Abstract:
A process and system for processing a silicon thin film on a sample are provided. In particular, an irradiation beam generator is controlled to emit irradiation beam pulses at a predetermined repetition rate. These irradiation beam pulses are then separated into a first set of beam pulses and a second set of beam pulses. The first set of beam pulses are caused to irradiate through a mask to produce a plurality of beamlets. The second set of beam pulses and the beamlets are caused to impinge and irradiate at least one section of the silicon thin film. When the second set of beam pulses and the beamlets simultaneously irradiate the section of the silicon thin film, this combination of the beamlets and second set of beam pulses provides a combined intensity which is sufficient to melt the section of the silicon thin film throughout an entire thickness of the section.

Description:
CLAIM OF PRIORITY  
       [0001]    This application claims priority based on U.S. provisional application serial No. 60/253,256 of James S. Im entitled “Mask Projection System For Laser Crystallization Processing Of Semiconductor Film Regions On A Substrate,” filed on Nov. 27, 2000. 
     
    
     NOTICE OF GOVERNMENT RIGHTS  
       [0002] The U.S. Government has certain rights in this invention pursuant to the terms of the Defense Advanced Research Project Agency award number N6600198-1-8913. 
     
    
     
       FIELD OF THE INVENTION  
         [0003]    The present invention relates to techniques for processing of semiconductor films, and more particularly to techniques for processing semiconductor films using patterned laser beamlets.  
         BACKGROUND OF THE INVENTION  
         [0004]    Techniques for fabricating large grained single crystal or polycrystalline silicon thin films using sequential lateral solidification are known in the art. For example, in U.S. patent application Ser. No. 09/390,537, the entire disclosure of which is incorporated herein by reference herein and which is assigned to the common assignee of the present application, particularly advantageous apparatus and methods for growing large grained polycrystalline or single crystal silicon structures using energy-controllable laser pulses and small-scale translation of a silicon sample to implement sequential lateral solidification have been disclosed. The sequential lateral solidification techniques and systems described therein provide that low defect density crystalline silicon films can be produced on those substrates that do not permit epitaxial regrowth, upon which high performance microelectronic devices can be fabricated.  
           [0005]    While the above-identified patent document discloses a particularly advantageous system for implementing sequential lateral solidification, there have been attempts to modify other systems to implement sequential lateral solidification. One such system is disclosed in U.S. Pat. No. 5,285,236 (“the &#39;236 patent”), the entire disclosure of which is incorporated herein by reference.  
           [0006]    Referring to FIG. 1, the &#39;236 patent discloses a 1:1 projection irradiation system. In particular, an illumination system 20 of this projection irradiation system generates a homogenized laser beam which passes through an optical system 22, a mask 14, a projection lens and a reversing unit to be incident on a substrate sample 10. However, in this prior art projection irradiation system, the energy density on the mask 14 must be greater than the energy density on the substrate 10. This is problematical when processes requiring high fluence on the substrate 10 are considered, as the high energy density incident on the mask 14 can cause physical damage to the mask 14. In addition, such high energy laser light can cause damage to the optics of the system. Accordingly, there exists a need for an improved projection irradiation system of the type described in the &#39;236 patent for implementing the sequential lateral solidification process without damaging the mask 14.  
         SUMMARY OF THE INVENTION  
         [0007]    One of the objects of the present invention is to provide an improved projection irradiation system and process to implement the sequential lateral solidification. Another object of the present invention is to provide a system and process using which, the mask of utilized for shaping the laser beams and pulses is not damaged or degraded due to the intensity of the beams/pulses. It is also another object of the present invention to increase the lifetime of the optics of the system by decreasing the energy being emitted through the optical components (e.g., projection lenses).  
           [0008]    In order to achieve these objectives as well as others that will become apparent with reference to the following specification, the present invention generally provides that an irradiation beam is caused to pass through a beam splitter to become two beams, each providing partial intensity of the energy of the original beam.  
           [0009]    In one exemplary embodiment of the present invention, a process and system for processing a silicon thin film on a sample are provided. In particular, an irradiation beam generator is controlled to emit successive irradiation beam pulses at a predetermined repetition rate. These irradiation beam pulses are then separated into a first set of beam pulses and a second set of beam pulses. The first set of beam pulses are caused to irradiate through a mask to produce a plurality of beamlets. The second set of beam pulses and the beamlets are caused to impinge and irradiate at least one section of the silicon thin film. When the second set of beam pulses and the beamlets simultaneously irradiate the section of the silicon thin film, this combination provides a combined intensity which is sufficient to melt the section of the silicon thin film throughout an entire thickness of the section. The irradiation beam generator arrangement may emit the successive irradiation beam pulses at a predetermined repetition rate.  
           [0010]    In another exemplary embodiment of the present invention, the irradiation beam pulses can be forwarded to a beam splitter which separates the irradiation beam pulses into the first set of beam pulses and the second set of beam pulses. The beam splitter is preferably located upstream in a path of the irradiation beam pulses from the mask, and separates the irradiation beam pulses into the first set of beam pulses and the second set of beam pulses prior to the irradiation beam pulses reaching the mask.  
           [0011]    In still another embodiment of the present invention, the first set of beam pulses has a corresponding intensity which is lower than an intensity required to damage, degrade or destroy the mask. Also, the second set of beam pulses can be prevented from being forwarded to the mask, e.g., by diverting the second set of beam pulses away from the mask prior to the second set of beam pulses reaching the mask. In addition, the second set of beam pulses preferably has a corresponding intensity which is lower than an intensity required to melt the section of the silicon thin film throughout the entire thickness thereof.  
