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The rate-limiting step for the plasma hydrogenation process is isolated and used to explain the effects of the hydrogenation process on the performance of thin-film transistors (TFTs). In well-hydrogenated TFTs device characteristics scale with device dimensions, but the performance of partially hydrogenated TFTs depends on device size and thickness, due to the mechanism of hydrogen diffusion through the quartz substrates into the channel polysilicon during hydrogenation. The mechanism was confirmed from results of experiments using quartz substrates coated with silicon nitride. The diffusion coefficient of hydrogen through the quartz and its activation energy are estimated.

Polysilicon thin-film transistors (TFT's) have been fabricated with the maximum processing temperature limited to 650°C. Best results were obtained when the gate oxide was grown by a two-step high-pressure oxidation process, using high-pressure steam and then dry oxygen both at 15 atm and 650°C. The TFT's exhibit a mobility of 34 cm'/V s, threshold voltage of 3.5 V, leakage current below 0.01 pA/pm, subthreshold slope of 0.18 V/decade, and an ON-OFF ratio of over 8 orders of magnitude. These values are comparable to those obtained with conventional polysilicon TFT's using high-temperature thermal oxidation.

Polysilicon TFT characteristics are shown to be dependent on the nature of the polysilicon film used as well as the TFT fabrication process. Best results were obtained when silicon self-implant and regrowth techniques were used together with plasma hydrogenation. TFTs exhibiting a mobility of 115 cm2/V-sec, subthreshold slope of 0.27 V/decade, leakage current below 0.01 pA/μ;m, and an on-off ratio of 10 orders of magnitude have been fabricated.