Desorption of Tungsten Fluorides from Tungsten

Abstract

Tungsten hexafluoride adsorbs on tungsten surfaces and reacts to form WFs, which desorbs at about 250 K. At higher temperatures, WEe desorbs. Tungsten fluoride desorption was not affected by co-adsorption of Hz or H20, so production of WF~ appears to be an unavoidable feature of tungsten chemical vapor deposition processes based on WF~. The initial sticking coefficient for WF 6 on tungsten at 240 K is about 10 -~.

Atomic Layer Epitaxy of Tungsten Oxide Films Using Oxyfluorides as Metal Precursors

“…Formation of subfluorides.-The conclusion that WF 6 adsorbs poorly on many oxide surfaces is in agreement with observations in the literature. [10][11][12] This is because there are no chemical bonds available in the WF 6 molecule for interactions with a substrate. Chemisorption can only occur by breaking of a W-F bond, allowing W to interact with the surface.…”

“…A problem, however, is that WF 6 is known to adsorb poorly on oxide surfaces. [10][11][12] The adsorption can be increased by modifying the precursor (e.g., form subfluorides, WF x , x < 6) or by an in situ generation of a modified precursor (e.g., tungsten oxyfluorides, WO x F y ), which can adsorb more easily on an oxide surface. In situ generation of precursors has previously been used in several ALE processes and may offer certain advantages, especially when the sublimation from a solid precursor material is affected by, for example, aging or unwanted chemical reactions during prolonged heating.…”

Thermodynamic Aspects of CVD Crystallization of Refractory Metals and Their Alloys

“…The tungsten coatings have found wide application in thin-film integral circuits when preparing the Ohmic contacts in the production of the silicon-, germanium-, and gallium-arsenide-based Schottky-barrier diodes. The tungsten selective deposition technology is perspective in the production of conducting elements at dielectric substrates [36]. Tungsten films are used for covering hot cathodes, improving their emission characteristics, and as protective coatings for anodes in extra-highpower microwave devices.…”

Real-time growth rate metrology for a tungsten chemical vapor deposition process by acoustic sensing

“…Under the conditions studied here, the response delay between a gas composition change ͑i.e., flow condition͒, change in the reactor, and stabilization of the Composer frequency signal was approximately 100 s. This delay was partially a function of the pumping speed. However, reactions and/or adsorption/desorption from internal surfaces of the reactor chamber and exhaust lines, which are well known in WF 6 -based systems, 25 affected the gas composition detected by the Composer. Similar response-time profiles were ob-served when the same process was analyzed using a differentially pumped closed-ion source residual gas analyzers.…”