Low-Temperature Crystallization of Amorphous Silicon by Atmospheric-Pressure Plasma Treatment in H2/He or H2/Ar Mixture

To crystallize amorphous silicon (a-Si) films at temperatures less than 600 °C, we propose an atmospheric pressure plasma (APP) treatment method using a H2/He or H2/Ar mixture. An atmospheric-pressure stable-glow plasma was generated using a 150 MHz very high frequency power supply. After APP treatment, the Si films were characterized by reflection high-energy electron diffraction analysis, Fourier-transform infrared spectroscopy and scanning electron microscopy. In addition, optical emission spectroscopy (OES) was employed to study the plasma. In the case of treatment with the H2/He plasma, the crystallization of the a-Si films started with in negligible incubation time at a substrate temperature as low as 200 °C, and the resulting Si crystallites showed anisotropic morphology. It was found that a-Si layers still existed under the crystallized layers. This result suggests that crystallization of a-Si by APP was predominated by chemical interactions between atomic hydrogen in the plasma and the treated surface. However, in the case of treatment with the H2/Ar plasma, Si crystallites of the treated film did not show anisotropic morphology, and film peeling was partly observed in the treated area. Additionally, from the OES, emission lines from atomic hydrogen were hardly observed in the H2/Ar plasma. This implies that physical interactions between Ar atoms and the film surface play a significant role in the crystallization of a-Si.