Rectangular scale-similar etch pits in monocrystalline diamond
Highlights
► Oxidation of monocrystalline diamond through pores in a passivating film produced smooth-walled rectangular cavities. ► Each cavity exhibited smooth, vertical sidewalls, a flat bottom, and depth equal to half its width. ► Cavity shapes were consistent across a range of widths from 1 µm to 72 µm. ► Cavity boundaries lie along slow-etching {100} crystallographic planes.
Introduction
The extreme material properties of diamond make it a compelling material for micro- and nanotechnology applications, including high-power electronics [1], micro-electromechanical systems [2], optical waveguides [3], and solid-state quantum devices [4]. Additionally, the material's hardness, inertness, and resistance to fouling make it an attractive candidate for atomic force microscope calibration artifacts and line width standards [5]. Outside of the electronic realm, most diamond devices are at the present time fabricated from polycrystalline thin films. However, the material properties of polycrystalline diamond are generally inferior to those of the monocrystalline material and can be much less consistent due to grain structure variations both from batch to batch and through the thickness of an individual film [6].
With recent developments improving the speed and cost of synthesizing monocrystalline diamond substrates, and with achievable substrate dimensions increasing [7], [8], the next bottleneck to the development of single-crystal diamond devices may be the difficulty of shaping the material into the necessary features and cavities [9]. Diamond micromachining techniques developed to date use plasma etchants, or utilize ion implantation to convert the diamond material to a more volatile sp2-bonded form for removal [9], [10], [11]. Ion implantation methods require focused ion beam milling to expose the damaged layers, while plasma etchants create trade-offs between etch rate, mask selectivity, surface roughness, and sidewall angle.
Crystallographic etching techniques have long been used for delineating defects in diamond [12], and orientation-dependent variations in oxidative etch rates have been noted [13], [14]. However, oxidative etching of diamond has not yet been explored as a micromachining technique. In contrast, crystallographic etching has been a workhorse technique for micromachining of silicon and other common materials, both in industry and in the research community [15]. A similar technique for diamond could be of considerable value, especially when near-atomically-smooth features are required, as is the case for linewidth standard reference materials [5].
Section snippets
Experimental
Here we report on deep rectangular etch pits produced by crystallographic etching of monocrystalline diamond in oxygen and water vapor. The etched material was a 3 mm × 3 mm × 0.5 mm (100)-oriented intrinsic monocrystalline diamond substrate manufactured by epitaxial chemical vapor deposition.1 The substrate was cleaned for 15 min by immersion in a 65 °C solution of sulfuric acid, peroxymonosulfuric acid, hydrogen peroxide, and water2
Results
Three-dimensional profiles of the etch pits were taken using interferometric microscopy, resulting in the measurements shown in Fig. 2. The pits had a square profile in the plane of the substrate and were approximately half as deep as they were wide in each case. Based on this, it was determined that the etch process was limited by slow-etching {100} planes in each of the three orthogonal axes. Inspection of the sample by electron microscopy confirmed the shape of the cavities, as shown in
Acknowledgments
This research was performed in the Physical Measurement Laboratory and the Center for Nanoscale Science and Technology at the National Institute of Standards and Technology. Certain commercial equipment, instruments, or materials are identified in this document. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the products identified are necessarily the best available for the purpose.
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Cited by (1)
Polishing, preparation and patterning of diamond for device applications
2019, Diamond and Related MaterialsCitation Excerpt :The preferential nature of these etchants has led to their use in diamond defect studies, where they can highlight the location and density of pre-existing surface defects. This effect has also been exploited for anistropic, crystallographic, etching for the purposeful realisation of 3D diamond structures [29,33–35]. Hausman et al. have reported the formation of so-called ‘nano-grass’ with O2 ICP RIE [25].