JP2005285827A - Method and device for crystallizing semiconductor thin film, thin film transistor and display device using the thin film transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystallizing method and a device of a semiconductor thin film which control crystal orientation, and to provide a phase shifter, a thin film transistor and a display device. <P>SOLUTION: Crystallization is performed in one direction growth with a condition that a distance between a top position 1b and a bottom position 1a in light intensity distribution becomes 3 to 10μm, by setting the film thickness of the non-single crystal semiconductor thin film 4 to be 50 to 200nm and using a phase shifter 6 forming V-type light intensity distribution 1 immediately after the irradiation of a laser on a substrate 2. Thus, the crystallized semiconductor thin film where a crystal growth orientation is preferentially orientated in ä100} with high growth speed, and the thin film transistor are obtained as a system where the normal orientation of a film face, and a grain widthwise orientation vertical to the growth orientation in the film face are not preferentially oriented in ä111}. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor thin film crystallization method and a crystallization apparatus for crystallizing a semiconductor thin film using laser light, a thin film transistor using this technique and a manufacturing method thereof, a semiconductor device, and a liquid crystal using this thin film transistor, The present invention relates to a display device such as an organic EL.

Conventionally, in order to increase the mobility of polysilicon thin film transistors and reduce the variation in threshold voltage, the polysilicon thin film (p-silicon thin film) has a large grain size and an array with large grain crystal grain position controllability. In addition, efforts related to surface orientation control are being made by companies, universities, research institutions, and the like. Among them, crystallization of an amorphous silicon thin film (a-silicon thin film) by an excimer laser using a phase shifter is introduced in Japanese Patent Laid-Open No. 2000-308859 (Patent Document 1). In addition, with respect to crystallization of a silicon thin film by excimer laser using a phase shifter, a Δ-type or strip-type large grain array can be formed with good position control. For example, surface science 21,278 ( 2000) (Non-Patent Document 1).
JP 2000-308859 A Surface Science 21,278 (2000)

  However, in the above prior art, when the a-silicon thin film is changed to the p-silicon thin film, the crystal grains can be enlarged, but the plane orientation of the enlarged crystal grains cannot be controlled. Since this is not possible, it is difficult to reduce the variation in threshold voltage.

  Accordingly, an object of the present invention is to provide a technique capable of crystallizing an amorphous semiconductor thin film with crystal grains having a large grain size so that the plane orientation can be controlled.

  In order to solve the above problems, a semiconductor thin film crystallization method according to one embodiment of the present invention includes a linear minimum temperature region on a semiconductor thin film, and linear maximum temperature regions on both sides of the minimum temperature region. And a temperature gradient direction according to the temperature distribution is in the plane of the semiconductor thin film and along a direction in the plane of the semiconductor thin film perpendicular to the direction of the temperature gradient. There is a crystallization start region in the line-shaped minimum temperature region, the thickness of the semiconductor thin film is in the range of 50 to 200 nm, and the distance between the minimum temperature region and the maximum temperature region is 3 to 10 μm. By crystallizing under conditions, the semiconductor thin film is crystallized mainly in the {100} orientation in the crystal growth direction, that is, the temperature gradient direction.

A crystallization apparatus according to another aspect of the present invention is an apparatus for crystallization by irradiating a semiconductor thin film formed on a substrate and having a thickness of 50 to 200 nm with laser light.
A laser light source;
At the start of crystallization of the semiconductor thin film, a temperature distribution of an inverse peak pattern having a line-shaped minimum temperature region and a line-shaped maximum temperature region on both sides of the minimum temperature region is formed on the semiconductor thin film, and this temperature The direction of the temperature gradient according to the distribution is in the plane of the semiconductor thin film, and there is a crystallization start region by the line-shaped minimum temperature region along the direction in the plane of the semiconductor thin film perpendicular to the direction of the temperature gradient. And a means for optically modulating the laser beam from the laser light source so that the distance between the minimum temperature region and the maximum temperature region is 3 to 10 μm.

  According to the present invention, it is possible to obtain a high-quality crystalline semiconductor thin film having, for example, a substantially triangular laterally grown crystal grain array structure whose position is controlled by one shot of laser irradiation and whose plane orientation is controlled in the crystal growth direction. In the thin film transistor using the crystallized semiconductor thin film obtained in the present invention, the crystal growth plane is preferentially oriented in {100} in the channel region. Therefore, by adjusting the current direction to the crystal growth direction, The mobility is higher than that of a silicon thin film transistor, and the variation in threshold voltage is particularly small. When the thin film transistor of the present invention is applied to a display device such as a liquid crystal display or an organic EL, it becomes possible to form a high-performance arithmetic element or the like in a peripheral circuit. Is big. In addition, since the phase shifter is simply inserted into the optical path, the optical system is not complicated and adjustment takes less time, which is suitable for mass production.

  The principle of crystallization of a semiconductor thin film according to the present invention and preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  Laser light that has been modulated using a dot-type or line-type phase shifter, which will be described later, as a light modulation element is composed of a linear minimum light intensity region and line maximums on both sides of this minimum light intensity region. The light intensity distribution has a reverse peak pattern having a light intensity region. When the phase shifter dots or lines are repeatedly formed, the light intensity distribution also appears to have the reverse peak pattern repeated. In the present specification, such a reverse peak pattern is described and illustrated as a substantially V-shaped pattern for ease of explanation. Therefore, a preferable light intensity distribution is a substantially V-shaped pattern repeat as indicated by reference numeral 1 in FIG. 1D and indicated by reference numeral 53 in FIG. In this V-shaped pattern, valleys (bottom positions) 1a and 53a correspond to the minimum light intensity region, and peaks (top positions) 1b and 53b correspond to the maximum light intensity region. It was found that these valleys and ridges had a line (straight line) shape extending perpendicular to the paper surface.

  By irradiating the semiconductor thin film with a laser beam having such a light intensity distribution at the start of crystallization of the semiconductor thin film, a temperature distribution corresponding to the light intensity pattern is formed on the semiconductor thin film, and the temperature gradient is the semiconductor. It occurs in the thin film and the crystal growth direction is limited to one direction. As a result, anisotropy is imparted to the crystal growth rate in the crystal growth direction, the normal direction (film thickness direction) of the film surface perpendicular to the growth direction, and the width direction of the crystal grains.

  Next, an example of a phase shifter (phase shift mask) used in the present invention will be described.

  Here, the “phase shifter” is a means for improving the resolving power of optical lithography, and is a spatial intensity modulation optical element that has a function of modulating the light intensity of transmitted light and modulating the phase according to the transfer pattern. Say.

  FIGS. 1A and 1B show a line type phase shifter 6. The phase shifter 6 is provided with adjacent regions having different thicknesses on a transparent medium, for example, a quartz base material, and diffracts and interferes the incident laser beam at the boundary of a step (phase shift portion) between these regions. A periodic spatial distribution is given to the intensity of the incident laser beam. The phase shifter 6 includes a first strip region (phase region) 6a in which the phases alternately arranged are, for example, π so that the adjacent patterns have an opposite phase (for example, a shift of 180 °), and the phase is 0 second strip region (phase region) 6b. These strip regions (phase shift line regions) have a width of 6 to 20 μm, for example 10 μm. In general, assuming that the wavelength of the laser beam is λ and the refractive index of the transparent medium is n, the film thickness t of the transparent medium necessary to give a phase difference of 180 ° between the regions is t = λ / 2 (n−1). Given in. Accordingly, when the refractive index of the quartz substrate is 1.5, when KrF excimer laser light is used as the laser light, this wavelength is 248 nm. Therefore, in order to give a phase difference of 180 °, a step of 248 nm May be provided between the regions by a method such as etching. The region thinly formed by this etching is the first strip region 6a, and the region not etched is the second strip region 6b.

