Ge Single-Crystal-Island (Ge-SCI) Technique and BEOL Ge FinFET Switch Arrays on Top of Si Circuits for Monolithic 3D Voltage Regulators

A Ge single-crystal-island (Ge-SCI) technique and thus fabricated monolithic 3D back-end of line (BEOL) Ge FinFET were demonstrated for the first time. The Ge-SCI laser crystallization step results in minimal heating of the underlying Si substrate (T<155°C according to thermal simulation) and the Ge circuit fabrication temperature was kept below 400°C. The functionality of the underlying Si standard logic cells and a 19-stage ring oscillator were unaffected by the Ge-SCI FinFET process as required for a monolithic 3D technology. Simulation results of a monolithic 3D voltage regulator (FIVR) shows Ge-SCI FinFET switch achieving 1.6x response time improvement and 36% reduction in voltage droop compared to the same design implemented with BEOL Si FinFETs.