Phosphorous doping from APCVD deposited PSG

Abstract

The phosphorous diffusion from atmospheric pressure chemical vapor deposition (APCVD) deposited phosphorus silicate glass (PSG) promises reduced process costs compared to the standard POCl3 diffusion process, since no POCl3 gas flow is necessary during the diffusion process. Therefore, much smaller or no spacing between the wafers is necessary and the throughput of the diffusion process can be significantly increased. Furthermore, it allows a structuring of the doping source prior to diffusion. We investigate the effect of basic process parameters concerning the deposition of the PSG and the capping layer on sheet resistance and uniformity. On standard aluminum back surface field (Al-BSF) solar cells, cell efficiencies of up to 19.6 % were achieved. In a high temperature co-diffusion process with reduced P content, the APCVD-PSG emitter passivated with fired PECVD-SiNX features low j0E of 100 fA/cm² at 50 Ω/sq. This results in a high cell VOC of 639 mV while leading to a jSC loss due to increased Auger recombination in the deep emitter profile. This loss can partly be compensated by a selective emitter etch-back. It would not occur, when the doping profile is located at the rear side of a bifacial or back contact solar cell as a BSF.