JP2004134577A - Manufacturing method of semiconductor thin film, tft, semiconductor device, thin film solar cell and composite semiconductor device, photoelectric device and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a semiconductor thin film, a thin film transistor and a solar cell which release a technique for forming a large grain size poly-Si film on a large area with a high throughput through a cryogenic temperature process, while retaining an inexpensive radiation source and realize the improvement of characteristics of a poly-Si TFT (thin film transistor) and a circuit as well as the reduction of varieties, and a photoelectric device as well as an electronic device at a low cost employing the manufacturing method. <P>SOLUTION: The manufacturing method of the semiconductor thin film 302 comprises at least a process for forming a semiconductor layer 302 on a substrate, a process for opposing a semiconductor light emitting device to the substrate and applying heat treatment on the semiconductor layer by moving the same relative to the substrate while irradiating light generated from the light emitting device against the semiconductor layer, a process for forming at least a first insulating layer 303 and a light absorbing layer 304 on the semiconductor layer formed on the substrate, and a process for opposing the light emitting device to the substrate and applying heat treatment on the semiconductor layer by moving the light absorbing layer relative to the substrate while irradiating light generated from the light emitting device against the light absorbing layer. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor thin film formed on a substrate such as a single crystal semiconductor substrate, an insulator or a metal substrate, a thin film transistor, and a logic circuit, a memory circuit, a liquid crystal device or an organic electroluminescence (EL) device formed by the thin film transistor. Method for manufacturing thin film transistor and solar cell used as a component of drive circuit such as display pixel or display device, method for manufacturing composite semiconductor device in which thin film transistor and thin film solar cell are mixed, and electro-optical device and electronic device manufactured using these Equipment related.
[0002]
[Prior art]
Conventionally, semiconductor thin films such as polycrystalline silicon (poly-Si) have been widely used for thin film transistors (TFTs) and solar cells. In particular, poly-Si TFTs have a higher carrier mobility than amorphous silicon TFTs and can be manufactured on a transparent insulating substrate such as a glass substrate, so that switching for liquid crystal display devices, liquid crystal projectors and organic EL display devices can be achieved. It is widely used as an element or a circuit element of a driver for driving a liquid crystal or an organic EL.
[0003]
Among poly-Si TFT manufacturing processes, a process of manufacturing a TFT on a relatively inexpensive heat-resistant glass substrate in a temperature environment having a maximum temperature of approximately 600 ° C. or less is generally called a low-temperature process. In a low-temperature process, a pulse laser crystallization technique for crystallizing a silicon film using a pulse laser having an extremely short oscillation time is widely used. Pulsed laser crystallization is a technique that utilizes the property of instantaneously melting a silicon thin film on a substrate by irradiating it with a high-powered pulsed laser beam and then crystallizing the solidified process. Recently, a technique for producing a large-area poly-Si film by scanning while repeatedly irradiating an amorphous silicon film on a glass substrate with an excimer laser beam has been widely used. As a gate insulating layer, silicon dioxide (SiO 2) is formed by a film forming method using plasma CVD.₂) A film can be formed on a large area substrate. With these techniques, a poly-Si TFT can now be manufactured on a large glass substrate having a side of about several tens of centimeters.
[0004]
However, a problem with this low-temperature process is that when a semiconductor layer (poly-Si film) to be an active layer is formed by pulse laser crystallization, the crystal grain size is as small as 0.5 μm at most, so that the poly- High threshold voltage of TFT manufactured using Si film and mobility of 100 to 200 cm²V^-1s^-1Degree and 600cm of single crystal Si field effect transistor (MOSFET)²V^-1s^-1It is low compared to. In addition, the excimer laser crystallization method has a problem that irregularities having a height equivalent to 30 to 40% of the film thickness are generated on the surface of the crystallized poly-Si film. This occurs at crystal grain boundaries where crystals grown from crystal growth nuclei collide with each other. At the protruding portion, the thickness of the gate insulating film is effectively reduced, so that dielectric breakdown occurs. This has been a major problem particularly in a TFT having a thin gate insulating film. In addition, since the excimer laser widely used in the laser crystallization process is a gas laser, there is a problem that energy stability between pulses is low, and it is difficult to reduce variation in TFT elements. Furthermore, excimer lasers have a problem that the unit cost of the excimer laser is high, the running cost by replacing the laser tube (oscillator) is high, and the throughput is low, so that the manufacturing cost of the product cannot be reduced.
[0005]
As means for solving the above problems, there are the following conventional technologies.
[0006]
As a first conventional technique, there is a technique of irradiating a beam spot of a continuous wave laser beam onto an amorphous semiconductor thin film while scanning the amorphous semiconductor thin film to melt-crystallize the amorphous semiconductor thin film into a silicon thin film (for example, see Patent Document 1). 1 and Non-Patent Document 1). Here, for example, a laser beam spot having a wavelength of 532 nm (the second harmonic of YAG) and a width of 20 μm × 400 μm is irradiated on the amorphous semiconductor thin film while scanning, and the scanning speed is set to 5 to 80 cm / s, thereby processing several tens μm. A technique for forming a large-sized poly-Si film having a large size is disclosed. In addition, the surface of the semiconductor thin film formed by such a technique has an extremely flat shape.
[0007]
As a second conventional technique, a semiconductor layer, an insulating film layer, and a light absorbing layer are formed on an insulator, and the semiconductor layer is crystallized by irradiating the semiconductor layer with an energy ray, a laser beam, or a lamp beam. Techniques are disclosed (for example, see Patent Documents 2 to 7). Here, for example, by using lamp light, the price and running cost of the manufacturing apparatus can be reduced, so that the manufacturing cost of the product can be reduced.
[0008]
The use of the above-described technique makes it possible to form a poly-Si film having a crystal grain size of 1 μm or more and a flat surface at a low cost even on an insulating substrate. It is possible to dramatically reduce the crystal grain boundaries inside, thereby improving the performance of the TFT and reducing the manufacturing cost.
[Patent Document 1]
JP-A-8-97141
[Patent Document 2]
JP-A-57-113217
[Patent Document 3]
JP-A-59-158515
[Patent Document 4]
JP-A-59-205712
[Patent Document 5]
JP-A-4-332120
[Patent Document 6]
JP-A-6-291034
[Patent Document 7]
JP-A-8-51076
[Non-patent document 1]
Hara, 7 others, Japanese Journal of Applied Physics, March 2002, Volume 41, pages L311-L313
[0009]
[Problems to be solved by the invention]
However, the above prior art has the following problems. First, in the first conventional technique, a continuous oscillation laser beam is directly absorbed by a Si film and melt crystallization is performed by generated heat. Therefore, it is necessary to use a laser beam having a wavelength that can be efficiently absorbed by the Si film, and it is essential that the Si film thickness is approximately equal to the absorption length of the laser beam. For this reason, the laser light source that can be used at present has a wavelength shorter than about 600 nm. In the conventional technology, an Ar laser (488 nm or 514.5 nm) and a YAG harmonic (532 nm) are used, and the Si film thickness is about 50 to 100 nm. Limited to. Since the usable wavelength is limited, the process throughput of the crystallization process is simply determined by the output of the laser light source. For example, in the case of a YAG harmonic laser, the output of one unit at present is about 20 W at the maximum, which is about 1/10 of the excimer laser widely used at present. Since the price of the laser device is high, if the process throughput is increased by using a plurality of such lasers, the price of the device increases. For the above reasons, it takes a very long time to process one substrate (the throughput of the process is low), and there is a problem that the product cost cannot be reduced. Further, since the thickness of the irradiated Si film is limited, for example, a Si film thinner than 50 nm cannot be crystallized, and a Si film thicker than 100 nm cannot be crystallized. Therefore, the application range of the poly-Si film formed by the conventional technique is limited. Specifically, since a Si film thinner than 15 nm cannot be used for the active layer, a TFT having a mobility higher than the universal mobility cannot be manufactured due to a quantum effect. Further, since a poly-Si film thicker than 100 nm cannot be formed, it cannot be applied to a solar cell. There is a problem of limiting the application range as described above. In addition, since the region where the large-grain poly-Si film is formed is determined only by the accuracy of the irradiation position of the laser beam, the desired crystal can be accurately formed by aiming at the formation position of the TFT element arranged with an accuracy of μm or less. There is no position controllability for growth, and as a result, there is a problem that variations in TFT characteristics cannot be reduced.
