In the Hyper-NA immersion age, it is essential to optimize all optical parameters, and so exposure tools must have
functions to precisely control the parameters.
There have been various reports indicating that polarization aberrations of projection optics affect imaging performance,
but there have been few reports on reducing their influence in tools. We have developed a new method to optimize
imaging performance with polarization taken into account.
This paper describes a theoretical analysis of polarization with Pauli decomposition. A strict vectorial calculation of
optical images matches our expression. Then, our solver software can determine the optimum conditions of all
aberration parameters of exposure tools for specific IC patterns.
The 65nm and the subsequent 45nm node lithography require very stringent CD control. To realize high-accuracy CD
control on an exposure tool, it is essential to reduce wavefront aberrations induced by projection optics design and
manufacturing errors and then stabilize the aberrations while the exposure tool is in operation. We have developed two
types of new hyper-NA ArF projection optics to integrate into our new platform exposure tool: a dry system and a
catadioptric system for immersion application. In this paper, aberration measurement results of these projection
systems are shown, demonstrating that ultra-low aberration is realized. In addition, a new projection optical system has
been developed which incorporates high degree-of-freedom Aberration Controllers and automatic aberration measuring
sensors. These controllers and sensors are linked together through Aberration Solver, a software program to determine
optimal target values for aberration correction, thereby allowing the projection optics to maintain its best optical
properties. The system offers excellent performance in correcting aberrations that come from lens heating, and makes it
possible to guarantee extremely low aberrations during operation of the exposure tool.
In the low-k<sub>1</sub> lithography age such as today, reducing wavefront aberrations of projection optics is of crucial importance. Whereas the NA of an exposure tool becomes close to 1.0 or more, its residual aberration has attained 10 milli-lambda or less. In order to guarantee such small aberrations, the development of its on-machine measurement system with high accuracy is an urgent need. Many methods have been proposed in the literature, but their applicability is questionable in this hyper-NA region because of the emerging non-linearity of the measurement. In order to meet the severe requirements from the projection optics, we have reviewed various measurement methods, in particular from the viewpoint of their applicability to the high NA including immersion. The usage of the exposure light source, the control of coherence, and hyper-NA light detection were the basic items of the development. In addition, as a projection optics is very sensitive to the circumstances in the region of less than 10 milli-lambda, its dynamic control is necessary to keep its performance. High-speed measurement is indispensable to control the aberration in the dynamic sense. With all these things into consideration, we have built a new on-machine measurement system to cope with the hyper-NA specific issues. In this paper, we will show the basic principle and the experimental data of our new system using a projection optics. In addition, its applicability to the immersion system will also be discussed.