JP3573969B2 - Semiconductor device manufacturing method - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a semiconductor device using a semiconductor having crystallinity and a manufacturing method thereof.
[0002]
[Prior art]
2. Description of the Related Art A thin film transistor (hereinafter, referred to as a TFT) using a thin film semiconductor is known. This TFT is formed by forming a thin film semiconductor on a substrate and using this thin film semiconductor. 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 as a driver element formed in a peripheral circuit portion. ing.
[0003]
Although it is convenient to use an amorphous silicon film as a thin film semiconductor used for a TFT, there is a problem that its electrical characteristics are low. In order to obtain an improvement in TFT characteristics, a silicon thin film having crystallinity may be used. The crystalline silicon film 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 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 10 hours or more, and has a problem that it is difficult to use a glass substrate as a substrate. For example, Corning 7059 glass, which is generally used for an active type liquid crystal display device, has a glass strain point of 593 ° C., and there is an industrial problem in that heating at 600 ° C. or more is considered in view of an increase in substrate area.
The crystallization method using a laser is an excellent method in which a short pulse laser such as an excimer laser can be used to almost completely ignore distortion due to heat of a glass substrate. , And a strong sense of next-generation technology. One of the causes of this variation is lack of stability of the laser beam, and this is thought to be gradually resolved in the future. However, an even greater factor is the temperature distribution of the laser beam irradiated portion.
This will be further described.
[0005]
[Background of the Invention]
The present inventors have studied two methods, a method for promoting thermal crystallization and a method for reducing variations in laser crystallization, in order to solve the problems accompanying the crystallization of amorphous silicon as described above. went.
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, whereby crystallization can be performed at 550 ° C. for about 4 hours. Make sure that.
[0006]
In order to introduce such a small amount of an element (a catalytic element that promotes crystallization), plasma treatment, vapor deposition, or ion implantation may be used. Plasma treatment refers to the use of a material containing a catalytic 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 catalytic element on an amorphous silicon film. Is a method of performing addition.
[0007]
However, the presence of a large amount of such elements in a semiconductor impairs the reliability and electrical stability of a device using such a semiconductor, and is not preferable.
[0008]
In other words, the above-described elements that promote crystallization such as nickel (in the present specification, the element that promotes crystallization is referred to as a catalyst element) are necessary when crystallizing amorphous silicon, It is desirable that the silicon should not be contained as much as possible. In order to achieve this object, select a catalyst element that has a strong tendency to be inert in crystalline silicon, and at the same time minimize the amount of the catalyst element required for crystallization, and perform crystallization with the minimum amount. I need to do it. For that purpose, it is necessary to precisely control and introduce the amount of the catalyst element.
[0009]
When nickel was used as a catalyst element, an amorphous silicon film was formed, nickel was added by a plasma treatment method to produce a crystalline silicon film, and the crystallization process and the like were examined in detail. The matter turned out.
(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 of 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 during low-temperature crystallization. It is concluded that it is necessary for nickel to be dispersed as finely as possible. That is, it is concluded that "what is necessary is to disperse and introduce as low an atomic concentration of nickel as possible in the vicinity of the surface of the amorphous silicon film in a range where low-temperature crystallization is possible".
[0011]
As a method of introducing a trace amount of nickel only near the surface of the amorphous silicon film, in other words, as a method of introducing a trace amount of a catalyst element that promotes crystallization only near the surface of the amorphous silicon film, a vapor deposition method is used. However, the vapor deposition method has a problem that controllability is poor and it is difficult to strictly control the introduction amount of the catalyst element.
[0012]
In addition, it is necessary that the amount of the catalyst element introduced be 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.
[0013]
Next, as for the variation in characteristics during laser crystallization, as a result of the investigation, two main causes are the difference in crystallinity due to the temperature distribution in the laser irradiation part and the accidental nucleation. And came to the recognition. The reason for this will be described in further detail. Generally, the intensity distribution of the laser beam 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 via 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 are not always present, and crystallization is expected to occur explosively when the supercooled liquid comes into contact with 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.
