Atomic force microscopy has been extensively used to investigate polysilicon deposited on silicon for times ranging from 10 s to 45 min. The temperature deposition was 620-degrees-C. Two different regimes have been singled out : one corresponding to isolated grain growth followed by another one which corresponds to coalescence growth. For short times (from 10 s to 1 min) the number of grains remains constant and they grow without any interaction with each other; the grain radii increase following a t1/3 law. When polysilicon grains have grown to a size large enough for them to interact with each other, coalescence takes place and the growth regime is modified; the grain number decreases following a 1/t law. For this second growth regime the surface exhibits a self-similarity type of behavior from which a dynamic scale law can be deduced.