  In the phase shifter having such a configuration, the phase of the laser beam that has passed through the thick second phase region 6b is delayed by 180 ° compared to the laser beam that has passed through the thin first phase region 6a. As a result, interference and diffraction occur between the laser beams, and a V-shaped continuous light intensity distribution 1 as shown in FIG. 1D is obtained. When a semiconductor thin film is irradiated with laser light having such a light intensity distribution, at the start of crystallization, a line-shaped minimum temperature region (bottom portion or valley portion) is formed on both sides of the minimum temperature region. A temperature distribution having an inverse peak pattern having a linear maximum temperature region (top portion or peak portion) can be formed.

  Next, another example of the method for manufacturing the phase shifter will be described.

  First, a light shielding film pattern is formed, and a transparent film having a predetermined thickness is formed thereon. SOG (Spin on glass) is used as the transparent film material. A spin coating method is used as a film forming method. The applied transparent film is baked at a predetermined temperature. Next, a resist is applied on the transparent film, and the resist film is exposed to form a pattern or dot pattern latent image of a predetermined line and space step, and the resist film is developed to form a predetermined line and space step pattern or dot. Form a pattern. Here, the predetermined pattern is periodically repeated at predetermined intervals.

  Next, the transparent film exposed to the opening of the resist film is selectively removed using a dry etching method such as plasma etching. Further, when the resist film and the light shielding film are removed from the transparent film by ashing or the like, a phase shifter having a predetermined pattern is obtained.

  The phase shifter thus produced causes Fresnel diffraction to occur independently in the divided light beam group at the level difference. Since these diffraction patterns are superimposed on the substrate surface by multiple reflection, the light intensity distribution on the substrate surface is highly dependent on the phase shifter parameters (gap d and phase difference θ), but affects the light intensity distribution. As other parameters, the spread amount (ε) of light beams incident on the phase shifter and the coherence between the light beams are complicatedly related. The phase difference does not necessarily need to be 180 °, and may be any phase difference that can realize the strength of the laser beam. The laser light transmitted through such a phase shifter has a light intensity distribution that becomes a V-type repetition shown in FIG. FIG. 1C shows an example of a semiconductor thin film irradiated with such a laser beam. In this figure, the semiconductor thin film is denoted by reference numeral 4 and is formed between the lower insulating film 3 and the upper insulating film 5 on the insulating substrate 2 such as glass.

  The dot-type phase shifter 51 shown in FIGS. 2A and 2B is formed by periodically forming, for example, a rectangular dot step (recess) 52 on a transparent medium, the size of which gradually decreases. is there. With such a phase shift, as shown in FIG. 2 (d), the laser beam is optically modulated, so that the valley 53 a corresponds to the maximum recess 52 and the peak corresponds to the minimum recess 52. A V-shaped repetitive light intensity distribution 53 in which the portion 53b is generated can be formed. 2 (c) is substantially the same as FIG. 1 (c), and a description thereof will be omitted.

  The inventors crystallized amorphous silicon thin films having different thicknesses by the laser annealing technique described in Non-Patent Document 1 using the phase shifters 6 and 51 as described above. The results when the film thicknesses at this time are 30 nm, 50 nm, 100 nm, and 200 nm are shown in FIG. In this figure, the horizontal axis indicates the film thickness (nm), and the vertical axis indicates the grain width (μm). In the present invention, the term “grain width” indicates the length in the direction perpendicular to the crystal growth direction of each grown crystal grain in the plane, and will be described later with reference to FIGS. Indicated by W. From FIG. 3, when the film thickness of the silicon thin film is in the range of 50 to 200 nm, the grain width decreases as the film thickness decreases, and even when the film thickness decreases to 30 nm, the film thickness is 50 nm. It can be seen that there has been little change.

  Furthermore, the present inventors changed the film thickness of the silicon thin film as described above and formed temperature distributions having various V-shaped intervals on the silicon thin film using various phase shifters having different phase intervals. Crystallized. FIG. 4 shows an example of the result at this time. In this figure, (a) shows the case where the film thickness is 200 nm, (b) shows the case where it is 100 nm, (c) shows the case where it is 50 nm, and (d) shows the case where it is 30 nm. Further, the V-shaped interval on the horizontal axis indicates the interval between the valley and the peak of the V-shaped temperature distribution. In this figure, dots indicate the measurement result of the grain width, and straight lines indicate the inclination of the light intensity distribution assumed based on the measurement result, that is, the temperature gradient. From this measurement result, it can be seen that although the degree of change in grain width decreases as the thickness of the silicon thin film decreases, the grain width increases as the temperature gradient decreases.

  From the results shown in FIG. 3 and FIG. 4, the thinner the silicon thin film is, and the steeper the temperature gradient on the surface of the silicon thin film is, the narrower the grain width of the grown crystal grains and the different the crystal growth. It can be seen that the directionality has increased.

  Next, based on the results of FIG. 3, the characteristics of the thin silicon thin film are shown by comparing the crystal morphology and crystallization process when the silicon thin film is thick and thin within the range of 30 and 200 nm. As shown in FIG. When the silicon thin film 4b is 30 nm (b), compared with the case (a) where the silicon thin film 4a is 200 nm, the heat capacity of the Si layer is small and the cooling rate during crystallization is large. In either case, according to the V-type light intensity distribution (temperature distribution), the growth crystal nuclei 12a and 12b are first generated in a line shape (indicated by a broken line) corresponding to the position of the valley (minimum temperature region) of the intensity distribution. To do. However, in the case of 200 nm, since the heat capacity is large and the cooling rate is low, the latent heat at the time of crystal nucleus generation is difficult to escape, and as a result, the generation interval of growth nuclei becomes wide. For this reason, growth in the grain width W direction is also possible within the range of the distance between the growth crystal nuclei, and Δ-shaped laterally grown grains 13a are generated as shown in FIG. On the other hand, in the case of 30 nm, since the latent heat easily escapes, the generation interval of the growth crystal nuclei becomes narrow. For this reason, as shown in (b), the growth in the grain width direction is restricted, and the width of the laterally grown grains 13b becomes narrow. In FIG. 5, since the temperature distribution of the sample and the laser beam is the same as that shown in FIGS. 1 and 2, the same reference numerals are given except that the silicon thin films are indicated by 4a and 4b, and the description is omitted. doing.

  FIG. 6 compares the difference in crystal form and crystallization process due to the difference in the slope of the V-type light intensity distribution based on the result of FIG. As shown in (a), when the temperature gradient becomes gentler, the fluctuation range from the temperature gradient direction in the crystal growth direction becomes larger and the grain width W becomes larger as compared with the steep case shown in (b).

  FIG. 7 shows the relationship between the slope of the silicon film thickness and the light intensity distribution, that is, the temperature gradient, and the plane orientation in the growth direction of the crystal structure. In this figure, the surface of the crystallized silicon thin film is etched by a predetermined distance, and the result measured by the Electron Back Scattering Pattern (EBSP) method is a simplified diagram of the inverse pole figure. In this figure, each vertex indicates each plane orientation of {001}, {101}, {111}, and the orientation is determined by the position of the hatched area in this area. This figure shows that when the film thickness is reduced and the inclination is made steep, the film starts to be oriented to {100} at a film thickness of 100 nm and an inclination of 5 μm, and is oriented to {110} at a film thickness of 30 nm. FIG. 8 illustrates the relationship between the crystal form and the crystal orientation in the growth direction of the laterally grown grains in relation to the thickness of each silicon thin film and the slope of the light intensity distribution. As the film thickness becomes thinner (the film thickness direction is perpendicular to the paper surface) and the inclination becomes steep, the grain width becomes narrower. When the film thickness is 200 nm and the inclination is 10 μm, the crystal orientation in the growth direction is easily oriented to {100} or {110}, but when the film thickness is 100 nm and the inclination is 5 μm, the crystal orientation is easily oriented to {100}. This is because the range of the growth direction is narrowed, and the growth direction is limited to {100}, which is the fastest growing, and is easily formed. When the film thickness is 30 nm, the preferred orientation in the growth direction changes from {100} to {110}. The reason for this will be described below.