[0010]
Next, the second problem of the prior art will be described. In the second prior art, there is little restriction on the wavelength and type of light (or energy beam) to be irradiated in order to absorb light energy by the light absorbing layer. In addition, there are few restrictions on the thickness of the semiconductor layer. However, although a lamp light source that can obtain the highest output is effective to increase the throughput of the process, it is more difficult to condense the lamp light using an optical system as compared with laser light. This is because the lamp light is not a single wavelength but a light having a broad wavelength distribution. When light irradiation with insufficient power and low power density is performed, the substrate temperature must be increased in order to increase the temperature of the light absorption layer and the semiconductor layer. At present, a lamp optical system which can collect light most efficiently is, for example, as shown in FIG. Even when such a reflection optical system and a plurality of lamp light sources are used, the power density on the light absorption layer is practically at most 500 W / cm.²Is the limit. In order to raise the temperature of the semiconductor layer (Si) to a temperature equal to or higher than the melting point by using this, a light irradiation time of at least 1 second (600 ms in half width) is required according to the irradiation profile shown in the upper diagram of FIG. The time change of the temperature at each position of the substrate depth is shown in the lower diagram of FIG. As can be seen from this, if the temperature of the light absorbing layer is raised above the melting point of Si, the substrate temperature naturally rises to near 1200 K. Therefore, low-heat-resistant low-cost substrates made of non-alkali glass or plastic are not used at all. I can't get it. That is, the second conventional technique has a problem that it is extremely difficult to apply it to a low-temperature process unless the optimum absorbing layer material and light source can be defined.
[0011]
As described above, each of the conventional techniques has several problems. The main cause of these problems is that the optimal combination of the structure of the object to be heated and the heating light source has not been clarified. As a result, it has not been possible to form a large grain size poly-Si film on an inexpensive glass substrate by a low-temperature process and with high throughput. In addition to these conditions, it was impossible to control the crystal growth position.
[0012]
In view of the above problems, the present invention discloses a technique for forming a large-grain poly-Si film in a large area with a high throughput by using a low-temperature process while using an inexpensive irradiation light source. It is an object of the present invention to provide a method of manufacturing a semiconductor thin film, a thin film transistor, and a solar cell which realizes improvement of characteristics and reduction of variation, and a technique of providing an electro-optical device and an electronic apparatus using the thin film at low cost.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a method of manufacturing a semiconductor thin film according to the present invention includes a step of forming a semiconductor layer on a substrate, a step of causing a semiconductor light emitting element to face the substrate, and transmitting light generated from the semiconductor light emitting element to the semiconductor Heat-treating the semiconductor layer by moving the layer relative to the substrate while irradiating the layer.
[0014]
According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor thin film, comprising: forming at least a first insulating layer and a light absorbing layer on a semiconductor layer formed on a substrate; And heat-treating the semiconductor layer by moving the light-absorbing layer relative to the substrate while irradiating the light-absorbing layer with light generated from the semiconductor light-emitting element. Here, the “semiconductor light emitting element” refers to a semiconductor element that emits light from the semiconductor layer itself. The terms “facing” and “irradiating light to the light absorbing layer” here refer to irradiating the light absorbing layer with light by facing the substrate at least without changing the wavelength of light emitted from the semiconductor light emitting element. For example, it does not include a laser irradiation method such as a conventional example in which wavelength conversion is performed through an optical crystal such as YAG or a harmonic generator to irradiate a light absorption layer with light having a wavelength different from the emission wavelength of a semiconductor light emitting element. . However, when an optical component that does not involve wavelength conversion, such as a lens for adjusting the power density of the irradiation light, is used between the semiconductor light emitting element and the light absorbing layer, the light is applied to the light absorbing layer. ".
[0015]
Preferably, the light absorbing layer is made of any material of Cr, Mo, Ta, Ti, and W, or an alloy or a multilayer structure containing at least one of the materials or two or more of them. Thereby, the irradiation light of the semiconductor light emitting element is efficiently absorbed at a low reflectance, and even when the semiconductor layer is subjected to the heat treatment, the light absorbing layer can be stably processed without ablation, peeling, or cracking.
[0016]
Preferably, the semiconductor light emitting device is a semiconductor laser having an oscillation wavelength between 200 nm and 2000 nm. Here, the “semiconductor laser” refers to a semiconductor light emitting device having an optical resonator structure in addition to a double heterojunction or a quantum well structure, and having a function of performing a laser amplification by an optical confinement effect. If the light is in the wavelength range, the light can be efficiently absorbed by the light absorbing layer. At the same time, since the light is a laser beam, it is necessary to extremely efficiently condense the light on the light absorbing layer using an optical component such as a lens. High irradiation power density can be easily achieved. Here, the semiconductor laser is often called a laser diode, and this is also included in the semiconductor laser.
[0017]
Preferably, in the heat treatment step, the power density of light generated from the semiconductor light emitting element on the light absorption layer is 1800 W / cm.²Above and under the condition that the light irradiation time at an arbitrary point of the irradiation area is 300 ms or less. Thus, even when inexpensive non-alkali glass is used as the substrate, heat treatment of the semiconductor layer can be performed while suppressing the temperature rise of the substrate to about 600 ° C.
[0018]
Preferably, in the heat treatment step, the power density of light generated from the semiconductor light emitting element on the light absorbing layer is 3000 W / cm.²The irradiation is performed under the condition that the light irradiation time at an arbitrary point of the irradiation area is 100 ms or less. This makes it possible to heat-treat the semiconductor layer while suppressing the temperature rise of the substrate to about 300 ° C., so that the thermal load on the substrate is reduced and the glass substrate is more thermally deformed or cracked than under the above processing conditions. Can be solved.
[0019]
More preferably, in the heat treatment step, the power density of light generated from the semiconductor light emitting element on the light absorbing layer is 4500 W / cm.²Above and under the condition that the light irradiation time at an arbitrary point of the irradiation area is 45 ms or less. As a result, the temperature rise of the substrate can be suppressed to about 200 ° C., so that a plastic substrate can be used as a substrate to which the present invention can be applied.
[0020]
More preferably, the distance between the light absorbing layer on the substrate and the semiconductor light emitting element facing the light absorbing layer is 1 μm or more and 30 cm or less. By making the distance between the light source and the light absorbing layer extremely small as described above, it is possible to directly irradiate the light absorbing layer with light at a high power density before the light from the semiconductor light emitting element spreads.
[0021]
More preferably, the method further includes a step of forming a second insulating layer having a thickness of t and a refractive index of n on the light absorbing layer, wherein the second insulating layer has a thickness of t when the emission wavelength of the semiconductor light emitting element is λ. = Nλ / 4n (N = 1, 2, 3,...). This can minimize the reflectance of the light emitted from the semiconductor light emitting element in the light absorbing layer, and at the same time, prevent a decrease in light absorption efficiency due to oxidation of the light absorbing layer during the heat treatment. In particular, when the semiconductor light emitting element is a semiconductor laser, this effect is remarkable, so that efficient injection of laser light into the light absorbing layer becomes possible.
[0022]
Preferably, a plurality of the semiconductor light emitting elements are arranged in a linear or lattice shape. This makes it possible to easily increase the total power of the irradiation light using the semiconductor light emitting element. The term "a plurality of semiconductor light-emitting elements" means that a plurality of semiconductor elements are counted as one semiconductor element with respect to a structure for obtaining light emission by injecting carriers into a double hetero junction or a quantum well structure. That is, a plurality of semiconductor light-emitting elements are arranged on a line (that is, the above-described double heterojunction or quantum well structure) to form a single light-emitting body, or a light-emitting body in which these are stacked to form a single light-emitting body as a stacked structure. Instead of one semiconductor light-emitting element, all are a plurality of semiconductor light-emitting elements. Since conventional laser light has a large laser body and is expensive, it is practically impossible to arrange many light sources in close proximity. However, the semiconductor light emitting device used in the present invention has a light emitting area as small as about 100 μm. It is possible to perform close proximity in units of several mm. As a result, the total power of the light source used for processing can be increased substantially in proportion to the number of semiconductor light emitting devices arranged. Therefore, the method for manufacturing a semiconductor thin film of the present invention can realize a high process throughput.
