Wet and dry etching of thin metallic multilayer structures is necessary for the development of sensitive magnetic field sensors and memory devices based on spin-valve giant magnetoresistance elements. While it is well established that Cu, Co, and Fe are soluble in HNO3 and H3PO4 at room temperature, little effort has been made to investigate selective wet and dry etch chemistries. For example, we find Ag is not etched in H2SO4, HCl, or H3PO4 under conditions where etch rates for the other metals are in the range of 2000-60 000 Angstrom/min. Electron cyclotron resonance (ECR) SF6/Ar plasmas provide etch selectivities of greater than or equal to 5:1 for Ag over Cu, Co, and Fe, while lower selectivities are obtained with CH4/H-2/Ar. Cl-2-based plasma chemistries leave significant metal-chlorine surface residues, which can be removed in situ by low ion energy H-2 or AT plasma treatments that eliminate corrosion problems. Cu etch rates in excess of 3000 Angstrom/min at 25 degrees C can be obtained in ECR Cl-2/Ar discharges because the high ion flux prevents formation of a CuClX-rich selvedge layer, which normally only is volatile for etch temperatures greater than or equal to 220 degrees C in conventional reactive ion etch systems. Photoresist masks suffer severe reticulation under ECR conditions, at least for microwave powers >400 W, and SiO2 or SiNX thin films offer much better etch resistance.