Paper PS1-WeA2
Chamber Walls Coatings during Hard Mask Patterning of Ultra Low-k Materials: Consequences on Cleaning Strategies

Wednesday, October 17, 2007, 2:00 pm, Room 606

Changes in chamber wall conditions (e.g., chemical surface composition) are identified as one of the main causes of process drifts leading to changes in the process performance (etch rates, etch profiles, selectivity, uniformity …). The impact of a metal hard mask on the coating formed on the chamber walls during dielectric etching processes and reactor dry cleaning procedure has been investigated. We have used a technique based on x-ray photoelectron spectroscopy (XPS) to monitor the chemical composition of the layer deposited on an electrically floating sample placed on the top of a patterned wafer exposed to typical plasma processing conditions. By using this simple technique, the Al₂O₃ sample surface (or other chamber walls materials) is, similarly than the chamber walls, bombarded by low energy ions. Since the wafer is simultaneously bombarded by high energy ions, the gas phase is fed by etch products which get redeposited on the electrically floating Al₂O₃ sample and on the chamber walls surfaces. We have patterned porous SiOCH damascene structures using a TiN hard mask. After hard mask opening in a silicon etcher using Cl₂ based plasmas, we have shown that the chamber walls are coated by a thin SiOCl layer containing small concentrations of Ti. After photoresist removal in the same etcher (with an O₂ plasma), the chamber walls coating is oxidized leading to the formation of a mixed SiOx-TiOx deposit. The cleaning strategy to remove this coating from the chamber walls consists in using a two step cleaning procedure: (1) a Cl₂ based plasma (Ti removal) followed by (2) a SF₆/O₂ plasma (SiOCl species removal). During low-k etch in an oxide etcher using fluorocarbon based chemistries, the chamber walls are coated by a fluorocarbon layer containing a significant Ti concentration. We have developed a two step cleaning procedure: (1) a SF₆ plasma to remove the fluorocarbon layer and Ti based species and (2) an O₂ flash plasma (for a short time) to clean up the remaining carbon from the chamber walls.