Considering each direction independently, the normal (film thickness) direction is limited by the growth of the film thickness, and the influence of the Si / SiO ₂ interface (the interface between the silicon thin film 4 and the insulating film 3) increases as the film thickness decreases. Therefore, it tends to be oriented to {111} at the slowest growth edge and {001} having the lowest Si / SiO ₂ interface energy. Growing crystal nuclei generated adjacent to each other in the grain width direction simultaneously grow in the lateral direction, so that the growth is limited and the crystal grains tend to be oriented at {111} at the slowest growth edge. The lateral growth direction is the direction of the temperature gradient of the ultra-quick solidification system, and it tends to be oriented at {001} and {101} at the growth edge where the speed is high.

  Considering the geometric conditions here, when the normal direction and the grain width direction are oriented in {111}, the lateral growth direction cannot be {001}. This is because they are not orthogonal. As a result, the orientation is {110}. For the same reason, the normal direction and the grain width direction cannot be simultaneously oriented to {111}. Therefore, either or both of the normal direction and the grain width direction are inclined from {111}, but the normal direction is less likely to be {101}, so the grain width direction is less likely to be {001}. , {111}, {101}.

Regarding the plane orientation in the normal direction of the laser crystallized silicon thin film, {100} has a feature that the Si / SiO ₂ interface energy is minimized. On the other hand, a thin film is characterized by being oriented in {111}, which is the closest packed surface of a diamond structure such as a silicon crystal.

Considering the above, the film thickness direction is oriented to {111} and {001} by the effect of the thin film and the effect of the Si / SiO ₂ interface energy in the normal direction. As a result, the grain width direction is oriented in {111} {101}.

  That is, the growth direction is preferentially oriented to {100} if a system that rapidly crystallizes in one direction under the condition that the normal direction and the grain width direction of the film surface are not easily {111}.

  As a laser beam, a KrF excimer laser beam having a wavelength of 248 nm was used, and the pulse duration of one shot was set to 20 to 200 ns. Under the above conditions, the phase shifter 6 is inserted between the laser light source and the sample made of the lower insulating film 3, the amorphous semiconductor thin film (silicon thin film) 4, and the upper insulating film 5 on the insulating substrate 2 such as glass, When the pulse laser beam is irradiated, the laser beam that has passed through the phase shifter 6 causes diffraction and interference at the stepped portion, and periodically becomes strong and weak. The semiconductor thin film 4 is completely melted at the portion where the laser beam is strong, and a temperature gradient is generated between the portion where the laser beam is weak. It was found that crystal nuclei were generated at the weakest part of the laser beam, and the molten silicon solidified along the temperature gradient with time, and one-dimensional lateral crystal growth proceeded.

  In the present invention, the non-single-crystal semiconductor layer to be crystallized is generally an amorphous silicon (a-Si) film having a predetermined thickness. It may be a mixed structure containing crystalline silicon, or may be a polycrystalline silicon (poly-Si) film. Further, the present invention is not limited to silicon and can be applied to other semiconductor thin films.

In the present invention, the film thickness of the non-single-crystal semiconductor layer is in the range of 50 to 200 nm from the above consideration. If the film thickness is less than 50 nm, the growth direction is not oriented to {100} due to the effect of the thin film thickness during crystallization as described in FIG. On the other hand, if the film thickness exceeds 200 nm, the range of the crystal growth direction becomes wide, and the orientation in the growth direction is lost. The range of the film thickness is preferably 50 nmu to 100 nm. This is because if the film thickness exceeds 100 nm, the final solidified portion may rise during crystallization, and the unevenness may increase. If such unevenness occurs, there may be a problem in the subsequent wiring process.
In the present invention, it is preferable that the non-single-crystal semiconductor layer is irradiated with laser light having a light intensity distribution through an insulating cap film. It is preferable to use a SiO ₂ film or a SiON film having a predetermined thickness for the cap film. The thickness of the cap film can be in the range of 50 to 500 nm. This is because when the film thickness is less than 50 nm, the function as a cap film is lost, and when the film thickness exceeds 500 nm, the attenuation of the laser beam intensity becomes excessive.

  The V-shaped period of the light intensity distribution in FIG. 1, that is, the interval is preferably 6 to 20 μm (the distance between the peak and valley is 3 to 10 μm). If the thickness is less than 6 μm, the grain length of the laterally grown grains is shortened, which is contrary to the object of the present invention of forming large crystal grains. On the other hand, if the grain size exceeds 20 μm, the lateral growth stops halfway. Therefore, the film cannot be filled with crystal grains. The interval of the repetitive V-shaped light intensity distribution is closely related to the grain length of the structure to be finally formed, and is a distance at which adjacent laterally grown grains can just meet each other, or a distance slightly shorter than that. Is most desirable.

Further, the fluence at the top position of the laser beam having the light intensity distribution is preferably set in a range of 700 to 1300 mJ / cm ² . Here, “fluence” is a scale representing the energy density of the laser, and refers to a time integral of the amount of energy per unit area. This is because if the average fluence is less than 700 mJ / cm ² , an uncrystallized non-crystallized portion tends to remain, whereas if the average fluence exceeds 1300 mJ / cm ² , the semiconductor thin film evaporates.

  The light modulation element of the present invention is preferably a phase shifter made of a light-transmitting material and having steps of a predetermined pattern periodically and repeatedly arranged on the light transmission surface side. The pattern only needs to form a V-type light intensity distribution. For example, when a line type phase shifter composed of repetition of a line and a space step is used by using a proximity type phase modulation optical system crystallization apparatus, the distance between the line and the space step is set to 6 μm or more and less than 20 μm. It is preferable. The reason for limiting the numerical value is the same as the reason for limiting the numerical value of the interval of the V-type light intensity distribution described above. By using a phase shifter with such an interval, approximately Δ-type crystal grains having a lateral growth length of 3 to 10 μm can be formed.

  When a phase shifter is used in a proximity optical system, the distance d from the light transmission surface of the phase shifter to the incident surface of the substrate can be variously changed, but is most preferably adjusted to a range of 50 to 500 μm. . This is because if the distance d is less than 50 μm, the multiple reflection between the phase shifter and the substrate becomes too strong, resulting in a light intensity distribution with a large variation in fluence on the substrate surface. On the other hand, if the distance d exceeds 500 μm, it becomes difficult to obtain a clear beam profile which is an advantage when using the phase shifter in the proximity method.

  In the present invention, for example, when a phase shifter is used in a projection type optical system (projection method) and a line type phase shifter is used, a value obtained by multiplying the interval between the line and the space step by the reduction magnification of the reduction lens is obtained. The thickness is 6 μm or more, preferably 8 μm or more and less than 20 μm. The reduction magnification of the reduction lens can be variously changed in the range from 1/1 to 1/20, but is preferably in the range from 1/4 to 1/8, most preferably about 1/5. preferable. In addition to the phase shifter, the optical system used for the projection method is an excimer laser generator for generating excimer laser light, a homogenizer for dividing and making the generated laser light uniform, and the divided laser light at the center of the mask surface. It includes a convex lens for collecting the region, a mask for determining the irradiation region, a telecentric reduction lens for reducing the irradiation region of the mask surface on the substrate surface, a phase shifter, and an XYZ substrate stage. In the projection method, the phase shifter is positioned at the mask surface.

  Hereinafter, various preferred embodiments of the present invention will be described with reference to the accompanying drawings.

First Embodiment As shown in FIG. 9, a laser annealing apparatus, that is, a crystallization apparatus 20 includes a proximity optical system 31. This optical system 31 includes a KrF excimer laser oscillator (generator) 21, a homogenizer 22, a first condenser lens 23, a second condenser lens 26, a mask 27, and a telecentric along the laser optical axis 24. The reduction lens 28 of the mold and the phase shifter 6 are sequentially provided. An XYZθ stage 29 is arranged at the image forming position of the telecentric reduction lens 28 so that the object to be processed 32 is aligned.

The KrF excimer laser oscillator 21 has an energy sufficient to melt an irradiation region of an amorphous silicon thin film 4 to be described later of the object to be processed 32, for example, 700 to 1300 (preferably 1000 on the object to be processed 32). ) It is set to output a laser beam of mj / cm ² .

