We deposit polycrystalline silicon (px‐Si) with mean grain diameter ∼400 A˚ using dc magnetron sputtering of a Si target in an Ar plasma. We analyze the nucleation process and crystallite size as a function of film thickness usinginsitu, real time spectroscopic ellipsometry. For direct deposition on glass substrates at 470 °C, the initial ∼0.3 &mgr;m is amorphous silicon, then crystalline nuclei appear, and the growth becomes fully polycrystalline by ∼0.6 &mgr;m. To promote nucleation, we deposit a 100 A˚ layer of &mgr;c‐Si:H (hydrogenated polycrystalline silicon with a mean grain diameter of ∼60 A˚) by sputtering in an Ar plus H2atmosphere at 210 °C. Returning to an Ar‐only plasma at 470 °C, px‐Si grows on this seeded substrate with no detectable amorphous interfacial layer. Since magnetron sputtering is a large‐area, high throughput technique, this two‐step process appears technologically attractive. ©1995 American Institute of Physics.