Chamber wall interactions with HBr/Cl2/O2 plasmas

Abstract

The authors have studied the interaction of HBr/Cl2/O2 inductively coupled plasmas with reactor chamber wall deposits, with and without Si etching, using the “spinning wall” technique. The spinning wall is part of the reactor chamber walls, allowing near-real-time analysis of the composition of surface layers via Auger electron spectrometry and determination of species desorbing off the walls by mass spectrometry. In HBr plasmas with no bias voltage on the Si substrate, and hence no Si etching, HBr is ∼30% dissociated, and H2 and Br2 form in the plasma. Layers deposited on the reactor chamber contained little if any Br under these conditions. Adding O2 to an HBr plasma leads to formation of H2O and increased Br2 (compared to a pure HBr plasma) products that desorb from the spinning wall. H2O has a very long residence time on the surface. With bias voltage applied to the Si substrate in an HBr plasma, mass spectrometer signals are prominent for SiBr and SiBr3, and weaker for SiBr2, SiBr4, Si2Br4, Si2Br5, and Si2OBr5. Under these conditions, a SiOxBry layer deposits on the spinning wall. Adding 20% O2 to HBr stops etching and eliminates Br from the surface layer, indicating that Br on the reactor walls is a result of SiBrx impingement and not from bromination by impinging Br. With HBr/Cl2 plasmas and no bias on the stage, a SiOxCly layer deposits, and no Br is detected. HCl, BrCl, and Br2 were detected in the line-of-sight leak, around the spinning wall, of a HBr/Cl2 (1:1) gas mixture in the absence of a plasma. Residence time analysis of species in the chamber and a change in the product distribution with a change in the composition of the layer deposited on the chamber wall suggest that reactions forming these products in the absence of a plasma occur on the reactor walls. With a plasma and bias on the Si substrate, both Br and Cl incorporate in the layer, and a rich spectrum with numerous SiClxBry peaks was observed up to at least 500 amu. The spectrum does not change with the addition of 6% O2. Adding 20% O2 suppresses Br adsorption, but Cl still adsorbs. In 40% O2/HBr/Cl2 plasmas with stage bias, Cl adsorption also ceases and no etching products are observed in the mass spectrum.