Impact of POCl3 Diffusion Process Parameters on Oxygen Precipitation in Czochralski-Grown Silicon

Oxygen precipitates can be formed in Czochralski-grown silicon (Cz-Si) wafers during high temperature processes. They decrease the bulk charge carrier lifetime and thereby reduce the efficiency of the affected devices. The most relevant process for passivated emitter and rear cells is the POCl3 diffusion. Therefore the influence of its process parameters on oxygen precipitation is highly relevant for industrial cell manufacturing. In this work, we investigate the impact of distinct POCl3 diffusion parameters on oxygen precipitation in both p-type and n-type Cz-Si. A full factorial variation of the drive-in parameters, such as temperature and duration, based on an industry relevant POCl3 diffusion process, is performed. The results show that the recombination activity of oxygen precipitates is increasing with both the temperature and the duration of the drive-in sequence. The oxygen diffusion length LOi during the process is identified to be a well-suited measure for the growth of oxygen precipitates in susceptible material and a threshold of LOi < 0,3 µm is proposed to limit detrimental effects on device performance. Similar trends for the oxygen precipitation were observed for p-type and n-type doped Cz-Si.