[0023]
Preferably, the plurality of semiconductor light emitting devices arranged in a linear or lattice shape are prepared in advance in the semiconductor light emitting device manufacturing process by forming the semiconductor light emitting devices on a wafer in a linear or lattice shape at a desired interval. Is used as it is. Since a semiconductor light emitting device is originally formed on a compound semiconductor substrate by using photolithography, the mutual positional accuracy when a plurality of semiconductor light emitting devices are formed becomes the accuracy of photolithography. That is, a plurality of light sources are arranged with much higher precision than when a plurality of light sources are arranged by mechanical processing or a plurality of irradiation spots are formed by dividing a beam with an optical system. Therefore, by irradiating the light absorbing layer with light obtained by directly applying power to the semiconductor light emitting element formed on the wafer, heat treatment of the semiconductor thin film can be performed in regions having extremely regular intervals. This is because if a semiconductor light emitting element is formed in advance in accordance with the pitch of a thin film transistor forming region, only a necessary region can be efficiently heat-treated, so that the throughput of the process can be further increased and, at the same time, a crystal of the same quality can be obtained. Since the growth can be performed at a desired position, when a thin film transistor is formed using the crystalline semiconductor thin film thus manufactured, the variation can be reduced.
[0024]
Preferably, the semiconductor thin film has a region 1 having a thickness of 100 nm or less and a region 2 having a thickness of 200 nm or more on the same substrate. According to the method of manufacturing a semiconductor thin film of the present invention, there is no limitation on the thickness of a semiconductor layer that can be heat-treated, so that elements having different functions are integrated by simultaneously forming semiconductor layers having different thicknesses on a substrate. sell. For example, a thin semiconductor layer region can be used as an active layer of a thin film transistor, and a thick semiconductor layer region can be used as an active layer of a solar cell.
[0025]
The present invention can also be applied to a method for manufacturing a thin film transistor, and uses a semiconductor layer formed by the above-described method for manufacturing a semiconductor thin film as an active layer. Accordingly, a thin film transistor having high mobility and small variation can be formed.
[0026]
Preferably, the thickness of the semiconductor thin film is 15 nm or less. In the present invention, a semiconductor thin film having excellent crystallinity can be provided even if it is as thin as 15 nm or less. Therefore, by using this as an active layer of a thin film transistor, a quantum effect can be obtained, and a thin film transistor with high mobility can be obtained. .
[0027]
The present invention is also applicable to a method for manufacturing a semiconductor device, and uses a semiconductor layer formed by the above-described method for manufacturing a semiconductor thin film as an active layer. Thus, a semiconductor device with high mobility and small variation can be formed.
[0028]
Preferably, the thickness of the semiconductor thin film is 15 nm or less. In the present invention, a semiconductor thin film having excellent crystallinity can be provided even if it is as thin as 15 nm or less. Therefore, by using this as an active layer of a thin film transistor, a quantum effect can be obtained, and a thin film transistor with high mobility can be obtained. . Needless to say, the present invention can be applied to the above-described semiconductor device.
[0029]
The present invention can also be applied to a method for manufacturing a thin-film solar cell, and uses the semiconductor layer subjected to the above-described heat treatment as an active layer. Thus, a semiconductor layer having a long carrier lifetime can be used as an active layer, so that a solar cell with extremely high photoelectric conversion efficiency can be provided.
[0030]
Preferably, the semiconductor thin film has a thickness of 200 nm or more. In the present invention, good crystal growth can be achieved even with a relatively thick semiconductor thin film of 200 nm or more, whereby a solar cell with sufficient power generation output with sufficient absorption of sunlight can be provided.
[0031]
In the composite semiconductor device of the present invention, a thin film transistor is formed in a semiconductor thin film region 1 having a semiconductor layer thickness of 100 nm or less on the same substrate, and a thin film solar cell is formed in a semiconductor thin film region 2 having a semiconductor layer thickness of 200 nm or more. . Since the thin-film semiconductor circuit can be driven by the power obtained from the solar cell, the semiconductor element can be driven under fluorescent light or under external light without external power supply from an electric wiring.
[0032]
The electro-optical device according to the present invention includes the thin film transistor manufactured by the manufacturing method as a driving element of a display pixel and a peripheral driving circuit. Accordingly, an electro-optical device with no display unevenness can be provided because variation in thin film transistors is small. Further, since the peripheral circuits can be driven at a sufficient circuit speed even with a low power supply voltage, the power consumption of the electro-optical device module is extremely low, and the battery can be used for a long time even when used as a display device of a portable information device.
[0033]
Electronic equipment of the present invention includes the electro-optical device. More preferably, it comprises an electro-optical device and a thin-film solar cell. This makes it possible to provide a self-contained electronic device capable of self-charging even when not in use and displaying a screen when necessary.
[0034]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a sectional view showing a semiconductor thin film manufacturing process according to the present invention.
[0035]
(1. Formation of semiconductor layer)
In order to carry out the present invention, a base protective film (301) is usually formed on a substrate (300) and a semiconductor thin film (302) is formed thereon. Therefore, a series of forming methods will be described.
[0036]
Examples of the substrate (300) to which the present invention can be applied include conductive materials such as metals, silicon carbide (SiC), and alumina (Al).₂O₃), A ceramic material such as aluminum nitride (AlN), a transparent or non-transparent insulating material such as fused quartz or glass, a semiconductor material such as a silicon or germanium wafer, and an SOI substrate or an LSI substrate obtained by processing the same. . The semiconductor film is deposited directly on the substrate or via a base protective film, a lower electrode, and the like.
[0037]
As a base protective film (301), a silicon oxide film (SiO_X: 0 <x ≦ 2) or a silicon nitride film (Si₃N_x: 0 <x ≦ 4). When it is important to control impurities in a semiconductor film such as when a thin-film semiconductor device such as a TFT is formed on a normal glass substrate, sodium (Na), potassium (K), etc. contained in the glass substrate are required. It is preferable to deposit the semiconductor film after forming the base protective film so that mobile ions do not enter the semiconductor film. In the case where a conductive material such as a metal material is used as the substrate and the semiconductor film must be electrically insulated from the metal substrate, a base protective film is indispensable to ensure insulation. Further, when a semiconductor film is formed on a semiconductor substrate or an LSI element, an interlayer insulating film between transistors and between wirings is also a base protective film.
[0038]
The undercoat protective film is first washed with an organic solvent such as pure water or alcohol, and then is deposited on the substrate by atmospheric pressure chemical vapor deposition (APCVD), low pressure chemical vapor deposition (LPCVD), or plasma chemical vapor deposition. It is formed by a CVD method such as a deposition method (PECVD method) or a sputtering method. (4) When a silicon oxide film is used as the underlayer protective film, the atmospheric pressure chemical vapor deposition method uses a monosilane (SiH₄) Or oxygen as a raw material. In the plasma chemical vapor deposition method and the sputtering method, the substrate temperature is from room temperature to about 400 ° C. The thickness of the base protective film must be sufficient to prevent diffusion and mixing of the impurity element from the substrate, and the value is at least about 100 nm or more. Considering the variation between lots and substrates, it is preferably about 200 nm or more, and if it is about 300 nm, it can sufficiently function as a protective film. When the underlying protective film also serves as an interlayer insulating film between IC elements and wiring connecting them, the thickness is usually about 400 nm to 600 nm. If the insulating film is too thick, cracks occur due to the stress of the insulating film. Therefore, the maximum thickness is preferably about 2 μm. When it is strongly necessary to consider productivity, the upper limit of the insulating film thickness is about 1 μm.
