Ion beam assisted ECR-PCVD applied for preparation of hydrogenated amorphous silicon

Abstract

In order to examine the effect of ion beam assistance on chemical vapor deposition (CVD), a study was carried out using electron cyclotron resonance plasma assisted chemical vapor deposition (ECR-PCVD), taking advantage of its low operating pressures for sufficiently long mean free paths. While hydrogenated amorphous silicon was deposited by the decomposition of SiH 4, an Ar ion beam from a Kaufman-type ion source was irradiated onto the film under pressures from 0.133 to 0.667 Pa. As the beam voltage was increased relative to the microwave power, optical absorption edge of the films shifted to longer wavelengths. The film color and the optical band gap were also changed accordingly. These results indicate a decrease in the hydrogen content. When the deposition was performed at 573 K, microvoids were formed in the films due to the evolution of molecular hydrogen, whereas irradiation of Ar ion beam completely eliminated the microvoids at all the pressures tested. From the above results, it is evident that an ion beam is able to interact with the films during the deposition by ECR-PCVD in a pressure range up to around 1 Pa. It is thus suggested that ion beam assisted CVD could be an effective means to control the properties of thin films, if appropriate ion species and deposition pressure were chosen.