Low-Temperature Annealing Combined with Laser Crystallization for Polycrystalline Silicon TFTs on Polymeric Substrate

Abstract

The formation of polycrystalline layers on flexible plastic substrates, through plasma enhanced chemical vapor deposition and excimer laser annealing, is investigated. Combining low-temperature annealing with laser dehydrogenation/crystallization produces good-quality polycrystalline silicon with a reduced shot density. By using optimal crystallization conditions it is possible to achieve a superlateral growth crystallization regime, with a grain size up to , and void-free material, as confirmed by the presented structural analysis. The beneficial effect of the low-temperature thermal annealing has been related to the removal of nonbound hydrogen, as supported by the elastic recoil detection analysis and IR analysis of the samples. To validate the process, we fabricated non-self-aligned polysilicon thin-film transistors (TFTs) directly on spin-coated polyimide substrates, with a maximum processing temperature of and with a relatively low shot density ( shots/point). The TFTs presented good electrical characteristics with an on/off ratio , a field-effect mobility up to , and a threshold voltage of . These results confirmed that the developed crystallization process is suitable to fabricate polysilicon TFTs on polymeric substrates, allowing an increased process throughput.