Feasibility of logic metal scaling with 0.55NA EUV single patterning

Abstract

By adopting the new design of the optics within the scanner, high-NA (0.55NA) EUV lithography enables higher resolution, which will push the EUV single patterning down to pitch 16nm (k1=0.34, the same k1 value as pitch 28nm for 0.33NA EUV single patterning). Therefore, 0.55NA EUVL is projected to print the most critical features of 2nm node (and beyond) logic chips with less patterning steps than 0.33NA EUVL, and is highly expected by the industry. Besides, novel low-n low-k absorber attenuated phase shift masks (low-n attPSMs) are commercially available recently, which have shown substantial imaging, as well as patterning performance improvements both in simulations and experiments. Thus, in this paper, we evaluate the feasibility and limits of logic metal scaling with 0.55NA EUV single pattering using source mask optimization tool, both binary and low-n attPSMs are used to pattern an imec N3 (pitch 28nm, foundry N2 equivalent) random logic metal design and the linear scaled versions (down to pitch 18nm). The impact of design orientations (horizontal vs. vertical) and mask tones (dark field vs. bright field) on patterning fidelity and overall process window is evaluated.

High-NA benefit assessment through Zeiss AIMS EUV for tip-to-tip patterning by EUVL

“…In more detail, some further comparison results, as obtained, show that horizontal orientation provides larger NILSCD than V for 0.55NA (as noted in Ref. [7] for smaller pitch), yet here with an exception found for 0.55 Ta LF. Our results show this also for 0.33 NA, where such is less expected: The magnification for the pitch (of horizontal orientation) is the same (unlike for 0.55NA) and horizontal lines in the center of the slit are maximally shadowed.…”

“…Fig. 1 (left panel) illustrates the opportunity of single patterning through high-NA EUVL by means of a representative test clip [7] of the Metal2 (M2) patterning layer for random logic. From an M2 pitch of about 28nm onwards such is considered a relevant layer to be realized by high-NA single print.…”

“…So far, it is rather through simulations [7] that the advantage of high-NA lithography for near future node M2-representative layouts was first studied. The study also included linearly down-scaled versions of the pattern clip shown in Fig.…”

“…An earlier study [8] for vertical orientation and limited to 0.33NA, had identified lightfield patterning with a low-n mask as the best option. The newer study [7] was mainly geared towards assessment of the advantages of high-NA. Beyond a variation of NA, the latter included mask tonality, pattern orientation and mask absorber type, hence respectively comparing 0.33/0.55NA, darkfield/lightfield (DF/LF), horizontal/vertical (H/V) and Ta-based/low-n absorber.…”

OPC and modeling solution towards 0.55NA EUV stitching

“…4 According to Rayleigh criterion (half-pitch=k 1 λ/N A, λ is the wavelength), the 0.55NA EUVL enables EUV single patterning down to pitch 16nm at technology factor k 1 =0.34, compared to pitch 28nm EUV single patterning by using 0.33NA EUVL with the same k 1 value. 5,6 However, due to 8× demagnifcation in y-direction and the unchanged six-inch square reticle, only half-field can be printed with single exposure. Thus, for the applications requiring larger than half-field size, in-die stitching between two exposures is needed.…”