Laplace Deep Level Transient Spectroscopy of ultra shallow implanted junctions in Si

Deep level transient spectroscopy (DLTS) and laplace DLTS (LDLTS) measurements have been carried out on very shallow implanted p-n junctions in Si. Lightly doped n or p type Si was implanted with high doses at low energy of B or As, followed by implants of lower doses at higher energies of n or p dopants respectively, to simulate a doping well. The double implants resulted in p⁺/n/n^- or n⁺/p/p^- structures, which calculation showed had two depletion regions, one at the end of range of each implanted region. The electric fields in the two depletion regions act in the opposite sense, and by selecting the correct bias conditions it was possible to measure DLTS at the end-of-range of the two implanted regions. DLTS of the n+/p diodes displayed a high temperature peak due to the end of range of the shallow As implant, together with a defect originating much deeper behind the surface observed at low temperatures. LDLTS of the defect in the end-of-range of the As implant revealed two closely spaced energy levels, indicative of a complex defect structure in this region. The DLTS also showed a minority emission peak in all of the p⁺/n/n^- and n⁺/p/p^- samples. Their emission rate in LDLTS did not change with measurement temperature, and is discussed in terms of a small region at the shallow junction that is efficiently confining carriers.