JPH09148251A - Semiconductor and method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a crystalline silicon film having higher crystallinity on an upper surface than that of a lower surface by a method wherein, after a catalyzer element which comes into contact with a lower surface of an amorphous silicon film, and which promotes crystallization of the amorphous silicon film is held, the amorphous silicon film is heated. SOLUTION: Glass is used as a substrate 11 and an amorphous silicon film 12 is formed thereon by a plasma CVD method. Then, hydrofluoric acid process is performed in order to remove contamination and a natural oxide film, and thereafter an oxide film 13 is formed. Next, a nickel salt solution containing a catalyzer element for promoting crystallization of the amorphous silicon film is dropped on a surface of the amorphous silicon film, and this condition is held for 1min., a thin nickel salt solution layer 14 is formed on a face of the amorphous silicon film. Thereafter, in a heating furnace, it is heated at 550 to 640 deg.C for 4 hours in a nitrogen atmosphere. As a result, it is possible to obtain the silicon thin film 12 having crystallinity formed on the substrate 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a crystalline semiconductor.

[0002]

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

[0003] As a thin film semiconductor used for a TFT,
Although it is easy to use an amorphous silicon film, there is a problem in that its electrical characteristics are low. In order to obtain improved TFT characteristics, 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 may be formed first, and then crystallized by heating.

However, crystallization by heating requires heating at a temperature of 600 ° C. or higher for 10 hours or longer, which makes it difficult to use a glass substrate as a substrate. For example, Corning 7059 glass used in an active type liquid crystal display device has a glass strain point of 593 ° C., and there is a problem in heating at 600 ° C. or higher in consideration of increasing the area of a substrate.

BACKGROUND OF THE INVENTION According to the research conducted by the present inventors, trace amounts of catalytic elements such as nickel, palladium, and lead are deposited or added on the surface of an amorphous silicon film.
It has been proved that crystallization can be carried out at a treatment time of 550 ° C. for about 4 hours by heating thereafter. And, it has been conventionally disclosed that the addition method by the plasma treatment or the liquid phase method is effective as the above-mentioned addition method of the catalyst element. (For example, Japanese Patent Laid-Open No. 07-130652)

The method of adding the catalytic element disclosed heretofore will be briefly described below. The above-mentioned plasma treatment is a parallel plate plasma CVD apparatus in which a material containing a catalytic element is used as an electrode and plasma is generated in an atmosphere such as hydrogen to add the catalytic element to the amorphous silicon film. Is the way.

However, the presence of a large amount of the above-mentioned elements in the semiconductor impairs the reliability and electrical stability of the device using these semiconductors and is not preferable.

That is, the above-mentioned element (catalyst element) that promotes crystallization, such as nickel, is necessary when crystallizing amorphous silicon, but the crystallized silicon should not be included as much as possible. Is desirable. To achieve this goal,
It is necessary to select a catalyst element that has a strong tendency to be inactive in crystalline silicon, at the same time reduce the amount of the catalyst element required for crystallization as much as possible, and perform crystallization with the 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 catalytic 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. 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.

From the above it is concluded that all the nickel introduced by the plasma treatment is not functioning effectively. Then, it is concluded that "what is necessary is to introduce a very small amount of nickel into the vicinity of the surface of the amorphous silicon film."

As a method of introducing a very small amount of nickel only in the vicinity of the surface of the amorphous silicon film, in other words, a very small amount of a catalyst element that promotes crystallization only in the vicinity of the surface of the amorphous silicon film is introduced. , Vapor deposition 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. Therefore, in order to satisfy the above object, the inventors have invented a liquid phase method. The liquid phase method is simply a method of "coating a solution containing a catalytic element on the surface of an amorphous silicon film, and thereby introducing the catalytic element".

The above configuration has the following basic significance. (A) The concentration of the catalyst element in the solution can be strictly controlled beforehand. (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 crystallization, the catalytic element can be introduced at the required minimum concentration.

As a method of applying a solution containing an element which promotes crystallization to the amorphous silicon film, a method of using an aqueous solution of nitrate, acetate or sulfate as the solution can be mentioned. In this case, if the above solution is applied directly to the amorphous silicon film, the solution will be repelled, so by forming a thin oxide film of 100 Å or less first and applying the solution containing the catalytic element on it. 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 an octylate or toluene solution as the solution, the solution can be directly applied to the surface of the amorphous silicon film. In this case, it is effective to pre-apply a material such as an adhesive used when applying the resist. 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 catalytic element contained in the solution depends on the type of the solution, but the general tendency is that the amount of nickel is not more than 200 ppm, preferably 50, based on the solution.
It is desirable to set it to ppm or less (weight conversion). This is a value determined in consideration of the nickel concentration in the film and the hydrofluoric acid resistance after completion of crystallization.

