Effective approaches to improve Au etching process performance in MEMS devices
A method to improve pattern critical dimension (CD) and reduce the metal residue level during gold (Au) and chrome (Cr) wet etch processes in MEMS devices is investigated. Instead of traditional single-step wet etch process, a multi-step wet etch method is used to etch Au with the etchant formulated by potassium iodide, iodine and deionized water (KI/I2/H2O). Compared with the single step wet etching process, the Au CD uniformity has been significantly improved from 10 um to 3.5 um in the experiment. Furthermore the Au undercut uniformity has been improved to 2 um which meets the requirements of mass production. Different etchant concentrations are also investigated to study the correlation between etch rate and potassium iodide concentration, and the efficiency of metal residue removal. In the chemical conditions of I2: KI: H2O=4:15:81, it is found that higher KI concentration brings AuI faster dissolution rate and metal residues are completely removed.