The formation of LPCVD tungsten by means of the reduction of WF6 with Si, H2 and SiH4 is monitored in situ using a wavelength adjustable reflectometer. The initial self stopping growth of W by Si reduction is strongly dependant on surface status [1]. SEM observations together with Auger depth profiling and weight measurements support a growth model of islands that grow laterally and vertically until islands touch. After the self stopping Si reduction the W layer was increased in thickness by either the h or SiH4 reduction. The surface roughness calculated from the reflectance appears to increase linearly with thickness in the case of H2 reduction. Typical rms roughness was found to be 7% of layer thickness in the H2 reduction case. The reflectance of H2 reduced W layers could be improved by interrupting the growth process with a renucleation step using SiH4. Selective deposition and in situ growth rate measurements can be monitored when the deposition is carried out on a grating of SiO2 as a mask. Precleaning of the reactor with an NF3 plasma results in a strong retardation of the H2 reduction reaction.