Adhesion Effects on the Recrystallization of Silicon Films

Laser processing of thin films of amorphous or polycrystalline silicon on insulator substrates, such as the glass normally used for liquid crystal displays, frequently leads to film thickness variations which are unacceptable for device fabrication. Some thickness variations are caused by the high surface tension of molten silicon and the poor adhesion of the silicon to the substrate. Techniques to reduce this problem by increasing the adhesion of the film to silicon dioxide coated Corning 7059 glass substrates have been investigated. Two different approaches were used. First, silicon ions were implanted into the silicon-glass interface to increase the direct bonding of the silicon to the silicon dioxide. Second, layers of material known to exhibit better adhesion to both silicon and silicon dioxide were introduced between the silicon film and the glass substrate. Both techniques produced films which, after subsequent laser processing, showed significantly reduced thickness variations. These procedures make it possible to laser process thin films of silicon on Corning 7059 glass substrates under conditions which produce large grain polysilicon films without producing unacceptably large thickness variations or film cracking.