Contamination and Uniformity Control in Plasma-Processing Tools

This project involves the design and evaluation of various ultraclean field-corrected electrodes, or wafer chucks, to improve process uniformity and particulate contamination in the plasma processing of semiconductor materials. Dust in plasmas, caused either by homogeneous nucleation or by film flaking, has been shown to be charged negatively, and is thus suspended in the presence of the electrical fields that accompany a plasma. A process has been developed for in-situ detection of suspended particles using a technique called laser light scattering. Some photos of suspended dust clouds in a low pressure, nonequilibrium plasma can be seen below. By designing a groove into the electrode of plasma tool, it is possible to "corral" the particles into a stream and then to watch them flow out of the plasma and into the pump port.

Electrodes used by our partner, the original equipment manufacturer to the semiconductor industry, will be modified for field tunability, which is achieved by designing dielectric and/or metal tuning elements in the electrodes to compensate for electrode-induced plasma electrical aberrations. The resulting trap-free discharge greatly reduces particle contamination by canceling the net electrostatic confinement of particles in the discharge. The field-corrected electrode also improves process uniformity at the same time. Both factors dramatically improve manufacturing yield and reduce product cost. The proposed program involves three goals: (1) a passive (or fixed) field-tunable electrode for a high-density or conventional plasma tool, (2) an active (or externally controllable) field-tunable electrode for a high-density or conventional plasma tool, and (3) a code to help predict tunable-electrode design for future plasma tools. The success of this program will be measured by the improvement in particle contamination performance and edge uniformity over the base, unmodified tools. This program will provide a boost in the effort to link Laboratory talents and capabilities with the national needs of industry.