Mapping of hydrogen bond energies in EFG silicon samples by analysis of spatially resolved minority charge carrier lifetimes after annealing steps

Abstract

Inspired by investigations on the average bond energies of hydrogen on various defect sites in silicon wafers a new method to determine these bond energies in a spatially resolved way was developed. This knowledge is useful for a better understanding of the hydrogenation process in defect-rich materials. Beyond that it serves to gain information about defect distributions especially in multicrystalline silicon material: as the bond energies of hydrogen depend on the defect type, mapping of the bond energies in principle permits to draw conclusions concerning the distribution of defects in multicrystalline silicon wafers. The method is based on minority charge carrier lifetime measurements by μ-PCD (microwave-detected PhotoConductance Decay). A hydrogen passivated EFG (Edge-defined Film-fed Growth) silicon sample is heated in a RTP (Rapid Thermal Processing) oven for one second at a specific temperature. Afterwards the minority carrier lifetime is measured and the wafer is exposed to the next temperature step (again one second but at a higher temperature). This is repeated until all hydrogen has left the sample and no significant further decrease in lifetime can be detected. From the lifetime decrease after the different temperature steps the bond energies of hydrogen in EFG samples can be calculated with the same resolution as the lifetime measurements. Provided a direct correlation between extracted bond energy and defect type can be established the different bond energies can be attributed to the different defect types. With that a fast and cost effective method to examine defect distributions spatially resolved is available, particularly on large area wafers. It could be shown that in EFG material regions with different hydrogen bond energies exist.