Step Coverage and Material Properties of CVD Titanium Nitride Films from TDMAT and TDEAT Organic Precursors
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Titanium nitride (TiN) films serve an important function as an adhesion layer and diffusion barrier in contact and via plug structures of ULSI devices. In this work., TiN films were deposited by chemical vapor deposition (CVD) at atmospheric pressure using the tetrakis (dimethylamido) titanium (TDMAT) and tetrakis (diethylamido) titanium (TDEAT) organic precursors over a range of temperatures and ammonia partial pressures. The step coverage and morphology of these films was evaluated at these various conditions by SEM of cross-sectioned contacts. In addition, material properties such as resistivity. surface roughness, and stoichiometry were assessed at some of the operating conditions.
Introduction Chemical Vapor Deposition (CVD) of titanium nitride (TiN) films produces more conformal films in contact and via structures than those deposited by the current technology of Physical Vapor Deposition (PVD). Chlorine-free titanium nitrides can be produced at relatively low temperatures (less than 400 0C) by CVD using metal-organic compounds. CVD TiN from two of these compounds, TDMAT and TDEAT, is currently being developed for commercial application. In this work, CVD films deposited from both these precursors were evaluated.
Experimental Films were deposited at atmospheric pressure in a prototype belt furnace from the WatkinsJohnson Company, model WJ-956. An inconel mesh belt, heated from below, delivered substrates to the deposition zone at 190-480 TC. Reactant gases were injected perpendicular to the substrates through three nozzles located approximately 3 mm above the
substrate. Diluted NH 3 passed through the center nozzle, and diluted metal-organic precursor vapor passed through the adjacent outer nozzles. Laminar flow conditions were used (Reynolds number < 30), though some turbulent mixing occurred near the inlets when dilution flows were too high. The injector head was cooled to 110-130 *C, providing a cold wall reactor configuration. A series of high volume nitrogen curtains and exhausts prevented atmospheric air from reaching the deposition zone.
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Mat. Res. Soc. Symp. Proc. Vol. 355 01995 Materials Research Society
TDMAT (99.999 % purity, Schumacher Corp.) was vaporized in a heated stainless steel bubbler. Precursor vapor pressures were calculated based on measurements by Schumacher Corp., with an estimated variability of ± 5 %from a value of 3.36 torr at 80 ± 1 °C bubbler temperature. Carrier gas ( N 2 ) flow rates were varied to change TDMAT flow rate. The bubbler effluent was further diluted with 4.4 to 14 standard liters/minute (slm) of N2 . For the TDEAT precursor, bubbler delivery was not possible due to the very low vapor pressure of TDEAT at temperatures low enough to avoid precursor decomposition over time. Instead, a prototype Direct Liquid Injection system developed by MKS Instruments was used to evaporate TDEAT. This system consisted of a precision metering pump delivering liquid precursor to a vaporizer designed to volatilize the precursor with minimal exposure to elevated temperature. Wi
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