JP2004186207A - Semiconductor device manufacturing method, semiconductor device, electro-optical device, and electronic equipment - Google Patents

Abstract

Provided is a method of manufacturing a semiconductor device which can obtain a thin film transistor having an S value which is an electrical characteristic of a sub-threshold region in a thin film transistor using a substantially single crystal grain of a semiconductor material for a channel formation region. .
A thin film transistor includes a gate electrode, a source region, a drain region, and a channel formation region. The silicon film used for forming the channel formation region is made of substantially single crystal silicon crystal grains grown from the starting point of crystal growth, and has a thickness of 30 nm to 150 nm. Thus, the number of crystal defects that can be included in the silicon crystal grains can be reduced, and a thin film transistor having an excellent S value can be realized.
[Selection diagram] Fig. 4

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor device, and a semiconductor device, an electro-optical device, and an electronic apparatus manufactured by the method.
[0002]
[Prior art]
In an electro-optical device, for example, a liquid crystal display device or an organic EL (electroluminescence) display device, switching of pixels and the like are performed using a thin film circuit including a thin film transistor as a semiconductor element. In a conventional thin film transistor, an active region such as a channel formation region is formed using an amorphous silicon film. Further, a thin film transistor in which an active region is formed using a polycrystalline silicon film has been put to practical use. By using a polycrystalline silicon film, electric characteristics such as field-effect mobility are improved as compared with a case where an amorphous silicon film is used, so that the performance of a thin film transistor can be improved.
[0003]
In addition, in order to further improve the performance of the thin film transistor, a technique of forming a semiconductor film including large crystal grains and forming a channel formation region of the thin film transistor with a single substantially single crystal grain is being studied. For example, a technique has been proposed in which fine holes (concave portions) are formed on a substrate, and the holes are used as starting points for crystal growth to crystallize a semiconductor film, thereby forming substantially crystal grains of silicon having a large grain size. I have. By forming a thin film transistor using a silicon film having a large crystal grain size formed by using this technique, a formation region (particularly, a channel formation region) of one thin film transistor is formed of a single substantially single crystal grain. Becomes possible. Thus, a thin film transistor having excellent electric characteristics such as field-effect mobility can be realized. (For example, see Non-Patent Document 1 or Non-Patent Document 2.)
[Non-patent document 1]
"Single Crystal Thin Film Transistors" (IBM TECHNICAL DISCLOSURE BULLETIN Aug. 1993 pp 257-258)
[Non-patent document 2]
"Advanced Excimer-laser Crystallization Techniques of Si Thin-Film For Location Control of Large Grain on Glass" (R. Ishihara et al. Proc.
[0004]
[Problems to be solved by the invention]
By the way, when a thin film transistor is formed using substantially single crystal grains formed according to the above-mentioned literature and its electric characteristics are actually examined, the field effect mobility can be realized as a very large value of about 500 cm ² / Vs. The sub-threshold hold swing (S value), which is an electrical characteristic in the sub-threshold region, is 0.45 V / dec. Experiments conducted by the inventors of the present application confirmed that the above characteristics were large and were inferior to the same characteristics (about 0.2 V / dec.) Of ordinary polycrystalline silicon thin film transistors. This is because, in the structure of the thin film transistor described in the above document, the thickness of the silicon film serving as a channel formation region is set to be about 250 nm or more, so that the total number of crystal defects contained therein increases. It is considered that the S value became worse.
[0005]
Therefore, an object of the present invention is to provide a method for manufacturing a semiconductor device which can obtain a thin film transistor having excellent field-effect mobility and S value in a thin film transistor formed using a substantially single crystal.
[0006]
Another object of the present invention is to provide a semiconductor device capable of obtaining a thin film transistor having excellent electric characteristics of field-effect mobility and S value.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method for manufacturing a semiconductor device in which a semiconductor film is formed on a substrate, and a thin film transistor is formed using the semiconductor film. A starting point forming step of forming a starting point to be a starting point of the semiconductor film forming step of forming the semiconductor film on the substrate on which the starting point is formed; A heat treatment step of forming substantially single crystal grains having a substantially center, a patterning step of patterning the semiconductor film containing the substantially single crystal grains to form a transistor region to be a source, drain, and channel formation region; Forming a gate insulating film and a gate film on a region to form a thin film transistor. Wherein the transistor region is formed so that the thickness of the body layer becomes 30nm to 150 nm.