Crystal growth can be selectively performed by selectively applying a solution containing a catalytic element. Particularly, in this case, crystal growth can be performed in the direction parallel to the surface of the silicon film from the area where the solution is applied, toward the area where the solution is not applied. In the present specification, a region in which crystal growth is performed in a direction parallel to the surface of the silicon film is referred to as a lateral crystal growth region.

It has been confirmed that the concentration of the catalytic element is low in the region where the crystal growth is carried out in the lateral direction.
Although it is useful to use a crystalline silicon film as the active layer region of the semiconductor device, it is generally preferable that the impurity concentration in the active layer region is low. Therefore, it is useful in device fabrication to form an active layer region of a semiconductor device using the region where the crystal growth has been performed in the lateral direction.

In the present invention, the most remarkable effect can be obtained when nickel is used as the catalyst element, but other types of catalyst element that can be used are Fe,
Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, C
It is also possible to use one or more kinds of elements selected from u and Au. It is preferable to use Ni as an element having a particularly remarkable effect.

[0019]

As described above, the inventors have made various studies on a method for adding a trace amount of a catalytic element,
Has been improved. Then, for example, even when the same catalytic element is added in the liquid phase method, the addition place (for example, whether the catalytic element is applied after forming an oxide film on the surface or after forming a base silicon oxide film) (Do you add a catalytic element and then form an amorphous silicon film on it?)
It was found that the obtained TFT characteristics differ from each other. In addition, it was also found that the film thickness will be large depending on the film forming conditions and the film forming method of the starting amorphous silicon film. The present invention discloses a method of forming polysilicon having a higher degree of perfection, based on the above findings.

[0020]

The present invention is basically based on Japanese Unexamined Patent Publication No. 07-130652, but in particular, 1) a catalyst is added to the surface of an underlayer, and an amorphous silicon film is formed thereon. To form a film. 2) As the amorphous silicon film, use amorphous silicon having a density approximately 0.9 times or more that of single crystal silicon as a starting film. It is characterized by two points.

First, a large number of compounds are disclosed in JP-A-07-130652. Both of these are effective for low-temperature crystallization, but according to the research conducted by the inventors, it is as described above that nickel has a particularly remarkable effect. In the following description, nickel will be described as an example. Will be added.

First, the effect of the addition place, which is the first feature of the present invention, will be described. It is considered that nickel is selected as a catalytic element and added into amorphous silicon by using a liquid phase method. Here, as an example, nickel nitrate which is a general salt is used as a solute, and pure water or ultrapure water is used as a solvent. According to the method disclosed in Japanese Patent Laid-Open No. 07-130652, the amorphous silicon film 1 is formed by spin coating.
000Å surface (strictly, about 15Å oxide film is formed on the surface) is applied over the entire surface, and then 5 in a nitrogen atmosphere.
Heat crystallization was performed at 50 ° C. for 4 hours. The other is to apply a similar aqueous nitrate solution onto the underlying silicon oxide, dry it and form a film of amorphous silicon on it, and then at 550 ° C. in a nitrogen atmosphere.
Heat crystallization was performed for 4 hours.

The polysilicon thus obtained was measured by Raman spectroscopy from the upper surface and the back surface of the polysilicon film, that is, from the glass substrate side, and the half width at half maximum was evaluated. First, an evaluation was performed on a conventional one in which the catalyst was added from the upper surface of the amorphous silicon film.

As a result, in the present measuring method, the half-width at half maximum is 2.0 in the single crystal (100) wafer.
± 0.1 cm −1, while 3.5 on the surface side
It was found that the crystallinity was higher on the back side, which was about cm-1 and about 2.5 m-1 on the back side.

Next, the same evaluation was carried out for a substrate having a catalyst added thereto. As a result, the surface side is 2.8 cm
It was found that the crystallinity was higher on the front surface side, that is, about −1 and about 3.3 m −1 on the back surface side. As a result, when the active region of the TFT is formed using these polysilicons, if the planar type has the gate electrode on the upper side, it is better to add a catalyst to the base because the region with higher crystallinity is used. It has been found possible to make a TFT.

