A. S. Yapsir

Epitaxial growth of Al(111)/Si(111) films using partially ionized beam deposition

We observed the growth of epitaxial Al(111) films on Si(111) at room temperature by the partially ionized beam deposition technique. The films were deposited in a conventional vacuum condition without in situ cleaning. The beam contained 0.3% of Al self‐ions and a bias potential of 1 kV was applied to the substrate during deposition. X‐ray diffraction (pole figure) revealed that one of the two possible twin structures, with the Al〈110〉∥Si〈110〉 orientation, was preferentially grown on the Si substrate.

Effects of hydrogen ion implantation on Al/Si Schottky diodes

Al/Si(p) and Al/Si(n) Schottky diodes were implanted with hydrogen ions such that the peak of the hydrogen distribution was localized at the metal‐semiconductor interface. Current‐voltage (I‐V) measurements indicated more ohmic behavior in the Al/Si(n) and more rectifying behavior in the Al/Si(p) diodes. For both cases, annealing at 200 °C for 30 min caused the I‐V curves to almost revert to the pre‐implantation characteristics. A similar behavior was observed using the capacitance‐voltage (C‐V) measurement technique. No significant change of the hydrogen concentration or redistribution of the concentration was observed after the 200 °C heat treatment. Correlation between the hydrogen depth profiling data and the electrical measurements indicated that, as far as I‐V and C‐V were concerned, the implanted hydrogens were electrically inactive.

Observation of a new Al(111)/Si(111) orientational epitaxy

A new Al(111)/Si(111) orientational epitaxy using x‐ray pole figure analysis is reported. The new structure has a 19° rotation with respect to the parallel epitaxy. The results are explained using a geometrical lattice matching concept.

Reduction of interface hydrogen content by partially ionized beam deposition technique

Hydrogen content at the Al/Si interface of samples with Al films deposited by conventional means and by a partially ionized beam (PIB) was measured using 1H(15N,αγ)12C nuclear resonance reaction. We observed that samples with PIB‐deposited Al film exhibited significantly lower hydrogen concentration at the Al/Si in interface than that of the sample deposited by conventional means. The results demonstrated the ability of the PIB technique to perform interface self‐cleaning, at least for hydrogen contaminant.

Channeling study of structural effects at the Al(111)/Si(111) interface formed by ionized cluster beam deposition

Epitaxial Al(111)/Si(111) films grown by the ionized cluster beam technique have been studied using the high‐energy He+ channeling technique. No observable strain has been detected between the Si substrate and the Al layer despite their large (∼25%) lattice mismatch. Displaced Al atoms have been observed in the Al film, which increases with the depth and reaches 30% near the Al/Si interface. A large step increase of dechanneling occurs at the Al/Si interface which might be accounted for by the existence of ‘‘semicoherent’’ interface in which four Al planes are matched to three Si planes.

Electromigration in Al/SiO2 films prepared by a partially ionized beam deposition technique

It has been found that the electromigration resistance of pure Al/SiO2 thin films prepared by the partially ionized beam (PIB) deposition technique can be improved significantly as compared to those deposited by the conventional means. The PIB contained 0.8–1.2% of Al self‐ions and a bias potential of 2–5 kV was applied to the substrate during deposition. The enhancement of the electromigration resistance of the Al films is believed to be associated with the strong preferred orientation (in the [111] direction) that these films have. Surprisingly the preferred orientation effect is not accompanied by an enlargement of the Al grain size. This combination of preferred orientation and small grain size may find important applications in future very large scale integrated metallization.

Formation of low‐temperature Al/n‐Si Schottky contacts using a partially ionized beam deposition technique

High quality Al/n‐Si Schottky contacts have been fabricated using the partially ionized beam (PIB) deposition technique in a conventional vacuum condition without post heat treatment. The electrical characteristics of the diodes were extremely uniform across a 3 in. wafer and were stable with respect to a furnance annealing performed at 450 °C for 30 min. Scanning electron microscope examination revealed much shallower pit formation on the Si surface, as compared to that deposited by conventional means, following the heat treatment. A completely smooth Si surface was observed after a 10 s rapid thermal annealing at 450 °C. The observed behavior could be attributed to the creation of ‘‘contact openings’’ in the native oxide during deposition by ion bombardment, allowing Al to make an intimate contact to Si. This PIB deposition of metal‐semiconductor contacts may be an important metallization scheme for the future low‐temperature processing of shallow junctions for very high speed integrated circuits.

Effects of deuterium plasmas on silicon near‐surface properties

The effects of reactive‐ion etching and plasma etching (using deuterium) on the electrical properties of silicon have been studied employing capacitance‐voltage measurements of Schottky diodes and secondary ion mass spectrometry. Both significant hydrogen penetration, which causes electrical deactivation of the boron dopant, and radiation damage result from the plasma exposure. A model is suggested to explain our results.

Electrical characteristics of hydrogen implanted silicon Schottky diodes having large difference in metal work function

Hydrogen ion implantation was carried out on Schottky diodes having large difference in metal work function, Ti/p‐Si and PtSi/p‐Si diodes. Current‐voltage (I‐V) measurements showed that, following ion implantation, Ti/p‐Si diodes exhibited rectifying characteristics; in contrast, no significant rectifying behavior was observed in the PtSi/p‐Si diodes. These results showed a dependence of the implantation effects upon metal overlayer work functions. Consequently, the observations did not seem to indicate the occurrence of Fermi level pinning due to a highly damaged near‐surface region after ion implantation, as previously suggested. Capacitance‐voltage (C‐V) measurements revealed a decrease in the diode capacitances along with a significant reduction of acceptor concentration following the implantation. In general, the results suggest that ion implantation alters the electrical characteristic of the diodes mainly by creating defects in the semiconductor depletion region. All such defects act as recombination centers giving rise to a deviation of the electrical characteristics from the normal behavior. They do not play a role in producing a Fermi level pinning.

PtSi/n-type Si Schottky barrier height change by H+ ion implantation near the interface region

PtSi/n-type Si Schottky diodes were implanted with hydrogen ions of 150 keV energy in order for the peak of the hydrogen distribution to be localized near the silicide-semiconductor interface. Following implantation at doses between 1 × 1017 H/cm2 and 5 × 1017 H/cm2, C-V measurements indicated that the barrier height had increased from 0.84 eV to ≈ 1.10 eV. One possible explanation for the increase in barrier height is hydrogen passivation of the surface states at the silicide-silicon interface. I-V measurements indicated that the leakage current had increased by a factor of nearly 10, as compared to the unimplanted case. The samples which had been implanted at a dose of 5 × 1017 H/cm2 were annealed in a nitrogen ambient at 200° C for 30 min, while those implanted at 1 × 1017 H/cm2 were subjected to a “Rapid Thermal Annealing” step at 450° C for 10 s. C-V measurements revealed that the barrier height value had nearly reverted to that of the unimplanted case. In addition, I- V measurements did not show any significant change in the leakage current, therefore most of the damage was observed to be still present following the annealing step. Based upon the fact that the damage had not yet been annealed, and that the barrier height had nearly reverted to its original value, it is proposed that the hydrogen atoms responsible for the increase in the value of the barrier height had diffused out of the interface region upon heat treatment.