Design criteria for uniform reaction rates in an oxygen plasma

The physical conditions necessary to obtain uniform and reproducible chemical reaction rates in an oxygen plasma are investigated by stripping photoresist from silicon wafers. An oxygen plasma was selected due to its simplicity and the availability of a simple technique for measuring the concentration of atomic oxygen which is the reagent of importance. However, many of the considerations will apply to the design of other plasmas for other chemical reactions. Due to the electrical Skin effect at 13.56 MHz, the atomic oxygen is created near the Walls in a cylindrical reactor. However, at flow rates corresponding to residence times in the range of 1-10 s, diffusion makes the concentration uniform within a few percent except near the walls. Under conditions such that there is no by-product inhibition, the chemical reaction rate is determined bythe atomic oxygen concentration and the temperature of the silicon substrate and the reactor walls. The rate is independent of the conbination of pressure and power used to produce the atomic oxygen concentration.