Numerical estimates for energy of sputtered target atoms and reflected Ar neutrals in sputter processes

During the sputtering process in Ar gas, the sputtered target atoms and the reflected Ar neutrals from the target have much higher energy than the background gas. In this study, the Thompson distribution and an updated Meyer model based on the elastic energy transfer between two colliding particles were used to obtain energy distributions and average energies for the sputtered metal atoms and the reflected Ar neutrals. An energy dependent elastic collision cross section was incorporated into Meyer’s model and a thermalization criterion based on power balance was used. Under typical sputtering conditions (0.5 mTorr and 1000 K Ar, 400 eV incident Ar ion), the model predictions indicate that for Cu, Ti and Ta targets, the sputtered metal atoms have initial average energies from 15 to 22 eV and thermalize with the background Ar gas between 10 and 20 collisions. The reflected Ar neutrals thermalize after about 10 collisions. Depending on the number of collisions, the energy dependent mean free path values of the sputtered metal atoms range from 300 to 100 cm while the mean free path values for the reflected Ar neutrals range from 200 to 100 cm.