AVS 61

AVS International Symposium and Exhibition is on in Baltimore between November 9 - 14. We will be exhibiting there and our own Shailesh Sharma will be giving a talk on Ion Angular Distributions Measured with a Planar Retarding Field Analyser. We look forward to hearing Shailesh and seeing you at booth 1502.

Ion Angular Distributions Measured with a Planar Retarding Field Analyzer

Shailesh Sharma

Abstract

Planar retarding field analyzers are commonly used to measure ion energy distributions but provide no
information about the angular distribution of ions bombarding the substrate surface. Here, we report on a novel
planar retarding field analyser design capable of resolving the angular distribution of the energetic ions. The
design has three active grids, a collector plate and an aperture with variable aspect ratio (height / diameter) to
control the angular spread of the ions allowed through the device for detection. First, the potential of the ion
energy discriminating grid is modulated to select ions with a specified energy resolution for analysis. Then, the
aspect ratio of the aperture is varied from large acceptance angle to narrow acceptance angle with specified angle
resolution - predetermined from the aperture geometry. The ion current is recorded for each acceptance angle to
give an integral form of the ion angular distribution at a given ion energy where the angular distribution can be
recovered by taking a first derivative. The procedure is then repeated for each ion energy. Once the angular
distribution is determined as a function of ion energy, the energy distribution as a function of ion angle is easily
calculated.

The analytical theory used to define ion current as a function of incident ion angle, ion energy and aperture aspect
ratio is presented. The method used to vary the aspect ratio of the additional aperture is also discussed. This novel
method allows ion angular distributions to be determined using a compact planar retarding field analyser.
With the modified retarding field analyzer design and advanced analytical technique, ion angular distributions
with angle resolution as low as 3 degrees have been measured. This technique adds important functionality to the
retarding field analyser technology - which has become one of the most important technologies in the field of plasma
diagnostics in recent years.