Influence of energy reflected from the target on thin film characteristics

Abstract

It has been recognized since the 1960’s that bombardment of a growing thin film by energetic particles strongly influences film properties. Particle bombardment has generally been accomplished by accelerating ions into the growing film. However, it has also been recognized since the 1960’s that energetic neutral particles originating at the target also bombard films grown by physical sputtering. It has been frequently suggested that the properties of sputtered films are influenced by bombardment with particles from this source. Nevertheless, a lack of the necessary information has made it difficult to make quantitative (or even semiquantitative) estimates of the magnitude of the energy deposited into the film. A systematic study of the energy reflected from the surface by normally incident, singly charged noble-gas ions on five substrates of different masses has recently been published. These data along with sputter yields from the literature allow estimates to be made which were previously unavailable. The energy reflected from the target is carried away by electrons, sputtered particles, and reflected ions (neutrals). The purpose of this article is to provide basic information which will allow thin film scientists to estimate the influence of various experimental parameters on the amount of energy arriving at the growing film. The energy reflected from the target per sputtered atom will be given as a function of ion mass, target mass, and ion energy. trim.sp Monte Carlo calculations will be used to estimate the ratio of the energy carried away by sputtered atoms to that carried away be reflected ions. Calculations will also be used to estimate the average energy of the sputtered atoms as a function of ion mass, substrate mass, and ion energy. It will be shown how data presented in this article can be used to make estimates for other elements in the periodic table. It will also be shown how this information can be used to guide the adjustment of experimental parameters in sputtering environments so as to control film characteristics.