Excimer Laser Annealing for Low-Temperature Polysilicon Thin Film Transistor Fabrication on Plastic Substrates

In this work we present a new low-temperature poly-silicon (LTPS) TFTs fabrication process, based on excimer laser annealing, on polyimide (PI) substrate. The PI is spun on Si-wafer, used as rigid carrier, thus overcoming difficulties in handling flexible freestanding plastic substrates, eliminating the problem of plastic shrinkage with high temperature processing and allowing the use of standard semiconductor equipments. LTPS TFTs are fabricated according to a conventional non self-aligned process, with source/drain contacts fabricated by deposition of a highly doped Si-layer and patterned by a selective wet-etching. Excimer laser annealing is performed providing simultaneous dopant activation and crystallization of the active layer. The maximum process temperature was kept below 350degC. After LTPS TFTs fabrication, the PI layer is mechanically released from the rigid carrier, which can be re-used for a new fabrication process. The devices exhibit good electrical characteristics with field effect mobility up to 50 cm²/Vs. Analysis of electrical stability and characteristics in presence of mechanical strain will be also shown.