to 10 the si n ratio in the silicon nitride film was found to be varied from 1 1 to 1 58 according to auger electron spectrophotometry on the other hand the composition of the silicon nitride film formed according to the reduced pressure cvd method by introducing sih 2 cl 2 gas and nh 3 gas under the conditions of a reduced pressure of 0 3 torr and a temperature of about 800 u00b0 c was found to be si 3 n 4 si n 0 75 which is approximately the stoichiometric ratio also the silicon nitride film formed by heat treatment at about 1200 u00b0 c in ammonia or n 2 hot nitrification method can be obtained with a composition further approximate to the stoichiometric ratio since the formation method is performed under thermal equilibrium by use of silicon nitrides formed by the various methods as described above as the material for forming nucleation surface s ndl with higher nucleation density than sio 2 the above nucleus of si can be grown on the nucleation surface s ndl comprising silicon nitride to form si single crystal based on the nucleation density nd corresponding to the chemical composition ratio of silicon nitride fig9 is a graph showing the relationship between si n composition ratio and nucleation density nd as shown in the same graph by varying the chemical composition ratio of the silicon nitride film the nucleation density of the si single crystal nucleus formed thereon changes to.