Optical lens specifications from the user's perspective

Abstract

We develop three main topics in support of further understanding and specifying wavefront aberrations from the lithographer's point of view. The concept of the Magnitude Weighted Aberration is introduced providing a convenient and rapid numerical method for assessing the interaction of wavefront aberrations with reticle pattern and illumination mode. This analysis suggests that the advanced lithographic lens user will require unprecedented correction on the total wavefront aberration to realize the full potential of the imaging system in high yielding integrated circuit fabrication. Specific details on the required aberration control are provided with a Monte Carlo tolerancing analysis of the RMS wavefront error using lithographic CD control and pattern placement as quality metrics. Pattern placement proves to be as sensitive to wavefront aberrations as CD control forcing a tight specification on the asymmetric aberration components even when a large focus and exposure latitude is available. Based on the wavefront specifications generated, it is imperative that the lithographic lens user be able to independently de-couple and quantify the state of certain aberration coefficients. Toward this goal, we demonstrate an aberration reverse engineering procedure using experimental pattern placement error as the input response.

Image placement error: closing the gap between overlay and imaging

“…Since lens aberrations vary as a function of slit position, and the diffraction spectrum in the lens pupil changes with pattern pitch and orientation, the final image placement error becomes a function of these three parameters. 12 To illustrate this, consider the x coma Z7 lens aberration in Fig. 1͑a͒, and the diffraction spectrum in Fig.…”

Aberration optimizing system using Zernike sensitivity method

“…Here, the mask parameter includes pattern shape and size, and optical parameter includes projection lens NA and illumination condition, and the wavefront aberration can be developed into Zernike terms. Due to the dependency of error sensitivity on optical parameter, mask parameter and each Zernike term, there are some imaging issue in which the imaging performance of actual device pattern is out of tolerance despite the imaging performance of standard specification is within the specification 2) . Currently, we know these phenomena are due to the impact of high order wavefront aberration, and for the moment, special lens tuning is required for each applications, because the high order wavefront is difficult to control without re-assemble of the lens.…”

Critical evaluation of photomask needs for competing 65-nm node RET options

“…For many years, the exposure tool community leveraged advanced metrology methods tied to simulation and modeling techniques for understanding tool error sources and their associated impact to the printed image [11,12,13]. Through this detailed understanding of exposure system defects, many critical problems have been resolved and exposure tooling is now on a path to be fully enabled for extreme low k imaging.…”