Loading Effects on Kinetical and Electrical Aspects of Silane-Reduced Low Pressure Chemical Vapor Deposited Selective Tungsten

The growth rate of selective tungsten using tungsten hexafluoride (WF6) and silane (SiH4) was measured in situ bymeasuring the time-reflectance curve during selective deposition on a grating or contact window pattern etched in oxideon a silicon substrate. Ex situ measurements were performed by step-height and weight-increase measurement. The growthrate and electrical resistivity depend on the loading, i.e., the density of the growing area in a selective deposition. Thedifference in growth rate between extreme cases, i.e., 100% vs. 0.04% growing surface of a 3-inch wafer for identical flowand pressure conditions can be as high as a factor of 20. The true surface kinetics were independent of the loading and canbe determined quantitatively by calculating the surface partial pressures using a mathematical model. At low growingsurface densities, the partial pressures at the wafer surface were approximately equal to the input partial pressures. Atlarge loading, significant differences were calculated between surface and input conditions. The apparent order of growthrate in SiH4 was 1 at low SiH4/WF6 ratios and increased at a critical SiH4/WF6 ratio. The order of growth rate in WF6 was–0.2 (±0.05) at SiH4/WF6 ratios below 0.5 and became approximately –0.7 at higher ratios. The temperature dependenceof the growth rate was small. The growth rate had a maximum at 300°C.