Stress in Vacuum Deposited Films of Silver

Abstract

Measurements have been made of the tensile stress in silver films evaporated in a vacuum of 1–2×10^-5 torr on to mica strips, electron microscopic observations of the film structure being carried out on the other hand. Films having various thicknesses ranging from about 30 Å to 1000 Å were under investigation. The tension per unit width of the film, S, increases sigmoidally with the film thickness d: In the initial stages of film growth in which the film is composed of isolated islands, S is very small; S increases rapidly during the late coalescence stage and the channel stage; after the completion of a continuous, hole-free film, S does increase with d, but at a much slower rate. The mean stress per unit cross section of the film, σ (=S/d), increases sharply with d to assume a maximum at a thickness around 200 Å where the “shoulder of the S-d curve is located, and decreases gradually as d increases further.