Large-grained polycrystalline Si films obtained by selective nucleation and solid phase epitaxy

We investigated the formation of large-grain polycrystalline silicon films on glass substrates for application in low-cost thin film crystalline silicon solar cells. Since the use of glass substrates constrains process temperatures, our chosen approach to form large-grain polycrystalline silicon templates is selective nucleation and solid phase epitaxy (SNSPE). In this process, selective crystallization of an initially amorphous silicon film, at lithographically predetermined sites, enables grain sizes larger than those observed via random crystallization. Selective heterogeneous nucleation centers were created for both P-doped, B-doped and undoped, 100 nm thick amorphous silicon films, by masked implantation of In or Ni islands, followed by annealing at temperatures below 600°C. Seeded crystallization begins at the metal islands and continues via lateral solid phase epitaxy (SPE), thus obtaining crystallized regions of several tens of square microns. The maximum achievable grain size depends on the product of the SPE rate and the incubation time for the spontaneous nucleation. We have studied the dependence of the SPE rate and the incubation time on the type of metal (In and Ni) inducing the nucleation and on the electronic dopant (e.g. P and B) concentration in the 1e19-1e21 cm^-3 range.