           [0012]    In yet another embodiment of the present invention, when the section of the silicon thin film is irradiated, this irradiated and melted section of the silicon thin film is allowed to re-solidify and crystallize. After the section of the silicon thin film re-solidifies and re-crystallizes, the sample is translated so that the beamlets and the second set of beam pulses impinge a further section of the silicon thin film. This further section at least partially overlaps the section that was allowed to re-solidify and re-crystallize. Also, the sample can be microtranslated so that the beamlets and the second set of beam pulses impinge at least one previously irradiated, fully melted, re-solidified and re-crystallized portion of the section of the silicon thin film.  
           [0013]    The beamlets and the second set of beam pulses can irradiate and fully melt the section of the silicon thin film from a microtranslated location of the sample. The mask may have a dot-like pattern such that dot portions of the pattern are the oblique regions of the mask which prevent the first set of beam pulses to irradiate there through. Also, the mask may have a line pattern such that line portions of the pattern are the oblique regions of the mask which prevent the first set of beam pulses to irradiate there through. Furthermore, the mask may have a transparent pattern such that transparent portions of the pattern do not include any oblique regions therein.  
           [0014]    It is also possible to provide beam extending devices in the path of the first set of beam pulses and/or the second set of beam pulses.  
           [0015]    The accompanying drawings, which are incorporated and constitute part of this disclosure, illustrate a preferred embodiment of the invention and serve to explain the principles of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a schematic block diagram of a prior art 1:1 projection irradiation system;  
         [0017]    [0017]FIG. 2 is a schematic block diagram of an exemplary embodiment of a projection irradiation system according to the present invention;  
         [0018]    [0018]FIG. 3A is an exemplary graph which represents the energy density pattern at a silicon film sample using the prior art projection irradiation system illustrated in FIG. 1;  
         [0019]    [0019]FIG. 3B is an exemplary graph which represents the energy density pattern at the silicon film sample using the exemplary projection irradiation system of the present invention illustrated in FIG. 2;  
         [0020]    FIGS.  4 A- 4 I are illustrations of a radiation beam pulse intensity pattern and the grain structure of exemplary sections of a film sample at different stages of lateral solidification (“LS”) processing in accordance with a first exemplary embodiment of a process of the present invention;  
         [0021]    [0021]FIG. 4J is an exemplary top view illustration of a thin film device which can be fabricated using the process illustrated in FIGS.  4 A- 4 I.  
         [0022]    FIGS.  5 A- 5 E are illustrations of a radiation beam pulse intensity pattern and the grain structure of exemplary sections of a film sample at different stages of the LS processing in accordance with a second exemplary embodiment of the process of the present invention;  
         [0023]    FIGS.  6 A- 6 D are illustrations of a radiation beam pulse intensity pattern and the grain structure of exemplary sections of a film sample at different stages of the LS processing in accordance with a third exemplary embodiment of the process of the present invention; and  
         [0024]    [0024]FIG. 7 is a flow diagram representing an exemplary LS processing procedure under at least partial control of a computing arrangement of FIG. 2 using the processes of the present invention of FIGS.  4 A- 4 I,  5 A- 5 E and  6 A- 6 D, as may be carried out by the system of FIG. 2.  
     
    
     DETAILED DESCRIPTION  
       [0025]    An exemplary embodiment of a projection irradiation system according to the present invention is shown as a schematic block diagram in FIG. 2. In particular, a beam source  200  (e.g., a pulsed excimer laser) generates an excimer laser beam  201  (composed of beam pulses) which passes through a beam splitter  210  to become two beams  211 ,  221 . In one exemplary implementation of the present invention, these two split beams  211 ,  221  may each have 50% of the energy that of the original beam  201 . It is within the scope of the present invention to possibly utilize other energy combinations with the exemplary system of the present invention illustrated in FIG. 2. Each of the beams  211 ,  221  is composed of a set of beam pulses.  
         [0026]    The first split beam  211  can be redirected by a mirror  212  toward a homogenizer  213 , which then outputs a homogenized beam  215 . Thereafter, the homogenized beam  215  (and its respective beam pulses) can be redirected by a second mirror  214  so as to be incident on a semiconductor sample  260  which is held by a sample translation stage  250 . It should be noted that other samples, such as metallic, dialectric, or polymeric films may be substituted for the silicon semiconductor sample  260 .  
         [0027]    During a substantially same time interval, the second split beam  221  (and its respective pulses) can be redirected by a mirror  222  to pass through a mask  230 . The mirror is arranged such that the second split beam  221  is aligned with the mask  230  to allow the second split beam  221  (and its pulses) to be irradiated there through and become masked beam pulses  225 . The masked beam pulses  225  can then be redirected by a second mirror  231  to pass through a projection lens  240 . Thereafter, the masked beam pulses  225  which passed through the projection lens  240  are again redirected to a reversing unit  241  so as to be incident on the semiconductor sample  260 . The mask  230 , the projection lens  240  and the reversing unit  241  may be substantially similar or same as those described in the above-identified &#39;236 patent. While other optical combinations may be used, the splitting of the original beam  201  should preferably occur prior to the original beam  201  (and its beam pulses) being passed through the mask  230 .  
         [0028]    It should be understood by those skilled in the art that instead of a pulsed excimer laser source, the beam source  200  may be another known source of short energy pulses suitable for melting a thin silicon film layer in the manner described herein below, such as a pulsed solid state laser, a chopped continuous wave laser, a pulsed electron beam or a pulsed ion beam, etc., with appropriate modifications to the radiation beam path from the source  200  to the sample  260 . The translations and microtranslations of the sample stage  250  are preferably controlled by a computing arrangement  270  (e.g., a computer which uses Intel Pentium® 4 microprocessor) which is coupled to the beam source  200  and the sample stage  250 . It is also possible for the computing arrangement  270  to control the microtranslations of the mask  230  so as to shift the intensity pattern of the first and second beams  211 ,  221  with respect to the sample  260 . Typically, the radiation beam pulses generated by the beam source  200  provide a beam intensity in the range of 10 mJ/cm 2  to 1J/cm 2 , a pulse duration (FWH) in the range of 10 to 103 nsec, and a pulse repetition rate in the range of 10 Hz to 104 Hz.  
