S. S. Lau

Implanted noble gas atoms as diffusion markers in silicide formation

Abstract Implanted noble gas atoms of Ar and Xe have been used as diffusion markers in growth studies of silicides formed by reacting metal films with silicon substrates. MeV 4He ion backscattering has been used to determine the displacement of the markers. Two approaches were used: either the silicon samples were implanted with Xe or Ar and then covered with a thin layer of metal, or the metal layer was implanted with the marker. When the sample was heated to form the silicide layer, the displacement of the marker relative to the surface determined the identity of the diffusing species. Diffusion markers have been used in growth studies of six silicides: Ni2Si, Mg2Si, FeSi, VSi2, TiSi2 and Pd2Si. We found that Si atoms are the predominant moving species in diffusion in VSi2, TiSi2 and FeSi, while Ni atoms are the moving species in Ni2Si and Mg in Mg2Si. In Pd2Si, both Pd and Si are diffusing species with Si the faster of the two. Chemical effects can play a role in marker studies. In the thermal oxidation of Si, the displacement of Xe markers is consistent with the fact that oxygen is the moving species. Implanted As, on the other hand, accumulates at the Si-SiO2 interface. Therefore, it is necessary to choose markers which are chemically inert.

Interactions in the Co/Si thin‐film system. I. Kinetics

Interactions in the Co/Si thin‐film system were investigated by MeV backscattering and x‐ray‐diffraction techniques. It was found that Si diffuses through the Co layer and accumulates at the sample surface at about 300u2009°C. Increasing the temperature causes the growth of the Co2Si phase, followed by the simultaneous growth of the CoSi phase. The growth rates for both phases have a square root of time dependence. The activation energies of growth are 1.5 and 1.9 eV for the Co2Si and CoSi phase, respectively. A model for the growth of multiple phases is suggested. The transformation between CoSi2 and CoSi is found to be a reversible reaction.

Improvement of crystalline quality of epitaxial Si layers by ion-implantation techniques

We demonstrate that the crystalline quality of Si layers grown on sapphire substrate (SOS) by the CVD method can be greatly improved through the use of implantation of Si ions and subsequent thermal annealing at relatively low temperatures (∼550u2009°C). This method utilizes an amorphous layer created by ion implantation near the sapphire/Si interface. Subsequent regrowth of this amorphous layer starting from the relatively perfect Si surface region leads to a much improved Si crystalline layer, as evidenced by MeV 4He+ channeling and TEM measurements. When the implantation‐formed amorphous layer is located at the outer portion of the Si layer, thermal annealing leads to only a small reduction in the amount of defects in the regrown layer as compared to the unimplanted sample. In these layers, epitaxial regrowth occurs with the same rate and activation energy observed in self‐ion‐implanted 〈100〉 Si.

Iron silicide thin film formation at low temperatures

Abstract The rate kinetics of the formation of compound phases from thin layers of 1000–1500 A α-Fe deposited onto single-crystal Si have been studied by MeV 4He+ backscattering spectrometry. Si is observed to dissolve into the thin α-Fe layer before compound formation. A compound layer of FeSi is produced at about 450°C and FeSi2 formation begins at about 550°C. The (100) surface of Si is slightly more reactive than the (111) surface. An inert diffusion marker of implanted Xe was used to investigate the relative movement of the two species. X-ray diffractometry identifies the structure of the compound species as identical to bulk FeSi and FeSi2. The compounds formed on both (111) n-Si and (100) n-Si are apparently polycrystalline and untextured.

Disorder produced by high‐dose implantation in Si

Channeling measurements with MeV 4He ions were used to investigate the disorder distributions produced in 〈111〉 and 〈100〉 Si samples by implantation at substrate temperatures from −180 to 300u2009°C. The results indicate that for high implantation doses (1015–1016 ions/cm2) a deep stable disordered region is present in both orientations for the samples implanted at temperatures above room temperature but is absent for room‐temperature and lower implants. The colors that have been observed on the surface of samples with similar implants are found to be correlated with the thickness of a thin crystalline layer at the surface.

