A KINETIC-STUDY OF REACTIVE ION ETCHING OF TUNGSTEN IN SF6/O2 RF PLASMAS

The reactive ion etching of chemically vapor deposited (CVD) tungsten in SF6/O2 plasma has been investigated by means of optical emission spectroscopy, mass spectrometry, and in situ x-rav photoelectron spectroscopy. This study is particularly focused on the etching Of WO3 over W, a native oxide 34-45 angstrom thick (WO3) always appearing on the CVD tungsten surface. Actinometry measurements show an excess of atomic fluorine and oxygen relative concentrations during the etching of the WO3 layer as compared to that of tungsten. Two etch products of tungsten are detected by mass spectrometry: WF6 and WOF4. In pure SF6 plasma, the main etched product Of WO3 and W is WF6. In SF6/O2 (40/60) plasma, WF6 is the dominant product of the etching of the WO3 layer and WOF4 that of W. In situ XPS analyses show the presence of fluorine, oxygen, and sulfur on the etched tungsten surface. The role of these elements in the formation of the two etch products of tungsten is discussed.