Shin Hashimoto

Steering effect at a strained NiSi2/Si (001) interface

Abstract In a 700 A thick NiSi 2 , epitaxial film grown on Si (001), tensile strain due to the lattice mismatch was observed by means of 1.0–3.5 MeV He ion channeling angular scans about three different off-normal channeling axes in major planes, i.e. [Ill] in (110), [112] in (110) and [Oil] in (100). Because of angular misalignment between the NiSi 2 ; and the Si substrate (Si sub ) off-normal channeling axes, peculiar behaviors of channeled ions were observed in the Si sub angular scan profiles. Namely, at ion incident angles corresponding to the NiSi 2 axes, the Si sub yield changed dramatically with the incident ion energy, while at incident angles corresponding to the Si Sub , axes, the Si Sub yield showed no energy dependence. Considering a relation between the angular misalignment and the channeling critical angle (which depends on the ion energy and the channeling axis), the energy dependent behavior is explained by the contribution of channeled ions steered into the Si Sub axial channels, i.e. the steering effect. The nature of the channeling minimum when ions are incident along the Si Sub axial direction suggests that a transition from planar-like motion to axial motion occurs.

Strain relief of large lattice mismatch heteroepitaxial films on silicon by tilting

Abstract In this paper, a general formula is calculated relating the misalignment of a heteroepitaxial overlayer with respect to the substrate to the defects at the interface. High resolution transmission electron microscopy studies are presented which show that the density of dislocations along the interface of GaAs grown in vicinal Si(100), with the Burgers vector perpendicular to the interface, is consistent with the amount of tilt observed in ion-channeling studies. Arguments are also presented which demonstrate that the tilt observed is an effective form of strain relief but that this mechanism can only operate when the heteroepitaxial growth is nucleated by island growth. One significant conclusion is that the lower bound observed on the threading dislocation density in GaAs on silicon is due to this mechanism of strain relief by tilting. These arguments should be valid for all large-lattice-mismatched heteroepitaxial systems in which the epitaxial layer has a larger lattice parameter than the substrate.

Growth of single-crystal columns of CoSi2 embedded in epitaxial Si on Si(111) by molecular beam epitaxy

The codeposition of Si and Co on a heated Si(111) substrate is found to result in epitaxial columns of CoSi2 if the Si:Co ratio is greater than approximately 3:1. These columns are surrounded by a Si matrix which shows bulk‐like crystalline quality based on transmission electron microscopy and ion channeling. This phenomenon has been studied as functions of substrate temperature and Si:Co ratio. Samples with columns ranging in average diameter from approximately 25 to 130 nm have been produced.

Channeling lattice location of Se implanted into InP by RBS and PIXE

Abstract The lattice location of Se atoms implanted into InP was studied by simultaneous RBS (for detecting In) and PIXE (for detecting Se), using 2.5 MeV proton ions in the channeling mode. For InP single crystals, the 〈111〉 atomic row consists of alternate In and P atoms, while in the 〈110〉 direction there exist pure In and P atomic rows. Since the channeling half-angle is proportional to Z 2 1/2 , where Z 2 is the average atomic number of the constituent atoms in the row, it is possible to determine the specific lattice location and the substitutional fraction of Se atoms in InP by measuring angular distributions of Se and In across the 〈111〉 and 〈110〉 axes. The results show that Se atoms occupy P sites with different fractions depending on the implantation temperature and dose.

Direct scattering probability for channeled ions near dislocations

Abstract A simple analytical model is offered to estimate the probability of direct scattering from crystal atoms in regions close to a dislocation. The model is based on previous analytical and computer calculations for dechanneling due to dislocations. The results predict that the direct scattering probability (i.e. number of scattering centers) should be proportional to the energy of the channeled ions. Experimental verification of this prediction is discussed as well as the consequences for channeling experiments with heteroepitaxial thin films.

Columnar epitaxy of PtSi on Si (111)

Columnar grains of PtSi surrounded by high quality epitaxial silicon are obtained by ultrahigh vacuum codeposition of Si and Pt in an 8:1 ratio on Si(111) substrates heated to 610–810 °C. The areal density of columns varies from 120 to 3.8 μm−2, and layers with thicknesses from 100 nm to 1 μm have been demonstrated. This result is similar to that found previously for CoSi2 (a nearly lattice‐matched cubic‐fluorite crystal) on Si(111), in spite of the orthorhombic structure of PtSi. The PtSi grains are also epitaxial and have one of three variants of the relation defined by PtSi(010)//Si(111), with PtSi[001]//Si〈110〉.

Linear energy dependence of the interface peak intensity

Abstract The MeV He ion channeling technique was utilized for characterizing the interfacial defects at MBE grown CaF2/Si (111) interfaces. The Ca interface peak (IP) intensity was measured as a function of the incident energy (E). The energy dependence of the IP intensity was observed to be E1 .This E1 dependence cannot be explained by scattering from random defects or by dechanneling. The E1 dependence is explained by considering direct scattering of channeled ions from curved atomic strings in misfit dislocation network regions.

Growth of IrSi3 by molecular beam epitaxy

Abstract Epitaxial IrSi 3 films have been grown on Si(111) by molecular beam epitaxy at temperatures ranging from 630 to 800°C. Good surface morphology was observed for IrSi 3 layers grown at temperatures below 680°C, and an increasing tendency to form islands is noted in samples grown at higher temperatures. Transmission electron microscopy analysis reveals that the IrSi 3 layers grow epitaxially on Si(111) with three epitaxial modes. A minimum channeling yield of 52% was observed for the IrSi 3 layer MBE grown at 630°C by Rutherford backscattering spectroscopy.

Columnar growth of CoSi2 on Si(111), Si(100) and Si(110) by molecular beam epitaxy

Abstract Codeposition of silicon and cobalt on heated silicon substrates in ratios several times the stoichiometry is found to result in epitaxial columns of CoSi2 surrounded by a matrix of epitaxial silicon. For (111)-oriented wafers, nearly cylindrical columns are formed, where both columns and surrounding silicon are defect free, as deduced from transmission electron microscopy. Independent control of the column diameter and separation is possible, and diameters of 27–135 nm have been demonstrated. On (100) wafers, columns are less regular in shape and show a strong tendency to form {111} interfaces with the surrounding silicon. On (110) wafers, columns are elongated parallel to a 〈110〉 direction, and planar twins are observed in the silicon.

STRAIN AND REORDERING IN CaF 2 /Si(lll) EPITAXY

Strains in CaF 2 films, grown by molecular beam epitaxy at 700oC on Si(lll) subsrates, have been measured by MeV 4 He + ion channeling. For CaF 2 films thinner than 200nm, the strain parallel to the (111) plane is found to be tensile. No strain is observed for films thicker than 200nm. The observed tensile strain cannot be explained by a simple pseudomorphic growth model because the larger lattice constant of CaF 2 relative to Si should result in a compressive misfit strain. The tensile strain is an indication of the relaxation of the compressive misfit strain at the growth temperature due to nucleation of interfacial defects. If these defects are not annealed out as the substrate temperature is lowered after growth, the tensile strain can result because of the larger thermal contraction of CaF 2 compared to Si. The final film quality near the interface improves as the film thickness is increased. This indicates that reordering of interfacial disorder is caused by the strain energy accumulated during the cooling process.