Impact of fluence-rate related effects on the sputtering of silicon at elevated target temperatures

In this work we show how ion-beam-induced epitaxial recrystallization plays a role in focused ion-beam (FIB) sputtering of silicon at elevated temperatures. The sputtering process is the key to all high-precision machining of microstructures and nanostructures by FIBs. A fluence-rate effect observed for the sputtering of silicon at elevated temperatures arises from competition between stabilizing interactions between populations of defects produced by consecutive ion impingement (damage buildup) and dynamic self-annealing. By high-resolution transmission electron microscopy analysis we show that the damage, produced by exposure of silicon to a 50 kV focused gallium (Ga) ion beam at elevated target temperatures, departs quite substantially from the expected damage based on the distribution of energy within the substrate due to nuclear stopping. An amorphous layer observed at room temperature is completely absent at higher temperatures. In contrast to FIB exposure at room temperature the implanted layers contain only point defects complexes and dislocations, thus suggesting that defect annealing takes place but it is incomplete. Correlating FIB sputtering experiments and high-resolution transmission electron microscopy, we discuss the lower sputtering yield at elevated target temperatures as the result of a higher surface binding energy of crystalline Si in comparison to amorphous silicon.