[0014]
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 and the portion where the crystal nucleus exists coincide. For this purpose, the inventors have tried to introduce a crystal nucleus controlled in advance before laser crystallization, and then to perform laser crystallization. As a result, when a crystal nucleus has a higher transmittance of laser light than amorphous silicon and a material 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, particularly as a material capable of epitaxial growth, fine crystal grains of crystalline silicon or after adding a nickel catalyst to amorphous silicon It has been found that nickel silicide or the like obtained by heating is particularly desirable.
[0015]
And, where the crystal nuclei are introduced, the crystal 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, and the irradiation direction of the laser beam. Irradiation from the interface side where the crystal nuclei were introduced, it was found that a crystalline silicon film with the best characteristics could be obtained. 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]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for forming a favorable crystalline silicon film on glass. It is still another object of the present invention to provide a method for obtaining a material having both the same stability as that using the solid phase growth method and the same high crystallinity as that using laser crystallization.
[0017]
[Means for Solving the Problems]
The present invention
Forming an amorphous silicon film;
Introducing a crystal nucleus into the amorphous silicon film;
Obtaining a crystalline silicon film by growing crystals from the crystal nuclei;
Having a basic configuration.
[0018]
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 energy is supplied by heating or light irradiation (irradiation of infrared rays). It is done by doing.
[0019]
Then, in order to perform crystal growth from this crystal nucleus, it is sufficient to irradiate a laser beam with strong light from the side where the crystal nucleus is formed.
[0020]
The present invention holds a simple catalytic element represented by nickel or a compound containing the catalytic element in contact with the amorphous silicon film and promotes the crystallization of the amorphous silicon film. In a state where the catalyst element alone or the compound containing the catalyst element is in contact with the glass substrate, heat treatment is performed at a low temperature that does not affect the glass substrate, and the amorphous silicon film is partially crystallized to form crystal nuclei. This is the first feature. Then, a crystal having good crystallinity is obtained by performing pseudo-epitaxial crystal growth with crystal nuclei of previously formed fine crystalline silicon by irradiating laser light or strong light for crystallization. A second feature is to obtain a conductive silicon thin film.
[0021]
As a method for introducing a catalytic element that promotes crystallization, a method in which a solution containing the catalytic element is applied to the surface of the amorphous silicon film is useful.
[0022]
Particularly, 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.
[0023]
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 on 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. Just fine.
[0024]
In a semiconductor device using the present invention, it is effective to form an active region having at least one PN, PI, NI, or other electrical junction using a crystallized silicon semiconductor film. As the semiconductor device, a thin film transistor (TFT), a diode, or an optical sensor can be used.
[0025]
By adopting the configuration of the present invention, the following basic significance can be obtained.
(A) The concentration of the catalytic 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.
[0026]
As a method for 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.
[0027]
As the solvent containing the catalyst element, a solvent selected from polar solvents such as water, alcohol, acid, and ammonia can be used.
[0028]
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.
[0029]
As the solvent containing the catalyst element, a non-polar solvent selected from benzene, toluene, xylene, carbon tetrachloride, chloroform, and ether can be used.
[0030]
In this case, nickel is introduced as a nickel compound. As the nickel compound, a compound selected from nickel acetylacetonate and nickel 2-ethylhexanoate can be typically used.
[0031]
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.
[0032]
When using nickel alone as a catalyst element, it is necessary to dissolve it in an acid to make a solution.
[0033]
Although the above is an example of using a solution in which nickel as a catalyst element is completely dissolved, even if nickel is not completely dissolved, powder composed of nickel alone or a nickel compound is uniformly dispersed in a dispersion medium. Materials such as dispersed emulsions may be used. Alternatively, a solution for forming an oxide film may be used. As such a solution, OCD (Ohka Diffusion Source) of Tokyo Ohka Kogyo Co., Ltd. can be used. When this OCD solution is used, 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.
[0034]
The same applies to the case where a material other than nickel is used as the catalyst element.
[0035]
When nickel is used as a catalyst element that promotes 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 is repelled. Sometimes. 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.
[0036]
In addition, by using a nonpolar 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.
[0037]
The amount of the catalyst element contained in the solution depends on the type of the solution, but as a general tendency, the amount of nickel is desirably 200 ppm to 1 ppm, preferably 50 ppm to 1 ppm (in terms of weight) based on the solution. . This is a value determined in view of the nickel concentration in the film after crystallization is completed.
