Ion Irradiation Effects on Pt Contacts To Si with and without Interfacial Chemical Oxide

Abstract

The electrical properties of ion irradiated metal-semiconductor contacts are investigated. Silicide contacts are fabricated by depositing Pt on chemically clean or slightly oxidized (∼14 Å SiO₂) n⁺-and n-type <111> Si, followed by a Si ion irradiation (10¹⁴ − 6×10¹⁵ Si/cm²) through the metal-Si interface at various substrate temperatures, and a final thermal annealing in vacuum to form the silicide. Forward I-V measurements are employed for electrical characterization. Metal-Si interaction and substrate damage are measured by MeV ion backscattering and channeling, and interfacial oxygen monitored by nuclear ¹⁶O(d,α)¹⁴N reaction.

Platinum contacts prepared on clean n-type substrates are Schottky diodes with a barrier height øBn = 0.83 eV. After Si irradiation, the forward I(V) is a power law whose form is largely independent of the dose. Subsequent thermal annealing induces silicide formation, but at a reduced rate compared to irradiated samples. The do characteristics is roughly exponential again, but departures from the original Schottky characteristics remain and are largest for the highest Si doses. The effect is attributed to radiation damage in the Si that is not consumed by the silicide reaction.

Platinum contacts prepared on chemically oxidized samples behave differently for different substrate materials, although the total amount of interfacial oxygen is always the same. On n^+-type samples, the silicide formation at 400°C is laterally uniform for Si doses ≥ 2 × 10¹⁴ cm⁻², but is nonuniform for all doses (≤ 2 × 10¹⁵ Si/cm²) on n-type samples. For n^+-type samples at 250°C, a dose of 2 × 10¹⁵ Si/cm² is required to induce (uniform) silicide formation; the kinetics displays a time delay compared with that of clean n⁺ substrates. On oxidized n-type substrates, the I(V) characteristics of Pt contacts before irradiation is not Schottky-like, but power-law-type. After irradiation, the characteristic is the same as for the clean irradiated samples. Thermal annealing induces only incomplete recovery toward an exponential behavior.

These results demonstrate that radiation damage in the unreacted Si remains significant for the electrical behavior of all.

These results demonstrate that radiation damage determines the I(V) characteristics of as-irradiated Pt contacts to n-type Si regardless of the presence of an interfacial oxide layer. After annealing at 400°C for 30 min, radiation damage is still significant, but the oxidized samples recover less than the clean ones. The results are attributed to radiation damage in the unreacted Si substrate.