Low-temperature dopant activation using nanosecond ultra-violet laser annealing for monolithic 3D integration

Nanosecond ultra-violet (UV) laser annealing was introduced to overcome the thermal degradation of the bottom layer device during top layer device junction formation in monolithic 3D integration. A simulation was performed to predict the thermal effects and the temperature distribution of the top and bottom layers during laser annealing. The dopant distribution, surface morphology, and crystallinity were characterized after laser annealing. The electrical properties were identified from the sheet resistance and current-voltage characteristics. A single crystal silicon phase was observed after applying top-hat shaped single pulse UV laser with the optimal fluence of 1.4 J/cm2. With a much lower thermal budget, the laser-annealed junction achieved an abrupt doping profile and low sheet resistance and low leakage current that were comparable to rapid thermal annealing or solid-phase epitaxial regrowth.