Microwave Window Refraction for Uniform High-Speed Wafer Processing

The microwave window is designed with a variable refractive index that changes according to the radial distance from the optical axis. The center region has a different refractive index than the edge region, allowing different parts of the microwave beam to be focused at different positions. This creates a more uniform plasma distribution across the wafer surface even at high process speeds, resolving the contradiction between productivity and plasma uniformity.

Instead of using complex mechanical focusing systems or adjustable components, the patent changes the optical parameter (refractive index) of the microwave window material itself. By selecting a material with a variable refractive index that varies radially from the optical axis, the system achieves beam cross-section control and plasma uniformity without adding mechanical complexity. The refractive index gradient naturally focuses the microwave beam to create a uniform plasma distribution.