Deposition of wide-area diamond films in magneto-microwave plasma

Wide-area chemical vapour deposition (CVD) of diamond films has become feasible using magneto-microwave plasma in CH₄/H₂ or CO/H₂ mixtures. The important point of the developed system is to set the electron cyclotron resonance (ECR) condition (875 G in the case of a 2.45 GHz microwave) at the deposition area. The high plasma density necessary for diamond formation can be obtained at the area. Under a pressure of 10 Torr, where complete electron gyrations cannot be expected, the size of the discharge area controlled by the magnetic field is 70-80 mm in diameter. High quality diamond films have been obtained with this pressure. Under a pressure of 0.1 Torr, where ample gyrations occur, the plasma density has been increased by the effective microwave absorption in a magnetic field higher than the ECR condition, i.e. in the so-called off-resonance mode. The plasma is quite uniform and the discharge area is all over the reactor, the size of which is 160 mm in diameter. Uniform diamond films with high quality have been obtained. In the low pressure diamond has been formed on positively, but not on negatively biased substrates. Accelerated ions are not suitable for diamond formation. The CVD of diamond from CO gas and at lower pressure than ever reported shows a different aspect of the mechanism of diamond formation. Atomic carbon or a radical having a simple form, containing one carbon atom, might be a candidate for the active species to form diamond from the vapour phase.