Silicon thin film, group of silicon single crystal grains and formation process thereof, and semiconductor device, flash memory cell and fabrication process thereof

Abstract

A process of forming a silicon thin film includes the steps of: irradiating a pulsed rectangular ultraviolet beam on an amorphous or polycrystalline silicon layer formed on a base body, to thereby form a silicon thin film composed of a group of silicon single crystal grains which are each approximately rectangular-shaped and which are arranged in a grid pattern on the base body. In this process, the moved amount of a ultraviolet beam irradiating position in a period from completion of an irradiation of the rectangular ultraviolet beam to starting of the next irradiation of the rectangular-ultraviolet beam is specified at 40 μm or less, and a ratio of the moved amount to a width of the rectangular ultraviolet beam measured in the movement direction thereof is in a range of 0.1 to 5%. Further, a selected orientation of the silicon single crystal grains to the surface of the base body is approximately the <100> direction.

What is claimed is:  
     
         1 . A process of forming a silicon thin film, comprising the step of: 
 irradiating a pulsed rectangular ultraviolet beam on an amorphous or polycrystalline silicon layer formed on a base body, to thereby form a silicon thin film composed of a group of silicon single crystal grains on said base body;    wherein the moved amount of a ultraviolet beam irradiating position in a period from completion of an irradiation of said rectangular ultraviolet beam to starting of the next irradiation of said rectangular ultraviolet beam is specified at 40 μm or less, and a ratio of said moved amount to a width of said rectangular ultraviolet beam measured in the movement direction thereof is in a range of 0.1 to 5%, whereby forming a silicon thin film composed of a group of silicon single crystal grains which are each approximately rectangular-shaped and which are arranged in a grid pattern on said base body, a selected orientation of said silicon single crystal grains to the surface of said base body being approximately the <100> direction.    
     
     
         2 . A process of forming a silicon thin film according to  claim 1 , wherein a length of one side of said silicon single crystal grain approximately rectangular-shaped is 0.05 μm or more.  
     
     
         3 . A process of forming a silicon thin film according to  claim 1 , wherein an average thickness of said silicon thin film is in a range of 1×10 −8  m to 1×10 −7  m.  
     
     
         4 . A process of forming a silicon thin film according to  claim 1 , wherein said base body is made of silicon oxide or silicon nitride.  
     
     
         5 . A process of forming a silicon thin film according to  claim 1 , wherein opposed sides of said silicon single crystal grain approximately rectangular-shaped are approximately in parallel to the movement direction of the ultraviolet beam irradiating position or intersect the movement direction of the ultraviolet beam irradiating position at approximately 45°.  
     
     
         6 . A process of forming a group of silicon single crystal grains comprising: 
 a step (a) of irradiating a pulsed rectangular ultraviolet beam on an amorphous or polycrystalline silicon layer formed on a base body, to thereby form a silicon thin film composed of a group of silicon single crystal grains which are each approximately rectangular-shaped and which are arranged in a grid pattern on said base body, a selected orientation of said silicon single crystal grains to the surface of said base body being approximately the <100> direction; and    a step (b) of separating adjacent ones of said silicon single crystal grains to each other;    wherein the moved amount of a ultraviolet beam irradiating position in a period from completion of an irradiation of said rectangular ultraviolet beam to starting of the next irradiation of said rectangular ultraviolet beam is specified at 40 μm or less; and a ratio of said moved amount to a width of said rectangular ultraviolet beam measured in the movement direction thereof is in a range of 0.1 to 5%.    
     
     
         7 . A process of forming a group of silicon single crystal grains according to  claim 6 , wherein said step (b) of separating adjacent ones of said silicon single crystal grains to each other comprises a step of oxidizing said silicon thin film formed in said step (a) to form each region made of silicon oxide between the adjacent ones of said silicon single crystal grains.  
     
     
         8 . A process of forming a group of silicon single crystal grains according to  claim 6 , wherein a length of one side of each of said approximately rectangular-shaped silicon single crystal grains in said silicon thin film formed in said step (a) is 0.05 μm or more.  
     