Further, when TFTs were actually manufactured, their variations were also very different, and the variation was much lower with the addition of the underlayer. It is considered that this is because the silicon oxide film formed on the surface (formed by UV irradiation) is not uniform, so that the addition state of the catalyst varies within the surface. Therefore, based on the present invention,
It means that a planar type TFT having a gate electrode on the upper surface by adding a catalyst to the base is desirable.

When a solution containing a catalytic element is applied to the surface of the underlayer and then an amorphous silicon film is formed by various methods, the compound contained in the solution contaminates the chamber of the film forming apparatus. There are cases. At that time, heat treatment is performed in advance, ultraviolet irradiation is performed, electromagnetic waves having a resonance wavelength are irradiated,
It is useful to decompose these in advance by a method such as.

Next, the density of the amorphous silicon film, which is the second feature of the present invention, will be described. In general, in the case of solid phase crystallization (without addition of a catalyst), it is possible to increase the crystal grain size by forming an amorphous silicon film so that the nucleus generation density becomes low. Well known. It is also well known that for laser crystallization using an excimer laser, an LP film having a small amount of hydrogen is effective in terms of laser resistance in order to prevent a hydrogen fountain phenomenon.
However, what kind of amorphous silicon film is effective when a catalytic element is added has not been known so far.

First, when compared with general solid phase crystallization,
Since the nucleation density can be controlled by adding a catalyst, the spontaneous nucleation density is not so important. Also, the amount of hydrogen is not so important. The most important issue this time is the generation of stress associated with crystal growth.

According to the research conducted by the inventors, it has been found that when these catalysts are added, these silicides are first formed, and columnar crystals are grown using these as nuclei like heteroepitaxial growth. Particularly when nickel is selected as the catalyst, nickel disilicide is very close to the lattice constant of silicon, so that almost perfect epitaxial growth can be performed.

Making the length of these columnar crystals as long as possible is almost equivalent to increasing the crystallinity of the obtained polysilicon crystal. Therefore, various starting amorphous silicon films were used, and these were evaluated in detail. When the starting film has a low density, a large volume change occurs when the columnar crystals are stretched, and a large amount of space is generated between them. It has been found that the crystal growth cannot be made sufficient due to the generated stress, and the crystal growth stops halfway or a stacking fault occurs between them to relax the stress. That is, what is important is not the amount of hydrogen or the manufacturing method, but the stress generated during crystal growth of the original amorphous silicon film.

The present inventors conducted film formation on a silicon wafer and heat crystallization in order to define these as stress values, and investigated the stress value generated at this time from the amount of warp of the wafer. However, unfortunately, the stress thus obtained is a macroscopic stress, which does not necessarily coincide with the microscopic stress exerted by the surroundings on the columnar crystal, and the correlation cannot be obtained clearly. Therefore, the inventor next decided to measure the density of the amorphous silicon film. Then, using various methods (plasma CVD, LPCVD, vapor deposition, sputtering), the densities of these were measured and the correlation with them was investigated.

Here, the vapor deposition method and the sputtering method can form a completely hydrogen-free film, and the density thereof can be as high as about 0.98 times that of single crystal silicon depending on the conditions. . Although the amount of hydrogen in LPCVD is lower than that in plasma CVD, it was possible to significantly increase the density by lowering the amount of hydrogen by increasing the temperature during film formation. This suggests that in amorphous silicon, which is a tetrahedral system, the amount of hydrogen and the density have a correlation, but they do not perfectly match, and other network connections also have an effect.

Finally, even in plasma CVD, which is generally said to be unsuitable for polysilicon formation, by raising the substrate temperature to about 300 ° C. or higher, a high density amorphous silicon that can withstand practical use is obtained. I could get a membrane.

The density is measured by the resonance nuclear reaction method,
Flotation method, α-ray elastic scattering method, etc. can be used, but even if any of them is used, a carefully measured experiment can obtain a measured value of two or more significant figures, which is sufficient for this evaluation. there were.

What is important is the specific density at which good polysilicon can be obtained, but first, at least about 0.9 times that of a single crystal was the minimum required. That is,
In the case of a plasma CVD film that is about 0.8 times as thick as a single crystal, the crystallization rate is low (calculated from the relative intensities of the crystalline peak and the amorphous peak by Raman spectroscopy), but after a slight hydrogen desorption, the catalyst This is because the crystallization rate rapidly increased in the materials that were added and crystallized. The density of the amorphous silicon film after dehydrogenation was 0.92 times that of the single crystal.

As the density becomes closer to that of a single crystal, the stress is relaxed, and polysilicon having good crystallinity can be obtained. However, as an exception, the sputtered film contained a large amount of argon in the film although it had a high density, so the crystallinity was not as high as other films of the same density.