The homogenizer 22 is for uniformizing the in-plane light intensity of the laser light emitted from the laser oscillator 21. For example, the homogenizer 22 includes a condenser lens and two fish-eye lenses, and divides the incident laser light. The light intensity is uniform.

  The first condenser lens (convex lens) 23 condenses the laser light from the homogenizer 22, and is arranged in a conjugate relationship with the second condenser lens 26 (convex lens). The mask 27 disposed in the emission side optical path of the second condenser lens 26 blocks the ineffective laser light out of the laser light passing through the lens 26 and irradiates only the effective laser light. And an irradiation area set to define the irradiation area.

  The reduction lens 28 is a lens that reduces to 1/1 to 1/20, for example, 1/5 times, and is arranged in a conjugate relationship with the surface of the workpiece 32. The reduction lens 28 is constituted by a telecentric reduction lens for allowing laser light that has passed through the irradiation area of the mask 27 to enter the reduced area on the substrate surface.

    The phase shifter 6 is disposed between the reduction lens 28 and the XYZθ stage 29 and is provided close to the upper surface of the object to be processed 32 placed on the XYZθ stage 29. In the proximity method of the present embodiment, the proximity distance d between the phase shifter 6 and the upper surface of the workpiece 32 is set to 300 μm, for example. In this embodiment, the phase shifter 6 shown in FIGS. 1A and 1B is used as the phase shifter 6, but other types of phase shifters, for example, FIG. The phase shifter 51 shown in b) may be used. In the phase shifter 6 of the present embodiment, lines and space steps (L & S steps) with an interval of 10 μm are arranged. These steps are processed to 248 nm and have a phase difference of 180 °.

  The XYZθ stage 29 can be adjusted so as to be rotatable in the XYZ axial directions and in the θ direction with the Z axis as the central axis. The XYZθ stage 29 has a built-in heater 30 and can heat the workpiece 32 to a predetermined temperature.

The object to be processed 32 has a laminated structure of a substrate 2, a buffer layer 3 sequentially laminated thereon, an amorphous silicon thin film 4, and an insulating cap film 5.

As the substrate 2, when a display device is formed, a transparent insulating substrate such as a glass substrate or a plastic substrate can be used. The buffer layer 3 has, for example, a two-layer structure of a SiO ₂ layer and a SiN layer, and has a function of preventing diffusion of impurities from the substrate 2 and a function of protecting the substrate 2 from heat during the crystallization process. doing. The amorphous silicon thin film 4 is a semiconductor layer that forms a functional element such as a thin film transistor by being polycrystallized or single crystallized. The insulating cap film 5 is formed of, for example, a SiO ₂ film, and the amorphous silicon thin film 4 is stored in a large crystal by storing a pulse laser beam of several tens of n seconds for a predetermined period as heat generated by irradiation. It is an insulating layer having a heat retention effect for crystallization for growing grains.

  Next, a method for crystallizing an amorphous silicon thin film as a non-single-crystal semiconductor thin film using the above apparatus will be described.

  Laser light 15 having a wavelength of 248 nm and a rectangular cross section emitted from the KrF excimer laser oscillator 21 is divided into a divergent beam by a homogenizer 22. Note that the pulse duration of one shot is 30 nanoseconds. Each central beam of the split beam is focused on the center (irradiation region) of the mask 27 by the first condenser lens 23. Since each laser beam is slightly divergent, 27 Illuminate the entire surface. All the light beam groups 25 that have exited the divided minute emission areas irradiate all points on the mask 27, so that even if there is in-plane fluctuations in the light intensity on the laser emission surface, The strength becomes uniform. Then, the central ray of the ray group that has passed through each region of the mask 27, that is, the divergent ray group that has passed through the lens pair in the central portion of the homogenizer 22 is incident on the second condenser lens 26 disposed near the mask 27. Then, it is emitted as a parallel light beam having a uniform light intensity. This parallel light beam passes through the telecentric reduction lens 28 and enters the workpiece 32 that is aligned and placed on the XYZθ stage 29 perpendicularly. Then, according to the emission timing of the pulse laser beam from the laser oscillator 21, the XYZθ stage 29 is stepped by a predetermined pitch distance in the X direction and the Y direction, and the irradiation area of the object to be processed 32 is shifted. In this manner, annealing is repeated, and the irradiated region of the amorphous silicon thin film 4 on the substrate 2 is sequentially crystallized, so that a crystallized region is formed over a predetermined size or the entire silicon thin film. In this way, it is possible to crystallize amorphous silicon of an amorphous silicon thin film on a large area LCD substrate having a side exceeding 1 m, for example, into polycrystalline silicon. In order to shift the irradiation region, any object 32 and laser light incident thereon can be moved relative to each other in the direction along the surface of the object 32 (X and Y directions). Such methods and means may be employed.

  In the apparatus having the above-described configuration, a group of light beams that have passed through the same portion of the mask 27 are collected on one surface of the object to be processed (specifically, the amorphous silicon thin film 4). That is, a reduced image of the mask 27 is projected on the upper surface of the amorphous silicon thin film 4 with uniform light intensity. At this time, a light beam group for irradiating an arbitrary point on the upper surface of the amorphous silicon thin film 4 is made up of light beams divided including the central light beam. The angle formed by a certain light beam and the central light beam is a value determined by multiplying the magnification of the telecentric lens 28 by the angle determined by the geometric shape of the homogenizer 22, that is, the angle formed by the light beam and the central light beam on the mask 27. become. The phase shifter 6 arranged close to the object to be processed 32 causes Fresnel diffraction to occur independently for each of the divided light beam groups. Since these diffraction patterns are superimposed on the upper surface of the amorphous silicon thin film 4, the light intensity distribution on the upper surface of the amorphous silicon thin film 4 has parameters of the phase shifter 6 (the object 32 and the phase shifter 6 In addition to the distance d and the phase difference θ), the spread amount (ε) of the light beam incident on the phase shifter 6 and the coherence between the light beams are complicatedly related.

  Even in the case of laser annealing by proximity method, the L & S interval of the phase shifter (line type phase shifter) or the period of the dot arrangement (dot type phase shifter) is in the range of 6 to 20 μm for the reason described above. It is set.

  In the case of laser annealing by the projection method, it is desirable that the value obtained by multiplying the L & S interval of the phase shifter or the dot array period by the magnification of the reduction lens 28 is in the range of 6 to 20 μm. When the projection method is used, it is relatively easy to move the workpiece 32 stepwise by the XYZθ stage 29, which is effective as a mass production process. The phase difference does not necessarily need to be 180 °, and the phase shift pattern does not necessarily need to be L & S, and any phase difference and phase shift pattern that can realize a V-type repetitive laser beam intensity distribution may be used. Also, the film structure during laser annealing is such that when the silicon thin film absorbs laser light and melts, heat is retained in the silicon thin film, and the substrate is heated suddenly by thermal diffusion from the silicon thin film. In this example, the cap layer 5 is formed on the upper surface of the amorphous semiconductor thin film 4 and the buffer layer 3 is formed on the lower surface. Are formed respectively.

Second Embodiment A laser annealing apparatus 40 shown in FIG. 10 differs from the proximity type apparatus shown in FIG. 9 in that a phase shifter 51 is arranged near the mask 27 and an image of the phase shifter 51 is processed. An optical system adapted to form an image on 32 is used. That is, this optical system is conjugate with an optical system in which the phase shifter 6 is projected onto the surface of the workpiece 32. As the phase shifter, the dot pattern step shown in FIG. 2 is arranged and the dot type phase shifter 51 is used. The other parts are substantially the same as those of the apparatus of FIG. 9, and the same parts as those of FIG.

Example 1
In the first embodiment, the proximity optical system shown in FIG. 9 is used, and the line type phase shifter 6 shown in FIG. 1 is used. The L & S interval of the phase shifter 6 was 10 μm, and the step depth t was 248 nm (phase difference was 180 °).

