In this study, a simple mathematical model has been developed for the description of amorphous layer growth by low ion energy implantation. The model concerns the lower and higher dose range. It has been assumed that the damage depth distribution can be approximated by a Gaussian. The thicknesses of the amorphous layer and voids film, obtained assuming multi-layer model, have been found in relation to the ion damage straggling and amorphization threshold. The model concept and the corresponding calculations are discussed in details.