substrate is heated to about 400 ° C. In this step, crystal growth is performed with the crystal nuclei existing in the crystal components as nuclei.

Next, island regions 104 are formed by patterning the crystallized silicon film. This island-shaped area 10
4 constitutes an active layer of the TFT. And the thickness 200 ~
The silicon oxide 105 is formed at 1500 °, here 1000 °. This silicon oxide film also functions as a gate insulating film. (FIG. 3 (A))

Attention should be paid to the production of the silicon oxide film 105. Here, TEOS is used as a raw material, and a substrate temperature is 150 to 600 ° C., preferably 300 to 45 ° C. together with oxygen.
Decomposition and deposition were performed at 0 ° C. by an RF plasma CVD method. TE
The pressure ratio between OS and oxygen is 1: 1 to 1: 3, the pressure is 0.05 to 0.5 torr, and the RF power is 100 to 25.
0 W. Alternatively, TEOS is used as a raw material together with ozone gas by a low pressure CVD method or a normal pressure CVD method.
The substrate temperature is set to 350 to 600 ° C, preferably 400 to 55.
Formed at 0 ° C. After the film formation, annealing was performed at 400 to 600 ° C. for 30 to 60 minutes in an atmosphere of oxygen or ozone.

By irradiating a KrF excimer laser (wavelength: 248 nm, pulse width: 20 nsec) or an equivalent strong light in this state, the crystallization of the silicon region 104 may be promoted. In particular, RTA using infrared light
(Rapid thermal annealing) can selectively heat only silicon without heating the glass substrate, and can reduce the interface state at the interface between silicon and the silicon oxide film. It is useful in manufacturing a field-effect semiconductor device.

Thereafter, an aluminum film having a thickness of 2000 to 1 μm is formed by an electron beam evaporation method, and is patterned to form a gate electrode 106. Aluminum may be doped with scandium (Sc) by 0.15 to 0.2% by weight. Next, the substrate is adjusted to pH ≒.
7, immersed in an ethylene glycol solution of 1 to 3% tartaric acid, and anodized using platinum as a cathode and the aluminum gate electrode as an anode. The anodic oxidation is performed by first increasing the voltage to 220 V with a constant current and maintaining the state for one hour to complete the process. In this embodiment, in the constant current state, the voltage rising speed is suitably 2 to 5 V / min. Thus, anodic oxide 109 having a thickness of 1500 to 3500 °, for example, 2000 ° is formed. (FIG. 3 (B))

Thereafter, an impurity (phosphorus) was implanted into the island-like silicon film of each TFT in a self-aligned manner by an ion doping method (also called a plasma doping method) using the gate electrode portion as a mask. Phosphine (PH ₃ ) was used as a doping gas. Dose amount is 1-4 × 10
¹⁵ cm ^-2 .

Further, as shown in FIG. 3C, a KrF excimer laser (wavelength: 248 nm, pulse width: 20 ns)
ec) is applied to improve the crystallinity of the portion where the crystallinity is deteriorated by the introduction of the impurity region. The energy density of the laser is 150 to 400 mJ / cm ² , preferably 200 to 250 mJ / cm ² . Thus, N-type impurity (phosphorus) regions 108 and 109 are formed. The sheet resistance in these regions was 200 to 800 Ω / □.

In this step, instead of using a laser beam, a flash lamp is used for a short period of time.
強 1200 ° C. (temperature of silicon monitor) and heat the sample, using strong light equivalent to so-called laser light such as so-called RTA (rapid thermal annealing) (RTP, also called rapid thermal process). You may.

Then, an interlayer insulator 110 is formed on the entire surface.
Plasma CVD of TEOS as raw material and oxygen
Method, reduced pressure CVD method with ozone, or normal pressure CV
A silicon oxide film having a thickness of 3000 is formed by method D. The substrate temperature is 250 to 450 ° C., for example, 350 ° C.
After the film formation, the silicon oxide film is mechanically polished to obtain a flat surface. (FIG. 3 (D))

Then, the interlayer insulator 110 is etched, contact holes are formed in the source / drain of the TFT as shown in FIG. 1E, and wirings 112 and 113 of chromium or titanium nitride are formed.

Conventionally, a crystalline silicon film into which nickel has been introduced by plasma treatment has a lower selectivity to buffered hydrofluoric acid than a silicon oxide film, so that it is likely to be etched in the contact hole forming step. There were many.

However, when nickel is introduced by using an aqueous solution at a low concentration of 10 ppm as in this embodiment, since the hydrofluoric acid resistance is high, the formation of the contact hole can be performed stably with good reproducibility. it can.

