Stress lithography boosts mirror quality

Researchers at MIT in the US have developed a new way to shape thin metal surfaces to create highly accurate mirrors in different, and changing, shapes.

Space telescopes, X-ray mirrors, semiconductor lithography and display panels rely on lightweight, high-precision optical systems, but the surfaces of mirrors and plates with microstructures that are necessary in these optical systems can be distorted by stressed surface coating materials, degrading optics quality. This is especially true for ultra-lightweight optical systems, such as space optics.

麻省理工学院researchers Youwei Yao, Ralf Heilmann, and Mark Schattenburg of the Space Nanotechnology Laboratory (SNL) in MIT’s Kavli Institute for Astrophysics and Space Research have devised new methods to compensate for distortions, even in real time.

The new approach eliminates distortion and enables researchers to bend surfaces more arbitrarily into the precise and complex shapes. Thin plate shaping is typically used for high-level, complex systems, like deformable mirrors or wafer-flattening processes during semiconductor manufacturing.

Stress lithography

“Using stress to deform optical or semiconductor surfaces is not new, but by applying modern lithographic technology, we can overcome many of the challenges of existing methods,” says Yao.

Substrates for optical surfaces are first coated on the backside with thin layers of high-stress film, made of materials like silicon dioxide. Novel stress patterns are lithographically printed into the film so that researchers can change the properties of the material in specific areas. Selectively treating the film coating in different areas controls where stress and tension is applied across the surface. Because the optical surface and the coating are adhered together, manipulating the coating material also reshapes the optical surface accordingly.