电化学刻蚀参数对高阻厚壁宏孔硅阵列表面形貌的影响

Effect of Electrochemical Etching Parameters on Surface Morphology of Thick-walled Macroporous Silicon Array

采用光电化学刻蚀方法,在电阻率为4～5 kΩ·cm的n-型[100]单晶硅片上制备了厚壁有序宏孔硅阵列。通过对比有限元法模拟诱导坑周围的电场分布,研究了刻蚀参数(电解液、光照、电压)对阵列表面形貌的影响。在刻蚀成孔的过程中,诱导坑对孔的限制受电场分布和实验条件的共同影响,出现刻蚀偏离的现象。模拟结果显示,诱导坑上的电场强度沿着单晶硅的[100]和[110]晶向的分布。这种分布的结果是,随着光照强度的提高和刻蚀溶液表面自由能的降低刻蚀由原光刻图形的(110)面向(100)面偏离。提高刻蚀电压可抑制刻蚀偏离,有利于诱导坑快速刻蚀成孔,从而形成规整的厚壁宏孔硅阵列。

Thick-walled macroporous silicon arrays(MSA)were fabricated on n-type monocrystalline silicon wafer with resistivity 4~5 kΩ·cm by photo-electrochemical etching in HF solutions.The surface and cross-sectional morphologies of the MSA were assessed by scanning electron microscope.The electric field distribution around the prefabricated pits were simulated by finite element method.By comparing with the simulation,the evolution of surface morphology of the prepared MSA was studied with the changing process parameters such as electrolyte,illumination,and applied voltage.During the etching process,deviations are found for the macropores despite of that there existed a restriction resulted from the prefabricated pits.This is due to the comprehensive effect of electric field distribution and etching parameters.The simulation results show that the electric field distribution on the prefabricated pits is featured by shapes along silicon orientation[100]and[110]at different values.Due to the existence of the above favorable influence factor,the etching face may tend to change from(110)to(100),in case that the illumination increases,while the surface free energy of the etching electrolyte decreases,which may be resulted from the stimulation of additives ethanol and hexadecyl trimethyl ammonium chloride(CTAC).Therefore,the increase of the applied voltage can restrain the etching deviation,which is conducive to rapidly transform the prefabricated pits into pores,hence,to promote the formation of thick-walled macroporous silicon array.