Water-based immersion technology has overcome various challenges and is starting to be used for the 45nm-node mass
production. However, even though immersion technology is being used in memory device production, significant
improvement in defect performance is needed before the technology can be used for logic devices. Canon has developed
an immersion exposure system, the FPA-7000AS7, with numerical aperture of 1.35. In the AS7 immersion tool, there is
little influence of vibration and evaporative cooling. The AS7 has an in-situ cleaning system in order to remove particles
carried into the exposure tool. We evaluated the contamination of the projection lens and immersion nozzle due to photoacid
generator (PAG) leaching from resist to water. We evaluated the cleaning effects of various cleaning processes and
found the suitable processes for cleaning the projection lens and immersion nozzle from the view that it does not
adversely affect the exposure tool: damage-free and easy drainage treatment. In addition, we evaluated the influence of
particles on the wafer stage, since there is a major concern that particles entering the water may increase the defects. The
number of particles adhering on the wafer during an exposure sequence can be reduced with the wafer stage cleaning.
Periodical cleaning keeps the wafer stage clean, thus preventing the increase of exposure defects caused by particles. We
performed a defect evaluation with the AS7. The average defect density was 0.042/cm<sup>2</sup> in the continuous exposure
process of 25 wafers with a developer-soluble topcoat. Circle defects and bubble defects were not observed.
Water-based immersion technology has overcome various obstacles and is approaching the mass production phase.
Canon is in the process of developing an ArF immersion exposure tool, FPA-7000AS7 (NA>1.3), to meet both mass
production of the 65nm HP and development of the 45nm HP, which starts in 2007.
In the Canon immersion nozzle, there is little influence of vibration on the lens and the stage, and particle generation
from the nozzle during treatment of the nozzle in the manufacturing process has successfully been prevented.
We evaluated contamination due to leaching and cleaning technology with a test bench. Contamination due to PAG
(Photo-acid Generator) leaching from resist to water could be completely eliminated by dipping it into a cleaning fluid.
With periodic cleaning, it is possible to keep the projection lens clean and to prevent particle generation from the
The defect was evaluated with FPA-6000AS4i (NA0.85) that had the same type of immersion nozzle as that of
FPA-7000AS7. The level of defect density was stable in a continuous exposure process of 25 wafers with a
developer-soluble topcoat. The defect density was 0.030/cm2 with a topcoat-less resist.
193-nm immersion lithography using water as the immersion fluid is the most promising technology candidate for achieving the 45nm HP node. We have been developing a high NA immersion exposure tool through collaboration with several companies in the industry. This paper presents the results we have obtained on various aspects of immersion exposure system development, and discusses the latest status on the issues that have been explored. In immersion lithography, leaching from resist raises concerns about lens contamination. Using a lens contamination test setup, we examined deposition that is formed on the lens surface when irradiated with a laser. It is estimated from the results that no contamination due to PAG will occur in the exposed area. The test results will be shown in detail. Using our immersion system, no defects have been found so far that are identified as bubble-induced. Therefore, we intentionally obtained bubble-induced defects by introducing micro bubbles into the immersion liquid. The findings will be discussed in this paper. Also, we established our "Immersion Evaluation Laboratory" to facilitate evaluation of all aspects of the immersion lithography process. The laboratory is equipped with (1) 193nm immersion scanner, FPA-6000AS4i with NA 0.85 and a 300mm wafer stage capable of 500mm/s scanning, (2) coater/developer, (3) defect inspection system and (4) SEM. We have performed full-wafer exposure tests using the AS4i, the result of which will be also presented.
Immersion lithography systems with a 193 nm light source are being pursued in the industry. This paper presents the results of the study we have made on various aspects of the exposure system, and gives the status of exposure system development together with the challenges involved. If there are fluctuations in the flow rate of immersion fluid, i.e. ultrapure water, the positioning accuracy of the wafer stage may be affected. Similarly, temperature changes in the fluid can significantly influence imaging performance of the projection optics. We have developed an ultrapure water supply control system which allows direct connection to the ultrapure water line of the existing fabs and enables constant-temperature, constant-flow rate control of the water with high stability. The evaluation results of this system will be shown. Photoresist materials such as photo-acid generator, PAG, dissolved into the water are a cause of concern for lens contamination. The challenge for exposure tool suppliers in terms of contamination control is to specify the permissible dissolution amount. To this end, wet contamination tests are in progress, and the findings to date will be discussed in this paper. Two verification tools for immersion exposure are built: a two-beam interference exposure tool and a full-field alpha-site scanner. Using the alpha tool, the evaluation results of full wafer CD uniformity including edge dies will be presented. Also, defect analysis results will be shown, specifically the impact of air bubbles on patterning.