Abstract
This work describes the fabrication of anisotropically etched, faceted pyramidal structures in amorphous layers of silicon dioxide or glass. Anisotropic and crystal-oriented etching of silicon is well known. Anisotropic etching behavior in completely amorphous layers of silicon dioxide in combination with purely isotropic hydrofluoric acid as etchant is an unexpected phenomenon. The work presents practical exploitations of this new process for self-perfecting pyramidal structures. It can be used for textured silica or glass surfaces. The reason for the observed anisotropy, leading to enhanced lateral etch rates, is the presence of thin metal layers. The lateral etch rate under the metal significantly exceeds the vertical etch rate of the non-metallized area by a factor of about 6-43 for liquid and 59 for vapor-based processes. The ratio between lateral and vertical etch rate, thus the sidewall inclination, can be controlled by etchant concentration and selected metal. The described process allows for direct fabrication of shallow angle pyramids, which for example can enhance the coupling efficiency of light emitting diodes or solar cells, can be exploited for producing dedicated silicon dioxide atomic force microscopy tips with a radius in the 50nm range, or can potentially be used for surface plasmonics.
Highlights
This work describes the fabrication of anisotropically etched, faceted pyramidal the fabrication of inverted silicon pyramids for various applications, e.g., for structures in amorphous layers of silicon dioxide or glass
Fast etching of sacrificial Ti layers was utilized to tune sidewall angles in silicon dioxide—a first report on interfacial etching as root cause for similar
The higher substrate temperature in our work reduced the etching rate due to slower hydrofluoric acid (HF) condensation as well as faster water desorption reaction compared to literature.[4,26,33]
Summary
This work describes the fabrication of anisotropically etched, faceted pyramidal the fabrication of inverted silicon pyramids for various applications, e.g., for structures in amorphous layers of silicon dioxide or glass. Our work on silica surfaces has potential for the observed anisotropy, leading to enhanced lateral etch rates, is the presence of thin metal layers. An isotropic silicon etch with about 5% HF used for a 5 nm Ti/50 nm Au stack on Si did not show any enhanced lateral under etch despite the presence of HF and Ti. Similar etch profiles were obtained for fused silica and borofloat wafers (Figure S9, Supporting Information).
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