As described above, the present invention is roughly divided into two components. Although each of them has a sufficient effect, it is possible to obtain a higher effect, that is, good polysilicon can be obtained by combining the two.
Examples of the above-described configuration of the present invention will be shown below, and a more detailed description will be given.

[0039]

【Example】

 [Example 1]

This embodiment shows an example of forming a crystalline silicon film on a glass substrate. First, referring to FIG. 1, description will be made up to the point where a catalyst element (here, nickel is used) is introduced. In this embodiment, Corning 1737 glass is used as the substrate 11. The size is 127 mm × 127 mm.

First, the amorphous silicon film 12 is subjected to plasma CVD.
Is formed at a temperature of 100 to 1500 ° by an LPCVD method. Here, the amorphous silicon film 12 is formed to a thickness of 1000 Å by the plasma CVD method. (Fig. 1 (A))

Then, a hydrofluoric acid treatment is performed to remove dirt and a natural oxide film.
Deposit on Å. Needless to say, this step may be omitted if the stain can be ignored, and a natural oxide film may be used as it is instead of the oxide film 13. Since the oxide film 13 is extremely thin, the exact film thickness is unknown.
It is considered to be about 0Å. Here, the oxide film 13 is formed by irradiation with UV light in an oxygen atmosphere. The film formation was performed by irradiating UV for 5 minutes in an oxygen atmosphere. As a method of forming the oxide film 13,
A thermal oxidation method may be used. Alternatively, it may be processed by a solution such as hydrogen peroxide or ozone water.

The oxide film 13 is provided in order to spread the nickel salt solution over the entire surface of the amorphous silicon film in the later step of applying an aqueous solution containing nickel, that is, for improving the wettability. . For example, when the acetate solution is directly applied to the surface of the amorphous silicon film, the amorphous silicon repels the nickel salt solution, so that nickel cannot be introduced to the entire surface of the amorphous silicon film. That is, uniform crystallization cannot be performed.

Next, a nickel salt solution is prepared. Nickel nitrate is used and the dose is 1 × 10 ¹³ atoms / cm ²
The nickel salt solution concentration was adjusted as much as possible. Then, these solutions are dropped onto the surface of the above-mentioned amorphous silicon film, and this state is maintained for 1 minute. At this time, a thin nickel salt solution layer 14 is formed on the surface of the amorphous silicon film. (Figure 1
(B))

The concentration of nickel contained in the silicon film 12 can be finally controlled also by this holding time, but the largest control factor is the concentration of the solution.
And spin dry (2000 rp using spinner)
m, 60 seconds). (Fig. 1 (D))

When the concentration of nickel in these nickel salt solutions was 1 ppm or more when the thickness of the amorphous silicon film was several hundreds to 1000 liters, crystallization was possible within a practical range. Then, the above dose amount is 1 × 10 ¹³ at
The solution concentration of oms / cm ² was less than 10 ppm in terms of nickel.

Then, in the heating furnace, heat treatment is performed in a nitrogen atmosphere at 550 to 640 ° C., this time 600 ° C. for 4 hours. As a result, the crystalline silicon thin film 12 formed on the substrate 11 could be obtained.

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 prolonged, and the production efficiency decreases. Further, if it is set to 650 degrees or more, the problem of heat resistance of the glass substrate used as the substrate comes to the surface. This is the case for the Corning 1737 substrate, and when Corning 7059 glass having lower heat resistance is used, it is necessary to further lower the temperature in the heat crystallization step. The polysilicon thus obtained was evaluated for crystallinity by Raman spectroscopy while etching from the surface. For etching,
A mixture of HF: HNO ₃ : H ₂ O = 1: 1200: 300 in a volume ratio was used. In addition, the surface roughness of the film due to the etching hardly occurred. The change in half-width at half maximum due to Raman thus obtained is shown in FIG. In addition, in the figure, the results of crystallization at many different temperatures are described. From these, it is clear that the half-width at half maximum becomes smaller as the film thickness decreases, that is, the closer to the back surface. In general solid-phase growth, nucleation occurs from the underlying interface, so that it is said that polysilicon has better crystallinity toward the surface (because stress is relaxed in the film thickness direction), but it is amorphous. When a catalyst is added to the surface of the silicon oxide film, the opposite phenomenon seems to occur. In this case, when it is used as a channel of a TFT, it is desirable to use a region having high crystallinity, and therefore it is considered to be suitable for a stagger type TFT in which a channel is formed on the lower side. On the contrary, when the same evaluation was performed for the substrate to which nickel was added, it was confirmed that the crystallinity was deteriorated as it was closer to the interface of the substrate, contrary to FIG.

