Formation of Bare Porous Surface on 6H-SiC Substrates by Photo-Electrochemical Etching

Abstract

A new method for obtaining a bare porous surface is proposed. Photo-electrochemical etching for forming a porous layer generally results a skin layer on it. The in-situ observation of the etching process revealed that the skin layer can be peeled off by introducing a dark period at the end of the porous formation process. The dark condition switched over the etching mode to an electro-polishing mode, and generated gas bubbles at the region just below the skin layer. The peeling of the skin layer is the result of lift-up by the increase of pressure in the confined bubbles.

Morphological Study on Porous Silicon Carbide Membrane Fabricated by Double-Step Electrochemical Etching

“…Taking into account the above experimental results, we discuss the self-fabrication mechanism of the porous membrane. As reported in former research papers, 13,15,18) we also observed small pores using the SEM on the surface layer along shallow grooves that were created during mechanical mirror polishing. The trigger of pore formation can be current crowding because of its lower resistivity due to a thinner oxide layer.…”

“…Finally, the UV-irradiation effect on the peeling-off process is discussed. In our former work, 13) peeling-off of the membrane was observed when the UV-irradiation was interrupted. This phenomenon can be explained by a similar mechanism to that in the double-step electrochemical etching process without UV-irradiation.…”

“…Owing to the technological interest in light-emitting and gassensor applications, formation processes of porous SiC by electrochemical etching have also been studied. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] The porous structures of SiC are covered with a nonporous surface layer that hinders the porous effect in practical applications. This surface layer was observed under various experimental conditions, such as certain compositions of electrolyte solution, 7) in an etching system equipped with an electrolyte circulator, 8) and in experiments with 11) and without UV irradiation.…”

“…We found that the surface layer can be removed by turning UV irradiation off during the photochemical etching process for both carbon and silicon faces of a SiC(0001) wafer. 13) On the other hand, the use of the removed porous membrane formed under the surface nonporous layer in biomedical applications has been reported. 14) For such applications, detailed structural analysis of the peeled-off membrane and an understanding of the mechanism behind the peeling-off process are important.…”

“…Therefore, studies to remove the surface nonporous layer have been performed. 8,10,12,13) The intentional removal method by changing the current was first reported by Kim et al for SiC. 12) Two other methods are also reported: the adoption of an additional vacuum process in reactive-ion etching, 8) and hydrogen etching at a high temperature.…”