Effect of Hydrophobicity and Surface Potential of Silicon on SiO₂ Etching in Nanometer-Sized Narrow Spaces

Abstract

Wet etching in nanometer-sized three-dimensional spaces creates new challengesbecause of the scaling of semiconductor devices with complex 3D architecture. Wet etching withinspaces is affected by the mass transport of the etchant ions that are impacted by the hydrophobicityand surface potential of surface. However, the kinetics of chemical reactions within the spaces is stillunclear.In this paper, we studied the effect of hydrophobicity and surface potential of silicon surface on SiO2etching in nanometer-sized narrow spaces by adding various additive components to etching solutions.We found that the transport of etchant ions into narrow spaces is governed by controlling thehydrophobicity and surface potential of the confined system walls.

Wet Etching of Silicon in Planar Nanochannels

“…Clearly, all results reveal linear relations between the etching length and the etching time, suggesting constant etching rates for wet Si etching in 2-D nanochannels. These findings align with previous observations in wet etching of TiN and SiO 2 -filled nanochannels 9,11 but are different from wet etching of Cr-filled nanochannels, 13 indicating that the wet KOH-Si etching reaction in the nanoconfinement is not limited by reactant/product diffusion but by the reaction kinetics.…”

“…Therefore, their corresponding etching reaction kinetics and specificity may vary from those of bulk/plain surfaces or microscale confinements, and the transport of reactants and products of the etching reaction may also affect the reaction. As a result, nonuniform etching rate and different selectivities have been observed when features with different nanoconfinements are present on the same wafer, which cause serious challenges for etching control and thus significantly affect the fabrication yield and quality. , To properly address this challenge, efforts have been made on investigating wet etching reactions in nanoconfinements (WERIN) filled with a variety of materials and several factors that could affect the etching reaction have been proposed. − Specifically, Okuyama et al studied diluted hydrofluoric acid (dHF) etching of SiO 2 -filled 2-D planar nanochannels and discovered that the etching length is a linear function of the etching time, suggesting a kinetics-limited reaction . They found that the resulting constant etching rate decreases with decreasing channel height and hypothesized that it is a result of reactant concentration changes due to electrostatic interactions.…”

“…They found that the resulting constant etching rate decreases with decreasing channel height and hypothesized that it is a result of reactant concentration changes due to electrostatic interactions. Following their study, Vereecke et al and Ueda et al investigated wet etching of TiN-filled and SiO 2 -filled 1-D/2-D nanoconfinements, respectively. , While they also observed time-independent etching rates and nanoconfinement-caused etching suppression, they pointed out that the electrostatic effect is not the only explanation, and other factors such as water structuring inside the nanoconfinement and hydrophobicity of the confinement surface can also play important roles in the change of the etching kinetics. Different from these studies, Kumar et al explored wet etching of chromium (Cr)-filled, graphene-coated 2-D nanochannels and found that the etching length actually showed a diffusion-limited, square root of time dependence .…”

Abnormal Silicon Etching Behaviors in Nanometer-Sized Channels

“…First, the electrical double layer (EDL) formed within the capillary reduces the effective width for ionic diffusion. 16 Second, gas bubble entrapment and poor wetting of the solution prohibit solution infiltration. 17 Third, limited diffusion causes the insoluble intermediate precipitation and congestion at the trench, 18−20 yet none of the hypotheses have been proven with direct evidence.…”

“…The potential causes of this unstripping phenomenon have been reported previously, and many hypotheses have been postulated. First, the electrical double layer (EDL) formed within the capillary reduces the effective width for ionic diffusion . Second, gas bubble entrapment and poor wetting of the solution prohibit solution infiltration .…”