Measurements of relative BCl density in $BCl3$-containing inductively coupled radio frequency plasmas

The relative density of BCl radicals in inductively coupled plasmas has been studied using laser-induced fluorescence (LIF), and the BCl excited state has been studied using plasma-induced emission (PIE). Measurements were made as a function of input power, pressure, position, and as a function of gas ratio for industry-relevant metal-etch gas mixtures containing $BCl3,$ $Cl2,$ Ar, and $N2.$ LIF was used to measure the ground state BCl population, whereas PIE monitored the BCl $A1Π$ excited state; the LIF and PIE intensities varied differently as the plasma parameters were changed. Between 150 and 400 W input power at 20 mTorr pressure, there was no variation in BCl density, indicating that the dissociation fraction for $BCl3$ to BCl was constant with power. No significant interactions between $BCl3$ and $Cl2$ or Ar were evident in the LIF measurements. However, the BCl density was suppressed by addition of nitrogen to the plasma. The BCl density was radially uniform for all gas mixtures, but axial measurements showed a slight decrease in BCl density near the upper electrode. After running the reactor with a $BCl3/N2$ mixture, BCl was observed for up to an hour after the discharge was switched to $Cl2:$ this is attributed to buildup of BN films on reactor surfaces and subsequent etching of the film by Cl.