Vacuum-ultraviolet irradiation produces trapped charges in dielectrics. The trapped charges often generate self-consistent electric fields. A Monte Carlo simulation coupled with a Poisson equation solver is used to model the relationship between the irradiation photon flux and electrostatic potential. The simulation includes photoconduction, photoemission, photoinjection, and the effects of self-consistent electric fields. Calculations show that photoemission and photoinjection are responsible for changes in the electric potential as photon dose or dielectric thicknesses are varied. Experimental surface-potential measurements were made to compare the results of the simulation.

Capacitance-voltage ͑C-V͒ measurements are used to determine the effect of vacuum ultraviolet ͑VUV͒ and ultraviolet irradiation on mobile charges in porous low-k organosilicate ͑SiCOH͒ dielectrics. Hysteresis in the C-V characteristics shows that VUV irradiation increases the number of mobile charges in the dielectric. This is because VUV photons excite the trapped electrons from defect states to make them mobile carriers. Conversely UV reverses this effect by reducing the mobile charges through photoemission of free electrons and repopulation of trap states. Thus UV irradiation can be used to improve the electrical properties of plasma-processed dielectrics that are subjected to VUV irradiation.

The surface potential due to charge accumulation during vacuum ultraviolet irradiation of high-k and low-k thin dielectric films is measured. Measurement of the substrate current, which is the sum of the charge-accumulation and photoinjection currents, allows an in situ monitoring of the charge accumulation during irradiation. The relationship between the substrate current and the calculated in situ surface potential is also found, eliminating the need for a separate surface-potential measurement. With a high photon dose, the surface potential and substrate current reach a steady-state value with no further net charge accumulation.

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