Research on thermal evolution of polydimethylsiloxane flexible sample with a practical 3-D FIB power deposition model

Focused ion beam (FIB) has been invented for several decades and widely utilized as a result of rapid development of integrated circuit industry and nanotechnology. Together with high resolution scanning electron microscopy (SEM), FIB can realize controllable micro-nano fabrication of metals and semiconductors. However, it is very difficult to guarantee the machining precision and quality when we extend the application to flexible materials. Severe damages such as the local thermal effect and chemical evolution will be induced with high-energy FIB bombarding on the flexible sample, so current models of FIB fabrication are no longer valid. In this paper, a practical 3-D FIB power deposition model was developed for studying the temperature rising mechanism and the according thermal evolution to realize controllable high-precision fabrication of flexible samples. Based on theories of ion transportation and ion-solid interaction, a new 3-D power deposition model including ion energy, aberrations, and Coulomb force among ions was built with Runge-Kutta method and Monte Carlo simulation. Thermal evolution of the representative flexible sample polydimethylsiloxane (PDMS) was studied with the finite element COMSOL-Multiphysics according to Fourier law of heat conductivity. The new model was improved by studying thermal effect under different dwelling times and beam currents, and verified by the related experiments. Results show that the local thermal effect of PDMS is very severe for high current density 30 keV Ga+ as its power density spatially can be compressed to 109W/cm3. Fabrication experiments on FIB-SEM system are in good agreement with simulations of heat accumulation and thermal evolution of polymer PDMS. This work will improve controllability and precision of FIB fabrication on the flexible sample by considering the incident beam and the sample thermal effect together.