[0039]
Next, the semiconductor thin film (302) will be described. As a semiconductor film to which the present invention is applied, in addition to a semiconductor film of a group 4 element such as silicon (Si) and germanium (Ge), silicon germanium (Si)_xGe_1-x: 0 <x <1) or silicon carbide (Si_xC_1-x: 0 <x <1) or germanium carbide (Ge_xC_1-x: A semiconductor film of a group 4 element complex such as 0 <x <1), a compound semiconductor film of a group 3 element such as gallium arsenide (GaAs) or indium antimony (InSb) and a group 5 element, or cadmium. -There is a composite compound semiconductor film of a group II element such as selenium (CdSe) and a group VI element. Alternatively, silicon, germanium, gallium, arsenic (Si_xGe_yGa_zAs_z: X + y + z = 1), an N-type semiconductor film in which a donor element such as phosphorus (P), arsenic (As), antimony (Sb) is added to these compound semiconductor films, or boron (B). The present invention is also applicable to a P-type semiconductor film to which an acceptor element such as), aluminum (Al), gallium (Ga), and indium (In) is added. These semiconductor thin films are formed by a CVD method such as an APCVD method, an LPCVD method, or a PECVD method, or a PVD method such as a sputtering method or an evaporation method. In the case where a silicon film is used as a semiconductor film, in the LPCVD method, the substrate temperature is set to about 400 ° C. to about 700 ° C. and disilane (Si₂H₆) Can be deposited as a raw material. In the PECVD method, monosilane (SiH₄) Can be deposited at a substrate temperature of about 100 ° C. to about 500 ° C. When using the sputter method, the substrate temperature is from room temperature to about 400 ° C. The initial state (as-deposited state) of the semiconductor film thus deposited includes various states such as amorphous, mixed crystal, microcrystalline, and polycrystalline. In the present invention, the initial state is any one. It may be in the state. In the specification of the present application, not only amorphous crystallization but also polycrystalline or microcrystalline recrystallization is referred to as crystallization. When the semiconductor film is used for a TFT, the thickness is suitably about 20 nm to about 100 nm.
[0040]
(2. Formation of first insulating layer)
Next, a first insulating layer (303) is formed on the semiconductor layer. The role of this insulating layer is to separate the light absorbing layer (304) and the semiconductor layer (302) formed in the next step. In order to prevent diffusion of impurities from the light absorbing layer to the semiconductor layer in a later heat treatment step, a silicon oxide film (SiO_X: 0 <x ≦ 2) or an insulating material such as a silicon nitride film (Si3 {Nx}: 0 <x ≦ 4). The first insulating layer is formed by etching a natural oxide film on the semiconductor layer with hydrofluoric acid, washing with pure water, and then performing a CVD method such as an APCVD method, an LPCVD method, a PECVD method, or a sputtering method. (4) When a silicon oxide film is used as the insulating layer, the substrate temperature is set to about 250 ° C. to about 450 ° C. in the atmospheric pressure chemical vapor deposition method.₄And oxygen can be deposited as a raw material. In the PECVD method and the sputtering method, the substrate temperature is from room temperature to about 400 ° C. The thickness of the first insulating layer must be large enough to prevent the diffusion and mixing of the impurity element from the light absorbing layer, while the heat insulating layer from the light absorbing layer can efficiently conduct heat to the semiconductor layer. Is a condition. For this reason, there is naturally an optimum range for the thickness of the insulating layer, and its value is at least about 50 nm and at most about 1 μm, which is about the same as the thermal diffusion length.
[0041]
(3. Formation of light absorption layer)
Next, a light absorption layer (304) is formed on the first insulating layer (303). The light absorbing layer has a role of efficiently absorbing the light irradiated in the next step, and raising the temperature of the semiconductor layer to a high temperature by heat generation and heat conduction. Therefore, the relationship between the wavelength region of the irradiated light, the reflectance and the absorption coefficient in that wavelength region, and the heat resistance are important. A refractory metal material is suitable for such a purpose. Since a high concentration of free carriers (electrons) exists in the metal, the components other than the reflection component of the irradiation light are completely absorbed. For this reason, it is important to use a high melting point metal thin film having a low reflectance in order to efficiently absorb light by the metal thin film. FIG. 4 shows reflectance spectra of various refractory metal films. As will be described later, in the present invention, a semiconductor light emitting device which is relatively inexpensive and can provide high output is used as a light source for light irradiation. ing. In discussing the optical characteristics of the material, it is a matter of course that the wavelength should be considered in accordance with the wavelength of the irradiation light to be used. In this specification, a wavelength of 100 nm is used as a representative value. Of course, the same argument holds true for different wavelengths, so that even if wavelengths are taken into consideration, the scope of the present invention is all applicable. As can be seen from FIG. 4, the materials of Ta, Mo, Cr, Ti, and W all have relatively low reflectance, and are suitable for application to the light absorbing layer of the present invention. In addition to such optical properties, the light absorbing layer is required to be a material that does not generate cracks or peel off due to heat treatment. Therefore, it is effective to use the above-mentioned alloy of Ta, Mo, Cr, Ti, and W, or a compound containing at least one metal (for example, silicide), or a laminated structure of these metals and metal alloys.
[0042]
The thickness of the absorbing layer is preferably thinner in order to reduce the tact time in the manufacturing process, but a minimum thickness that can sufficiently absorb the irradiation light is required. The upper part of FIG. 5 shows the dependency of the reflectance on the film thickness at a wavelength of 1 μm when Cr and W are used for the absorption layer. In both materials, when the film thickness is 50 nm or less, the reflectance is extremely small. This is because the film is too thin to absorb the irradiation light and generate a transmission component. At a film thickness of 50 to 100 nm, the reflectance increases due to the interference effect between light reflected from the film lower surface and light reflected from the film surface. As can be seen from the above, it is important that the light absorbing layer has a thickness of 100 nm or more, more preferably 150 nm or more, in order to sufficiently absorb the irradiation light and realize a stable reflectance.
[0043]
As a method for forming these materials as a light absorbing layer on an insulating layer, there are a vacuum evaporation method and a sputtering method. Since these materials are high melting point metals, sputtering is most effective, and the sputtering method is also advantageous in that a film can be formed over a large area at high speed.
[0044]
(4. Formation of second insulating layer)
A second insulating layer is formed on the light absorbing layer thus formed (FIG. 3 shows a case without the second insulating layer). This second insulating layer has two important roles.
[0045]
One is to prevent the light absorbing layer from being oxidized due to an increase in the temperature of the absorbing layer due to light irradiation. The light irradiation easily raises the temperature of the absorption layer to 1000 ° C. or higher. When this treatment is performed in the air, oxygen in the air reacts with the metal of the light absorption layer to form an oxide. Since the metal oxide becomes optically transparent, the light absorption efficiency of the light absorbing layer is significantly reduced during processing, and the temperature of the semiconductor layer cannot be increased or the reproducibility of the processing cannot be secured. Cause problems. By providing the second insulating layer, the atmosphere and the light absorbing layer can be shut off, so that the problem of oxidation of the light absorbing layer during such processing can be completely prevented. Further, the case where the second insulating layer is not provided is also considered in the present invention, and when the second insulating layer is not provided, it is effective to perform the light irradiation treatment in an inert gas atmosphere. This method has an advantage that oxidation of the light absorbing layer can be prevented without increasing the number of steps for forming the second insulating layer.
[0046]
Another role of the second insulating layer is to reduce the reflectance of the light absorbing layer by an anti-reflection film effect. In the lower diagram of FIG. 5, Cr and W are used for the light absorbing layer, and SiO is used as the second insulating layer.₂4 shows the dependency of the reflectance of light having a wavelength of 1 μm on the thickness of the second insulating layer when a film (n = 1.47) is used. Since the light absorption layer suitable for the present invention is a metal film, the refractive index difference from air is large. Therefore, in order to reduce the reflectance by the light absorbing layer, it is extremely effective to provide a layer having a refractive index (n) closer to air than a metal film. Since the antireflection film lowers the reflectance by the interference effect, the reflectance periodically changes depending on the thickness of the second insulating layer on the light absorbing layer as can be seen from the lower diagram of FIG. Of course, there are several film thicknesses that can function as an anti-reflection film, but a minimum film thickness with a short film formation time is most preferable for shortening the process tact. Although it depends on what is used as the material of the second insulating film, the method includes a step of forming a second insulating layer having a thickness t and a refractive index n, and the second insulating layer has an emission wavelength of the semiconductor light emitting element. May be formed so as to satisfy a condition of t = Nλ / 4n (N = 1, 2, 3,...). Thus, for example, when W is used as the light absorbing material, 140 to 150 nm SiO 2 is used as the second insulating layer.₂If a film is formed, the reflectance can be drastically reduced from 48% to less than 20%, which is extremely effective in efficiently absorbing irradiation light to the light absorbing layer.