         [0029]    [0029]FIG. 3A shows is an exemplary graph which represents the energy density pattern at a silicon film sample using the prior art projection irradiation system illustrated in FIG. 1. In particular, this graph illustrates the energy density pattern at the plane of the substrate sample  10  when there is no beam splitter  201 , as provided in the prior art system of FIG. 1. As shown in FIG. 3A, in order for particular portions of the silicon thin film of the sample to be fully melted throughout its thickness, the energy of the laser pulses E melt ) has to be high enough for such melting, and likely exceeds the damage threshold (E damage ) for the mask  230 .  
         [0030]    [0030]FIG. 3B shows an exemplary graph which represents the energy density pattern at the silicon film sample using the exemplary embodiment of the projection irradiation system illustrated in FIG. 2, in which the beam splitter  211  is being used to split the original beam  201  into the two split beams  211 ,  221 . In particular, the energy density pattern of the second split beam  221  is selected to be below the damage threshold (E damage ) at the plane of the mask  230 . In this manner, the mask  230  would not be damaged or degraded by the beam generated by the irradiation beam emitted by the beam source  200 . Meanwhile, the homogenized beam pulses  216 , which correspond to the pulses of the first split beam  211 , can irradiate the sample  260  such that the intensity of the pulses  216  is not enough to melt the silicon thin film of the sample  260  throughout its thickness. When the intensity of the second split beam  221  is added to that of the first split beam  211 , the resultant combination of beam pulses has the intensity which is enough to melt the silicon thin film of the sample  260  throughout its entire thickness.  
         [0031]    A first exemplary embodiment of the process of the present invention shall now be described with reference to FIGS.  4 A- 4 I. In particular, FIG. 4A shows an exemplary region of the sample  260 , such as a partially fabricated integrated circuit device, which includes at least one section  82  (and preferably more than one section) of the silicon thin film thereon. This section  82  may be composed of certain areas extending in a horizontal direction, as well as other areas extending in a vertical direction. The section  82 , as well as other section of the silicon thin film on the sample  160  have small grains and grain boundaries randomly oriented in various directions therein. The thickness of the section  82  may be in the range of less than 20 nannometers to 2 μm. Other thicknesses of the silicon thin films and sections thereof are conceivable for use, and are within the scope of the present invention.  
         [0032]    [0032]FIG. 4B shows the section  82  after being irradiated by a first radiation beam pulse having a desired intensity pattern. In the present exemplary embodiment, this pattern is a “pocka-dot” pattern which is preferably aligned with certain areas of the section  82 . The mask  230  of FIG. 2 can be used to effectuate such pattern upon it being irradiated by the second split beam pulses  221 . In particular and to add further detail, the mask  230  has a pattern which consists of one or more sets of 1-micrometer orthogonally positioned opaque dot-like regions. Thus, the set of the opaque regions on the mask  230  do not allow the pulse of the second split beam  221  to pass there through so as to prevent the irradiation of the corresponding areas on the section  82 . However, the regions on the mask  230  surrounding the opaque dot-like regions allow the pulses to pass there through so as to allow the exiting irradiation beam pulses to irradiate and melt the respective other areas of the section  82  (melted regions  50 ). The resultant beam pulse would have an intensity pattern which includes “shadow” regions  61  corresponding to the opaque dot-like regions of the mask  230 .  
         [0033]    When the second split beam pulses  221  are passed through the mask  230 , with the first split beam pulses irradiating (but not melting) the sample  260 , the combined first and second split beam pulses  211 ,  221  completely melt areas  50  of the section  82 , but not dot-shaped unmelted areas  61 . According to the exemplary embodiment shown in FIG. 2B, the unmelted areas  61  are provided at regular intervals along the centerline of the section  82 . In particular, when the section  82  of the silicon thin film is irradiated by a first set of the first and second split beam pulses  211 ,  221  (with the second split beam pulses  221  having the intensity pattern defined by the mask  230 ), each area irradiated by the unblocked second split beam pulses  221  is melted throughout its entire thickness, while each area of the section  82  that is blocked by the opaque pattern of the mask  230  remains at least partially unmelted. Therefore, the unmelted area  50  of the section  82  has the original grain structure of the section  82  of the silicon thin film as it was originally formed.  
         [0034]    The shadow regions of the intensity pattern, the shape of which corresponds to that of the unmelted areas  61 , which may have any shape, such as a circle, a square, etc., have a small cross-sectional area. It is preferable for the shadow regions to be large enough so that the melted surrounding areas of the silicon thin film provided on the sample  260  does not cause a complete melting of the areas  61  on the section  82  that are associated with the respective shadow regions. In accordance with the invention and as described above, the areas  61  of the section  82  overlapped by respective ones of the shadow regions should preferably remain at least partially unmelted.  
         [0035]    Turning to FIG. 4C, after the section  82  of the silicon thin film provided on the sample  260  is irradiated via a first set of the first and second split beam pulse  211 ,  221 , the melted areas of the section  82  are permitted to cool and re-solidify. Since the at least partially unmelted areas  63  of the section  82  of the silicon thin film have the original grain structure of the areas  61  of the section  82 , such grain structure in each-at least partially unmelted area  63  seeds lateral growth of grains into the adjoining re-solidifying melted regions of the section  82 . During such re-solidification of each melted area, the grains grow outward from each one of the at least partially unmelted areas  63  in a respective re-solidification area  55  immediately surrounding the at least partially unmelted area  63  in the section  82  of the silicon thin film. After the re-solidification of the regions  55 , areas  52  are formed at the edges or borders of these regions  55 . The areas  52  are small grained polycrystalline silicon areas formed due to a nucleation, i.e., the sections of the silicon thin film corresponding to these areas  52  have been partially melted and re-solidified with small grains provided therein. Each re-solidification region  55  is bounded by the respective areas  52  and the neighboring re-solidification region  55 , as well as the areas  52 . The grain growth in each of the melted and re-solidifying regions  55  is effectuated by seeding thereof via the at least partially unmelted region  63  within the respective re-solidification region  55 .  