[0038]
After performing a heat treatment on the amorphous silicon film to which the catalytic element is added to form a crystal nucleus, laser light irradiation is performed to uniformly crystallize the entire amorphous silicon film into a crystalline silicon film. be able to.
In the laser crystallization process, a very specific phenomenon has been observed. In the case where no crystal nucleus is introduced, the same level of crystallization can be achieved with a considerably small laser power as compared with the laser power required for performing the entire crystallization. Generally, a higher laser power is required to crystallize a microcrystallized amorphous film than to crystallize a film that does not contain a crystalline component. (Because the power is small), it is the opposite trend, which is one of the great advantages of the present invention.
Here, by adjusting the introduction amount of the catalyst element, 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.
[0039]
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, the silicon thin film formed on a glass substrate can be selectively heated, which is useful. This method using infrared light is called rapid thermal annealing (RTA) or rapid thermal process (RTP).
[0040]
In the present invention, the most remarkable effect can be obtained when nickel is used as the catalyst element. However, other usable catalyst elements are preferably Ni, Pt, Cu, Ag, Au, In, Sn, and Sn. , Pd, P, As, and Sb. In addition, one or more elements selected from Group VIII elements, IIIb, IVb, and Vb elements can also be used.
[0041]
In addition, the method for introducing the catalytic element is not limited to the use of an aqueous solution or a solution such as alcohol, and a substance containing the catalytic element can be widely used. For example, a metal compound or oxide containing a catalyst element can be used.
[0042]
【Example】
[Example 1]
This embodiment is an example in which a catalyst element that promotes crystallization is contained in an aqueous solution, applied to an amorphous silicon film, then crystallized by heating, and furthermore, the crystallinity is increased by laser light irradiation. .
[0043]
With reference to FIG. 1, the process up to the point where a catalytic element (here, nickel is used) is introduced will be described. In this embodiment, Corning 7059 glass is used as the substrate. The size is 100 mm × 100 mm.
[0044]
First, an amorphous silicon film is formed by a plasma CVD method or an LPCVD method to form an amorphous silicon film at 100 to 1500 degrees. Here, the amorphous silicon film 12 is formed to a thickness of 1000 ° by a plasma CVD method. (Fig. 1 (A))
[0045]
Then, a hydrofluoric acid treatment is performed to remove dirt and a natural oxide film, and then an oxide film 13 is formed to a thickness of 10 to 50 °. If the contamination can be ignored, a natural oxide film may be used as it is instead of the oxide film 13.
[0046]
The exact thickness of the oxide film 13 is unknown because it is extremely thin, but it is considered to be about 20 °. Here, the oxide film 13 is formed by irradiation with UV light in an oxygen atmosphere. The film was formed by irradiating UV in an oxygen atmosphere for 5 minutes. As a method of forming the oxide film 13, a thermal oxidation method may be used. Further, the treatment may be carried out with hydrogen peroxide.
[0047]
The oxide film 13 is used to spread the acetate solution over the entire surface of the amorphous silicon film in the subsequent step of applying an acetate solution containing nickel, that is, to improve wettability. For example, when an acetate solution is directly applied to the surface of an amorphous silicon film, nickel cannot be introduced to the entire surface of the amorphous silicon film because the amorphous silicon repels the acetate solution. That is, uniform crystallization cannot be performed.
[0048]
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. Then, spin drying (2000 rpm, 60 seconds) is performed using a spinner. (Fig. 1 (C), (D))
[0049]
If the concentration of nickel in the acetic acid solution is 1 ppm or more, preferably 10 ppm or more, it is practical. When a nonpolar solvent such as a toluene solution of nickel 2-ethylhexanoate is used as the solution, the oxide film 13 is unnecessary, and the catalyst element can be directly introduced onto the amorphous silicon film.
[0050]
This nickel solution application step is performed once to plural times to form a layer containing nickel having an average film thickness of several to several hundreds on the surface of the amorphous silicon film 12 after spin drying. be able to. 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.
[0051]
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 control factor is the concentration of the solution.
