| Summary: | 碩士 === 國立清華大學 === 電機工程學研究所 === 85 ===
Low temperature fabrication of polycrystalline silicon thin film transistors (poly-Si TFTs), solar cells and other semiconductor memory application is the new trend of development in recent years. Our group has succeeded to grow large grain undoped poly-silicon [5], phosphorus doped poly-silicon and high quality silicon nitride films [6] at 250℃ by electron cyclotron resonance chemical vapor deposition (ECR-CVD). However the electrical properties of in-situ doped poly-sillicon is inferior to those grown by LP-CVD at 620℃. The inferior properties of the poly-Si films may be attributed to higher trap density in the grain boundary grown at low temperature. Therefore, how to improve the electrical properties of doped poly-silicon films grown at low temperature is the key issue for low temperature device fabrication.
This thesis presents the result of phosphorus in-situ doped poly silicon grown at 250℃ by ECR-CVD.
First, the effect of deposition parameters on electrical properties of doped poly silicon films were investigated and an optimal way was found to deposit good quality of poly silicon film from this experiment. Second, we used RTA treatment to improve the electrical properties of poly silicon films.
In addition, the reaction of the doped poly silicon films at different annealing temperature was studied. The best electrical properties can be obtained at the annealing temperatures of 900℃. The major factor of this result may be attributed to the recrystallization of poly silicon films and their reduction of the trap density in the grain boundaries. Therefore, the carrier mobility and carrier concentration could be enhanced.
For phosphorus doped poly-silicon before RTA, the resistivity was 0.036Ω-cm the carrier mobility was 1.21 cm2/V ×sec, and the doping efficiency was 10.97％. After 900℃ RTA for 1 minute, the resistivity, carrier mobility and doping efficiency were 0.016 Ω-cm, 4.29 cm2/V ×sec and 7.35％, respectively.
In this experiment, the electrical properties can be improved. Consequently we can apply it to low temperature device fabrication.
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