Three-dimensional surface figure measurement of high-accuracy spherical mirror with nanoprofiler using normal vector...

Area of Science:

• Optics and Metrology
• Advanced Manufacturing Technologies

Background:

• Next-generation lithography demands high-accuracy mirrors, particularly aspherical and free-form types.
• Conventional processing and measurement methods struggle to meet the stringent precision requirements for these advanced optics.

Purpose of the Study:

• To develop a novel nanoprofiler for measuring high-accuracy mirrors without relying on a reference surface.
• To enable precise 3D shape reconstruction of free-form mirrors for advanced optical applications.

Main Methods:

• Development of a novel nanoprofiler capable of measuring mirror surface figures independently of a reference surface.
• Utilizing an algorithm to process normal vectors and coordinate values for 3D shape reconstruction.
• Experimental validation using a concave spherical mirror with a 1000-mm radius of curvature.

Main Results:

• The nanoprofiler achieved a measurement repeatability of 0.6 nm for a concave spherical mirror.
• The measurement uncertainty was estimated at approximately 10 nm via numerical simulation.
• Results showed consistency with a Fizeau interferometer within the uncertainty range for the mirror's central region.

Conclusions:

• The developed nanoprofiler offers a promising solution for high-accuracy mirror metrology, crucial for extreme ultraviolet lithography.
• The reference-free measurement capability opens possibilities for measuring complex free-form optics.
• Further improvements in dynamic stiffness could enhance the nanoprofiler's repeatability beyond sub-nanometer levels.