Thin film transistors fabricated by in-situ doped unhydrogenated polysilicon films obtained by solid phase crystallization

Laurent Pichon (1) , K. Mourgues F. Raoult T. Mohammed-Brahim K. Kis-Sion D. Briand O. Bonnaud (1)

1 Groupe de Microélectronique et Visualisation

High mobility low temperature (≤ 600°C) unhydrogenated in-situ doped polysilicon thin film transistors are made. Polysilicon layers are grown by a LPCVD technique and crystallized in vacuum by a thermal annealing. Source and drain regions are in-situ doped. Gate insulator is made of an APCVD silicon dioxide. Hydrogen passivation is not performed on the transistors. One type of transistors is made of two polysilicon layers, the other one is constituted of a single polysilicon layer. The electrical properties are better for transistors made of single polysilicon layer: a low threshold voltage (1.2 V), a subthreshold slope S = 0.7 V/dec, a high field effect mobility (≈ 100 cm2/Vs) and a On/Off state current ratio higher than 107 for a drain voltage Vds = 1 V. At low drain voltage, for both transistors, the Off state current results from a pure thermal emission of trapped carriers. However, at high drain voltage, the electrical behavior is different: in the case of single polysilicon TFTs, the current obeys the field-assisted (Poole-Frenkel) thermal emission model of trapped carriers while for TFTs made of two polysilicon layers, the higher Off state current results from a field-enhanced thermal emission.

Domaines: Micro et nanotechnologies/Microélectronique

Laurent Pichon, K. Mourgues F. Raoult T. Mohammed-Brahim K. Kis-Sion D. Briand O. Bonnaud. Thin film transistors fabricated by in-situ doped unhydrogenated polysilicon films obtained by solid phase crystallization. Semiconductor Science and Technology, 2001, 16, pp.918-924. ⟨hal-00994988⟩