INSITU MEASUREMENTS OF FILM STRESS IN AIN SPUTTERED ONTO MOVING SUBSTRATES

An apparatus has been built, using a compact laser ranging device, which measures the in situ deflection of a cantilevered beam during thin-film deposition. The device can be transported in front of a source to study the evolution of stresses in films, analogous to those deposited in a web or in-line palletized coating process. We have measured the stress profile in direct-current reactively sputtered A1N on glass and polyimide as a function of total gas pressure and argon-to-nitrogen partial pressure ratio. We have also studied stress anisotropy by changing the beam orientation with respect to the transport direction. Typical film thicknesses were 250 nm and shielding restricted the incoming and outgoing angles of incidence to approximately 45-degrees. Beam deflections for A1N on glass are typically linear with film thickness, revealing a constant incremental stress. However, beam deflections for the same films deposited on polyimide are highly nonlinear with thickness. For films deposited on glass at an argon-to-nitrogen ratio of 5:1, a sharp transition from neutral to a tensile stress of 11.5 Gdyn/cm2 takes place as the total gas pressure is raised from 3 to 5 mTorr. The stress in films deposited at ratio of 2:1 increases smoothly from 4.5 to 8.5 Gdyn/cm2 over the total gas pressure range of 2.5-7.5 mTorr. No significant stress anisotropy is observed. Repeated measurements give an estimate of the standard deviation for an individual stress value of 0.5 Gdyn/cm2, which includes the variability of the sputtering process as well as the error in the measurement technique.