[0052]
Then, in a heating furnace, heat treatment is performed at 550 ° C. for one hour in a nitrogen atmosphere. As a result, a partially crystalline silicon thin film 12 formed on the substrate 11 can be obtained. That is, crystal nuclei can be introduced in this step. FIG. 2A schematically shows this state. FIG. 2A shows a state in which crystal nuclei 21 formed by the introduction of nickel are formed on the surface of amorphous silicon film 12 formed on glass substrate 11.
[0053]
The above 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 the glass substrate used as the substrate will surface.
[0054]
In the present 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, the catalyst element may be introduced onto the base film using a solution containing the catalyst element before the formation of the amorphous silicon film.
[0055]
After the silicon film 12 having partial crystallinity is obtained by the heat treatment, a KrF excimer laser (wavelength: 248 nm, pulse width: 30 nsec) is irradiated with a few shots at a power density of 200 to 350 mJ / cm ^{2 in} a nitrogen atmosphere to obtain silicon. The film 12 is completely crystallized. This step may be performed by the above-described 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 catalytic element is introduced and the crystal nuclei are formed. FIGS. 2A and 2B show a state in which the crystal growth is performed as indicated by 22 from the crystal nucleus indicated by 21 by irradiating the laser light 20. 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 crystal nuclei are formed on the surface of the amorphous silicon film formed on the glass substrate by introducing nickel, and the crystal nuclei have grown 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.
[0056]
[Example 2]
This embodiment is different from the first embodiment in that the concentration of the nickel salt as the catalyst element is 10 ppm. All other processing is 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 increased as compared with the case of Example 1 by reducing the solution concentration as in this case.
[0057]
[Example 3]
This embodiment is an example in which a TFT is obtained by using a crystalline silicon film manufactured 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 goes without saying that TFTs can be applied not only to liquid crystal display devices but also to thin film integrated circuits generally referred to as TFTs.
[0058]
In this embodiment, a TFT is manufactured using a technique in which a crystal nucleus is introduced into the surface side of an amorphous silicon film, and then a laser beam is irradiated from the side where the crystal nucleus is introduced to obtain a crystalline silicon film. About the method. 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 extremely small as compared with the case where crystallization is performed by laser light alone. are 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 less laser light and is less likely to be 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 such as carrier scattering in the TFT, it is extremely useful to adopt the configuration as in this embodiment.
[0059]
FIG. 3 shows an outline of the manufacturing process of this embodiment. First, an underlying silicon oxide film (not shown) is formed to a thickness of 2000 mm on a glass substrate. This silicon oxide film is provided to prevent diffusion of impurities from the glass substrate.
[0060]
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 formed to a thickness of about 20 ° 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.
[0061]
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.
[0062]
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. By this step, crystal growth is performed with the crystal nuclei existing in the crystal components as nuclei.
[0063]
Next, an island-shaped region 104 is formed by patterning the crystallized silicon film. This island-shaped region 104 forms an active layer of the TFT. Then, silicon oxide 105 having a thickness of 200 to 1500 °, here 1000 °, is formed. This silicon oxide film also functions as a gate insulating film. (FIG. 3 (A))
[0064]
Care must be taken in manufacturing the silicon oxide film 105. Here, TEOS was used as a raw material, and was decomposed and deposited by RF plasma CVD at a substrate temperature of 150 to 600 ° C., preferably 300 to 450 ° C. together with oxygen. The pressure ratio between TEOS and oxygen was 1: 1 to 1: 3, the pressure was 0.05 to 0.5 torr, and the RF power was 100 to 250 W. Alternatively, the substrate was formed at a substrate temperature of 350 to 600 ° C., preferably 400 to 550 ° C., using TEOS as a raw material by a low pressure CVD method or a normal pressure CVD method together with an ozone gas. After the film formation, annealing was performed at 400 to 600 ° C. for 30 to 60 minutes in an atmosphere of oxygen or ozone.
[0065]
By irradiating a KrF excimer laser (wavelength: 248 nm, pulse width: 20 nsec) or intense light equivalent thereto in this state, crystallization of the silicon region 104 may even be promoted. In particular, RTA (rapid thermal annealing) using infrared light 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. Since it can be reduced, it is useful in manufacturing an insulating gate type field effect semiconductor device.
