Systems and methods for implementing an interaction between a laser shaped as a line beam and a film deposited on a substrate

Abstract

A laser crystallization apparatus and method are disclosed for selectively melting a film such as amorphous silicon that is deposited on a substrate. The apparatus may comprise an optical system for producing stretched laser pulses for use in melting the film. In still another aspect of an embodiment of the present invention, a system and method are provided for stretching a laser pulse. In another aspect, a system is provided for maintaining a divergence of a pulsed laser beam (stretched or non-stretched) at a location along a beam path within a predetermined range. In another aspect, a system may be provided for maintaining the energy density at a film within a predetermined range during an interaction of the film with a shaped line beam.

1 . A system for maintaining an energy density at a film within a preselected range during an interaction of the film with a line beam shaped from a light source by a shaping optic, said film having an imperfect, non-planar surface, said system comprising: 
 an autofocus sensor for measuring a distance between the film and the focusing lens; and    a controller using said measurement to adjust a light source parameter to maintain the energy density at the film with the preselected range.    
   
   
       2 . A system as recited in  claim 1  wherein said light source is a pulsed laser source and said light source parameter is pulse energy.  
   
   
       3 . A system as recited in  claim 2  wherein said laser source is a gas discharge laser source and said pulse energy is adjusted by altering a laser source discharge voltage.  
   
   
       4 . A system as recited in  claim 1  wherein said controller adjusts a variable attenuator to maintain the energy density at the film with the predetermined range.  
   
   
       5 . A system as recited in  claim 1  wherein said light source generates a light source spectrum and said controller alters the light source spectrum to maintain the energy density at the film with the predetermined range.  
   
   
       6 . A system for maintaining beam divergence of a pulsed laser beam at a location along a beam path within a predetermined range, said system comprising: 
 an adjustable beam expander;    an instrument for measuring divergence and generating a signal indicative thereof; and    a controller responsive to said signal to adjust said beam expander and maintain the divergence of the pulsed laser beam within the predetermined range.    
   
   
       7 . A system as recited in  claim 6  wherein said instrument measures a wavefront of light passing through said location to generate said signal.  
   
   
       8 . A system as recited in  claim 7  wherein said instrument comprises a DSP based processor and a high speed CMOS linear photodiode.  
   
   
       9 . A system as recited in  claim 6  wherein said beam expander comprises at least two spaced apart optical elements and is adjusted by varying said spacing.  
   
   
       10 . A system as recited in  claim 6  wherein said beam expander comprises a linear motorized drive to move a first beam expander optical element relative to a second beam expander optical element.  
   
   
       11 . A system as recited in  claim 6  wherein said beam expander allows independent beam expansion control in two orthogonal directions.  
   
   
       12 . An optical system for stretching an incoming laser pulse, said system comprising: 
 a beam splitter for directing a first portion of said pulse along a first beam path and a second portion of said pulse along a second delaying beam path; and    a plurality of reflective elements positioned along said delaying beam path and arrange to invert the second beam portion and cooperate with the beam splitter to place at least a portion of the inverted second beam portion for travel on the first beam path.    
   
   
       13 . An optical system as recited in  claim 12  further comprising a beam pointing correction system positioned to steer the incoming laser pulse prior to reaching said beam splitter.  
   
   
       14 . An optical system as recited in  claim 12  wherein said incoming laser pulse is amplified in a power amplifier prior to reaching said beam splitter, said amplifier having an optic for directing said pulse through a discharge region of said amplifier, and wherein said beam pointing correction system comprises; 
 an instrument for conducting a divergence measurement of light on said first beam path and producing a signal indicative thereof; and    a mechanism responsive to said signal to move said optic and orient a pulse traveling toward said beam splitter with a beam pointing angle within a predetermined beam pointing angle range.    
   
   
       15 . An optical system as recited in  claim 12  wherein said plurality of reflective elements comprises an odd number of mirror pairs.  
   
   
       16 . A thin beam laser crystallization apparatus for selectively melting a film deposited on a substrate, said apparatus comprising: 
 a laser source producing a pulsed laser output beam;    an optical system stretching pulses in said laser output beam to produce a pulse stretcher output; and    an optical arrangement focusing said pulses in a first axis and spatially expanding said pulses in a second axis to produce a line beam from the pulse stretcher output.    
   
   
       17 . An apparatus as recited in  claim 16  wherein said optical system comprises: 
 a beam splitter for directing a first portion of each pulse along a first beam path and a second portion of each pulse along a second delaying beam path; and    a plurality of reflective elements positioned along said delaying beam path and arranged to invert the second beam portion and cooperate with the beam splitter to place at least a portion of the inverted second beam portion for travel on the first beam path.    
   
   
       18 . An apparatus as recited in  claim 17  further comprising a beam pointing correction system positioned between said laser source and said beam splitter.  
   
   
       19 . An apparatus as recited in  claim 18  wherein said beam pointing correction system comprises a beam pointing measurement instrument for producing a beam pointing parameter signal and at least one moveable reflector responsive to said signal to altering said beam pointing parameter.  
   
   
       20 . An apparatus as recited in  claim 17  wherein said plurality of reflective elements comprises an odd number of mirror pairs.