Langasite (La3Ga5SiO14) wet-etching experiments and simulations

This paper reports characterization and simulation of wet etching of grooves on Langasite (La₃Ga₅SiO₁₄) wafers using phosphoric acid (H₃PO₄) and polymer mask layers. Wafers with orientation (0°,138.5°,26.7°), which are commonly used for SAW(Surface Acoustic Waves) devices, were investigated. 85% H₃PO₄ was chosen as the etchant and photoresist AZ nLOF 2070 was decided as the mask material. The experiments show that the groove profiles are governed by the anisotropic etch properties of the material in this etchant (H₃PO₄) as well as an anomalous etch along the LGS-mask interface that leads to large undercuts. Wet etching at different temperatures, groove orientations and groove widths were explored. For the (0°,138.5°,0°) plane, the etch rate vs. etch temperature fits well to the Arrhenius equation with an activation energy of 0.84 eV. A simulator was programmed in MATLAB. The simulation shows good agreement with experiments and confirms that the etching is well described by the anisotropic etch properties of the exposed surfaces and a constant interface etch rate.