Transport and Agglomeration of Dust Contaminant Particles in Reactive Ion Etch Reactors by Frederick

Dust particle contamination in plasma etching reactors continues to be a major concern to microelectronic device manufacturers. Dust particulates as small as tens of nanometers in dimension can produce killer defects on the substrate surface. These contaminants are produced either through gas-phase nucleation processes in the discharge, or through interaction with surfaces in the reactor. Their transport is governed by the forces exerted upon them in the reactor, primarily electrostatic, ion drag, neutral drag, thermophoresis, and gravitational forces. Dust particulates collected from reactive ion etching (RIE) reactors are commonly found to be agglomerate structures consisting of smaller, spherical " primary particles. " These primary particles grow to a terminal size in the reactor and then combine to form the larger agglomerates. This agglomeration phenomenon requires a certain amount of kinetic energy from the primary particles, which typically charge negatively in such discharges. With sufficient kinetic energy, primary particles can overcome their mutual electrostatic repulsion and join together to form an agglomerate particle. The transport and agglomeration of dust particles in RIE reactors has been studied using a series of numerical simulations. These computational models have demonstrated that both dust transport and agglomeration are highly dependent on reactor geometry and discharge operating conditions, as well as the size of the primary particle. In general, higher radio-frequency (RF) iv powers and larger primary particles lead to more agglomeration. This in turn typically results in a larger amount of substrate contamination. The morphology of the agglomerates formed was also found to be dependent on plasma conditions. Agglomerates generally grow either in a diffusive or ballistic manner. Neutral gas flow in the reactor has been found to be a useful means of controlling contamination. Higher flow rates can sweep dust particles away from sensitive areas of the reactor before they reach the surfaces.