High density plasma etching of aluminum alloys

High density plasma etching of aluminum alloys was performed at RF frequencies and low pressure in a modified parallel-plate reactor. Very high density plasmas (10¹⁰ to 10¹¹ ions/cm³ ) were measured with fast injection Langmuir probes. Ion energy perpendicular to the wafer surface can be controlled from a separate bottom-powered electrode. A mixture of Cl₂ and BCl₃ was used for the study. Response Surface Methodology (RSM) was used to understand the trends of the aluminum etch performance versus process parameters. Experimental matrices were designed and run to understand etch results such as aluminum etch rate, feature profile, and residue removal as functions of independent variables such as source-coil power, bias power, and gas flow ratio. Aluminum etch rates of one micron per minute can be achieved at 5 to 10 mTorr pressure. Anisotropic etching photoresist selectivity greater than 2.5:1 and silicon dioxide selectivity greater than 10:1 are achieved by controlling wafer DC-bias separately from plasma density. The hardware used is very simple and the chamber size is small