| Summary: | 碩士 === 國立交通大學 === 電子工程系 === 88 === This thesis studies the characterization of ultra-shallow junctions with different formation methods and the material characterization of CoSi2 with Ti-capped staked structure. As the dimension scales down, the short channel effects become more serious. The formation of ultra-shallow junctions is essential to minimizing the punch-through and short channel effects. This thesis presents a method to fabricate ultra-shallow junctions that combine the merits of ion implantation and diffusion. Specifically, in the diffusion from implanted oxide (DIO) method, low energy ion implantation is used to highly dose a very thin screening oxide. In a subsequent RTP step, the dopants then diffuse into the underlying silicon, and ultra-shallow junctions are formed. Leakage current density of the resultant p＋n junction is found to be less than 0.2 nA/cm2 and junction depth is 0.0375μm.
In addition to DIO, Si pre-amorphization ion implantation（PAI）, and the low energy ion implantation（LEI） are also tried to form p＋n ultra-shallow junctions. However, both of these methods have more than two orders of reverse junction leakage current than DIO. This is because that ion implantation produces more defects. The junction depths for LEI are 0.07μm because TED, oxide enhanced diffusion, larger boron concentration gradient, energy contamination and channeling effect. The junctions depths for PAI are only 0.05μm, because pre-amorphization can mitigate diffusion speed and channeling effect.
CoSi2 is a promising alternative for TiSi2. Ti-capped CoSi2 have been found to depict wider RTA process window, better thermal stability, and smaller reverse junction leakage, compared to the conventional COSi2. This is because Ti atom can reduce native oxide between cobalt and silicon and diffuse into grain boundary of CoSi2 to retard the agglomeration.
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