It has been successfully demonstrated that the scattered-light intensity of thermally grown particle clouds consisting of particles of less than 20 nm in size above wafers in a real tungsten (W) chemical vapor deposition (CVD) chamber correlate well with both the surface roughness of the W-CVD film measured by atomic force microscopy and with the gas-flow ratio SiH4/WF6. In addition, we can observe the appearance and motion of particle clouds corresponding to the transient variation of the ratio SiH4/WF6 at the conversion of gases and at the change of the flow ratio. These features of our in situ particle monitor enable us to achieve the mass-production conditions for particle-free and smooth surfaces of W films with short cycle time. Moreover, our particle monitor is sensitive enough to adopt in the development of process conditions as the reduction of design rules for large-scale integrated circuit proceeds. Therefore, applying our in situ particle monitor above wafers for developing mass-production conditions is a notable method to minimize the monitor wafers and to realize short cycle time. © 2001 American Vacuum Society.