W/Cu TSVs for 3D-LSI with minimum thermo-mechanical stress

High density 3D-LSI with W-TSV for signal line and Cu-TSV for power/GND line, and Cu-TSV containing W stress absorbing layers were investigated for the induced thermo-mechanical stress in 3D-LSI Si die/wafer after wafer thinning and bonding using micro-Raman spectroscopic technique. Stress mapping analysis revealed that W-TSV has induced less thermo-mechanical stress in LSI Si, whereas the Cu-TSV has induced large amount of stress. Further, Cu-TSV with W stress absorbing layer showed much reduced residual thermo-mechanical stress as compared to the pure Cu-TSV, i.e for 6 μm diameter Cu-TSV with W layer showed < +100 MPa of tensile stress after heating at 400 °C, whereas the Cu-TSV without W layer revealed > -300 MPa of compressive stress after heating at 400 °C. This property can be readily employed to minimize the residual thermo-mechanical stress in the bonded high density 3D-LSI.