         [0036]    The abutting grain growth distance of the grains growing from each one of the at least partially unmelted areas  63  is approximately half the width of the melted regions as defined by the width of the beamlets (or shaped beam pulses) exiting from the mask  230 . In this manner, larger grains  62  are formed in each of the re-solidification areas  55  after the re-solidification of the melted regions of the section  82  is completed. The spacing between the adjacent at least partially unmelted areas  63  should be such that the grains growing from each such unmelted area  63  abuts the grains growing from its two adjacent at least partially unmelted areas  63  before the re-solidification of the melted regions of the section  82  of the silicon thin film is completed (i.e., before the nucleation of new grains occurs in the intervening spaces). The characteristic growth distance of the grains is the distance that the grains grow before the nucleation of new grains occurs.  
         [0037]    Turning to FIG. 4D, because the position of impingement of the first and second split beam pulses  211 ,  221  on the section  82  of the silicon thin film is preferably fixed, the sample  260  is then repositioned by the sample translation stage  250  under the control of the computing arrangement  270 . This is done so that the shadow regions  64  of the intensity pattern of a second set of the first and second split beam pulses  211 ,  221  (generated when the second set of the second split beam pulses  221  are passed through the mask  230 ) can each be slightly shifted by a distance less than the largest abutting grain growth distance (due to the irradiation of the first set of the first and second split beam pulses  211 ,  221  with respect to the previous positions on the section  82  of the shadow regions  61  of the intensity pattern of the first set of the first and second split beam pulses  211 ,  221 ). The abutting grain growth distance is the distance that a grain grows from an at least partially unmelted region in an adjoining melted region before abutting another grain growing in the same melted region and before abutting the area  52  (i.e., a nucleation region). In this manner, when the second set of first and second split beam pulses  211 ,  221  is irradiated on the section  82  of the silicon thin film, each shadow region  64  overlaps a different section within the same re-solidification area  55  formed after the irradiation by the first set of the first and second split beam pulses  211 ,  221 , which is different from the previous shadow region.  
         [0038]    For example, the position of the new shadow regions  64  can be shifted from the previous position of the shadow regions  61  by a distance in the range of 0.01 m to 10 m. Such minor repositioning shall be referred to hereinafter as a “microtranslation”. Optionally, the mask  230  may be microtranslated (i.e., instead of or together with) the sample  260  to obtain the desired shift of the shadow regions  64  of the intensity pattern when the second set of the first and second split beam pulses  211 ,  221  irradiates the section  82 . Although the beamlets of the intensity pattern of the second set of the first and second split beam pulses  211 ,  221  are also shifted with respect to that of the intensity pattern of the first set of the first and second split beam pulses  211 ,  221 , the shifted beamlets still overlap all regions of the section  82  not overlapped by the respective shifted shadow regions  64 .  
         [0039]    As shown in FIG. 4D, after the above-described microtranslation of the sample  260 , the system of FIG. 2 irradiates the section  82  with the second set of the first and second split beam pulses  211 ,  221 . This is done so that each region of the section  82  of the silicon thin film that is overlapped by the shifted and unblocked beamlet is melted throughout its entire thickness, and each area of the section  82  which is prevented from being irradiated by a respective region of the dot-type pattern of the mask  230  (i.e., the respective shifted shadow region  64 ) remains at least partially unmelted. Each one of the at least partially unmelted areas adjoins respective adjacent melted areas. The sample  260  may be microtranslated in any direction so long as each one of the shifted shadow regions  64  overlaps a portion within the same re-solidification area  55  as a portion overlapped by a corresponding one of the shadow regions  61  of the intensity pattern of the first set of the first and second split beam pulses  211 ,  221 . For example, the sample  260  can be microtranslated in the −A direction which is at minus 135° with respect to the X axis, where rotation of the angles in the counterclockwise direction are taken as positive, or the sample  260  can be microtranslated in the +A direction which is at an angle of 45° with respect to the X axis.  
         [0040]    [0040]FIG. 4E shows the section  82  of the silicon thin film provided on the sample  260  after the completion of the re-solidification of the melted regions following the irradiation by the second set of the first and second split beam pulses  211 ,  221 . There will be a greater number of the grains that will be grown in a corresponding one of new re-solidification regions  55 ′ upon the re-solidification of each melted region of the section  82  after the irradiation by the second set of the first and second split beam pulses  211 ,  221 . This is because each one of the at least partially unmelted areas  65  after the first microtranslation of the sample  260  and the irradiation by the second set of the first and second split beam pulses  211 ,  221  contains a smaller number of grains than was contained in each one of the at least partially unmelted areas  63  after irradiation by the first set of the first and second split beam pulses  211 ,  221 . As illustrated in FIG. 4E, the growth of the grains takes place laterally from each of the shifted at least partially unmelted areas  65  to either reach the nucleated areas  52  of the section  82  formed after the re-solidification, or to abut the grains growing from the adjacent shifted at least partially unmelted regions  65  to define the new re-solidification areas  55 ′, the abutting grains having grown by respective abutting growth distances. Referring again to FIG. 4E, each of the new re-solidification areas  55 ′ has fewer and larger grains  66  than those in the previous re-solidification areas  55  as illustrated in FIG. 4C.  
