AVS 59th Annual International Symposium and Exhibition
    Plasma Science and Technology Tuesday Sessions
       Session PS2-TuA

Paper PS2-TuA3
Cl Atom Reactions on Silicon Oxy-Chloride Layers Deposited on Chamber Walls in Chlorine-Oxygen Plasmas

Tuesday, October 30, 2012, 2:40 pm, Room 25

Session: Plasma Surface Interaction during Plasma Etching
Presenter: A.K. Srivastava, University of Houston
Authors: A.K. Srivastava, University of Houston
R. Khare, Lam Research Corp
V.M. Donnelly, University of Houston
Correspondent: Click to Email
The effects of O2 addition to a Cl2 inductively-coupled plasma (ICP) on the heterogeneous reactions of Cl atoms during silicon etching has been studied, using the “spinning wall” method with line-of-sight mass spectrometry, optical emission spectroscopy and Auger electron spectroscopy. A cylindrical substrate embedded in the wall is rotated so that its surface periodically passes through the plasma chamber and then through the differentially pumped diagnostic chambers. Langmuir-Hinshelwood desorption products are detected as a function of time after leaving the plasma, established by the variable rotation frequency. A silicon wafer electrode placed inside the plasma chamber was etched for 10 min with -119 Vdc self-bias in a 2.5 mTorr, 400 W Cl2 ICP, depositing etching products on the chamber walls and spinning substrate. The Si-electrode bias was turned off and the chamber walls were conditioned with a Cl2 ICP for an hour. A silicon oxy-chloride (SiOxCly) layer of stoichiometry Si:O:Cl = 1:0.38:0.38 was formed, with the O being a result of slow etching of the quartz discharge tube. No significant Cl recombination on this layer was observed (recombination probability, γCl < 0.001). With the addition of 5% O2 to the feed gas, the Si-wafer was again biased for 10 min to deposit SiOxCly products on the chamber walls, which were then conditioned with a no-bias ICP for another hour, leaving a film with Si:O:Cl = 1:1.09:0.08. Cl recombination was observed on this surface, with γCl = 0.03. No etch products were detected in the mass spectrometer and hence there is no significant etching of the silicon oxy-chloride layer deposited on the chamber walls at this oxygen fraction. On further treating the surfaces with a pure O2 plasma for 60 min, the surface composition became Si:O:Cl = 1:1.09:0.04. On this surface the Cl-atom recombination was further enhanced, with γCl = 0.04. We attribute this behavior to Cl recombination occurring at chlorinated O sites rather than chlorinated Si sites on silicon oxy-chloride surface, because of the weak Cl-O bond compared to the Cl-Si bond.