Shapes of agglomerates in plasma etching reactors
Dust particle contamination of wafers in reactive ion etching (RIE) plasma tools is a continuing concern in the microelectronics industry. It is common to find that particles collected on surfaces or downstream of the etch chamber are agglomerates of smaller monodisperse spherical particles. The shapes of the agglomerates vary from compact, high fractal dimension structures to filamentary, low fractal dimension structures. These shapes are important with respect to the transport of particles in RIE tools under the influence electrostatic and ion drag forces, and the possible generation of polarization forces. A molecular dynamics simulation has been developed to investigate the shapes of agglomerates in plasma etching reactors. We find that filamentary, low fractal dimension structures are generally produced by smaller (<100s nm) particles in low powered plasmas where the kinetic energy of primary particles is insufficient to overcome the larger Coulomb repulsion of a compact agglomerate. This is analogou...
Spatial distributions of dust particles in plasmas generated by capacitively coupled radiofrequency discharges
The transport of particles ('dust') in low-pressure electrical glow discharges is of interest with respect to contamination of semiconductor wafers during plasma etching and deposition. The distribution of dust particles in these reactors is determined by a variety of forces, the most important being electrostatic, viscous ion drag, gravitational, thermophoretic and neutral fluid drag. In this paper we present results from a series of computer models to predict the spatial distribution of dust particles in capacitively coupled electrical glow discharges considering these forces. The results are parametrized over power deposition, gas flow and particle size. We find that the spatial distribution of dust depends on the spatial dependence of the sheaths and plasma potential in bulk plasma which in turn depend upon the electrical topography of the surfaces. Experimentally observed 'dome' and 'ring' distributions of dust particles are computationally reproduced for specific combinations of discharge power particle size and substrate topography.
Ballistic deposition onto inclined surfaces.
Simulations of ballistic deposition onto an inclined surface (deposition at non-normal incidence) have been carried out using two-dimensional lattice and off-lattice models and three-dimensional off-lattice models. For most of these models the relationship between the angle of incidence (\ensuremath{\theta}) and the angle of growth (\ensuremath{\varphi}) is given by \ensuremath{\varphi}=${C}_{1}$\ensuremath{\theta} for small angles of incidence and \ensuremath{\varphi}=\ensuremath{\theta}-${C}_{2}$ for large angles of incidence. The constant parameters ${C}_{1}$ and ${C}_{2}$ are sensitive to model details. All of our results deviate strongly from the tangent rule (tan\ensuremath{\varphi}=(1/2tan\ensuremath{\theta}). For small (near-normal) angles of incidence the thickness of the deposit surface (\ensuremath{\xi}) is related to the mean height of the surface (h\ifmmode\bar\else\textasciimacron\fi{}) by \ensuremath{\xi}\ensuremath{\sim}h${\ifmmode\bar\else\textasciimacron\fi{}}^{\ensuremath{\beta}}$ where the exponent \ensuremath{\beta} has a value of about (1/3. As \ensuremath{\theta} is increased \ensuremath{\beta} increases and approaches a limiting value of about (1/2 for \ensuremath{\theta}\ensuremath{\rightarrow}\ensuremath{\pi}/2. Similarly, the exponents ${\ensuremath{\nu}}_{?}$ and \ensuremath{\tau} which describe the internal substructure of these compact deposits change from values of 0.6 and 1.4 for normal incidence to values of about (2/3 and (4/3 for grazing incidence.