Anisotropy and Mechanism of Wet Etching of Sapphire Crystal

Abstract

Abstract: Due to the fact that the current mechanism of anisotropic wet etching of sapphire has not been fully revealed, it is difficult to accurately predict and control the evolution process and morphology of its etching microstructure, which brings great challenges to the processing and quality control of patterned structures on sapphire substrates. In this paper, based on the experimental data of sapphire crystal plane etching rates, the etching process and etching mechanism of its microstructure were analyzed in detail, and the influence of the change of etching conditions on the sapphire etching microstructure and surface morphology was compared and analyzed. The experimental results show that: the etching efficiency can be improved by appropriately increasing the etching temperature, but the surface quality will be reduced; weak electrolytes represented by phosphoric acid can be used as etching buffers to improve the quality of etched structural surfaces; the (275±10) ℃, 98%H₂SO₄∶85%H₃PO₄ (volume ratio)=3∶1 is the optimal etching solution, which can obtain the best etching rate and surface quality.

Key words: sapphire, wet etching, anisotropic, etching condition, etching mechanism, surface morphology

CLC Number:

O732

ZHANG Hui, QIAN Jun, HONG Lili. Anisotropy and Mechanism of Wet Etching of Sapphire Crystal[J]. Journal of Synthetic Crystals, 2023, 52(6): 1128-1135.

References

[1] ZHANG H, XING Y, GOSÁLVEZ M A, et al. Removal probability function for kinetic Monte Carlo simulations of anisotropic etching of silicon in alkaline etchants containing additives[J]. Sensors and Actuators A: Physical, 2015, 233: 451-459.
[2] XING Y, GOSÁLVEZ M, SATO K, et al. Evolutionary determination of kinetic Monte Carlo rates for the simulation of evolving surfaces in anisotropic etching of silicon[J]. J Micromech Microeng, 2012, 22: 085020.
[3] GOSÁLVEZ M A, CHENG D, NIEMINEN R M, et al. Apparent activation energy during surface evolution by step formation and flow[J]. New Journal of Physics, 2006, 8(11): 269.
[4] WANG J, GUO L W, JIA H, et al. Fabrication of patterned sapphire substrate by wet chemical etching for maskless lateral overgrowth of GaN[J]. Journal of The Electrochemical Society, 2006, 153(3): C182-C185, 2006
[5] GROSSE A, GREWE M, FOUCKHARDT H. Deep wet etching of fused silica glass for hollow capillary optical leaky waveguides in microfluidic devices[J]. Journal of Micromechanics and Microengineering, 2001, 11(3): 257-262.
[6] CHEN Y C, LIN B W, HSU W C, et al. The formation of smooth facets on wet-etched patterned sapphire substrate[J]. ECS Journal of Solid State Science and Technology, 2014, 3: R5-R8.
[7] GAO Z D, WANG Q J, ZHANG Y, et al. Etching study of poled lithium tantalate crystal using wet etching technique with ultrasonic assistance[J]. Optical Materials, 2008, 30(6): 847-850.
[8] LIN Y C, ONO T, ESASHI M. Fabrication and characterization of micromachined quartz-crystal cantilever for force sensing[J]. J Micromech Microeng, 2005, 15: 2426.
[9] GOSÁLVEZ M, FERRANDO N, XING Y, et al. Simulating anisotropic etching of silicon in any etchant: evolutionary algorithm for the calibration of the continuous cellular automaton[J]. Journal of Micromechanics and Microengineering, 2011, 21: 065017.
[10] FERRANDO N, GOSÁLVEZ M A, COLÓM R J. Evolutionary continuous cellular automaton for the simulation of wet etching of quartz[J]. Journal of Micromechanics and Microengineering, 2012, 22(2): 025021.
[11] CHENG D, SATO K, SHIKIDA M, et al. Development of quartz etching database and 3-D micromachining simulation system[C]//MHS2003. Proceedings of 2003 International Symposium on Micromechatronics and Human Science (IEEE Cat. No.03TH8717). October 19-22, 2003, Nagoya, Japan. IEEE, 2003: 281-285.
[12] DWIKUSUMA F, SAULYS D, KUECH T F. Study on sapphire surface preparation for III-nitride heteroepitaxial growth by chemical treatments[J]. Journal of the Electrochemical Society, 2002, 149(11): G603.
[13] 幸研, 张辉, 李源. 用于半球试件湿法刻蚀各向异性速率测试的可调整式夹具: CN104924234B[P]. 2016-11-23.
XING Y, ZHANG H, LI Y. An adjustable fixture for testing the anisotropy rate of wet etching of hemispherical specimens: CN104924234B[P]. 2016-11-23.
[14] 蔡鹏鹏. 石英各向异性湿法刻蚀特性及模拟研究[D]. 南京: 东南大学, 2016.
CAI P P. Characteristics and simulation of anisotropic wet etching in Shi Ying[D]. Nanjing: Southeast University, 2016 (in Chinese).
[15] 幸研, 朱鹏, 倪中华, 等. 多次掩模湿法腐蚀硅微加工过程的蒙特卡罗仿真[J]. 机械工程学报, 2009, 45(1): 239-243.
XING Y, ZHU P, NI Z H, et al. Monte Carlo simulation of multiple masking processes for anisotropic wet etching[J]. Chinese Journal of Mechanical Engineering, 2009, 45(1): 239-243 (in Chinese).
[16] 郭志越.单晶蓝宝石湿法刻蚀机理及表面形貌研究[D].南京:东南大学,1998.
GUO Z Y. The anisotropic mechanism and topography research of wet etching of single-crystal sapphire[D]. Nanjing: Southeast University, 1998 (in Chinese).
[17] 王树桥, 幸研, 田秘, 等. 混合进化算法的Metropolis蒙特卡罗MEMS单晶硅湿法刻蚀工艺模型[J]. 机械工程学报, 2013, 49(5): 167-172.
WANG S Q, XING Y, TIAN M, et al. Hybrid evolutionary-metropolis Monte Carlo algorithm for wet etching of silicon MEMS fabrication process[J]. Journal of Mechanical Engineering, 2013, 49(5): 167-172 (in Chinese).
[18] ZHANG H, XING Y, ZHANG J, et al. Evolutionary kinetic Monte Carlo method for the simulation of anisotropic etching of Z-cut, at-cut and BT-cut quartz[C]//2017 19th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS). June 18-22, 2017, Kaohsiung, Taiwan, China. IEEE, 2017: 1308-1311.
[19] TANG B, SHIKIDA M, SATO K, et al. Study of surfactant-added TMAH for applications in DRIE and wet etching-based micromachining[J]. J Micromech Microeng, 2010, 20: 065008.