Rapid thermal annealing effects on the properties of plasma-enhanced chemical vapor deposited tungsten films

Abstract

Tungsten films have been deposited onto single-crystal silicon (Si) and silicon dioxide (SiO2) by plasma-enhanced chemical vapor deposition with WF6-SiH4-H2 chemistry: the annealing effect on these films has been investigated by rapid thermal annealing. The deposition rate of the tungsten films on both sides of Si and SiO2 is linearly dependent on the SiH4/WF6 ratio up to 1 and the deposition rate is not increased beyond this ratio (SiH4/WF6=1). Phase transition from α-W to β-W and silicidation are observed under the annealing at 900 °C for 15 s in W films on Si. On the other hand, resistivities of W films on SiO2 are decreased under the same annealing condition. The resistivity reduction in W films on SiO2 is believed to be the results of the grain growth and point, line defect removal, and out-diffusion of impurity atoms such as oxygen, fluorine, and silicon. In addition to this grain growth, the intensities of x-ray diffraction peaks are increased after the rapid thermal annealing. Etching process of the tungsten layer has been performed with a reactive ion etcher using CF4-O2 etchant. The etch rate of the as-deposited tungsten film is about 7800 Å/min, and decreases with increase of annealing temperature to about 4600 Å/min for the tungsten films annealed at 1000 °C for 15 s. This decrease in etch rate is believed to be caused by the decreases of the absorption site for etching sources due to grain growth and defect removal.