Imprint lithography has been shown to be an effective technique for replication of nano-scale features. Jet and Flash* Imprint Lithography (J-FIL*) involves the field-by-field deposition and exposure of a low viscosity resist deposited by jetting technology onto the substrate. The patterned mask is lowered into the fluid which then quickly flows into the relief patterns in the mask by capillary action. Following this filling step, the resist is crosslinked under UV radiation, and then the mask is removed, leaving a patterned resist on the substrate. Criteria specific to any lithographic process for the semiconductor industry include overlay, throughput and defectivity. The purpose of this paper is to describe the technology advancements made in the reduction of particle adders in an imprint tool and introduce the new mask replication tool that will enable the fabrication of replica masks with added residual image placement errors suitable for memory devices with half pitches smaller than 15nm. Hard particles on a wafer or mask create the possibility of creating a permanent defect on the mask that can impact device yield and mask life. By using material methods to reduce particle shedding and by introducing an air curtain system, test stand results demonstrate the potential for extending mask life to better than 1000 wafers. Additionally, a new replication tool, the FPA-1100 NR2 is introduced. Mask chuck flatness simulation results were also performed and demonstrate that residual image placement errors can be reduced to as little as 1nm.
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
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
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.
In this paper, we present an evaluation system for F2 laser lithography masks and resists and we report preliminary test results. The evaluation system has two subsystems that are based on very accurate measurement technology. One subsystem is used for mask evaluation, the other subsystem for resist evaluation. The mask subsystem consists of two units. One unit evaluates real size 6025 binary masks placed horizontally as inside steppers. This unit measures three parameters: 1) the real time in-situ transmittance at 157nm during F2 laser irradiation, 2) the in-situ VUV transmittance using a VUV spectrophotometer and 3) the deformation of the pellicle. The precision of transmittance measurement at 157nm is +/-0.5%. The precision of the pellicle deformation measurement is +/-0.1μm. The second unit of the mask subsystem collects samples of the mask outgassing and analyzes them in a gas chromatograph mass spectrometer. The resist evaluation subsystem consists of three units. 1) One unit determines negative effects of outgassing resist contaminants on the transmittance of optical materials under F2 laser irradiation, 2) the second unit analyzes the outgassing from resists and 3) the third unit examines the effectiveness of exposure tool purge nozzles to reduce outgassing contamination.
157 nm lithography has made further progress over the past year, steadily advancing towards the realization of the 65 nm era. In particular, exposure tools have moved on to the assembly phase, with new functions and performance now under evaluation. This paper presents our technical progress in our 157nm full field exposure tool, focusing on two key technologies: projection optics and environmental control with highly purified gasses. The high NA projection optics were 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. The birefringence effect caused by CaF2 has been reduced to acceptable levels by clocking and combining <111> and <100> oriented crystals. Polishing and optical coatings consisting of glass materials were completed at targeted accuracy. At the present time, assembly and tuning of the projection optics is being performed. A simulation based on the inspection data from each production step predicts that the desired image performance will be attained. The total efficiency of the exposure system is expected to be higher than previously announced, due to the improvement of both CaF2 transmittance and AR/HR coatings. One of two keys issues in environmental control is to purge the projection optics which are permanently sealed. Purging performance was tested using a mockup of the projection optics. The second issue is to purge the areas around reticles and wafers which are continually carried into and out of the exposure system. Using the actual platform, the wafer and reticle purging performance was evaluated. It has been demonstrated that both of our purging systems are effective in keeping the environment at minimum contamination levels. This contributes to the increase of throughput.
As the 130 nm era is approaching, requirements for lithography are becoming more and more rigorous. We have developed a 193nm scanner for below 130nm geometries capable of handling either 200 mm or 300 mm wafers. This paper describes the lithography tool performance required for printing 130nm features, focusing on a new 193nm excimer laser exposure tool developed for that age.