The initial operation of an electron cyclotron resonance (ECR) plasma etch tool, utilized in a downstream configuration for SF6etching of polysilicon is described. Practical operational characteristics that are generic to high‐density, wave‐supported plasma sources operated in downstream configurations were explored. A method for improved coupling of the microwave power to the ECR source is described. This method eliminates the need for external tuning. The effect of wall impurities on the plasma and etching characteristics is also considered. A scheme for conditioning the walls to alleviate the effects of impurities is presented. Finally, the complicated relationship between the ECR source plasma and the downstream wafer is considered, by examining the scaling of the plasma electron density in the two regions with microwave power and gas pressure. The phenomena discussed here apply to other etching chemistries and can have a significant impact on process integrity and ease of operation.