[0047]
(5. Light irradiation)
Light irradiation is performed on the laminated structure formed as described above. As described above, since the irradiation light is required to be efficiently absorbed by the light absorbing layer, its wavelength is important. In other words, what kind of light source is used largely determines the wavelength of the light source. The light source applicable to the present invention is a semiconductor light emitting device. Typical examples include light emitting diodes and semiconductor lasers (sometimes called laser diodes). In order to enable processing in a large area, the output must be high, and in order to obtain sufficient power density on the light absorbing layer by condensing light, the emission wavelength width must be narrow. For these reasons, a semiconductor laser is most suitable as the light source of the present invention. Some semiconductor lasers use various compounds such as GaAs, AlGaAs, InGaAs, InGaAsP, GaN, and ZnS for the active layer, and the oscillation wavelength changes depending on the band gap of each. At present, the semiconductor laser which can obtain the highest output is a GaAs-based semiconductor laser of an edge emitting type. These high-power semiconductor lasers have a peak wavelength in the vicinity of 700 to 900 nm, and can easily achieve a high output of 2 W or more as a single unit output. Also, even such a high-power semiconductor laser costs less than 50,000 yen per laser diode and has a lifetime of 10,000 hours or more. Therefore, even if 100 laser diodes are used, it can be replaced in three to four months. It is cheap compared to the required excimer laser tube of 15 million yen.
[0048]
In FIG. 3, in the present invention, for example, a semiconductor laser (305) having a single output of 2 to 5 W is used. The semiconductor laser easily oscillates when a voltage equal to or higher than a threshold is applied from a power supply (306), and generates laser light having a wavelength of 700 to 900 nm. Laser light generated from the semiconductor laser is focused on the light absorbing layer by the lens (308). Since it is a laser beam, it is easy to narrow the beam spot to a minute spot having a diameter of 300 μm or less, and the depth of focus is deep enough to cause no practical problem. As a result, the temperature of the irradiation point (309) on the light absorption layer rapidly rises, and a high-temperature region (310) is also formed in the semiconductor layer by heat conduction. In this state, the high-temperature region (310) in the semiconductor layer is moved into the amorphous Si layer by relatively moving the substrate and the semiconductor laser. If appropriate processing conditions described later are selected, the high-temperature region (310) in the Si layer becomes a molten Si layer. Therefore, crystal growth as if zone melting is performed in a very microscopically close area of nanometers (this technologyNnano-VicinityZoneMAfter the scanning with light, a polycrystalline Si layer (311) having a large grain size formed by crystal growth from a liquid phase is formed. In order to successfully apply the NZM method, it is necessary to appropriately select the power density of the irradiation laser light on the light absorption layer and the moving speed of the laser light. Hereinafter, the temperature rise of the light absorption layer and the semiconductor layer under each processing condition when the reflectance of the light absorption layer is 50%, and the time change of the temperature at each depth from the surface of the glass substrate are shown. The lower diagram in FIG. 6 shows that the power density of the laser beam on the light absorbing layer is 1800 W / cm.²6 shows a case where the heat treatment time at an arbitrary point on the light absorption layer is 300 ms (rise 130 ms, peak 40 ms, fall 130 ms: see the upper diagram in FIG. 6). The temperature of the light absorbing layer reaches 1450K. Since the thermal diffusion length on this time scale (on the order of ms) is much longer than the total thickness of the light absorbing layer, the first insulating layer, and the semiconductor layer, the temperatures of these three layers are almost the same. That is, when Si is used as the semiconductor layer, the Si layer is melted because it rises above the melting point of 1687K. When the molten layer is moved together with the semiconductor laser light source in such a state, lateral crystal growth occurs in a cooling process in which the laser light source has passed. However, since the substrate temperature also rises to about 600 ° C. under such processing conditions, at least the irradiation power density must be 1800 W / cm to apply the present invention to a low-temperature process.²In addition, it is necessary to set the heat treatment time to 300 ms or less. In order to stably realize NZM crystallization using an inexpensive alkali-free glass substrate, it is necessary to apply a condition in which thermal stress on the substrate is smaller. For example, the irradiation power density is 3000 W / cm²FIG. 7 shows the temperature change when the heat treatment time is 100 ms. Since the irradiation power density is increased and the processing time is shortened, the heat treatment of the semiconductor layer is performed in a non-thermal equilibrium. In this case, the temperature of the light-absorbing layer and the semiconductor layer has reached about 2100 K, although the substrate temperature has risen only to about 300 to 400 ° C. at the most. By using such processing conditions, desired NZM crystallization can be performed while avoiding the problem that the glass substrate warps or the light absorbing layer is cracked or peeled off. Further, if the degree of non-thermal equilibrium is increased, NZM crystallization can be performed even on a plastic substrate. Irradiation power density of 4500 W / cm²FIG. 8 shows a temperature change when the heat treatment time is 45 ms. In this case, since the temperatures of the light absorption layer and the semiconductor layer have reached about 1950 K, the Si layer is melted and NZM crystallization is possible, and the substrate temperature rises only to about 210 ° C. Therefore, the NZM crystallization of the present invention can realize high-quality large-grain crystal growth even on a plastic substrate by appropriately selecting the processing conditions.
[0049]
In the NZM crystallization of the present invention, since the temperature of the Si layer only needs to reach the melting point or more, the process window for the spatial or temporal fluctuation of the power density of the irradiation laser is wide. That is, it is only necessary to always irradiate the light absorption layer with a power higher than the minimum required power density, which is far more than a process in which the energy variation can be tolerated by only about 2 to 3% as in the conventional pulse laser crystallization. High controllability.
[0050]
As described above, NZM crystal growth is possible by condensing and irradiating the semiconductor laser light, which means that desired crystal growth can be realized at an arbitrary position on the substrate. This can be easily realized by using a stage having a mechanism capable of relative positioning between the semiconductor laser and the substrate. Therefore, it is also possible to selectively crystallize only a specific portion on the substrate where a high-quality crystal is required. As a result, it is not necessary to grow a crystal at an unnecessary portion, so that the process throughput can be increased.
[0051]
Although the case where a single semiconductor laser is used has been described above, the method for manufacturing a semiconductor thin film of the present invention can be easily extended to large-area processing. This can be realized by using a plurality of semiconductor lasers. A semiconductor laser is formed on a compound semiconductor crystal as a substrate. By cutting out these chips and arranging them in a line as shown in the upper diagram of FIG. 9, and performing NZM crystallization using light emission from these multiple elements, it is possible to process a large area at once It becomes. If the linear light sources are further stacked, a high-output linear light source or a lattice laser light source can be prepared. Simultaneously performing NZM crystallization at a plurality of locations as shown in the lower diagram of FIG. 9 can be easily realized. The difference from the conventional laser crystallization technique is that the semiconductor laser elements themselves are extremely small and can be arranged close to each other at a very small pitch. For example, if 100 semiconductor laser chips each having an output of 5 W are arranged at a pitch of 500 μm, a linear light source having a width of 5 cm is obtained, and the output is 500 W. This is much higher power than conventional laser crystallization light sources. In this case, the relative movement distance between the substrate and the semiconductor laser corresponds to the distance between the semiconductor laser light sources as can be seen from the lower diagram of FIG. Therefore, in this case, it is 500 μm. Therefore, the time required for the processing is extremely short. Now, semiconductor lasers are arranged one-dimensionally and the light from each laser is focused individually. However, this idea can be easily extended to a high power light source. That is, if the density of the semiconductor lasers to be arranged is increased, a uniform high-power linear light source can be easily realized, and this will be described in a fourth embodiment. As described above, the output of the semiconductor laser can be increased in proportion to the number of elements simply. This is a practically feasible concept because the unit price of the semiconductor laser is low, and it cannot be realized in terms of cost with a conventional YAG harmonic laser or the like. Therefore, if a light source having the number of elements required for large-area processing is manufactured, it is possible to easily increase the process throughput while suppressing the manufacturing cost.
[0052]
Further, it is also possible to use the semiconductor laser as a light source in a state of being manufactured on a wafer without cutting out the semiconductor laser as a chip. In this case, since the position of each semiconductor laser light source is determined by photolithography in its manufacturing process, it is arranged with extremely high accuracy. Therefore, if the light to be emitted is used as it is, the position of NZM crystallization performed on the substrate to be processed can be determined with the same high accuracy.
