CONSTRAINED-FILM SINTERING OF A BOROSILICATE CLASS - IN-SITU MEASUREMENT OF FILM STRESSES

We have measured in-plane stresses developed in a borosilicate glass ( BSG) film during its constrained sintering on a rigid substrate. sampl es were prepared by casting BSG slurries on a silicon substrate and si ntered inside a hot stage at 715 degrees C just above the glass-soften ing temperature, Inplane stresses from the constrained-film sintering were determined by wafer-curvature measurements using an optical syste m, The measured stresses were tensile and rose rapidly from zero to a maximum level of 20 kPa during the initial stage of sintering and grad ually decreased to zero at the final stage; these stresses were consid erably smaller than those calculated from available microstructural mo dels, We also measured the densification profiles of the free and cons trained films. The stresses had no apparent effect on the densificatio n profile of the constrained film up to 90% relative density; but beyo nd that, the densification kinetics were reduced in the constrained fi lm. We believe that the stresses could have prevented a few large pore s from shrinking during the initial stage of sintering, which then lea ds to an overall lower density and larger pores in the constrained fil m.