Deposition of a SiOx Film Showing Enhanced Surface Passivation

A new process for deposition of silicon oxide films with excellent passivation properties was developed using an atmospheric pressure plasma reactor. This process consists of fast deposition at room temperature of a SiCxOyHz film followed by a rapid thermal anneal in air (similar treatment to a contact firing step) to convert it to a dense inorganic SiOx material. The material formed using this process shows improved passivation compared to low pressure PECVD films. The firing process and more particularly the firing temperature appears to play a critical role in passivation performance, and an optimum temperature was identified. Capacitance-Voltage measurements on a MOS structure show that the oxide layer has a very low Dit value with fixed negative charges, which has not been reported before for thick silicon oxide. This uniqueness is attributed to measured over-stoichiometry in oxygen in the dense film owing to the presence of bulk silanols. These films were successfully incorporated in PERC solar cells with cells showing efficiencies up to 19.7%