Nucleation and growth of strontium titanate (SrTiO3,) films, prepared by pulsed laser ablation deposition, has been investigated during on a (100) silicon substrate surface, using atomic force microscopy. A nucleation kinetic model has been derived from an analysis of the particle size distribution. The reconstructed nucleation trend was characterised by a systematic behaviour : the nucleation rate, negligible at the beginning, reaching a maximum after a certain time and tending to zero for longer deposition time. This behaviour prompted the design of a simple model which correlates these phenomena to two specific aspects : i) the nucleation occurs at certain limited number of sites on the substrate surface; ii) the nucleation process shows a temperature-dependent incubation time. In this model, the incubation time is related to the formation time of a 'critical SrTiO3 cluster'. The size of the critical cluster is determined both by thermodynamic quantities and by the amount of interface misfit strain energy of SrTiO3 lattice with respect to substrate.