[0008]
In the present invention, by setting the semiconductor film to an appropriate thickness, the absolute number of defects included in substantially single crystal grains is reduced, and the S value of a thin film transistor formed using the same in a channel formation region is reduced to a normal value. It is improved to be equal to or more than the S value of the polycrystalline silicon thin film transistor.
[0009]
Preferably, the patterning step is performed such that at least the starting point and the vicinity thereof are not included in the channel formation region. Crystal grains formed substantially at the center of the starting point may have crystal defects at and near the starting point, resulting in disordered crystallinity. Therefore, by preventing the semiconductor film in the starting portion and the region in the vicinity thereof from being included in the channel formation region, it is possible to avoid the semiconductor film having poor crystallinity from being included in the channel formation region, and to further improve the characteristics of the thin film transistor. It can be improved.
[0010]
Preferably, the above-mentioned starting point is a recess formed in the substrate. Thereby, it is possible to easily form a portion to be a starting point of crystallization.
[0011]
Preferably, the heat treatment in the above-described heat treatment step is performed under such a condition that a non-melted portion remains in the semiconductor film in the concave portion and the other portion is melted. Thus, the crystallization of the semiconductor film after the heat treatment starts from the inside of the concave portion in a non-molten state, particularly from the vicinity of the bottom, and proceeds to the periphery. At this time, by appropriately setting the size of the concave portion, only one crystal grain reaches the upper portion (opening) of the concave portion. In the melted portion of the semiconductor film, crystallization is performed with one crystal grain reaching the upper portion of the concave portion as a nucleus. (Single crystal grains) can be formed.
[0012]
Preferably, the heat treatment is performed by pulsed laser irradiation having a pulse width of 150 ns to 250 ns. By using a laser having a relatively long pulse width in this manner, the melting time of the semiconductor film is lengthened, and it becomes possible to promote the growth of crystal grains from the concave portion which is the starting point of crystal growth.
[0013]
Preferably, the semiconductor film formed on the substrate is an amorphous or polycrystalline silicon film. This makes it possible to form substantially single crystal silicon crystal grains in a range substantially centered on the starting point, and to form a thin film transistor using the high quality silicon crystal grains.
[0014]
Further, the present invention is a semiconductor device formed using a semiconductor film formed over a substrate and including a thin film transistor having a source, a drain region, and a channel formation region, wherein the semiconductor film is provided over the substrate. The thin film transistor is formed so as to include substantially single crystal grains formed from the obtained starting point, and the thickness of the semiconductor film in the channel formation region of the thin film transistor is 30 nm to 150 nm.
[0015]
Here, the density of the crystal defects contained in the substantially single crystal grains is estimated to be very small as compared with the density of the crystal defects in the semiconductor film used in the ordinary polycrystalline silicon thin film semiconductor. When the thickness is increased, the total number of crystal defects increases, and as a result, the S value of the thin film transistor formed there increases. Therefore, the present invention makes it possible to obtain an excellent semiconductor device by setting the semiconductor film to an appropriate film thickness in order to realize characteristics equal to or more than the S value of a normal polycrystalline silicon thin film transistor.
[0016]
Preferably, the semiconductor film in the channel formation region is patterned so as not to include the starting point and a region in the vicinity thereof. In the crystal grains formed substantially at the center of the starting point, the corresponding grain boundaries are concentrated at the starting point and in the vicinity thereof, and crystal defects may be generated and crystallinity may be disturbed. Therefore, by using a semiconductor film patterned so as not to include the starting portion and a region in the vicinity thereof, it is possible to avoid including a semiconductor film having poor crystallinity in the channel formation region and to further improve the characteristics of the thin film transistor. Becomes possible.
[0017]
Preferably, the starting portion is a concave portion formed in the substrate, and the semiconductor film is formed by performing heat treatment and crystallization so that a non-melted portion remains in the semiconductor film in the concave portion and the other is melted. ing. Thus, a thin film transistor can be formed using a substantially single-crystal semiconductor film (substantially single-crystal grains) formed in a range substantially centered on the concave portion.
[0018]
Preferably, the semiconductor film is obtained by subjecting an amorphous or polycrystalline silicon film to heat treatment with a pulse laser having a pulse width of 150 ns to 250 ns. Thereby, even for a relatively thin silicon film, it is possible to obtain a large single crystal grain having a large grain size centered on the starting point.
