AVS 51st International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS2-WeM

Paper PS2-WeM7
Comparison of Fluorocarbon Gases and NF3 for Plasma Chamber Cleaning with Transformer-Coupled, Toroidal Source

Wednesday, November 17, 2004, 10:20 am, Room 213B

Session: Plasma Sources
Presenter: B. Bai, Massachusetts Institute of Technology
Authors: B. Bai, Massachusetts Institute of Technology
H.H. Sawin, Massachusetts Institute of Technology
L. Gary, DuPont Electronic Gases
M. Mocella, DuPont Electronic Gases
Correspondent: Click to Email
In recent years, remote chamber cleaning has begun to replace in situ chamber cleaning for Chemical Vapor Deposition (CVD), due to the lower occurrence of chamber wall erosion and lower perfluorocompound (PFC) gas emission. We have tested a high-power transformer-coupled toroidal plasma source typically used with NF3 to produce fluorine atoms for chamber cleaning. The ASTRONex unit couples high power levels (<10 kW) into the feed gases, leading to high neutral temperatures (as high as 6000K) under conditions that produce relatively low electron temperatures. These condition produce very high degrees of dissociation of not only NF3, but also for fluorocarbon compounds â?" contrary to what has been seen in lower power and/or microwave units for remote chamber cleaning. In this work, a systematic comparison has been made among various fluorocarbon compounds (with added O2) including CF4, C2F6, C3F8, and C4F8, along with NF3. Trends in cleaning rates, which are significantly different from earlier studies in other units, will be described. Tool emission studies with Fourier Transformed Infrared Spectroscopy (FTIR), along with analysis of the cleaned surfaces via X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM), will also be presented. Plasma parameters were also measured to better understand the kinetics in the source. Neutral gas temperatures were obtained by fitting rovibrational bands of diatomic species like CO, CF or added N2. Electron temperature and electron density were determined by the atomic argon spectrum, while the atomic concentrations of fluorine and oxygen species in the plasma source were measured by advanced actinometry. For these two optical emission spectroscopy measurements, a full consideration of optical cascading and radiation trapping was necessary due to the high source pressure (~1 torr).