Maximizing helium-neon laser optical absorption with micromachined single-crystal silicon wafer surfaces coated with antireflective thin films

The optical absorptivity (helium-neon laser illumination, lambda =632.8 nm) of [100]- and [110]-oriented single-crystal silicon wafers was enhanced by synergistically combining etching, isotropic etching, and antireflection coatings (silicon nitride, tantalum pentoxide, titanium dioxide, and zirconium dioxide) with four distinct micromachined structures (V-shaped grooves, deep vertical-wall grooves, inverted pyramids, and randomly spaced and sized pyramids). The uncoated, deep vertical-wall groove structure and the titanium-dioxide-coated randomly spaced and sized pyramids yielded the most significant reduction in the bidirectional reflectance distribution function's peak and average values when compared to the performance of an unprocessed silicon wafer control sample.<>