[Embodiment 2] In this embodiment, the density of the amorphous silicon film is changed from 0.85 to 0.97 of single crystal silicon by changing the film forming temperature of LPCVD from 400 ° C. to 500 ° C. The changes in the physical properties of polysilicon when the conditions are changed are shown. Conditions other than the above film forming temperature were typically Si ₂ H ₆ 100 to 500 sccm He 500 sccm, film forming pressure 0.1 to 1 Torr, and film thickness of amorphous silicon was 800 Å. First, an underlying silicon oxide film of 2000 liters was formed, and then a nickel nitrate salt solution (10 ppm) was applied, and then an amorphous silicon film was formed at each of the above temperatures. Subsequently, polysilicon was formed through a heating crystallization process in nitrogen at 600 ° C. for 4 hours. Then, these polysilicons were subjected to seco etching to evaluate the crystal grain size. First, since the LPCVD film at low temperature (400 ° C) has a low density, it is very weak against seco-etching, and the film after etching is quite porous, and the crystal grain size (columnar crystal, width is 500Å). Since the length is constant, the length and the particle size are about 2000Å. On the other hand, in a higher density amorphous silicon film (amorphous silicon having a density 0.97 times that of single crystal silicon), the average crystal grain size was extended to about 1 μm, and the resistance to secco etching was high. The film having a density 0.93 times as high as that of single crystal silicon had an intermediate value between them. From this, the effectiveness of using a high-density amorphous silicon film having a density close to that of a single crystal was clarified.

[Embodiment 3] In this embodiment, a 1200 Å silicon oxide film is selectively provided by using the low-density amorphous silicon film and the high-density amorphous silicon film described in Embodiment 2. In this example, nickel is selectively introduced using the silicon oxide film as a mask.

FIG. 2 shows an outline of the manufacturing process in this embodiment. First, on a glass substrate 11 (Corning 1737, 127 mm square) on which an underlying silicon oxide film is formed, an amorphous silicon film 12 having a different density as in Example 2 is formed in a thickness of 500 Å. After that, a silicon oxide film 21 to be a mask
Is formed to a thickness of 1000 Å or more, here 1200 Å. The thickness of the silicon oxide film 21 has been confirmed by experiments by the present inventors to be satisfactory even at 500 °, and it is considered that the thickness may be further reduced if the film quality is dense.

Then, the silicon oxide film 21 is patterned into a required pattern by a normal photolithographic patterning process. Then, a thin silicon oxide film 20 is formed by ultraviolet irradiation in an oxygen atmosphere. This silicon oxide film 2
The production of No. 0 is performed by irradiating UV light for 5 minutes in an oxygen atmosphere. The thickness of the silicon oxide film 20 is considered to be about 20 to 50Å (FIG. 2 (B)). still,
When a silicon oxide film for improving the wettability matches the size of the solution and the pattern, the silicon oxide film may be added just by the hydrophilicity of the silicon oxide film of the mask. However, such an example is special, and it is generally safer to use the silicon oxide film 20.

In this state, as in Example 1, 10
10 ml of a nitrate solution containing 0 ppm of nickel is dropped (in the case of a 127 mm square substrate). At this time, spin coating is performed with a spinner at 50 rpm for 10 seconds to form a uniform water film 14 on the entire surface of the substrate. In this state, hold for 1 minute and then spinner 15 to 2000
Spin dry for 60 seconds at rpm. This holding may be performed while rotating the spinner 15 at 0 to 100 rpm. (Fig. 2 (C))

Then, the amorphous silicon film 12 is crystallized by performing heat treatment at 550 ° C. (nitrogen atmosphere) for 4 hours. At this time, crystal growth is performed laterally from the region of the portion 22 into which nickel has been introduced to the region into which nickel has not been introduced, as indicated by 23. Although this region is referred to as a lateral growth region in the present specification, this varies depending on the temperature and is about 20 μm in 550 ° C. (nitrogen atmosphere) for 4 hours, but the crystallization temperature is increased to about 600 ° C. By doing so, it is possible to extend the lateral growth region to about 60 to 80 μm by the same heating crystallization for about 4 hours. The lateral growth amounts obtained this time were not so different for the two types of films having different densities. However, as a result of Secco etching the lateral growth region in the same manner as in Example 2 to evaluate the grain size, a low density (0.85 times that of a single crystal) amorphous silicon film has a stacking fault of about 5000 Å at each time. , And the stress relaxation occurred, but in the case of high density (0.97 times of single crystal), 2μ depending on the material.
Long columnar crystals exceeding m were obtained.