[0019]
Further, it is preferable to form an electro-optical device such as a liquid crystal display device or an organic electroluminescence display device using the above-described thin film transistor. Accordingly, it is possible to configure an electro-optical device having excellent display quality, and it is possible to configure a high-quality electronic device by using the electro-optical device.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0021]
The manufacturing method of this embodiment includes (1) a step of forming a silicon film for use as a source region, a drain region, and a channel formation region of a thin film transistor on a glass substrate; and (2) a thin film transistor using the formed silicon film. Forming step. Hereinafter, each step will be described in detail.
[0022]
FIG. 1 is an explanatory diagram illustrating a process of forming a silicon film. As shown in FIG. 1A, a silicon oxide film 12 is formed on a glass substrate 10 as a substrate. The silicon oxide film 12 is preferably formed by a film forming method such as a plasma enhanced chemical vapor deposition (PECVD), a low pressure chemical vapor deposition (LPCVD), or a sputtering method.
[0023]
Next, a concave portion (hereinafter, referred to as a “grain filter”) 52 is formed in the silicon oxide film 12. The grain filter is a starting point to be a starting point in the later crystallization of the semiconductor film, and is a hole for growing only one crystal nucleus. The grain filter 52 is preferably formed in a cylindrical shape having a diameter of about 50 nm or more and 150 nm or less and a height of about 750 nm, for example. The grain filter 52 may have a shape other than a cylindrical shape (for example, a prism shape).
[0024]
The grain filter 52 has, for example, a photomask having an opening that exposes and develops a photoresist film applied to a silicon oxide film using a mask in which the grain filter 52 is disposed, thereby exposing a position where the grain filter 52 is formed. A resist film (not shown) is formed on the silicon oxide film 12, reactive ion etching is performed using the photoresist film as an etching mask, and then the photoresist film on the silicon oxide film 12 is removed. Can be formed. When forming the grain filter 52 having a smaller diameter, it is possible to reduce the hole diameter of the concave portion by removing the photoresist film and depositing a silicon oxide film by a method such as PECVD or LPCVD. .
[0025]
Next, as shown in FIG. 1B, an amorphous silicon film 14 as a semiconductor film is formed on the silicon oxide film 12 and in the grain filter 52 by a film forming method such as an LPCVD method. The thickness of the amorphous silicon film 14 is set to about 30 nm to 150 nm. Note that a polycrystalline silicon film may be formed instead of the amorphous silicon film 14.
[0026]
Here, the amorphous silicon film 14 needs to have a thickness enough to bury the grain filter 52. For example, if the diameter of the grain filter is 50 nm, the thickness of the amorphous silicon film is Needs to be about 30 nm or more. If a thinner silicon film is deposited, the grain filter will not be sufficiently buried, resulting in a gap. If the diameter of the grain filter is made smaller than 50 nm, the thickness of the amorphous silicon film can be reduced in principle. However, a grain filter having such a small diameter can be formed stably. This is very difficult in the manufacturing process, and it is not possible to sufficiently supply amorphous silicon to the inside of the grain filter when depositing an amorphous silicon film. From these facts, the minimum thickness of the amorphous silicon film 14 is 30 nm in order to stably grow substantially single crystal grains of silicon described later. The reason why the maximum thickness of the amorphous silicon film is 150 nm will be described later.
[0027]
Next, as shown in FIG. 1C, the silicon film 14 is subjected to laser irradiation as a heat treatment. This laser irradiation is preferably performed using, for example, a XeCl pulse excimer laser having a wavelength of 308 nm and a pulse width of about 200 ns so that the energy density becomes about 0.4 to 1.5 J / cm ² . By performing laser irradiation under such conditions, most of the irradiated laser is absorbed near the surface of the silicon film 14. This is because the absorption coefficient of amorphous silicon at the wavelength (308 nm) of the XeCl pulse excimer laser is relatively large at 0.139 nm ⁻¹ .
