Properties and microstructure of tungsten films deposited by ion-assisted evaporation

The modification of film properties in evaporated tungsten was studied as a function of deposition environment. Using concurrent argon ion bombardment of the growing film, the stress varied in the same manner at all ion energies and substrate temperatures. Initial increases in tensile stress are followed by a monotonic trend toward compressive stress, for all sets of films. On the other hand, the qualitative changes in film resistivity with concurrent bombardment were dependent on the ion energy and substrate temperature, showing increases at high temperature and energy and decreases at low temperature and energy. Changes in the microstructure and impurity content in deposited films were found to be strongly linked to stress and resistivity changes. The trend toward compressive stress induced by high levels of ion bombardment is primarily reflected in an increase in (110) orientation. Increased resistivity is related to decreased grain size, increased (110) texture, and increased levels of film argon and oxygen content. By choice of deposition conditions, both the resistivity and stress can be minimized.