     
         9 . A process of forming a group of silicon single crystal grains according to  claim 6 , wherein an average thickness of said silicon thin film formed in said step (a) is in a range of 1×10 −8  m to 1×10 −7  m.  
     
     
         10 . A process of forming a group of silicon single crystal grains according to  claim 6 , wherein said base body is made of silicon oxide or silicon nitride.  
     
     
         11 . A process of forming a group of silicon single crystal grains according to  claim 6 , wherein opposed sides of each of said approximately rectangular-shaped silicon single crystal grains in said silicon thin film formed in said step (a) are approximately in parallel to the movement direction of the ultraviolet beam irradiating position or intersect the movement direction of the ultraviolet beam irradiating position at approximately 45°.  
     
     
         12 . A silicon thin film comprising a group of silicon single crystal grains which are each approximately rectangular-shaped and which are arranged in a grid pattern on a base body, wherein a selected orientation of said silicon single crystal grains to the surface of said base body is approximately the <100> direction.  
     
     
         13 . A silicon thin film according to  claim 12 , wherein a length of one side of said silicon single crystal grain approximately rectangular-shaped is 0.05 μm or more.  
     
     
         14 . A silicon thin film according to  claim 12 , wherein an average thickness of said silicon thin film is in a range of 1×10 −8  m to 1×10 −7  m.  
     
     
         15 . A silicon thin film according to  claim 12 , wherein said base body is made of silicon oxide or silicon nitride.  
     
     
         16 . A silicon thin film according to  claim 12 , wherein said group of silicon single crystal grains are formed by irradiating a pulsed rectangular ultraviolet beam on an amorphous or polycrystalline silicon layer formed on said base body, and 
 wherein the moved amount of a ultraviolet beam irradiating position in a period from completion of an irradiation of said rectangular ultraviolet beam to starting of the next irradiation of said rectangular ultraviolet beam is specified at 40 μm or less, and a ratio of said moved amount to a width of said rectangular ultraviolet beam measured in the movement direction thereof is in a range of 0.1 to 5%.    
     
     
         17 . A silicon thin film according to  claim 16 , wherein opposed sides of said silicon single crystal grain approximately rectangular-shaped are approximately in parallel to the movement direction of the ultraviolet beam irradiating position or intersect the movement direction of the ultraviolet beam irradiating position at approximately 45°.  
     
     
         18 . A group of silicon single crystal grains, comprising a plurality of silicon single crystal grains which are each approximately rectangular-shaped and which are arranged in a grid pattern on a base body, wherein a selected orientation of said silicon single crystal grains to the surface of said base body is approximately the <100> direction, and adjacent ones of said silicon single crystal grains are separated from each other.  
     
     
         19 . A group of silicon single crystal grains according to  claim 18 , which are formed by a process comprising: 
 a step (a) of irradiating a pulsed rectangular ultraviolet beam on an amorphous or polycrystalline silicon layer formed on a base body, to thereby form a silicon thin film composed of a group of silicon single crystal grains which are each approximately rectangular-shaped and which are arranged in a grid pattern on said base body, a selected orientation of said silicon single crystal grains to the surface of said base body being approximately the <100> direction; and    a step (b) of separating adjacent ones of said silicon single crystal grains to each other;    wherein the moved amount of a ultraviolet beam irradiating position in a period from completion of an irradiation of said rectangular ultraviolet beam to starting of the next irradiation of said rectangular ultraviolet beam is specified at 40 μm or less, and a ratio of said moved amount to a width of said rectangular ultraviolet beam measured in the movement direction thereof is in a range of 0.1 to 5%.    
     
     
         20 . A group of silicon single crystal grains according to  claim 19 , wherein said step (b) of separating adjacent ones of said silicon single crystal grains to each other comprises a step of oxidizing said silicon thin film formed in said step (a) to form each region made of silicon oxide between the adjacent ones of said silicon single crystal grains.  
     
