Effect of Temperature and Bias on Glass-Silicon Interfaces

New technologies for deposition of thin glass films on silicon substrates have generated interest in the resulting glass-silicon interface potentials and the interface stability under conditions of bias and temperature that might be experienced in device operation. Experiments are described which show accumulation of space-charge layers at glass-silicon interfaces under combined conditions of electric field applied normal to the surface, and elevated temperature. The glasses studied are lead-alumino-borosilicates and zinc-alumino-borosilicates and were applied in films several microns thick by sedimentation techniques. Measurements were made on metal-glass-silicon capacitor structures. The silicon at the interface may be shifted strongly n-type or strongly p-type, depending on applied field direction, during a heating cycle of a few minutes. Surface charge densities up to 10
¹³
electronic charges/cm
²
have been observed. The temperatures required for such shifts vary over the range 100° to 300°C, depending on glass composition. Conductivity through the films during the combined bias-temperature treatment is compared with interface charge build-up. The data suggest a mechanism in which the bias-temperature combination causes movement of ions (possibly sodium) with a resultant build-up of space charge in the glass near the interface. The long-term stability of this “locked-in” charge indicates that interface potential with the more stable glasses may be permanently tailored to a desired value by bias-temperature treatment.