Patent Publication Number: US-2007096103-A1

Title: Semiconductor device, annealing method, annealing apparatus and display apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation of application Ser. No. 11/041,413 filed Jan. 25, 2005 which is a continuation of application Ser. No. 10/668,285, now U.S. Pat. No. 6,870,126, filed Sep. 24, 2003 and is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2002-279608, filed Sep. 25, 2002; and No. 2003-110861, filed Apr. 15, 2003, the entire contents of both of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a technology for manufacturing a field-effect transistor on the surface layer portion of a polycrystalline film (polycrystalline semiconductor thin film), a polycrystalline semiconductor thin film substrate for manufacturing the Field-Effect Transistor, and a semiconductor device for manufacturing electronic devices, such as liquid crystal display apparatuses and information processing devices, having the Field-Effect Transistor installed therein. The present invention also relates to an annealing method, an annealing apparatus for manufacturing the semiconductor device, and a display apparatus using the semiconductor device.  
      2. Description of the Related Art  
      As a display system of a liquid crystal display (LCD), use is made of an active matrix system in which display is performed by turning on each pixel. To turn on individual pixels in the active matrix system, a kind of field-effect transistor, an amorphous silicon thin film transistor (hereinafter, referred to as “a-SiTFT”), is mostly used.  
      Liquid crystal displays have been investigated and developed with the view toward attaining the technical purposes: (i) improving accuracy, (ii) increasing an aperture ratio, (iii) reducing weight, and (iv) reducing cost. To attain these purposes, Field-Effect Transistor, namely, a polycrystalline silicon thin film transistor (hereinafter referred to as “poly-SiTFT”) has been recently received attention in place of the a-SiTFT. Poly-SiTFT has a field-effect mobility of carrier higher than a-SiTFT by two orders of magnitude. By virtue of this, the device formed of the poly-SiTFT can be reduced in size and a circuit can be integrated. As a result, a driving circuit and an arithmetic circuit can be mounted on a liquid crystal display.  
      Such a Poly-SiTFT is manufactured by an excimer laser crystallization method, which is detailed in “flat panel display” 1999, Nikkei Micro Device, Supplemental Edition (Nikkei BP Co., Ltd. 1998, pp. 132-139).  
      Referring now to  FIGS. 1A  to  1 D, a method of manufacturing a poly-SiTFT by conventional excimer laser crystallization will be explained. As shown in  FIG. 1A , first, an underlying layer protection film  102  (e.g. SiO 2  film, SiN film, and SiN/SiO 2  laminate film) and an amorphous silicon thin film  103  are sequentially deposited on a glass substrate  5 . Then, as shown in  FIG. 1B , when the amorphous silicon thin film  103  is irradiated with an excimer laser  50  (e.g., XeCl, KrF) having a square or rectangular shape formed by use of an optical system, the amorphous structure of the amorphous silicon thin film  103  is changed into a polycrystalline structure within an extremely short period of 50 to 100 nanoseconds through a melting/solidification step. When the excimer laser  50  is scanned over the substrate in the direction of the arrow  105 , and locally and rapidly heated and cooled, a polycrystalline silicon thin film  106  is formed as shown in  FIG. 1C .  
      Using the polycrystalline silicon thin film  106  shown in  FIG. 1C , the thin film transistor shown in  FIG. 1D  is manufactured. On the polycrystalline silicon thin film  106 , a SiO 2  gate insulating film  107  is formed. Furthermore, an impurity element is doped into predetermined regions of the polycrystalline silicon thin film  106 , a source and drain regions  109 ,  108  are formed. A channel region  106  is located between the source region  109  and the drain region  108 . A gate electrode  110  is formed on the gate insulting film  107 ; a protection film  111  is formed; and then a source electrode  112  and a drain electrode  113  are formed. When voltage is applied to the gate electrode  110  of the poly-SiTFT, the current flowing between the source region  109  and the drain region  108  is controlled.  
      In general, the TFT used in a pixel under the active matrix control is required for maintaining charge but not required to have an extremely high mobility (field-effect mobility). Rather, a low off-state current (quiescent current) must be supplied. To reduce the off-state current, it is necessary to increase the channel length of the TFT so as not to reduce the aperture ratio of a pixel by reducing the electric field strength of the end of the drain region, with the result that the pixel TFT becomes relatively large.  
      On the other hand, it is necessary that the TFT used in a driving circuit and an arithmetic circuit is operated at a high speed. Consequently, a high mobility but the off-state current is a matter of concern. In particular, the high-speed operation can be attained effectively by reducing the channel length. Therefore, the channel length of a TFT is reduced. As a result, the size of a TFT for use in driving circuit and arithmetic circuits becomes small.  
      As described above, the characteristics and sizes of TFTs required for a pixel and for driving/arithmetic circuits completely differ. All these TFTs are desirably formed together on the same substrate by substantially the same step. If not, economical merits brought by the integration of different type TFTs in a liquid crystal display cannot be obtained.  
      However, the conventional laser annealing method mentioned above has a problem in that only a poly-Si thin film having a uniform crystallinity is formed. If different-sized TFTs are formed on the same substrate formed by the conventional method, the following problems (i) and (ii) may inevitably occur.  
      (i) A large TFT has a large number of grain boundaries in the channel region. As a result, the variance of voltages becomes low (off-state current is low); however, the operation is performed at a low speed.  
      (ii) A small TFT has a small number of grain boundaries in the channel region. As a result, the operation can be performed at a high speed; however, variance of voltage becomes large (off-state current is high).  
      As described above, in the conventional method, it has been impossible to form various TFTs different in size and characteristics on the same substrate.  
     BRIEF SUMMARY OF THE INVENTION  
      An object of the present invention is to provide a semiconductor device capable of forming a semiconductor layer having not smaller than two types of crystal grains different in average diameter directly or indirectly on the same substrate, with the result that the diameter of the crystal grains is controlled so as to have the same average number (Na) of crystal grain boundaries across the current direction in a channel region (serving as an active layer) of TFTs different in size. The present invention is also directed to providing an annealing method, annealing apparatus and display apparatus for manufacturing the semiconductor device.  
      The semiconductor device of the present invention comprises a semiconductor layer having not smaller than two types of crystal grains different in average grain diameter in a semiconductor device circuit on a same substrate.  
      A semiconductor device comprising not smaller than two types of field effect transistors using a semiconductor layer directly or indirectly formed on the substrate as a channel region, in which, a frequency distribution with respect to ratios of Na/L of the transistors falls within ±5%, where the L is a gate length of a transistor, and the Na is an average number of crystal grain boundaries across the direction of current flowing through the transistor.  
      The frequency distribution with respect to ratios of the Na/L of the transistors falls within ±2%. Further, the device may have a circuit layer on the substrate for actuating the transistor.  
      The annealing method of the present invention comprises the steps of;  
      setting target values with respect to intensity of laser light and distribution of the intensity in advance;  
      preparing a beam profile modulating section between a laser source and an irradiation region and preparing a substrate and a beam profile measuring section so as to interchangeably load and unload into the irradiation region;  
      placing the beam profile measuring section in the irradiation region, emitting laser light from the light source, modulating the intensity of the laser light and distribution of the intensity by the beam profile modulating section, and measuring the intensity of the laser light and incident on the irradiation region and the distribution of the intensity by the beam profile measuring section;  
      adjusting parameters of the beam profile modulating section based on the measuring results such that the measuring results match with the target values;  
      placing the substrate in the irradiation region such that the incident surface of the substrate is positioned in the irradiation region, thereby aligning the substrate with the beam profile modulating section;  
      irradiating the substrate with the laser light modulated by the beam profile modulating section when the measurement results match with the targets; and  
      repeating the alignment step and the laser irradiation step to form a semiconductor substrate having not smaller than two types of crystal grains different in diameter therein.  
      The annealing apparatus of the present invention comprises  
      a laser source;  
      a beam profile modulating section arranged between the laser source and an irradiation region, for modulating intensity of laser light and distribution of the intensity;  
      a beam profile measuring section for measuring intensity of laser light of an incident surface of the irradiation region and the distribution of the intensity;  
      means for setting target values with respect to the intensity of laser light and distribution of the intensity in advance; and  
      a control section for controlling parameters of the beam profile modulating section such that the results measured by the beam profile measuring section match with the target values set above.  
      The beam profile measuring section is preferably arranged in the same plane as the substrate.  
      The beam profile modulating section uses an image forming optical system having a phase shifter as a spatial intensity modulating optical element.  
      An annealing method according to the present invention comprises  
      setting and storing a target beam profile in a memory apparatus, recalling the target beam profile from the memory apparatus and setting an annealing beam profile with reference to the target beam profile thus recalled, and irradiating an amorphous single crystalline semiconductor layer with laser light.  