[0053]
Further, according to the NZM crystallization technique of the present invention, the limit on the thickness of the semiconductor layer that can be crystallized is much smaller than that of the conventional laser crystallization. For example, in the case of a thin Si film having a thickness of about 15 nm, the conventional light having a wavelength of 532 nm is hardly absorbed, so that it cannot be crystallized. However, in NZM crystallization, light absorption is determined by the light absorption layer, and therefore a large grain crystallization can be achieved even with a thin Si film of 15 nm or 10 nm. When such a thin large-diameter Si crystal is used as an active layer of a TFT, an effect of increasing mobility by a quantum effect can be obtained. That is, since the carriers are confined in the Si layer, the degeneracy of the Si band is released, and an effect of increasing the mobility accompanying a decrease in the effective mass is obtained. On the other hand, crystallization of a thick Si film is also possible. For example, in consideration of application to a solar cell having a thickness of 200 nm, crystalline Si having a thickness of 1 μm is required. If the NZM crystallization technique is applied, even with such a thick film, crystal growth of a large grain size can be performed in exactly the same manner as described above, so that a high-quality Si crystal having a long carrier lifetime can be provided.
[0054]
As described above, by using the NZM crystallization technique of the present invention, crystal growth can be performed without any problem even when there are regions having different semiconductor layer thicknesses on the same substrate. If such high-quality Si crystals having different film thicknesses can be formed, semiconductor elements having different functions can be formed on the same substrate. For example, when a TFT and a solar cell are formed on the same substrate, a low power consumption TFT circuit can be driven by power supplied from the solar cell. Then, there is no need to supply power from the outside with electric wires, and an extremely portable electronic device can be realized. This is a new electronic device that has never existed before, and the technology of the present invention for realizing them has extremely high potential.
[0055]
Embodiment 1
An embodiment of the method for manufacturing a semiconductor thin film according to the present invention will be described with reference to FIG. The substrate and the underlayer protective film used in the present invention are in accordance with the above description, but here, a 300 mm × 300 mm square general-purpose non-alkali glass (300) is used as an example of the substrate. First, a base protective film (301), which is an insulating material, is formed on a substrate 100. Here, a silicon oxide film having a thickness of about 200 nm is deposited by an ECR-PECVD method at a substrate temperature of 150 ° C. Next, a semiconductor film (302), such as an intrinsic silicon film, which will be an active layer of the thin film transistor later, is deposited. Here, the thickness of the semiconductor layer is about 50 nm. In this example, a high-vacuum type LPCVD apparatus is used, and disilane (Si₂H₆) Is flowed at 200 SCCM, and an amorphous silicon film 102 is deposited at a deposition temperature of 425 ° C. First, a plurality of (eg, 17) substrates are placed inside a reaction chamber of a high-vacuum LPCVD apparatus at 250 ° C. with the front side facing downward. After this, the operation of the turbo-molecular pump is started. After the turbo-molecular pump has reached steady rotation, the temperature in the reaction chamber is raised from 250 ° C. to a deposition temperature of 425 ° C. over about one hour. During the first 10 minutes after the start of the temperature rise, the temperature is raised in a vacuum without introducing any gas into the reaction chamber. Thereafter, nitrogen gas having a purity of 99.9999% or more is continuously supplied at 300 SCCM. The equilibrium pressure in the reaction chamber at this time was 3.0 × 10^-3Torr. After reaching the deposition temperature, disilane (Si₂H₆) At 200 SCCM and helium (He) for dilution having a purity of 99.9999% or more at 1000 SCCM. The pressure in the reaction chamber immediately after the start of the deposition is about 0.85 Torr. As the deposition proceeds, the pressure in the reaction chamber gradually increases, and the pressure immediately before the end of the deposition is approximately 1.25 Torr. The silicon film (302) thus deposited has a thickness variation within ± 5% within a 286 mm square region excluding the peripheral portion of about 7 mm of the substrate. Next, a first insulating layer (303) is formed. Here, SiO having a thickness of 100 nm is formed by ECR-PECVD.₂The film was deposited. SiH as source gas₄And O₂Were flowed at 30 sccm and 40 sccm, respectively, and plasma discharge was started while the substrate was heated to 100 ° C. to form a film. Next, as a light absorption layer (304), a laminated structure film of TaN and Ta was formed to 50 nm and 200 nm by sputtering, respectively. The purpose of forming a TaN film is to increase the adhesion of the Ta film which plays a major role as a light absorbing layer. Irradiation light can be stably absorbed by forming Ta having this thickness, and the temperature of the light absorbing layer during processing was extremely stable because cracks and film peeling did not occur.
[0056]
Next, a second insulating layer (320) is formed on the light absorbing layer by SiO 2.₂A film was formed at 137 nm. This was formed under exactly the same conditions as the first insulating layer. 137 nm of SiO is used as a second insulating layer using Ta as a light absorbing material.₂Since the film was formed, the effective reflectance could be reduced to about 50%. Thereafter, a semiconductor laser (305) having an intensity peak at 808 nm is opposed to the substrate, a lens (308) having an NA of 0.3 is provided between the semiconductor laser (305) and the substrate, and a semiconductor laser beam (307) is applied to the light absorbing layer. Was collected. The beam spot shape of the laser light on the light absorbing layer is elliptical. The length in the major axis direction was 600 μm, and the length in the minor axis direction was 300 μm. At this time, the power density at the peak is 1800 W / cm²Met. Under such irradiation conditions, the substrate is moved at a speed of 1 mm / s in a direction parallel to the short axis of the beam to induce lateral crystal growth from liquid Si by NZM crystallization, and has a width of about 20 μm and a length of about 100 μm. A high quality polycrystalline region (311) having single crystal grains was formed. Since this crystal is sufficiently larger than the element size of the TFT, it is possible to manufacture a high-performance TFT having almost the same performance as a single-crystal MOSFET by forming a TFT in this crystal grain. Since the substrate temperature rises to about 600 ° C. under the heat treatment conditions of this example, it is applicable to a non-alkali glass substrate, but it was formed on a quartz substrate or a single crystal Si substrate having higher heat resistance via an insulating layer. It is preferably applied to crystallization of a Si film.
[0057]
Embodiment 2
In the second embodiment of the present invention, a semiconductor thin film was manufactured under different light irradiation conditions. The steps of forming the underlayer, the semiconductor layer, the first insulating layer, the light absorbing layer, and the second insulating layer are exactly the same as those in the first embodiment. The semiconductor laser and the optical system for irradiating light are the same as in the first embodiment. Here, the output of the semiconductor laser was increased, and a lens (308) with NA = 0.4 was further installed between the semiconductor laser and the substrate, so that a higher power semiconductor laser beam (307) was focused on the light absorption layer. The beam spot shape of the laser light on the light absorbing layer is elliptical. The length in the major axis direction was 300 μm, and the length in the minor axis direction was 150 μm. At this time, the power density at the peak is 3000 W / cm.²Met. Under such irradiation conditions, the substrate is moved in a direction parallel to the short axis of the beam at a speed of 1.5 mm / s to induce lateral crystal growth from liquid Si by NZM crystallization, and has a width of 20 μm and a length of 100 μm. A high quality polycrystalline region (311) having crystal grains substantially consisting of a single crystal was formed. In this case, the temperature rise of the substrate was at most about 300 ° C., so that even when non-alkali glass was used, the substrate was not deformed, and a poly-Si film of the same quality as that of Example 1 could be obtained.