As a crystallization condition, the film structure of the object to be processed 32 as a sample (cap layer 5 / amorphous semiconductor thin film (silicon thin film) 4 / buffer layer 3 / substrate 2) is SiO ₂ (300 nm) / a-Si. (100 nm) / SiO ₂ (1000 nm) / glass substrate. The average laser fluence was 980 mJ / cm ² . The distance d between the upper surface of the substrate and the phase shifter 6 was 300 μm. The laser beam was a KrF excimer laser beam with a wavelength of 248 nm, and the pulse duration of one shot was 30 nanoseconds.

  The laser light emitted from the excimer laser transmitter 21 has a uniform intensity by the homogenizer 22 and the two lenses 23 and 26, and is modulated by the phase shifter 6 to form a V type as shown in FIG. The object 32 is irradiated with the repeated light intensity distribution.

  FIG. 11 shows the orientation of the crystal structure obtained in Example 1 with respect to the normal direction of the film surface, the crystal grain growth direction, and the crystal grain width direction (direction perpendicular to the crystal grain growth direction). FIG. 8 is a simplified diagram of an inverted pole figure analyzed by EBSP, as in FIG. 7. In this EBSP analysis, a region was specified long in the grain width direction so that orientation could be understood, so that many crystal grains entered. From the inverse pole figure in each direction, it can be seen that the crystal growth direction is oriented to {100}, as can be seen from the deviation of the area indicated by hatching.

Example 2
The crystallization test was performed as follows using the apparatus of the second embodiment shown in FIG. As a condition for crystallization in this demonstration test, the film structure (cap layer 5 / amorphous semiconductor thin film 4 / buffer layer 3 / substrate 2) of the workpiece 32 as a sample is SiO ₂ (300 nm) / a-Si. As a / SiO ₂ (1000 nm) / glass substrate, the thickness of the a-Si layer was changed to 30, 50, 100, and 200 nm. Since the telecentric reduction lens 28 having a magnification of 1/5 was used, the pattern of the phase shifter 51 was converted to a 1/5 pattern on the non-processing body 32.

The laser light emitted from the excimer laser transmitter 21 has a uniform intensity by the homogenizer 22, is modulated by the phase shifter 51, and has a V-type repetitive light intensity distribution as shown in FIG. Then, the workpiece 32 is irradiated. The phase shifter 51 has a dot step so that the period of the V-type light intensity distribution is 10 μm and 20 μm so that the irradiation film surface is filled with laterally grown grains having crystal grain lengths of 5 μm and 10 μm, respectively. Two types having a set period were used. The phase shift of the phase shifter 51 was 180 °. The film thickness of the amorphous semiconductor thin film 4 (a-Si layer) is 30, 50, 100, and 200 nm, and the laser fluence to be irradiated is 820, 920, 1040, and 1280 mJ / cm ² , respectively. . The laser beam was a KrF excimer laser beam with a wavelength of 248 nm, and the pulse duration of one shot was set to 30 nanoseconds.

  Under the above conditions, four amorphous semiconductor thin films 4 having film thicknesses of 30, 50, 100, and 200 nm were crystallized, and the obtained crystals were analyzed. The result is shown in FIG. 7 described above. From this figure, when the combination of the thickness of the silicon thin film and the period of the light intensity distribution is 100 nm and 5 μm, 50 nm and 10 μm, and 50 nm and 5 μm, the growth direction of the crystal grains is oriented to {100}, respectively. I know that. It can also be seen that when the film thickness is 30 nm, the growth direction of the crystal grains is oriented in {110} regardless of the period of the light intensity distribution. At this time, the normal direction of the film surface is unlikely to be {110}, and the grain width direction perpendicular to the growth direction is unlikely to be {100}. This is due to the crystallization process described with reference to FIGS.

Example 3
In Example 3, the projection type optical system shown in FIG. 10 was used. However, the phase shifter 51 having a dot arrangement period of 50 μm and a step depth t of 83 nm (a phase difference of 60 °) was used.

As a crystallization condition, the film structure of the sample was SiO ₂ (300 nm) / a-Si (100 nm) / SiO ₂ (1000 nm) / glass substrate. The laser fluence at the top position (maximum intensity position) of the light intensity distribution was 1040 mJ / cm ² . The magnification of the telecentric reduction lens was 1/5. The laser beam was a KrF excimer laser beam with a wavelength of 248 nm, and the pulse duration of one shot was 30 nanoseconds.

  FIG. 12 shows an inverted pole figure showing the orientation of the crystal structure obtained in Example 3. In the EBSP analysis, a region was specified long in the grain width direction so that orientation could be understood, so that many crystal grains entered. From the reverse pole figure in each direction, it can be seen that the crystal growth direction is oriented in {100}. It can also be seen that the normal direction of the film surface is unlikely to be {111}, and is oriented in the crystal orientation obtained when the rotation axis from {100} to {110} is rotated. However, the orientation in the grain width direction perpendicular to the growth direction is not clearly seen.

Example 4
Also in the fourth embodiment, the projection type optical system of FIG. 10 is used, the magnification of the telecentric reduction lens is set to 1/5, and the period of the V-type light intensity distribution is set to 20 μm in combination with the phase shifter 51. . The phase shifter 51 has a step depth t of 83 nm (phase difference is 60 °).

As a crystallization condition, the film structure of the sample was SiO ₂ (300 nm) / a-Si (50 nm) / SiO ₂ (1000 nm) / glass substrate. The laser fluence at the top position (maximum light intensity position) of the light intensity distribution was 920 mJ / cm ² . The laser beam was a KrF excimer laser beam with a wavelength of 248 nm, and the pulse duration of one shot was 30 nanoseconds.

  FIG. 13 is an inverted pole figure showing the orientation of the crystal structure obtained in Example 4. In the EBSP analysis, a region was specified long in the grain width direction so that orientation could be understood, so that many crystal grains entered. From the inverse pole figure of each direction, it can be seen that the crystal growth direction is oriented to {100}. It can also be seen that the normal direction of the film surface is unlikely to be {111}, and is oriented in the crystal orientation obtained when the rotation axis from {100} to {110} is rotated. Note that no clear orientation is observed in the grain width direction perpendicular to the growth direction.

Third embodiment
Next, with reference to FIGS. 14A to 14D, a thin film transistor having a bottom gate structure will be described together with a manufacturing method thereof. Note that although a manufacturing method of an N-channel thin film transistor is described in this embodiment for convenience, the P-channel type is substantially the same except that the impurity species (dopant species) are changed. In the drawing, one transistor is shown to be formed. However, in practice, a large number of transistors are generally formed on the same insulating substrate at one time.

  As shown in FIG. 14A, on the insulating substrate 2 made of a transparent material such as glass supported on an XYZθ stage 29 (FIGS. 9 and 10), Al, Ta, Mo, W, Cr, A metal film made of Cu or an alloy thereof is formed to a thickness of 100 to 300 nm, patterned, and processed into the gate electrode 101.

Next, as illustrated in FIG. 14B, gate insulating films 102 and 103 are sequentially formed on the insulating substrate 2 including the gate electrode 101. The gate insulating films 102 and 103 of this embodiment have a two-layer structure of gate nitride film (SiN _x ) / gate oxide film (SiO ₂ ). The lower gate nitride film 102 is formed to a thickness of 50 nm by a plasma CVD method (PE-CVD method) using a mixture of SiH ₄ gas and NH ₃ gas as a source gas. Note that other methods such as atmospheric pressure CVD or reduced pressure CVD may be used instead of plasma CVD.

Following the formation of the gate nitride film 102, an upper gate oxide film 103 is formed to a thickness of about 200 nm continuously. Further, an amorphous silicon thin film 4 is continuously formed with a thickness of 100 nm on the gate oxide film 103. After this film formation, dehydrogenation annealing is performed by heat treatment for about 2 hours in a nitrogen atmosphere at a temperature of 550 ° C., and hydrogen contained in the amorphous semiconductor thin film 4 is released. Then, a cap film 5 made of SiO ₂ is formed on the amorphous silicon thin film 4 with a thickness of 300 nm.

  The two-layered gate insulating films 102 and 103, the amorphous silicon thin film 4 and the cap film 5 are continuously formed in the same chamber without changing the processing gas without breaking the vacuum system of the film forming chamber. It is preferable to form a film.

