Sputtering yield amplification of Si through the addition of Cu, Mo, or Ta

Sputtering yield amplification, SYA, is a term created by S. Berg (1996) to describe the effect of modifying the momentum transfer collision-cascade in the surface of a target through the addition of heavy dopant atoms. This phenomenon can promote an increase in the emission of the target atoms, which are generally lighter than the dopant ones. SYA has been demonstrated experimentally for C, Al, and Si when heavy atoms such as Ti and W are added. However, there is a limit to the number of dopant atoms, and there are doubts as to why some dopant elements do not produce SYA. In experiments where a target is co-sputtered with small pieces of dopant material, it is assumed that, to cause SYA over all of the target, the dopant material is sputtered and redeposited over the surface of the target. Gas-phase collisions between the sputtered dopant atoms and argon are the principal mechanism for redeposition, and obviously the gas pressure is an important factor. In this article we studied the effect of the gas pressure on the SYA produced by Mo, Ta, or Cu on a Si target. Using profilometry and Rutherford Backscattering Spectrometry we measured the thickness of the deposited films, and the total number of atoms deposited on the substrate, under the different pressures. Optical Emission Spectroscopy was used to measure the intensity of the emission lines of neutral and ionised species in the sputtering plasma. Furthermore, with the SIMTRA code, we theoretically estimated the spatial distribution of atoms that were redeposited on the target. The results indicate that, for all pressures and dopant elements used, there was significant SYA.