Formation kinetics and control of dust particles in capacitively-coupled reactive plasmas

Formation kinetics and behavior of dust particles below about 10 nm in size , referred to as clusters, in silane capacitively-coupled RF plasmas are st udied using double pulse discharge and photon-counting laser-light-scatteri ng methods. Even under so-called device quality conditions, clusters of sim ilar to 10(11) cm(-3) high compared to a plasma ion density of similar to 1 0(-9) cm(3) are found at t similar to 50 ms after the discharge initiation. Clusters begin to be composed of two size groups at t similar to 10 ms. Th e ones in the small size group have an almost constant average size of simi lar to 0.5 nm during the discharge period, while the ones in the large size group grow at a rate of similar to 4 nm/s. This result indicates that the large clusters are nucleated by the small ones containing 3-4 Si atoms. Various methods for suppressing cluster growth have also been studied using two in situ cluster detection methods. Since species contributing to the i nitial growth of clusters are principally produced in the radical productio n region around the plasma/sheath boundary near the rf electrode, the pulse discharge modulation which has the discharge-off period in one modulation cycle longer than the diffusion time of clusters through the radical produc tion region is effective in reducing the growth of clusters. Thermophoretic force due to heating of the grounded electrode drives neutral clusters abo ve a few nm in size toward the cool RF electrode which is at room temperatu re. Periodical pulse discharge modulation is much more effective in reducin g the cluster density when it is combined with grounded electrode heating. Hydrogen dilution of a high H-2/SiH4 concentration ratio above about 5 is u seful for suppressing cluster growth especially in the radical production r egion near the RF electrode.