The Diffusion of Cu Through Si and Gettering at Ion Damaged Surface Layers in the Presence of O

Abstract

The diffusion of Cu through silicon and gettering at ion damaged surface layers in the presence of oxygen annealing atmospheres have been studied using the Rutherford backscattering of ⁴He ions. Very high levels of gettered Cu, ~10¹⁷/cm², are observed for the following experimental conditions: 1) high implantation damage levels ~10¹⁶(100 keV)Si/cm², 2) oxygen concentrations in the annealing atmosphere of ~10%, 3) “infinite source” of Cu (from a 1000 A evaporated Cu film on the back of the 200 μm wafers) and 4) annealing temperatures ~ 900°C and times of 30 minutes. Spatially associated with this giant gettering of Cu are even higher levels of O (~10¹⁸/cm²). The giant gettering complex of Cu and O extends some 5000 Å into the silicon, well beyond the implantation damage layer thickness of 1000 Å. Comparable experiments for the damage gettering of Au showed no dependence on oxygen in the annealing atmosphere. Damage gettering measurements have also been carried out on wafers saturated with Cu to the solubility limit at elevated temperatures. Oxygen is seen to enhance the gettering of Cu in the damage layers.

The behaviour of the evaporated Cu films under the various annealing conditions has been investigated for the purpose of preparing the infinite source. Cu films annealed in N₂ at 500°C form a Cu₃Si alloy which, upon further heating at 900°C in O₂, act as an infinite source of Cu. In contrast to this, Cu films heated directly at 900°C in O₂ are oxidized to such an extent that little Cu is available for diffusion. These source conditions and the appearance of giant gettering have been correlated.