Fabrication Of High Performance Germanium Devices Using Spin-on Dopant And Laser Annealing

With the continued device scaling to its physical limitation following the Moore's law,it would not be feasible to improve device performance by decreasing the gate length.So the introduction of new materials,structures,processes and theories is compulsory for developing the integrated circuit(IC)technology.Germanium,in the same element group of silicon,is a promising new material candidate for the future semiconductor industry because of its high carrier mobility.So we choose Germanium as the subject for discussion and device preparation in this research work.Two well-developed doping techniques in integrated circuits were gaseous heat diffusion and ion implantation.Both have its limitations in forming the ultra-shallow doped junction which is necessary for the 3-D Germanium devices.However,we found that the spin-on dopant(SOD)technique is more feasible in the application of ultra-shallow-junction for Ge devices..We first introduced the fundamentals of SOD and the basic process flow of the SOD technique.The selection of the suitable doping element in SOD is based on the properties of Germanium and the compatibility with the CMOS IC fabrications.Then the laser annealing,instead of furnace annealing or rapid thermal annealing(RTA),is used to improve the doping profile.This improvement of the laser annealing over the thermal annealing(RTA/furnace annealing)has been confirmed by a model based on the first principle of the diffusion.A p-n junction was realized by SOD and the laser annealing.The samples show normal performance of p-n junction,and the on-off ratio of the laser annealed sample was an order of magnitude larger than that by the thermal-annealing.C-V measurement of the p-n junction also shows that the junction depth by the laser annealing is for small than that by the normal thermal annealing.This work demonstrates that the laser annealing can improve the p-n junctions' performance.After the successful fabrication of the p-n junction,the SOD technique was introduced to the Germanium MOSFET process.The devices by the first trial run already show certain gate voltage control over the channel conductivity,i.e.,laser annealing after the SOD is suitable for the Ge MOSFET.Possible problems were analyzed and the suggestion for improving the MOSFET performance were proposed.