A 3-DIMENSIONAL MODEL FOR INDUCTIVELY-COUPLED PLASMA-ETCHING REACTORS- AZIMUTHAL SYMMETRY, COIL PROPERTIES, AND COMPARISON TO EXPERIMENTS

Inductively coupled plasma (ICP) etching reactors are rapidly becoming the tool of choice for low gas pressure, high plasma density etching of semiconductor materials. Due to their symmetry of excitation, these devices tend to have quite uniform etch rates across the wafer. Howev er, side to side and azimuthal variations in these rates have been obs erved, and have been attributed to various asymmetries in pumping, rea ctor structure and coil properties. In this article, a three-dimension al computer model for an ICP etching reactor is reported whose purpose s is to investigate these asymmetries. The model system is an ICP reac tor powered at 13.56 MHz having flat coils of nested annuli powering A r/N-2 and Cl-2 plasmas over a 20-cm diam wafer. For demonstration purp oses, asymmetries were built into the reactor geometry which include a wafer-load lock bay, wafer clamps, electrical feeds to the coil, and specifics of the coil design. Comparisons are made between computed an d experimentally measured ion densities and poly-silicon etch rates in Cl-2 plasmas. We find that the electrical transmission line propertie s of the coil have a large influence on the uniformity of plasma gener ation and ion fluxes to the wafer. (C) 1996 American Institute of Phys ics.