I n s i t u measurements of film stress in AlN sputtered onto moving substrates

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Abstract
An apparatus has been built, using a compact laser ranging device, which measures the i n s i t u 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 sputteredAlN 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°. Beam deflections for AlN on glass are typically linear with film thickness, revealing a constant incremental stress. However, beam deflections for the same filmsdeposited on polyimide are highly nonlinear with thickness. For filmsdeposited 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 filmsdeposited 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.

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