Methods and apparatus for radiation processing of semiconductor substrates using microwave or millimeter wave energy are provided. The microwave or millimeter wave energy may have a frequency between about 600 MHz and about 1 THz. Alternating current from a magnetron is coupled to a leaky microwave emitter that has an inner conductor and an outer conductor, the outer conductor having openings with a dimension smaller than a wavelength of the emitted radiation. The inner and outer conductors are separated by an insulating material. Interference patterns produced by the microwave emissions may be uniformized by phase modulating the power to the emitter and/or by frequency modulating the frequency of the power itself. Power from a single generator may be divided to two or more emitters by a power divider.