Microstructural evolution of low-dose separation by implanted oxygen materials implanted at 65 and 100 keV

Abstract

Thin separation by implanted oxygen substrates are attractive candidates for low-power, low-voltage electronic devices and can be obtained by low-dose, low-energy oxygen–ion implantation. We report in this study a variation of the process parameters that have never been investigated before, particularly for implantation with a high current density implanter. Characterization of the sample sets by transmission electron microscopy, secondary ion mass spectroscopy (SIMS), and Rutherford backscattering spectrometry (RBS) shows an optimum dose of 3.0 to 3.5 × 10¹⁷ O⁺/cm² at 100 keV for forming a continuous buried oxide (BOX) layer compared to 2.5 × 10¹⁷ O⁺/cm² at 65 keV. At this optimum condition for 100 keV, the thickness of Si top layers and BOX layers is in the range of 175–185 nm and 70–80 nm, respectively. Analysis of the breakdown voltage of small area capacitors shows a breakdown field in the range of 6.0–7.0 MV/cm, which is adequate for low-power, low-voltage devices. SIMS analysis shows that the maximum oxygen concentration of as-implanted samples is located at depths of 160 and 240 nm for the implantation energy of 65 and 100 keV, respectively. A significant redistribution of oxygen occurs at temperatures above 1300 °C during the ramping process. RBS analysis showed that a high-quality crystalline Si layer was produced after annealing at 1350 °C for 4 h. The defect density determined by the chemical etching method was found to be very low (<300 defects per cm2) for all samples with a dose range of 3.0 × 10¹⁷ O⁺/cm² to 6.0 × 10¹⁷ O⁺/cm² implanted at 100 keV. However, a 65 keV sample with a dose of 4.5 × 10¹⁷ O⁺/cm² contains about 10⁹ defects per cm². The larger defect density in the 65-keV sample may be due to the shift of oxygen depth distribution toward the surface, resulting in easier defect extension during the annealing process. The oxide precipitates in the Si overlayer play a key role in defect reduction by blocking the extension of dislocations to the surface.