Energy dependence of vacuum-ultraviolet-induced radiation damage to electronic materials

Dielectric charging plays a key role in processing damage of semiconductor devices. VUV radiation with energies in the range of 4-30 eV can induce charge on electronic materials. Radiation charging of Si wafers coated with 3000A of Si₃N₄ from synchrotron VUV exposure with photon fluxes in the range of 10⁹-10¹³ photons/sec cm^-2 were measured with a Kelvin probe. The photoemission current and substrate voltage were monitored during each exposure. The integral of photoemission current was compared to the net charge measured with the Kelvin probe for VUV photon energies between 7-21 eV. The net charge induced on the dielectric results from both photoemission (which saturates for long exposure times) as well as from charge carriers generated within the dielectric. Since the threshold photon energy for photoemission is higher than that for electron-hole pair production, it is seen that photoemission can be minimized if the photon energies are below the threshold energy.