Low temperature (<150°C) doping techniques for polysilicon TFT's

Doping of polysilicon (poly-Si) films was performed at a low temperature (<150°C), by using three different dopant incorporation methods: ion shower, dopant layer deposition and plasma immersion. All three techniques were shown to be capable of obtaining sheet resistance values that were smaller than 10⁴ Ω /sq., which were considered to be sufficient to form good source-drain contacts. Also, a sheet resistance value that is as low as 300 Ω /sq. was demonstrated. It was found that the laser energy used for dopant activation was the major parameter to control the sheet resistance of the poly-Si films. The lowest attainable sheet resistance was not affected much by the ion dose, as long as the initial dose is higher than 10¹⁵ cm^-2. The plasma immersion method was shown to be a good alternative to the ion shower, as the doping could be performed in a relatively short time without causing a structural damage to the poly-Si film.