A mechanism for selectivity loss during tungsten CVD

Journal Article · Sun Jan 01 04:00:00 EST 1989 · J. Electrochem. Soc.; (United States)

DOI:https://doi.org/10.1149/1.2096601· OSTI ID:5998563

Creighton, J R

The authors have investigated possible mechanisms for the loss of selectivity (i.e., deposition on silicon dioxide) during tungsten CVD by reduction of tungsten hexafluoride and found strong evidence that selectivity loss is initiated by desorption of tungsten subfluorides formed by the reaction of WF/sub 6/ with metallic tungsten surfaces. Adsorption and disproportionation of the tungsten subfluorides on the silicon dioxide surface produces a reactive state of tungsten that can lead directly to selectivity loss. The key feature of the experimental setup is the ability to independently heat a tungsten foil and a nearby oxide-covered silicon sample in the presence of tungsten hexafluoride. With the tungsten foil at 600/sup 0/C and the SiO/sub 2//Si sample at --30/sup 0/C under a WF/sub 6/ ambient, a tungsten subfluoride was found to deposit on the SiO/sub 2/ surface. Auger electron spectroscopy was used to measure a F/W ratio of 3.7 +- 0.5. Heating this tungsten subfluoride overlayer resulted in disporportionation to yield gas-phase WF/sub 6/ and metallic tungsten which remained on the surface. With the tungsten foil at 600/sup 0/C and the SiO/sub 2//Si sample at 300/sup 0/C in the presence of WF/sub 6/, metallic tungsten deposited directly on the SiO/sub 2/ without stopping at the subfluoride adsorption step. The net effect of this tungsten subfluoride desorption-disproportionation mechanism is the transport of tungsten from tungsten surfaces to silicon dioxide surfaces as well as other regions in the deposition chamber. Extrapolated rates for this process are high enough to explain the magnitude of the selectivity loss seen at normal CVD temperatures.

• Research Organization: Sandia National Labs., Albuquerque, NM (US)
• OSTI ID: 5998563
• Journal Information: J. Electrochem. Soc.; (United States), Journal Name: J. Electrochem. Soc.; (United States) Vol. 136:1; ISSN JESOA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360601* -- Other Materials-- Preparation & Manufacture
360602 -- Other Materials-- Structure & Phase Studies
CHALCOGENIDES
CHEMICAL COATING
CHEMICAL VAPOR DEPOSITION
DEPOSITION
ELEMENTS
EXTRAPOLATION
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
METALS
NUMERICAL SOLUTION
OXIDES
OXYGEN COMPOUNDS
PHASE STUDIES
REFRACTORY METAL COMPOUNDS
SILICON COMPOUNDS
SILICON OXIDES
SURFACE COATING
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
TUNGSTEN
TUNGSTEN COMPOUNDS
TUNGSTEN FLUORIDES