High-resolution Rutherford backscattering spectrometry with an optimised solid-state detector

Abstract

Rutherford Backscattering Spectrometry (RBS) is a powerful ion beam analysis technique in frequent use within materials science. The recent emergence of targets incorporating complex features such as ultra-scaled diffusion barriers and isotopically-enriched films has started to push the limits of the technique, ecessitating the expanded use of systems with a higher energy resolution. The increased cost and complexity of these systems based on already well-established schemes may present a barrier to their more widespread adoption. Here, we present an RBS detection system specifically designed for simple integration into existing nuclear probe infrastructure, but with a considerably higher energy resolution than a standard passivated planar detector. We employ a modified silicon p–i–n photodiode integrated within an optimised in-vacuum preamplifier to achieve a relative energy resolution of 3 × 10−3 with 2.2 MeV He+ ions. In a glancing angle geometry, this corresponds to a depth resolution of ∼1.5 nm and a mass resolution of <1 u from light elements up to Cu. We demonstrate the use of this detector to measure the thermal diffusion of near-surface As implants in a Si substrate, important for the formation of ultra-shallow junctions; and the residual 29Si concentration in an isotopically enriched 28Si specimen, a promising platform for quantum computation.