      The annealing apparatus according to the present invention is characterized in that a target beam profile is set and stored in a memory apparatus, the target beam profile is recalled from the memory apparatus, an annealing beam profile is set with reference to the target beam profile thus recalled, and a non single crystalline semiconductor layer is irradiated with laser light.  
      The display apparatus according to the present invention comprises a pair of substrates mutually joined with a predetermined gap and an electrochemical substance held in the gap, a counter electrode formed on one of the substrates, a pixel having electrode formed on other substrate a crystalline semiconductor thin film electrically connected the pixel electrode, a pixel drive circuit for driving the pixel, and a semiconductor thin film formed on the pixel drive circuit.  
      Each of the crystalline semiconductor thin film is formed:  
      (a) inserting a spatial intensity modulating optical element between a laser source and a beam profile measuring section;  
      controlling gap d 1  between an incident surface of the beam profile measuring section and the spatial intensity modulating optical element at 500 μm or less;  
      measuring intensity of laser light modulated by the spatial intensity modulating optical element and applied to the incident surface of the beam profile measuring section, distribution of the intensity and the gap d, individually;  
      (b) inserting the spatial intensity modulating optical element between a substrate having a non single crystalline semiconductor thin film and the laser source, controlling gap d 1  between an incident surface of the substrate and the spatial intensity modulating optical element to 500 μm or less, irradiating the incident surface of the substrate with the laser light modulated by the spatial intensity modulating optical element, and measuring the intensity of laser light, distribution of the intensity and the gap d 1  when it is confirmed that lateral crystallization of the semiconductor thin film proceeds by irradiation of the modulated laser light;  
      (c) setting the measurement results in step (a) corresponding to those in step (b) as target values of the intensity of laser light, distribution of the intensity, and the gap d 1 ;  
      (d) controlling intensity of laser light, distribution of the intensity and the gap d 1  so as to match with the target values and irradiating the incident surface of the substrate with the laser light modulated by the spatial intensity modulating optical element under the control conditions; and  
      (e) forming a semiconductor layer having not smaller than two types of crystal grains different in average diameter in the same substrate by repeating steps (b) to (d) mentioned above.  
      As described above, a semiconductor layer having not smaller than two types of crystal grains different in average diameter in the same substrate can be formed by repeating measurement of an average intensity (laser fluence) of laser light and distribution of the intensity (beam profile), gap arrangement and alignment, and laser irradiation.  
      Note that measurement, aligning, and irradiation are not necessarily repeated every time. Instead, all measurements are first performed, the measurement results are stored, the operational amounts required for alignment are obtained based on the measurement results recalled, the alignment and irradiation may be simultaneously performed for each crystallization region.  
      The present invention is concerned with a so-called proximity system comprising placing a phase shifter at a predetermined portion in the proximity of a substrate and irradiating laser light having a predetermined fluence. The proximity system may be used in combination with a projection system in which a phase shifter is arranged at a position near a laser source away from a substrate.  
      The term “beam profile” used in the specification refers to a two-dimensional intensity distribution of light incident upon an amorphous crystalline semiconductor layer for use in crystallization. Note that the beam intensity of the profiler (beam profile) may be low since the beam profile is normalized.  
      The term “laser fluence” used in the specification is a unit indicating the energy density of laser light, which is obtained by integrating the energy amount per unit area by time. To be more specifically, the “laser fluence” is an average intensity of laser light measured at a laser source or in an irradiation region.  
      The term “phase shifter” used in the specification refers to a spatial intensity modulating optical element for modulating light such as laser light to distribute light such that its intensity varies spatially. The “phase shifter” used herein is a spatial intensity modulating optical element used in an excimer laser crystallization method but differs from a “phase shift mask” used in a light-exposure step of a photolithography process of a semiconductor device. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       FIGS. 1A  to  1 C are schematic sectional views for illustrating a conventional annealing method;  
       FIG. 1D  are a schematic sectional view of the structure of a conventional semiconductor device;  
       FIG. 2  is a schematic view of the entire structure of an annealing apparatus, a projection type laser annealing apparatus, according to the present invention;  
       FIG. 3  is a perspective view of an optical system of the annealing apparatus;  
       FIG. 4  is an illustration showing the optical system of the annealing apparatus of  FIG. 2 ;  
       FIG. 5  is a circuit diagram showing a laser source with a block diagram of peripheral structural elements;  
       FIG. 6  is a sectional view of an alignment mechanism of a substrate stage with a block diagram of peripheral structural elements;  
       FIG. 7  is a plan view of an alignment mechanism of a phase shifter;  
       FIG. 8  is a magnified sectional view of a part of the alignment mechanism of the phase shifter;  
       FIG. 9  is a flowchart of an annealing method of the present invention;  
       FIG. 10A  shows beam profile A;  
       FIG. 10B  is a schematic view showing a crystal region of small grains formed by irradiation with a laser having beam profile A;  
       FIG. 10C  shows beam profile B;  
       FIG. 10D  is a schematic view showing a crystal region of large grains formed by irradiation with a laser having the beam profile B;  
       FIG. 11A  is a schematic sectional view for illustrating the annealing method of the present invention;  
       FIG. 11B  is a schematic sectional view showing a semiconductor device of the present invention;  
       FIG. 12A  is a schematic view of laser markers provided on an active layer of TFT;  
       FIG. 12B  is a schematic view of laser markers provided on the TFT active layer after removal of a gate interlayer film;  
       FIG. 13  is a characteristic line graph showing the relationship between the stage height hz and the number of grain boundaries (average value Na) per 1 μm;  
       FIG. 14A  is a scanning electron-microscope (SEM) photograph showing a one-dimensional beam profile on a beam profiler fluorescent surface;  
       FIG. 14B  is a characteristic line graph of the one-dimensional beam profile;  
       FIG. 15A  is a computer simulation image of a two-dimensional beam profile;  
       FIG. 15B  is a scanning electron-microscope (SEM) photograph showing a second-dimensional beam profile on the beam profiler fluorescent surface;  
       FIG. 16A  is a characteristic line graph of a beam profile in which crystallization simulation results and actual results are shown;  
       FIG. 16B  is an SEM photograph showing amorphous Si and crystalline Si of the laser irradiation region;  
       FIG. 17A  is a characteristic line graph showing the relationship between lateral growth/film breaking and laser-fluence;  
       FIG. 17B  is an SEM photograph of a Si thin film during the lateral growth;  
       FIG. 18A  is a characteristic line showing a beam profile;  
       FIG. 18B  is an SEM photograph showing a pattern repeat of the laser irradiation region;  
       FIG. 18C  is a magnified SEM photograph showing a partially magnified the SEM photograph shown in  FIG. 18B ;  
       FIG. 19  is a schematic view of the entire structure of another annealing apparatus (proximity-type laser annealing apparatus) of the present invention;  
       FIG. 20  is a sectional view of the optical system of the annealing apparatus of  FIG. 19 , together with a block diagram of peripheral structural elements;  
       FIG. 21  is a characteristic line graph showing the relationship between gap d 1  and the number of grain boundaries (average value Na) per 1 μm; and  
       FIG. 22  is a perspective view of the display apparatus of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Preferable embodiments of the present invention will be now explained with reference to the accompanying drawings.  
     First Embodiment  
       FIG. 2  shows a laser crystallization apparatus  10  of this embodiment, a projection type laser annealing apparatus, which has an attenuator  2  and a beam profile modulator  3  near a laser source  1 . A mirror  4  is arranged downstream of the beam profile modulator  3  for reflecting laser light  50  to apply it to a substrate  5  arranged at the target end of a laser optical axis  50   a.    
      On a movable stage  7 , the substrate  5  and a beam profiler  6  are arranged next to each other. They are independently moved in the directions X, Y, and Z by the movable stage  7  and aligned with light derived from the light source.  
      The movable stage  7  generally has three stages  71 ,  72  and  73 , as shown in, for example,  FIG. 6 . To explain more specifically, the X stage  71  is movably held on a linear guide (not shown). On the X stage  71 , the Y stage  72  is movably held. Further on the Y stage  72 , the Z stage  73  is movably held. The substrate is mounted on the Z stage  73 . Furthermore, a driving mechanism, a θ rotation stage (not shown) for rotating the Z stage  73  about the Z-axis may be added. The movable stage  7  has a heater  7   a  for heating the substrate  5  to a predetermined temperature.  
