Laser Silicon Interaction Study on Ring Oscillators to Establish Temperature Voltage Dependency Trends on 14 nm and Future FinFET Technologies

Critical speed path analysis using Dynamic Laser Stimulation (DLS) technique has been an indispensable technology used in the Semiconductor IC industry for identifying process defects, design and layout issues that limit product speed performance. Primarily by injecting heat or injecting photocurrent in the active diffusion of the transistors, the laser either slows down or speeds up the switching speed of transistors, thereby affecting the overall speed performance of the chip and revealing the speed limiting/enhancing circuits. However, recently on Qualcomm Technologies’ 14nm FinFET technology SOC product, the 1340nm laser’s heating characteristic revealed a Vt (threshold voltage) improvement behavior at low operating voltages which helped identify process issues on multiple memory array blocks across multiple cores failing for MBIST (Memory Built-in Self-test). In this paper, we explore the innovative approach of using the laser to study Vt shifts in transistors due to process issues. We also study the laser silicon interactions through scanning the 1340nm thermal laser on silicon and observing frequency shifts in a high-speed Ring Oscillator (RO) on 16nm FinFET technology. This revealed the normal and reverse Temperature Dependency Gate voltages for 16nm FinFET, thereby illustrating the dual nature of stimulation (reducing mobility and improving Vt) from a thermal laser. Frequency mapping through Laser Voltage Imaging (LVI) was performed on the Ring Oscillator (RO) using the 1340nm thermal laser, while concurrently stimulating the transistors of the RO. Spatial distribution of stimulation was studied by observing the frequency changes on LVI.