Control of the buried SiO 2 layer thickness and Si defect density in SIMOX substrates — structural investigation and process optimisation

Abstract

The microstructure of SIMOX structures implanted at 200 keV with doses between 0.55 × 10 18 O +/cm 2 and 1.8 × 10 18 O +/cm 2, as-implanted and annealed in N 2 or Ar + 1 2% O 2 , have been investigated by TEM, SIMS and RBS. Structur buried oxide layers thicknesses from 100 to 420 nm, Si layer thicknesses from 250 to 430 nm and threading dislocation densities from < 10 5/cm 2 to 10 8/cm 2 have been formed. The presence of damage at the wafer surface after implantation is critical role in determining the threading dislocation density after annealing. The influence of background heating compared to beam only heating upon the as-implanted and annealed microstructure along with the two different anneal treatments are discussed. The experimentally determined values of layer thicknesses and critical doses are compared with values calculated from two process models and processing conditions to produce SIMOX substrates with a low dislocation density (< 10 5/cm 2) and a thin continuous oxide layer are identified. It is found that the optimum dose is close to the minimum dose that forms a continuous buried layer after annealing.