A hand-held smart wet etch monitor: Design, theory, and test

The theory, design, and tests are presented for a handheld unit that accurately monitors (and controls) the etch depth, rate, and surface roughness during wet etching; The unit features a noncontact optical probe using a low-power pulsed laser that circumvents light-induced etching. The etch monitor incorporates a 16-bit analog-to-digital converter with sample and hold, parallel "single chip" processors, liquid crystal display and keypad, Personal Computer Memory Card International Association-based data storage, battery charger, an RS-232 COM port, and a parallel programming port. Tests performed on GaAs heterostructure etched in the phosphoric acid system indicate etch depth control better than 250 angstrom. The results include composition profiles and etch rates for reaction and diffusion rate limited etches.