The Anisotropic Mechanism And Topography Research Of Wet Etching Of Single-Crystal Sapphire

Single-crystal sapphire has been widely used in the fabrication of LED light-emitting devices and microelectromechanical systems?MEMS?,and its wet etching process can efficiently reduce the development cycle of specific microstructures and save experimental costs.As a typical trigonal material,sapphire possesses complex atomic species and crystal structure.It is necessary to clarify the anisotropic etching characteristics and surface topography of single-crystal sapphire in concentrated sulfuric acid and phosphoric acid mixed solutions.The main research contents are as follows:Firstly,to establish etching process database of single-crystal sapphire,a large number of etching experiments are carried out on single-crystal sapphire hemispheres with different etching conditions?etching temperatures:236?,223?and 202?;etching solutions:H₂SO₄:H₃PO₄=1:1?3:1 and 6:1?.Then the characteristics of anisotropic etch rate are analyzed as well in detail,including the division of high and low etch rate zone,the position distribution of the maximum and minimum values,and the symmetry characteristics of the etch rate with respect to the crystal structure.Secondly,the structural sidewall planes appearing on etched structures on c-plane sapphire wafers are investigated by using various masks,such as rectangular grooves,mesas,trenches and micro-array.Furthermore,the rectangular grooves with different angles are calculated by using the simplified Wulff-Jaccodine?WJ?method.The steady and transient structural planes in the sidewall are marked at corresponding positions on the full etch rate ball.Then continues by discussing the cross-sectional etch rate of the two typical directions of<11-20>and<1-100>that can be extracted from the experimental hemisphere data in order to describe the formation of the structural planes on both concave and convex structures,i.e.grooves and mesas,respectively.Thirdly,the activation energy and reaction frequency factor of the main crystal structure planes are calculated by the full etch rate under different etching temperatures,which explains the root cause of the anisotropic etch rate during the wet etching of single-crystal sapphire;In order to investigate the effect of etching solution concentration on the full etch rate,the rectangular groove inclinations are calculated under different concentration conditions by using the simplified WJ method.The variation regular pattern of the inclination angle of the sidewall with respect to the rotate angle of the rectangular grooves,which can extremely shorten the design period of the patterned sapphire substrate.Finally,the section focuses on researching the relationship between the microscopic atomic arrangement of single-crystal sapphire and macroscopic etching anisotropic,dividing the step-flow of two main cut planes{1-10h}and{11-2k}that based on the highly stable planes a?11-23?and m?1-100?.According to the characteristics of chemical bonds between aluminum atoms and oxygen atoms,classifying several main structural planes by the type of atomic groups,and demonstrating the mechanism and effect of different types of atoms in the etching process.Eventually,the section continues by discussing the surface micro-morphology that can be observed from the experimental hemispheres with different etching conditions in order to discriminate the formation of triangular pyramid hills on c-plane of sapphire at the atomic level.