Thermochemical etching of polycrystalline diamond films by nickel

Abstract

This study investigates the deep etching characteristics of microcrystalline diamond films using a Ni-catalyzed thermochemical process conducted at different temperatures (750–975 °C) and gas compositions. Under H₂ microwave plasma conditions, minimal etching was observed beneath the Ni mask. Although introducing CO₂ into the gas mixture enhanced the etching rate by factors of 2–3, it resulted in non-selective etching of unmasked regions.

Changing to water vapor conditions led to superior etching selectivity, though the process was still pressure-dependent. At low pressure (65 mbar), catalytic etching achieved a maximum depth of 5–6 μm due to saturated graphitization around Ni. This limitation was overcome by increasing atmospheric pressure, enabling the formation of depth structures up to 20 μm with an etching rate of 45 μm/h. Temperature-dependent studies were conducted to evaluate the etch profile evolution. Using a 200 nm thick Ni mask at 900 °C under atmospheric pressure conditions, we achieved highly anisotropic etching with vertical sidewalls, contrasting with the sloped profiles typically observed in single-crystal diamond etching. This technology presents a cost-effective alternative to conventional dry plasma etching processes for fabricating complex 3D structures.