C. W. Nieh

Formation of epitaxial NiSi2 of single orientation on (111) Si inside miniature size oxide openings

Epitaxial NiSi2 of single orientation was grown on (111) Si inside miniature size oxide openings. 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. The results are discussed in terms of the variation in tensile stress exerted by oxide near the silicon surface and small free‐energy difference between type A and type B NiSi2 epitaxy inside small size oxide openings.

Formation of bubbles in BF+2‐implanted silicon

Fluorine bubbles were observed in 5×1015/cm2 BF+2 ‐implanted (001) and (111) Si annealed at 1000–1100 °C. Bubbles were found to form in samples annealed at 1100 °C for a time as short as 10 s. The bubbles were distributed mostly near the original amorphous/crystalline interface and silicon surface. The growth of bubbles was seen to be intimately related to the presence of residual defects. Possible ramifications of bubble formation in device applications are discussed.

Epitaxial growth of NiSi2 on ion‐implanted silicon at 250–280 °C

Striking effects of dopant atoms on the formation of Ni silicides were observed. Epitaxial NiSi2 was found to grow on both BF+2‐ and B+‐implanted (001) and (111)Si at 250–280 °C. The formation of Ni2Si was suppressed. It is conjectured that the presence of dopant atoms may lower the activation energy substantially to promote the formation of epitaxial NiSi2 at low temperatures. The effects may be exploited to grow other epitaxial silicides on silicon at low temperatures.

Investigations of dynamical changes in metal/silicon and ion‐implanted silicon thin films by cross‐sectional transmission electron microscopy with intermittent annealings in N2 ambient

The feasibility of studying dynamical changes in metal/silicon and ion‐implanted silicon thin films by cross‐sectional transmission electron microscopy with intermittent annealings in N2 ambient up to 900 °C is demonstrated. Interactions of nickel thin films with oxidation‐induced stacking faults and fluorine bubbles, the evolution of microstructural defects and solid‐phase epitaxial growth in BF+2 ‐implanted silicon are provided as examples. The technique may be applied to clarify a number of important issues encountered in the study of the reactions and diffusion of thin films and obtain information otherwise unattainable.

Nanometer thick single crystal Y2O3 films epitaxially grown on Si (111) with structures approaching perfection

Cubic phase Y2O3 films 1.6–10nm thick of excellent quality have been epitaxially grown on Si (111) with Y2O3(111)∥Si(111) using electron beam evaporation of Y2O3 in ultrahigh vacuum. Structural and morphological studies were carried out by x-ray scattering and reflectivity and high-resolution transmission electron microscopy, with the growth being in situ monitored by reflection high energy electron diffraction. There are two Y2O3 domains in the initial stage of the oxide growth with equal population, and the B-type domain of Y2O3[21¯1¯]∥Si[112¯] becomes predominating over the A-type domain of Y2O3[21¯1¯]∥Si[21¯1¯] with increasing film thickness. Besides the excellent crystallinity of the films as derived from the small ω-rocking curve width of 0.014°, our results also show atomically sharp smooth surface and interfaces.

High-quality nanothick single-crystal Y2O3 films epitaxially grown on Si (111): Growth and structural characteristics

High-quality single-crystal nanothick Y2O3 films have been grown epitaxially on Si (111) despite a lattice mismatch of 2.4%. The films were electron beam evaporated from pure compacted powder Y2O3 target in ultrahigh vacuum. Y2O3 3nm thick exhibited a bright, sharp, streaky reconstructed (4×4) reflection high energy electron diffraction pattern. Structural studies carried out by x-ray diffraction with synchrotron radiation and high-resolution transmission electron microscopy show that the films have the cubic bixbyite phase with a remarkably uniform thickness and high structural perfection. Two Y2O3 domains of B-type Y2O3[21¯1¯]∥Si[112¯] and A-type Y2O3[21¯1¯]∥Si[21¯1¯] coexist in the initial film growth with B type predominating over A type in thicker films as studied using x-ray diffraction. The narrow full width at half maximum of 0.014° in the ω-rocking curve is the characteristic of excellent crystalline films. High-resolution transmission electron microscopy and fast Fourier transform analysis show ...

Partial epitaxial growth of HfSi2 films grown on silicon

Epitaxial HfSi2 has been grown locally on (001)Si. In samples annealed in one step at 1100 °C or in two steps at 450–1100 °C, islands of HfSi2 of 0.8 μm in average grain size were found to cover about 40% of the surface area. About 70% of the disilicide in areal fraction was found to be epitaxial silicide, 0.6–1.2 μm in size. The orientation relationships between epitaxial HfSi2 and (001)Si substrate were analyzed to be [010]HfSi2∥[001]Si and (002)HfSi2∥(220)Si (with about 1° misorientation). Interfacial dislocations, 75 A in average spacing, were identified to be of edge type with 1/2〈110〉 Burgers vectors. No HfSi2 epitaxy was found to form on (111)Si.

Cross‐sectional transmission electron microscope study of intrinsic solid‐phase epitaxial growth in self‐ion‐implanted (001) Si

A cross‐sectional transmisson electron microscope (XTEM) study of intrinsic solid‐phase epitaxial (SPE) growth in self‐ion‐implanted (001) Si has been carried out. The activation energy of the self‐ion‐implanted silicon was measured to be 2.6±0.2 eV. The value is remarkably close to those obtained in the two most recent studies by other techniques. The pre‐exponential factor is lower than that reported by Lietoila et al. [J. Appl. Phys. 53, 4399 (1982)] annealed under similar conditions. The variation in proximity to the surface and difference in the distribution of the microstructural defects in the two studies are suggested to be possible causes for the discrepancy. The advantages of utilizing the XTEM technique to study epitaxial growth of self‐ion‐implanted amorphous thin films are demonstrated. The accuracy in the XTEM measurement of the SPE regrowth rate in Si+‐implanted (001) Si is discussed.

Lattice strain and in situ chemical depth profiling of nanometer-thick molecular beam epitaxy grown Y2O3 epitaxial films on Si (111)

The strain/relaxation behavior of nanometer thick Y2O3 (111) epitaxially grown on Si (111) has been investigated with x-ray diffraction using synchrotron radiation. The authors systematically measured a series of Bragg reflections to determine the lattice parameters of Y2O3 films with thickness ranging from 1.6 to 9.5 nm. The strain state of the oxide lattice along surface normal and lateral directions is analyzed as a function of the oxide thickness. The spectra of Si 2p and Y 3d, obtained with in situ angle-resolved x-ray photoelectron spectroscopy on Y2O3 5 nm thick, showed no Y silicide but a very small incorporation of Si into the Y2O3 films at the interface.

Effects of Dopants on the Nucleation and Growth of NiSi 2 on Silicon

The influences of implantation impurities, including BF 2 , B, F, As and P on the formation of epitaxial NiSi 2 in nickel thin films on ion-implanted silicon have been investigated by transmission electron microscopy. The presence of BF 2 , B, and F atoms was observed to promote the epitaxial growth of NiSi 2 at low temperatures. Little or no effect on the formation of NiSi 2 was found in samples implanted with As or P ions. The results indicated that the influences of the implantation impurities are not likely to be electronic in origin. Good correlation, on the other hand, was found between the atomic size factor and resulting stress and NiSi 2 epitaxy at low temperatures.