Advanced polysilicon SFT's (Super-thin-Film Transistor) were fabricated on quartz at a low temperature process below 610°C. Using the technique of Si+ ion implanted amorphization and subsequent solid phase growth and making a super-thin-film structure, superior electrical characteristics such as high electron mobility of 60 cm2/(V·s) were obtained. The oscillation of a 19 stage ring oscillator with a channel length of 8.4 µm was observed. Propagation delay time of 8.13 ns/stage was attained. The device is expected to be applied to monolithic liquid-crystal-display on low temperature glass and three dimensional LSI technology.

The random solid‐phase grain growth behavior of Si+‐implanted very thin silicon films and its related electronic properties have been investigated. Si+‐implanted disordered silicon films showed variable range hopping conduction and high electron spin resonance (ESR) center density of more than 1019/cm3. Two‐dimensional dendritic crystal grains grew with subsequent furnace annealing at 600°C. Nucleation time retarded for the increase of Si+ dose. Maximum grain size of 5 μm was obtained. Moreover, remarkable photoconductivity was seen and films changed to activated type of conduction after polycrystallization. We have fabricated a superthin film transistor using these films and obtained field effect electron mobility more than 100 cm2/V · s. Mobility value depended on grain size, i.e., the Si+ dose that corresponded to the ESR center density in disordered Si+‐implanted films.

The application of poly Si super thin film transistors to VLSI technology, in which the active layer poly Si is 200-5OOA thick, has been investigated. The average grain size,of poly Si increased to more than lpm from 200-300A by solid phase recrystallization. Sub-um poly Si super thin film transistors and 19-stage CMOS ring oscillators were fabricated on 5inch insulator substrates. The mobility was about 100cm'/V.s for an N-channel and about 80cm2/V's for a P-channel transistor. The leakage current of transistors was O.lpA/um. The threshold voltage was 0.8V for an N-channel and -0.8V for a P-channel transistor, respectively. ,150~s of the delay time per stage and 0.15pJlgate 'of power-delay product at VDD=5V were obtained in the ring oscillator.

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Improved characteristics of electronic conduction and grain growth effect of super thin CVD polysilicon films after thermal oxidation (less than 1000 Å thick) were investigated. After oxidation of CVD silicon, grain size grew two-dimensionally to as large as 1500 Å in diameter with a thickness of 300 Å. In contrast, temperature dependence of conductivity changed from T -(1/4) rule to T -1 rule after oxidation. The grain growth effect after oxidation to super thin films (200–300 Å thick) was found to affect the decrease in grain boundary barrier height, which resulted in the increase of carrier mobility.