Fabrication Mechanism for Patterned Sapphire Substrates by Wet Etching

Abstract

Patterned sapphire substrate (PSS) was fabricated by wet etching solutions with different mixture ratios of H2SO4 to H3PO4 and different temperatures to investigate the fabrication mechanisms. It was found that the mixture ratio and temperature of the etching solutions affect the ratio of the pattern diameter to the pattern depth. In addition, the observed pattern shape was strongly affected by the mixture ratio. To discuss the reaction mechanisms of sapphire with H2SO4 and H3PO4 separately, we estimated the activation energies and reaction frequency factors for each reaction. By the estimated results, the behavior of the observed pattern shape for the etching conditions was well explained. To confirm the fabrication mechanism of pattern shape in the microscopic scale, the electron probe microanalysis (EPMA) inspection of the sapphire surface after H2SO4 and H3PO4 etching were carried out. As a result, it was indicated that the pattern shape is controlled by the step flow reaction with and without impurities in the etching solutions. From the observation of the pattern shape, the estimation of the activation energies and reaction frequency factors, and EPMA inspection of the reaction products for each reaction, a schematic model of the fabrication mechanisms for the wet etching of a PSS was established.

AFM and SEM Study on Crystallographic and Topographical Evolution of Wet-Etched Patterned Sapphire Substrates (PSS)

“…However, to our surprise, AFM study on crystallographic and topographical evolution of PSS was only scarcely reported. 20,30 Therefore, it is promising that complementary SEM and AFM characterizations of PSS can overcome the shortcomings of two techniques and provide more reliable and accurate dimensional/profile information.…”

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

“…23 The E a was only estimated for the diameter and depth of etched holes instead of crystallographic planes. However, this results in unrealistic low E a values-only 9.1 kJ/mol and 51.4 kJ/mol for the diameter of holes.…”

“…28,31,32 Alunogens are insoluble in H 2 SO 4 and preferentially nucleate and grow on the reaction active sites (step edges and defects) of crystallographic planes. 23 At the same time, H 3 PO 4 in M5-1 can remove insoluble alunogens to expose the underlying fresh surface, thus enabling H 2 SO 4 and H 3 PO 4 to etch the exposed step-terrace structures of crystallographic planes. It is thus reasonable to propose that, for high Miller index planes, higher density of step-terrace structures (with more reaction active sites) may favor more abundant nucleation sites and thus smaller alunogen particles, leading to faster removal of alunogens and hence higher etching rate of sapphire; lower E a for these planes can thus 21,23 we can explain the finding that E a for c-plane in M5-1 (94.5 kJ/mol) is slightly less than that in H 3 PO 4 (96.9 kJ/mol).…”

“…However, relevant reports in the literature are scarce. 23 Aota et al estimated the activation energy of etching * Electrochemical Society Member. z E-mail: ygan@hit.edu.cn reactions for the hole-shaped PSS in H 2 SO 4 and H 3 PO 4 etchants.…”

Study on the morphology and shape control of volcano-shaped patterned sapphire substrates fabricated by imprinting and wet etching

“…The reaction products from H 3 PO 4 and sapphire are soluble, while those from H 2 SO 4 and sapphire are insoluble. 4,9,10 Aota et al thought that the step flow reaction with or without the impurities might control the pattern shape of the PSS. 9 The insoluble products would block the reaction step, which led to reduction in the rate of the step flow reaction.…”