Elucidating the Growth Mechanisms of Electron Beam Induced Deposition via a Three Dimensional, Monte-Carlo Based Simulation

The rapid and precise direct-write growth of nanoscale features by electron-beaminduced deposition (EBID) and etching (EBIE) requires the optimization of the growth parameters to maintain nanoscale feature dimensions. The tremendous and complex EBID parameter space includes the precursor gas pressure, the primary electron beam energy, the electron beam current, surface diffusion rates of adsorbed precursor species, thermal effects on desorption, and the cascade of electron species produced by elastic and inelastic scattering processes. These variables determine the feature growth velocity and the size of the structure through a series of complex, coupled nonlinear interactions. A dynamic computer simulation based on Monte-Carlo calculation sequences was created to aide in the interpretation of experimental observations by simulating experimental EBID growth conditions for a nanoscale stationary and scanned electron beam with properties characteristic of a conventional SEM.

In this dissertation, initially the Monte Carlo EBID simulation details are presented. Subsequently, four specific case studies are simulated. The details of the mechanisms and electron types responsible for vertical and lateral growth are presented. Initially, EBID growth was compared in a reaction rate limited regime at different beam energies (1keV versus 5keV). This yielded lower growth rates at higher energy due to a combination of variables, including a lower dissociation cross section and a decreased secondary electron coefficient. Second, reaction rate versus mass transport limited growth of tungsten from a WF6 precursor was studied, and the lateral broadening associated with mass transport limited growth was elucidated. Third, a study was performed to determine the effects of precursor surface diffusion on pillar growth rates and morphology. The changes were attributed to a shift in the otherwise mass transport limited growth with no surface diffusion to a pseudo reaction rate limited growth when the surface diffusion coefficient was sufficiently high. Fourth, two different materials were simulated and compared: tungsten from WF6, and SiO2 from Si(OC2H5)4. The different growth rates and pillar morphology correlated to the different dissociation cross sections, secondary electron yields, and the electron range, respectively.

Sample applications of the simulation are provided, including rastered depositions, via filling, and duplication of “volcano-like” structures.