Deposition of tungsten by plasma enhanced chemical vapour deposition

Abstract
The standard method of depositing tungsten is by LPCVD using SiH₄-H₂-WF₆ chemistry at temperatures of >300°C. This work has studied the use of PECVD with H₂-WF₆ for tungsten deposition. It was found that at deposition temperatures below 200°C, the layers are polycrystalline beta phase tungsten, resistivity 50µΩcm. Annealing at 900°C decreases the resistivity to 10µΩcm. The tungsten layers deposited at 200°C and above are of the alpha phase and exhibit an as deposited resistivity of 15µΩcm for 150nm layers. For the layers deposited on titanium at T>300°C the initial deposition is dominated by the reduction of WF₆ by the titanium until a self limiting thickness is produced. This results in titanium fluoride species being incorporated at the titanium-tungsten interface.