An atomic-scale analysis based on molecular dynamics simulations of the interactions of small thermal and energetic SinKm, n > 1, clusters observed in various plasmas with crystalline-and amorphous Si surfaces is presented. The experimental literature has assumed and employed a unit reaction probability for clusters of various sizes on all Si surfaces in phenomenological models for obtaining hydrogenated amorphous Si film growth rates, while the reaction mechanisms of clusters with the deposition surfaces have remained unexplored. In addition, it is widely speculated that clusters have a detrimental effect on: the film quality. Our study shows that the clusters react with high (> 85%) probability with crystalline surfaces and with surfaces of amorphous Si films. The structure and energetics of the corresponding adsorbed cluster configurations on these surfaces are analyzed and discussed. Furthermore, the simulations provide insight into possible mechanisms for the formation of defects, such as voids and dangling bonds, in plasma-deposited amorphous Si films through reactions of the clusters with the deposition surfaces.