Deposition of polycrystalline Si and SiGe by ultra-high vacuum chemical molecular epitaxy

Abstract

The polycrystalline Si1-xGex (poly-Si1-xGex) films have better properties than poly-Si for device fabrications, such as lower proceeding temperature and process thermal budget. For these reasons, the poly-Si1-xGex films have been utilized for low-temperature thin film transistor fabrications and gate electrodes of metal-oxide-semiconductor transistors. In this work, disilane and germane were used to grow poly-Si1-xGex films at low temperature (<600 degrees C) by the cold-wall type ultrahigh vacuum chemical molecular epitaxy system. The poly-Si1-xGex films were deposited on oxide and nitride surfaces. The Ge fraction x was evaluated from x-ray diffraction and Auger electron spectroscopy. It is observed that the Ge fraction increases with the increase of the GeH4 flow rate. The result is only slightly related to the substrate type. The growth rate increases with the Ge fraction at lower values and then decreases with the Ge fraction in the higher composition range. This implies that the growth mechanism of poly-Si1-xGex films is different from that of epitaxial Si1-xGex on Si. The uniformity of poly-Si1-xGex films depends on the Ge fraction, and it is improved-by the addition of germanium. The result can be explained by the lower activation energy (<0.25 eV) of poly-Si(1-x)G(x), deposition as compared to that of poly-Si (similar to 2.1 eV). From the x-ray diffraction and atomic force microscopy analyses, the crystallinity and surface roughness of films are suitable for device fabrications. (C) 2000 American Vacuum Society. [S0734-2101(00)07704-6].