Growth Of CoSi2 Research Articles

Epitaxy of CoSi2 on Si (111) at low temperature (≤400 °C)

The epitaxial growth of thin CoSi2 films on a Si(111) surface has been studied using surface techniques such as low-energy electron diffraction and photoemission spectroscopy. Various preparation methods at low temperature (≤400 °C) are investigated. Both layer by layer growth and coevaporation invariably exhibit a bulk and surface excess of Si. In contrast a different preparation method where the Co atoms were evaporated onto the Si(111) substrate maintained at ∼360 °C produces CoSi2 films exposing a Co-rich CoSi2 surface without any Si excess in bulk. It is concluded from these experiments that at ∼360 °C diffusion of Si from substrate through the CoSi2 layer is much easier than usually expected and quite sufficient to sustain further CoSi2 growth without any extra Si supply.

Properties of CoSi2 formed on (001) Si

Properties of CoSi2 films formed on (001) Si have been investigated for silicide films formed by solid-state reaction of either evaporated or sputtered Co with (001) Si substrates. It turns out that CoSi2 films formed from evaporated Co have a systematically higher resistivity than films formed from sputtered Co, which can be attributed to contaminants that were present in the evaporated metal film. Silicide films formed from evaporated Co develop a strong (110) texture, which becomes more pronounced with increasing annealing temperature. Microstructural analyses revealed that this is due to epitaxial growth of (110) CoSi2 upon (001) Si. This is a surprising phenomenon as the epitaxy of (001) CoSi2 on (001) Si would be expected in view of the similarity of the crystal structure and the small lattice mismatch of CoSi2 and Si. The expected epitaxy of (001) CoSi2 on (001) Si is also present but for a smaller fraction of the silicide grains. The film stress has been analyzed in terms of thermal and intrinsic stress. From the thermal stress contribution, a value of 140 GPa was calculated for the biaxial elastic constant of CoSi2. Using this value, it was also possible to interpret the intrinsic stress in terms of the density change upon silicide formation. Transmission electron microscopy and x-ray diffraction revealed that CoSi2 can not only grow epitaxially on (001) Si in a (001) and a (110) orientation but that there is also epitaxy close to these orientations with tilts of around 10° relative to the substrate normal. Simple geometrical calculations show that there is a good match for both (001) and (110) CoSi2 on (001) Si and for a slight tilt from these orientations, all in very good agreement with the observations.

CoSi2 and Si epitaxial growth in 〈111〉 Si submicron lines with application to a permeable base transistor

We report for the first time the epitaxy of CoSi2 on 〈111〉 Si submicron lines together with the overgrowth of Si on top of the resulting grating. Results indicate that strain fields and huge mass transport control the morphology of the resulting structures. Silicon is shown to grow two dimensionally when the grating period is in the submicrometer range. Preliminary results on the electrical performance of those Si/CoSi2 /Si permeable base transistors are presented.

I n s i t u study of the molecular beam epitaxy of CoSi2 on (111) Si by transmission electron microscopy and diffraction

The growth of CoSi2 has been studied by deposition and reaction of Co on clean Si (111) surfaces in situ in a modified ultrahigh vacuum transmission electron microscope. On deposition of nominally 20 Å Co at room temperature, strong interaction between Si and Co occurs yielding an epitaxial film which is believed to be a hexagonally distorted form of the Co2Si structure. On heating to ∼350 °C the growth of epitaxial CoSi is observed, which transforms to CoSi2 at ∼450 °C. Silicon-rich phases propagate by lateral motion of phase boundaries. Substantial pinhole density arises in films only after annealing at higher temperatures. The B orientation dominates under similar annealing conditions. In contrast to NiSi2, the growth of cobalt silicide films on Si is dominated by bulk phase formation, with interfacial energy minimized in all cases by epitaxy.

Growth of single-crystalline CoSi2 on (111) Si in solid phase epitaxy regime by a nonultrahigh vacuum method

Single-crystal CoSi2 films have been grown in solid phase epitaxy regime under nonultrahigh vacuum conditions on (111) Si by electron gun deposition of Co thin films followed by rapid thermal annealing in Ar ambient. The single-crystal films were analyzed by transmission electron microscopy to share the (111) Si surface normal but are rotated 180° about that axis with respect to the substrate. The effect of gas ambient was found to be of critical importance in the growth of single-crystal CoSi2 on (111) Si. The present nonultrahigh vacuum treatments to grow single-crystal films on silicon shall greatly facilitate the fabrication of novel classes of high-speed and high-frequency devices employing buried silicide layers.

