STRESS-STRAIN BEHAVIOUR OF ELECTROPLATED GOLD THIN FILMS

This work presents the characterization of the stress-strain behavior of an electroplated gold layer deposited on thin chromium layer (thickness: 1500nm, 10nm respectively). The stress of the composite layer is measured by wafer curvature. The strain is applied through a series of thermal cycles at temperatures ranging from 50 to 240°C. The sample stays at high temperature for a long time (18h) to let its structure plastically flow and release all extrinsic stress. After this, the ramp down step induces a known strain due to the mismatch between film’s and substrate’s TCE. From studies on gold [1] it is documented that crystal grain growth activates at temperatures of about 300°C: this leads to the assumption that grain growth is not relevant in the examined temperature range and therefore the intrinsic stress at curing temperature has to be constant. By consequent correction of the calculated thermal stress we obtain a stress-strain curve for our material, which is consistent with literature [4]. A Young’s modulus of about 108 GPa, yield strength of 160 MPa and tensile strength of 190 MPa are calculated. The obtained stress-strain behavior is employed in the modeling of diagnostic test structures, leading to consistent results.