X-ray mirror figure correction using differential deposition

TL;DR

This paper presents a method for improving x-ray mirror surface accuracy through differential deposition of thin films, involving precise substrate movement and iterative correction, achieving significant error reduction.

Contribution

It introduces a novel differential deposition technique combined with a deconvolution algorithm for precise x-ray mirror figure correction.

Findings

Shape errors reduced by a factor of 20-30

Surface errors lowered below 0.5 nm RMS

Effective correction demonstrated on multiple mirrors

Abstract

The surface figure of x-ray mirrors can be improved by differential deposition of thin films. To achieve the required corrections, WSi2 layers of variable thickness were deposited through beam-defining apertures of different openings. The substrates were moved in front of the particle source with specific velocity profiles that were calculated with a deconvolution algorithm. Two different DC magnetron sputter systems were used to investigate the correction process. Height errors were evaluated before and after each iteration using off-line visible light surface metrology. Four 300 mm long flat Si mirrors were used to study the impact of the initial shape errors on the performance of the correction approach. The shape errors were routinely reduced by a factor of 20-30 down to levels below 0.5 nm RMS.