[0066]
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 immersed in an ethylene glycol solution of tartaric acid having a pH of about 7 and 1 to 3%, and anodic oxidation is performed 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 1500-3500 °, for example, 2000 ° is formed. (FIG. 3 (B))
[0067]
Thereafter, impurities (phosphorus) were implanted in an island-like silicon film of each TFT in a self-aligned manner 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 is 1-4 × 10 ¹⁵ cm ⁻² .
[0068]
Further, as shown in FIG. 3C, irradiation with a KrF excimer laser (wavelength: 248 nm, pulse width: 20 nsec) improves 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 / □.
[0069]
In this step, a so-called RTA (Rapid Thermal Annealing) (RTP) method is used in which a flash lamp is used to quickly raise the temperature to 1000 to 1200 ° C. (temperature of a silicon monitor) and heat the sample instead of using a laser beam. , A rapid thermal process) or the like.
[0070]
Thereafter, a silicon oxide film having a thickness of 3000 .ANG. Is formed as an interlayer insulator 110 on the entire surface by using TEOS as a raw material and plasma CVD with oxygen, reduced pressure CVD with ozone, or normal pressure CVD. The substrate temperature is 250 to 450 ° C., for example, 350 ° C. After the film formation, the silicon oxide film is mechanically polished in order to obtain a flat surface. (FIG. 3 (D))
[0071]
Then, the interlayer insulator 110 is etched to form contact holes in the source / drain of the TFT as shown in FIG. 1E, and wirings 112 and 113 of chromium or titanium nitride are formed.
[0072]
Conventionally, a crystalline silicon film into which nickel is introduced by using a plasma treatment has a low selectivity to buffered hydrofluoric acid as compared with a silicon oxide film, and thus is often etched in the step of forming the contact hole. .
[0073]
However, when nickel is introduced using an aqueous solution at a low concentration of 10 ppm as in this embodiment, the contact hole can be formed stably with good reproducibility because of its high hydrofluoric acid resistance.
[0074]
Finally, annealing in hydrogen at 300 to 400 ° C. for 0.1 to 2 hours completes the hydrogenation of silicon. 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 type liquid crystal display device. This TFT has a source / drain region 108/109 and a channel forming region 114. Reference numeral 115 denotes an NI electrical junction.
[0075]
When the configuration of the present 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 ¹⁸ atoms cm ^−. It is considered to be ³ .
[0076]
The TFT manufactured in this embodiment has an N-channel mobility of 200 cm ² / Vs or more. It has also been confirmed that _Vth is small and has good characteristics. Further, it has been confirmed that the variation in the mobility is also within ± 10%. This small variation is considered to be due to the fact that crystal nuclei were uniformly introduced by heat treatment and then crystallized by irradiating 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.
[0077]
[Example 4]
In this embodiment, a crystal nucleus is introduced under the amorphous silicon film (on the side in contact with the substrate), and then a laser beam is irradiated from the lower surface of the substrate to form an amorphous silicon film formed on the substrate. This is an example of manufacturing a TFT by employing a method of crystallizing a TFT.
[0078]
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, a KrF excimer laser is used as a laser beam, and thus a quartz glass substrate that transmits a KrF excimer laser (wavelength: 353 nm) is used as the substrate. When a XeF excimer laser (wavelength 353 nm) or a laser having a longer wavelength is used as the laser, a glass substrate (Corning 7059) can be used.
[0079]
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 formed to a thickness of about 20 ° 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.
[0080]
Then, an acetate solution containing 10 ppm of nickel is applied, held for 5 minutes, and spin-dried using a spinner. Thereafter, an amorphous silicon film is formed to a thickness of 500 ° by a plasma CVD method. The amorphous silicon film may be formed by a low pressure thermal CVD method.
[0081]
Next, the silicon film is partially crystallized by heating at 550 ° C. for one hour. 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.
[0082]
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. By this step, crystal growth is performed with the crystal nuclei existing in the crystal components as nuclei.
