Microwave plasma enhanced CVD of aluminum oxide films: OES diagnostics andinfluence of the RF bias

Aluminum oxide films are obtained in a remote-microwave-plasma-enhanced che mical vapour deposition (RMPECVD) reactor. In this technique, only oxygen g as plasma is generated while trimethylaluminum (TMA) carried by argon is fe d near the substrate holder which can be RF biased and deposition occurs at the surface of a silicon wafer. Optical emission spectroscopy (OES) is use d in order to gain information on the plasma excitation of various species. The presence of an inert gas (argon) allows an evaluation of the relative densities of reactive species by the actinometry technique. A comparison ha s been done with and without RF biasing or TMA injection at different micro wave powers in the same conditions of Ar and O-2 flow rates. The RF biasing creates an additional plasma near the substrate holder but has a weak infl uence on the OES signal. The microwave plasma is the major mode in the pres ent experimental set up. Less than 2% of TMA modifies the plasma chemistry by improving the atomic oxygen formation. In addition, the TMA. decompositi on involves a cooling effect of the electron energy. Although this dual mod e configuration of the plasma production induces a slight decrease of the d eposition rate, it limits the incorporation of impurities (O, H) in the lay er by improving the ion bombardment and etching of the growing layer. (C) 2 001 Elsevier Science B.V. Ah rights reserved.