Chemical Etching of Silicon Assisted by Graphene Oxide in an HF–HNO₃ Solution and Its Catalytic Mechanism

Abstract

Chemical etching of silicon assisted by various types of carbon materials is drawing much attention for the fabrication of silicon micro/nanostructures. We developed a method of chemical etching of silicon that utilizes graphene oxide (GO) sheets to promote the etching reaction in a hydrofluoric acid–nitric acid (HF–HNO3) etchant. By using an optimized composition of the HF–HNO3 etchant, the etching rate under the GO sheets was 100 times faster than that of our HF–H2O2 system used in a previous report. Kinetic analyses showed that the activation energy of the etching reaction was almost the same at both the bare silicon and GO-covered areas. We propose that adsorption sites for the reactant in the GO sheets enhance the reaction frequency, leading to a deeper etching in the GO areas than the bare areas. Furthermore, GO sheets with more defects were found to have higher catalytic activities. This suggests that defects in the GO sheets function as adsorption sites for the reactant, thereby enhancing the etching rate under the sheets.

Vapor-Phase Chemical Etching of Silicon Assisted by Graphene Oxide for Microfabrication and Microcontact Printing

“…After oxygen moieties on GO sheets were removed at the beginning of the etching process, the chemical condition of GO sheets was not changed. This behavior was consistent with our previous findings 22,23 and indicated that a strong oxidant, H 2 O 2 or HNO 3 , in the vapor etchant did not oxidize GO sheets but was consumed in the etching reaction.…”

“…48 We also discussed the relationship between GO structures and the etching rate and proved that defects on GO contributed to its catalytic property in liquid-phase etching. 23 The surface chemical condition of silicon after vapor-phase etching depended on the composition of the etching solution prepared; however, GO-covered areas were etched faster than noncovered areas under all conditions in our experiments. With a high oxidant concentration etchant, a silicon oxide layer formed on the silicon surface.…”

“…Inherent edges, defects, and heteroatoms (such as nitrogen and sulfur) on GO sheets function as active sites because these parts alter the local density of π-electrons . We also discussed the relationship between GO structures and the etching rate and proved that defects on GO contributed to its catalytic property in liquid-phase etching …”

“…Various types of carbon materials, including graphite particles, , carbon nanotubes, and graphene, have been shown to enhance the etching reaction with optimized etching solutions. We also suggested the application of graphene oxide (GO) to the assisted etching of silicon because it has the potential to catalyze the oxidant reduction reaction. , GO is a two-dimensional (2D) carbon material that contains oxygen functional groups due to the oxidative production process of graphite. These oxygen functional groups enable GO to disperse in water or some organic solvents without aggregation, and thus, GO has been deposited on some types of substrates using a facile solution process.…”

“…We also reported that GO promoted the etching reaction in a mixture of HF-H 2 O 2 and HF–HNO 3. Although a more detailed understanding of the reaction mechanism of silicon etching assisted by carbon materials has been obtained and the reaction may be controlled, a number of difficulties remain. One issue is the peeling of GO sheets by the gases or bubbles produced during the etching process, such as hydrogen and nitrogen dioxide .…”