Semiconductor thin film decomposing method, decomposed semiconductor thin film, decomposed semiconductor thin film evaluation method, thin film transistor made of decomposed semiconductor thin film, and image display device having circuit constituted of thin film transistors

Abstract

A surface roughness of a polycrystalline semiconductor film to be formed by a laser annealing method is reduced. A transmittance distribution filter is disposed at the optical system of a laser annealing apparatus. The transmittance distribution filter controls an irradiation light intensity distribution along a scanning direction of a substrate formed with an amorphous silicon semiconductor thin film to have a distribution having an energy part equal to or higher than a fine crystal threshold on a high energy light intensity side and an energy part for melting and combining only a surface layer. This transmittance distribution filter is applied to an excimer laser annealing method, a phase shift stripe method or an SLS method respectively using a general line beam to thereby reduce the height of protrusions on a polycrystalline surface.

1 . A laser annealing apparatus for decomposing an amorphous semiconductor thin film into a polycrystalline semiconductor thin film by scanning a laser beam having a shape of a line beam and irradiating said laser beam to said amorphous semiconductor thin film to conduct crystallization of said amorphous semiconductor thin film, 
 wherein said crystallization is executed by controlling an irradiated beam intensity distribution profile by disposed a transmittance distribution filter near a focussing plane of an optical system of the laser annealing apparatus, said transmittance distribution filter controlling a light intensity distribution of said line beam to have a constant transmittance in-plane distribution.    
   
   
       2 . A polycrystalline semiconductor thin film decomposed by irradiating a laser beam having a shape of a line beam to an amorphous semiconductor thin film by scanning said laser beam along a direction crossing a axis direction of said line beam to conduct crystallization of said amorphous semiconductor thin film, 
 wherein crystal grains of said decomposed polycrystalline semiconductor thin film have a shape laterally grown along one direction, protrusions exist at boundaries between said crystal grains and in said crystal grains, and only one period of changing layout positions of said protrusions along one direction exists.    
   
   
       3 . A polycrystalline semiconductor thin film decomposed by irradiating a laser beam having a shape of a line beam to an amorphous semiconductor thin film by scanning said laser beam along a direction crossing a axis direction of said line beam to conduct crystallization of said amorphous semiconductor thin film, 
 wherein crystal grains of said decomposed polycrystalline semiconductor thin film have a shape laterally grown along two in-plane directions, protrusions exist at boundaries between said crystal grains and in said crystal grains, and only one period of changing layout positions of said protrusions exists along each of said two in-plane directions.    
   
   
       4 . The polycrystalline semiconductor thin film according to  claim 2 , wherein the polycrystalline semiconductor thin film includes crystal grains whose grain boundary size is 1.5 μm or larger along one direction and 0.5 μm or smaller along another direction generally perpendicular to said one direction, and heights of said protrusions on a surface of the polycrystalline semiconductor thin film correspond to a PV value of 70 nm or smaller in an area of a several μm square.  
   
   
       5 . The polycrystalline semiconductor thin film according to  claim 3 , wherein the polycrystalline semiconductor thin film includes crystal grains whose grain boundary size is 1.5 μm or larger along one direction and 1.5 μm or larger along another direction generally perpendicular to said one direction, said protrusions on a surface of the polycrystalline semiconductor thin film are arranged on generally perpendicular straight lines, and heights of said protrusions correspond to a PV value of 70 nm or smaller in an area of a several μm square.  
   
   
       6 . A semiconductor film evaluation method of evaluating a semiconductor film on a transparent substrate, 
 wherein a reflectance and a transmittance of said semiconductor film are measured by irradiating a laser beam to said semiconductor film and a value of “1−reflectance+transmittance)” is calculated.    
   
   
       7 . A polycrystalline semiconductor thin film evaluation apparatus for evaluating a polycrystalline semiconductor thin film, 
 wherein a polycrystalline surface roughness and a grain size are evaluated by measuring an intensity of a diffraction spot on a light diffraction pattern plane and an angular distribution of a scattered light intensity, respectively of the polycrystalline semiconductor thin film.    
   
   
       8 . A thin film transistor made of a polycrystalline semiconductor thin film, wherein the polycrystalline semiconductor thin film includes crystal grains whose grain boundary size is 1.5 μm or larger along one direction and 0.5 μm or smaller along another direction generally perpendicular to said one direction, and protrusions on a surface of the polycrystalline semiconductor thin film arranged on generally perpendicular straight lines, and heights of said protrusions correspond to a PV value of 70 nm or smaller in an area of a several μm square.  
   
   
       9 . A thin film transistor having a polycrystalline semiconductor film, wherein the polycrystalline semiconductor film includes crystal grains whose grain boundary size is 1.5 μm or larger along one direction and 1.5 μm or larger along another direction generally perpendicular to said one direction, and protrusions on a surface of the polycrystalline semiconductor thin film arranged on generally perpendicular straight lines, and heights of said protrusions correspond to a PV value of 70 nm or smaller in an area of a several μm square.  
   
   
       10 . An image display device including a thin film transistor circuit made of polycrystalline semiconductor thin films, wherein the polycrystalline semiconductor thin film includes crystal grains whose grain boundary size is 1.5 μm or larger along one direction and 0.5 μm or smaller along another direction generally perpendicular to said one direction, and protrusions on a surface of the polycrystalline semiconductor thin film arranged on generally perpendicular straight lines, and heights of said protrusions correspond to a PV value of 70 nm or smaller in an area of a several μm square.