Sensitivity of a Rotating Beam Sensor for Stress Evaluation in Aluminium Thin Films
The evaluation of stress in sub-micron tracks is critical for the microelectronics industry and there is a need for new methods of measurement. This paper advocates the use of a rotating beam sensor structure which can be fabricated on the wafer along side electronic devices and used to monitor stress generation and relaxation as a function of processing. The rotation can be observed with a reflected light microscope and correlated to the actual stress level. Several samples, assputtered and sintered, were prepared with the aim of having different residual stress states. X-ray diffraction with a low incident angle geometry, was used to evaluate the residual stresses on the aluminum layer. Computer simulations using ANSYS were also performed in order to correlate the sensor rotation with the experimental stress values. It was observed that the extrinsic stress from the mismatch in expansion coefficients between the aluminum layer and the silicon substrate dominates over the compressive stress from the sputter growth. Sintering the layers at temperatures above 150°C reduces this compressive stress due to the action of creep. The calibration of the rotation of the device with the direct measurements of the X-ray diffraction shows that the sensor has a resolution better than 2.8 MPa.
Sabine Denis, Takao Hanabusa, Bob Baoping He, Eric Mittemeijer, JunMa Nan, Ismail Cevdet Noyan, Berthold Scholtes, Keisuke Tanaka, KeWei Xu
J.M.M. dos Santos et al., "Sensitivity of a Rotating Beam Sensor for Stress Evaluation in Aluminium Thin Films", Materials Science Forum, Vols. 490-491, pp. 649-654, 2005