The development of stress and surface temperature during deposition of lithium fluoride films

Abstract

Apparatus is described for the measurement of stress in thin vacuum deposited films. It consists of a mechanical probe that can detect the movement of the free end of a thin cantilever beam used as a substrate. The sensitivity is such that observations can be made of the stress developed during the initial stages of growth (film thickness < 100 Å). The results for films of lithium fluoride have been correlated with electron microscopy observations and it is shown that stresses exist even when the films consist of completely separate islands. The stress increases as the average film thickness increases and becomes constant with thickness when the films become continuous. It is also shown that the mechanical probe provides a sensitive method of detecting very small temperature differences developed across thin substrates (0•01°C in 0•01 cm). This has enabled measurements to be made of the substrate heating resulting from the deposition of lithium fluoride.