| Summary: | 碩士 === 國立交通大學 === 電子工程系所 === 96 === ABSTRACT
The thermal stability of NiSi/Si structure is one of the important research topics in the nano CMOS area. Several methods have been proposed to improve the thermal stability of NiSi. In this thesis ,a novel method of using Ge ion implantation( Ge I/I) to improve the thermal stability of the NiSi/Si structure is proposed. High quality NiSi-contacted N+P and P+N junctions are fabricated to demonstrate the feasibility of using the Ge I/I technique in nano CMOS process.
Two kinds of Ge I/I schemes are used in this thesis to investigate the influence of Ge on NiSi , the Ge I/I After Silicidation (GIAS) and the Ge I/I Before Silicidation (GIBS). The GIAS scheme retard phase transformation to 850℃ but can not suppress agglomeration , so thermal stability is not improved obviously. The GIBS scheme can raises the phase transformation temperature to 850℃ and the agglomeration temperature to 800℃. These temperatures are 100℃ higher than those for the NiSi/Si structure without Ge I/I. This observation is explained by the stress balance due to high concentration Ge pile-up at the NiSi/Si interface. Transmission electron microscope inspection also reveals that the Ge I/I results in a very smooth NiSi/Si interface.
Applying GIBS scheme to N+P and P+N junctions, although the phase transformation temperature of NiSi is raised, the agglomeration temperature of NiSi in N+P junction is not improved due to the high concentration As dopants. Although the thermal stability of both N+P and P+N junctions can not be improved obviously by Ge I/I, the NiSi/Si interface roughness is improved. This phenomenon should be benefit to ultra-shallow junctions.
Electrical measurement indicates that the Ge I/I junctions exhibit higher leakage current at low temperature. This result is explained by the Ni diffusion and dissolution enhancement due to Ge I/I induced defects. However, acceptable NiSi-contacted N+P and P+N junctions are still obtained. It is suspected that the energy gap of Si is narrowed by the Ge I/I from the activation energy measurement. If it is true , the contact resistance between NiSi and Si could be reduced and is worthy to study furthermore.
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