Through-wafer via fabrication in gallium arsenide by excimer laser projection patterned etching

Through-wafer vias, in high density, can be fabricated in GaAs by excimer laser projection patterned etching in a chlorine atmosphere. The via, if circular of diameter (B), decreases in diameter (A) with depth (W), according to the relation A≊B−0.65W. This corresponds to a sidewall slope of ∼18°. Etch rates up to 3 μm/min using a 20 Hz laser (248 nm) have been obtained, with good sidewall quality; the technique would appear to be suitable as a manufacturing method.