[Embodiment 4] This embodiment is an example of manufacturing a TFT provided in each pixel portion of an active matrix type liquid crystal display device using a crystalline silicon film manufactured by using the method of the present invention. Indicates. 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.

FIG. 4 shows an outline of the manufacturing process of this embodiment.
First, an underlying silicon oxide film (not shown) is formed on a glass substrate 11.
To a thickness of 2000Å, plasma C using TEOS as a raw material
The film is formed by the VD method. The film forming conditions are shown below. TEOS / O ₂ = 10/100 sccm RF power 350 W Substrate temperature 400 ° C. Film forming pressure 0.25 Torr In the above reaction, C ₂ F ₆ was added to form SiO 2.
Film may be formed as shown in F _x. This silicon oxide film is provided to prevent diffusion of impurities from the glass substrate. Then, a nitrate solution containing 10 ppm of nickel is applied, held for 5 minutes, and spin-dried using a spinner. Then, the amorphous silicon film is formed into 100 to 1 by the LPCVD method in the same manner as in the first embodiment.
Deposit 500Å, preferably 200-800Å. LP
The film forming conditions in the CVD method are shown below. As mentioned above, the density of the amorphous silicon film is important. From this viewpoint, LPCVD is easy because a high density amorphous silicon film can be obtained. It is suitable. The film forming conditions at that time are typically Si ₂ H ₆ 100 to 500 sccm He 500 sccm, film forming temperature 450 ° C. to 500 ° C., film forming pressure 0.1 to 1 Torr.

Next, in a nitrogen atmosphere, 500 to 600 ° C. 4
Heat crystallization of hr is performed. In this embodiment, 550 ° C. for 4 hours
r. Next, the crystallized silicon film is patterned to form the island-shaped region 104. This island area 10
Reference numeral 4 constitutes an active layer of the TFT. And thickness 200 ~
The silicon oxide 105 of 1500 Å, here 1000 Å, is formed. This silicon oxide film also functions as a gate insulating film. (Fig. 4 (A))

Attention must 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.
It was set to 0W. Alternatively, by using TEOS 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.

In this state, a KrF excimer laser (wavelength 248 nm, pulse width 20 nsec) or strong light equivalent thereto may be irradiated to promote crystallization of the silicon region 104. 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 the silicon and the silicon oxide film. It is useful in the fabrication of a field effect semiconductor device.

After that, an aluminum film having a thickness of 2000 Å to 1 μm is formed by electron beam vapor deposition, and this 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. 4 (B))

After that, an impurity (phosphorus) was self-alignedly injected into the island-shaped silicon film of each TFT by an ion doping method (also referred to as a plasma doping method) using the gate electrode portion as a mask. Phosphine (PH ₃ ) was used as a doping gas. The dose amount is 1 to 4 × 10
¹⁵ cm ^-2 .

Furthermore, as shown in FIG. 4C, a KrF excimer laser (wavelength 248 nm, pulse width 20 ns) is used.
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 process, instead of using a laser, a flash lamp is used, and 1000 to
Raise to 1200 ° C (temperature of silicon monitor)
So-called RTA (Rapid Thermal Annealing) (RTP, also called rapid thermal process) for heating the sample may be used.

After that, 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 Å is formed by the D method. 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. Further, an ITO film is deposited by the sputtering method and patterned to form the pixel electrode 111. (FIG. 4 (D))

Then, the interlayer insulator 110 is etched to form contact holes in the source / drain of the TFT, and wirings 112 and 113 of chromium or titanium nitride are formed.
And the wiring 113 is connected to the pixel electrode 111.

Since the crystalline silicon film into which nickel is introduced by the plasma treatment has lower selectivity to buffer hydrofluoric acid than the silicon oxide film, it is often etched in the step of forming the contact hole. It was

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

Finally, in hydrogen at 300-400 ° C.
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.

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

In this embodiment, an example was shown in which the portion into which nickel was introduced was crystallized. However, as shown in Example 2, nickel was introduced selectively, and from that portion in the lateral direction (parallel to the substrate). The electronic device may be formed by using the region in which the crystal is grown in the (direction). In this case, the nickel concentration in the active layer region of the device can be further reduced,
An extremely preferable configuration can be obtained from the viewpoint of electrical stability and reliability of the device. [Embodiment 5] This embodiment shows an example of manufacturing a TFT provided in each pixel portion of an active matrix type liquid crystal display device using a crystalline silicon film manufactured by using the method of the present invention. 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.