[0028]
Here, as the excimer laser to be irradiated, it is preferable to use an excimer laser having a pulse width of about 150 ns to 250 ns, rather than an excimer laser having a pulse width of about 20 ns to 30 ns, which is widely used in the past. This is because the irradiation time of the excimer laser having such a relatively long pulse width significantly increases the melting time of the silicon film. This is reported in "Experimental and numerical analysis of surface melt dynamics in 200 ns-excimer laser crystallization of 1, 3, 48, 48, and 48. I have. The size of the crystal grain when the molten silicon film solidifies and crystallizes depends on the multiplication of the crystal growth rate and the melting time. That is, when the melting time of the silicon film is lengthened by irradiating the excimer laser having the relatively long pulse width, it is possible to form large substantially single crystal grains. For example, in the experiments of the present inventors, a silicon film sample at room temperature is irradiated with the excimer laser having the relatively long pulse width. The formation of grains has been confirmed (FIG. 2A). On the other hand, R.S. In the literature of Ishihara et al., A conventional excimer laser having a relatively short pulse width is used, and the maximum single crystal grain size when the silicon film thickness is 90 nm is about 2.5 μm (FIG. 2B). ). Although these two have slightly different silicon film thicknesses, the use of the above-described excimer laser having a long pulse width can achieve the growth of crystal grains of about several tens%. The same applies to other silicon film thicknesses as shown in FIG.
[0029]
Furthermore, in the experiments of the present inventors, the silicon film sample was heated to about 200 ° C. during the irradiation with the excimer laser having a long pulse width, so that the sample having a silicon film thickness of 100 nm had a maximum single crystal grain size of about 7 μm. The formation of large crystal grains of about 8 μm was confirmed in the sample having the same thickness of 150 nm.
[0030]
On the other hand, a technique for crystallizing a silicon film using a laser having a long pulse width is also disclosed in, for example, JP-A-2000-36464 and JP-A-7-283151. However, in these techniques, the silicon film does not have a starting point which is a starting point of crystallization, and the place where crystal growth starts is not controlled. In other words, irradiation with a laser having a long pulse width increases the melting time of the silicon film, but crystal nuclei are generated at random positions and crystal grains grow from each crystal nucleus, resulting in a final crystal grain. No large change is recognized in the size of the conventional method. On the other hand, in the present embodiment, since the starting point of crystallization of the silicon film is controlled by forming a concave portion (grain filter), crystal growth starts preferentially from here, and laser irradiation with a long pulse width is performed. Due to the effect of increasing the melting time, as described above, the formation of crystal grains that are several tens of percent larger than in the past is realized.
[0031]
By appropriately selecting the above-described laser irradiation conditions, the silicon film 14 is left in a non-molten state inside the grain filter 52, particularly near the bottom, and is almost completely melted in the other parts. State. As a result, the crystal growth of silicon after laser irradiation starts first in the vicinity of the non-molten silicon in the grain filter 52, and proceeds to the vicinity of the surface of the silicon film 14, that is, a substantially completely molten portion.
[0032]
Some crystal grains may be generated inside the grain filter 52 after the laser irradiation. At this time, by setting the cross-sectional dimension (diameter of a circle in this embodiment) of the grain filter 52 to be about the same as or slightly smaller than one crystal grain, the upper part (opening) of the grain filter 52 is formed. Comes to reach only one crystal grain. As a result, in the substantially completely melted portion of the silicon film 14, crystal growth proceeds with the crystal grains reaching the upper portion of the grain filter 52 as nuclei, and as shown in FIG. A substantially single crystal grain 16a of silicon is formed around the filter 52.
[0033]
According to the experiments of the present inventors, the defect density in a substantially single crystal grains of the thus formed silicon is estimated to be approximately ^{3.2 × 10 1 6 cm -3 eV} -1. This is a value much smaller than the defect density of 10 ¹⁸ cm ⁻³ eV ⁻¹ in the polycrystalline silicon film by the conventional laser crystallization technique, and the present method can obtain excellent substantially single crystal grains having a small defect density. You can see that it is done. However, the thickness of the silicon film including the substantially single crystal grains is set to the value of R.S. When the thickness is set to about 250 nm or more as described in the literature of Ishihara et al., The total number of defects in the substantially single crystal grains becomes large, and the S value of the thin film transistor formed there is realized by a conventional polycrystalline silicon thin film transistor. The characteristic is inferior to the S value (about 0.2 V / dec.). In view of the above, in the present invention, in consideration of the defect density in the substantially single crystal grains, the thickness of the silicon film is appropriately adjusted in order to realize characteristics equal to or higher than that of a conventional polycrystalline silicon thin film transistor in a thin film transistor using the same. Film thickness.
