Extension of Hydrogen Passivation of Intragrain Defects and Grain Boundaries in Cast Multicrystalline Silicon

Abstract

The recombination activity of crystal defects was studied along cross-sections of cleaved multicrystalline silicon wafers (Silso®) grown by block casting. The temperature dependence of the electron-beam-induced current (EBIC) contrast c(T) was analyzed to study defect passivation by remote hydrogen plasma treatment with respect to (i) the extension and (ii) the degree of passivation. Based upon model calculations, the c(T) behavior allows estimating the degree of contamination of recombination active crystal defects. After hydrogen treatment of 1 h at 310 °C the number of defect-related deep levels at grain boundaries is reduced by a factor of three to four. Low-temperature EBIC reveals that hydrogenation also reduces the density of active centers at defects which exhibit already very low or no (detectable) EBIC contrast at room temperature such as intragrain defects. Both defects in intragrain regions and grain boundaries are passivated down to about 100 μm. No indications were found for significantly enhanced hydrogen diffusion along grain boundaries.