Finally, at 300 to 400 ° C. in hydrogen at 0.
Anneal for 1-2 hours to complete silicon hydrogenation. Thus, the TFT is completed. Then, a large number of TFTs manufactured at the same time are arranged in a matrix to complete an active matrix liquid crystal display device.
This TFT has source / drain regions 108/109 and a channel formation region 114. 115 is N
It becomes an electrical junction of I.

When the structure of this embodiment is adopted, the concentration of nickel present in the active layer is about 3 × 10 ¹⁸ cm ⁻³ or less, that is, 1 × 10 ¹⁶ atoms cm ^{−3 to} 3 × 10 3.
It is considered to be ¹⁸ atoms cm ^-3 .

The TFT manufactured in this embodiment has an N channel mobility of 200 cm ² / Vs or more. It has also been confirmed that V _th is small and has good characteristics. ± 10% variation in mobility
It is confirmed that it is within. This small variation is considered to be due to the fact that crystal nuclei were uniformly introduced by heat treatment and then crystallized by irradiation with laser light, whereby uniform crystal grains were formed. When only the laser beam is used, an N-chaquer type of 150 cm ² / Vs or more can be easily obtained, but the variation is large and the uniformity as in this embodiment cannot be obtained.

[Embodiment 4] In this embodiment, a crystal nucleus is introduced under the amorphous silicon film (on the side in contact with the substrate), and thereafter, a laser beam is irradiated from the lower surface side of the substrate to form on the substrate. A method of crystallizing the amorphous silicon film,
This is an example of manufacturing T.

The details of the TFT are the same as those shown in FIG. In this embodiment, it is necessary for the laser to pass through the substrate. In this embodiment, Kr is used as the laser beam.
Since an F excimer laser is used, KrF
A quartz glass substrate that transmits an excimer laser (wavelength: 353 nm) is used. When a XeF excimer laser (wavelength: 353 nm) or a laser having a longer wavelength is used as a laser, a glass substrate (Corning 705) can be used.
9) can be used.

First, a hydrofluoric acid treatment for removing a natural oxide film is performed on the quartz glass surface, and then a thin oxide film is removed.
A film is formed to a thickness of about 0 ° by irradiation with UV light in an oxygen atmosphere. The thin oxide film may be formed by a method using a water treatment or thermal oxidation.

Then, an acetate solution containing 10 ppm of nickel is applied, held for 5 minutes, and spin-dried using a spinner. After that, the amorphous silicon film is plasma C
A film is formed to a thickness of 500 ° by the VD method. The formation of the amorphous silicon film may be performed by a low pressure thermal CVD method.

Next, by heating at 550 ° C. for one hour,
The silicon film is partially crystallized. Through this step, crystal nuclei are generated on the lower surface of the amorphous silicon film (the surface in contact with the quartz substrate). This crystal nucleus functions as a crystal nucleus in a subsequent laser crystallization step. By performing this heat treatment, a silicon film in which an amorphous component and a crystalline component are mixed can be obtained.

Then, a crystalline silicon film is obtained by irradiating a KrF excimer laser beam from the substrate side at 200 to 300 mJ. In the laser light irradiation step,
The substrate is heated to about 400 ° C. by an infrared lamp.
In this step, crystal growth is performed with the crystal nuclei existing in the crystal components as nuclei.

When a crystalline silicon film is thus obtained,
Through the same steps as in the third embodiment, a TFT as shown in FIG.
To complete. The TFT obtained in this example had the same characteristics as the TFT manufactured by the method shown in Example 3.

[Comparative Example] In this comparative example, the irradiation direction of the laser beam in the structure shown in the fourth embodiment was changed from the upper surface side (front surface side) of the amorphous silicon film having crystal nuclei introduced into the lower surface. It is. In this case, the effect of the step of introducing crystal nuclei was hardly observed, and only the same effect as in the case where crystallization was performed by simply irradiating a laser beam was obtained. From this comparative example, it is confirmed that a large effect cannot be obtained by introducing a crystal nucleus on one side of the amorphous film and irradiating a laser beam from the other side.

[Embodiment 5] In this embodiment, in the step of introducing crystal nuclei using a catalytic element, the generation of crystal nuclei is performed not by heating but by irradiation of intense light. In this embodiment, a method of forming an amorphous silicon film first and then introducing a catalytic element to generate crystal nuclei as described in Embodiment 3 will be described.

First, an amorphous silicon film is formed on a glass substrate as in the third embodiment. Then, an extremely thin silicon oxide film is formed, and an acetate solution containing 25 ppm by weight of nickel is applied in the same manner as the process shown in Embodiment 1.

