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, λ=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