Lithography-Induced Limits to Scaling of Design Quality

Quality and value of an IC product are functions of power, performance, area, cost and reliability. The forthcoming 2013 ITRS roadmap observes that while manufacturers continue to enable potential Moore’s Law scaling of layout densities, the “realizable” scaling in competitive products has for some years been significantly less. In this paper, we consider aspects of the question, “To what extent should this scaling gap be blamed on lithography?” Non-ideal scaling of layout densities has been attributed to (i) layout restrictions associated with multi-patterning technologies (SADP, LELE, LELELE), as well as (ii) various ground rule and layout style choices that stem from misalignment, reliability, variability, device architecture, and electrical performance vs. power constraints. Certain impacts seem obvious, e.g., loss of 2D flexibility and new line-end placement constraints with SADP, or algorithmically intractable layout stitching and mask coloring formulations with LELELE. However, these impacts may well be outweighed by weaknesses in design methodology and tooling. Arguably, the industry has entered a new era in which many new factors – (i) standard-cell library architecture, and layout guardbanding for automated place-and-route; (ii) performance model guardbanding and signoff analyses; (iii) physical design and manufacturing handoff algorithms spanning detailed placement and routing, stitching and RET; and (iv) reliability guardbanding – all contribute, hand in hand with lithography, to a newly-identified “design capability gap”. How specific aspects of process and design enablements limit the scaling of design quality is a fundamental question whose answer must guide future R&D investment at the design-manufacturing interface.