Tai-Chen Kuo, Chao-Yi Lin and Wen-Hsi Lee
The strain engineering of the source/drain has been applied from the N45 till now. When the size of the transistor is reduced continuously, it is necessary to increase the germanium concentration to add more stress, but it reduces boron concentration with increasing the germanium. The use of ion implantation compensates for the boron concentration well, while caused some problems, including ion implantation damage, diffusion, and activation of dopant ions. Therefore, to activate dopants by tuning different Ge content or pre-amorphized implantation. In the meantime, in order to cope with the low-temperature process for Ge, microwave annealing was added to compare with rapid thermal annealing.
In this paper, silicon germanium film covered with Si, Ge and uncovered before ion implantation is investigated. The sample deposit with Ge capping layer undergoes surface loss after annealing, and the Si capping layer can effectively prevent the surface from roughness. Next, the trend of the Boron activation in SiGe alloys with different Ge contents is discussed. The boron activation level increases with the increase of Ge content, but the trend will gradually saturate, and even segregate to cause the device degradation. From 20% to 40% Ge with a dose of B (ISD 3.2 x 1020 cm-2+I/I 3 x 1015 cm-2 and 2 x 1015cm-2, Si0.65Ge0.35 is an optimum value. For dopants activation in SiGe material, the thermal process is dominant, but the influence of SiGe composition is gradually increasing. The control of in-situ doping concentration has become an important issue. Finally, the diffusion and electrical properties of various species pre-amorphized implantation, repair implant damage by microwave annealing and rapid thermal annealing are investigated. Boron distribution, sheet resistance, and mobility were checked to infer the activation level and defect evolution. The best performance is the sample with Ge PAI, and it can effectively enhance the boron activation by microwave annealing while preventing the diffusion.
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