Cavity Etching Behavior on the M‐Plane of Sapphire Crystal

Abstract

Wet etching has been a fundamental process for the fabrication of sapphire crystal substrates with critical position in the current semiconductor devices industry. The present work reveals the etching behaviors of cavities on the M‐plane {11¯${{\bar 1}}$00} of sapphire crystal by the hot KOH etchant. It is shown that the boundary of cavities changes from smooth circle to octagon‐like and the edges evolve sharper as the etching temperature increases. Carefully analyzing the structure of the etched cavities suggests they are partially framed by low index planes (2true1¯true1¯${{\bar 1\bar 1}}$0) (1¯${{\bar 1}}$21¯${{\bar 1}}$0), (101¯${{\bar 1}}$0), (011¯${{\bar 1}}$0), and (112¯${{\bar 2}}$0).

Fabrication of microstructures in the bulk and on the surface of sapphire by anisotropic selective wet etching of laser-affected volumes

“…When in contact with an acid, in fact, crystalline material undergoes a phenomenon called decrystallization in which the crystalline structure is broken down and this phenomenon typically starts from the discontinuities of the exposed surfaces [51]. In case of anisotropic etching of crystalline sapphire, differences in the etching rates of (main) crystal planes appear to be related to the atomic arrangement [52]. The anisotropic etchant used in this study, a mixture of sulphuric and phosphoric acid, is selected for its known property of etching sapphire anisotropically [53], by means of which crystallographically determined structures can be created on/in sapphire.…”