SELECTIVE R.T.L.P.C.V.D. OF TUNGSTEN BY SILANE REDUCTION ON PATTERNED PPQ/Si WAFERS

Organic dielectrics are an attractive alternative to silicon oxide commonly used in multilevel metallization schemes. In this work, tungsten films are selectively deposited on substrates covered by patterned organic dielectric through a Rapid Thermal Low Pressure Chemical Vapor Deposition system by using the WF,-SiH4-H, gas phase. In the entire range of parameters, a-W is the only phase obtained. The resistivity of the films is about 20 @cm. The SiH4/WFB ratio and the deposition temperature appear to be the decisive parameters. With determined optimal experimental conditions (SiH4/WF6 ratio of 3/4 and deposition temperature of 350°C) W films are deposited with a good selectivity at 400 nm/min. These characteristics are improved when the etched area/wafer area ratio (called 'load ratio") decreases. Adherence problems limit the thickness of the deposited W films. The maximum thickness is higher when deposition occurs on chromium covered silicon rather than on bare silicon.