Investigation On Precise Alignment Of EUVL Projection Optics

With the development of electronic industry, integrated circuit(IC) technology plays an important role in the modern industry. As the technology of optical lithography acting as the kernel of 1C fabrication technology, it is attracted by all the countries of the world. Extreme ultraviolet lithography is being developed as one of the most important candidates to fabricate a sub-O.lum-pattern. In recent years, several key technologies have been developed rapidly such as laser producing plasma source, extreme ultraviolet multilayer, optical fabrication and metrology, projection-camara alignment, low-defect mask and control technology of stage. Being one of the key technologies of EUVL, the alignment of optical lithography system affects directly the final imaging quality of the system.The Schwarzschild objective with eccentric aperture and off-axis illumination is designed on the basic of common-axis illuminated structure. A detailed theoretical analysis of the alignment is taken. The mathematical model is established and the relation between aberration and construction is described. Then the alignment scheme is drawn. The main factors that influence the wavefront error (WFE) are analysed. To validate this analysis and to obtain a more accurate characterization of the system, simulated alignments of the Schwarzschild objective are performed.Using Bruning method, the two spherical mirrors of the Schwarzschild objective are measured and the measurement accuracy is improved obviously.Finally, the Schwarzschild objective of EUVL is assembled and aligned on the common-axis illuminated structure with the WFE of 0.0202X(A,=632.8nm) RMS. Using an off-axis circular subaperture of the full annular pupil, the WFE of the Schwarzschild objective is 0.0144A,(X=632.8nm) RMS.