AN OVERVIEW OF X-RAY-LITHOGRAPHY

Current achievements and future prospects of SR base x-ray lithography are explained through an account of research and development efforts made by NTT LSI Laboratories. The SR lithography system, including the compact SR light source Super-ALIS and beamlines with efficient mirro rs, is now at the stage of practical use. The vertical x-ray steppers SS-l and SS-2 have attained a repeatability of overlay accuracy as hig h as 25 nm (3 sigma). High-accuracy x-ray masks can be fabricated by a pplying the multiple-exposure method. Further improvement in pattern p lacement accuracy is expected with application of distortion compensat ion writing. Intense efforts made in development of x-ray mask inspect ion and repair technology resulted in the fabrication of defect-free x -ray masks. Test fabrication of CMOS/SIMOX LSIs has yielded fully func tional devices, with an improved overlay accuracy of 0.1 to 0.15 mu m (3 sigma), and a CD control of +/-10% in 0.2 mu m regions. Further app lication of SR lithography to the test fabrication of future LSIs will prompt the implementation of this technology into the practical proce ss.