Purpose:
in the diffusion process, POCI, is decomposed under high temperature and generate phosphorus. Then, The phosphorus diffused on the P-type substrate to form a PN junction. A negative concertration gradient and proper phosphorus content are desired for homogeneous sheet resistance and eletrode ohm contact. The concentration of the phosphorou source, diffusion temperature and diffusion time are are the main varibles in this proess "Definition of diffusion:" Micro definition: The movement of micro particles(atoms, ions, molecule) because of thermal motion.