      On the main body of the Z stage  73 , right and left sliders  74   a ,  74   b  are arranged to slidably move along the linear guide (not shown). The surfaces of both sliders  74   a  and  74   b  facing each other are inclined such that the sliders taper from bottom to top. Between the both sliders  74   a  and  74   b , an up-and-down table  76  is provided so as to slidably move along the inclined surface. In other words, the inclined surfaces of the up-and-down table  76  match with the inclined surfaces of both sliders  74   a  and  74   b . The substrate  5  is mounted on the up-and-down table  76 . The side portions of the sliders  74   a  and  74   b  are respectively connected to the corresponding ends of ball screws  75   a  and  75   b . The other ends of the ball screws  75   a  and  75   b  are jointed to a rotation driving shaft of an up-and-down driving mechanism  9  formed of a precision electric motor such as a stepping motor or a servomotor. A capacity sensor  78  is provided (above the up-and-down table  76 ) so as to detect the level of the upper surface of the up-and-down table  76 . When a height detection signal is sent from the sensor  78  to a controller  8 , the controller controls the operation of the up-and-down driving mechanism  9  to rotate both the ball screws  75   a  and  75   b , thereby moving up and down the up-and-down table  76 . In this manner, the substrate  6  can be precisely aligned with the light derived from the laser source.  
       FIG. 3  shows the optical system of the beam profiler  6 , which is arranged such that its optical axis matches with that  50   a  of the laser source. The beam profiler  6  is mounted on an alignment mechanism  80 , which is moved in the X, Y, and Z directions in synchronisms with the movable stage  7 . Incidentally, the alignment mechanism  80  may be formed on the movable stage  7 .  
      The alignment mechanism  80  has X, Y and Z stages  81 ,  82  and  83 . The X stage  81  is movably held on a linear guide (not shown). On the X stage  81 , the Y stage  82  is movably held. On the Y stage  82 , the Z stage  83  is movably held. Further on the Z stage  83 , a holding table  66  of the beam profiler  6 . The level of the upper surface of the Z stage  83  is detected by a sensor (not shown). The height hz of the Z stage  83  is controlled by a personal computer  8  based on the height detection signal.  
      The holding table  66  has an optical wave-guide  64 . The optical wave-guide  64  arranged horizontal is bent upward at a right angle at one side. A mirror  62  is arranged at the bending portion and an objective lens  65  is arranged at the top end. The objective lens  65  are arranged in proximity with the rear surface of a transparent fluorescent plate  61 . The other end of the optical wave-guide  64  is optically connected to a CCD camera  63 .  
      When ultraviolet excimer laser  50  is received by the fluorescent plate  61  of the beam profiler  6  it is converted into visible light, which is reflected at the mirror  62  and received by the CCD camera  63 . In this manner, the beam profiler  6  measures the intensity of laser light and beam profile simultaneously.  
      In addition, a personal computer  8  is arranged to control the attenuator  2 , beam profile modulator  3 , and movable stage  7 . The beam profiler  6  is connected to an input terminal of the personal computer  8 , whereas the attenuator  2 , the profile modulator  3 , and movable stage  7  serving as a control system, are individually connected to the output terminal thereof. The picture data taken by the CCD camera  63  is transmitted to the personal computer  8  and processed therein.  
      The laser source  1  has a laser system (laser oscillator) emitting a KrF excimer laser of 248 nm wavelength. The laser system is capable of emitting laser light  50 , which has a fluence sufficient to melt an amorphous silicon film  303  on the substrate  5 , along the optical axis  50   a.    
      The attenuator  2  has a function of optically modulating the intensity (amplitude) of laser light by controlling the angle of dielectric multi-film coating filter and also has a sensor, motor, and a control system (not shown). In the apparatus  10  of this embodiment, the laser light  50  is emitted from the light source  1  and modulated by the attenuator  2  into the fluence having a desired level intensity. However, the laser source  1  itself may have a laser fluence adjusting function. More specifically, a control circuit  14 , an optical sensor  15 , an optical/electrical converter  16 , and a comparator  17  are arranged in the light source  1 , as shown in  FIG. 5 . The laser light  50  emitted from a vacuum container  11  of the laser oscillation apparatus is detected by the sensor  15  and converted into an electrical signal S 1  by the optical/electrical converter  16 , compared with a threshold signal S 2  by the comparator  17 . Based on the comparative results, the control circuit  14  controls a power source  13  to regulate the current to be applied across electrodes  12   a  and  12   b  of the laser oscillation apparatus in a feedback manner. If the light source  1  configured as mentioned above, the attenuator  2  may not be used.  
      The beam profile modulator  3  has a function for modulating the spatial distribution of the intensity of laser light and configured of a phase shifter  31  and image-forming optical system  32 . According to the apparatus  10  of the embodiment, a projection system is employed in which the phase shifter  31  is arranged close to the laser source  1  far away from the substrate  5 .  
      As shown in  FIG. 4 , the image forming optical system  32  is configured of a homogenizer  32   a , a first condenser lens  32   b , a second condenser lens  32   c , a mask  32   d , a phase shifter  31 , and telecentric type reducing lens  32   e , which are arranged sequentially from the light source side along the laser optical axis  50   a.    
      The homogenizer  32   a  has a function of equalizing the laser beams emitted from the light source  1 . The first condenser lens  32   b , which is arranged in couple with the second condenser lens  32   c , converges the equalized laser beams from the homogenizer  32   a . In the optical path of the light beams emitted from the second condenser lens  32   c , the mask  32   d  is arranged, which interrupts a non-effective laser beam. The reducing lens  32   e  has a function of reducing the size of an image in the range of between 1/1- 1/20 and arranged in couple with the insulating cap film  305  formed on the substrate  5 .  
      The phase shifter  31  is arranged in the close proximity of the mask  32   d  so as to cover the opening of the mask  32   d . Note that the phase shifter  31  has an alignment mechanism having a sensor, an actuator, and a control system, for exchanging the mask  32   d  and aligning with the optical axis. As described later, the distance between the phase shifter  31  and the mask  32   d  can be controlled accurately by an alignment mechanism described later.  
      The alignment mechanism of the phase shifter  31  will be explained with reference to  FIGS. 7 and 8 . The phase shifter  31  is movably held by the holder  90 . As shown in  FIG. 7 , the holder  90  has a concentric outer ring  91  and inner ring  92  mutually connected. The outer ring  91  is movably supported by the X driving mechanism  93  and Y driving mechanism  94  so as to move in the X and Y directions with fine pitches.  
      The inner ring  92  has a plurality of stoppers  92   a  for holding the phase shifter  31 , as shown in  FIG. 8 . The phase shifter  31  is fit inside the inner ring  92  and the stoppers  92   a  hold its periphery. The inner ring  92  is supported by pivots  95   a ,  95   b  and  95   c . Two of the pivots  95   a ,  95   b  and  95   c  are connected to a rod of a cylinder  96   a  (only one is shown in the figure for convenience sake). The controller  8  controls the moving amount of the Z direction of each cylinder rod based on the position-detecting signal sent from a capacity sensor (not shown) to thereby align the phase shifter  31  with the X-Y surface (called surface alignment of the phase shifter).  
      In this manner, the phase shifter  31  is precisely aligned with other members of the image forming optical system  32 . The height (gap d) of the phase shifter used herein is defined as the distance between the phase shifter and the mask.  
      Now, referring to  FIG. 9 , the case where a specific region of the amorphous silicon film is crystallized by the annealing apparatus of the present invention will be explained.  
      First, the magnification of the attenuator is adjusted at 1/100 (Step S 1 ). Then, the profiler  6  is allowed to enter to position at the irradiation region (Step S 2 ). The optical axis of the profiler  6  is roughly aligned with that  50   a  of the light source by use of alignment mechanisms  7  and  80  (Step S 3 ). The optical axis of the profiler  6  is precisely aligned with the light axis  50   a  of the light source by the alignment mechanisms  7  and  80  (Step S 4 ).  
      Subsequently, the phase shifter  31  is aligned with the mask  32   d  by the alignment mechanism  90  to set gap d between the phase shifter  31  and the mask  32   d  at a predetermined value. In this manner, a modulation optical system is prepared (Step S 5 ).  
      In a laser crystallization step, first, the movable state  7  is moved horizontally to bring the tip of the optical axis  50   a  of the laser source  1  to point at the fluorescent plate  61  of the beam profiler  6 . laser light is applied to the fluorescent plate  61  and the intensity of beam profile is measured (Step S 6 ). At this time, a desired beam profile is determined with reference to the shape of the phase sifter  31  and the distance between the phase shifter and a semiconductor substrate  5 , the intensity distribution of laser light, and the angular distribution of laser light. The image forming optical system  32  is composed of optical parts such as lenses. Laser light is applied to the substrate  5  while the substrate  5  is held on a position out of the focus of the image forming optical system  32 . Based on the mask pattern used at this time and the defocus amount, the shape and width of a beam profile of the reverse peak pattern are controlled. The width of the peak pattern increases in proportional to square root of the defocus amount. In this manner, a beam profile is measured (Step S 6 ).  
