Very low-roughness diamond film deposition using a surface-wave- sustained plasma

Abstract

We have investigated the operating parameters controlling the average roughness Ra of diamond films obtained through chemical-vapor deposition using microwave-sustained plasmas. The plasma was provided by a surface-wave discharge in the form of a convex hemisphere facing the substrate and the films were deposited on Si(100) substrates. The procedure leading to fine grain, low-roughness diamond films called for high microwave power density absorbed in the plasma and very small grain size powder for substrate pretreatment in an ultrasonic bath, using hexane as the suspension liquid. Pretreating then with ≤ 0.25 μm diamond grit and operating, for example, with a microwave power density of 25 W/cm3 (1.2 kW total absorbed power) and 0.75% CH4 in a CH4–H2 mixture, we got Ra = 6 nm for a 1-μm-thick film with an average crystallite size of 50 nm. The corresponding nucleation density was remarkably high, at 7.5×1010 cm−2; diamond film isoquality was good and adhesion to the substrate strong.