THE EFFECT OF DEPOSITION PARAMETERS ON THE COMPRESSIVE STRESS IN A-C-H THIN-FILMS

Beam-bending techniques for the measurement of the internal stress in thin films are well known. The thickness of the film is generally required as a parameter in the equations used, but it has been noted that in practice the measured stress does not generally extrapolate to zero for zero film thickness. Measurements of stress as a function of film thickness performed on a-C:H films deposited by means of a capacitive r.f. technique from a methane-hydrogen glow discharge are presented. Results support the postulate that the non-zero extrapolation of measured stress can be explained by assuming that the forces required to bend a beam originate from the bulk of the film as well as from sources such as surface and interfacial phenomena. Both bulk and interfacial contributions are separated and discussed in terms of deposition parameters such as self-induced bias, deposition rate, chamber pressure and degree of methane dissociation.