      The bundle of light applied to a given point of the substrate surface is composed of split beams including the center beam passing through the optical axis  50   a . The angle of a certain beam with respect to the center beam is determined by multiplying the angle of the certain beam with respect to the center beam on the mask  32   d , which is determined by a geometric shape of the homogenizer  32   a , by the magnification of the telecentric type lens  32   e.    
      The phase shifter  31  has a predetermined step portion  31   a , which causes the Fresnel diffraction to individual split beams. Since the diffraction patterns of the individual beams are superposed on the substrate surface, the light intensity distribution of the substrate surface is determined by not only parameters (gap d, phase difference θ) of the phase shifter  31  but also the degree (ε) of spreading the beams incident upon the phase shifter  31  as well as the interference between the beams. The phase shifter  31  shifts the phase of the light  50  passed through the mask  32   d  along the optical axis  50   a  alternately between 0 and π. After the beam profile is measured, the profiler  6  is removed from the irradiation area (Step S 7 ) and the substrate stage is introduced into the irradiation region (Step S 8 ). By using the alignment mechanisms  7  and  80 , the incident surface of the substrate  5  is roughly aligned with the optical axis  50   a  of the light source (Step S 9 ). Subsequently, the incident surface of the substrate  5  is precisely aligned with the optical axis  50   a  of the light source by the alignment mechanisms  7  and  80 . (Step S 10 ). When the substrate  5  is aligned with the optical system  32  in this manner, the substrate  5  is positioned at a image-forming site of the reducing lens  32   e.    
      Next, the angle of the attenuator  2  is adjusted such that the measured intensity and the beam profile match with preset targets, respectively. More specifically, the initial magnification of the attenuator ( 1/100) is multiplied 100 fold to 1, equal to the size of the real image (Step S 11 ).  
      After the movable stage  7  is moved horizontally to bring the tip of the optical axis  50   a  to point at a predetermined crystal region of the semiconductor substrate  5 , the substrate  5  is irradiated with laser light having a predetermined intensity and beam profile. More specifically, the amorphous silicon film  303  is irradiated with pulse laser light having the beam profile A shown in  FIG. 10A  and annealed to form small crystal grains r 1  shown in  FIG. 10B  (Step S 12 ). The laser light  50 , whose fluence is first optically modified by adjusting the angle of the dielectric multi-film coating filter at the attenuator  2 , is divided into scattered beams by the homogenizer  32   a  formed of two pairs of small lenses (respectively placed in the X axis and Y axis). One shot is given for 30 nanoseconds. The center-axis beams of individual scattered beams thus split are converged into the center of the mask  32   d  by the condenser lens  32   b . Since individual beams are slightly scattered, the entire surface of the mask  32   d  can be illuminated. All light beams emitted from micro emission regions divided are applied to all points on the mask  32   d . Therefore, even if the light intensity of the laser emission surface slightly varies depending upon points within the plane of the laser emitting surface, the light intensity of the mask  32   d  becomes uniform.  
      The center-axis light beams of the beams passing through individual regions of the mask  32   d , in other words, the scattered light beams passed through the lens pairs  32   b ,  32   c  placed in the middle of the homogenizer  32   a  are formed into parallel beams by the convex lens  32   c  arranged in the vicinity of the mask pattern, pass through the telecentric type reducing lens  32   e , and vertically enters into the substrate  5 .  
      When the amorphous silicon film  303  is irradiated with a pulse laser beam having the beam profile shown in  FIG. 10C  and annealed, large crystal grains r 2  shown in  FIG. 10D  are formed (Step S 12 ). In this manner, the large crystal grains r 2  are formed in a predetermined region of the silicon film.  
      The position of the movable stage  7  can be changed by moving it step by step at predetermined intervals within the X-Y plane. Annealing is repeated while gradually changing the irradiation region in this manner to perform crystallization of a large area (Step S 13 ). The light beams passed through the same point of the mask  32   d  are converged into a single point of the substrate surface. More specifically, a reduced image of the mask  32   d  is formed in the substrate surface with uniform intensity. Reference symbols X and Y used herein refer to the X-axis and Y-axis, and reference symbol Z refers to the perpendicular axis to the horizontal plane.  
      The intensity of laser light may be separately measured by a semiconductor power meter. Alternatively, ultraviolet excimer laser may be directly applied to the CCD  63 .  
      The fluorescent plate  61  is arranged on the same plane as the semiconductor substrate  5  or on the plane vertically in parallel to the semiconductor substrate  5 . When the fluorescent plate  61  is arranged on the plane vertically in parallel to the semiconductor substrate  5  at a different level, the movable stage  7  is moved up and down to position the fluorescent plate  61  at the same level as the semiconductor substrate  5 .  
      In this manner, the beam profile of the laser applied on the substrate surface can be measured under the same conditions of actual irradiation time.  
      The image formed on the CCD  63  is input in the personal computer  8  and sliced by a given scanning line (sampled on a raster basis) to measure the intensity. The intensity and the beam profile of the laser light are measured based on the intensity distribution of the image signal.  
      Next, by comparing the measured intensity to a preset target intensity, the operation amount of the attenuator  2  is determined. The angle of attenuator  2  is controlled by sending an operation signal to the attenuator  2  in a feed back manner until a measured intensity reaches the target intensity.  
      On the other hand, by comparing the measured beam profile to a preset target beam profile, the operation amounts of the beam profile modulator  31  and the movable stage  7  are determined. The position of the phase shifter  31  and the height of the movable stage  7  are controlled by sending operational signals to the beam profile modulator  3  and the movable stage  7 , in a feedback manner, until a measured beam profile reaches a the target beam profile.  
      It is determined whether the region irradiated just before should be the last one or not (Step S 14 ). When the determination result of Step S 14  is “NO”, the annealing step of Step S 12  is performed. In contrast, when the determination result of Step S 14  is “YES”, the substrate stage is returned to a home position, thereby terminating the crystallization process.  
      By repeating measurement, alignment, and irradiation, it is possible to simultaneously form the TFT substrate having different crystalline regions in the channel region, more specifically, the crystalline regions formed of different-size grains but having the same average number (Na) of grain boundaries across the current direction.  
      The measurement, alignment and irradiation may not be necessarily performed alternately. Instead, all measurements are first performed to obtain the operational amounts required for alignment. Thereafter, the alignment and irradiation may be simultaneously performed at every crystallization region.  
     EXAMPLE  
      As an example of the present invention, TFT-A (small size TFT) and TFT-B (large size TFT) having the same characteristics but different in size were prepared as follows.  
      First, a substrate was prepared as shown in  FIG. 11A . On the surface of an insulating substrate  5  (formed of, for example, coming  1737  glass, molten quartz, sapphire, plastic, or polyimide), an insulating protecting film  302  formed of 300 nm thick is formed. On the insulating substrate  5 , an insulating protecting film  302  of 300 nm thick is formed. The insulating protecting film  302  may be a SiO 2  film formed by plasma chemical vapor deposition using, for example, tetraethylorthosilicate (TEOS) and O 2 , SiN/SiO 2  laminate film, alumina, or mica. On the protecting film  302 , an amorphous semiconductor film  303  (100 nm thick) such as a Si film or a SiGe film is formed by plasma chemical vapor deposition. On the amorphous semiconductor film  303 , further a gate insulating film  305  (100 nm thick) such as a SiO 2  film is formed by plasma chemical vapor deposition using tetraethylorthosilicate (TEOS) and O 2 . After the film formation, these thin films  302 ,  303 , and  305  are subjected to the dehydrogenation treatment performed by heating under a nitrogen atmosphere at 600° C. for one hour.  
      As a next step, laser crystallization is performed by using the apparatus shown in  FIG. 2 . As a laser source  1 , a high-energy laser emitting light by pulse oscillation, such as a KrF excimer laser, is used.  
      The laser light emitted from the laser source  1  passes through an attenuator  2  and a beam profile modulator  3  capable of modulating power and beam profile As a result, the power and the beam profile are modulated. Thereafter, the laser light passes through an optical element such as a mirror  4  and reaches the movable stage  7  having the semiconductor substrate  5  mounted thereon. The laser crystallization is performed by irradiating the semiconductor substrate  5  with the modulated laser light. On the movable stage  7 , a beam profiler  6  capable of measuring beam profile And possibly used as a power meter is set up. The beam profiler  6  linked to a personal computer  8  to set the height hz of the movable stage  7  and optical parameters (the angle of the attenuator  2  and the position of a phase shifter  31 , etc.), capable of modulating power and a beam profile so as to give a preferable beam profile.  
