Improving the Quality of Delay-Based PUFs via Optical Proximity Correction

Silicon physically unclonable functions (PUFs) are circuits that exploit modern manufacturing variations to generate unique signatures for chip authentication and cryptographic key generation. Existing research has focused on improving PUF quality at architectural or design levels, but has ignored opportunities available during fabrication, which is the source of systematic and random variation in (ICs)/PUFs. For typical ICs (where security is not a concern), optical proximity correction (OPC) is used to suppress both these types of variations. However, several prior works have shown that only systematic variations negatively impact PUF quality and random variations are beneficial for PUFs. In this paper, we propose two PUF-aware OPC cost functions: 1) P-OPC generates a PUF lithography mask that increases all variations in PUF circuitry (the opposite of state-of-the-art OPC), and 2) SVC-OPC generates mask patterns that reduce the systematic variation found in PUFs for better quality. Simulation results for ring oscillator (RO) PUFs show that the proposed techniques can improve PUF signature quality compared to current state-of-the-art OPC.