Characterization of wafers and supply materials

The technological development of silicon wafer processing for solar cells by multiwire sawing is mainly driven by the need to reduce cost but under the condition to maintain or even improve the wafer quality. This additional requirement becomes even more important because wafer and wire thickness will decrease in the future and the standard loose abrasive sawing technique will be replaced by the fixed abrasive sawing technique. The essential quality parameters for wafers are total thickness variations (TTV), roughness and grooves, subsurface damage, and fracture strength stability. These factors depend on the properties of wires, consumables, and machine sawing parameters. Their investigation and determination require adequate characterization methods. The chapter describes standard and new methods, which have been developed to characterize wafers, wires, and consumables. Today's optimization processes also require a basic understanding of the interaction processes between wires, sawing fluid, and the silicon material. Special experimental methods, which have been developed to investigate the fundamental micromechanical processes and their ramifications on the wafer quality parameters, are presented.