      The beam profile A shown in  FIG. 10A  is used for forming small grain crystal region r 1  and the beam profile B shown in  FIG. 10C  is used for forming a large grain crystal region r 2 . The conditions for beam profiles A and B are set under the system in couple with the personal computer  8 .  
      When the laser light  50  having beam profile A or B is applied to the amorphous silicon film  303 , a poly-Si crystalline film having desired size crystal grains is formed. When the laser light of beam profile A is applied to a selected region r 1 , small grain size crystal is formed in the selected region r 1 , as shown in  FIG. 10B . Also, when the laser light of beam profile B is applied to a selected region r 2 , large grain size crystal is formed in the selected region r 2 , as shown in  FIG. 10D . In this manner, the crystalline regions different in size can be formed in the same substrate.  
      A thin film transistor shown in  FIG. 11B  is formed in this way.  
      An average number Na of grain boundaries across the current direction in the TFT channel region is evaluated as follows.  
      To clearly distinguish the edge of the active layer of TFT, four sites are marked with a laser marker Mb as shown in  FIG. 12A . Next, as shown in  FIG. 11B , the source electrode  312 , drain electrode  313 , gate electrode  309 , and the interlayer insulating film  314  are removed with an acid such as hydrochloric acid or hydrofluoric acid to expose the active layer of the TFT, poly-Si layer  306 . Subsequently, the TFT formation region is exposed to a mixing solution containing HF:K 2 CrO 3  (0.15 mol/l)=2:1 for 30 seconds. This is called “Secco etching”. In this way, the grain boundary is clearly differentiated. The etching surface is washed with water, dried and subjected to observation under scanning electromicrography. As the image observation apparatus, a surface roughness tester, or an inter atomic force microscope may be used.  
      The number of grain boundaries across the current in the channel region is counted as follows. The source region between two marking sites Mb and the drain region between two marking sites Mb each is divided into 10 equal portions to give straight lines in parallel to each other. The number of straight lines crossing the grain boundaries are counted and averaged to obtain the number of grain boundaries.  
      Since the size of grains is controlled by the beam profile, grain boundaries are present more densely in the small grain size crystal region r 1  than in the large grain size crystal region r 2 .  
      The gate length La of TFT-A is set at 2 μm and the gate length Lb of the TFT-B was set at 4 μm. The width W of each of TFT-A and TFT-B was set at 2 μm.  
      To obtain TFT having the same performance, the beam profiles A and B shown in  FIGS. 10A and 10C  were previously determined. As shown in  FIG. 13 , a desired profile was determined by an hz value based on the relationship between the height hz of the stage and the number of crystal grain boundaries per 1 μm. More specifically, assuming that the height d of the phase shifter is 0 (d=0 μm), the intensity of beam profile A required for TFT-A1 was 500 mJ/cm 2  (Condition 1) at hz=30 μm and the intensity of beam profile B required for TFT-B1 was 700 μm/cm 2  (Condition 2) at hz=20 μm.  
      Under the conditions 1 and 2, a plurality of regions in the substrate (amorphous silicon film) were irradiated with lasers having beam profiles A and B shown in  FIGS. 10A and 10C  to crystallize the amorphous silicon film.  
      The crystallized regions formed by these methods were patterned in accordance with TFT-A1 and TFT-B1 and the following process was performed.  
      As shown in  FIG. 11B , the gate electrode  309  (high-phosphorus doped polysilicon, W, TiW, Wsi 2 , or MoSi 2 ) was formed on the gate insulating film. Ions were implanted by using the gate electrode  309  as a mask to form a source region  311  and the drain region  310 . More specifically, in the case of an N-type TFT, P+ ions were implanted in an order of 10 15  cm −2 . In the case of a P-type TFT, BF 2+  ions were implanted in an order of 10 15  cm −2 . Thereafter, annealing was performed in an electric furnace at 500° C. to 600° C. for about one hour by using nitrogen as a carrier gas to activate impurities. Furthermore, rapid thermal annealing (RTA) was performed at 700° C. for one minute. Finally, the interlayer insulating film  314  was formed, a contact hole was formed and then the source and drain electrodes  312 ,  313  were formed. As the materials for the source and drain electrodes  312  and  313 , Al, W or Al/TiN may be used.  
      (Evaluation Test)  
      In evaluating the obtained TFTs, five points of the substrate (350 mm×400 mm) were chosen. More specifically, four corner points and the intersectional point of two diagonal lines were evaluated.  
      In a region, thin film transistors (TFT-A1) of 2 μm width (d) and 2 μm length (La), and thin film transistors (TFT-B1) of 2 μm width (d) and 4 μm length (Lb) were formed with a predetermined pattern. TFT characteristics were measured at each of the 5 points. The same characteristics of TFT-A1 as those of TFT-B1 were obtained.  
      Furthermore, the ratio of Na/L, where Na is the average number Na of crystal grain boundaries across the current direction in the channel region and L is the gate length, was determined as follows. To distinguish the poly-Si layer of the TFT whose characteristics were determined, positional marking Mb and the upper layer structure were removed. The range of 50 μm×50 μm was evaluated by a scanning electromicroscope. The ratio of Na/L, where Na is the average number of crystal grain boundaries across the current direction in the channel region  306 , and L is the gate length, in each of TFTs (TFT-A1 and TFT-B1) measured, was within the range of a frequency distribution of ±5% (standard deviation; meaning differences from a median value falls within a ±5% range of the median value).  
      When characteristics of TFTs formed in the present invention, were evaluated, TFT-A1 and TFT-B1 had the same performance (electron mobility: 250 cm 2  V/sec.), even though they were different in size.  
      When the most suitable height d was determined at the time of the beam profile determination while changing the height d of the phase shifter  31  under Conditions 1 and 2, the height d was 5 μm in TFT-A 1 and 1 μm in TFT-B1.  
      In these conditions, TFT-A1 and TFT-BI were manufactured. The ratio of Na/L, where Na is the average number of crystal grain boundaries across the current direction in the channel region, and L is the gate length, in each of TFTs (TFT-A1 and TFT-B1) measured, was within ±2% of the frequency distribution (standard deviation; meaning differences from a median value falls within a ±2% range of the median value).  
      When characteristics of TFTs formed in the present invention, were evaluated, TFT-A1 and TFT-B1 had the same performance (electron mobility: 250 cm 2  V/sec.), even though they were different in size.  
      Now, an application example in which the thin film transistor as obtained in the aforementioned embodiment was actually applied to an active matrix type liquid crystal apparatus, will be explained.  
       FIG. 22  is a perspective view of an active matrix type display apparatus using a thin film transistor. A display apparatus  120  has a panel structure comprising a pair of insulating substrates  121  and  122  and an electrochemical substance  123  sandwiched between them. As the electrochemical substance  123 , a liquid crystal material has been widely used. On the lower insulating substrate  121 , a pixel array portion  124  and a driving circuit portion are integrally formed. The driving circuit portion is divided into a vertical driving circuit  125  and a horizontal driving circuit  126 . Each of the driving circuits  125  and  126  has the thin film transistor, TFT-A1 (shown in  FIGS. 11B and 10B ), manufactured in accordance with the present invention.  
      On the insulating substrate  121  and at the upper side of the  FIG. 22 , terminals  127  for connecting to external elements are formed. The terminals  127  are also connected to the vertical driving circuit  125  and the horizontal driving circuit  126  via wiring  128 . In the pixel array portion  124 , gate wiring  129  and signal wiring  130  are formed as columns and rows. At the intersection between both wiring elements, a pixel electrode  131  and a thin film transistor  132  for driving the pixel electrode  131  are formed. The thin film transistor  132  corresponds to TFT-B1 ( FIG. 11B  and  FIG. 11D ) manufactured in accordance with the present invention and drives the pixel electrode  131  by turning on a switch.  
      The gate electrode  309  of TFT  132  for a pixel is connected to the corresponding gate wiring  129 , the drain region  305  is connected to the corresponding pixel electrode  131 , and the source region  310  is connected to the corresponding signal wiring  130 . Furthermore, the gate wiring  129  is connected to the vertical driving circuit  125  and the signal wiring  130  is connected to the horizontal driving circuit  126 .  
      In the driving circuit TFT-A1, variation of the threshold voltage is low compared to that of a conventional Poly-SiTFT, and therefore off-state voltage is low. TFT-A1 exhibits the same carrier mobility as the conventional Poly-SiTFT and can be operated at a high speed by turning on a switch.  
      On the other hand, the pixel TFT  132  (TFT-B1) has a large carrier mobility compared to a conventional Poly-SiTFT. High-speed operation can be made. TFT 132  (TFT-B1) has the same variation of threshold voltage as the conventional Poly-SiTFT and operated by a low off-state current.  
     Second Embodiment  
      As a second embodiment, a proximity type laser annealing apparatus and a method using the apparatus will be explained.  
