AVS 52nd International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS1-MoA

Paper PS1-MoA4
The Role of Inert Diluents in Low Pressure Electronegative Fluorinated Gas Discharges under Dual Frequency Excitation

Monday, October 31, 2005, 3:00 pm, Room 302

Session: Dielectric Etch I
Presenter: M. Hussein, Intel Corporation
Authors: M. Hussein, Intel Corporation
M. Abdelrahman, Intel Corporation
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We investigated the role of argon (Ar) and helium (He) dilution on the discharge characteristics and etch rate performance of NF3 plasma under single and dual excitation frequency conditions. The discharge complex impedance was measured using an advanced, passive I-V probe installed between the match network and the bottom electrode of a dual frequency, fixed gap, capacitively-coupled parallel plate commercial etch system. We studied the relationship between the etch performance of NF3/Ar/He plasma and the discharge complex impedance and dissipated power. A 300mm diameter test wafer substrate, with ~3-5% of its surface area occupied by vias patterned into a 360nm thick carbon-doped oxide (CDO) deposited on top of a 300nm silicon carbide (SiC) layer, was utilized for etch rate characterization. Both the CDO and SiC films were exposed to the plasma and etched at the same time, mimicking the process of SiC barrier etch used at the end of a dual damascene patterning process flow. We varied the NF3 flow rate form 0 to 18% of the total flow over a pressure range from 10mT to 150mT. Under dual frequency excitation, where 400Watts 60MHz and 50 Watts13.56MHz were applied to the top and bottom electrodes, respectively, the discharge complex impedance changed drastically over the tested pressure range. Below 40mT, the discharge is characterized by low impedance (~10-20 ohm). As the pressure increases, the impedance increases and reaches an asymptote at the 20-25 ohm range. This general trend was not observed under the 13.56MHz single frequency excitation mode, where a monotonic decrease in impedance with increasing pressure was observed regardless of diluents. We propose a model, similar to Langan's et al.,@footnote 1@ suggesting that the dominant role of the diluent in NF3 plasmas is to control the electronegativity of the discharge, and thus to control real power dissipation. @FootnoteText@@footnote 1@J. Langan, S. Beck, B. Felker and S. Rynders, J. Appl. Phys. 79(8), pp.3886, 15 April 1996.