Plasma processing apparatus

1. A plasma processing apparatus that performs a plasma processing on an object, the plasma processing apparatus comprising:

a processing container configured to accommodate the object, the processing container having at least one side wall;

a dielectric window provided to seal an opening formed in a top portion of the processing container, and configured to transmit microwaves into the processing container; and

a slot plate located on a top surface of the dielectric window, the slot plate having at least one slot to radiate microwaves to the dielectric window,

wherein the dielectric window has a thickness of 3λ/8 or less (here, λ is a wavelength of the microwaves) at least at a predetermined position where a microwave power is concentrated,

wherein the dielectric window comprises at least one protrusion located at the predetermined position on a bottom surface of the dielectric window, and each protrusion protrudes downward from the bottom surface,

wherein each protrusion is disposed at a position corresponding to a location of a respective slot, and

wherein none of the at least one protrusion is in contact with any of the at least one side wall.

2. The plasma processing apparatus of claim 1 , wherein the at least one slot comprises a plurality of slots to radiate microwaves to the dielectric window.

3. The plasma processing apparatus of claim 2 , wherein the predetermined position includes a position where an electron density becomes maximum within a plane of the dielectric window.

4. The plasma processing apparatus of claim 1 , wherein each protrusion has a width in a range of λ/8 to 3λ/8.

5. The plasma processing apparatus of claim 1 , wherein each protrusion has a height of λ/16 or more.

6. The plasma processing apparatus of claim 1 , wherein the at least one protrusion includes a plurality of protrusions provided on the bottom surface of the dielectric window.

7. The plasma processing apparatus of claim 2 , wherein the at least one protrusion includes a plurality of protrusions provided on the bottom surface of the dielectric window.

8. The plasma processing apparatus of claim 7 , wherein the plurality of protrusions are positioned along circles concentric to the slot plate with a predetermined interval in a radial direction.

9. The plasma processing apparatus of claim 1 , wherein each protrusion has a downwardly elongated rectangular cross-section when viewed from a side.

10. The plasma processing apparatus of claim 1 , wherein each protrusion is ring-shaped when viewed from below.