We have successfully improved the surface roughness and crystalline fraction of polycrystalline silicon (poly-Si) films formed on quartz substrates at 300 degrees C by controlling its initial growth. Seed layers were formed by eliminating charged species incident on the substrate during the initial growth in electron cyclotron resonance silane and hydrogen plasma-enhanced chemical vapor deposition and poly-Si films were subsequently formed on the seed layers with charged species. As a result, control of ion bombardment on the initial growth was found to be a key factor for forming poly-Si films with smooth surfaces and high crystallinity at low temperatures.