     
         21 . A group of silicon single crystal grains according to  claim 19 , wherein a length of one side of each of said approximately rectangular-shaped silicon single crystal grains in said silicon thin film formed in said step (a) is 0.05 μm or more.  
     
     
         22 . A group of silicon single crystal grains according to  claim 19 , wherein an average thickness of said silicon thin film formed in said step (a) is in a range of 1×10 −8  m to 1×10 −7  m.  
     
     
         23 . A group of silicon single crystal grains according to  claim 19 , wherein opposed sides of each of said approximately rectangular-shaped silicon single crystal grains in said silicon thin film formed in said step (a) are approximately in parallel to the movement direction of the ultraviolet beam irradiating position or intersect the movement direction of the ultraviolet beam irradiating position at approximately 45°.  
     
     
         24 . A group of silicon single crystal grains according to  claim 18 , wherein said base body is made of silicon oxide or silicon nitride.  
     
     
         25 . A process of fabricating a semiconductor device, comprising the steps of: 
 irradiating a pulsed rectangular ultraviolet beam on an amorphous or polycrystalline silicon layer formed on a base body, to form a silicon thin film composed of a group of silicon single crystal grains on said base body; and    forming a source/drain region and a channel region in said silicon thin film or said silicon single crystal grains;    wherein the moved amount of a ultraviolet beam irradiating position in a period from completion of an device according to  claim 25 , wherein opposed sides of said silicon single crystal grain approximately rectangular-shaped are approximately in parallel to the movement direction of the ultraviolet beam irradiating position or intersect the movement direction of the ultraviolet beam irradiating position at approximately 45°.    
     
     
         30 . A process of fabricating a flash memory cell, comprising: 
 a step (a) of irradiating a pulsed rectangular ultraviolet beam on an amorphous or polycrystalline silicon layer formed on a tunnel oxide film, to form a silicon thin film composed of a group of silicon single crystal grains which are each approximately rectangular-shaped and which are arranged in a grid pattern on said tunnel oxide film, a selected orientation of said silicon single crystal grains to the surface of said tunnel oxide film is approximately the <100> direction; and    a step (b) of separating adjacent ones of said silicon single crystal grains to each other, whereby forming a floating gate composed of said group of silicon single crystal grains;    wherein the moved amount of a ultraviolet beam irradiating position in a period from completion of an irradiation of said rectangular ultraviolet beam to starting of the next irradiation of said rectangular ultraviolet beam is specified at 40 μm or less, and a ratio of said moved amount to a width of said rectangular ultraviolet beam measured in the movement direction thereof is in a range of 0.1 to 5%.    
     
     
         31 . A process of fabricating a flash memory cell according to  claim 30 , wherein said step (b) of separating adjacent ones of said silicon single crystal grains to each other comprises a step of oxidizing said silicon thin film formed in said step (a) to form each region made of silicon oxide between the adjacent ones of said silicon single crystal grains.  
     
     
         32 . A process of fabricating a flash memory cell according to  claim 30 , wherein a length of one side of each of said approximately rectangular-shaped silicon single crystal grains in said silicon thin film formed in said step (a) is 0.05 μm or more.  
     
     
         33 . A process of fabricating a flash memory cell according to  claim 30 , wherein an average thickness of said silicon thin film formed in said step (a) is in a range of 1×10 −8  m to 1×10 −7  m.  
     
     
         34 . A process of fabricating a flash memory cell according to  claim 30 , wherein opposed sides of each of said approximately rectangular-shaped silicon single crystal grains in said silicon thin film formed in said step (a) are approximately in parallel to the movement direction of the ultraviolet beam irradiating position or intersect the movement direction of the ultraviolet beam irradiating position at approximately 45°.  
     
     
         35 . A semiconductor device comprising a source/drain region and a channel region formed in a silicon thin film composed of a group of silicon single crystal grains which are each approximately rectangular-shaped and which are arranged in a grid pattern on a base body or formed in said silicon single crystal grains, wherein a selected orientation of said silicon single crystal grains to the surface of said base body is approximately the <100> direction.  
     
