Determination of carbon impurities in epitaxial layers from semiconductor silicon by means of charged particles

Abstract

The energy-dependent range of charged particles in activation analysis according to the reaction¹²C(d,n)¹³N permits the method to be applied to carbon determination in model epitaxial layers of sufficient thickness. We investigated 100 μm epitaxial layers of the n-type and undoped 50 μ layers as to p⁻ Czochralski substrates. Deuterons were slowed down with Cu and Ta foils having a limiting energy of 13.5 MeV, to 4.2 MeV and 2.9 MeV, respectively. In the resulting activation depths of 52 and 102 μm, the sensitivity of the method, which is 3·10¹⁴ at ·cm⁻³C at E_d=10 MeV in silicon, is reduced to 25% and 10%, respectively. An optimal flux of 0.9 μA·cm⁻² was maintained. After irradiation, 20 or 10 μm were etched off. The sample was inductively fused at 1500 K in a Pb₃O₄/B₂O₃ mixture.¹³N was passed with He as carrier gas into an absorption vessel kept at 77 K, and its activity was measured in γ, γ-coincidence.