An overview of on-chip interconnect variation

ABSTRACT

On each manufactured chip, every wire and via is a little bit different. Most of this variation is accounted for by chip-to-chip, wafer-to-wafer, and lot-to-lot variation. These make chips different from each other, but affect all features on the same chip in the same way. These models predict, for example, that the thickness of a given metal layer may vary considerably, but on a single chip all wires on the same layer are the same thickness. However, there is also on-chip (also called intra-chip, or cross-chip) variation, causing even nominally identical wires and vias on the same chip to differ from each other. This survey looks at some of the physical reasons behind these differences (such as lithography, etching, polishing, alignment, and gradients), how these differences are currently treated by fabs, tools, and designers (in a very ad-hoc manner), and how this topic might be addressed in the future.

INDEX TERMS

Primary Classification:
  J. Computer Applications
  J.6 COMPUTER-AIDED ENGINEERING
      Subjects: Computer-aided design (CAD)

General Terms:
Design, Performance, Verification

Keywords:
causes of variability, design rules, on-chip variation