Film stress of sputtered W/C multilayers and strain relaxation upon annealing

Sensitive curvature measurements were performed on 40 Å period W/C multilayer structures on Si substrates using a two beam laser reflection technique. A compressive stress of approximately 1530 MPa was measured in these sputtered multilayer films. Thermal annealing to 500 °C resulted in very little strain relaxation in the multilayers but x-ray diffraction data show a slight increase of the multilayer period. Significant strain relaxation, though, was observed when a 400 Å W buffer layer was included. Thermal annealing of these samples to 400-500 °C resulted in large strain relaxation due to the growth of α-W crystals in the buffer layer. Large oxide formation on air annealed samples did not significantly change the strain state of the films.