Transmission electron microscopy study of hydrogen defect formation at extended defects in hydrogen plasma treated multicrystalline silicon

Abstract

Hydrogenation of multicrystalline silicon for solar cell applications is considered to be an effective method of increasing the lifetime by passivating defects and impurities. Hydrogen plasma treated as-cut and chemically etched multicrystalline silicon samples have been studied by electron microscopy in order to investigate hydrogen defect formation at extended bulk defects. In chemically etched samples, the texture of the surface after hydrogen plasma treatment differs between different grains depending on grain orientation. In as-cut samples, hydrogen induced defects are formed on sawing defects that extend up to ∼5 μm below the Si surface. Intragranular defects are also observed in the ∼1 μm subsurface region. The density of defects is higher in as-cut samples than in chemically etched samples and the size of the defects increases with depth. Hydrogen induced structural defects on bulk dislocations and on dislocations in twin grain boundaries and stacking faults are found several microns below the sample surface. It is concluded that (i) the passivation efficiency of multicrystalline silicon substrates after H plasma treatment can be limited by the formation of hydrogen induced structural defects and that (ii) such defects can be used to getter unwanted impurities upon high temperature processing of the Si wafers.