     
         36 . A semiconductor device according to  claim 35  wherein a length of one side of said silicon single crystal grain approximately rectangular-shaped is 0.05 μm or more.  
     
     
         37 . A semiconductor device according to  claim 35 , wherein an average thickness of said silicon thin film is in a range of 1×10 −8  m to 1×10 −7  m.  
     
     
         38 . A semiconductor device according to  claim 35 , wherein said base body is made of silicon oxide or silicon nitride.  
     
     
         39 . A semiconductor according to  claim 35 , wherein said group of silicon single crystal grains are formed by irradiating a pulsed rectangular ultraviolet beam on an amorphous or polycrystalline silicon layer formed on said base body, and 
 wherein the moved amount of a ultraviolet beam irradiating position in a period from completion of an irradiation of said rectangular ultraviolet beam to starting of the next irradiation of said rectangular ultraviolet beam is specified at 40 μm or less, and a ratio of said moved amount to a width of said rectangular ultraviolet beam measured in the movement direction thereof is in a range of 0.1 to 5%.    
     
     
         40 . A semiconductor device according to  claim 39 , wherein opposed sides of said silicon single crystal grain approximately rectangular-shaped are approximately in parallel to the movement direction of the ultraviolet beam irradiating position or intersect the movement direction of the ultraviolet beam irradiating position at approximately 45°.  
     
     
         41 . A semiconductor device according to  claim 35 , which is a thin film transistor of a bottom gate type.  
     
     
         42 . A flash memory cell comprising a floating gate composed of a plurality of silicon single crystal grains which are each approximately rectangular-shaped and which are formed on a tunnel oxide film, a selected orientation of said silicon single crystal grains to the surface of said tunnel oxide film being approximately the <100> direction; 
 wherein said silicon single crystal grains are arranged in a grid pattern on said tunnel oxide film and adjacent ones of said silicon single crystal grains are separated from each other.  
 
     
     
         43 . A flash memory cell according to  claim 42 , wherein said plurality of silicon single crystal grains are formed by a process comprising: 
 a step (a) of irradiating a pulsed rectangular ultraviolet beam on an amorphous or polycrystalline silicon layer formed on said tunnel oxide film, to thereby form a silicon thin film composed of a group of silicon single crystal grains which are each approximately rectangular-shaped and which are arranged in a grid pattern on said tunnel oxide film, a selected orientation of said silicon single crystal grains to the surface of said tunnel oxide film being approximately the <100> direction; and    a step (b) of separating adjacent ones of said silicon single crystal grains to each other;    wherein the moved amount of a ultraviolet beam irradiating position in a period from completion of an irradiation of said rectangular ultraviolet beam to starting of the next irradiation of said rectangular ultraviolet beam is specified at 40 μm or less, and a ratio of said moved amount to a width of said rectangular ultraviolet beam measured in the movement direction thereof is in a range of 0.1 to 5%.    
     
     
         44 . A flash memory cell according to  claim 43 , wherein said step (b) of separating adjacent ones of said silicon single crystal grains to each other comprises a step of oxidizing said silicon thin film formed in said step (a) to form each region made of silicon oxide between the adjacent ones of said silicon single crystal grains.  
     
     
         45 . A flash memory cell according to  claim 43 , wherein a length of one side of each of said approximately rectangular-shaped silicon single crystal grains in said silicon thin film formed in said step (a) is 0.05 μm or more.  
     
     
         46 . A flash memory cell according to  claim 43 , wherein an average thickness of said silicon thin film formed in said step (a) is in a range of 1×10 −8  m to 1×10 −7  m.  
     
     
         47 . A flash memory cell according to  claim 43 , wherein opposed sides of each of said approximately rectangular-shaped silicon single crystal grains in said silicon thin film formed in said step (a) are approximately in parallel to the movement direction of the ultraviolet beam irradiating position or intersect the movement direction of the ultraviolet beam irradiating position at approximately 45°.