Thermally induced stress changes in high-density plasma deposited silicon nitride films

Silicon nitride (SiN) films of various compositions and with compressive or tensile stress were deposited on GaAs substrate from mixtures of Ar, N2 and SiH4 as precursors using electron cyclotron resonance plasmaenhanced chemical vapor deposition (ECR-PECVD) technique. Upon heating these films the stress in the as-deposited compressive film reduced or even changed to tensile, while the stress in the as-deposited tensile film increased. As long as the temperature did not exceed 200 dec C the stress change was linear and reversible for both types of films. When heated beyond this temperature the stress change was not linear for films deposited with non optimized parameters. Additionally, upon subsequent cooling the stress change did not follow the same path as of heating, thus exhibiting a hysteresis in the stress with a thermal cycle. The hysteresis, however, decreased with the number of thermal cycles. It almost vanished after five cycles. The magnitude of the hysteresis has also been found to depend significantly on the deposition parameters. Using a careful combination of the deposition parameters it was possible to deposit at low temperatures (90 dec C) a stable SiN film with low stress. This film shows negligible hysteresis in stress with thermal cycling.