[0058]
Embodiment 3
In the third embodiment of the present invention, a plastic substrate having relatively high heat resistance is used as the substrate. The steps of forming the underlayer, the semiconductor layer, the first insulating layer, the light absorbing layer, and the second insulating layer are exactly the same as those in the first embodiment. The semiconductor laser that irradiates light is the same as in the first embodiment. Here, the output of the semiconductor laser was increased, and a lens (308) with NA = 0.5 was further installed between the semiconductor laser and the substrate, and the semiconductor laser light (307) was focused on the light absorbing layer. The beam spot shape of the laser light on the light absorbing layer is elliptical. The length in the major axis direction was 150 μm, and the length in the minor axis direction was 100 μm. At this time, the power density at the peak is 4500 W / cm.²Met. Under such irradiation conditions, the substrate is moved in a direction parallel to the short axis of the beam at a speed of 2.2 mm / s to induce lateral crystal growth from liquid Si by NZM crystallization, and has a width of 20 μm and a length of 100 μm. A high quality polycrystalline region (311) having crystal grains substantially consisting of a single crystal was formed. Here, during the laser beam irradiation, a substrate cooling method of spraying He gas having an extremely high thermal conductivity and vacuum-chucking the substrate holder circulating the cooling water to adhere the substrate in close contact is used, so that the temperature of the substrate rises at a maximum. The temperature was about 180 ° C., and the plastic substrate was not melted or deformed, and a high-quality poly-Si film could be obtained.
[0059]
Embodiment 4
In the fourth embodiment of the present invention, a linear beam was produced using a plurality of semiconductor laser light sources, and the NZM crystallization treatment of the semiconductor layer was performed using the linear beam. In order to obtain a sufficient semiconductor laser light output, as shown in FIG. 9, three semiconductor laser arrays in which 600 semiconductor lasers (901) are arranged at 500 μm intervals are vertically stacked while being shifted by 167 μm. By supplying power, a laser light source having a total output of 9 kW was produced. The length in the longitudinal direction of this laser light source is 300 mm, and the width is 6 mm. This laser light was condensed in the short axis direction through a cylindrical lens having a length of 330 mm and a width of 30 mm, and was irradiated onto the light absorbing layer. The arrangement of the linear beam and the substrate at this time is as shown in the upper diagram of FIG. As a result, the irradiation laser light (190) made the NZM crystal growth process by scanning the laser beam in the uniaxial direction (195) with the length being parallel to one side of the substrate. At this time, the profile of the irradiation laser light in the minor axis direction is a profile close to a Gaussian distribution as shown in the lower diagram of FIG. The full width at half maximum in the minor axis direction was 500 μm. Thereby, the power density of the irradiation laser light on the light absorption layer is 4800 W / cm.²Met. In the longitudinal direction of the linear laser beam, there was a periodic intensity distribution due to the emission mode of the semiconductor laser.However, if a power density sufficient to melt the semiconductor layer was given even in a portion where the intensity was low, the molten Si layer could be formed. Because it can be formed, the process window of the crystallization method of the present invention is extremely wide. The substrate was relatively moved at a speed of 11 mm / s, and the light irradiation time at an arbitrary point (for example, 194) on the substrate was 45 ms. As a result, the semiconductor layer was completely melt-crystallized in the beam, and a high-quality poly-Si film having a large grain size could be formed on the entire 300 mm substrate as in Examples 1 to 3. At this time, the processing time for one substrate was only 27 seconds. As can be seen from the above, since the semiconductor thin film manufacturing method of the present invention has a very high process throughput, it can be sufficiently applied to even larger large-area substrates. In the present embodiment, three semiconductor laser arrays arranged at 500 μm intervals are vertically stacked in three stages while being shifted from each other by 167 μm. However, the present invention is not limited to this. For example, 500 semiconductor laser arrays are arranged at 500 μm intervals. The semiconductor laser arrays arranged in this manner may be vertically stacked in three stages while being shifted from each other by 167 μm, or the semiconductor laser arrays arranged in 400 at 550 μm intervals may be vertically stacked in four stages while being shifted by 137 μm from each other. The distance between semiconductor lasers, the number of semiconductor lasers, and the number of stacked semiconductor lasers can be appropriately changed according to the total output of laser light.
[0060]
Embodiment 5
A fifth embodiment of the method for manufacturing a thin film transistor according to the present invention will be described with reference to FIG. Although the crystallization condition of the semiconductor layer used in this embodiment may be any of the conditions of Embodiments 1 to 5, a high-quality semiconductor layer is formed under the conditions of Embodiment 5. In this embodiment, the second insulating layer, the light absorbing layer and the first insulating layer were removed by etching in order to use the thus formed single crystal Si film as an active layer, exposing the semiconductor layer (501). SiO₂The film was etched with a 5% HF solution, and the light absorbing layer W was removed by dry etching using radicals generated by plasma discharge of a chlorine-based gas. The substrate with the exposed Si film 501 is set in the plasma processing chamber. In the plasma processing chamber, the substrate temperature was set to 250 ° C., oxygen gas was flowed at 80 sccm, and plasma discharge was performed at a pressure of 1 Torr and a power of 1 kW using a parallel plate RF electrode. As a result, a trap level (defect) passivation process for the crystal grain boundaries at various places in the Si film was performed. As described above, the Si film obtained in this example is a single crystal, but some defects such as dislocations, point defects, and electrically active crystal grain boundaries have occurred. The purpose of this step is to inactivate. After removing the oxide film formed on the surface by hydrofluoric acid wet etching, the surface was washed with pure water for 10 minutes to form a hydrogen-terminated clean semiconductor layer surface. Thereafter, a photoresist pattern is formed by photolithography on the Si film region formed under the light absorbing layer, and CF is formed.₄And O₂Dry etching by remote plasma discharge using a mixed gas was performed. The substrate is set in an insulating film forming chamber to form a gate insulating film (502) on the island-shaped patterned Si film. 10 in the chamber^-6(Torr), the chamber was evacuated to a vacuum degree, silane gas and oxygen gas were introduced at a flow ratio of 1: 6, and the chamber pressure was set to 2 × 10^{− 3}(Torr). When the gas pressure in the chamber is stabilized, the ECR discharge is started, and the formation of the insulating film is started. The inputted microwave power was 1 kW, and the microwave was introduced from the introduction window in parallel with the magnetic force lines. There is an ECR point at a position 14 cm from the introduction window. The film was formed at a film formation rate of 10 nm / min. Thus, a gate insulating film (502) was formed to a thickness of 100 nm. Subsequently, a thin film serving as a gate electrode (505) is deposited by a PVD method or a CVD method. Normally, since the gate electrode and the gate wiring are made of the same material in the same process, it is desired that this material has low electric resistance and is stable to a heat process at about 350 ° C. In this example, a tantalum thin film having a thickness of 600 nm is formed by a sputtering method. The substrate temperature when forming the tantalum thin film is 180 ° C., and an argon gas containing 6.7% of a nitrogen gas is used as a sputtering gas. The tantalum thin film thus formed has an α-structure crystal structure, and its specific resistance is about 40 μΩcm. After depositing a thin film to be a gate electrode, patterning is performed, and then impurity ions are implanted into the semiconductor film to form source / drain regions (503, 504) and a channel region. At this time, since the gate electrode serves as a mask for ion implantation, the channel has a self-aligned structure formed only under the gate electrode. As a source gas for the ion doping method, phosphine (PH) having a concentration of about 0.1% to about 10% diluted in hydrogen is used.₃) Or a hydride of an implantation impurity element such as diborane (B2H6). In this example, phosphine (PH3) having a concentration of 5% diluted in hydrogen is injected at an accelerating voltage of 100 keV by using an ion doping apparatus in order to form an NMOS. PH₃ ⁺And H₂ ⁺Total ion implantation amount including ions is 1 × 10¹⁶cm^-2It is.
[0061]
Next, an interlayer insulating film was formed by using the PECVD method. The source gas is TEOS (tetraethoxysilane), N₂Electric discharge was performed using O and Ar gases at a pressure of 1.5 Torr and a power of 1 kW to form an interlayer insulating film (506) of 800 nm. Next, a contact hole is formed on the source / drain, and the source / drain extraction electrodes (507, 508) and wiring are formed of aluminum by a PVD method, a CVD method, or the like, thereby completing a thin film transistor. As a result, a high-performance TFT having almost the same performance as that of a single-crystal Si MOSFET could be manufactured with extremely uniformity.