Since the outline of the manufacturing process of this embodiment has already been described in [Embodiment 4], only the changes will be described here.

In this embodiment, in order to further enhance the crystallinity of the crystalline silicon film after heat crystallization, an excimer laser is used.
Laser annealing is performed.

In this embodiment, KrF was used as the laser source, but ArF, ArCl, KrCl, XeF and X were used.
An excimer laser such as eCl may be used.

The irradiation energy is set to 180 to 230 mJ / cm ^{2 on the} surface of the crystalline silicon film,
The irradiation repetition frequency is adjusted to be 35 to 45 Hz. Laser irradiation is a step of holding the substrate.
While moving the sheet at a speed of 2.0 to 8.0 mm / sec. At that time, the atmosphere in the processing chamber and the substrate temperature are appropriately determined. In this embodiment, the processing is performed in the air atmosphere and the substrate temperature is room temperature.

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

After heating and crystallization of the amorphous silicon film,
By performing the annealing, a crystalline silicon film having higher crystallinity can be obtained. Therefore, the mobility of the thin film transistor can be improved.

[Embodiment 6] In this embodiment, when the metal element for promoting crystallization of [Embodiment 5] is added, those containing carbon and those not containing carbon, specifically, acetate aqueous solution and nitrate aqueous solution are used. Is compared by using. The added nickel concentration was adjusted to be exactly the same, and the steps other than nickel addition were exactly the same as in [Example 5], so only the results are shown.

When an acetate solution is used, a field effect mobility of 150 cm ² / V · s and an S value of about 0.3 are obtained as standard. When a nitrate solution is used, a field effect mobility of 180 c is obtained.
m ² / V · s and S value of about 0.25 were obtained with good reproducibility. [Embodiment 7] This embodiment shows an example of manufacturing a TFT provided in each pixel portion of an active matrix type liquid crystal display device by using a crystalline silicon film manufactured by using the method of the present invention. 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.

Since the outline of the manufacturing process of this embodiment has already been described in [Embodiment 4], only the changes will be described here.

In this embodiment, after heat crystallization, heat treatment by rapid thermal anneal (RTA) is performed to further enhance the crystallinity of the crystalline silicon film.

RTA is a technique for heat-treating a substrate with an infrared lamp, a xenon lamp, an arc lamp or the like, and the temperature is raised and lowered within an extremely short time. Therefore, there is an advantage that only the thin film can be heat-treated without giving thermal damage to the substrate body. Also,
Since the heat treatment is completed in a short time, the throughput is improved.

According to this embodiment, a crystalline silicon film having higher crystallinity can be obtained by performing the heat treatment by RTA after the amorphous silicon film is heated and crystallized. for that reason,
The mobility of the thin film transistor can be improved.

[Embodiment 8] This embodiment is an example of manufacturing a TFT provided in each pixel portion of an active matrix type liquid crystal display device using a crystalline silicon film manufactured by using the method of the present invention. Indicates. 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.

Since the outline of the manufacturing process of this embodiment has already been described in [Embodiment 4], only the changes will be described here.

In this embodiment, in order to further enhance the crystallinity of the crystalline silicon film after heat crystallization, an excimer laser is used.
Laser anneal using
(RTA) heat treatment in combination.

In this embodiment, first, laser annealing is performed. At this time, KrF was used as a laser source,
An excimer laser such as ArF, ArCl, KrCl, XeF and XeCl may be used.

The irradiation energy is adjusted to 180 to 230 mJ / cm ^{2 on the} surface of the crystalline silicon film, and the irradiation repetition frequency is adjusted to 35 to 45 Hz. Laser irradiation is performed while moving the stage holding the substrate at 2.0 to 8.0 mm / sec. that time,
The atmosphere in the processing chamber and the substrate temperature are appropriately determined. In this embodiment, the processing is performed in the air atmosphere and the substrate temperature is room temperature.

Then, rapid thermal malaniles (RT
The heat treatment according to A) is performed. RTA is a technique for heat-treating a substrate with an infrared lamp, and temperature rise and fall are performed within an extremely short time. Therefore, there is an advantage that only the thin film can be heat-treated without giving thermal damage to the substrate body. Moreover, since the heat treatment is completed in a short time, the throughput is improved.

According to this embodiment, a crystalline silicon film having higher crystallinity can be obtained by using heat treatment by laser annealing and RTA after heat crystallization of the amorphous silicon film. You can Therefore, the mobility of the thin film transistor can be improved.

