Differential etching of ion-implanted garnet

Abstract

A new technique for generating precise surface structures in single-crystal garnet materials is described. The crystals are ion implanted in localized areas using photoresist as an implantation mask. The photoresist is removed and the crystals are etched in phosphoric acid. The damaged volumes produced by the ion implantation etch at a substantially greater rate than the undamaged material, thereby producing surface structures. Groove depth can be precisely defined and reproduced by controlling the implantation parameters: ion species, energy, and dose. Undercutting is minimal and etching conditions are not stringent. The method is superior to both standard chemical etching and ion milling. The process has been characterized for H, He, and Ne implantations. It is shown that the temperature dependence of the etching rates for damaged and undamaged material is the same. The increase in etching rate is proportional to the damage concentration. The etching rate profiles are therefore synonymous with the damage profiles produced by the implantation. Etching rates more than three orders of magnitude greater than that of undamaged material have been observed. The etching rates for the three elements used correlate fairly well with the theoretical nuclear stopping power, and the groove depths obtained correlate with the theoretical ion ranges. This method has been used to produce serrated edge grooves which serve as rails for magnetic bubble propagation in conductor-groove bubble propagation circuits.