Solution-derived SiO₂ gate insulator formed by CO₂ laser annealing for polycrystalline silicon thin-film transistors

The formation of perhydropolysilazane (PHPS)-based SiO₂ films by CO₂ laser annealing is proposed. Irradiation with a CO₂ laser with optimum fluence transformed a prebaked PHPS film into a SiO₂ film with uniform composition in the thickness direction. Polycrystalline silicon thin-film transistors (poly-Si TFTs) with a SiO₂ film as the gate insulator were fabricated. When the SiO₂ film was formed by CO₂ laser annealing (CO₂LA) at the optimum fluence of 20mJ/cm², the film had fewer OH groups which was one-twentieth that of the furnace annealed PHPS film and onehundredth that of the SiO₂ film deposited by plasma-enhanced chemical vapor deposition (PECVD) using tetraethyl orthosilicate (TEOS). The resulting TFTs using PHPS showed a clear transistor operation with a field-effect mobility of 37.9 ± 1.2cm²V^-1 s^-1, a threshold voltage of 9.8 ± 0.2 V, and a subthreshold swing of 0.76 ± 0.02V/decade. The characteristics of such TFTs were as good as those of a poly-Si TFT with a SiO₂ gate insulator prepared by PECVD using TEOS.