Thereafter, a crystal nucleus is generated on the surface of the amorphous silicon film by irradiating infrared light having a wavelength of 1.2 μm from the surface side of the amorphous silicon film. A halogen lamp is used as an infrared light source. The intensity of the infrared light is adjusted so that the temperature on the single crystal silicon wafer of the monitor is between 900 and 1200 ° C. Specifically, the temperature of the thermocouple embedded in the silicon wafer is monitored, and this is fed back to the infrared light source. In the present embodiment, the temperature is raised at a constant rate of 50 to 200 ° C./sec, and the temperature is lowered by natural cooling to 20 to 100 ° C. This infrared light irradiation selectively heats the silicon film, so that heating of the glass substrate can be minimized.

By this step, crystal nuclei can be generated on the surface of the amorphous silicon film. Subsequent steps are described in Example 3.
Is the same as Further, as shown in Example 4, a catalytic element is introduced into the surface of the amorphous silicon film which is in contact with the substrate, and then infrared light is irradiated from the amorphous silicon film side or the back surface of the substrate. Thereby, a crystal nucleus can be generated on the surface of the amorphous silicon film which is in contact with the substrate.

[Embodiment 6] FIG. 4 is a sectional view showing a manufacturing process of this embodiment. First, the substrate (Corning 7059) 50
A silicon oxide base film 502 having a thickness of 2000 ° is formed on the substrate 1 by a sputtering method. The substrate is annealed at a temperature higher than the strain temperature before or after the formation of the base film, and then slowly cooled to a strain temperature or lower at 0.1 to 1.0 ° C./min. Substrate shrinkage in the accompanying steps (including the thermal oxidation step of the present invention and the subsequent thermal annealing step) is small, and mask alignment is ready. For Corning 7059 substrate, 1-4 at 620-660 ° C.
After annealing for an hour, the temperature is gradually reduced at 0.03 to 1.0 ° C./min, preferably 0.1 to 0.3 ° C./min.
It is good to take out at the stage when the temperature has dropped to ° C.

Next, a thickness of 5
An intrinsic (I-type) amorphous silicon film having a thickness of 00 to 1500 °, for example, 1000 ° is formed. Then, nickel is introduced into the surface of the amorphous silicon film as a catalyst element for promoting crystallization by the method described in the first embodiment. Then, annealing is performed at 550 ° C. for 1 hour in a nitrogen atmosphere (atmospheric pressure) to introduce crystal nuclei on the surface of the amorphous silicon film. Further, it is irradiated with a KrF excimer laser to be crystallized. Then, the silicon film is
An island-like silicon film (TFT active layer) 503 is formed by patterning to a size of 1000 μm square. (FIG. 4
(A))

Thereafter, an oxygen atmosphere containing 70 to 90% of water vapor at 1 atm, 500 to 750 ° C., typically 600 ° C. is subjected to a pyrogenic reaction method at a ratio of hydrogen / oxygen = 1.5 to 1.9. It is formed by using. The silicon film surface is oxidized by being left in such an atmosphere for 3 to 5 hours to form a silicon oxide film 504 having a thickness of 500 to 1500 °, for example, 1000 °. It should be noted that due to such oxidation, the surface of the initial silicon film is reduced by 50 ° or more, and as a result, contamination of the outermost surface of the silicon film is reduced by silicon-
That is, it does not reach the silicon oxide interface. That is, a clean silicon-silicon oxide interface is obtained. Since the thickness of the silicon oxide film is twice that of the silicon film to be oxidized, the silicon film having a thickness of
When a silicon oxide film of 00 ° is obtained, the thickness of the remaining silicon film is 500 °.

In general, the thinner the silicon oxide film (gate insulating film) and the active layer, the better characteristics such as improvement of mobility and reduction of off-current can be obtained. On the other hand, in the initial crystallization of the amorphous silicon film, the larger the film thickness, the easier the crystallization. Further, in this thermal oxidation, an amorphous component and a crystal grain boundary where recombination centers are apt to exist are easily oxidized, and as a result, recombination centers in the active layer are reduced.
This increases the product yield.

After forming the silicon oxide film 504 by thermal oxidation, the substrate is placed in a dinitrogen monoxide atmosphere (1 atm, 100 atm).
%) And annealed at 600 ° C. for 2 hours. (FIG. 4 (B)) Subsequently, a thickness of 3000 to 8 is applied by a low pressure CVD method.
000 °, for example, 6000 ° of polycrystalline silicon (0.01 to
(Containing 0.2% phosphorus). Then, the gate electrode 505 is formed by patterning the silicon film. Further, using the silicon film as a mask, an impurity (here, phosphorus) imparting an N conductivity type to the active layer region (which constitutes the source / drain and the channel) is self-aligned by an ion doping method (also referred to as a plasma doping method). ) Is added. Phosphine (PH ₃ ) as doping gas
And the acceleration voltage is set to 60 to 90 kV, for example, 80 kV. The dose is 1 × 10 ¹⁵ to 8 × 10 ¹⁵ cm ⁻² , for example, 5 × 10 ¹⁵ cm ⁻² . As a result, N-type impurity regions 506 and 507 are formed.

