Fabrication of SIMOX Wafers by Plasma Immersion Ion Implantation

Separation by implantation of oxygen (SIMOX) is an attractive approach to fabricate silicon-on-insulator (SOI) materials for radiation hardened electronic devices and high speed CMOS circuits. However, the cost is high for materials prepared by the conventional beamline ion implantation method. The novel technique of plasma immersion ion implantation (PIII) emulates the traditional technique in many aspects. Some of the advantages are: no mass selection, no beam transport optics, large area implantation, high ion flux, short implantation time, and low costs. In PIII, the silicon substrate is immersed in an electron cyclotron resonance (ECR) plasma from which oxygen ions are drawn onto the silicon surface by a negative DC bias. The space charge region between the plasma and the negatively biased silicon substrate can sustain a potential difference of up to tens of keV. DC oxygen implantation (nominal dose: 5 x 10¹⁷ atoms/cm²) was carried out in the sub-mtorr operating pressure regime. Thin SIMOX structures with a Si overlayer thickness of 20 to 50 nm and a buried oxide layer thickness of 20 to 50nm were fabricated in about 5 minutes. The implanted wafers were capped with an oide layer and subsequently annealed for 6 hours at 1300ºC in argon ambient to remove the damages. The resulting wafers were analyzed using a variety of techniques, including RBS and XTEM.