[0034]
Specifically, the thickness of the gate insulating film (silicon oxide film) is set so that the interface state density between the silicon film and the silicon oxide film becomes 3.0 × 10 ¹⁰ cm ⁻² eV ⁻¹ by a method described later. In a thin film transistor formed with a thickness of 100 nm, an S value of about 0.2 V / dec. Can be realized. This can be determined by the following equation for determining the S value.
[0035]
S-value _{= kT / q · ln10 · (} 1+ (qN bk t s i + qD it) / C o x)
Where k is Boltzmann coefficient, T is the absolute temperature, q is the elementary charge _{quantity, N bk} defect density in the silicon _{film, t s i} is a silicon film _{thickness, D it} is the interface state _{density, C o x} is silicon oxide This is the capacity per unit area of the film.
[0036]
According to this equation, the S value is reduced by further reducing the silicon film thickness (the film thickness of the substantially single crystal grain), and the characteristics are superior to those of a conventional polycrystalline silicon thin film transistor. In addition, since the S value can be improved by reducing the thickness of the silicon oxide film serving as the gate insulating film, the silicon film thickness can be increased accordingly. When the silicon oxide film is deposited on the silicon film containing crystal grains, the silicon oxide film at the corners (edges) of the island-shaped silicon film becomes thinner. Undesirable characteristics such as an increase in leakage current and off current are obtained. Therefore, in the present invention, the thickness of the silicon film serving as a channel formation region is set to 150 nm or less in order to realize an S value superior to that of the conventional polycrystalline silicon thin film transistor in the thin film transistor using the substantially single crystal grains. Further, as described above, a thin film transistor having an even higher S value can be realized by reducing the thickness of the silicon oxide film (gate insulating film) to 100 nm or less to such an extent that the undesirable characteristics of the thin film transistor do not occur.
[0037]
FIG. 3 is a plan view showing a substantially single crystal grain 16 a of silicon formed on the glass substrate 10. As shown in the figure, the substantially single crystal grains 16a of silicon are formed in a range substantially centered on the grain filter 52. A thin film transistor is formed using such a substantially single crystal grain 16a as described below.
[0038]
FIG. 4 mainly shows the gate electrode, the source region, the drain region, and the channel formation region of the thin film transistor using a part of the substantially single crystal grain 16a of silicon as the transistor region 18 shown in FIG. It is the top view which omitted the structure and showed. In the thin film transistor T of the present embodiment, the grain filter 52 is included in the source or drain region of the transistor region 18, and more preferably, the region including the grain filter 52, which is likely to be disordered in crystallinity, is formed in the channel formation region. It is arranged not to be included. Specifically, it is preferable that the grain filter is separated from the channel formation region by about 0.5 μm to 1 μm.
[0039]
Next, a step of forming the thin film transistor T shown in FIG. 3 will be described. FIG. 5 is an explanatory diagram illustrating a process of forming the thin film transistor T. FIG. 4 is a cross-sectional view taken along the line AA ′ shown in FIG.
[0040]
As shown in FIG. 5A, the silicon film 16 including the substantially single crystal grains 16a of silicon is patterned, and a portion unnecessary for forming the thin film transistor T is removed and shaped.
[0041]
Next, as shown in FIG. 5B, a silicon oxide film 20 is formed on the upper surfaces of the silicon oxide film 12 and the silicon film 16 by electron cyclotron resonance PECVD (ECR-PECVD) or PECVD. Especially in the case of using the ECR-PECVD method, _{"Low temperature formation of high quality SiO 2} / Si interface using ECR-PECVD " (D.Abe et al., AM-LCD 2001, p.98) have been reported in the street In addition, the interface state density between the silicon film and the silicon oxide film can be set to a very small value of about 3.0 × 10 ¹⁰ cm ⁻² eV ⁻¹ , and a good interface can be formed. The silicon oxide film 20 has a thickness of about 100 nm or less and functions as a gate insulating film of a thin film transistor.
[0042]
Next, as shown in FIG. 5C, a gate electrode 22 and a gate wiring film are formed by patterning after forming a metal thin film such as tantalum or aluminum by a film forming method such as a sputtering method. Then, a source region 24, a drain region 25, and a channel forming region 26 are formed in the silicon film 16 by performing a so-called self-aligned ion implantation in which an impurity element serving as a donor or an acceptor is implanted using the gate electrode 22 as a mask. For example, in this embodiment, phosphorous (P) is implanted as an impurity element, and then the XeCl excimer laser is adjusted to an energy density of about 200 mJ / cm ^{2 to} about 400 mJ / cm ² and irradiated to activate the impurity element. , N-type thin film transistors are formed. Note that the activation of the impurity element may be performed by performing heat treatment at a temperature of about 250 to 400 ° C. instead of laser irradiation.