  Next, as shown in FIG. 14B, the amorphous semiconductor thin film 4 is irradiated with the laser beam 25 using the crystallization apparatus described in the first and second embodiments, for example. The crystalline semiconductor thin film 4 is crystallized as follows. As the laser beam 25 at this time, for example, a KrF excimer laser beam having a wavelength of 248 nm is preferably used, but is not limited thereto. Then, after adjusting the irradiation region of the laser light 25 to the amorphous semiconductor thin film 4, the laser light 25 is focused and irradiated so that the periodic pattern of the phase shifter can be transferred to the irradiation region, and further overlapped. In order to prevent this, the XYZθ stage is moved intermittently in the X direction and the Y direction, so that the irradiation region is shifted and repeatedly irradiated to crystallize a region of a predetermined size.

Next, the cap insulating film 5 is peeled off by an etching method, and the crystallized semiconductor thin film 4 (hereinafter referred to as a polycrystalline semiconductor thin film 105) is patterned as shown in FIG. Then, Vth ion implantation is performed for the purpose of controlling Vth of the thin film transistor. In this embodiment, B ⁺ is ion-implanted (indicated by an arrow 104) into the polycrystalline semiconductor thin film 105 so that the dose amount is about 5 × 10 ¹¹ to 4 × 10 ¹² / cm ² . In this Vth ion implantation, for example, an ion beam accelerated at 10 KeV is used.

Subsequently, an SiO ₂ layer having a thickness of about 100 nm to 300 nm is formed on the polycrystalline semiconductor thin film 105 by plasma CVD. In this example, this layer is formed by plasma decomposition of silane gas SH ₄ and oxygen gas to deposit SiO ₂ . The SiO ₂ layer thus formed is patterned into a predetermined shape and processed into a stopper film 106 as shown in FIG. In this case, the stopper film 106 is patterned so as to be aligned with the gate electrode 101 (FIG. 14D) to be formed later by using the back exposure technique. As a result, the portion of the polycrystalline semiconductor thin film 105 located immediately below the stopper film 106 is protected as the channel region Ch, and the upper surface of the other portion is exposed. As described above, B ⁺ ions are implanted in the channel region Ch in advance at a relatively low dose by Vth ion implantation. Subsequently, using the stopper film 106 as a mask, impurities (here, P ⁺ ions) are implanted into the semiconductor thin film 105 by ion doping to form LDD regions on both sides of the stopper film 106. The dose amount at this time is, for example, 5 × 10 ¹² to 1 × 10 ¹³ / cm ² , and the acceleration voltage is, for example, 10 KeV.

Further, after forming a photoresist patterned so as to cover the stopper film 106 and the LDD regions on both sides thereof, the semiconductor thin film 105 is implanted with a high concentration of impurities (here, P ⁺ ions) using this as a mask. The source region S and the drain region D are formed. Various methods can be applied to the impurity implantation, but ion doping (ion shower) is used here. In this method, impurities are implanted by electric field acceleration without applying mass separation. In this embodiment, the impurities are implanted at a dose of about 1 × 10 ¹⁵ / cm ² by using an acceleration voltage of 10 KeV. Thus, a source region S and a drain region D are formed. Although not shown, in the case of forming a P-channel thin film transistor, after covering the region of the N-channel thin film transistor with a photoresist, the impurity is switched from P ⁺ ions to B ⁺ ions, and the dosage is 1 × 10 ¹⁵ / cm. Ion doping may be performed at about ² . Here, impurities may be implanted using a mass separation type ion implantation apparatus.

  Thereafter, the impurities implanted into the polycrystalline semiconductor thin film 105 are activated by RTA (rapid thermal annealing) in which heat is applied by ultraviolet rays 104 from an ultraviolet lamp (not shown). Instead, laser activation annealing (ELA) using an excimer laser may be performed. Thereafter, unnecessary portions of the semiconductor thin film 105 and the stopper film 106 are simultaneously patterned to separate the thin film transistors for each element region.

Finally, as shown in FIG. 14D, a SiO ₂ film having a thickness of about 100 to 200 nm is formed as the interlayer insulating film 107. On the interlayer insulating film 107, as a passivation film 108, SiN _x is formed to a thickness of about 200 to 400 nm by plasma CVD. Next, heat treatment is performed in a vacuum atmosphere (which may be nitrogen gas or forming gas) at a temperature of about 350 to 400 ° C. for 1 hour to diffuse hydrogen atoms contained in the interlayer insulating film 107 into the semiconductor thin film 105. Thereafter, contact holes are opened in the interlayer insulating film 107 and the passivation film 108, and Mo, Al, etc. are sputtered to a thickness of 100 to 200 nm, and then patterned into a predetermined shape to form wiring electrodes 109. Then, the thin film transistor 112 is completed. Further, a planarizing layer 110 made of acrylic resin is applied on the passivation film 108 including the wiring electrode 109 with a thickness of about 1 μm, and contact holes that are continuous to the interlayer insulating film 107, the passivation film 108, and the planarizing layer 110 are formed. Form.

  Next, a transparent conductive film made of ITO or the like is sputtered on the planarizing layer 110 and then patterned into a predetermined shape to be processed into the pixel electrode 111.

  With the above method, the gate electrode 101 formed on the insulating substrate 2, the gate insulating films 102 and 103 provided on the gate electrode, the source region S, the drain region D, and the channel region Ch are formed. In addition, a bottom-gate thin film transistor including a crystallized semiconductor thin film provided to cover the gate electrode through the gate insulating film is formed. In such a transistor, the crystallographic structure of the crystallized semiconductor thin film is composed of a periodic array of substantially triangular crystal grains {100} oriented in the crystal growth direction, and the crystal growth direction {100} is the current direction. The channel region Ch, the source region S, and the drain region D are arranged so as to be.

Fourth Embodiment Next, a thin film transistor having a top gate structure will be described together with a manufacturing method thereof with reference to FIGS.

First, as shown in FIG. 15 (a), base films 121 and 122 having a two-layer structure serving as a buffer layer are sequentially formed on a transparent insulating substrate 2 by a plasma CVD method. At this time, the first underlayer 121 is made of SiN _x and has a thickness of 100 to 500 nm. Further, the second underlayer 122 is made of SiO ₂ and has a thickness of 100 nm to 500 nm. On the base film 122, the semiconductor thin film 4 made of amorphous silicon is formed with a thickness of 50 nm by plasma CVD or LPCVD. Further, a cap film 5 made of SiO ₂ is formed on the semiconductor thin film 4 with a thickness of 300 nm. When the plasma CVD method is used for forming the semiconductor thin film 4, annealing is performed for about 1 hour in a nitrogen atmosphere at 400 to 450 ° C. in order to desorb hydrogen in the film.

  Next, the amorphous semiconductor thin film 4 is crystallized using the crystallization method used in the third embodiment. At this time, after adjusting the irradiation area of the laser beam 25, the laser beam 25 is focused and irradiated so that the arrangement of the periodic pattern of the phase shifter can be transferred to the irradiation area. Repetitively irradiating and crystallizing a predetermined area (this crystallized amorphous semiconductor thin film 4 is a polycrystalline semiconductor thin film 105 (shown in FIG. 15B) below) As described).

Subsequently, the cap film 5 is peeled off from the amorphous semiconductor thin film 4 by a method such as etching. If necessary, Vth ion implantation is performed in the same manner as in the above-described embodiment, and B ⁺ ions are formed at a dose of about 5 × 10 ¹¹ to 4 × 10 ¹² / cm ² , for example. Inject into. The acceleration voltage in this case is about 10 KeV.

Subsequently, as shown in FIG. 15B, the polycrystalline semiconductor thin film 105 is patterned into an island shape. Next, SiO ₂ is grown to 100 to 400 nm on the base film 122 including the polycrystalline semiconductor thin film 105 by plasma CVD method, atmospheric pressure CVD method, low pressure CVD method, ECR-CVD method, sputtering method or the like. Then, the gate insulating film 103 is formed. In this embodiment, the thickness of the gate insulating film 103 is 100 nm.

