Tsuneo Kanda

Alignment sensor corrections for tool-induced shift (TIS)

As the most critical semiconductor device geometries shrink down to the quarter micron order, requirements for overlay accuracy also become increasingly critical in the actual semiconductor manufacturing process. Factors in overlay error (especially, alignment error) originate in the interaction of process and tool. It is therefore necessary to improve alignment accuracy from both the process and the tool sides. In an effort to solve this as a tool supplier, we at Canon must minimize tool factors to reduce alignment errors caused by the interaction of process and tool factors. We though that we needed some evaluation criteria with such interaction take into account, and redefined the concepts of tool induced shift and wafer induced shift as a criterion. This paper introduces these new concepts and discusses validity of the criteria showing experimental results of alignment accuracy implementing the idea in the real process.

Performance of the FPA-7000AS7 1.35 NA immersion exposure system for 45-nm mass production

Canon has developed an immersion exposure tool, the FPA-7000AS7 (AS7), with the industrys highest NA of 1.35. This paper reports on its performance. The AS7s 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.

0.85-NA ArF exposure system and performances

At the time when the 90nm node is near at head, the era for ArF exposure tool is expected in the near future. In this paper, the extension possibility to over the 65 nm node with the FPA-6000AS4, which equips a lens with 0.85 of the numerical aperture (NA) and some indispensable functions with the future lithography for extending the patterning capabilities down to 65nm node and beyond it, is discussed. In the development of the 0.85NA exposure system, we would like to introduce the three major topics. Firstly, the exposure tool equips an illuminator providing flexibly variable illumination modes. Secondly, we newly developed a metrology for determining the aberrations on the exposure tool in order to achieve extremely low aberrations, with the method applying Haltman. And lastly, exposure performances, and the flare, are discussed.

New-generation projection optics for microlithography

In order to meet the requirements of the Semiconductor industry, Canon has developed two new optical systems. First is an extension of KrF technology, with the introduction of high NA0.73 lens for KrF scanner that will cover the 130 nm device node. Second is the 0.57NA optics for wide field (30 mm square) i-line stepper, to be used cost-effectively on Mix & Match modes. These new generation lenses behave very low aberration. Wavefront is accurately measured by PMI (Phase Measurement Interferometer). At each tuning process, many image performance items are estimated by simulations, and then the results feed back to tuning. Further, not only we make Wavefront RMS minimum, but also each Zernike coefficients are balanced for the various pattern models. So the lens may perform to the level of the industrys requirement. This paper reports the imaging performance; simulation result calculated with final PMI data, and exposed image performance, of the above two new generation optics.

New lens barrel structure utilized on the FPA-6000AS4 and its contribution to the lens performance

In order to respond to the requirements from the semiconductor industry, a projection optics utilizing an ArF laser as the illumination source is being developed. The projection optics equipped on the FPA-6000AS4 has been designed with 0.85 NA and field size is 8 mm X 26 mm. The goal was to achieve an extremely small aberration level in order to satisfy the requirements for the 90nm node patterning device manufacturing. In addition, to achieve this performance, the lens-barrel structures have been redesigned from the conventional barrel type. Thus, it becomes possible to lower the aberrations generated in the lens manufacturing process to the minimum level. We developed the new lens-barrel structure to minimize the stress induced deformation placed on an optical element. This structure, which is called the SP-barrel structure, allows stable lens performance in spite of temperature change and the mechanical impact, compared with earlier structures. Moreover, it has been proven that this structure can reduce the deterioration of the lens performance due to manufacturing errors. This allows the lens performance to closely approach the intentions of the optical design. This report describes the performance enhancements for the FPA-6000AS4 projection optics. In particular, we discuss the lens barrel design, along with exposure test results and wavefront aberration measurement results.