AVS 56th International Symposium & Exhibition
    Plasma Science and Technology Wednesday Sessions
       Session PS1-WeM

Invited Paper PS1-WeM5
Probe Measurements in a Very High Frequency CCP Discharge

Wednesday, November 11, 2009, 9:20 am, Room A1

Session: Plasma Diagnostics, Sensors, and Control I
Presenter: L. Dorf, Applied Materials
Authors: L. Dorf, Applied Materials
S. Rauf, Applied Materials
K. Ramaswamy, Applied Materials
K. Collins, Applied Materials
Correspondent: Click to Email
Langmuir probe (LP) measurements in a realistic very high frequency (VHF) capacitively coupled plasma (CCP) discharge are complicated by a number of factors, such as absence of a well-defined DC ground reference and unpredictable behavior of standard electronic components at VHF. The amplitude of RF potential in a VHF CCP discharge can be large (few tens of volts), especially compared to that in an ICP discharge with similar parameters. RF potential distorts both electron and ion parts of the measured probe V-I characteristic, resulting in unrealistic plasma parameters, and therefore needs to be compensated for. Here, we present results of measurements performed in a 300 mm 162 MHz dielectric plasma etcher using a compensated LP (CLP) and a floating double probe (DP). Probe designs employ a number of previously developed techniques. The probes were used to study the effects of magnetic field, input power, pressure, and chemistry on plasma density radial profiles. The electron part of the CLP V-I characteristic was also used to study the effect of the input power on the electron energy distribution function (EEDF). For all operating conditions – input power of 100 - 1400 W and neutral pressure of 10 - 300 mT – the measured electron temperature was found to lie in the range of 2 - 4 eV, and the plasma density in the range of a few 1010 to a few 1011 cm-3, increasing with power. In Argon, at 10 – 50 mT, the density was found to increase with pressure (due to higher ionization rate). At higher pressure, 50 – 100 mT, the density profile was found to become more uniform, but no significant change in maximum density was observed; further increase in pressure (100 - 300 mT) leads to a decrease in plasma density. Applying a magnetic field of a few tens of Gauss (generated by solenoidal coils placed above the top electrode) was confirmed to have a significant effect on the radial density distribution. Due to a difference in electron residence time caused by the difference in field lines geometry, edge density increases with magnetic field, whereas center density decreases. In electronegative chemistries, the effects of pressure and magnetic field are different. Namely, in O2 at 15 – 100 mT: (a) positive molecular ion density decreases with pressure (possibly due to higher attachment), and (b) center density decreases with magnetic field, but edge density remains largely unchanged. In CF4, the effect of pressure is similar to that in O2, whereas the effect of magnetic field is like that in Ar at low pressure (15 mT), and like that in O2 at high pressure (100 mT). Experimental results were found to be in general agreement with results of applicable simulations.