Patent ID: 7923357

Claim:
A poly-silicon film formation method for forming a poly-silicon film doped with phosphorous or boron, the method comprising: performing a film formation process of depositing an amorphous silicon film doped with phosphorous or boron on a target substrate, by setting an interior of a reaction container accommodating the target substrate at a first pressure of a vacuum atmosphere and a first temperature of 400 to 650° C. and supplying into the reaction container a silane family gas at a first flow rate, a doping gas for doping a film with phosphorous or boron at a second flow rate smaller than the first flow rate, and C 2 H 4 as a grain size adjusting gas, which contains a component to retard columnar crystal formation to promote miniaturization of poly-silicon crystals, at a third flow rate smaller than the first flow rate; and performing an annealing process on the amorphous silicon film, while setting the interior of the reaction container accommodating the target substrate at a second pressure higher than the first pressure and a second temperature of 550 to 1,100° C. and higher than the first temperature, thereby transforming the amorphous silicon film into a poly-silicon film that is doped with phosphorous or boron, and that has an average grain size of 100 nm or less, wherein said method further comprises conducting an experiment, which includes performing the film formation process with different values of the third flow rate followed by the annealing process to form poly-silicon film examples, and measuring grain sizes of the examples to obtain values of the third flow rate that make the grain size 100 nm or less.