Design and Test of a Rapid Thermal Annealing Furnace for Improving Surface Properties of Silicon Brick in Multi-Wire Sawing Process

Abstract

Multi-wire sawing process with free abrasive slurry or called multi-wire slurry wire sawing (MW-SWS) process has been popularly adopted in slicing of silicon substrates for solar cell application. However, the chipping or edge cracking of thin thickness as 200 μm of such silicon substrates need to be improved in current mass production. The potential subsurface cracks induced by previous edge grinding or brush polishing of silicon brick may be the main cause. This paper is to develop a rapid thermal annealing (RTA) process for thermal annealing of the surface quality of silicon brick before MR-SWS. In this study, a RTA furnace is designed and used to improve the material property of surface of silicon brick. A quartz crucible is used as heating source with the maximum heated specimen size of 156×156×100 mm (W×H×L). The bulk silicon brick used in this study is selected with a size of 20×10×20 mm (W×H×L) and supplied by the Sino-American Silicon Ltd. (SAS) in Hsinchu, Taiwan. The nitrogen gas is also injected as a protective gas for target heating temperature around 550°C with rapid heating rate of 50°C per second. The micro-Vickers (Akashi MVK-H1) and SEM (JSM-6500F, JOEL) instruments have been used to observe the improvement of rectified material properties of bulk silicon substrate. Experiments of silicon wafers have been first performed for obtaining the recipe of RTA testing and then adjusting for silicon brick testing. Results have been verified by the lower surface hardness and larger crystal grain size after RTA treatment. Furthermore, such treated silicon brick can be further adopted for MW-SWS process to identify the effects of reducing chipping or edge cracking of silicon substrates for solar cell application.