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 degrees C, we propose an atmospheric pressure plasma (APP) treatment method using a H-2/He or H-2/Ar mixture. An atmospheric-pressure stable-low 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 H-2/He plasma, the crystallization of the a-Si films started with in negligible incubation time at a substrate temperature as low as 200 degrees C, and the resulting Si crysiallites 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 H-2/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 H-2/Ar plasma. This implies that physical interactions between Ar atoms and the film surface play a significant role in the crystallization of a-Si.