Luc Stafford

Effect of Cu contamination on recombination of O atoms on a plasma-oxidized silicon surface

In the dual damascene microelectronics integration scheme during the last stage of plasma etching of dielectrics down to underlying Cu layers, Cu is sputtered onto the reactor walls and is believed to cause a drift in etching rates. For photoresist etching in an O2-containing plasma, a drop in etching rate suggests that Cu could cause a decrease in the O-atom concentration in the plasma, due perhaps to an increase in the O recombination rate on the chamber walls. We therefore studied the effects of traces of Cu on O recombination on an oxygen plasma-conditioned surface, using the spinning wall technique. With this method, a cylindrical substrate, here coated in situ with sputter-deposited Si and then oxidized in an O2 plasma, is rotated past skimmers, allowing the surface to be periodically exposed to the plasma and an Auger electron spectrometer with a pressure gauge in a differentially pumped chamber. Between plasma exposures, the sample could also be dosed with Cu from an evaporation source in a differ...

Recombination probability of oxygen atoms on dynamic stainless steel surfaces in inductively coupled O2 plasmas

The authors have investigated the influence of plasma exposure time (t) on the Langmuir-Hinshelwood (i.e., delayed) recombination of O atoms on electropolished stainless steel surfaces using the spinning-wall method. They found a recombination probability (γO) of 0.13±0.01 after about 60min of plasma exposure. γO decreased to 0.09±0.01 for t⩾12h and was independent of the O flux impinging onto the surface. These recombination probabilities are much lower than those obtained in plasma chambers exclusively made of stainless steel, but similar to values recorded in stainless steel reactors with large silica surfaces exposed to the plasma. Near real-time elemental analysis by in situ Auger electron spectroscopy showed that the stainless steel surface became rapidly coated with a Si-oxide-based layer (Fe:[Si+Al]:O≈2:1:9 for t=60min and 1:2:9 for t=12h), due to the slow erosion of the silica discharge tube and anodized Al chamber walls. Thus, the recombination probability of oxygen atoms on stainless steel in p...

In-situ Surface Recombination Measurement of Oxygen and Chlorine Atoms on Dynamic Stainless Steel Surfaces in Inductively Coupled O2 and Cl2 Plasmas

Over the last three decades, semiconductor technology has been aggressively scaled down from micron sized features to 45 nm features. For the upcoming 32 nm technology node, total variation from all sources for a typical gate etch process in low pressure (<100 mTorr) plasmas is expected to be less than 2 nm. Because wall reactions are the dominant loss pathways for reactive neutrals in such low-pressure conditions, the control of chamber wall conditions is crucial for minimizing process drifts and achieving the desired process capability. However, the highly dynamic nature of reactor walls with simultaneous bombardment by neutrals, positive ions, electrons, and UV photons makes measurements of surface reactions kinetics under actual plasma etching conditions an extremely difficult task. A new “spinningwall” method was recently reported for studying such complex interactions, bringing the established ultra-highvacuum techniques of desorption mass spectrometry (MS) and Auger electron spectroscopy (AES) to the highpressure, high charge density plasma environment [1]. In this set-up, a small, cylindrical section of the wall is rotated up to 100,000 rpm through closely-fitted skimmers. This allows the flux of reactants to be rapidly halted, and then products on the surface and desorbing from the surface to be analyzed as soon as 300 μs thereafter in separate, differentially-pumped chambers. In the present work, we take advantage of this method to investigate the influence of surface conditioning on the recombination kinetics of O and Cl atoms on stainless steel, which is a widely used wall materials in the development of plasma etching tools for nanometer scale pattern transfer in semiconductor technology. Figure 1 presents the recombination coefficient of oxygen atoms (γO) on stainless steel as a function of the oxygen flux impinging onto the substrate, ΓO, for different plasma exposure times, t. γO values were determined by measuring the pressure rise in the AES chamber as a function of reaction time, tr, probed by varying the substrate rotation frequency (tr=(2f)). As the substrate is exposed to the plasma, O atoms stick to the surface and then recombine over a time comparable to the rotation period, forming O2 that desorbs and thus producing a pressure rise. Pressure rises were then converted into absolute desorption flux using the calibration procedure described in ref. [2]. Plots of desorption flux versus reaction time were extrapolated to tr→ 0 to obtain the desorption flux at pseudo-steady state condition, Dtr→0, where the rotation frequency is much faster than the rate-limiting step in O recombination and desorption. Finally, γO was calculated from the relation