mechanism 206 includes a plurality of gas ports 100 which are configured to eject the source gas upwards as gas jets into the interior of the plasma processing chamber although gas distribution mechanism 206 represents a gas distribution ring that is disposed near and encircles the substrate in the example of fig2 the gas distribution mechanism may also have other configurations such as a shower head configuration a gas distribution plate configuration or the like the ejected gas is then energized to form a plasma suitable for processing the surface of substrate 202 the by product gas as well as any unused source gas is then exhausted out of the chamber through exhaust manifold 208 in fig2 exhaust manifold 208 is shown disposed along a sidewall of the chamber however the exhaust manifold port may be in the floor of the chamber itself to allow by product gas to be exhausted through exhaust ports in the chamber floor if particulate contaminants in the regions outside of gas distribution mechanism 206 e g region 210 in fig2 are entrained back into the inlet gas jets prior to being exhausted away from the chamber interior such particulate contaminants may be redeposited back on the surface of substrate 202 to cause an increase in the density of particulate contaminants.