Characterization of a Microwave Plasma Etching Reactor

Abstract

Summary form only given. Plasma-assisted etching is used extensively for device fabrication processes in the semiconductor and MEMS fabrication industries. One variation of low-pressure, high-density plasma-assisted etching machines is the microwave ECR etcher. In this paper, a plasma etcher based on low pressure microwave plasmas built by Lambda Technologies is characterized for its operating properties. It is investigated at low pressures from 1 m Torr and up as it is operated both with and without ECR magnets. The 2.45 GHz microwave plasma-assisted etching reactor consists of a 25 cm diameter discharge located inside a 30 cm cavity applicator and operates in two distinct excitation modes: (1) an ECR (electron cyclotron resonance) plasma source operating at pressures of 1-10 mTorr and (2) a non-ECR, non-magnetized mode operating at higher pressures of 4 mTorr-10 Torr. The different modes of operation and the wide pressure operating region of this plasma source provide a wide range of atomic and molecular radicals and ions enabling a variety of etching recipes. Both conducting and insulating substrates can be etched because the plasma source has an independent rf bias capability for the substrate holder which facilitates controlled reactive ion etching at low pressures. Additionally, the plasma etching system includes temperature control for the substrate holder. In this paper, the operating modes and plasma behavior of ECR and non-ECR plasma discharges are investigated. The electron temperature, Te, charge density ne and electron energy distribution function (EEDF) are studied using single Langmuir probe (SLP). Direct comparisons are made at selected pressures for the reactor operating with and without ECR magnets. For example, at a pressure of 4 mTorr, the electron distribution function (EEDF) measurement results follow closer to the Maxwellian distribution without magnets and follow closer to the Druyvesteyn distribution with ECR magnets. The charge density uniformity of plasma is also investigated. At a pressure of 10 mTorr and without ECR magnets, the charge density of the plasma is as high as 5x1012 cm-3.