[0090]

[Effect] By changing the method of adding the catalyst element in accordance with the structure of the target semiconductor device, it becomes possible to use a region having higher crystallinity as an active region. Further, by making the amorphous silicon film have a high density, it is possible to relax the stress generated during heteroepitaxial growth from the silicide of the catalytic element, and obtain polysilicon having a larger grain size and good crystallinity. It was

[Brief description of the drawings]

FIG. 1 is a diagram showing a manufacturing process of an example.

FIG. 2 is a diagram showing a manufacturing process of an example.

FIG. 3 is a diagram showing a difference in crystallinity in a thickness direction.

FIG. 4 shows a process for manufacturing a TFT in an example.

[Explanation of symbols]

 11 glass substrate 12 amorphous silicon film 13 silicon oxide film 14 solution containing nickel 15 spinner 20 silicon oxide film 21 mask of silicon oxide film 22 nickel addition region 23 lateral growth region

Claims (13)

[Claims] 1. A step of holding a catalytic element in contact with a lower surface of the amorphous silicon film to promote crystallization of the amorphous silicon film, and subjecting the amorphous silicon film to a heat treatment to crystallize the upper surface thereof. And a step of obtaining a crystalline silicon film having higher crystallinity than the crystallinity of the lower surface thereof. 2. A step of applying a solution containing a metal element that promotes crystallization of an amorphous silicon film onto a substrate having an insulating surface, and a step of forming an amorphous silicon film on the substrate. And a step of heat-treating the amorphous silicon film to obtain a crystalline silicon film whose upper surface has higher crystallinity than its lower surface. 3. The method according to claim 2, further comprising the step of applying energy after the step of applying a solution containing a metal element that promotes crystallization of the amorphous silicon film to decompose the compound in the solution. A method for manufacturing a semiconductor, comprising a step of forming an amorphous silicon film after the step. 4. The energy applied to decompose the compound in the solution according to claim 3, is heat, light,
A method for manufacturing a semiconductor, which is characterized by using electromagnetic waves. 5. The method according to claim 1, 2 or 3.
Alternatively, in claim 4, Ni is used as a catalyst element, and the method for manufacturing a semiconductor is characterized. 6. The method according to claim 1, wherein said first and second means are different from each other.
Alternatively, in claim 4, Fe, Co, Ni, Ru, Rh, Pd, and
A method for manufacturing a semiconductor, which comprises using one or more kinds of elements selected from Os, Ir, Pt, Cu, and Au. 7. A step of holding a catalytic element that promotes crystallization of the amorphous silicon film in contact with an upper surface or a lower surface of the amorphous silicon film, and crystallizing the amorphous silicon film by heat treatment. And a step of converting the amorphous silicon film to have a density of 0.9 times or more that of single crystal silicon. 8. The method of forming an amorphous silicon film according to claim 7, wherein the low pressure thermal CVD method, the plasma CVD method, and the photo CVD method are used.
A method for manufacturing a semiconductor, which is any one of a method, a vapor deposition method, and a sputtering method. 9. A step of holding a catalytic element that promotes crystallization of the amorphous silicon film in contact with the upper surface or the lower surface of the amorphous silicon film, and crystallizing the amorphous silicon film by heat treatment. And a step of converting the amorphous silicon film into a film. The amorphous silicon film is a film formed by a low pressure thermal CVD method. 10. A step of holding a catalytic element in contact with a lower surface of the amorphous silicon film to promote crystallization of the amorphous silicon film, and crystallizing the amorphous silicon film by heat treatment. A semiconductor manufacturing method comprising: a step of: forming the amorphous silicon film by a low pressure thermal CVD method. 11. A step of selectively holding a catalytic element that promotes crystallization of the amorphous silicon film in contact with a part of the amorphous silicon film, and heat-treating the amorphous silicon film. And a step of crystallizing from a region in contact with the catalyst element according to the above method, wherein the amorphous silicon film has a density of 0.9 times or more that of single crystal silicon. A method for manufacturing a semiconductor. 12. A method of manufacturing a semiconductor device comprising: a crystalline silicon film obtained by crystallizing an amorphous silicon film; and a gate insulating film arranged in contact with the crystalline film. And a metal element that promotes crystallization of silicon is held in contact with the surface of the amorphous silicon film opposite to the side where the gate insulating film is formed; And a step of crystallizing the silicon film. 13. The method for manufacturing a semiconductor device according to claim 12, wherein the density of the amorphous silicon film is 0.9 times or more that of single crystal silicon.