Fabrication of SOI Films with High Crystal Uniformity by High-Speed Zone-Melting Crystallization

Silicon-on-insulator (SOI) films for solar cells were fabricated by zone-melting re-crystallization (ZMR) and by zone-melting crystallization (ZMC). For ZMR, polycrystalline Si (poly-Si) films were deposited on SiO 2 layers by chemical vapor deposition, and for ZMC, amorphous Si (a-Si) films by radio-frequency sputtering. After another SiO 2 layer was deposited on the SO1 film (Si/SiO 2 ) to form a sandwich structure (SiO 2 /Si/SiO 2 ), the SOI films were crystallized or recrystallized by ZMC or ZMR. The effects of Si film thickness, temperature of the lower heater (used in the ZMC or ZMR process), and scan speed, which is the dominant factor in the fabrication cost on the structural change in the films after ZMR and ZMC and on the crystal orientations were determined. Comparison between ZMC films and ZMR films showed that for all scan speeds, the a-Si ZMC films had much higher uniformity in their crystal orientations than did the poly-Si ZMR films. Results showed that at a high scan speed of 7.0 mm/s, an SOI with high crystal uniformity [over 90% Si (100) texture] with no voids could be fabricated by ZMC at optimized conditions (i.e., lower heater temperature of 1893 K and a-Si film thickness of 0.1 μm).