Ballistic electron emission microscopy has been used to study physical damage effects on PtSi/n-Si Schottky contacts. The physical damages are introduced into Si substrates by ion bombardment with well-defined energies in an ion-milling process. Schottky barrier height (SBH) distribution is measured on the subsequently formed PtSi/n-Si Schottky diodes. The results show that mean SBH decreases with ion energy in a square-root relation. A simple SBH model is developed to consider image-force lowering effect for a semiconductor with a step-function distribution of donor concentration. The model is successfully used to explain quantitatively the experimental relation between SBH and ion energy.