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
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. The results include composition profiles and etch rates for reaction and diffusion rate limited etches.