During plasma etching processes, organic or mineral layers are deposited on the chamber walls. In general, these layers cause large and uncontrolled shifts in the etch process, which is becoming a major issue in some of the plasma processes used in integrated circuit fabrication. The chemical nature of these layers and their deposition mechanisms remain poorly understood due to the lack of in situ surface diagnostics available to monitor the reactor walls. In this article, we present a simple technique using x-ray photoelectron spectroscopy (XPS) analyses to monitor the chemical composition of the layer deposited on a sample floating on top of a 200-mm-diam wafer where the layers deposited are identical to those deposited on the chamber walls. The principle of the technique is to stick a small Al2O3 sample onto the 200-mm-diam silicon wafer, with an air gap between the sample and the wafer. Providing that the air gap is thick enough, the Al2O3 surface will be electrically floating even when the silicon wafer is rf biased. During the etching process, the Al2O3 sample thus experiences exactly the same plasma conditions as the reactor walls. As the sample is physically clamped on the wafer, it can then be transferred under vacuum to an XPS analyzer, allowing quasi-in situ analyses of the deposited layers. The validity of the technique has been tested during silicon gate etching in HBr/Cl-2/O-2 plasmas, which are known to deposit silicon oxychloride layers on the chamber walls. The influence of CF4 addition in the plasma which has been recently introduced in gate etching manufacturing is also analyzed using the same technique. In a second step, we show that the presence of photoresist on the etched wafer profoundly affects the chemical nature of the layers formed on the chamber walls, mainly by significantly increasing the carbon concentration in the deposited layer. (C) 2004 American Vacuum Society.