  Next, Al, Ti, Mo, W, Ta, polycrystalline silicon doped with impurities, or an alloy or composite layer thereof is formed to a thickness of 200 to 800 nm on the gate insulating film 103, and has a predetermined shape. The gate electrode 101 is processed by patterning.

Next, P ⁺ ions are implanted into the polycrystalline semiconductor thin film 105 by ion implantation using mass separation to form an LDD region. This ion implantation is performed on the entire surface of the insulating substrate 2 using the gate electrode 101 as a mask. The dose at this time is 6 × 10 ¹² to 5 × 10 ¹³ / cm ² , and the acceleration voltage is 90 KeV, for example. The channel region Ch located immediately below the gate electrode 101 is protected by the gate electrode 101, and B ⁺ ions previously implanted by Vth ion implantation are held as they are.

After ion implantation into the LDD region, a resist pattern is formed so as to cover the gate electrode 101 and its surroundings, and P ⁺ ions are implanted at a high concentration by a mass non-separation type ion shower doping method. A drain region D is formed. In this case, the dose amount is, for example, about 1 × 10 ¹⁵ / cm ² , and the acceleration voltage is, for example, 90 KeV. As a doping gas, hydrogen diluted 20% PH ₃ gas can be used. When forming a CMOS circuit, after forming a resist pattern for a P-channel thin film transistor, the doping gas is switched to a 5 to 20% B ₂ H ₆ / H ₂ gas system, and the dose amount is set to 1 × 10 ¹⁵ to Ion implantation may be performed at about 3 × 10 ¹⁵ / cm ² and an acceleration voltage of, for example, 90 KeV. The source region S and the drain region D may be formed using a mass separation type ion implantation apparatus. Thereafter, the dopant implanted into the polycrystalline semiconductor thin film 105 is activated. As this activation treatment, RTA using ultraviolet rays 104 can be used as in the above embodiment.

Finally, as shown in FIG. 15C, an interlayer insulating film 107 made of PSG or the like is formed on the gate insulating film 103 so as to cover the gate electrode 101. Thereafter, SiN _x is deposited on the interlayer insulating film 107 by a plasma CVD method to a thickness of about 200 to 400 nm to form a passivation film 108. At this stage, annealing is performed in a nitrogen gas at a temperature of 350 ° C. for about 1 hour to diffuse hydrogen contained in the interlayer insulating film 107 into the polycrystalline semiconductor thin film 105. Thereafter, contact holes are formed in the interlayer insulating film 107 and the passivation film 108 so as to expose the source region S. Further, after a metal film such as Al—Si is formed on the passivation film 108 by sputtering, the metal film is patterned into a predetermined shape and processed into the wiring electrode 109, thereby completing the thin film transistor 123. Further, a planarizing layer 110 made of acrylic resin is applied on the passivation film 108 including the wiring electrode 109 with a thickness of about 1 μm, and contact holes that are continuous to the interlayer insulating film 107, the passivation film 108, and the planarizing layer 110 are formed. Form. Next, a transparent conductive film made of ITO or the like is sputtered on the planarizing layer 110 and then patterned into a predetermined shape to be processed into the pixel electrode 111.

  The top-gate thin film transistor thus formed is formed on the insulating substrate 2, and includes a crystallized semiconductor thin film 105 including the source region S, the drain region D, and the channel region Ch, and the crystallized semiconductor thin film. And a gate electrode 101 provided on the crystallized semiconductor thin film via the gate insulating film. In this transistor, the crystallographic structure of the crystallized semiconductor thin film is composed of a periodic array of substantially triangular crystal grains {100} oriented in the crystal growth direction, and the {100} crystal growth direction is the current direction. As described above, the channel region Ch, the source region S, and the drain region D are arranged.

  In the manufacturing method described with reference to FIG. 15, the amorphous semiconductor thin film 4 is crystallized in the same manner as the manufacturing method described with reference to FIG. 14. However, in the present embodiment relating to the method for manufacturing the top-gate thin film transistor, unlike the previous embodiment related to the method for manufacturing the bottom-gate thin film transistor, crystallization is performed in the step before the pattern of the gate electrode 101 is formed. Therefore, the tolerance of the shrinkage of the insulating substrate made of glass or the like is larger than that of the semiconductor device having the bottom gate structure. For this reason, there exists an effect which can perform a crystallization process using the laser irradiation apparatus of higher output.

Fifth embodiment
FIG. 16 shows an example of an active matrix display device using thin film transistors manufactured by the methods according to the third and fourth embodiments. The display device 130 includes a pair of transparent insulating substrates 131 and 132 (the lower insulating substrate 131 corresponds to the insulating substrate 2) and an electro-optical material 133 held between the two. The panel structure is provided. As the electro-optical material 133, an organic EL material or a liquid crystal material is widely used. A pixel array part 134 and a drive circuit part are integrated on the lower insulating substrate 131. This drive circuit section is divided into a vertical drive circuit 135 and a horizontal drive circuit 136.

  A terminal portion 137 for external connection is formed on the upper end of the peripheral portion of the lower insulating substrate 131. These terminal portions 137 are connected to the vertical drive circuit 135 and the horizontal drive circuit 136 via wiring 138. In the pixel array section 134, row-shaped gate wirings 139 and column-shaped signal wirings 140 are formed. A pixel electrode 111 and a thin film transistor 112 (or 123) for driving the pixel electrode 111 are formed at each intersection of these wirings. The gate electrode of the thin film transistor 112 (or 123) is connected to the corresponding gate wiring 139, the drain region D is connected to the corresponding pixel electrode 111, and the source region S is connected to the corresponding signal wiring 140. The gate wiring 139 is connected to the vertical driving circuit 135, and the signal wiring 140 is connected to the horizontal driving circuit 136.

  In addition to the thin film transistor 112 (or 123) for switching and driving the pixel electrode 111, the thin film transistors included in the vertical drive circuit 135 and the horizontal drive circuit 136 may be manufactured by the method of manufacturing a thin film transistor according to the present invention. Therefore, these thin film transistors use a semiconductor thin film crystallized mainly in the {100} orientation in the crystal growth direction, that is, in the direction of the temperature gradient. Therefore, not only the drive circuit but also a higher-performance processing circuit can be integrated.

  When the thin film transistor of the present invention is applied to a display device such as a liquid crystal display or an organic EL, it becomes possible to form a high-performance arithmetic element or the like in a peripheral circuit. Is big. Further, since the present invention is a method in which the phase shifter is simply inserted into the optical path, the optical system is not complicated and adjustment thereof does not take time, so that it is suitable for mass production.

(A) is a plan view of a line type phase shifter, (b) is a side view of the line type phase shifter, (c) is a side view showing the irradiated object, and (d) is incident of the irradiated object. It is a laser beam intensity distribution figure (beam profile figure) on a surface. (A) is a plan view of the dot-type phase shifter, (b) is a side view of the dot-type phase shifter, (c) is a side view showing the irradiated object, and (d) is incident of the irradiated object. It is a laser beam intensity distribution figure (beam profile figure) on a surface. It is a graph which shows the relationship between the thickness of a silicon thin film, and the width | variety of a lateral growth grain. It is a graph which shows the relationship between the inclination of V-type light intensity distribution, and the width | variety of a lateral growth grain. It is a schematic diagram explaining the difference in the crystal form when the silicon thin film thickness is thick and thin. It is a schematic diagram explaining the difference in crystal form between when the inclination of the V-type light intensity distribution is gentle and when it is steep. It is a reverse pole figure which shows the orientation of the horizontal growth direction in each silicon thin film thickness and the inclination of each V-type light intensity distribution. It is a schematic diagram explaining the relationship between the crystal form and crystal orientation of a lateral growth structure corresponding to the thickness of each silicon thin film and the inclination of each V-type light intensity distribution. 1 is a schematic configuration diagram of a crystallization apparatus according to a first embodiment of the present invention and having a proximity optical system. It is a schematic block diagram of the crystallization apparatus which concerns on the 2nd Embodiment of this invention and has an optical system of a projection system. 3 is a reverse pole figure showing the orientation of the crystal structure of the crystallized silicon thin film obtained in Example 1. FIG. 6 is a reverse pole figure showing the orientation of the crystal structure of the crystallized silicon thin film obtained in Example 3. FIG. It is a reverse pole figure which shows the orientation of the crystal structure of the crystallized silicon thin film thickness obtained in Example 4. FIG. (A) thru | or (d) is process drawing which shows the manufacturing process of the bottom gate type thin-film transistor which concerns on the 3rd Embodiment of this invention. (A) thru | or (c) are process drawings which show the manufacturing process of the top gate type thin-film transistor which concerns on the 4th Embodiment of this invention. It is a perspective view which shows the outline | summary of the display apparatus which concerns on the 5th Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,53 ... Almost V-shaped pattern, 1a, 53a ... Valley part (bottom position, minimum light intensity area), 1b, 53b ... Mountain part (top position, maximum light intensity area) 2 ... Substrate, 3 ... Buffer layer (Underlying protective film), 4 ... amorphous semiconductor layer (silicon thin film), 5 ... cap film, 6 ... phase shifter (spatial intensity modulation optical element),

