High dose rate effects in silicon by plasma source ion implantation

Abstract

An investigation of high dose rate effects in silicon subsurface morphology has been performed. The unique capability of plasma source ion implantation to operate in the high current/low energy regime, where the near-surface structure can be effectively controlled, has been studied. At an ion energy of ∼40 keV and an estimated dose of 1×1015 cm−2 Ar ions were implanted at various instantaneous dose rates (0.75–8.3 mA/cm2) and two different pulse widths (25–50 μs) into 2 in. diam silicon wafers at a constant repetition rate of 10 Hz. The irradiation damage to the wafers’ structures was characterized by Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). A visual observation indicated amorphization of the silicon at 0.75 mA/cm2, but not at 8.3 mA/cm2. The transition from the crystalline-to-amorphous phase was confirmed by TEM electron diffraction studies. RBS data, however, indicated there was a large discrepancy in the total dose retained between the high dose rate (8.3 mA/cm2) and the low dose rate (0.75 mA/cm2). Two simulation methods for the substrate temperature profile have been compared to predict the profile. A comparison of the fraction of irradiation damage from the RBS data indicated that the substrate heating effects are more dominant then the dose rate effects. Improved methods of cooling the wafer are presently being investigated.