Thereafter, annealing is performed by laser light irradiation. As the laser light, a KrF excimer laser (wavelength: 248 nm, pulse width: 20 nsec) was used, but another laser may be used. The irradiation condition of the laser beam is such that the energy density is 200 to 400 mJ / cm ² ,
For example, 250 mJ / cm ^2, and ² to 10
A shot, for example, two shots is irradiated. The effect may be increased by heating the substrate to about 200 to 450 ° C. during the irradiation with the laser light. (FIG. 4 (C))

This step may be performed by lamp annealing using near-infrared light. Near infrared rays are more easily absorbed by crystallized silicon than amorphous silicon, and effective annealing comparable to thermal annealing at 1000 ° C. or higher can be performed. On the other hand, a glass substrate (far-infrared light is absorbed by the glass substrate, but visible / near-infrared light (wavelength 0.5 to 4
(μm) is hardly absorbed), so it is not necessary to heat the glass substrate to a high temperature and requires only a short processing time. Therefore, it is the most suitable method in the process where shrinkage of the glass substrate becomes a problem. It can be said that.

Subsequently, a silicon oxide film 50 having a thickness of 6000.degree.
8 is formed as an interlayer insulator by a plasma CVD method. Polyimide may be used as the interlayer insulator. Further, a contact hole is formed, and TF is formed by a metal material, for example, a multilayer film of titanium nitride and aluminum.
T electrodes / wirings 509 and 510 are formed. Finally, 1
Annealing is performed at 350 ° C. for 30 minutes in a hydrogen atmosphere at atmospheric pressure to complete the TFT. (FIG. 4 (D))

The mobility of the TFT obtained by the above method is 110 to 150 cm ² / Vs, and the S value is 0.2 to 0.5.
V / digit. In addition, a P-channel TFT in which the source / drain was doped with boron was manufactured by the same method, and the mobility was 90 to 120 cm ² / Vs.
The S value is 0.4 to 0.6 V / digit, the mobility is 20% or more higher than the case where a gate insulating film is formed by a known PVD method or CVD method, and the S value is 20% or more. Diminished. Also, from the viewpoint of reliability, the T
FT is TF manufactured by high temperature thermal oxidation at 1000 ° C.
Good results were shown, which were comparable to T.

[Embodiment 7] FIG. 7 is a block diagram of an electro-optical system using an integrated circuit in which a display, a CPU, and a memory are mounted on one glass substrate. The present embodiment relates to an example in which an integrated electrical engineering system (liquid crystal display) is configured using a TFT utilizing the present invention.

Here, the input port means that a signal inputted from the outside is read and converted into an image signal, and the correction memory is unique to a panel for correcting an input signal or the like in accordance with the characteristics of the active matrix panel. Memory. In particular, this correction memory is used for financing and individually correcting information unique to each pixel as a nonvolatile memory. That is, if a pixel of the electro-optical device has a point defect, a signal corrected in accordance therewith is sent to pixels around the point to cover the point defect and make the defect inconspicuous. Or, if the pixel is darker than the surrounding pixels,
A larger signal is sent to the pixel to make it the same brightness as the surrounding pixels. The pixel has a liquid crystal 7
3, a capacitor 72 and a TFT 71 are arranged.

The CPU and the memory are the same as those of an ordinary computer. In particular, the memory has an image memory corresponding to each pixel as a RAM. Further, the backlight that irradiates the substrate from the back surface can be changed according to the image information.

[0101]

[Effect] By introducing a catalytic element to generate crystal nuclei on the surface side of the amorphous silicon film, and then irradiating the laser light or intense light to the surface on which the crystal nuclei have been introduced, a crystal having good crystallinity is obtained. The conductive silicon film can be obtained.

[Brief description of the drawings]

FIG. 1 shows the steps of an example.

FIG. 2 shows a process of an example.

FIG. 3 shows a manufacturing process of an example.

FIG. 4 shows a manufacturing process of an example.

FIG. 5 shows a manufacturing process of an example.

FIG. 6 shows a cross-sectional photograph of a crystallized silicon thin film.

[Explanation of symbols]

 11 ··· glass substrate 12 ··· amorphous silicon film 13 ··· silicon oxide film 14 ··· acetic acid solution film containing nickel 15 ··· spinner 11 ··· glass substrate 104 active layer 105 silicon oxide film 106 gate electrode 109 oxide layer 108 source / drain region 109 drain / source region 110 interlayer insulating film ( 112 ... electrode 113 ... electrode

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/336

Claims (1)

[Claims] 1. A non-single-crystal semiconductor film containing silicon is formed on an insulating surface, crystalline silicon is partially formed in the semiconductor film by heat treatment, and the crystalline silicon is grown by light irradiation. Semiconductor device manufacturing method.