      As shown in  FIG. 19 , in a laser annealing apparatus  10 A, an attenuator  2  and a homogeneous optical system  32  of a beam profile modulator  3  are arranged near the starting point of the optical axis  50   a  from a laser source  1 . The optical axis passes through a mirror  4 , and goes to a semiconductor substrate held on a movable stage  7 . A phase shifter  31  of the beam profile modulator  3  is arranged near the incident surface of the semiconductor substrate  5  on the movable stage  7 .  
      In the laser annealing apparatus  10 A, a beam profiler  6  and the semiconductor substrate  5  are arranged next to each other and fixed on the movable stage  7 .  
      In addition, a computer  8  is arranged for a control operation. A beam profiler  6  is connected to the input terminal of the computer  8  and the attenuator  2 , the beam profile modulator  3 , and control system C for the movable stage  7  are connected to the output terminals of the computer  8 . The computer  8  independently controls the functions of these elements  2 ,  3 , and  7 .  
      The attenuator  2  optically modulates the light intensity (laser fluence) by controlling the angle of a dielectric multi-film coating filter and comprises a sensor, motor, and control unit (not shown) under the control of the computer  8 . The term “laser fluence” is a yardstick expressing an energy density of a laser and obtained by integrating energy amount per unit area by time.  
      The beam profile modulator  3  modulates the spatial intensity distribution of laser light and comprises the phase shifter  31  and the homogeneous optical system  32 .  
      The phase shifter  31  comprises a sensor, actuator, and control unit (not shown) for exchanging mask patterns and aligning with the optical axis.  
      The phase shifter  31  shifts the phase of light passing through the mask  32   d  alternately between 0 and π to produce a reverse peak pattern having a minimum light intensity at a phase shift portion. Using the reverse peak pattern, the position of a crystal nuclei of the amorphous semiconductor film on the semiconductor substrate  5 , which is a region first solidified, can be controlled. By growing a crystal laterally (lateral growth, which is a two-dimensional growth along a film surface) from the crystal nuclei, the large-diameter crystal grain is formed at a predetermined position. At this time, a desired beam profile is set based on the shape of the phase shifter and the distance of the phase shifter from the semiconductor substrate  5 , and angular distribution of laser light (the angle of incident laser light).  
      Homogeneous optical system  32  is composed of an optical part such as a lens. The semiconductor substrate  5  is placed at an off-focus position of the homogeneous optical system  32  and irradiated with laser light. The shape and width of the reverse pattern are controlled by the mask pattern and the distance from the focus.  
      The width W of the reverse peak pattern increases in proportional to square root of gap d 1  where d 1  is the gap between the phase shifter  31  and the semiconductor substrate  5 . That is W=k×d 1/2  (k is the coefficient).  
      The beam profiler  6  converts ultraviolet excimer laser into a visible light upon receiving the ultraviolet excimer laser by a fluorescent plate  61 . The visible light is reflected by the mirror  62  and received by the CCD  63 . In this manner, the intensity of laser beam and beam profile are simultaneously measured. The light intensity of measurement system may not be limited as long as it is sufficient to measure a beam profile.  
      The intensity of laser light may be separately measured by use of a semiconductor power meter. Alternately, ultraviolet excimer laser may be directly received by the CCD  63 .  
      The fluorescent plate  61  is placed on the same plane as the semiconductor substrate  5  or on the plane parallel to the semiconductor substrate  5 . When the fluorescent plate  61  is arranged on the plane vertically in parallel to the semiconductor substrate  5  at a different level, the movable stage  7  is moved up and down to position the fluorescent plate  61  at the same level as the semiconductor substrate  5 . In this manner, the beam profile of the laser applied on the substrate surface can be measured under the same conditions of actual irradiation time.  
      It is desirable that the fluorescent plate  61  is placed at an optically equivalent position as the surface of the semiconductor substrate  5 . At that time, the fluorescent plate  61  has a moving mechanism for moving along the optical axis of the incident laser. When the fluorescent plate  61  is moved, the moving stage  7  may be moved up and down by the moving amount of the fluorescent plate  61 .  
      The image formed on the CCD  63  is input into the computer  8  and sliced by a given scanning line (sampled on a raster basis). The intensity and the beam profile of the laser light are measured based on the intensity distribution of the image signal.  
      Next, by comparing the measured intensity to a preset target intensity, the operation amount of the attenuator  2  is determined. The angle of attenuator  2  is controlled by sending an operation signal to the attenuator  2  in a feed back manner until a measured intensity reaches the target intensity.  
      Alternatively, by comparing the measured beam profile to a preset target beam profile, the operation amounts of the beam profile modulator  3  and the movable stage  7  are determined. The position of the phase shifter  31  and the height of the movable stage  7  are controlled by sending operational signals to the beam profile modulator  3  and the movable stage  7 , in a feedback manner, until a measured beam profile reaches a the target beam profile. In this embodiment, the intensity of laser light, laser light distribution, and gap d 1  are controlled in a feedback manner. However, the present invention is not limited to this embodiment. Instead, all of the intensity of laser light, laser light distribution, and gap d 1  are measured and stored in a memory as target values. These values may be separately recalled when laser irradiation is needed. In this way, it is possible to attain laser irradiation with high reproducibility and the crystallization of the TFT channel portion can be constantly performed.  
      The movable stage  7  may be moved three-dimensionally, that is, moved back and forth, left and right, and up and down. For alignment in in-plane and optical-axis directions, a sensor, actuator, and control system (not shown) are provided.  
      The term “a preset target intensity” is the laser intensity (laser fluence) or the distribution of the intensity (beam profile A) at mentioned later proof test (see  FIG. 14A  to  FIG. 18C ) which it is confirmed that an amorphous semiconductor thin film is crystallized, crystal grains laterally grows, and a crystallized film is not destroyed by thermal contraction.  
      Referring now to  FIG. 20 , the optical system of an annealing apparatus will be more specifically described.  
      The annealing apparatus  10 A is used for irradiating a sample (refer to  FIG. 11A ) formed by stacking the underlayer protecting film  302 , the amorphous Si film  303 , and the cap film  305  sequentially on the substrate  5 , with laser light  50  whose intensity and beam profile have been modified. The amorphous Si film  303  is the target to be crystallized. Both the underlying protection film  302  and the cap film  305  are SiO 2  insulating films.  
      A light source, a KrF excimer apparatus  1 , emits a long laser beam  50  of a wavelength of 248 nm. The laser beam  50  is first modified by the attenuator  2 . More specifically the laser fluence is optically modified by controlling the angle of the dielectric multi-film coating filter. Then, the laser beam  50  is divided into scattered beams by the homogenizer  32   a  comprising two small lens pairs in the X and Y directions. Note that one shot pulse is given for 30 nanoseconds. The center-axis beams of individual scattered beams thus divided are converged into the center of the mask  32   d  by the condenser lens  32   b . (convex lens # 1 ).  
      Since individual beams are slightly scattered, the entire surface of the mask  32   d  can be illuminated. All light beams emitted from micro emission regions divided are applied to all points on the mask  32   d  Therefore, even if the light intensity of the laser emission surface slightly varies depending upon points within the plane of the laser emitting surface, the light intensity of the mask  32   d  becomes uniform.  
      The center-axis light beams of the beams passing through individual regions of the mask  32   d , in other words, the scattered light beams passed through the lens pairs placed in the middle of the homogenizer  32   a  are formed into parallel beams by the convex lens  32   c  arranged in the vicinity of the mask pattern, pass through the telecentric type reducing lens  32   e , and vertically enters into the substrate  5  mounted on the movable stage  7  with a heater  7   a.    
      The movable stage  7  can be moved in the X, Y and Z directions. If the substrate is irradiated while changing the irradiation regions by sliding the movable stage  7 , and repeatedly annealed, it is possible to crystallize a large area of the substrate. The beams passed through the same site of the mask  32   d  are converged onto a single point of the substrate surface. In other words, a reduced image of the mask  32   d  can be formed on the substrate surface with a uniform intensity. Note that X and Y denotes the X axis and Y axis. Z denotes a perpendicular axis to a horizontal plane.  
      The light applied to a given point of the substrate surface is composed of beams including the center beam passing through the optical axis  50   a . The angle of a certain beam with respect to the center beam is determined by multiplying the angle of the certain beam with respect to the center beam on the mask  32   d , which is determined by a geometric shape of the homogenizer  32   a , by the magnification of the telecentric type lens  32   e.    
      The phase shifter  31  arranged at the distance of 500 μm from the sample has a step portion  31   a , which causes Fresnel diffraction of individual beams. Since the diffraction patterns of the individual beams are superposed on the substrate surface, the light intensity distribution of the substrate surface is determined by not only parameters (gap d, phase difference θ) of the phase shifter  31  but also the degree (ε) of spreading the beams incident upon the phase shifter  31  as well as the interference between the beams.  
