Formation and Electrical Properties of Buried Oxide Layers in Thin Simox Materials

Abstract

The effects of implantation conditions and annealing conditions on the formation of buried oxide layers in the low-dose low-energy SIMOX materials were investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance spectroscopy (EPR). The electrical properties of the buried oxide layers were investigated using current-voltage (I-V) and capacitance-voltage (C-V) measurements.The distribution of oxygen and defects in the as-implanted materials due to the implantation conditions (oxygen dose and energy) had significant effects on the formation of the buried oxide layer in low-dose low-energy SIMOX substrates. Multiply faulted defects (MFDs) and small oxide precipitates were observed in the projection range (Rp) in as-implanted samples. As increasing the dose, the mixture of silicon and oxide (silicon striations) also formed around Rp. The locations and shapes of the silicon striations control the density and size of silicon islands in the fully-annealed SIMOX at 1350oC.Upon annealing, the buried oxide layers become stoichiometric. Also, different domains including round, square, and pyramid shapes with the step-terrace structure were observed at the top silicon and buried oxide interface. Round domains are observed in the early stage of the annealing process, while the square and pyramid domains are observed after the high temperature annealing. The mean RMS roughness decreases with increasing time and annealing temperature and decreases with either increasing the implantation dose or decreasing implantation energy. Qualitative mechanisms of Si-SiO2 surface flattening are presented in terms of the variations of morphological features with the processing conditions.In the fully-annealed SIMOX wafers, the silicon pipes and silicon islands were observed in the sample implanted with the dose below 3.0×1017 O+/cm2 and above 3.5×1017 O+/cm2, respectively for the samples implanted at 100 keV. The presence of silicon pipes and islands degrades the quality of the buried oxide layer by reducing the breakdown field strength. It was found that proper annealing ambient and ramping rates would allow the formation of the buried oxide layer containing no silicon island. By controlling the oxygen content in the ambient, the growth of the buried oxide can be enhanced.