This paper takes a look at the evolution of lithography during the last 50 years and projects its future beyond the era of Next Generation Lithography (NGL). The technologies beyond NGL will require a paradigm shift from the way things are done today. Many new disciplines and processes will emerge that will need to be integrated into existing systems and procedures.
Mask making in the coming years will face major challenges. Feature measurements in the mask will no longer be restricted to 2D but will require information on the third dimension as well. High precision AFMs will be needed not only for measuring feature dimensions but also as a diagnostic tool for the fabrication of high quality masks.
As the industry moves into the next millennium it faces new challenges that are not only in the fabrication of the sub- 150 nm features but also in the ability to measure those features. The focus of this paper is not as much on the building of machines to measure those small features but rather on the methodologies of interpreting and handling of data and developing intelligence for identifying the edge- positions that have significant contribution on the value of the critical dimensions or CDs.
The AIMS Tool, manufactured by the Zeiss of Jena, Germany, is a unique combination of sophisticated optics and ingenious software designed to simulate the image of mask pattern as it would be created by a stepper on its wafer plane. This paper reviews some of the machine' capabilities and potentials, and shows its role in complementing the state of the art metrology tools. Most importantly, the paper explores ways of enhancing the productivity and utilization of the tool by strong participation of the newly formed AIMS Tool User's Group.
One method for making the alternating phase-shift mask involves cutting a trench into the quartz of the mask using an anisotropic dry etch, followed by an isotropic etch to move the corners of the trench underneath the chrome to minimize problems caused by diffraction at the bottom corners of the phase-trench. This manufacturing method makes the addition of subresolution scattering bars and serifs problematic, because the amount of the undercut causes chrome lifting of these small features. Adding an additional anisotropically etched trench to both cut and uncut regions is helpful, but the etch does not move the trench corners under the chrome and result in a loss to intensity and image contrast. At 248 nm illumination and 4X magnification, our work shows that a combination of 240 nm dual-trench and 5 nm to 10 nm undercut produces images with equal intensity between shifted and unshifted regions without loss of image contrasts. This paper demonstrates optical proximity correction for doing 100 nm, 120 nm, 140 nm and 180 nm lines of varying pitch for a simple alternating phase-shift mask, with no dual-trench or undercut. Then the electromagnetic field simulator, TEMPEST, is used to find the best combination of dual-trench depth and amount of undercut for an alternating phase-shift mask. Phase measurement using 248 nm light and depth measurement of thirty-six unique combinations of dual-trench and phase-shift trench are shown. Based on modeling and experimental results, recommendations for making a fine tuned dual-trench 248 nm mask, as well as an extension of the dual-trench alternating phase-shift technique to 193 nm lithography, are made.
This paper presents a review and critique on the 1997 edition of the National Technology Roadmap for Semiconductors. The '97 roadmap provides more details and is more comprehensive than the 94-roadmap in many ways. However, there are areas where even more details and better definitions of terminologies are needed. This is especially important when one has to make comparative evaluations among the new generation of lithographic machines based upon their specification. There are also questions of the extent to which lithography could be and should be pushed in order to achieve smaller features; since at some stage the smaller features may reach their point of diminishing return due to RC delays in interconnects. The question is then what challenges lithography will face at 0.01 micrometers nodes and beyond.
Continued demands on shrinking features with tighter tolerance on Critical Dimensions (CDs) and overlays are placing stringent requirements on parameters that are essentially the building blocks of the metrologies for CDs and overlays. This paper conducts a reality check on the precision and error budgets assigned to CD and overlay controls by the National Technology Roadmap for Semiconductors in light of constraints on parameters that are fundamental to the above measurements.
Continued demands on shrinking features with tighter tolerance on critical dimensions (CDs) and overlays (OL) are placing stringent requirements on parameters that are essentially the building blocks of the metrologies for CDs and overlays. This paper conducts a reality check on the precision and error budgets assigned to CD and overlay controls by the National Technology Roadmap for Semiconductors (NTRS) in light of constraints on parameters that are fundamental to the above measurements.
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