Industrial feasibility of an in-situ-doped (ISD) polycrystalline Si process using chemical vapor deposition for advanced BiCMOS technologies is presented. ISD As-doped amorphous and polycrystalline Si layers have been deposited on Si substrates at 610°C and 660°C, respectively, with the deposition rate varying from 120 to 128Å /minute. Samples are compared on the basis of having been subjected to a substrate preclean prior to deposition using an HF solution and an in-situ H2 bake. TEM micrographs reveal the presence of a thin (10-15 Å) native oxide at the deposited layer/substrate interface for samples not precleaned. This is confirmed for both the amorphous and polycrystalline Si depositions. However, for the 610°C-deposited samples given the substrate preclean, a polycrystalline structure with partial epitaxial layer growth is observed. Twins and stacking faults are found at the poly Si/single crystal Si interface, causing interfacial roughness. Post-deposition annealing of the Si films typically generates grain growth, but RBS-channeling characterization of the annealed Si provides evidence of some recrystallization, the extent of which is affected by the original growth condition. Analysis shows that the amorphous deposition at 610°C results in a mixture of epitaxial and polycrystalline Si. Epitaxial realignment of the polycrystalline Si film by post deposition annealing can result in significantly improved device performance.

Biaxially textured MgO buffer layers were deposited on metal substrates using “inclined substrate deposition” (ISD). The influence of the substrate inclination angle, deposition rate, and film thickness on the texture is shown. Scanning electron microscopy reveals columnar growth. We developed a growth model to explain the texturing. To test this model we have carried out 3D Monte-Carlo simulations. We find that the preferred orientation arises from mutual shadowing of the columns and directional surface diffusion due to their initial momentum.

YBa2Cu3O7 (YBCO) films deposited on the ISD buffer layers are highly textured. The ab-planes of the YBCO are tilted with respect to the surface by typically 25° towards the direction of MgO vapor incidence. Therefore, the critical current density jc is anisotropic with up to 8 × 105MA/cm2 in one direction and 4 × 105MA/cm2 in the other. For tape coating the MgO deposition direction can be chosen so that the high jc is along the tape.

Si-Ge monocrystals up to 50 mm diameter and up to 17 at% germanium were grown using a modified Czochralski technique. Pre-grown large diameter silicon seeds with various crystallographic orientations were used as templates for the alloy solidification to reduce cap crystallization time and insure monocrystallinity at desired diameters. Discussed are the influences that seed preparation, crystal growing parameters, and post-growth processing have on the material that was produced using this new technique.

The essential features of the deposition process and the film properties of borosilicate glasses are presented here as an alternative to pure SiO2in wafer bonding and compliant substrates. While the deposition of SiO2 is a well-studied system, the deposition of boron-doped films is less understood. The deposition rate of the SiO2 mole fraction in the films was accelerated by the presence of trimethylborate and oxygen and this is associated with an increased adsorption of the tetraethylorthosilicate related precursor in the presence of boranols. Typical deposition conditions result in borosilicate glass films with an r.m.s. roughness of ∼0.5 nm as measured by atomic force microscopy. Annealing the films at temperatures above 550°C reduces the film roughness via glass reflow. Room temperature bonding of these films was achieved after a 250 WO2 plasma surface treatment. Fourier-transform infrared investigations of the bonded interface revealed the importance of the role of surface OH and H2O groups in the bonding of these films.

Selective area growth of magnetic garnet crystals was studied by liquid-phase epitaxy. The garnet layers grown on Ti-masked substrates were analyzed under a scanning electron microscope, and by X-ray diffraction measurements, energy-dispersive X-ray analysis and reflection high-energy electron diffraction. Narrow stripes in the Ti mask were designed to form waveguides by one-step growth. The light waves could be guided within the waveguide fabricated by selective area liquid-phase epitaxy.

In this paper we describe observations on the stability of extremely large Si(001) and (111) terraces that are formed by a technique described previously. Following annealing at high temperature and quenching, a series of concentric pits of monoatomic depth are observed with spacing between successive pits of the order of several microns; pits do not form on (111) until the terraces get extremely large. The occurrence of small islands or small pits on the terraces of quenched samples gives information on the majority point defect at the annealing temperature. On (001) samples that are slowly cooled from the annealing temperature, it is observed that pairs of atomic steps have formed on the large terrace; we believe that these result from the tendency of the surface to minimize the strain energy associated with the (2 × 1) reconstruction.

In this paper, we review and highlight the central role that infrared spectroscopy has played in elucidating the microscopic details of the bonding and exfoliation processes and we introduce a novel technique for imaging and measuring strain with submicron resolution. The mechanism for chemical bond formation between two interfaces is derived from monitoring the chemical evolution of interfacial species as a function of annealing. The mechanism for silicon shearing upon Himplantation/annealing is understood as an evolution of H-passivated point defects into H-stabilized internal surfaces, together with H2 formation. The nucleation and propagation of microbubbles that form prior to exfoliation is imaged with x-rays and a detailed strain map in the vicinity of bubbles just prior to exfoliation can be made.

We use an Atomic Force Microscope (AFM) to study changes in the surface of single-crystal SrTiO3 etched in HF-based solutions. Attention in this work has been focused upon observations of pyramidal pitting – both because of an interest in avoiding etch pits during substrate preparation prior to heteroepitaxial growth, and because of an interest in micromachining this highly polarizable material. We note that (110) SrTiO3 is surprisingly robust against the formation of pits, while pitting is significant on {100} surfaces. Particular etch rates have been measured, and we discuss anisotropies in the rates of dissolution. These data are combined to extract a macroscopic model describing processes relevant to the most extreme pitting, which we show to be associated with surface defects.

