A MECHANISM OF THE SIDEWALL PROCESS INDUCED JUNCTION LEAKAGE CURRENT OF LDD STRUCTURE

In MOSFETs with lightly doped drain (LDD) sidewall spacers, drain-to-substrate leakage is caused by the crystalline defects at the sidewall edge. To clarify the mechanism of the defect generation, the recrystallization process after high-concentration As+ implantation was observed by means of cross-sectional TEM with in situ annealing. During the heating process, solid phase epitaxial regrowth did not proceed in the lateral direction at the Si surface of the sidewall edge and the defects were pinning there. However, during a subsequent quick cooling period, the crystalline defects grew to a high degree in the (111) direction at the sidewall edge. When the recrystallization was performed without the sidewall, the defects are not generated. From these results, it was determined that the stress from the sidewall contributes greatly to the defects growth. The crystalline defects at the sidewall edge can be suppressed by fabricating a smoothly shaped sidewall that decreases stress, so that stable drain-to-substrate properties can be obtained.