         [0041]    Referring to FIG. 4F, after the re-solidification of the melted areas that followed the irradiation thereof by the second set of the first and second split beam pulses  211 ,  221  is completed, the sample  260  may be further microtranslated (with respect to the first and second split beam pulses  211 ,  221 ) in any direction by a distance less than the largest abutting grain growth distance (after the second set of the first and second split beam pulses  211 ,  221  irradiated the section  82 ). This is done so that the twice-shifted shadow regions  67  of the intensity pattern of a third set of the first and second split beam pulses  211 ,  221  each overlaps or irradiates a different area within a respective one of the re-solidification areas  55 . In the exemplary illustration of FIG. 2F, the direction of the further microtranslation B is at 45° with respect to the X axis. After the sample  260  is microtranslated in this direction, the section  82  is irradiated by a third set of the first and second split beam pulses  211 ,  221  having the same intensity pattern defined by the mask  230 , but in the portions where the shadow regions  67  each have been shifted twice. The twice-shifted shadow regions  67  are displaced from respective previous shadow regions  64  by a distance less than the largest abutting grain growth distance after the irradiation by the second set of the first and second split beam pulses  211 ,  221 , for example, in the range of 0.01 m to 10 m. Although the beamlets of the intensity pattern of the third set of the first and second split beam pulses  211 ,  221  are also shifted with respect to that of the intensity pattern of the second set of the first and second split beam pulses  211 ,  221 , the twice-shifted beamlets still overlap all areas of the section  82  not overlapped by a respective one of the twice-shifted shadow regions  67 .  
         [0042]    [0042]FIG. 4G illustrates the re-solidified section  82  of the silicon thin film provided on the sample  260  after being irradiated by the third set of the first and second split beam pulses  211 ,  221 , and shows the completion of the re-solidification of the melted areas. Because the twice-shifted at least partially unmelted areas  71  each contain a smaller number of grains than was contained in the once-shifted at least partially unmelted areas  65 , there will be an equal or smaller number of grains that will be grown in a corresponding one of new re-solidification areas  69  upon the completion of the re-solidification of each melted area of the section  82  (after the section  82  is irradiated by the third set of the first and second split beam pulses  211 ,  221 ). As shown in FIG. 4G, the growth of the grains takes place laterally from each of the twice shifted at least partially unmelted areas  71  to either reach the again-nucleated area  52 , or to abut grains growing from adjacent twice shifted at least partially unmelted areas  71  to define the new re-solidification areas  69 , the abutting grains having grown by respective abutting grain growth distances. Each of the new re-solidification areas  69  has fewer and larger grains  68  than the previous re-solidification areas  55 ′ illustrated in FIG. 4E.  
         [0043]    Turning now to FIG. 2H, after each melted area of the section  82  is re-solidified (i.e., following the irradiation by the third set of the first and second split beam pulses  211 ,  221  is completed), the sample  260  may be further microtranslated with respect to the first and second split beam pulses  211 ,  221  in any direction by a distance less than the largest abutting grain growth distance after the irradiation by third set of the first and second split beam pulses  211 ,  221 . In this manner, the thrice-shifted shadow regions  63  of the intensity pattern of a fourth set of the first and second split beam pulses  211 ,  221  overlaps a different area within a respective one of the re-solidification areas  69 . In the exemplary embodiment illustrated in FIG. 4H, the direction of a further microtranslation in a direction C is at −135° with respect to the X axis, and the distance of the further microtranslation is in the range of 0.01 m to 10 m. After the sample  260  is microtranslated in this direction by the above noted distance, the section  82  of the silicon thin film is irradiated by the fourth set of the first and second split beam pulses  211 ,  221  having the same intensity pattern as that of the third set of the first and second split beam pulses  211 ,  221  illustrated in FIG. 4F, but where the shadow regions  72  and the respective intensity pattern each have been shifted thrice with respect to the section  82 .  
         [0044]    [0044]FIG. 4I show the re-solidified section  82  after it is irradiated by the fourth set of the first and second split beam pulses  211 ,  221 , along with the completion of the re-solidification of each melted area. The at least partially unmelted areas  73  overlapped or irradiated by respective ones of the thrice-shifted shadow regions  63  (i.e., the thrice-shifted at least partially unmelted areas) each contain a single grain. Thus, there would likely be an equal or greater number of the grains that will be grown in a corresponding one of the new re-solidification areas  70  upon the completion of the re-solidification of the melted areas of the section  82 . As illustrated in FIG. 4I, the growth of the grains takes place laterally from each one of the thrice-shifted at least partially unmelted areas  73  to either reach the again-nucleated area  52  or to abut the grains growing from adjacent thrice-shifted at least partially unmelted areas  73  to define the new re-solidification areas  70 . Each of the new re-solidification areas  70  of the section  82  has a single grain being grown therein, and each grain boundary is substantially perpendicular to a respective one of the section  82  at the location of the grain boundary. It should be understood that the section  82  may be subjected to more or less of the microtranslation, irradiation and re-solidification steps, as described with reference to FIGS.  4 A- 4 I, so as to obtain the desired long-grained crystalline structure illustrated in FIG. 4I in the section  82 .  
         [0045]    After the completion of the above-described LS processing to obtain a desired crystalline grain structure in the section  82  of the silicon thin film, the sample  260  may be translated to a next section for LS processing therein. For example, the sample  260  may translated in −K direction (which is a direction that is +135° with respect to the X axis) for a distance that is preferably slightly smaller than the diameter of the longest distance between the side walls of the re-solidified areas of the section  82 . In this manner, the translated intensity pattern generated by the first and second split beam pulses  211 ,  221  irradiates a neighboring section of the silicon thin film provided on the sample  260  with is provided at an offset and −45° from the re-solidified areas of the section  82 .  
