In-situ doping of LPCVD poly silicon (II). Temperature influence

Poly silicon deposition by pyrolysis of silane under low pressure conditions has been investigated with respect to the influence of temperature when simultaneously in-situ doping of the deposited layer takes place. The growth rate of poly silicon is retarded in the presence of phosphine provided that a certain lower PH3/SiH4-ratio has been exceeded. It has been shown how that lower ratio depends on temperature. Increasing PH3/SiH4-ratio not only slows down layer growth rate but also the apparent activation energy of the layer forming reaction. An empirical equation describing the temperature dependence of that activation energy has been derived. Phosphine adsorption has been discussed as a cause of both layer growth rate and activation energy reduction. Additionally, incorporation of phosphorus during layer growth has been investigated with respect to the total amount and the electrically active concentration, the latter measured after a postdeposition anneal at 1000 °C.