      The annealing apparatus of the present invention used in this embodiment is constructed as mentioned above. In the laser crystallization step, first the stage  7  is moved horizontally to bring the tip of the light axis  50   a  of the laser source  1  to point the fluorescent plate  61  of the beam profiler  6 , and then laser beam is applied to the board  61  to measure the intensity of the laser beam and the beam profile.  
      Next, the angle of the attenuator  2 , the position of the phase shifter  31 , the height of the movable stage  7  are aligned with each other such that the measured intensity and the beam profile match with the preset target ones.  
      Subsequently, the movable stage  7  is horizontally moved to bring that the tip of the optical axis to point a predetermined crystallization region of the semiconductor substrate  5 . The gap is set at d 1 . Thereafter, laser light having a predetermined intensity and beam profile is applied.  
      By repeating measurement, alignment, and irradiation, it is possible to simultaneously form the TFT substrate having different crystalline regions in the channel region, more specifically, the crystalline regions formed of different-size grains but having the same average number (Na) of grain boundaries across the current direction.  
      The measurement, alignment and irradiation may not be necessarily performed alternately. Instead, all measurements are first performed to obtain the operational amounts required for alignment. Thereafter, the alignment and irradiation may be simultaneously performed for each crystallization region.  
      (Proof Test)  
      Referring now to  FIGS. 14A  to  18 C, the characteristics of modulated laser light are defined from the measurement results of the beam profile on the surface of a sample. The actual results were compared with simulation results; at the same time, the actual results and the morphology of the crystallized film are investigated. In addition, critical light intensity values are revealed.  
       FIG. 14A  shows a one-dimensional normalized Fresnel diffraction pattern obtained by an isolated phase shifter (optical-path difference δ is 180°) when a parallel light is used. The distance between the phase shifter and the profiler (equal to the gap d 1  between the phase shifter and the substrate) is set at 110 μm.  FIG. 14B  is a characteristic view of a one-dimensional beam profile of the diffraction pattern of  FIG. 14A . Characteristic line C (thin line) in the figure indicates a one-dimensional beam profile obtained by computer simulation; on the other hand, characteristic line D (thick line) indicates a one-dimensional beam profile measured on the surface of the beam-profiler fluorescent plate. The actual measurement results (characteristic line D) satisfactorily match with theoretical results (characteristic line C) including high-frequency oscillation. In particular, the fact that the minimum strength is nearly zero indicates that excimer laser has a strong self-coherence. The resolving power of the beam profiler  6  is desirably smaller by about one order of magnitude than a crystalline grain diameter. The resolving power obtained in  FIGS. 14A and 14B  was 0.4 μm. The two-dimensional normalized Fresnel diffraction image formed by in-plane cross-coupled phase shifter is shown in  FIGS. 15A and 15B . The gap d is 30 μm. The phase difference was set at 180°. A tetragonal lattice surrounded by the thick line in the figure has a side length of 5 μm.  FIG. 15A  is a computer simulation image.  FIG. 15B  is an actual image of laser fluence emerging on the fluorescent plate surface of the beam profiler. Two-dimensional micro pattern (thin line) inside the lattice pattern other than the main lattice pattern (thick line) is captured. It was proved that the profiler effectively used to evaluate the two-dimensional pattern.  
       FIG. 16A  is a characteristic line graph showing a profile formed of multi-beam by a homogenizer. The horizontal axis indicates the distance (μm) from the laser optical acid  50   a  and the vertical axis indicates the normalized laser intensity index (arbitrary unit). The normalized intensity index of the vertical axis is a parameter or yardstick of crystallization. When these indexes are averaged, a value approximates to 1.0. In  FIG. 16A , an intensity index of 1.0 corresponds to a laser fluence of 0.2 J/cm 2 , which is further multiplied by the coefficient of 0.95, leading to a critical light intensity of 0.19 J/cm 2 , at which polycrystallization takes place.  
      In the figure, characteristic line (thin line) E indicates simulation results and the characteristic line F (thick line) indicates actual measurement results. The actual measurement matches with the simulation results very well except for a high spatial frequency composition due to a limited number of beams.  
       FIG. 16B  shows the morphology of a film crystallized under low average light intensity conditions. The sample has a 300 nm-thick SiO 2  cap film/200-nm thick a-Si film/1000-nm thick SiO 2  film/Si structure crystallized at a substrate temperature of 500° C. A polycrystallized portion (light portion) corresponds to a site exhibiting high intensity. A low intensity site corresponding to a dark portion is a non-crystallized region. The dark portion well matches with the points below the line of 0.19 J/cm 2  (intensity index: 0.95) of  FIG. 16A . The critical light intensity at which polycrystallization takes place is about 0.19 J/cm 2 , which is the value obtained when irradiation is uniformly made. Based on the experiment performed by applying light having a high average intensity, it was found that the critical light intensity value at which lateral crystallization is initiated is 0.48 J/cm 2 , and the critical light intensity value at which film breakdown takes place is 0.90 J/cm 2 . Furthermore, it was found that the crystal can be grown about 7 micron by a single shot.  
      In  FIG. 17A , the horizontal axis indicates the distance (μm) from the laser optical axis a and the vertical axis indicates the normalized laser intensity index (no unit). The  FIG. 17A  shows a characteristic line graph showing the relationship between crystallized Si and the laser fluence, thereby showing whether crystallized Si is laterally grown or not, and whether the laterally grown crystallized film is destroyed or not due to excessive contraction force. Characteristic line P in the figure is a critical line of the lateral growth. A Si crystal is laterally grown in the region above line P, whereas it is not laterally grown in the region below the line. Characteristic line Q is a critical line at which the crystallized film is broken. The Si crystalline film is destroyed by excessive contraction in the region above the line, whereas it is not destroyed in the region below the line. The laser fluence conversion values obtained by multiplying the index of the characteristics lines P and Q by the coefficient were about 0.5 J/cm 2  and about 0.9 J/cm 2 , respectively. Characteristic line R, which is in the region sandwiched by both the characteristic lines P and Q, indicates the crystalline film stably and laterally grown without breakdown of the film.  
       FIG. 17B  is an SEM image of a Si thin film during the lateral growth. A laterally grown Si crystal is observed from the optical axis  50   a  to one side thereof up to 10 μm. However, in the region beyond 10 μm from the optical axis  50   a , since the intensity of a laser greatly varies, debris of broken film (scattered white-lumps) is observed in the figure. Around the laser optical axis  50   a , the film remains in an amorphous state since intensity of laser fluence is insufficient, so that no lateral growth is observed.  
      Using the aforementioned results, an optical system capable of growing large crystallized grains (average diameter: 5 micron) with a high density was obtained. The light intensity distribution and film morphology obtained in the experiment are shown in  FIGS. 18A  to  18 C. The vertical axis of  FIG. 18A  indicates the normalized laser intensity (no unit), which is a yardstick parameter of a crystallization state. The average of there parameters approximates to 1.0. Characterization line G of the figure indicates the simulation results, and characterization line H indicates the result of a profile image actually emerging on the fluorescent plate surface of the laser profiler. In  FIG. 18A , when the minimum value of the vertical axis, 0.6, is multiplied by an average laser fluence, 0.70 J/cm 2 , the critical light intensity (at which lateral crystallization is obtained), 0.42 J/cm 2  is obtained. On the other hand, when the maximum value 1.3 is multiplied by the coefficient, 0.70 J/cm 2 , the critical light intensity, 0.91 J/cm 2 , at which film breakdown takes place, is obtained.  
       FIG. 18B  is an SEM image (0.24 mm×0.24 mm) showing a repeated image pattern in the laser irradiation region (J=0.7 mJ/cm 2 ).  FIG. 18C  shows a partially enlarged SEM image (20 μm×20 μm) of  FIG. 18 . From these, it was found that Si crystal grains are grown laterally and stably from the laser optical axis  50   a  to one side thereof up to 5 μm. As a result, large crystal grains are uniformly formed with a high density over the entire irradiation region (0.24 mm×0.24 mm).  
      The nature of an excimer laser was analyzed by a high-resolution beam profiler. As a result, the light intensity distribution on the surface of a sample can be designed. Various samples were evaluated for critical light intensity. Based on integral analysis of these results, an optical system capable of growing large crystal grains with a high density (large charging rate) was designed. The efficiency of the optical system thus designed was experimentally confirmed.  
      The embodiment mentioned above, the annealing apparatus and the annealing method of the present invention are applied to a crystallization apparatus. The present invention may be applied to any steps such as annealing step to be performed after impurities are doped.  