         [0046]    [0046]FIG. 4J shows a top view of exemplary thin film transistor devices  90 ,  90 ′ which can be fabricated using the exemplary process illustrated in FIGS.  4 A- 4 I and described above. Each of the transistor devices  90 ,  90 ′ includes a source (S) terminal  91 ,  91 ′ and a drain (D) terminal  92 ,  92 ′. In addition, these transistor devices  90 ,  90 ′ have respective active channel region  93 ,  93 ′ which are positioned within the large grained silicon area. Such positioning will yield an improved electrical performance, and permit the incorporation of highly functional electrical circuitry.  
         [0047]    A second exemplary embodiment of the process according to the present invention shall now be described with reference to FIGS.  5 A- 5 E. For purposes of illustration, the same configuration of the section  82  of the silicon thin film provided on the sample  260  used to describe the first exemplary embodiment of the process (as illustrated in FIGS.  4 A- 4 I) is used herein to describe the present embodiment of the process according to the present invention. As in the first exemplary embodiment of the process, the section  82  initially has small grains and grain boundaries that are oriented in random directions.  
         [0048]    Referring to FIG. 5B, the section  82  of the silicon thin film is irradiated by a first set of the first and second split beam pulses  211 ,  221  having an intensity pattern as defined by another exemplary embodiment of the mask  230 . This exemplary mask  230  includes a relatively narrow opaque strip which is surrounded by the transparent segments of the mask. The opaque strip is configured such that it does not allow the portion of the second split beam pulse  221  irradiating it to pass there through, while the transparent segments surrounding the opaque strip allow portions of the second split beam pulses  221  to be irradiated there through. Accordingly, when the second split beam pulse  221  is applied to this mask  230 , the intensity pattern of the resultant beam pulses has strip-like shadow regions  83  corresponding in shape to the opaque strips of the mask  230 . In addition to the shadow regions  83 , the intensity pattern of the first radiation beam pulses, as defined by the mask  230 , also includes the beamlets that irradiate all areas of the section  82  not overlapped by the shadow regions  83 . Advantageously, the width of the shadow regions  83  can be in the range of 0.01 m to 5 m.  
         [0049]    Initially, the sample  260  is positioned so that the shadow regions  83  of the intensity pattern of a first set of the first and second split beam pulses  211 ,  221  overlaps the section  82  along the center line of the section  82  of the silicon thin film. Upon being irradiated by the first set of the first and second split beam pulses  211 ,  221 , each of areas  85 ,  86  of the section  82  that is overlapped by the non-shadowed region of the intensity pattern of the second split beam pulses  221  is melted throughout its entire thickness, while each portion of the section  82  overlapped by the respective shadow region  83  remains at least partially unmelted. The shadow regions  83  of the intensity pattern of the second split beam pulses  211  are sufficiently wide so that the thermal diffusion from the melted areas  85 ,  86  in the section  82  does not significantly melt the areas of the section  82  overlapped by the respective shadow regions  83 . After the irradiation by the first set of the first and second split beam pulses  211 ,  221 , the at least partially unmelted regions  84  (see FIG. 5C) in the section  82  will have the original grain structure of the section  82  before the LS processing.  
         [0050]    Turning now to FIG. 5C, upon the cooling and re-solidification of the melted areas  85 ,  86  in the section  82  after the irradiation by the first set of the first and second split beam pulses  211 ,  221 , a lateral growth of the grains will occur outwardly from each one of the at least partially unmelted areas  84  to the area  52  which was not fully melted and then re-solidified (i.e., the nucleated small grain area). In this manner, the re-solidification areas  87 ,  88  are formed in the section  82  with each one of the re-solidification areas  87 ,  88  having a respective row  73 ,  74  of larger crystal grains with grain boundaries oriented at larger angles with respect to the section  82 .  
         [0051]    Turning now to FIG. 5D, after the completion of the re-solidification of the melted areas  85 ,  86  in the section  82  that follows the irradiation by the first set of the first and second split beam pulses  211 ,  221 , the sample  260  is microtranslated in the −M direction at 135° with respect to the X axis, or the mask  230  (shown in FIG. 2) may be microstranslated in the −M direction at −45° with respect to the X axis, to cause the shadow regions  76  of the intensity pattern of a second set of the first and second split beam pulses  211 ,  221  to be shifted so as to overlap respective ones of the rows  73  of the grains in the section  82 . It should be understood by those skilled in the art that either the sample  260 , the mask  230  or both may be microtranslated so as to cause the shadow regions  76  of the intensity pattern of the second set of the first and second split beam pulses  211 ,  221  to overlap respective ones of the rows  74  of grains. Although the beamlets of the intensity pattern of the second set of the first and second split beam pulses  211 ,  221  are also shifted with respect to the position of the intensity pattern of the first set of the first and second split beam pulses  211 ,  221 , the shifted beamlets still overlap all areas of the section  82  not overlapped by a respective one of the shifted shadow regions  76 . Except for the shifting of the shadow regions  76  and the beamlets, the intensity pattern of the second set of the first and second split beam pulses  211 ,  221  is the same as that of the first set of the first and second split beam pulses  211 ,  221 .  