Nucleation and Growth of Cosi2 on (001) and (111) Si

ABSTRACTNucleation and growth of epitaxial CoSi2 on Si by the thermal reaction of vapour deposited Co on (001) and (111) Si have been studied by transmission electron microscopy (TEM). On (001)-Si the layer consists of CoSi2 grains. Apart from an aligned (a)-orientation, CoSi2 occurs in a number of orientations, including a (110) preferential (b)-orientation. On (111) Si, single-crystalline layers are obtained, predominantly in the B-type orientation, which is rotated through 180° relative to the aligned (111)-orientation (A-type). The interfacial defect structure consists of misfit dislocations of edge-type with Burgers vector b=a/6<112>, running in <110> directions. The observations for both (001) and (111) Si are related to geometrical lattice match between CoSi2 and Si. In addition to the experimental results, a computer program has been made which calculates the matching between various orientations of CoSi2 and Si. The nucleation of B-type CoSi2 for (111) Si and the different oriented grains for (001) Si are discussed in terms of a nucleation mechanism at steps at the interface in combination with a relatively large mismatch.

Investigation of Interface States on Mbe CoSi2/Si Schottky Contacts by Forward Bias Capacitance Measurement

ABSTRACTThe properties of the interface states of MBE grown CoSi2/n-Si(111) intimate contacts has been investigated using forward bias capacitance measurement. The barrier height øbn for this structure is 0.66±0.01 V. It has been found that there is an interface state band located in 0.44–0.50 eV bfow the conduction band edge of Si. The density of states D it is about 4×1012 cm−2 eV−1, lower than those made by other methods. This intrface state band is in equilibrium with Si and the charge exchange occurs mainly with the electrons in the conduction band of Si. The electron capture cross section oa is about 3×10−15 cm2 . In addition, some discrete interface states were found at 0.53 eV, 0.51 eV and 0.47 eV below the conduction band edge of Si, respectively for several samples. The density of states D it ranges (1.5–3.5)×1010 cm−2 . They are probably caused by localized point defects formed during CoSi2 growth.

Ultrathin Single Crystal CoSi2 Layers on Si(111) and Si(100)

ABSTRACTThe growth of ultrathin epitaxial CoSi2 layers on Si by molecular beam epitaxy has been studied. This paper briefly outlines recent progress in the growth on Si(111) substrates. New results on the growth of epitaxial CoSi2 on Si(100) are also presented.

Formation of Epitaxial NiSi2 and CoSi2 On Laterally Confined (111)Si

ABSTRACTEpitaxial NiSi2 of single orientation was grown on laterally confined (111)Si. Striking oxide opening size effects on the growth of NiSi2 epitaxy were observed. The formation temperature of NiSi2 on (111)Si was found to be as low as 550°C inside oxide openings 1.8 μm or smaller in size. Epitaxial NiSi2 of single orientation which is identical to that of (111)Si substrate was formed inside oxide openings of or smaller than 1.8, 1, and 0.8 μm in size in samples annealed at 550-750, 800, and 850-900°C, respectively. Preliminary results on the epitaxial growth of CoSi2 are also reported.

Characterization of Ultrathin Cosi2 on Si(111) Layers.

ABSTRACTUltrathin epitaxial CoSi2 films on Si(111) have been grown in ultrahigh vacuum by room temperature deposition of Co on Si(111) followed by a high temperature anneal at ~600°C. Characterization of the thin films with transmission electron microscopy has revealed pseudomorphic growth up to thicknesses ~30Å. Pinholes present in the pseudomorphic thin films are thought to prevent the trapping of dislocations within the film. A clear transition to films containing a regular network of misfit dislocations occurs at ~40Å. Evidence for the growth of CoSi2 via intermediate metal-rich silicide phases is observed.

Epitaxial Growth of Near Noble Silicides on (111)Si by Rapid Thermal Annealing

AbstractThe epitaxial growth of near noble silicides, including CoSi2, NiSi2, FeSi2, Pd2 Si, and PtSi on (111)Si, by rapid thermal annealing was studied by transmission electron microscopy. Single-crystalline CoSi2 was formed on (111)Si in the solid phase epitaxy regime by a non-ultra-high vacuum method. The effect on gas ambient was found to be of critical importance on the growth of single-crystal CoSi2 on (111)Si. The best NiSi2, FeSi2, Pd2 Si, and PtSi epitaxy grown on (111)Si by rapid thermal annealing were found to be of comparable quality to those grown by conventional furnace annealing.

Effects of two-step annealing on the epitaxial growth of CoSi2 on silicon

The formation of epitaxial CoSi2 on silicon by both conventional and two-step annealing of cobalt thin films on silicon was studied by transmission electron microscopy.For two-step annealing, samples were first annealed at 350 °C for 1 h, followed by high temperature annealing at 650–950 °C for 1 h. The scheme was found to be very effective in promoting the epitaxial growth of CoSi2 on silicon as well as eliminating faceted structures on Si(111). The results are discussed in terms of the driving away of impurities from the interfaces.

Effects of Two-Step Annealing on the Epitaxialgrowth of CoSi2 on Silicon

The formation of epitaxial CoSi2 on silicon by both conventional and two-step annealing of cobalt thin films on silicon was studied by transmission electron microscopy.For two-step annealing, samples were first annealed at 350°C for 1 h, followed by high temperature annealing at 650–950°C for 1 h. The scheme was found to bevery effective in promoting the epitaxial growth of CoSi2 on silicon as well aseliminating faceted structures on Si(111). The results are discussed in terms of the driving away of impurities from the interfaces.