[0043]
Next, as shown in FIG. 5D, a silicon oxide film 28 having a thickness of about 500 nm is formed on the upper surfaces of the silicon oxide film 20 and the gate electrode 22 by a film forming method such as a PECVD method. Next, contact holes are formed to penetrate the silicon oxide films 20 and 28 and reach the source region 24 and the drain region 25, respectively. In these contact holes, aluminum, tungsten, or the like is formed by a film forming method such as a sputtering method. The source electrode 30 and the drain electrode 31 are formed by embedding and patterning a metal. The thin film transistor T of the present embodiment is formed by the manufacturing method described above.
[0044]
As described above, in the present embodiment, by setting the thickness of the silicon film 16 to 30 nm to 150 nm, the total number of crystal defects in the substantially single crystal grains 16a of silicon can be reduced, and a thin film transistor having good characteristics can be obtained. It becomes. In addition, since the grain filter 52 and the silicon film in the vicinity thereof are arranged so as not to be included in the channel formation region 26, it is possible to prevent the channel formation region 26 from including a silicon film having poor crystallinity. The characteristics of the thin film transistor can be further improved. Further, when forming the substantially single crystal grains 16a, an excimer laser having a relatively long pulse width of about 150 ns to 250 ns is used, so that even the relatively thin silicon film 16 can be used to form the substantially single crystal grains 16a. Can be formed.
[0045]
Next, an application example of the thin film transistor according to the present invention will be described. The thin film transistor according to the present invention can be used as a switching element of a liquid crystal display device or as a driving element of an organic EL display device.
[0046]
FIG. 6 is a diagram illustrating a connection state of the display device 100 which is an example of the electro-optical device according to the embodiment. As shown in FIG. 5, the display device 100 is configured by disposing a pixel region 112 in a display region 111. The pixel region 112 uses a thin film transistor for driving an organic EL light emitting element. A thin film transistor manufactured by the manufacturing method of the above-described embodiment is used. From the driver region 115, a light emission control line (Vgp) and a write control line are supplied to each pixel region. From the driver region 116, a current line (Idata) and a power supply line (Vdd) are supplied to each pixel region. By controlling the write control line and the constant current line Idata, current programming is performed for each pixel region, and light emission is controlled by controlling the light emission control line Vgp. Is also available transistor of the present invention for the driver area 115 and 116, it is also suitable for a buffer circuit for selecting the particular light emitting control line included in 115 the driver region (V g _{a p)} and a write control line.
[0047]
The display device 100 is applicable to various electronic devices. FIG. 7 is a diagram illustrating an example of an electronic device to which the display device 100 can be applied.
[0048]
FIG. 7A illustrates an example of application to a mobile phone. The mobile phone 230 includes an antenna unit 231, a voice output unit 232, a voice input unit 233, an operation unit 234, and the display device 100 of the present invention. . Thus, the display device of the present invention can be used as a display unit.
[0049]
FIG. 7B illustrates an example of application to a video camera. The video camera 240 includes an image receiving unit 241, an operation unit 242, an audio input unit 243, and the display device 100 of the present invention. Thus, the display device of the present invention can be used as a finder or a display unit.
[0050]
FIG. 7C shows an example of application to a portable personal computer (so-called PDA). The computer 250 includes a camera unit 251, an operation unit 252, and the display device 100 of the present invention. As described above, the display device of the present invention can be used as a display unit.
[0051]
FIG. 7D shows an example of application to a head-mounted display. The head-mounted display 260 includes a band 261, an optical system storage unit 262, and the display device 100 of the present invention. Thus, the display panel of the present invention can be used as an image display source.
[0052]
FIG. 7E shows an example of application to a rear-type projector. In the projector 270, a light source 272, a synthetic optical system 273, mirrors 274 and 275, a screen 276, and a display of the present invention are provided in a housing 271. An apparatus 100 is provided. Thus, the display device of the present invention can be used as an image display source.
[0053]
FIG. 7F shows an example of application to a front type projector. The projector 280 includes an optical system 281 and a display device 100 of the present invention in a housing 282, and can display an image on a screen 283. Thus, the display device of the present invention can be used as an image display source.
