Masahiro Nei

Evaluating next-generation reticle demands on lithography equipment

Industry trends indicate that the next generation of exposure tool will be scanning steppers. Scanning steppers have a 25 mm by 33 mm field using 6 inch reticles. For device manufacturing, first generation 256M DRAM chips are roughly 12.5 mm by 25 mm, while 1G DRAM are expected to be 30 mm by 15 mm. As a result, a 25 mm by 33 mm field does not allow the exposure of two or more chips per shot. Therefore introduction of a larger mask is expected. To determine next generation reticle size standard, many factors have been investigated. First, an assumption was made that DRAM chip size trends will remain constant. Then, the throughput of scanning stepper was calculated with 6, 7, 8 and 9 inch reticles. The advantages were dependent on chip generation and device (memory or logic). Finally, a 9 inch reticle standard was chosen. Making the leap to a 9 inch reticle standard avoids the development time and costs of incremental changes in the standard. The thickness of a reticle is dependent upon reticle distortions, projection lens focus error. The deformation of the reticle has been simulated for the 0.25 to 0.5 inch thickness range. The final outcome of these simulations was that 9 mm (approximately 0.35 inch) was selected as the best thickness.

Mass production level ArF immersion exposure tool

VLSI chips are becoming denser and the industry is now moving to the development of devices at the 65nm node. While Nikon is working toward the development of next-generation lithography tools, we are also making efforts to extend the life of DUV excimer steppers by continuing reductions in feature size without any major changes to the conventional process. Nikons new model, the ArF Immersion Scanner NSR-S609B, utilizes immersion lithography in which the space between the projection lens and the wafer is filled with ultra pure water with a refractive index of 1.44. This immersion technology enables the NSR-S609B to break through the N.A. 1.0 barrier to achieve the worlds highest N.A. of 1.07, an impossible feat by a conventional lithography or dry exposure. This system will contribute to the production of advanced 55nm and smaller devices. Latest evaluation results of the immersion imaging system and the new stage system are presented.

New advanced lithography tools with mix-and-match strategy

Nikon has developed cutting-edge lithography tools, and its product lineup encompasses all exposure wavelengths. They are: the NSR-S307E ArF scanner for the 90nm node; the NSR-S207D KrF scanner for the 110nm node; the NSR-SF130 i-line stepper for the middle layer and the new concept NSR-SF200 KrF stepper, which offers unparalleled productivity and cost performance. In addition, a powerful support system is provided, the Lithography Equipment Engineering System, which will allow its customers to use all of these exposure tools simultaneously and derive the maximum benefit of the mix-and-match strategy. The use of this system will increase the uptime and enable their combined performance to exceed that of a stand-alone tool.Latest actual performance data from each of the tools and the result of the optimization performed using application software will be reported.

Latest results from the hyper-NA immersion scanners S609B and S610C

Nikon released the worlds first hyper-NA immersion scanner, the NSR-S609B with NA 1.07 at the beginning of 2006. With the highest NA lens using all-refractive optics, a flexible illumination system, and POLANOTM polarized illumination, the NSR-S609B is capable of manufacturing devices with better than 55 nm resolution. In addition, Nikon has announced the release of the NSR-S610C. With the worlds highest NA lens (NA=1.30), the S610C can comfortably achieve 45 nm critical layer volume production with k1=0.30. Nikons proprietary catadipotric lens design for the S610C provides the lowest flare and eliminates lens heating, resulting in stable imaging. Because the S609B and the S610C are built on the same platform, a number of advantages can be realized. First, both the S609B and the S610C utilize a tandem stage optimized for immersion lithography. The tandem stage consists of separate exposure and calibration stages. This allows for continuous flow of immersion water, and for calibration of the exposure tool during wafer exchange. As a result, throughput of greater than 130 wph is achieved, evaporative cooling of the stage during wafer exchange is prevented, and focus drift, baseline changes, and other issues with tool stability are eliminated. In this way, the tandem stage can achieve productivity and accuracy at the same time. In addition to the calibration functions described above, the Integrated Projection Optics Tester (iPot) mounted on the calibration stage can manage the long term performance of the projection optics. By measuring the wavefront aberration, the polarization quality of POLANOTM, and the pupil fill, iPot supports the optimization of the imaging performance. Nikons polarized illumination system POLANOTM provides improved contrast with no loss of illumination power. This provides increased process margin for 45 nm volume production using immersion lithography. Finally, Nikons proprietary local fill nozzle installed on the S609B and the S610C has been shown to eliminate immersion defects from bubbles, watermarks, and particles. Various data showing that the NSR-S609B meets requirements for 55nm and below production and the status of the development of Nikons newest immersion scanner NSR-S610C are introduced here.

Progressive ArF exposure tool for 65nm node lithography

To meet shrinkage demands of device pattern size, a new platform ArF exposure tool , NSR-S308F, has been developed with an extremely high NA projection lens. This equipment has been developed not only for ensuring better imaging of dry ArF, but also for achieving imaging enhancement of immersion ArF. To satisfy imaging and overlay accuracy requirements for 65nm node lithography, the heat management, body stiffness, and reaction force canceling system have been drastically improved. Optimized illumination conditions and polarized illumination1 have been developed to expand the severe process margin for ArF dry exposure tools. In addition, some applications support: the maximization of imaging performance of S308F; the aerial image measurement function2 to correct aberration of projection lens; the optimization software of lens aberration in a specific device pattern, and special software to realize excellent mix and match accuracy. Latest evaluation results and the improvement items of S308F will be presented.