Interaction of metal layers with polycrystalline Si

Auger electron spectroscopy, MeV /sup 4/He/sup +/ backscattering spectrometry, and scanning electron microscopy were used to investigate interactions between Al films and polycrystalline layers of chemical vapor deposited Si on SiO/sub 2/. Depth profiling techniques showed that intermixing of the Al and Si occurred in 400--560/sup 0/ t. Dissolution of the polycrystalline Si into the Al film occurs followed by nucleation and growth of Si crystallites in the Al film. The morphology of the final structure depends on the relative thicknesses of the as-deposited Al and Si layers. For Al layers thinner than those of the Si, a nearly continuous film is formed on the outer surface. The thickness of this final Si film is approximately that of the original Al layer. The remaining Si and the Al form a two-phase layer between the outer Si film and the SiO/sub 2/ substrate. (WDM)

Kinetics of phase formation in Au—A1 thin films

Abstract Phase formation was studied in Au-A1 thin films by means of MeV He+ back-scattering and glancing angle X-ray diffraction techniques. In the initial stages of compound formetion where both unreacted Au and unreacted A1 layers are present, the phases Au5Al2 and Au2Al are found. The end phases of the low-temperature treatments (150–300°C) are AuAl2 or Au4Al in the presence of only unreacted Al or Au, respectively. The kinetics of the growth of the Al-rich compounds follow a (time)1/2 dependence. The activation energies for the growth of Au2Al and AuAl2 are 1.0 and 1.2 eV, respectively.

Evaluation of glancing angle X-ray diffraction and MeV 4He backscattering analyses of silicide formation

Nickel and palladium silicide films have been used in an evaluation of MeV 4He backscattering, the Read X-ray camera and the Seemann-Bohlin X-ray diffractometer. Identical samples of untextured, textured and epitaxial crystalline layers have been studied by all three techniques. Backscattering spectrometry techniques give concentration ratios and and silicide layer thicknesses. Glancing angle X-ray diffraction is required for positive phase identification and structural analysis. The Seemann-Bohlin diffractometer is capable of quantitative structural analysis; however, the Read camera is adequate in phase identification of silicide formation.

Silicide formation with Pd‐V alloys and bilayers

Solid phase reactions in the temperature range between 250 and 600u2009°C between Si and V‐Pd bilayers as well as alloy layers have been studied by MeV 4He+ backscattering and x‐ray diffraction techniques. When a Pd layer is interposed between Si and V, the bilayer system starts to react at <300u2009°C with the formation of Pd2Si. Annealing at higher temperatures (∼600u2009°C) leads to a uniform layer of VSi2 formed on top of the Pd2Si. Reversing the bilayer sequence (Si/V/Pd) raises the reaction temperature of the system to ∼500u2009°C with V mixing into the Pd layer. Annealing at higher temperature leads to the formation and accumulation of Pd2Si at the interface and a mixed (nonuniform) structure of Pd2Si and VSi2 in the outer surface region. For a Pd‐rich alloy (Pd80V20), a reaction started at about 300u2009°C and produced Pd2Si by depleting Pd from the alloy. This resulted in a mixed structure of Pd2Si and VSi2 in the outer region, similar to the final stage of the Si/V/Pd system. For a V‐rich alloy (Pd90V10), the forma...

Solid‐state epitaxial growth of deposited Si films

Epitaxial growth by furnace annealing of amorphous Si layers deposited onto 〈100〉 Si substrates is demonstrated. Substrate cleaning prior to the evaporation includes only conventional chemical procedures without any attempt to achieve an atomically clean substrate layer interface. The crystalline quality of the grown layers near the surface is comparable to that of 〈100〉 Si regrown layers amorphized by Si implantation. Residual damage is usually found near the substrate‐layer interface. The growth mechanism is believed to be vertical growth of isolated epitaxial columns which subsequently grow laterally to consume the remaining amorphous Si.