Abstract

The development of compressive biaxial stress in a film as the result of energetic impact during growth has been demonstrated in a number of experimental studies. In a study of sputtered metal films, Hoffman and Thornton showed that there is a tendency towards compressive stress as the pressure of the Ar sputtering gas is reduced^[1]. Because the effect of collisions is to thermalise the sputtered vapour to a temperature approaching that of the background gas, low pressure sputtering generally produces a higher flux of energetic atoms onto the growing film. In some cases, the data show a maximum in compressive stress as pressure is reduced, showing that even though the average energy of the sputtered atoms is increased by further reduction of pressure, the compressive stress is actually reduced. For Pd films subjected to Kr ion bombardment during growth, Ziemann and Kay^[2] showed the presence of a maximum in the compressive stress for an impact energy of 80eV per Pd atom. In the case of sputtering in which the substrate is biased with respect to the plasma so that the energy of impact of ions onto the film may be varied, a maximum compressive stress in several metal films has been observed for bias voltages of approximately - 50V^[3]. The situation in non-metallic films is similar. For TiN, the compressive stress also shows a maximum in the impact energy range less than 200eV^[4].

© 1992 Optical Society of America