High performance 20nm-node PCRAM cell switching was successfully realized with the remarkable I on /I off characteristics employing low aspect ratio poly PN diode on metal. Nice I on /I off ratio was obtained by modifying stack of diode adopted in-situ boron-doped poly SiGe and thermal optimization with spike RTA. Basically, boron has high solubility and activation rate in SiGe matrix. In-situ boron-doped poly SiGe on P+ region is expected to contribute to P+ R c improvement. In this study, we found the unusual phenomenon that thermal process after pillar patterning does not influence dopant diffusion due mainly to isotropic thermal behavior. It means that RTA process before pillar patterning will be more effective for doping profile and activation engineering. By applying spike RTA and in-situ boron-doped poly SiGe on diode, P+ R c was not degraded despite of skipping additional P+ADD IMP and P+ ADD RTA process. As a result, I on and I off of 393uA/cell on the 2.8V and 92pA/cell on the -3.5V at 75°C were achieved at height of diode down to 1000Å.