In this paper we study the growth of nanometer particles in low pressure plasmas due to coagulation. We describe results of a model which involves the self-consistent determination of plasma properties, the description of particle charging, as well as the description of the particle size distribution via solution of the general dynamic equation for an aerosol. Our results show that particle coagulation in the low pressure plasma is enhanced compared to coagulation in neutral aerosols due to the attraction of oppositely charged particles. The temporal behavior of the coagulation follows the same laws as coagulation of neutral particles as long as the density of nanometer particles is larger than the positive ion density in the plasma. The positive ion density can be considered as the critical density for coagulation to occur. We also show that the details of the particle charging mechanism are only of minor importance for the coagulation dynamics but of great importance for the accurate prediction of plasma parameters.

A new silicon hydride clustering model was developed to study the nucleation of particles in a low-temperature silane plasma. The model contains neutral silanes, silylenes, silenes and silyl radicals as well as silyl and silylene anions. Reaction rates were estimated from available data. Simulations were carried out for typical discharge parameters in a capacitive plasma. It was shown that the main pathway leading to silicon hydride clustering was governed by anion-neutral reactions. SiH 2 radical insertion was found to be important only in the initial stages of clustering, whereas electron-induced dissociations were seen to lead to dehydrogenation. Increased ion density (radiofrequency power density) leads to faster clustering due to increased formation of reactive radicals.

Particle nucleation in silane plasmas has attracted interest for the past decade, both due to the basic problems of plasma chemistry involved and the importance of silane plasmas for many applications. A better understanding of particle nucleation may facilitate the avoidance of undesirable particle contamination as well as enable the controlled production of nanoparticles for novel applications. While understanding of particle nucleation has significantly advanced over the past years, a number of questions have not been resolved. Among these is the delay of particle nucleation with an increasing gas temperature, which has been observed in experiments in argon-silane plasmas. We have developed a quasi-one-dimensional model to simulate particle nucleation and growth in silane containing plasmas. In this paper we present a comparative study of the various effects that have been proposed as explanations for the nucleation delay. Our results suggest that the temperature dependence of the Brownian diffusion coefficient is the most important effect, as diffusion affects both the loss rate and growth rate of particles.

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