AFM and SEM Study on Crystallographic and Topographical Evolutions of Wet-Etched Patterned Sapphire Substrate (PSS): Part III. Cone-Shaped PSS Etched in H₂SO₄and H₃PO₄Mixture at Various Temperatures

Abstract

The effect of etching temperature (473-543 K) on the crystallographic and topographical evolutions as well as the etching rate of crystallographic planes of cone-shaped patterned sapphire substrate (PSS) etched in both H 2 SO 4 -based (H 2 SO 4 :H 3 PO 4 = 5:1 at volume ratio) and H 3 PO 4 etchants was systematically studied. For H 2 SO 4 -based etchant, higher temperature favors larger etching rate ratio of slant planes (S 1 {11 0 5}, S 3 {45 1 38}, S 4 {11 0 12}, and S 5 {1 1 0 37} planes) to c-plane, thus leading to smaller filling factor (FF) of patterns; the Arrhenius activation energy (E a ) of etching reactions for various crystallographic planes follows the order: E a (c) < E a (S 1 ) < E a (S 3 ) < E a (S 4 ). For H 3 PO 4 , higher temperature favors smaller etching rate ratio of slant planes (S 1 {11 0 5} and S 6 {11 0 8} planes) to c-plane and larger FF of patterns; the E a follows the order: E a (S 1 ) < E a (S 6 ) < E a (c). This work will contribute to elucidating the etching mechanism and fabricating optimized PSS for enhanced performance of light emitting diodes.

Continuum level-set model for anisotropic wet etching of patterned sapphire substrates

“…The etching process is controlled by the kinetics of the reaction, resulting in significant temperature dependence of the etch rates [31][32][33]. In the particular case of sapphire etched with mixtures of H 2 SO 4 and H 3 PO 4 , Shen et al have reported high activation energies (87.0-108.3 kJ mol −1 ), supporting the reactionlimited characteristics of the etching [28]. Thus, the impact of reactant diffusion can be neglected and the etching reaction can be characterized with the orientation dependence of the etch rate [7], i.e.…”

“…Whereas the wet etching of Si is well studied, the etch rate anisotropy of single-crystal sapphire is still being investigated. Several studies measured the etch profile evolution and characterized the crystal facets observed in the experiment [11,14,[25][26][27][28]. In these studies, only a small number of etch rate/crystal direction pairs have been identified, due to the limited number of distinct crystal facets emerging during the etching process.…”

“…In section 2, we present a general interpolation methodology which enables practical modeling of highly anisotropic processes with trigonal symmetry by a level-set method. In section 3, we give a short overview of a comprehensive series of experiments conducted by Shen et al [26][27][28] which lay the groundwork for validating our model. In particular, we show that insights into the etch rate anisotropy can be deduced from geometrical considerations, even if a full characterization of the etchant is not available.…”

Suppressing the Initial Growth of Sidewall GaN by Modifying Micron-Sized Patterned Sapphire Substrate with H3PO4-Based Etchant

“…As shown in Figure 1, two kinds of PSS samples were used to investigate the effect of modification of micron-sized PSS patterns on the GaN growth mechanism: (1) RPSS (regular PSS without etching) and (2) PSSE (RPSS etched in sulfuric–phosphoric acid (ratio 3:1) at 270 °C for 30 s). As shown in Figure 1b, 3T {11¯05} facets were observed on the pattern of PSSE [19,20,21,22,23].…”

Analysis of Etch Profiles on C-Plane Wafers in Wet Etching of Sapphire Based on Undercutting Rate Distributions in Mixture of H2SO4 and H3PO4 at 236 °C

“…[9][10][11] According to the analysis of previous wet etching experiments of sapphire, a mixed solution of concentrated sulfuric acid and concentrated phosphoric acid is usually as the etchant, [12][13][14] and the etching temperature is usually in the range of 200 °C-300 °C. [15][16][17][18] Considering the operability and safety of wet etching experiments of sapphire, the etching temperature was set to 250 °C at first. However, it was found that the temperature of the solution was balanced at 236 °C.…”