Inlet Hole Shape Analysis Depending on the Focus Conditions for Electron Beam Micro-hole Drilling

Electron beam micro-drilling processes have some advantages, such as high aspect ratio of 3-10, and applicable usages of difficult-to-cut material. The process has always required some lensing system optimization with an electromagnetic system for a high-density electron beam profile. This paper suggests the inlet hole characteristics depending on the focus conditions with a 120 kV electron beam. Normally charged particles during the focusing process could be affected by circular and focusing motions in the magnetic force field. However, it always has space charging forces between each electron particle. Therefore, we could analyze the effect of the inlet hole shape depending on the focus conditions that have different space charging conditions, such as converging and diverging beam envelopes. This study analyzed the effects of the shape and size of the burr of drilled holes with respect to converging and diverging focus conditions. In addition, a Monte Carlo simulation was conducted to verify the effect of the focus condition on the scattering process. The experimental results show that converging electron beams are more effective on the reducing burr at the edge of the inlet hole. The simulation results suggest that the behavior of back scattered electrons can be altered under different focus conditions and that it can affect energy absorption by BSEs.