Analyses of chamber wall coatings during the patterning of ultralow-k materials with a metal hard mask: Consequences on cleaning strategies

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, etc.). The impact of a metal hard mask on the coating formed on the chamber walls during the dielectric etching process and reactor dry cleaning procedure has been investigated. The authors have used a technique based on x-ray photoelectron spectroscopy 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 (coatings deposited on the floating sample are representative of those deposited on the chamber walls). They have patterned porous SiOCH damascene structures using a TiN hard mask. After hard mask opening in a silicon etcher using Cl₂ based plasmas, they have shown that the chamber walls are coated by a thin SiOCl coating containing small concentrations of Ti. After photoresist ashing in the same etcher (with an O₂ plasma), the chamber wall coating is oxidized leading to the formation of a mixed SiO_x–TiO_x 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 etching in an oxide etcher with a fluorocarbon based chemistry, the chamber walls are coated by a fluorocarbon layer containing a significant concentration of Ti. They 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 chamber walls from the remaining carbon.