Summer02 exposing scaam

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Exposing the SCAAM Theory, Characterization, and Confirmation of the Validity of an Innovative Optical Extension Technique Marc D. Levenson, M.D. Levenson Consulting, Takeaki (Joe) Ebihara, Canon USA Inc., Sunil Desai and Sylvia White, KLA-Tencor Corporation

The Sidewall Chrome Alternating Aperture Mask (SCAAM), a next generation alternating Phase Shift Mask (altPSM) structure, has printed 75 nm semi-dense lines (220 nm pitch) without characteristic PSM anomalies, thus offering the potential for sub-100 nm imaging with 248 nm light. The even-lower-cost Phase Phirst! paradigm would employ ready-to-write SCAAM blanks with pre-patterned surface topography, chrome and resist, eliminating the cost of writing a custom phase pattern on every plate. Circuit designers, however, would have to place every minimum-sized circuit feature at a predefined phase-step location. This system is economically superior to other advanced lithography schemes when standard pre-patterned substrates can be mass-produced using wafer fab techniques, which requires standardization of design grids. Using a conventional or attenuated phase-shift trim mask in a two-exposure lithography scheme facilitates arbitrary interconnections.

It has long been known that alternating aperture phase-shifting masks (alt-PSMs) can project images with pitches down to 0.5位/NA (about 170 nm for 248 nm light) and almost unlimitedly small dark lines. (The current record is 9 nm1) and low CD variation. However, widespread implementation of alt-PSM technology has been delayed by various challenges, including imaging artifacts and the high cost of production-quality reticles. By addressing the manufacturability issues of alt-PSMs, we have found a mask structure and production technology that realizes the full theoretical resolution and CD control potentials of these reticles and promises low cost implementation.2 Low cost is important, as roughly half of all reticles are used for chip designs that have production runs under 600 wafers.3 In such

short production runs, the reticle cost already dominates all other factors at 250 nm and the high projected cost of sub-100 nm reticles cannot be borne by this industry segment. The Phase Phirst! PSM paradigm discussed here can result in lower overall cost of production for chips with wafer runs of one thousand 200 mm-equivalent and below. However, certain chip-design constraints are necessary to achieve the necessary economies of scale, and it has proved difficult to interest the design community in implementing these design rules. The key innovation is the Sidewall Chrome Alternating Aperture Mask (SCAA mask or SCAAM), a next generation alternating Phase Shift Mask (alt-PSM) structure shown in Figure 1(a).2, 4 The SCAAM process etches the phase topography first and then sputters an opaque chrome layer over the phase layer, finally coating with resist. A second write step then forms transparent openings in the conformal chrome layer to define the image. The great optical advantage of this structure is that the physical environment is the same for all Summer 2002

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