Focused ion beam micromachining (FIBM) of integrated circuits continues to be an important tool for design debug, editing, and verification; for metrology; and for process control. FIBM of copper interconnects has presented challenges not faced when micromachining aluminum interconnects and the introduction of low-k dielectrics present additional challenges. A new approach to chemically assisted FIBM of thin film Cu, SiO2, and SILK low-k material using polar precursor molecules has been investigated. Polar alcohols were used to reduce the sputter rate of SiO2 and SILK while having a minimal effect on the Cu sputter rate. A new FIBM process based on the reduction of the FIB Ga+ energy from the typical 25 to 15 keV is also introduced. The new low energy FIBM process was shown to increase the sputter rate of polycrystalline Cu with strong (111) crystallographic texture by a factor of 2.5. This increase in the sputter rate of Cu combined with a slight reduction of the sputter rate of SiO2 and SILK results in a Cu/SiO2 selectivity of greater than 7 and a Cu/SiLK selectivity of approximately 3. These are the largest selectivity values reported until now for both systems. The Onderdelinden theory of single-crystal sputtering was used to explain this seemingly anomalous increase of the Cu sputter rate with the reduction of the FIB Ga+ energy.