Growth of High Quality Fluorinated Silicon Dioxide for Thin Film Transistors

Abstract

AbstractThin film transistors(TFT) in microcrystalline and amorphous Si require high quality gate insulators that can be grown at low temperatures. In this paper, we show that one can oxidize Si wafers to produce high quality fluorinated silicon dioxide gate insulator using a low pressure remote plasma. The insulating film was grown on c-Si substrates using a low pressure ECR oxygen plasma, with small quantities of fluorine added to the mixture. Helium was used as the carrier gas for both oxygen and fluorine. The growth temperatures were in the range of 400–450 C. MOS type capacitors were made to judge the quality of the oxide/semiconductor interface, and interface defect densities were measured using capacitance-voltage techniques. It was found that when no fluorine was present in the oxide, the interface defect density was ∼1-2 x 1011/cm2 eV. The addition of F2 to oxygen immediately reduced the defect density by an order of magnitude, to ∼1.5 x 1010/cm2eV. The addition of more F2 slowly increased the defect density. Thermal cycling measurements showed that the semiconductor/oxide interface is very stable under cycling.