O2/Ar inductively coupled plasma etching of boron-doped single-crystal diamond

Diamond is an attractive semiconductor for extreme-environment electronics due to its ultrawide bandgap, high breakdown field, and exceptional thermal conductivity. However, reliable microfabrication requires controllable dry etching techniques because diamond is chemically inert and difficult to pattern using conventional wet processes. In this work, the etching behavior of boron-doped single-crystal diamond was systematically investigated using an Ar/O2 inductively coupled plasma (ICP) process. The samples consisted of a 5 μm boron-doped epitaxial layer grown on a type IIa (001)-oriented single-crystal diamond substrate. The effects of oxygen fraction, RF bias power, and ICP source power on the etch rate and DC bias voltage were examined. The etch rate increased with oxygen concentration up to approximately 80% O2 and decreased at higher oxygen fractions, indicating that efficient etching requires both reactive oxygen species and ion-assisted bond breaking. Increasing RF bias power significantly enhanced the etch rate due to higher ion bombardment energy but also increased surface damage, as evidenced by an increased sp2 carbon component in x-ray photoelectron spectroscopy. Increasing ICP power enhanced plasma density and chemical etching while reducing ion bombardment energy. A threshold ion energy of approximately 67 eV was extracted from the RF-power series, indicating the minimum ion energy required to initiate efficient etching. Post-treatment studies showed that ozone effectively reduces sp2 carbon and recovers a more diamond-rich surface, while short N2 annealing is ineffective. These results provide insights into the interplay between ion-assisted and chemical mechanisms in diamond etching and offer guidance for optimizing plasma processes for diamond device fabrication.