Deleterious electrostatic interaction in silicon passivation stack between thin ALD A1203 and its a-SiNx:H capping layer: numerical and experimental evidences

摘要

This study focuses on the electrostatic interaction between the ALD A1203 passivation layer and the PECVD a-SiNx:H capping layer, while reducing ALD A1203 thickness. The first one embeds negative fixed charges while the second is well known to possess a fixed charge density with an opposite polarity. We reduced the A1203 thickness from 20 to 2 nm while keeping constant ,- the a-SiNx:H thickness. To increase the magnitude of the field effect passivation provided by A1203, we used an original light-induced field effect enhancement strategy. QSS-PC was used to quantify the initial passivation properties. We monitored the evolution of the passivation quality under low-intensity light-soaking until its stabilization. We report here a minority carrier lifetime enhancement up to 900% and surface recombination velocity reduction below 10 cm.s"1. The evidence of field effect compensation at c-Si surface due to a-SiNx:H positive charges has been supported by numerical simulations (SILVACO ATLAS). While keeping the parameters of the a-SiNx:H layer constant, the configuration of the A1203 layer (thickness and fixed charge density) were varied. These results allow us to conclude that in order to use thinner A1203 passivation layer (2 nm), ideal capping layer has to be free of positive fixed charges and to release enough hydrogen at desired temperature to ensure the chemical passivation.