CHARACTERIZATION OF SELECTIVE CHEMICAL VAPOR-DEPOSITED TUNGSTEN USING SIH4 REDUCTION

The growth rate, resistivity, and selectivity of selective chemical vapor deposition of tungsten using SiH4 reduction of WF6 has been examined as a function of SiH4 partial pressure (PP), WF6 PP, growth temperature, total pressure, average residence time, and fraction of exposed area. The growth rate is proportional to the SiH4 PP, decreases with increased temperature, and decreases with increased exposed area. The deposition rate also decreases slightly as the WF6 to SiH4 ratio increases. With a constant SiH4 PP, the growth rate decreases as the total pressure increases (the SiH4 flow rate is decreased at higher total pressures). The SiH4 conversion efficiency increases as the residence time and fraction of exposed area increase. The resistivity decreases as the growth temperature increases or the deposition rate decreases. The resistance increases with increasing Si and F concentrations in the films. Low temperature residual resistance measurements indicated that the increase in resistance is due to impurity scattering. The selectivity is better at lower temperatures, low growth rates, high WF6 to SiH4 ratios, and intermediate pressures (25-100 mTorr). A mechanistic model of the deposition process is presented which explains much of the observed phenomenology.