5 - Implementations of Rapid Thermal Processes in Polysilicon TFT Fabrication

Abstract

This chapter focuses on the crystallization of amorphous silicon for the formation of the polysilicon Thin Film Transistor (TFT) active layer and presents recent advances on the Excimer Laser Annealing (ELA) as well as xenon-lamp based Rapid Thermal Processing (RTP). TFT technologies have facilitated the realization of active matrix liquid crystal flat panel displays, which have contributed to the widespread use of laptop computers. Currently, emphasis is being placed in the replacement of the Cathode Ray Tube (CRT) displays with flat panel displays in desktop computer systems. The realization of such highly integrated systems will require the performance of the thin film transistors to approach that of silicon single-crystal Complementary Metal-Oxide Semiconductor (CMOS) devices. The fabrication of these devices needs to take place at low thermal budgets to be compatible with low cost glass substrates. The polycrystalline silicon (polysilicon) TFT technology is being currently actively pursued for such system on panel applications. A critical feature of the polysilicon TFT technology is the use of RTP to achieve both the high-performance and the low-thermal budget requirements. The fabrication of polysilicon TFTs requires three different high temperature process steps: dehydrogenation of amorphous silicon, crystallization of amorphous silicon, and activation of ion-implanted dopants.