Ion-implantation-induced fluorine agglomeration in tungsten disilicide prepared by low-pressure chemical vapour deposition
Boron and antimony were implanted in tungsten disilicide/silicon structures. The silicide films with a Si/ ratio of 2.3 were prepared by low pressure chemical vapour deposition (LPCVD) from a mixture of WF 6 and SiH 4. The films were subsequently annealed at 1000° C prior to implantation. The effect of implantation and subsequent heat treatments on the distribution of fluorine have been investigated by means of transmission electron microscopy (TEM), secondary ion mass spectroscopy (SIMS) as well as the nuclear resonance broadening technique using the reaction 19F(p, αγ) 16O. After implantation with 5 × 10 14 150 keV 121Sb + ions cm[su-2] the fluorine depth distribution was bimodal with one peak located about the silicide/silicon interface and a second peak at a depth corresponding approximately to the limit of the implant range distribution. This is also the position in the film where TEM revealed the presence of a large number of voids. The same observations were made in samples implanted with 11B. Some of the fluorine is lost from the implantation-induced peak after heat treatment at 300° C for 30 min, yet most of the fluorine remains even after annealing at 900° C. The overall picture is not substantially modified by raising the substrate temperature during implantation to 400° C.