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Low temperature (T?600°C) polycrystalline silicon thin film transistors (poly-Si TFTs) have been fabricated by solid phase crystallization (SPC) of amorphous silicon (a-Si) films deposited by low pressure chemical vapor deposition (LPCVD). These TFTs are distinguished by the very thin nature of the channel Si layer (25 nm) and the use of an SiO2gate insulator deposited by electron cyclotron resonance chemical vapor deposition (ECR-CVD). The present process eliminates the need for hydrogenation and produces mobilities greater than 20 cm2/V·s and on/off current ratios greater than 107.

This paper investigates the role of silane partial pressure (PSiH4) in VLPCVD on the as-deposited poly-Si film quality. The film quality strongly depends on the PSiH4when deposition temperature is kept constant. Higher pressure and excessively lower pressure have been found to be not adequate for thin film transistors (TFTs). By optimizing the deposition conditions, excellent TFTs can be fabricated through a low temperature process without relying on any other special processes. This paper also suggests the possibility of further improvement of as-deposited poly-Si films.

As-deposited poly-crystalline silicon (poly-Si) films have been applied to low temperature processed complementary metal oxide semiconductor (CMOS) thin film transistors (TFTs). Continuous two-step deposition of poly-Si films in the infra-low pressure chemical vapor deposition (ILPCVD) reduces the silane partial pressure to 0.10 mTorr to obtain high quality films. The maximum processing temperature of 555° C through the CMOS TFT fabrication is during the poly-Si deposition. Since the as-deposited poly-Si films are good in quality, CMOS static shift registers have been successfully integrated on a glass substrate with the as-deposited poly-Si TFTs.

The fundamental characteristics of a rapid thermal annealing (RTA) technique that has been applied to polycrystalline silicon thin-film transistors (poly-Si TFTs) have been investigated and short channel (less than 3 µ m) poly-Si TFTs have been achieved. The annealing characteristics of a thin silicon film on a transmissive substrate are entirely different from those of a silicon wafer. An arc lamp is essential as the RTA light source. A self-controlled effect in activation annealing was observed. Size and pattern density of silicon islands affect the uniformity of annealing. An absorption layer of a silicon film makes the use of RTA practical. A shift-register circuit composed of short channel TFTs was also evaluated.

Stoichiometric change of underlying silicon oxide has been found to have a great influence upon the properties of thin poly-crystalline silicon (poly-Si) films deposited on an underlying silicon oxide, resulting in important characteristics changes of the poly-Si thin film transistors (TFTs) made on it. The silicon oxide containing excessive silicon atoms has fairly good wettability with silicon so that the thin poly-Si deposited on it is in a continuous film state even if it is as thin as 25 nm and is deposited under infra-low pressure. The thin poly-Si on the stoichiometricaly perfect silicon dioxide, on the other hand, is in a separate island-like state but consists of large crystallites. The best TFTs will be fabricated by optimizing the amount of silicon content in the underlying silicon oxide, the poly-Si deposition condition, and the thickness of poly-Si film.