New Measurements of Scattering from Multilayer Mirrors
Experimenters using the CXRO Calibration and Standards Beamline (Beamline 6.3.2) have made the first direct measurements of nonspecular scattering from multilayer mirrors at normal incidence. This advancement in characterizing extreme ultraviolet (EUV) optics will aid the develoment of mirrors for use in fields such as astronomy and EUV lithography, an emerging technique for manufacturing the next generation of computer chips.
The images above show nonspecular scattering from a Mo/Si-coated multilayer mirror. To obtain the images, the researchers used an annular microchannel plate to collect scattered light from the mirror over a broad range of angles at once (to measure total integrated scatter). They directed light from the ALS near normal incidence to the mirror under test, which reflected light back toward the microchannel plate (MCP). Specularly reflected light passed through the central hole in the plate, but nonspecularly scattered light at angles between 8 and 45 degrees was collected. A phosphor screen behind the plate allowed the researchers to see the signal and record it with a CCD camera. By scanning through a range of wavelengths, they created a digital movie showing how the scattering pattern changes with the wavelength of reflected light. The images clearly show an asymmetry in the mirror and less nonspecular scatter at the longer wavelength. Another digital movie shows how the pattern changes with the scattering position (from the top, center, or bottom of the mirror). (The movies here are in QuickTime format, and each is about 1 MB in size.)
This work was done in support of a cooperative research and development agreement between the EUV Limited Liability Corporation and Lawrence Livermore National Laboratory, Sandia National Laboratory, and Berkeley Lab (collectively known as the "Virtual National Laboratory") for the development of EUV lithography.
Research conducted by E.M. Gullikson (principal investigator, Berkeley Lab), D.G. Stearns and D.P. Gaines (Lawrence Livermore National Laboratory), and J.H. Underwood (Berkeley Lab) using the reflectometry endstation at Beamline 6.3.2.
Funding: EUV Limited Liability Corporation, Office of Basic Energy Sciences of the U.S. Department of Energy.
ALSNews article about this science highlight
More ALS Science