[0062]
The thin film transistor obtained by the manufacturing method of the present invention is applicable to various electronic devices including an electro-optical device. Examples of the electro-optical device include a liquid crystal device and an organic EL device. FIG. 12 illustrates an example of an electronic device to which the electro-optical device can be applied. FIG. 9A shows an example of application to a mobile phone. A mobile phone 230 includes an antenna unit 231, an audio output unit 232, an audio input unit 233, an operation unit 234, and the electro-optical device 10 of the present invention. . Thus, the electro-optical device 10 of the present invention can be used as a display unit of the mobile phone 230. FIG. 8B shows an example of application to a video camera. The video camera 240 includes an image receiving unit 241, an operation unit 242, and the electro-optical device 10 of the present invention. As described above, the electro-optical device according to the invention can be used as a finder or a display unit. In addition, the present invention can be applied to portable personal computers, head mounted displays, rear projectors, and front projectors. As described above, the electro-optical device of the present invention can be used as an image display source.
[0063]
The electro-optical device 10 of the present invention is not limited to the above example, and can be applied to any electronic device to which an active matrix type electro-optical device can be applied. For example, in addition to the above, the present invention can be applied to a fax device with a display function, a finder of a digital camera, a portable TV, a DSP device, a PDA, an electronic organizer, an electronic bulletin board, and a display for advertising.
[0064]
As described above, according to the conventional technology, an effective process for forming a Si film having a large crystal grain size and substantially the same quality as a single crystal and having a flat surface with a low temperature process, a high throughput, and a low cost is clearly defined. Was not. However, as described above, an extremely high-quality Si film can be formed by using the method for manufacturing a semiconductor thin film and a thin film transistor according to the present invention. As a result, it is possible to manufacture a thin film transistor having a high mobility, a low threshold voltage and an extremely small variation, realize an ultra-low power consumption circuit, and provide a multifunctional electro-optical device and an electronic device at a low price. it can.
[Brief description of the drawings]
FIG. 1 is a sectional structural view of a conventional high-power lamp processing apparatus.
FIG. 2 is a diagram showing an input power profile when processing is performed using the lamp of FIG. 1 and a temporal change in temperature at each depth of a substrate at that time.
FIG. 3 is a view showing a method of manufacturing a semiconductor thin film according to the present invention.
FIG. 4 is a diagram showing reflectance spectra of various refractory metals.
FIG. 5 is a diagram showing a change in reflectance when the thickness of a light absorbing layer and the thickness of a second insulating layer are changed.
FIG. 6 is a diagram showing a light irradiation profile of the present invention and a temperature rise at each depth of a light absorbing layer / semiconductor layer and a glass substrate.
FIG. 7 is a diagram showing a light irradiation profile of the present invention and a temperature rise at each depth of a light absorbing layer / semiconductor layer and a glass substrate.
FIG. 8 is a diagram showing a light irradiation profile of the present invention and a temperature rise at each depth of a light absorbing layer / semiconductor layer and a glass substrate.
FIG. 9 is a view showing an irradiation light source in which a plurality of semiconductor light emitting devices are arranged according to the present invention and a method for crystallizing a semiconductor thin film using the irradiation light source.
FIG. 10 is a process sectional view showing the method for manufacturing the thin film transistor of the present invention.
FIG. 11 is a view showing a method of applying the method for manufacturing a semiconductor thin film of the present invention to a large-area substrate.
FIG. 12 is a diagram showing an application to an electro-optical device and an electronic apparatus using the thin film transistor of the invention.
[Explanation of symbols]
110. . . Lamp unit
111. . . Lamp light source
112. . . Reflective optical system / reflective surface
113. . . Radiation thermometer
114. . . Scan direction
115. . . slit
190. . . The linear laser light of the present invention
195. . . Scanning direction of linear laser light
300. . . substrate
301. . . Base insulating film
302. . . Semiconductor layer
303. . . First insulating layer
304. . . Light absorbing layer
305. . . Semiconductor light emitting device (semiconductor laser)
306. . . Power supply
307. . . Irradiation light
308. . . lens
309. . . High temperature region of light absorption layer
310. . . Fused Si layer
311. . . Large particle size poly-Si layer
312. . . Direction of relative movement between semiconductor light emitting device and substrate
901. . . Semiconductor laser
902. . . Laser light
903. . . lens
501. . . Poly-Si film formed by NZM crystallization of the present invention
502. . . Gate insulating film
503, 904. . . Source and drain regions
505. . . Gate electrode
506. . . Interlayer insulating film
507, 508. . . Source and drain electrodes

Claims (22)

Forming a semiconductor layer on a substrate; and causing the semiconductor light emitting element to face the substrate, and moving the semiconductor light emitting element relative to the substrate while irradiating the semiconductor layer with light generated from the semiconductor light emitting element. And a heat treatment of the semiconductor thin film. A step of forming at least a first insulating layer and a light absorbing layer on a semiconductor layer formed on a substrate, and a semiconductor light emitting element opposed to the substrate, and light generated from the semiconductor light emitting element is applied to the light absorbing layer. Heat-treating the semiconductor layer by moving the semiconductor layer relatively to the substrate while irradiating the semiconductor layer. 3. The manufacturing of a semiconductor thin film according to claim 2, wherein the light absorbing layer is a material of any one of Cr, Mo, Ta, Ti, and W, or an alloy containing at least one of the materials or two or more, or a multilayer structure. 4. Method. 4. The method according to claim 1, wherein the semiconductor light emitting device is a semiconductor laser having an oscillation wavelength between 200 nm and 2000 nm. 5. 3. The heat treatment step is performed under conditions such that the power density of light generated from the semiconductor light emitting element on the light absorption layer is 1800 W / cm ² or more and the light irradiation time at an arbitrary point in the irradiation region is 300 ms or less. The method for manufacturing a semiconductor thin film according to claim 1. 3. The heat treatment step is performed under conditions such that the power density of light generated from the semiconductor light emitting element on the light absorption layer is 3000 W / cm ² or more and the light irradiation time at an arbitrary point in the irradiation region is 100 ms or less. The method for manufacturing a semiconductor thin film according to claim 1. 3. The heat treatment step is performed under conditions such that the power density of light generated from the semiconductor light emitting element on the light absorption layer is 4500 W / cm ² or more and the light irradiation time at an arbitrary point in the irradiation area is 45 ms or less. The method for manufacturing a semiconductor thin film according to claim 1. The method according to claim 1, wherein a distance between the light absorbing layer on the substrate and the semiconductor light emitting element facing the light absorbing layer is 1 μm or more and 30 cm or less. Forming a second insulating layer having a thickness of t and a refractive index of n on the light absorbing layer, wherein the second insulating layer has a wavelength of t = Nλ / 9. The method of manufacturing a semiconductor thin film according to claim 2, wherein the semiconductor thin film is formed so as to satisfy a condition of 4n (N = 1, 2, 3,...). The method of manufacturing a semiconductor thin film according to claim 1, wherein a plurality of the semiconductor light emitting devices are arranged in a linear or lattice shape. The method of manufacturing a semiconductor thin film according to claim 10, wherein the plurality of semiconductor light-emitting elements arranged in a line or in a lattice are formed in advance in a line or in a lattice at desired intervals on a wafer. The method of manufacturing a semiconductor thin film according to claim 2, wherein a region 1 having a thickness of 100 nm or less and a region 2 having a thickness of 200 nm or more are provided on the same substrate. A thin film transistor using the semiconductor layer subjected to the heat treatment according to claim 1 as an active layer. 14. The thin film transistor according to claim 13, wherein the semiconductor thin film has a thickness of 15 nm or less. A semiconductor device comprising a semiconductor layer subjected to the heat treatment according to claim 1. Forming a semiconductor layer on a substrate; and causing the semiconductor light emitting element to face the substrate, and moving the semiconductor light emitting element relative to the substrate while irradiating the semiconductor layer with light generated from the semiconductor light emitting element. And a heat treatment of the thin film transistor. 13. A thin-film solar cell using the semiconductor layer subjected to the heat treatment according to claim 1 as an active layer. The thin-film solar cell according to claim 17, wherein the semiconductor layer has a thickness of 200 nm or more. A composite semiconductor device in which a thin film transistor is formed in a semiconductor thin film region 1 in which the thickness of a semiconductor layer formed on the same substrate is 100 nm or less and a thin film solar cell is formed in a semiconductor thin film region 2 in which the semiconductor layer thickness is 200 nm or more. Manufacturing method. An electro-optical device comprising the thin film transistor according to claim 13 as a driving element for a display pixel and a peripheral driving circuit. An electronic apparatus comprising the electro-optical device according to claim 20. An electronic device comprising the thin-film solar cell according to claim 17.

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