Direct Imprinting of Porous Silicon via Metal‐Assisted Chemical Etching

Abstract

2929wileyonlinelibrary.com drug delivery, [ 8,9 ] and biosensing [ 10,11 ] are derived from such integration. However, micro-and nanopatterning of PS has remained a challenge due to the inability of standard microfabrication processes (e.g., photolithography, wet and dry etching) to effectively pattern PS. [ 12 ] In this paper, we demonstrate a low-cost, low-stress, ambient and high-throughput chemical nanoimprint approach to patterning smooth 3D curvilinear PS surfaces in a single imprinting operation. As a demonstration of this process, sinusoidal and parabolic surfaces with potential uses as diffraction gratings and concentrators are fabricated to demonstrate potential onchip micro-optical components.Traditional approaches to patterning Si do not extend to PS because of the permeability and reactivity of the latter. During photolithography and micromachining, photoresist, developers, and etchants infi ltrate the pores, leading to contamination of the substrate, poor sidewall control and over-etching and, in general, poor fi delity of pattern transfer. [ 12,13 ] A simple route to bypass these issues is to perform lithography prior to anodization. The patterned photoresist fi lm is used as a mask during the anodization step leading to 2D embedded PS patterns with micron-scale resolution. [ 14 ] Cost-effective wet-etching processes such as KOH cannot selectively etch PS since multi ple crystal facets are exposed. Recipes for dry etching methods must be specifi cally tailored to a particular pore morphology of the PS being etched and high-aspect ratio features are seldom reported. [ 12 ] To circumvent these issues, micro-contact printing (MP), [ 15 ] dry-removal soft-lithography (DWSL), [ 16 ] and direct imprinting of PS (DIPS) [ 17,18 ] methods have been developed to pattern PS. The MP method uses a stamp that blocks diffusion of reactants during anodization of the silicon surface. As a result, it offers few degrees of freedom for 3D patterning and, thus, is limited to fabricating shallow corrugated patterns. The latter two patterning methods exploit the controlled fracturing or collapsing of the brittle porous material to selectively strip or compress PS. While DWSL is restricted to 2D patterning with microscale resolution, DIPS can generate 3D features with sub-100 nm resolution. DIPS relies on the compaction of PS leading to permanent deformation of the substrate and, thus, modifying spatially the porous morphology and the optical Conventional lithographical techniques used for bulk semiconductors produce dramatically poor results when used for micro and mesoporous materials such as porous silicon (PS). In this work, for the fi rst time, a high-throughput, single-step, direct imprinting process for PS not involving plastic deformation or high-temperature processing is reported. Based on the underlying mechanism of metal-assisted chemical etching (MACE), this process uses a pre-patterned polymer stamp coated with a noble metal catalyst to etch PS immersed in an HF-oxidizer mixture. The process not only overcome...

3D patterning of silicon by contact etching with anodically biased nanoporous gold electrodes

“…Similarly, cone-shaped pores were etched in Si with a Pt/Ir needle [10] and metal meshes (10 µm wires and 50 µm openings) on sponge-like stamps have been used, but only the largest features were transferred (50 µm pillars). Very recently, pattern transfer by contact etching in HF-H2O2 has been successfully achieved by Azeredo et al in porous Si by using macroscopic Au metallized pre-patterned stamps with a sinusoidal shape [11]. The process was shown to be capable of centimeter-scale parallel 3D patterning with sub-20 nm resolution.…”

Contact electrification induced interfacial reactions and direct electrochemical nanoimprint lithography in n-type gallium arsenate wafer

“…The second case using a MacEtch configuration was reported very recently. 34 Unfortunately, the author neglected the chemical kinetics of MacEtch and claimed that only porous silicon was applicable due to the mass balance problem. From the viewpoint of electrochemistry, we demonstrate that ECNL can be applied to crystalline semiconductors as a direct nanoimprint lithography technique.…”

Holographic Recording and Hierarchical Surface Patterning on Periodic Submicrometer Pillar Arrays of Azo Molecular Glass via Polarized Light Irradiation

“…Recently, micro/nanofabrication techniques with varying levels of complexity have emerged for fabricating large‐area patterns used in advanced optics, photonics, and flexible optoelectronics . The well‐designed structures have been fabricated by nanoimprint lithography, interference lithography, electron‐beam lithography, focused ion beam lithography and others . Soft lithography using patterned elastomers as stamps, molds, and masks have been widely used to fabricate a variety of micro/nanostructures .…”