Formation of shallow n+p junctions

Abstract

The effects of preamorphization and rapid thermal annealing (RTA) on the formation of shallow arsenic junctions have been investigated. Single-crystal silicon substrates were preamorphized with a Si+ implant (3.0×1015 ions/cm2 at 60 keV) followed by an As+ implant (1.0×1015 to 1.0×1016 ions/cm2 at 50 keV) through a 200-Å oxide cap. As+implantation into single-crystal silicon was also investigated. RTA and reference furnace anneals were carried out to recrystallize the amorphous layers into single crystals and to activate the arsenic implants. Experimental results have been obtained for amorphous layer characteristics, residual damage, dopant profiles, junction depth, sheet resistance, and carrier concentration. Measurements were made by spreading resistance probe (SRP) and secondary ion mass spectrometry (SIMS) profiling, Rutherford backscattering spectrometry (RBS), and transmission electron microscopy (TEM); a limited amount of junction leakage data was also obtained. Arsenic depth profiles as measured by SIMS, RBS, and SRP are compared. The agreement between the three profiling techniques is fair to good. RTA resulted in junctions with crystal quality and dopant activation similar to those of furnace annealed junctions with less impurity profile broadening. Preamorphization did not result in a significant reduction in the junction depth and inhibited complete removal of extended defects. Two criteria for an acceptable anneal were considered; damage removal was not considered to be as significant as leakage current reduction. An optimum RTA cycle was determined to be 1050 °C for 20 s.