POLY-SI ETCHING USING ELECTRON-CYCLOTRON RESONANCE MICROWAVE PLASMA SOURCES WITH MULTIPOLE CONFINEMENT

In this study, mirror field and single coil 2.45 GHz electron cyclotron resonance microwave plasma sources were coupled to a multipole, multicusp plasma confinement system and used to produce chlorine plasmas for poly-Si etching. Scanning Langmuir probes were used to study the effect of process parameters on plasma potentials, plasma density, plasma density uniformity, and electron temperature, while poly-Si etching experiments on 150 mm diam wafers were used to relate process parameters and Langmuir probe results to etch rate, SiO2 selectivity, photoresist selectivity, and etch uniformity. Radio-frequency substrate bias at 13.56 MHz was used for ion energy control, and the addition of a third coil below the substrate plane was found useful for fine-tuning the radial plasma uniformity. Undoped poly-Si etch rates >3000 angstrom/min, Si/SiO2 etch selectivities >25 and 150 mm diam etch uniformities <2% at 1-sigma were obtained, but not simultaneously. Tradeoffs in choosing operating conditions for optimum poly-Si etch performance will be discussed.