Measurement and Impact of Surface Transition Metal Contamination of Textured Multicrystalline Silicon Wafers

A method for transition metal sampling on the surface of as-cut and isotextured multicrystalline silicon wafers that allows quick and easy sampling without clean room environment is presented. The obtained samples were analysed via ICP-MS. The samples were tested for the presumably most harmful species identified from literature: Ag, Al, Cr, Cu, Fe, Mn, Mo, Ni, and Ti. The method was applied to the isotexture process. The cleaning cascade after the etching was investigated and it was found that initial as-cut wafers surface contamination is reduced significatly. As-cut wafers were identified as main source of contamination of the isotexture etch bath. With the help of the measured concentrations the enrichment of transition metals in the etch bath was simulated. Due to bleed/feed processing the equilibrium of metal intake to the etch bath is reached after 6.000 – 10.000 wafers. Additionally, the cleaning efficiency of standard cleaning procedures was studied. The influence of surface contamination on the oxidation step for a SiO2/SiNx passivation stack was investigated and it was shown that surface contamination can vastly decrease the lifetime of a wafer during a high temperature process.