[0083]
After obtaining a silicon film having crystallinity in this manner, the TFT shown in FIG. 3 is completed through the same steps as in the third embodiment. The TFT obtained in this example had the same characteristics as the TFT manufactured by the method shown in Example 3.
[0084]
(Comparative example)
This comparative example is an example in which, in the configuration shown in the fourth embodiment, the irradiation direction of the laser beam is from the upper surface side (front surface side) of the amorphous silicon film having the crystal nuclei introduced into the lower surface. In this case, almost no effect of the step of introducing crystal nuclei was 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.
[0085]
[Example 5]
This embodiment is an example in which, in the step of introducing crystal nuclei using a catalytic element, the generation of crystal nuclei is performed not by heating but by intense light irradiation. 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.
[0086]
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 in the process shown in Embodiment 1.
[0087]
Then, 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 of the monitor on the single crystal silicon wafer 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 this 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 the heating of the glass substrate can be minimized.
[0088]
Through this step, crystal nuclei can be generated on the surface of the amorphous silicon film. The subsequent steps are the same as in the third embodiment. 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 side of the amorphous silicon film which is in contact with the substrate.
[0089]
[Example 6]
FIG. 4 shows a cross-sectional view of the manufacturing process of this embodiment. First, a 2000-nm-thick silicon oxide base film 502 is formed on a substrate (Corning 7059) 501 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 gradually 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. The Corning 7059 substrate is annealed at 620 to 660 ° C. for 1 to 4 hours, and then gradually cooled 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.
[0090]
Next, an intrinsic (I-type) amorphous silicon film having a thickness of 500 to 1500 Å, for example, 1000 例 え ば is formed by a plasma CVD method. Then, nickel is introduced as a catalytic element for promoting crystallization to the surface of the amorphous silicon film 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, a KrF excimer laser is irradiated for crystallization. Then, the silicon film is patterned into a size of 10 to 1000 μm square to form an island-shaped silicon film (TFT active layer) 503. (FIG. 4A)
[0091]
Thereafter, an oxygen atmosphere containing 70 to 90% water vapor at 1 atm, 500 to 750 ° C., typically 600 ° C. is formed using a pyrogenic reaction method in a ratio of hydrogen / oxygen = 1.5 to 1.9. I do. In this atmosphere, the surface of the silicon film is oxidized by being left 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 such oxidation reduces the surface of the initial silicon film by 50 ° or more, and as a result, contamination of the outermost surface portion of the silicon film does not reach the silicon-silicon oxide interface. is there. That is, a clean silicon-silicon oxide interface is obtained. Since the thickness of the silicon oxide film is twice the thickness of the silicon film to be oxidized, when the silicon film having a thickness of 1000 mm is oxidized to obtain a silicon oxide film having a thickness of 1000 mm, the thickness of the remaining silicon film is reduced. The thickness is 500 mm.
[0092]
In general, as the silicon oxide film (gate insulating film) and the active layer are thinner, better characteristics such as improved mobility and reduced 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, in which recombination centers are easily present, are easily oxidized, and as a result, recombination centers in the active layer are reduced. This increases the product yield.
[0093]
After the silicon oxide film 504 is formed by thermal oxidation, the substrate is annealed at 600 ° C. for 2 hours in a dinitrogen monoxide atmosphere (1 atm, 100%). (FIG. 4 (B))
Subsequently, polycrystalline silicon (containing 0.01 to 0.2% phosphorus) having a thickness of 3000 to 8000, for example, 6000, is formed by a low pressure CVD method. Then, the gate electrode 505 is formed by patterning the silicon film. Further, using this 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 channel) is self-aligned by an ion doping method (also referred to as a plasma doping method). ) Is added. Used as the doping gas, phosphine (PH _3), the acceleration voltage 60～90KV, eg, 80 kV. The dose is set to 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.
[0094]
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 conditions of the laser beam are such that the energy density is 200 to 400 mJ / cm ² , for example, 250 mJ / cm ^2, and ² to 10 shots, for example, 2 shots are irradiated at one place. The effect may be increased by heating the substrate to about 200 to 450 ° C. at the time of irradiation with the laser light. (FIG. 4 (C))
[0095]
In addition, this step may be a method 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, the glass substrate is hardly absorbed by the 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). Since no heating is required and the treatment is performed in a short time, it can be said that the method is an optimal method in a process in which shrinkage of the glass substrate becomes a problem.