[0054]
The display device 100 using the transistor of the present invention is not limited to the above-described example, and can be applied to any electronic device to which an active or passive matrix liquid crystal display device and an organic EL display device can be applied. For example, in addition to the above, the present invention can also be used for a fax device with a display function, a finder of a digital camera, a portable TV, an electronic organizer, an electronic bulletin board, a display for advertising, and the like.
[0055]
【The invention's effect】
As described above, according to the present invention, when forming substantially single crystal grains of a semiconductor used for a channel formation region of a thin film transistor, the thickness of the semiconductor is set to an appropriate value. It is possible to realize an S value equal to or greater than that of a thin film transistor. This makes it possible to obtain a thin film transistor having excellent field-effect mobility and S value and excellent characteristics.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating a step of forming a silicon film.
FIG. 2 is an explanatory diagram illustrating the maximum grain size of substantially single crystal grains of silicon.
FIG. 3 is a plan view showing substantially single crystal grains of silicon formed on a glass substrate.
FIG. 4 is a plan view of a thin film transistor formed using substantially single crystal grains of silicon, mainly showing a gate electrode, a source region, a drain region, and a channel formation region, and omitting other components. is there.
FIG. 5 is an explanatory diagram illustrating a step of forming a thin film transistor.
FIG. 6 is a diagram illustrating a connection state of a display device as an example of the electro-optical device.
FIG. 7 illustrates an example of an electronic device to which a display device can be applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Glass substrate 12, 20, 28 Silicon oxide film 14, 16 Silicon film 16a Substantially single crystal grain 18 of silicon Transistor region 22 Gate electrode 24 Source region 25 Drain region 26 Channel formation region 30 Source electrode 31 Drain electrode 52 Grain filter 100 Display device T Thin film transistor

Claims (12)

A method for manufacturing a semiconductor device, wherein a semiconductor film is formed on a substrate and a thin film transistor is formed using the semiconductor film,
A starting point forming step of forming a starting point to be a starting point during crystallization of the semiconductor film on the substrate;
A semiconductor film forming step of forming the semiconductor film on the substrate on which the starting portion is formed,
Performing a heat treatment on the semiconductor film, a heat treatment step of forming substantially single crystal grains having the center substantially at the starting point;
Patterning the semiconductor film, a patterning step of forming a transistor region to be a source, drain region and a channel formation region;
An element forming step of forming a thin film transistor by forming a gate insulating film and a gate film on the transistor region,
The method of manufacturing a semiconductor device, wherein in the patterning step, a transistor region is formed so that a thickness of the semiconductor film is 30 nm to 150 nm. 2. The method according to claim 1, wherein, in the patterning step, a transistor region is formed such that the starting point of the substantially single crystal grain is not included in the channel formation region. The method according to claim 1, wherein the starting point is a concave portion formed in the substrate. 4. The method according to claim 3, wherein the heat treatment is performed under a condition that the semiconductor film in the concave portion is in a non-melted state and other portions are melted. 5. The method according to claim 1, wherein the heat treatment is performed by pulsed laser irradiation having a pulse width of 150 ns to 250 ns. The method according to claim 1, wherein the semiconductor film is an amorphous or polycrystalline silicon film. A semiconductor device formed using a semiconductor film formed over a substrate and including a thin film transistor having a source, a drain region, and a channel formation region,
The semiconductor film includes substantially single crystal grains formed from a starting point provided on the substrate as a starting point,
A semiconductor device, wherein a thickness of a semiconductor film in the channel formation region of the thin film transistor is 30 nm to 150 nm. The semiconductor device according to claim 7, wherein the semiconductor film in the channel formation region is further patterned so as not to include the starting portion and a region in the vicinity thereof. The starting point is a recess formed in the substrate,
The semiconductor film according to claim 7, wherein the semiconductor film is formed by performing heat treatment and crystallization so that a non-melted portion remains in the semiconductor film in the concave portion and the other is melted. Semiconductor device. 10. The semiconductor device according to claim 7, wherein the semiconductor film is obtained by subjecting an amorphous or polycrystalline silicon film to heat treatment by a pulse laser having a pulse width of 150 ns to 250 ns. Semiconductor device. An electro-optical device comprising the thin-film transistor according to claim 7 as a driving element of a display pixel. An electronic apparatus comprising the electro-optical device according to claim 11.

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