Shigeyuki Suda

Realization of very small aberration projection lenses

To implement low-k1 lithography, it is most fundamental to reduce aberrations of projection lenses for the exposure tools, not only in the optical design, but also in the manufacturing process. This paper will reveal a new lens manufacturing concept utilizing Zernike circle polynomials to overcome such difficulties. Sets of Zernike coefficients are used to describe the surface accuracy of each element or wavefront aberrations of assembled lens, and each coefficient itself becomes the target of element polishing or lens tuning. Adopting these targets is the most effective way to control actual optical performance and result in a great improvement of the projection lenses. We present some topics of our new manufacturing process and the performance progress up to our latest KeF stepper, FPA-3000EX6.

Analysis of precise CD control for 45nm node and beyond

Semiconductor device shrink progresses steadily at a speed of one generation every two years and CD uniformity (CDU) requirement becomes severer as shown in ITRS. Higher level of CD control performance is the most important item for semiconductor exposure tools to meet 45nm node requirements. For this higher accuracy it is of course necessary to brush up the projection optics and the illuminator system in every detail. We need to reassess items which were ignored as error factor until now and include them into the CD budget and thereby control in high accuracy. These small factors include the effects of birefringence caused by glass materials and coating, transmission distribution at the pupil of projection optics and influence of spectrum stability of a laser used in Hyper NA lens, and so on. They will come into the budget in addition to the conventional aberration and illuminator uniformity as we start to use new exposure technology such as immersion or polarized illumination after 45nm node. In this paper, we list up items which influence CDU in the node after 45nm, and estimate sensitivity for CDU for each item. Then we set the target values of every item by breaking the CDU target value of ITRS in terms of projection optics, illumination system, and total performance of exposure equipment. We show data for some items, and describe a prospect for 45nm node era and beyond.

Development of 157-nm full-field scanners

This paper discusses the technical progress to date in 157 nm full field scanners, which are in the process of final tuning. The high NA projection optics was designed to meet accelerating demands for smaller geometries. A catadioptric system with a line-selected laser was chosen to solve the problem of chromatic aberrations. Wavefront aberration of the catadioptric system was measured using a 157 nm PMI, based on which the projection optics has been tuned up to achieve the target performance. The exposure results show that 60 nm L&S were resolved in accordance with λ/NA improvement, demonstrating the basic potentials of 157 nm lithography. CD uniformity within the wafer is comparable to KrF and ArF systems while the purge system, the main body, and the resist process have been confirmed to be stable. When compared to ArF, local flare increases significantly. However, it has been confirmed that local flare can be greatly mitigated by improving lens surface accuracy. Further reduction in local flare, needed for commercialization of 157 nm tools, is expected to be achieved by extending the current improvement as the CaF2 performance has rapidly approached next generation specifications over the past year.