A low temperature process for depositing a coating containing any of silicon, nitrogen, hydrogen or oxygen on a workpiece includes placing the workpiece in a reactor chamber facing a processing region of the chamber, introducing a process gas containing any of silicon, nitrogen, hydrogen or oxygen into the reactor chamber, generating a torroidal RF plasma current in a reentrant path through the processing region by applying RF plasma source power at an HF frequency on the order of about 10 MHz to a portion of a reentrant conduit external of the chamber and forming a portion of the reentrant path, applying RF plasma bias power at an LF frequency on the order of one or a few MHz to the workpiece, and maintaining the temperature of the workpiece under about 100 degrees C.