Electric field sensor, surface wave plasma source, and surface wave plasma processing apparatus

An electric field sensor for detecting an electric field of microwaves in generating surface wave plasma by emitting microwaves transmitted through a microwave transmission path into a chamber through slots of a planar slot antenna and a microwave transmission window made of a dielectric material, the electric field sensor comprising:

• a probe serving as an inner conductor of a coaxial transmission path and having a built-in spring and a portion forming a monopole antenna at a tip end thereof so that the tip end of the probe is in constant contact with a rear surface of the microwave transmission window by a pressing force of the built-in spring;
• a cylindrical probe guide disposed at an outer side of the probe, serving as an outer conductor of the coaxial transmission path, and having a tip end to be in contact with a rear surface of the planar slot antenna;
• an insulating member disposed between the probe and the probe guide;
• a preload spring configured to preload the probe guide downward and press the probe guide so that the tip end of the probe guide comes in constant contact with the planar slot antenna;
• and
• a connector connected to the probe and the probe guide and configured to connect coaxial signal cables for extracting signals.