Vertex - the theory behind ion current as a function of angle

Ion angular distribution measurements with a planar retarding field analyser

Ion angle determination with current derivative
The Vertex Multi Sensor measures the ion energy distribution as a function of aspect ratio hitting a surface inside a plasma reactor from multiple locations to analyse the uniformity of ion interactions across a substrate.

Abstract

In this application note, we present a novel method which can be applied to a planar retarding field energy analyser (RFEA) for the measurement of ion angular distributions. Ion energy and angular ion distributions play a critical role in plasma assisted etching and conformal deposition processes. Ion impact at wider angles may be required for better step coverage in certain sputter deposition and ion implantation processes while large angle ion impact can be detrimental to anisotropic etch processes. In the early 80’s, Stenzel et al 1, 2 developed a directional RFEA where particles are geometrically filtered through a micro-capillary plate prior to energy analysis. The high aspect ratio (AR) of the holes/channels in the plate allowed them to select particles within a geometric acceptance angle. The Vertex RFEA design has a variable AR, controlled using a potential difference between two grids (see application note VE02). A variable AR controls the ion angular spread passing through the sensor for detection. The Vertex product produces a plot of ion energy distribution versus AR.

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