[0096]
Subsequently, a 6000 ° thick silicon oxide film 508 is formed as an interlayer insulator by a plasma CVD method. Polyimide may be used as the interlayer insulator. Further, contact holes are formed, and electrodes / wirings 509 and 510 of the TFT are formed of a metal material, for example, a multilayer film of titanium nitride and aluminum. Finally, annealing is performed at 350 ° C. for 30 minutes in a hydrogen atmosphere at 1 atm to complete the TFT. (FIG. 4 (D))
[0097]
The mobility of the TFT obtained by the method described above was 110 to 150 cm ² / Vs, and the S value was 0.2 to 0.5 V / digit. Further, a P-channel TFT in which the source / drain is doped with boron by the same method was also manufactured. The mobility was 90 to 120 cm ² / Vs, and the S value was 0.4 to 0.6 V / digit. As compared with the case where the gate insulating film was formed by the PVD method or the CVD method, the mobility was higher by 20% or more, and the S value was reduced by 20% or more.
Further, from the viewpoint of reliability, the TFT manufactured in this example showed a good result that is comparable to that of the TFT manufactured by high-temperature thermal oxidation at 1000 ° C.
[0098]
[Example 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.
[0099]
Here, the input port is a memory peculiar to the panel for reading an externally input signal, converting the signal into an image signal, and correcting an input signal or the like in accordance with the characteristics of the active matrix panel. is there. In particular, this correction memory is used to finance information unique to each pixel as a non-volatile memory and to individually correct the information. That is, when a pixel of the electro-optical device has a point defect, a signal corrected in accordance with the defect is sent to pixels around the point to cover the point defect and make the defect inconspicuous. Alternatively, when a pixel is darker than the surrounding pixels, a larger signal is sent to the pixel so that the brightness is the same as that of the surrounding pixels. In each pixel, a liquid crystal 73, a capacitor 72, and a TFT 71 are arranged.
[0100]
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】
Crystalline nuclei are generated on the surface side of the amorphous silicon film by introducing a catalytic element, and thereafter, the crystalline silicon film having good crystallinity is irradiated with laser light or strong light on the surface side on which the crystal nuclei are introduced. Can be obtained.
[Brief description of the drawings]
FIG. 1 shows the steps of an example. FIG. 2 shows the steps of an example.
FIG. 3 shows a manufacturing process of the example.
FIG. 4 shows a manufacturing process of an example.
FIG. 5 shows a manufacturing process of the 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 ( Silicon oxide film)
112 ... electrode 113 ... electrode

Claims (5)

Forming an amorphous silicon film on a substrate having an insulating surface,
After heating the amorphous silicon film to form a crystal nucleus on a part of the upper surface of the amorphous silicon film and in the vicinity thereof, laser light or strong light is applied from the upper surface side of the amorphous silicon film. In a method for manufacturing a semiconductor device, which irradiates the amorphous silicon film to crystallize,
Prior to heating the amorphous silicon film, using a solution containing an element which promotes crystallization, characterized in that to hold the element for promoting the crystallization on the amorphous silicon film A method for manufacturing a semiconductor device. 2. The method according to claim 1, wherein the element that promotes crystallization is nickel. 2. The method according to claim 1, wherein the element that promotes crystallization is Pt, Cu, Ag, Au, In, Sn, or Pd. 4. The method according to claim 1, wherein a concentration of the element promoting the crystallization in the crystallized silicon film is 1 × 10 ¹⁶ atoms cm ^{−3 to} 3 × 10 ¹⁸ atoms cm ^−3. A method for manufacturing a semiconductor device, comprising: The method according to claim 1, wherein the crystallized silicon film is patterned to form an island region, a gate insulating film is formed on the island region, and a gate insulating film is formed on the gate insulating film. A method for manufacturing a semiconductor device, comprising: forming a gate electrode; forming an interlayer insulating film on the gate electrode; etching the interlayer insulating film to form a contact hole; and forming a wiring.

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