PATTERNING OF CU, CO, FE, AND AG FOR MAGNETIC NANOSTRUCTURES

Wet and dry etching of thin metallic multilayer structures is necessar y for the development of sensitive magnetic field sensors and memory d evices 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 select ive wet and dry etch chemistries. For example, we find Ag is not etche d in H2SO4, HCl, or H3PO4 under conditions where etch rates for the ot her metals are in the range of 2000-60 000 Angstrom/min. Electron cycl otron resonance (ECR) SF6/Ar plasmas provide etch selectivities of gre ater than or equal to 5:1 for Ag over Cu, Co, and Fe, while lower sele ctivities are obtained with CH4/H-2/Ar. Cl-2-based plasma chemistries leave significant metal-chlorine surface residues, which can be remove d 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 2 5 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 nor mally only is volatile for etch temperatures greater than or equal to 220 degrees C in conventional reactive ion etch systems. Photoresist m asks suffer severe reticulation under ECR conditions, at least for mic rowave powers >400 W, and SiO2 or SiNX thin films offer much better et ch resistance. (C) 1997 American Vacuum Society.