We report the pulsed laser recrystallization and doping of thin film amorphous silicon deposited on oxide-coated polyester substrates. Although our heat-flow simulation of the laser recrystallization process indicates that the plastic is briefly subjected to temperatures above its softening point, we see no evidence of damage to the plastic or film delamination from the substrate. Film grain size is found to vary up to ∼0.1 μm. Electrical characteristics obtained from simple strip line resistors and thin film transistors indicate that device-quality silicon films have been produced on an inexpensive flexible plastic substrate.

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We present device results from polysilicon thin film transistors (TFTs) fabricated at a maximum temperature of 100 °C on polyester substrates. Critical to our success has been the development of a processing cluster tool containing chambers dedicated to laser crystallization, dopant deposition, and gate oxidation. Our TFT fabrication process integrates multiple steps in this tool, and uses the laser to crystallize deposited amorphous silicon as well as create heavily doped TFT source/drain regions. By combining laser crystallization and doping, a plasma enhanced chemical vapor deposition SiO2 layer for the gate dielectric, and postfabrication annealing at 150 °C, we have succeeded in fabricating TFTs with ION/IOFF ratios >5×105 and electron mobilities >40 cm2/V s on polyester substrates.

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The fabrication of ultra-shallow high-concentration boron profiles in silicon has been carried out utilizing a XeCl excimer laser. The Gas Immersion Laser Doping (GILD) process relies on a dopant species, in this case diborane (BIHs), to be adsorbed on the clean silicon surface and subsequently driven in during a melthegrowth process initiated upon exposure to the short laser pulse. Secondary Ion Mass Spectrometry and spreading resistance profiles show peak boron concentrations from 5 X 1019 to 5 X 1O'O depending on the number of laser pulses, with junction depths from 0.08 to 0.16 pm depending on the laser energy. Electrical characteristics show essentially ideal diode behavior following a 10-s 950°C anneal.