Photoemission and conduction currents in vacuum ultraviolet irradiated aluminum oxide

Abstract

A temporary increase in the conductivity of aluminum oxide sputter deposited on the surface of aluminum wafers was made by exposure to vacuum ultraviolet ͑VUV͒ radiation produced by a synchrotron light source. The oxide was charged, either positively or negatively, by exposure to a nonreactive inductively coupled plasma, under typical plasma processing conditions. We show the dependence of the conductivity on the energy of the incoming radiation, and conclude that only those photons whose energy is above the band gap of the oxide are capable of producing a temporary increase in the conductivity. Two processes, photoemission and enhanced conductivity, create currents flowing across the oxide layer. A circuit model was developed to show the contributions from both processes to the total current. We conclude that VUV radiation may be used to significantly decrease plasma-induced surface charging of dielectrics.

Bandgap measurements of low-k porous organosilicate dielectrics using vacuum ultraviolet irradiation

“…1,2 These processes depend on the incident photon energy and the dielectric thickness. Electron-hole pairs will be formed if electrons are excited into the conduction band from the valence band or from defect states within the dielectric.…”

Monte Carlo simulation of the effects of vacuum-ultraviolet radiation on dielectric materials

“…The surface potential on the dielectric was measured with the Kelvin probe. 3,4 The photon flux in the VUV beam is roughly Gaussian in shape. The background potential on the dielectric ranged from 0-1 V. At the center of the beam, the surface potential was 2.65 V, which is comparable to the potential obtained from the Monte Carlo simulation.…”

“…To compare the simulation with experiment, the surface potential on a dielectric charged with a beam of VUV photons produced by a synchrotron was measured using a Kelvin probe. 3 The process can be broken down into several parts. They are: ͑1͒ Photoelectric absorption, which leads to electronhole pair production, ͑2͒ electron excitation, and/or ͑3͒ photon ͑Rayleigh͒ scattering.…”

“…1, the expelled electrons are collected by a plate located 3 cm above and parallel to the dielectric and biased to +48 V. 3 The plate has a circular aperture to allow the VUV beam to reach the dielectric. By plotting the instantaneous value of the collected current versus substrate voltage, which can be obtained point by point from Fig.…”

“…1 However, vacuumultraviolet ͑VUV͒ radiation emitted by the plasma can be beneficial and can deplete charge by temporarily increasing the conductivity of the dielectric. [2][3][4] The increase is caused by electron-hole-pair production 4 which occurs when photons of energy higher than the band-gap energy strike the dielectric. 5 Electrons photoemitted from the dielectric lead to the formation of a positive potential.…”