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/cm<sup>2</sup> from 25 wafers in a lot and average 0.046 defect
count/cm<sup>2</sup> 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.
Canon has renewed its platform of exposure tools. The new platform, the FPA-7000, is designed to cover multiple
generations. The lens performance of the FPA-7000AS5 achieves less than 6m&lgr;, while that of the AS7 is estimated to
be less than 4m&lgr;. The illumination performance meets the target required for the 45nm node. The in-situ aberration
monitor, called iPMI, attains the measurement repeatability of 1.45m&lgr;. Focus and overlay units have improved process
robustness. A solution tool for optimization is introduced to be connected with the FPA-7000. Moreover, latest studies
of immersion, such as nozzle pressure, temperature control and defect inspection result are reported, and we also
discuss the possibility of high-refractive-index 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 F<sub>2</sub> 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 F<sub>2</sub> 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 F<sub>2</sub> 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.
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.
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.
Two key technologies of 157nm exposure tools are projection optics and the environment control with highly purified gasses. For the projection optics, the NA is required to be extremely high even from the beginning to meet the accelerated ITRS roadmap, while compensating for the chromatic aberration issues with a line selected laser. In addition, the NIST has raised an issue of intrinsic birefi-ingence with the CaF2 materials, which has serious effects on the image quality if left uncorrected. We have found answers to suppress the intrinsic birefringence effects in the practical sense for the newly designed high NA system. One solution is to optimize the combination of the rotational positions of [1 11] crystals used for the projection optics, and to combine some  crystals with [1 11] crystals. Looking at the environmental control issue, there are two points. One is the purging of the constantly-sealed projection optics. We have experimented on the components in the projection optics, and have achieved the purging target for them. The second point is the purging around the reticle and the wafer both of which are continually carried in and out. We have got a practical solution, partial purge system, through simulations and basic experiments using a mock-up. The partial purge mechanism is effective in keeping the environment at high purity, capable of assuring the target purging level. It can also solve the problem of lens contamination due to outgas from the resist.