Magnetically confined inductively coupled plasma etching reactor

Abstract

A planar radio frequency (rf) inductively coupled plasma etching system has been constructed. The plasma is confined by an external multidipole magnetic bucket made of Nd–Fe–B magnets. This magnetically confined inductively coupled plasma system is equipped with a helium backside-cooled electrostatic wafer chuck and a loadlock chamber. A single-sided planar Langmuir probe was used to map electron velocity distribution functions (EVDFs) radially and axially for both Ar and N2 plasmas with rf power up to 1 kW at low pressure (2 mTorr). By rotating the single-sided probe, the authors found that the EVDFs are noticeably anisotropic. The values of the plasma potential, which were highly uniform radially, were independent of the probe orientation, but those of the floating potential depended strongly on it. The radial uniformity and the absolute magnitude of the plasma potential are confirmed by measurements using an emissive probe. The Langmuir probe measurements showed some deviations from Maxwellian EVDFs for both Ar and N2 plasmas. Because of the multidipole confinement the plasma densities are quite uniform axially, and the radial uniformity improves as the axial distance from the quartz window increases. The rf plasma potential fluctuations were also measured, using a capacitive probe.