Electron-density and energy distributions in a planar inductively coupled discharge

Abstract

Electron-density and electron energy distribution functions (EEDFs) are measured in a 20-cm-diam by 14-cm-long cylindrical, inductively coupled plasma source driven by fields from a planar, spiral coil at 13.6 MHz. Radio-frequency (r-f) -filtered Langmuir probes are used to obtain spatial profiles of electron population characteristics in argon at powers and pressures of interest for etching and plasma-assisted deposition (l-100 mT). Electron densities range from lOlo to 10" cm3 with lOO-500 W of rf power and peak on axis in the center of the cylindrical volume. The EEDFs show that the observed average electron energy varies by 1-2 eV spatially, with the highest values of average energy occurring at those regions of strongest rf electric field. The EEDF measurements also reveal a significant population of cold electrons trapped in a potential well at the location of peak electron density. From these spatial measurements, spatial estimates of conductivity and ionization rate are deduced.

An rf sustained argon and copper plasma for ionized physical vapor deposition of copper

“…A tuned resonant rf filter in combination with a low-pass filter was used to maximize the probe impedance and to minimize the rf distortion to the probe measurements. 10,11 All the Langmuir probe measurements were conducted in an argon plasma while the magnetron was off. Argon was assumed as the only species present in the plasma.…”

Plasma properties determined with induction loop probes in a planar inductively coupled plasma source

“…The figure suggests that Re͑⑀͒, which is proportional to the electron density n e , has a maximum on axis, consistent with n e measurements on this system with Langmuir probes. 2,3 The maximum measured value of Re͑⑀͒ in the 50 mTorr case is nearly five times larger than in the 10 mTorr case. In addition, the lowerpressure case shows a flatter radial density profile near the discharge axis ͑weaker radial density gradient͒ than the higher-pressure case, also in agreement with the probe measurements.…”

“…In the 50 mTorr case, the peak observed value of the drift velocity is v 0D ϭ4.5ϫ10 5 m/s as compared to the thermal velocity V T ϭ1.0ϫ10 6 m/s for electrons with temperature T e ϭ2.3 eV determined from Langmuir probe measurements. 3 Because the amplitude of the rf drift velocity is found to be of the same order as the thermal velocity, the associated local enhancement of electron energy is likely to affect electron impact reaction rates in this region of the discharge.…”

“…2,3,5,7 Briefly, rf current at 13.56 MHz in the four-turn, 16.5-cm-diam, spiral planar coil couples power to the plasma through a radially spoked Faraday shield and a 1.27 cm quartz window. Argon is fed into the system through an annular gap around the edge of the quartz window.…”

“…1 Characterization of source operation is important both for benchmarking of simulations as part of the development of reactor computeraided design tools and in gaining basic understanding which can be applied directly to process development and reactor scale-up for uniform processing of larger substrates. Although much characterization has been done with Langmuir probes, [2][3][4] that technique is limited to chemistries which neither corrode probe surfaces nor deposit insulating films. This prevents application of Langmuir probes in many gas mixtures of interest for etching and deposition applications.…”