AVS 53rd International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS2+TF-WeM

Paper PS2+TF-WeM9
The Use of Pulse-Shaped Substrate Bias for Energy-Selective Ion Bombardment During Amorphous Si Deposition

Wednesday, November 15, 2006, 10:40 am, Room 2011

Session: Plasma Deposition
Presenter: I.T. Martin, Eindhoven University of Technology, The Netherlands
Authors: I.T. Martin, Eindhoven University of Technology, The Netherlands
M.A. Blauw, Eindhoven University of Technology, The Netherlands
R. Engeln, Eindhoven University of Technology, The Netherlands
W.M.M. Kessels, Eindhoven University of Technology, The Netherlands
M.C.M. Van De Sanden, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
The role of neutrals during expanding thermal plasma (ETP) deposition of a-Si:H has been thoroughly studied in the literature. Less attention has been paid to ions, both because ion flux is low compared to neutral flux, and the remote nature of the plasma source results in low ion energies, <2eV. Ion bombardment effects depend on ion energy as different thresholds exist for enhancing vs. damaging processes. RF-biasing has previously been used to increase ion energy; appropriate substrate voltages resulted in an increase in the photoconductivity of a-Si:H. A disadvantage of rf-biasing is that the resulting ion energy distributions (IEDs) are broad and bimodal. We have applied the pulse-shaped substrate bias technique developed by Wendt and coworkers@footnote 1@ to ETP a-Si:H deposition, which results in narrow IEDs. This improves ion energy control, allowing further optimization of materials properties. Preliminary data demonstrate that the effect of this bias varies for different plasma conditions; materials deposited in plasmas with low ion currents (<3mA) and high deposition rates (~5nm/s) are unaffected by the bias. The setup also allows us to determine ion flux to the substrate. Data show that increasing H@sub 2@ flow results in decreased ion flux, consistent with earlier Langmuir probe measurements. Interestingly, ion flux increases with increasing substrate potential, suggesting the formation of additional plasma in front of the substrate. Materials were deposited with varying Ar:H@sub 2@:SiH@sub 4@ flows, and a range of substrate biases (0 to -140V). Films were characterized using FTIR and photoconductivity measurements; differences in deposition rate, refractive index, hydrogen content and photoconductivity as a function of substrate bias will be discussed. Results are compared to a-Si:H deposited using rf-biasing, and to other materials deposited using a pulse-shaped bias. @FootnoteText@ @footnote 1@S.B. Wang and A.E. Wendt, J. Appl. Phys. 88, 643 (2000).