Optimized molecule supply from nozzle-based gas injection systems for focused electron- and ion-beam induced deposition and etching: simulation and experiment

We simulated and measured near-field distributions of molecules impinging on a flat substrate from tube-based nozzles with varying exit aperture geometries (straight, bevelled and doubly perforated). Simulations were performed with the test-particle Monte Carlo approach taking into account the Knudsen number (molecular/transient flow) at the nozzle exit. Distributions were measured via thermal decomposition of Co-2(CO)(8) molecules on a homogeneously heated substrate. For all geometries and Knudsen numbers a good match between the simulation and experiment was found. For the first time the maximum accessible molecule flux with respect to the total flux exiting the nozzle could be quantified: it is around 7% for a straight cylindrical tube, around 27% for a bevelled tube and around 32% for a doubly perforated tube, all nozzles being 300 mu m distant from the substrate and having a 400 mu m aperture. Optimum substrate-nozzle angles were determined and shadow effects quantified.