On improving the uniqueness of silicon-based physically unclonable functions via Optical Proximity Correction

Physically Unclonable Functions (PUFs) are effective for security applications because they generate unique signatures that are resistant to cloning attempts as well as physical tampering. A silicon PUF is a special circuit embedded in an IC that relies on random fabrication process variations to produce a unique signature for its native IC. While current research directions have focused on improving PUF quality at the architectural level, little work has explicitly targeted their fundamental source of randomness, the fabrication process. During IC fabrication, Optical Proximity Correction (OPC) is typically used to suppress manufacturing variations. In this paper, we recognize that this is actually counterintuitive for PUFs. We provide a novel framework which enables OPC to increase the effects of manufacturing variations within PUF circuitry and produce more randomness in PUFs for greater uniqueness and reliability. The proposed OPC techniques are validated using a population of 100 ring oscillator PUFs. Results show that our schemes provide over five times larger variation in ring oscillator delay, improve PUF uniqueness by 5%, and improve PUF reliability by as much as 70% when compared to conventional OPC.