A high purity thin film deposition method has been established, which consists of ion beam sputtering with negative ions. The most important characteristic of this method is that high purity film synthesis by self-sputtering occurs under an ultra-high vacuum: this results in deposited films that contain no gas elements such as Ar and Kr, which are found using standard general sputtering apparatus. This is made possible by the negative ion source of the Cs sputter type which needs no discharge gas. In this report the formation of Si, Si-C and Si-Fe films is demonstrated. The purity of deposited alms is analyzed using the Rutherford backscattering method. The dependence of the composition of deposited films of the target materials: Si, C, SiC and Fe, and the beam species and energies of Si(-) are reported.