Improving the Security of Split Manufacturing Using a Novel BEOL Signal Selection Method

Split manufacturing of integrated circuits (IC) was proposed as a possible defense against security issues arising from the use of potentially untrusted foundries. However, split manufactured designs were shown to be vulnerable to a new form of attack known as the proximity attack which attempts to reverse engineer the BEOL (Back End of Line) signals. Hence, care must be exercised in identifying the BEOL signals and their placement and routing. In this paper, we present a secure BEOL signal selection algorithm to defeat proximity attacks. Our method is based on two novel features: First, we introduce a new metric for signal selection based on the effect each signal has on the outputs. Second, we use a multiway partitioning algorithm to find a 'secure' cut-set which is the set of signals assigned to the BEOL layers. Our approach increases the number of BEOL nets while minimizing the impact on performance. We present experimental results which show significant improvement in security (on average by 800%) with only a modest effect on performance (less than 4% on average).