         [0052]    After the microtranslation of the sample  260  or the mask  230  (or both), the section  82  is irradiated by the second set of the first and second split beam pulses  211 ,  221 . This is done because each area of the section  82  overlapped by the shifted beamlet is melted throughout its entire thickness, while each area of the section  82  overlapped by a respective one of the shifted shadow regions  76  remains at least partially unmelted. Each at least partially unmelted areas adjoins adjacent melted areas. Because the at least partially unmelted areas will contain larger grains with grain boundaries forming larger angles with respect to the section  82  than the grains and grain boundaries of the original section  82 , upon the re-solidification of the melted areas  77 ,  78  in the section  82 , these larger grains will seed the growth of the grains laterally in each direction from the at least partially unmelted areas  85  towards the re-nucleated areas  52  of the section  82  so that the section  82  will have larger grains as illustratively represented in FIG. 5E. After re-solidification of the melted areas  77 ,  78  and following the irradiation of the section  82  by the second set of the first and second split beam pulses  211 ,  221  is completed, additional iterations of the microtranslation of the either the sample  260  or the mask  230  in an appropriate direction, the irradiation by a further set of the first and second split beam pulses  211 ,  221 , and the re-solidification of each melted area of the section  82  of the silicon thin film provided on the sample  260  may be carried out to further reduce the number of grains in the section  82 .  
         [0053]    After completion of the LS processing of the section  82  to obtain a desired crystalline grain structure in the section  82  of the silicon thin film as described above with reference to FIGS.  5 A- 5 E, and as discussed above with reference to the exemplary process of FIGS.  4 A- 4 I, the sample  260  may be translated to a next section of the silicon thin film for LS processing therein. In particular, the sample  260  may be translated to a further section so that the LS processing can be performed therein. For example, the sample  260  may translated in −M direction for a distance such that the next irradiation by the first and second split beam pulses  211 ,  221  slightly overlaps the previously irradiated, completely melted and re-solidified areas of the section  82 . In this manner, the translated intensity pattern generated by the first and second split beam pulses  211 ,  221  irradiates a neighboring section of the silicon thin film provided on the sample  260 , which is provided at an offset and 45° from the re-solidified areas of the section  82 .  
         [0054]    A third exemplary embodiment of the process according to the present invention shall now be described with reference to FIGS.  6 A- 6 D. In this exemplary embodiment of the process, as shown in FIG. 6A, the mask  230  includes at least two sets of slits  300 ,  310  which have respective opaque regions  307 ,  317  surrounding corresponding transparent regions  305 ,  309  and  315 ,  319  of the mask  230 . The mask  230  used in this exemplary embodiment of the process according to the present invention does not have any opaque regions inside the transparent regions  305 ,  309 ,  315 ,  319 . Accordingly, with the use of the slits  300 ,  310 , the second split beam pulse  221  is shaped to have the irradiation pattern substantially corresponding to the pattern of the slits  300 ,  310  of the mask  230 .  
         [0055]    Turning now to FIG. 6B, the same configuration of the section  82  of the silicon thin film provided on the sample  260  used to describe the first and second exemplary embodiments of the process (as illustrated in FIGS.  4 A- 41  and  5 A- 5 E, respectively) is used herein to describe the present embodiment of the process according to the present invention. As in the first and second exemplary embodiment of the process, the section  82  initially has small grains and grain boundaries that are oriented in random directions. Initially, areas  320 ,  328 ,  330 ,  338  of the section  82  of the silicon thin film are irradiated by a first set of the first and second split beam pulses  211 ,  221  having an intensity pattern as defined by the exemplary embodiment of the mask  230  shown in FIG. 6A. In particular, the areas  320 ,  328  are irradiated by the portion of the intensity pattern of the second split beam pulses  221  which are shaped by the slits  305 ,  309  of the mask  230 , and the areas  330 ,  338  are irradiated by the portion of the intensity pattern of the second split beam pulses  221  which are shaped by the slits  315 ,  319  of the mask  230 . Since the oblique regions of the mask  230  prevent the second split beam pulses  221  from irradiating the areas  329 ,  339  of the section  82  which are immediately adjacent to the areas  320 ,  328 ,  330 ,  338 , these areas  329 ,  339  are at least partially unmelted. After the irradiation by the first set of the first and second split beam pulses  211 ,  221 , the areas  320 ,  328 ,  330 ,  338  are melted throughout their entire thickness.  
         [0056]    Thereafter, the at least partially unmelted areas  329 ,  339  of the section  82  of the silicon thin film re-solidify and crystallize to form nucleated areas corresponding to the at least partially unmelted areas  329 ,  339 . Also, after the irradiation thereof by the first set of the first and second split beam pulses  211 ,  221 , the melted areas  320 ,  328 ,  330 ,  338  in the section  82  cool and re-solidify, and the lateral growth of the grains occurs outwardly from the nucleated areas  329 ,  339  toward respective centers  322 ,  332  of the completely melted and resolifying areas  320 ,  328 ,  330 ,  338 . In this manner, the re-solidification areas  320 ,  328 ,  330 ,  338  are formed in the section  82  with each one of the re-solidification areas  320 ,  328  and  330 ,  338  having two respective rows  322 ,  324  and  332 ,  334  of larger crystal grains.  
         [0057]    After the completion of the re-solidification of the melted areas  320 ,  328  and  330 ,  338  in the section  82 , and following the irradiation by the first set of the first and second split beam pulses  211 ,  221 , the sample  260  is translated in the M direction at 135° with respect to the X axis, or the mask  230  (shown in FIG. 2) may be microstranslated in the −M direction at −45° with respect to the X axis, so as to cause the intensity pattern of a second set of the first and second split beam pulses  211 ,  221  to be shifted to overlap at least one entire row  324 ,  334  of the re-solidified areas  320 ,  328  and  330 ,  338  in the section  82  (e.g., preferably to overlap the respective centers  322 ,  332  thereof). It should be understood by those skilled in the art that either the sample  260 , the mask  230  or both may be translated to cause the intensity pattern of the second set of the first and second split beam pulses  211 ,  221  to slightly overlap at least one row  324 ,  334 . It should be understood that the intensity pattern of the second set of the first and second split beam pulses  211 ,  221  is the same as that of the first set of the first and second split beam pulses  211 ,  221 . It is also within the scope of the present invention for the intensity pattern of a second set of the first and second split beam pulses  211 ,  221  to slightly overlap a small section of at least one row  324 ,  334  of the re-solidified areas  320 ,  328  and  330 ,  338  in the section  82 .  
