# Process Modelling

VUV irradiation produces trapped charges in dielectrics. The trapped charges often generate self-consistent electric fields. Monte Carlo simulation coupled with a Poisson-equation solver is used to model the relationship between the irradiation photon flux and surface 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 surface potential as photon dose or dielectric thicknesses are varied. Experimental surface potential measurements were made to compare the results of the simulation.

Electron and hole distributions in SiN-Si after irradiation with 20 eV photons at at dose of 5.6 x 1012 photons/cm2. The position scale is logarithmic.

Electrostatic potential as a function of depth in a 250-nm thick SiN dielectric layer with an underlying Si substrate as a function of dose of 20-eV photons. (a) potential distribution from substrate to vacuum (b) potential distribution near the dielectric-vacuum interface.