Design and fabrication of soft x-ray photolithography experimental beam line at Beijing National Synchrotron Radiation Laboratory

Abstract

The synchrotron radiation (SR) soft x-ray photolithography experimental beam line (3B1 beam line) at Beijing National Synchrotron Radiation Laboratory, was completed and tested in June 1990. A soft x-ray photolithography experiment was successfully completed, and the width of linear etch on a silicon chip by the device with a 3B1 beam line is up to 0.5 micrometers . This SR soft x-ray photolithography experiment was done successfully for the first time in China. This paper describes the design of the beam line and the fabrication of the most important optical element--the cylindrical scanning mirror in the beam line. The 3B1 beam line consists of the shielding light plate with water-cooling, laser simulation light source system, 3-D adjustable scanning mirror, high pass-band filer (beryllium window), acoustic sensor, helium gas chamber, and vacuum system. The main specifications of the 3B1 beam line are as follows: spectral range 0.4-2 nm; horizontal acceptance angle 7.5 mrad; vertical acceptance angle 0.4 mrad; grazing incidence angle 1.5 deg; light spot size 35 nm X 12 nm; vacuum degree of the mirror box 5 X 10-10 torr (static). The cylindrical scanning mirror in grazing incidence is used in the beam line for photolithography to obtain uniform distributed intensity of illumination of the SR source in the vertical direction (Gaussian distribution) and sufficiently concentrated energy. It is made of aluminum alloy LD2 with a supersmooth optical surface. The curvature radius of the cylindrical surface is 527.5 mm; surface figure error is less than (lambda) /10; surface roughness is better than 1 nm RMS, and fold coating on the surface of the mirror under UHV of 109 torr. The laser simulation light source system is used for adjusting the optical system in the beam line instead of the SR source. The cylindrical mirror was polished supersmoothly using Al2O3 ultra micropower grinding material made in TOMAS in Japan on modified traditional machine tools, and surface roughness is better than 1 nm RMS.