Transformer-coupled plasma (TCP) technology has been applied to the etching of aluminum alloys. High density plasmas can be obtained at low pressures (approximately 10 mTorr) by inductive coupling of externally applied radio frequency (rf) power at the frequency of 13.56 MHz. The energy of the ions incident to the substrate is controlled by a separate capacitively coupled rf power supply. Cl2 and BCl3 gas chemistries were used for the etching. The characteristics of the plasma have been studied with a Langmuir probe and the "complex conjugate method." The ion current density is mainly dependent on the rf power to the coil and gas pressure. The energy of ions bombarding the substrate surface can be controlled by changing the rf power to the bottom electrode and the coil. A statistical experimental method and optical emission spectroscopy were used to study the etching of the aluminum alloys with a TCP source. The results indicate that etching of aluminum alloys is dominated by chemical interaction with Cl2 gas whereas photoresist is etched by the bombardment of energetic ions.