Cryogenic Etching of Silicon: An Alternative Method for Fabrication of Vertical Microcantilever Master Molds

Abstract

This paper examines the use of deep reactive ion etching (DRIE) of silicon with fluorine high-density plasmas at cryogenic temperatures to produce silicon master molds for vertical microcantilever arrays used for controlling substrate stiffness for culturing living cells. The resultant profiles achieved depend on the rate of deposition and etching of a SiOxFy polymer, which serves as a passivation layer on the sidewalls of the etched structures in relation to areas that have not been passivated with the polymer. We look at how optimal tuning of two parameters, the O2 flow rate and the capacitively coupled plasma (CCP) power, determine the etch profile. All other pertinent parameters are kept constant. We examine the etch profiles produced using e-beam resist as the main etch mask, with holes having diameters of 750 nm, 1 µm, and 2 µm.

High‐Aspect‐Ratio Nanostructured Surfaces as Biological Metamaterials

“…The limitations include the challenge of uniform etching over large areas, and the formation of scalloped vertical edges caused by the cyclical etching process. These can prevent the nanostructured substrate from being used as a master mold for other materials (e.g., poly(dimethylsiloxane) (PDMS)), by preventing clean detachment . Scalloped edges can be reduced by careful tuning of the etch and passivation cycle parameters, or by applying a subsequent isotropic wet or dry etching process to smooth the surface .…”

“…[39][40][41][42][43][44][45][46] The description "high aspect ratio" is loosely defined in the literature, but is typically applied to structures with an aspect ratio equal to or greater than 10:1. [6,[47][48][49][50] In this context, this means the majority of nanostructures we review here are less than 10 µm high, with sub-micron tips (with a few exceptions), see Figure 3. We do not consider micropatches (also referred to as microneedles) in this review, which can share similar aspect ratios, but have heights an order of magnitude larger.…”

“…These can prevent the nanostructured substrate from being used as a master mold for other materials (e.g., poly(dimethylsiloxane) (PDMS)), by preventing clean detachment. [50] Scalloped edges can be reduced by careful tuning of the etch and passivation cycle parameters, or by applying a subsequent isotropic wet or dry etching process to smooth the surface. [209] Cryogenic deep reactive-ion etching is a variant of the etching process, which allows greater control over the vertical sidewalls of structures by cooling the substrate and modifying the composition of etch gases.…”

“…Here, we examine surfaces, rather than untethered high‐aspect‐ratio nanostructures, or single‐cell probes . The description “high aspect ratio” is loosely defined in the literature, but is typically applied to structures with an aspect ratio equal to or greater than 10:1 . In this context, this means the majority of nanostructures we review here are less than 10 µm high, with sub‐micron tips (with a few exceptions), see Figure .…”

Design and additive manufacture for flow chemistry

“…48 The Bosch process is a two-step method involving alternate passivation and etching steps. The passivation step involves the use of octafluorocyclobutane (C 4 F 8 ) based plasma, to generate a PTFE like fluoro-polymer over the surface of the silicon.…”