Abstract

Laser-induced photoelectrochemical (PEC) etching of semiconductor compounds offers the possibility for a in maskless, simple, surface-patterning process.¹ The thin reaction cell configuration offers some advantages over bulk cells, among which are its ease of use and the potential for a true three-dimensional (holographic) etching process. In this configuration an electrolyte layer of about 50 µm is held by capillary action between a semiconductor wafer and a microscope cover glass. The cover glass face, in contact with the electrolyte, may be coated with a transparent conductor (such as indium tin oxide) to form one of the biasing electrodes. We have suggested before^2–3 that a. nonlinear diffusion process governs the PEC reaction; oxide is built and then dissolves during the reaction. Here, we assess multiple, etched gratings using light beams from two lasers at different wavelengths; a HeCd laser at λ = 0.442 μm and a HeNe laser at λ − 0.63 μm. The difference in the reaction rate at these wavelengths may result in pattern modulation. Under external biasing conditions, we have found that although the etch rate is more or less constant in time for a single wavelength, the two etching wavelengths are coupled in a nonlinear etching relationship. The etched pattern was assessed with the help of a third laser, which was diffracted from the pattern, and by measuring the intensity of the higher orders of diffraction. The effect of the biasing on the multiple-wavelength etching process was investigated too. Under biasing, the pattern amplitude was first developed linearly with time and then reduced gradually to zero. We suggest that under nonequilibrium conditions, etching was also taking place in unilluminated areas.

© 1991 Optical Society of America