Impact of ICP Etching on the Formation of Surface Defects on Hydrogen Terminated Diamond

Crawford, K. G., Tallaire, A. and Moran, D. A. J. (2015) Impact of ICP Etching on the Formation of Surface Defects on Hydrogen Terminated Diamond. In: MRS Fall Meeting: Materials Research Society, Boston MA, USA, 29 Nov - 4 Dec 2015,

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The transfer doping mechanism used to generate charge carriers in hydrogen terminated diamond occurs at the interface between the diamond surface and an adjacent material. This process is likely influenced by increased values of surface roughness, polishing induced crystal damage and reduced hydrogen coverage which may impact the electrical performance [1]. Bulk dislocations can occur during crystal growth, while surface damage may occur from polishing. These non-sp3 bonded dislocations at the surface are susceptible to etching by hydrogen plasma. The etching of pits on the surface of diamond after hydrogen treatment is a known phenomenon; work by [2] showed defects at the surface can be revealed by H2/O2 etching with low amounts of oxygen, presenting as pits in the form of inverted pyramids. Single crystal [100] CVD plates acquired from Element Six are subject to an acid cleaning process before treatment in hydrogen plasma. Surface scans using Atomic Force Microscopy (AFM) on samples prior to hydrogen treatment show polishing grain and a Ra of ~0.7nm for a 5um scan window. After acid cleaning and hydrogen termination the surface exhibits etch pits which increases Ra values to greater than 3nm. The pits present as inverted pyramids and are typically ~18nm deep and ~450nm wide. In this work defects of polished samples are reduced by use of reactive ion etching (ICP) after polishing to remove damaged layers. AFM scans were taken of a polished diamond sample which had been etched by ICP at a rate of approximately 10nm per minute using Ar/Cl2. The etching mechanism of diamond using Ar/Cl2 plasma is reported to be: C + Cl2→CClx. Ar ions sputter the diamond surface enabling the reaction of chlorine with carbon atoms to form the volatile etch product CClx [3]. A Ra value of ~0.7nm was measured after polishing and a reduced value of ~0.5nm obtained after etching. This indicates the process can be used to smooth the diamond surface due to isotropic etching. Attempts were made to reduce existing etch pits on an already hydrogen terminated sample by use of ICP etching. AFM scans show that while the pits are not removed once already formed, due to isotropic etching the pits can be made shallower and the surface smoother. Polished samples etched with Ar/Cl2 are then hydrogen terminated and compared to non-etched samples. The formation of large ~450nm wide pits is supressed for the etched samples. Instead much smaller pits are formed ~25nm wide and ~4nm deep. In conclusion ICP etching has been demonstrated as a method of removing several microns from the diamond surface without increasing roughness, this can be employed as a means of removing polishing defects. Future work will investigate the impact on electrical performance of surface etching prior to hydrogen termination.

Item Type:Conference Proceedings
Glasgow Author(s) Enlighten ID:Crawford, Mr Kevin and Moran, Professor David
Authors: Crawford, K. G., Tallaire, A., and Moran, D. A. J.
College/School:College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
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