Diffusion properties of ion-implanted vanadium in PECVD-SiO2 and PECVD-SiNx

This paper presents data on the diffusion barrier efficiency of plasma-enhanced chemical vapor deposited SiO2 and SiNx layers against vanadium. In addition, an experimental method is proposed which is generally applicable to investigate barrier properties against diffusion of other transition metals (e.g., Fe and Cr). Crystalline silicon thin films (CSiTF) have a good potential for the manufacturing of cost effective solar cells. In order to take advantage of this potential, inexpensive and therefore often highly impure substrates must be used. If diffusing into the active silicon layer, impurities from the substrate may act as very efficient lifetime-killers in the electrically active layer and considerably reduce the solar cell efficiency. For this reason, diffusion barrier layers are necessary to avoid contamination of the electrically active silicon layer. Therefore, the barrier efficiency of potential barrier layer materials such as SiO2 and SiNx at high temperatures is of utmost technological importance. Diffusion coefficients of vanadium in both SiO2 and SiNx were calculated for the temperature range from 950 to 1350degreesC. The segregation coefficient of vanadium at the Si-SiO2 interface was calculated at temperatures between 1150 and 1350degreesC. For the Si/SiNx interface, a lower bound for the segregation coefficient could be defined within the same temperature range. (C) 2003 The Electrochemical Society.