Densification of SIPOS

Semi- insulat ing polycrystall ine silicon (SIPOS) can be used as part of a passivation scheme on semiconductor devices. During processing the film ex-periences temperatures several hundred degrees higher than the SIPOS dep-osition temperature of 640 ~ We have investigated the effect of high tempera-ture anneals on the physical properties of SIPOS films containing 25 atomic percent oxygen. Heat-treatments of 900 ~ or greater in inert ambients densify the film resulting in a film thickness decrease (densification) on the order of 10 % and decrease the etch rate of the film by a factor of 6 in a 6H202: 1HF: I0 NH4F SIPOS etch solution. Also, the infrared transmission spectrum of the SIPOS film changes as a result of annealing. Similar infrared changes in SiO~ films have been interpreted to be due to a relaxation of bond strain and a decrease in film porosity. Fi lm stress has also been investigated before and after anneal ing and was found to change from tensile to compressive. This is consistent with the interpretation f the infrared data