Recent advances in multilayer mirror technology meet many of the stringent demands of soft X-ray projection lithography(SXPL). The maximum normal-incident reflectivity achieved to data

is 66% for Mo/Si multilayers at 13.4 nm

which is sufficient to satisfy the X-ray throughput requirements of SXPL. These high-performance coatings must be deposited on figured optics with layer thickness error controled in ~0.5%. Uniform multilayr coatings are required for SXPL imaging optics

so maintaining the surface figure is critical to achieve diffraction-limited performance. In this paper

the figured substrate is considered as small super polished planes on the figured curve. By measuring the periods of multilayer on every small plane with small angle diffraction

the deposition speed of the figured substrate can be obtained. For improving the accuracy

every multilayer is measured repeatedly to wipe off the crude and systematic errors

acquire the best value

and calculate limiting error.