EFFECTS OF F+ IMPLANTATION ON THE CHARACTERISTICS OF POLY-SI FILMS AND LOW-TEMPERATURE N-CH POLY-SI THIN-FILM TRANSISTORS

Abstract

Fluorine was implanted onto poly-Si films through an oxide layer and its passivation effect on poly-Si films and low-temperature n-ch TFTs was investigated. The implant energy of F+ ions was 40 KeV, and the Fe+ dose was varied from 5 x 10(12) to 4 x 10(15) cm(-2). The fluorine implanted inside poly-Si film preferentially diffused toward the poly-Si/SiO2 interface during annealing at 600 degrees C. The residual implant damage was found to remain inside poly-Si films after annealing at 600 degrees C when the F+ dose was greater than or equal to 5 x 10(14) cm(-2). The resistivity and activation energy of the p-type poly-Si resistors were increased as the F+ dose increased, resulting from the increase of residual implant damage. However, the characteristics of the n-ch poly-Si TFT were clearly improved when the F+ dose was in the range of 5 x 10(14) to 2 x 10(15) cm(-2), where the.trap state density at the poly Si/SiO2 interface was found to be reduced because of the passivation effect by fluorine atoms. These results indicated that the fluorine passivation at the poly-Si/SiO2 interface was eff ective in an appropriate F C dose range, while the passivation inside the poly-Si film (or grain boundary passivation) was not.