Formation of polycrystalline silicon films with μm-order-long grains through liquid-phase explosive crystallization by flash lamp annealing

Flash lamp annealing (FLA) is a short-time annealing technique which can heat and crystallize μm-order-thick amorphous silicon (a-Si) films without inducing serious thermal damage onto whole glass substrates thanks to its proper fluence on the order of several tens of J/cm² and millisecond-order duration. The FLA of a-Si films leads to lateral explosive crystallization (EC), driven by the release of latent heat, with a lateral crystallization speed on the order of m/s. When we use electron-beam- (EB-) evaporated a-Si films as precursors, EC only through liquid-phase epitaxy (LPE) occurs, resulting in the formation of polycrystalline Si (poly-Si) films with μm-order-long grains stretching along lateral crystallization directions. We see no remarkable difference in the microstructure of poly-Si films on various glass substrates, and this crystallization can take place also when doped EB-evaporated a-Si films are used. We have confirmed the simultaneous crystallization of pn-stacked a-Si films by FLA, and according to the data of scanning spread resistance microscopy (SSRM), the diffusion of dopants, B and P, can be sufficiently suppressed to a level at which the pn-stacked poly-Si films can be used as solar cells. The advantages of rapid crystallization and the formation of large grains would contribute to the establishment of the low-cost fabrication process of thin-film poly-Si solar cells.