Furnace and rapid thermal crystallization of amorphous GexSil _x and Si for thin film transistors

The crystallization behavior of polycrystalline silicon (Si) and germanium-silicon alloys (GexSil-x) from Sill4 and GeH4, where x is in the range of 0-0.32, has been investigated for thin film transistor (TFT) applications. Furnace anneals as well as rapid thermal anneal (RTA) and combinations of these two techniques have been used to crystallize amorphously deposited thin ( _< 100 nm) films. The effects of time and temperature for the furnace anneals and time, temperature and pulse rate for the RTA have been investigated. Smooth Si and Ge~Sii_x layers with a surface roughness <0.6 nm have been obtained using an initial Si layer for the Ge;~Si, _x material, since GexSi~_x shows a nucleation problem on oxide surfaces which influences the resulting surface roughness and grain size. For TFT applications the optimaI film properties cannot be obtained with a single crystallization anneal. Conventional furnace crystallization results in smooth layers with Si furnace crystallized films exhibiting small grains with many intra-grain defects. An average grain size of approximately 300 nm for Ge0.~Sio.75 and slightly larger grains for Geo.3aSio.6a with less defects is obtained at lower temperature. RTA results for Si and Ge~Si~ -x in fine grained material with lower defect density. © 1997 Elsevier Science S.A.