     EXAMPLE  
      As an examples of the present invention, TFT-A2 (small size TFT) and TFT-B2 (large size TFT) having the same characteristics but different in size were formed as follows.  
      First, a substrate was prepared as shown in  FIG. 11A . On the surface of an insulating substrate  5  (formed of, for example, coming  1737  glass, molten quartz, sapphire, plastic, or polyimide), a first thin film  302  of 300 nm thick is formed. The first thin film  302  may be a SiO 2  film, which is formed by plasma chemical vapor deposition using, for example, tetraethylorthosilicate (TEOS) and O 2 , SiN/SiO 2  laminate film, alumina, or mica. On the surface of the first thin film  302 , a second thin film, namely, an amorphous semiconductor film  303  (100 nm thick) is formed of amorphous Si or SiGe by plasma chemical vapor deposition. On the amorphous semiconductor film  303 , further a SiO 2  film  305  of 100 nm thick is formed as a gate insulating film, by plasma chemical vapor deposition using tetraethylorthosilicate (TEOS) and O 2 . Thereafter, these thin films are subjected to the dehydrogenation treatment performed by heating under a nitrogen atmosphere at 600° C. for one hour.  
      As a next step, laser crystallization is performed by using the apparatus shown in  FIG. 19 . As a laser source  1 , a high-energy laser emitting light by pulse oscillation, such as a KrF excimer laser, is used.  
      The laser light emitted from the laser source  1  passes through an attenuator  2  and a beam profile modulator  3  modulating power and a beam profile, respectively. As a result, the power and the beam profile are modulated. The laser light thus modulated reaches the movable stage  7  having the semiconductor substrate  5  mounted thereon. The laser crystallization is performed by irradiating the semiconductor substrate  5  with the modulated laser light. On the movable stage, a beam profiler  6  for measuring a beam profile and also used as a power meter, is arranged. The beam profiler works in couple with a personal computer  8  to set the height z of the movable stage  7  and optical parameters (angle of the attenuator  2 , position of a phase shifter  31 , and gap d, etc.) for modulating power and a beam profile, so as to give a preferable beam profile.  
      The beam profile A shown in  FIG. 10A  is used for forming small grain crystal region r 1  and the beam profile B shown in  FIG. 10C  is used for forming a large crystal grain region r 2 . The conditions for beam profiles A and B are set under the system in couple with the personal computer  8 .  
      As a result of crystallization in accordance with beam profile A or beam profile B, poly-Si having crystal grains of a desired size. When crystallization is performed by laser irradiation according to beam profile A, a small crystal grain region r 1  is formed in a predetermined region shown in  FIG. 10B . On the other hand, when crystallization is performed by laser irradiation according to beam profile B, a large crystal grain region r 2  is formed in a predetermined region shown in  FIG. 10D . Different crystalline regions can be formed by changing the beam profile of a laser in this manner.  
      The average number Na of crystal grain boundaries across the current direction in the channel region is evaluated as follows.  
      To clearly distinguish the edge of the active layer of a TFT, four sites are marked with a laser marker Mb as shown in  FIG. 12A . Next, as shown in  FIG. 1B , the source electrode  312 , drain electrode  313 , gate electrode  309 , and the interlayer insulating film  314  are removed with an acid such as hydrochloric acid or hydrofluoric acid to expose the poly-Si layer  306  as the active layer (channel region) of the TFT. Subsequently, the channel region  306  is subjected to wet etching for 30 seconds with a Secco etching solution, which is a mixed solution containing HF:K 2 CrO=2:1. In this way, the grain boundary is clearly differentiated. The etching surface is washed with water, dried, and subjected to observation under scanning electromicrography. As the image observation apparatus, a surface roughness measuring means, or an atomic force microscope may be used.  
      The number of grain boundaries across the current in the channel region  306  is counted as follows. The source region between two marking sites Mb and the drain region between two marking sites, Mb, each is divided into 10 equal portions to give straight lines in parallel to each other. The number of straight lines crossing the grain boundaries is averaged to obtain the number of grain boundaries.  
      Since the size of grains is controlled by the beam profile, grain boundaries are present more densely in the small grain size crystal region r 1  than in the large grain size crystal region r 2 .  
      The gate length La of TFT-A2 is 2 μm and the gate length Lb of TFT-B2 is 4 μm. Each of the widths W is set at 2 μm. To obtain a TFT having the same ability, the beam profiles A and B shown in  FIGS. 10A and 10C  were previously determined.  
      As shown in  FIG. 21 , a desired profile was determined by changing the value of gap d 1  based on the relationship between the height z of the stage and the number of crystal grain boundaries per 1 μm. In this example, the beam profile required for TFT-A2 was gap d=300 μm and a laser intensity of 0.55 J/cm 2 . The beam profile required for TFT-B2 was gap d=100 μm and a laser intensity of 0.66 J/cm 2 .  
      Under these conditions, a plurality of regions on the substrate were crystallized by applying lasers having beam profile A and B shown in  FIGS. 10A and 10C .  
      The crystallized regions formed by these methods are patterned into sizes suitable for TFT-A1 and TFT-B1 and the following process was performed.  
      As shown in  FIG. 11B , on the gate insulating film, the gate electrode  309  was formed by using, for example, high-phosphorus doped polysilicon, W, TiW, Wsi 2 , or MoSi 2 . Ions were implanted with the gate electrode  309  used as a mask to form a source region  311  and the drain region  310 . More specifically, in the case of N-type TFT, P+ ions were implanted in an order of 10 15  cm −2 . In the case of P-type TFT, BF 2+  ions were implanted in an order of 1015 cm −2 . Thereafter, annealing was performed in an electric furnace at 500° C. to 600° C. for about one hour by using nitrogen as a carrier gas to activate impurities. Furthermore, rapid thermal annealing (RTA) was performed at 700° C. for one minute. Finally, after the interlayer insulating film  314  was formed, a contact hole was formed, and then the source and drain regions  312 ,  313  were formed. As the materials for the source and drain regions  312  and  313 , Al, W or Al/TiN may be used.  
      In evaluating the obtained TFTs, five points of the substrate (350 mm×400 mm) were chosen. More specifically, four corner points and the intersectional point of two diagonal lines were evaluated.  
      In the region, transistors (TFT-A2) of 2 μm width (d) and 2 μm length (La) and transistors (TFT-B2) of 2 μm width (d) and 4 μm length (Lb) were formed with a predetermined pattern. TFT characteristics were measured at each of the 5 points. The same characteristics were obtained in both TFT-A2 and TFT-B 2 .  
      Furthermore, the ratio of Na/L, where Na is the average number of crystal grain boundaries across the current direction in the channel region  306 , and L is the gate length, was determined as follows. To distinguish the poly-Si layer of the TFT whose characteristics have been determined, Mb marking and the upper layer structure were removed. The field of view of 50 μm×50 μm was evaluated by a scanning electromicroscope. As a result, the ratio of Na/L, where Na is the average number of crystal grain boundaries across the current direction in the channel region  306  and L is the gate length, in each of TFT-A2 and TFT-B2, was within ±5% of frequency distribution (or standard deviation).  
      When characteristics of TFTs formed in the present invention were evaluated, TFT-A1 and TFT-B1 had the same performance (electron mobility: 250 cm 2  V/sec.), even though they were different in size.  
      As shown in Table 1, when the substrate temperature is room temperature, Si grains stably and laterally grow at a laser fluence ranging from 0.6 to 1.3 (J/cm 2 ). When the substrate temperature is 300□, Si grains stably and laterally grow at a laser fluence ranging from 0.5 to 1.2 (J/cm 2 ). When the substrate temperature is 500□, Si grains stably and laterally grow at a laser fluence ranging from 0.4 to 1.1 (J/cm 2 ).  
      If these results are integrated, it was found that the laser fluence must be limited within the range of 0.6 to 0.9 (J/cm 2 ) in order to obtain the Si crystalline film grown stably and laterally. In other words, the peak and bottom of the light intensity modulated is limited.  
                           TABLE 1                                       Substrate           Threshold   temperature           (J/cm 2 )   500□                          Crystallization   0.1 to 0.2           Lateral growth   0.5 to 0.4           Film breakdown   1.1 to 0.9                      
 
      According to the present invention, it is possible to form different crystalline regions having predetermined grain sizes in the same substrate, for various TFTs different in size having a given performance.  
      According to the present invention, since a Si crystalline film is grown laterally and stably without breaking the film, a TFT operated at a high-speed and having a constant threshold (variance in threshold is low) can be provided.  
      According to the present invention may be applied not only to an excimer laser crystalline method for crystallizing a thin film texture of an amorphous semiconductor and an amorphous single crystalline semiconductor but also to a laser annealing method for activating impurities doped in a semiconductor layer.