The behavior of suspended particles at the proximity of the membrane in cross-flow microfiltration is studied to better understand how the first layer of particle deposit is built at the membrane surface. The membrane model is a 3D spatially bi-periodic porous surface with circular holes of finite thickness. A semi-analytical model based on a thin screen assumption for fluid flow calculation and on correction factors to Stokes law for drag force is used to compute the particle trajectory. First, the trajectories given by this simplified model compare favorably to trajectories obtained using a complete model based on a boundary element method to compute the Stokes flow in the domain in the presence of the particle at each time step. Second the simplified model is applied to determine the capture probability density function at the membrane surface from trajectory impact points. The effect of membrane porosity, capture distance and wall shear rate are then discussed. Finally the trajectories of one single particle and a couple of particles given by the complete model are analyzed.