Claims (14)

  A method of crystallizing a semiconductor thin film, wherein a semiconductor thin film formed on a substrate is crystallized by irradiating a laser beam. At the start of crystallization, a line-shaped minimum temperature region and a minimum temperature are formed on the semiconductor thin film. Forming a temperature distribution of an inverse peak pattern having linear maximum temperature regions on both sides of the region, the direction of the temperature gradient according to the temperature distribution being in the plane of the semiconductor thin film, and orthogonal to the direction of the temperature gradient A crystallization start region is formed in the line-shaped minimum temperature region along the in-plane direction of the semiconductor thin film, and the minimum temperature region and the maximum temperature region are provided under the condition that the thickness of the semiconductor thin film is in the range of 50 to 200 nm Characterized in that the semiconductor thin film is crystallized mainly by {100} orientation in the crystal growth direction, that is, in the direction of the temperature gradient, by crystallization under the condition of a distance of 3 to 10 μm. A method of crystallizing a semiconductor thin film that.   A method for crystallizing a semiconductor thin film, wherein a semiconductor thin film having a thickness of 50 to 200 nm is crystallized by irradiating the semiconductor thin film with a laser beam, wherein the laser light is crystallized on the semiconductor thin film. The line-shaped minimum light intensity region and the line-shaped maximum light intensity region are alternately formed, and crystallization is performed using laser light having a distance between the minimum temperature region and the maximum temperature region of 3 to 10 μm. Thus, the semiconductor thin film is crystallized by crystallizing the semiconductor thin film with {100} orientation in the crystal growth direction.   The minimum temperature region or the minimum light intensity region and the maximum temperature region or the maximum light intensity region are formed according to the light intensity distribution of the laser light, and this light intensity distribution is provided in the irradiation light path of the laser light. 3. The method of crystallizing a semiconductor thin film according to claim 1, wherein the light modulation element is used to modulate laser light from a light source.   4. The semiconductor thin film crystal according to claim 3, wherein the light modulation element is a dot type phase shifter having a periodic dot step or a line type phase shifter in which lines and space steps are arranged. Method. 5. The semiconductor thin film according to claim 1, wherein an irradiation fluence in a maximum temperature region of the intensity distribution of the laser beam having the light intensity distribution is set in a range of 700 to 1300 mJ / cm ² . Crystallization method. An excimer laser generator for emitting an excimer laser beam, a homogenizer for making the light intensity of the emitted laser beam uniform, a mask for defining an irradiation area on the semiconductor thin film, and the light intensity made uniform An optical element for condensing the laser light on the mask, a telecentric reduction lens for making the laser light that has passed through the irradiation area of the mask incident on the reduced area of the semiconductor thin film, and the light of the laser light that irradiates the semiconductor thin film Using a device comprising a phase shifter that modulates the intensity distribution,
A projection method in which the phase shifter is inserted at the position of the mask surface of the mask is used, and a value obtained by multiplying the period of dot arrangement of the phase shifter or the interval between the line and the space and the reduction magnification of the reduction lens is 6 μm. The method for crystallizing a semiconductor thin film according to claim 4, wherein the thickness is 20 μm or less. An apparatus for crystallizing a semiconductor thin film formed on a substrate and irradiating a semiconductor thin film having a thickness of 50 to 200 nm with laser light,
A laser light source;
At the start of crystallization of the semiconductor thin film, a temperature distribution of an inverse peak pattern having a line-shaped minimum temperature region and a line-shaped maximum temperature region on both sides of the minimum temperature region is formed on the semiconductor thin film, and this temperature The direction of the temperature gradient according to the distribution is in the plane of the semiconductor thin film, and there is a crystallization start region by the line-shaped minimum temperature region along the direction in the plane of the semiconductor thin film perpendicular to the direction of the temperature gradient. And a means for optically modulating laser light from the laser light source so that the distance between the minimum temperature region and the maximum temperature region is 3 to 10 μm.   The means for modulating the light is such that the laser beam has a light intensity distribution of an inverse peak pattern having a line-shaped minimum light intensity region and a line-shaped maximum light intensity region on both sides of the minimum light intensity region. 8. The apparatus according to claim 7, further comprising a phase shifter for modulating, the phase shifter being arranged so as to be close to the semiconductor thin film. Further, a homogenizer for making the light intensity of the laser light from the laser light source uniform, a mask for determining the irradiation area, and a laser light whose light intensity is made uniform by the homogenizer are collected in the irradiation area of the mask. An optical system comprising: a convex lens; and a telecentric reduction lens for reducing the irradiation area of the mask to an area reduced on the imaging surface of the semiconductor thin film,
The phase shifter is a dot type phase shifter having a periodic dot step or a line type phase shifter in which lines and space steps are arranged, and is arranged at a position of the mask surface of the mask. 9. The apparatus according to claim 8, wherein a value obtained by multiplying a period of a dot step of a shifter or an interval between a line and a space step and a reduction magnification of the reduction lens is set to 6 μm to 20 μm.   A crystallized semiconductor thin film on a substrate for manufacturing a device, wherein the crystal structure of the crystallized semiconductor thin film is oriented in {100} in the crystal growth direction. A crystallized semiconductor thin film formed on an insulating substrate and including a source, a drain, and a channel region;
A top gate type thin film transistor comprising a gate insulating film provided on the crystallized semiconductor thin film and a gate electrode provided on the crystallized semiconductor thin film through the gate insulating film;
The crystal structure of the crystallized semiconductor thin film is a periodic arrangement of substantially triangular crystal grains {100} oriented in the crystal growth direction, and the channel so that the {100} crystal growth direction is the current direction. A thin film transistor comprising a region, a source region, and a drain region. A gate electrode formed on an insulating substrate, a gate insulating film provided on the gate electrode, a source, a drain, and a channel region are provided so as to cover the gate electrode through the gate insulating film A bottom gate type thin film transistor comprising the crystallized semiconductor thin film obtained,
The channel region is formed such that the crystallographic structure of the crystallized semiconductor thin film is a periodic arrangement of substantially triangular crystal grains {100} oriented in the crystal growth direction, and the crystal growth direction {100} is the current direction. And a source region and a drain region.   13. The thin film transistor according to claim 11, wherein a lateral growth length of the substantially triangular crystal grains is 3 to 10 [mu] m. A pair of substrates bonded to each other through a predetermined gap; and an electro-optic material held in the gap; a counter electrode is formed on one substrate, and a pixel electrode and the electrode are formed on the other substrate A thin film transistor to be driven is formed, and the thin film transistor is a display device including a crystallized semiconductor thin film including a source, a drain, and a channel region, a gate insulating film, and a gate electrode,
The crystal structure of the crystallized semiconductor thin film is composed of a periodic array of substantially triangular crystal grains {100} oriented in the {100} crystal growth direction, and the channel is set such that the crystal growth direction is a current direction. A display device comprising a region, a source region, and a drain region.

Images