Thermal etching of nanocrystalline diamond films

•A dry non-plasma selective etching process for nanocrystalline diamond is reported.•Masked films can be controllably etched by heating to 700–800 °C in O2.•Films etch both vertically (slower) and laterally (faster) underneath the mask.•Etching occurs via decomposition of disordered grain boundaries/nucleation layers.•PECVD SiNx, SiO2, and ALD Al2O3 were evaluated as mask materials for this process.

A dry process for selective etching of nanocrystalline diamond thin films has been developed as an alternative to plasma etching. This process relies on subjecting masked diamond films to a controlled oxygen atmosphere at temperatures of 700–800 °C to controllably etch both vertically through the film and laterally underneath the mask. SiO2, SiNx, and Al2O3 films constitute viable mask materials for this process, provided that the underlying diamond film is fully outgassed before mask deposition and diamond etching. As expected, etching occurred more rapidly at higher temperatures. The etch rate was higher in the lateral direction than the vertical direction, which has been attributed to accelerated etching along disordered grain boundaries and the underlying nucleation layer. Similar activation energies (136–140 kJ/mol) were obtained for both lateral and vertical etching from 700 to 800 °C. Using the dry etch process developed in this research, diamond films can be removed from exposed features and undercut masked regions at a controlled rate, as indicated by microscopy and Raman spectroscopy.

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