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/cm2 in the continuous exposure
process of 25 wafers with a developer-soluble topcoat. Circle defects and bubble defects were not observed.
Canon has developed an immersion exposure tool, the FPA-7000AS7 (AS7), with the industry's highest NA of 1.35.
This paper reports on its performance. The AS7's projection lens achieves ultra-low aberration with total RMS of less
than 5 mλ and flare of less than 0.5%. The resolution capability is 37 nm with k1 = 0.259, and DOF of 0.8 μm was
obtained owing to the ultra-low aberration and low flare. Regarding focus performance, a 3σ value of 19.3 nm for Lstage
and 16.1nm for R-stage were attained in a whole area. The result of CD uniformity of 1.91nm (3σ) was obtained
across the wafer with a total of 4032 measurement points. Distortion was 3.9 nm at the worst value. On the other hand
the most critical issue of immersion is defects, so the nozzle, lens and stage must be cleaned to reduce defects. The result
of defect evaluation of the AS7 was an average of 0.042 defect/cm2 from 25 wafers in a lot and average 0.046 defect
count/cm2 from long-term defect evaluation for two months. From these results, we are confident that the AS7 is capable
of 45-nm node device production.
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
immersion nozzle.
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.
A great deal of research effort is focused on accelerating the development of 193-nm immersion lithography because
it appears to be the most suitable lithographic solution available for 65-nm-and-below semiconductor devices.
To realize a 193-nm immersion process, we must find ways to detect and analyze immersion specific defects, and
then establish processes that let us avoid such defects.
In this paper, we examine immersion specific defects and ways to detect and eliminate them in production processes.
Through comparison of dry exposure and immersion exposure processes, we have found that "bridges" and
"water-marks" are the most significant immersion specific defects using current developable top-coats. Although we
confirmed that the current solvent-removable top-coat process is better for avoiding immersion specific defects, we also
found that the defect density with a developable top-coat was still low enough for volume production.
We also investigated the causes of immersion specific defects and hypothesized that DI water permeation and the
local topology of the top-coat play an important role in the generation of immersion specific defects. To test whether this
was so, we evaluated the change in the top-coat film thickness by the quartz crystal microbalance technique. We
confirmed that top-coat swelling caused by water permeation into the top-coat film is a major cause of immersion
Conference Committee Involvement (5)
Photomask and Next Generation Lithography Mask Technology XIV
17 April 2007 | Yokohama, Japan
Photomask and Next-Generation Lithography Mask Technology XIII
18 April 2006 | Yokohama, Japan
Photomask and Next-Generation Lithography Mask Technology XII
13 April 2005 | Yokohama, Japan
Photomask and Next-Generation Lithography Mask Technology XI
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