Semiconductor device and method of manufacturing the same

Abstract

An improved polycrystalline or polysilicon film having large grain size, such as 1 μm to 2 μm in diameter or greater, is obtained over the methods of the prior art by initially forming a silicon film, which may be comprised of amorphous silicon or micro-crystalline silicon or contains micro-crystal regions in the amorphous phase, at a low temperature via a chemical vapor deposition (CVD) method, such as by plasma chemical vapor deposition (PCVD) with silane gas diluted with, for example, hydrogen, argon or helium at a temperature, for example, in the range of room temperature to 600° C. This is followed by solid phase recrystallization of the film to form a polycrystalline film which is conducted at a relatively low temperature in the range of about 550° C. to 650° C. in an inert atmosphere, e.g., N or Ar, for a period of about several hours to 40 or more hours wherein the temperature is gradually increased, e.g., at a temperature rise rate below 20° C./min, preferably about 5° C./min, to a prescribed recrystallization temperature within the range about 550° C. to 650° C. Further, between the step of film formation and the step of solid phase recrystallization, the film may be thermally treated at a relatively low temperature, e.g., over 300° C. and preferably between approximately 400° C. to 500° C. for a period of several minutes, such as 30 minutes, to remove hydrogen from the film prior to solid phase recrystallization.

What is claimed is:  
     
         1 . A method of forming a semiconductor device comprising: 
 a first step of forming a noncrystalline semiconductor film above a substrate, and    a second step of forming an insulation film above said semiconductor film by gradually heating said semiconductor film to a predetermined temperature at a rise rate not higher than 20° C. per minute.    
     
     
         2 . The method of  claim 1  wherein said rise rate is at most 5° C. per minute.  
     
     
         3 . The method of  claim 1  further including applying a heat treatment to said semiconductor film prior to said second step.  
     
     
         4 . The method of  claim 1  wherein said semiconductor film is modified to achieve a crystallization volume fraction in the range of 40% to 85%.  
     
     
         5 . The method of  claim 1  wherein said semiconductor film in said first step is initially a noncrystalline semiconductor film, and said first step further including a thermal treatment to bring about solid phase recrystallization in said noncrystalline semiconductor film.  
     
     
         6 . The method of  claim 5  wherein said thermal treatment includes increasing the temperature from room temperature toward a prescribed temperature for achieving solid phase recrystallization, said thermal treatment initiating said second step uninterruptedly without the use of an intervening annealing stage between said first and second steps, whereby said noncrystalline semiconductor film is recrystallized during said second step prior to reaching said predetermined temperature.  
     
     
         7 . The method of  claim 6  wherein said the thermal treatment during said first step increases the temperature uniformly at a first rise rate, and said second step continues to increase the temperature uniformly at said first rise rate until reaching said predetermined temperature, said first rise rate being not higher than 10° C. per minute.  
     
     
         8 . The method of  claim 7  wherein said first rise rate is 2° C. per minute.  
     
     
         9 . The method of  claim 6  wherein said thermal treatment during said first step has a first temperature rise rate; and 
 said second step of forming an insulation film includes at least first and second heating stages, said first heating stage having a second temperature rise rate and said second heating stage having a third temperature rise rate, said second rise rate being greater than said first rise rate and said third rise rate being greater than said second rise rate.  
 
     
     
         10 . The method of  claim 9  wherein the difference between said first, second, and third rise rates is less than 5° C. per minute.  
     
     
         11 . The method of  claim 10  wherein said first rise rate is 2° C. per minute between room temperature and 600° C., said second rise rate is 4° C. per minute between 600° C. and 800° C., and said third rise rate is 6° C. per minute between 800° C. and said predetermined temperature.  
     
     
         12 . The method of  claim 6  wherein said thermal treatment includes at least first, second, and third heating stages having respective first, second, and third temperature rise rates, said first heating stage being between room temperature and a prescribed hydrogen removal temperature, said second heating stage being between said prescribed hydrogen removal temperature and prescribed solid phase recrystallization temperature, said third heating stage being between said prescribed solid phase recrystallization temperature and the beginning of said second step, said first rise rate being greater than said second rise rate, said second rise rate being greater than said third rise rate.  
     
     
         13 . The method of  claim 12  wherein said first rise rate is at most 40° C./min., said second rise rate is at most 10° C./min., and said third rise rate is at most 5° C./min.  
     
     
         14 . The method of  claim 13  wherein said prescribed hydrogen removal temperature is at least 300° C. and said second rise rate is 4° C./min.  
     
     
         15 . The method of  claim 13  wherein said prescribed solid phase recrystallization temperature is in the range of 500° C. to 700° C., and said third rise rate is 2° C./min.  
     
     
         16 . The method of  claim 13  wherein said third rise rate of said second step is uniformly maintained until reaching said predetermined temperature.