         [0058]    After the translation of the sample  260  or the mask  230  (or both), new areas  340 ,  342 ,  350 ,  352  of the section  82  (which are overlapped by the relatively translated first and second split beam pulse  211 ,  221 ) are irradiated by the irradiation pattern of the second set of the first and second split beam pulses  211 ,  221 . As with the areas  320 ,  328 ,  330 ,  338 , the new areas  340 ,  342 ,  344 ,  346  of the section of the silicon thin film are completely melted throughout their thickness. As discussed previously, due to the fact that the oblique regions of the mask  230  prevent the second split beam pulses  221  from irradiating the areas  343 ,  347  of the section  82  which are immediately adjacent to the areas  340 ,  342  and  344 ,  346 , respectively, these adjacent areas  343 ,  347  are at least partially unmelted. FIG. 6C shows the sample  260  when the completely melted areas  340 ,  342 ,  344 ,  346  have re-solidified after being irradiated by the first and second split beam pulses  211 ,  221 . Also shown are the areas  343 ,  347  which were partially melted.  
         [0059]    As shown in FIG. 6D, upon the re-solidification of the fully melted areas  340 ,  342 ,  344 ,  346  in the section  82 , the areas  343 ,  347  re-solidify and nucleate such that the grains of the nucleated areas  343 ,  347  will seed the growth of the grains of the melted areas  340 ,  342 ,  344 ,  346  laterally toward the respective centers of these areas  340 ,  342 ,  344 ,  346 . At the same time, the grains of the solidified and not re-melted portions of the areas  320 ,  328 ,  330 ,  338  will also seed the grain growth of the areas  340 ,  342 ,  344 ,  346  laterally toward the respective centers of these areas  340 ,  342 ,  344 ,  346 . In this manner, the grains extending from the solidified and not re-melted portions of the areas  320 ,  328 ,  330 ,  338  will extend into the newly solidifying areas  340 ,  342 ,  344 ,  346  so as to form long crystalline grains which extend up to the respective centers  352 ,  356  and  362 ,  366  of the re-solidified areas of the section  82  of the silicon thin film which correspond to the melted areas  340 ,  342  and  344 ,  346 , respectively. Therefore, the grains in the rows  324 ,  334  will be longer than the grains in rows  350 ,  354 ,  360 ,  364 .  
         [0060]    In this manner, the LS processing of the section  82  to obtain a desired long crystalline grain structure in the section  82  of the silicon thin film as described above with reference to FIGS.  6 A- 6 D can be achieved. It should be understood that the translation of the sample  260  in the +M direction or the mask  230  in the −M direction may continue until the entire sample has been irradiated in the manner described above with reference to the third exemplary embodiment of the process according to the present invention.  
         [0061]    [0061]FIG. 7 is a flow diagram representing an exemplary LS processing procedure under at least partial computer control using the processes of the present invention of FIGS.  4 A- 4 I,  5 A- 5 E and  6 A- 6 D, as may be carried out by the system of FIG. 2. In step  500 , the hardware components of the system of FIG. 2, such as the beam source  200  and the homogenizer  213 , are first initialized at least in part by the computing arrangement  270 . The sample  260  is loaded onto the sample translation stage  250  in step  505 . It should be noted that such loading may be performed either manually or automatically using known sample loading apparatus under the control of the computing arrangement  270 . Next, the sample translation stage  250  is moved, preferably under the control of the computing arrangement  270 , to an initial position in step  510 . Various other optical components of the system are adjusted manually or under the control of the computing arrangement  270  for a proper focus and alignment in step  515 , if necessary. In step  520 , the irradiation/laser beam  201  is stabilized at a predetermined pulse energy level, pulse duration and repetition rate. Then, the irradiation/laser beam  201  is directed to the beam splitter  210  to generate the first split beam pulse  211  and the second split beam pulse  221  in step  525 . In step  530 , the second split beam  221  is aligned with the mask  230 , and the second split beam pulse  221  is irradiated through the mask  230  to form a masked beam pulse  225 .  
         [0062]    In step  535 , if the current section of the sample  260  is unmelted or has already solidified, this current section of the sample  260  is irradiated with the first split beam pulse  211  and the masked beam pulse  225  which has an intensity pattern controlled by the mask  230 . During this step, the sample  260  can be microtranslated as described above with reference to the processes illustrated in FIGS.  4 A- 4 I and  5 A- 5 E, and the corresponding sections again irradiated and melted throughout their entire thickness. In step  540 , it is determined whether there are any more sections of the sample  260  that need to be subjected to the LS processing. If so, the sample  260  is translated using the sample translation stage  250  so that the next section thereof is aligned with the first and second split beam pulses  211 ,  221  (step  545 ), and the LS processing is returned to step  535  to be performed on the next section of the sample  260 . Otherwise, the LS processing has been completed for the sample  260 , the hardware components and the beam of the system shown in Figure can be shut off (step  550 ), and the process terminates.  
         [0063]    The foregoing merely illustrates the principles of the invention. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. For example, while the above embodiment has been described with respect to sequential lateral solidification, it may apply to other materials processing techniques, such as micro-machining, photo-ablation, and micro-patterning techniques, including those described in International patent application no. PCT/US01/12799 and U.S. patent application Ser. Nos. 09/390,535, 09/390,537 and 09/526,585, the entire disclosures of which are incorporated herein by reference. The various mask patterns and intensity beam patterns described in the above-referenced patent application can also be utilized with the process and system of the present invention. It will thus be appreciated that those skilled in the art will be able to devise numerous systems and methods which, although not explicitly shown or described herein, embody the principles of the invention and are thus within the spirit and scope of the invention.