STRESS-RELAXATION IN SI-RICH SILICON-NITRIDE THIN-FILMS

Si-rich silicon nitride thin films have been deposited by low pressure chemical vapor deposition, at 850 degrees C from mixtures of dichloro silane and ammonia. The films' elastic properties have been studied as a function of film composition. Fourier transform infrared spectrosco py and ellipsometric data indicate that the local atomic strain is a s trong function of the calculated volume fraction of Si contained in th e films. A relationship is observed that shows the strain to be invers ely proportional to the cube root of the Si volume fraction. A model t hat accounts for distortion in Si-SixN4-x tetrahedra (x=0-4), upon sub stitution of silicon for nitrogen in the film is applied to the data. The model is shown to be consistent with measurements of intrinsic fil m stress across a compositional range from stoichiometric silicon nitr ide, Si3N4, to nitrogen-free amorphous silicon, a-Si. (C) 1998 America n Institute of Physics.