Microwave plasma reactor for manufacturing synthetic diamond material

A microwave plasma reactor for manufacturing synthetic diamond material via chemical vapour deposition, the microwave plasma reactor comprising:

• a plasma chamber comprising a base, a top plate, and a side wall extending from said base to said top plate defining a resonance cavity for supporting a microwave resonance mode, wherein the resonance cavity has a central rotational axis of symmetry extending from the base to the top plate, and wherein the top plate is mounted across said central rotational axis of symmetry;
• a microwave coupling configuration for feeding microwaves from a microwave generator into the plasma chamber;
• a gas flow system for feeding synthetic diamond material process gases into the plasma chamber and removing them therefrom;
• and
• a substrate holder disposed in the plasma chamber and comprising a supporting surface for supporting a substrate on which the synthetic diamond material is to be deposited in use;
• wherein the resonance cavity is configured to have a height, as measured from the base to the top plate of the plasma chamber, which supports a TM011 resonant mode between the base and the top plate at a frequency in the range 400 to 500 MHz, 800 to 1000 MHz, or 2300 MHz to 2600 Mz,
• wherein the resonance cavity is further configured to have a diameter, as measured at a height less than 50% of the height of the resonance cavity as measured from the base, which satisfies the condition that a ratio of the resonance cavity height/the resonance cavity diameter is in the range 0.3 to 1.0,
• wherein the resonance cavity comprises internal walls configured to be exposed to a plasma formed within the resonance cavity in use, said internal walls comprising metallic surfaces forming at least 75% of a total surface area of said internal walls within the resonance cavity,
• wherein a portion of said internal walls is formed by a dielectric window, formed in one or several sections, said dielectric window forming no more than 25% of the total surface area of the internal walls within the resonance cavity, and
• wherein the plasma chamber does not contain a quartz process gas confinement element;
• and
• wherein the microwave plasma reactor further comprises an electrically conductive non-planar surface located within the plasma chamber over a high electric field anti-node region which would exist in a corresponding plasma chamber which did not comprise the conductive surface.