Abstract

The development of multilayer soft x-ray mirrors (also called layered synthetic microstructures) for use at angles close to normal incidence has increased the demand for extremely smooth substrates (usually case, rms roughness ≦ 0.5 nm) because the surface roughness or interfacial roughness strongly affects the soft x-ray reflection efficiency. Recent experiments show that,¹ to maintain high reflectance, the rms surface roughness of x-ray optics must less than ~0.1 nm over the range of spatial frequencies extending approximately from 1 to 100 µm⁻¹ (i.e., spatial wavelength from 1 µm to 10 nm). So the scanning probe metrology techniques, such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM), can be used for measuring the range of spatial frequencies that deleteriously affects the soft x-ray reflectance of multilayer optics. This paper demonstrates the feasibility of using STM and AFM to estimate the x-ray optics performance.

© 1995 IEEE