A study of ion beam analysis techniques using non-Rutherford scattering, nuclear reactions and channeling.

Abstract

Rutherford Backscattering Spectrometry (RBS) is a very popular, fast, and non-destructive technique that has been used extensively for Ion Beam Analysis (IBA). However, RBS with ⁴He⁺ ion beams, in many cases, is ineffective for light element analysis due to overlapping signals. This project is an attempt to develop special techniques using non-Rutherford elastic scattering, nuclear reactions and elastic scattering under channeling conditions for light element analysis in cases where regular RBS is ineffective. The ⁴He-N elastic scattering cross sections for He⁺ ion energies from 1750 KeV to 5000 KeV at a lab angle of 170.5° were measured. Non-Rutherford elastic backscattering of He⁺ from nitrogen near an energy of 3500 KeV was applied to improve mass resolution; an example is described resolving the signals from nitrogen and oxygen in a target. A narrow resonance at He energy of 3575 KeV (Γ = 4 ± 1 KeV) was used for nitrogen depth profiling. The (ɑ,p) nuclear reaction for nitrogen, boron and silicon analysis in thin films was investigated. The excitation functions for the reactions at a lab angle of 135° were measured. The ¹⁴N(ɑ,p₀) ¹⁷O and ¹⁰B(ɑ,p) ¹³C reactions were used for nitrogen and boron content determination in thin films in cases where regular RBS is ineffective because of signal interference. The resonance in the ²⁸Si(ɑ,p)³¹ reaction near He ion energy of 3875 KeV was used to determine the thickness of silicon backed films. The (p,ɑ) nuclear reactions for boron and fluorine analysis in thick targets was investigated. The ¹¹B(p,ɑ₀) ⁸Be and ¹⁹F(p,ɑ₀) ¹⁶O reactions were applied to quantify boron and fluorine in thick targets. A technique of non-Rutherford backscattering combined with channeling was used for quantifying carbon and silicon in a SiₓC overlayer on a single crystalline Si substrate. The He-C non-Rutherford scattering enhanced the backscattering from carbon and the channeling condition improved the signal-to-background ratio. An example of use of this technique for determination of a small dose of carbon implanted in a single Si crystal is also presented to show the sensitivity of the measurement.