Thin films of Sr2TiO4 were grown using pulsed laser deposition (PLD) and laser-MBE on [100]-SrTiO3single crystal substrates. Films grown by standard PLD display only a single peak in the X-ray diffraction spectra, corresponding to the (006) peak of the K2NiF4 parent structure. Using a Laser-MBE, controlled two-dimensional growth and RHEED intensity oscillations can be routinely obtained. The period of the RHEED intensity oscillations was confirmed to correspond to the deposition of one-half the unit cell. In contrast to PLD-grown films, the (004) and (006) peaks are observed in XRD spectra for the Laser-MBE-grown films. The intensity of the (004) peak is discussed and modeled with respect to in-plane disorder arising from substrate step-edges and out-of-plane film-substrate structural mismatches. That a single, half unit-cell can be deposited allows one to "flip" the terminating surface of SrTiO3 in a controlled and simple manner from a pure TiO2 layer to a SrO layer. Experimental evidence of the importance of such surface control is given for the SrCuO2 structural stability.

High quality and lattice matched buffer layers are needed for the growth of device quality GaN thin films on sapphire for optoelectronic applications. In this context, we report the fabrication of AlN thin films having low defect densities through a novel process called solid phase epitaxial recrystallization (SPER). In this process, as-grown crystalline AlN thin films, having a large defect concentration (such as threading dislocations due to a large lattice mismatch between AlN and sapphire and low angle grain boundaries), were thermally annealed in an inert atmosphere at various temperatures ranging from 1200-1600° for 30 min. The as-grown and annealed samples were characterized using x-ray diffraction, transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM) and UV-visible spectroscopy. The ion channeling/RBS and TEM results clearly indicate a substantial reduction in the defect density for the recrystallized AlN films. The surface morphology of the SPER AlN films was smooth with a surface roughness close to the unit cell height. The optical bandgap was sharp as compared to as-grown films, with a bandgap of 6.2 eV. The recrystallized films having smooth surface morphology and low defect densities may be useful for the growth of device quality GaN films on sapphire.

Atomic-scale surface/termination of single-crystal oxide substrates were examined by coaxial impact collision ion scattering spectroscopy (CAICISS) and atomic force microscopy (AFM). CAICISS enabled us to determine the terminating atomic species and their arrangements of single crystal oxide substrates and epitaxial oxide films. Through thermal-annealing of the single crystal oxide substrates, atomically flat terrace and stepped structures were developed on the surface. The molecular layer-by-layer growth was verified by in situ monitoring of reflection high energy electron diffraction (RHEED) intensity oscillation. The atomic-scale substrate engineering made it possible to attain the novel heteroepitaxial growth such as step-decoration epitaxy resulting in the nanowire structures and diamond epitaxy on the ultrasmooth sapphire substrate. The diamond films could be grown epitaxially only on the atomically flat sapphire substrates by pulsed laser ablation of graphite. The novel application of the ultrasmooth sapphire substrate to the AFM observation stage for DNA molecules was also presented.

The effects of electric field on the rate of metal induced lateral crystallization (MILC) of amorphous silicon were investigated. Nickel silicide, which is known to be a key species for the low temperature crystallization, was driven by an electric field. As a result, the crystallization velocity of EMILC was much faster than that of conventional MILC methods. Directional crystallization of amorphous silicon thin film was successfully achieved by applying a DC field during heat treatment. The crystallization was performed at different temperatures (500-625°) by employing a thin layer of nickel (30°). The directionality of the resulting crystallization depended on the polarity of the electric field. The lateral crystallization velocity was three to four times faster than MILC when an electric field of 53.5V/cm was applied.

Sol-gel bonding was produced between smooth, clean substrates of silicon and polycrystalline alumina by spin-coating solutions containing partially hydrolysed silicon alkoxides. The two coated-substrates were assembled and the resulting sandwich was fired at temperatures ranging from 300 to 600°C. The coatings and bonded substrates were investigated using SEM, TEM and micro-indentation. For silicon wafers, an optimum water-to-alkoxide molar ratio of 10 and hydrolysis water pH of 2 was found. Such conditions led to relatively dense films (>90%), resulting in bonds with a fracture energy of 3.5 J/m2, which is significantly higher than those obtained using hydrophilic wafer bonding (typically 1.5 J/m2).

Poly-crystalline alumina substrates were similarly bonded at 600°C; the opt imised silica sol-gel chemistry yielded interfaces with fracture energy of 4 J/m2.

We describe the growth and properties of epitaxial (001) CeO2 on a (001) Ge surface using a hydrogen-assisted pulsed-laser deposition method. Hydrogen gas is introduced during film growth to eliminate the presence of the GeO2 from the semiconductor surface during the initial nucleation of the metal oxide film. The hydrogen partial pressure and substrate temperature are selected to be sufficiently high such that the germanium native oxides are thermodynamically unstable. The Gibbs free energy of CeO2 is larger in magnitude than that of the Ge native oxides, making it more favorable for the metal oxide to reside at the interface in comparison to the native Ge oxides. By satisfying these criteria, the metal oxide/semiconductor interface is shown to be atomically abrupt with no native oxide present. Preliminary structural and electrical properties are reported.

In oxide electronics substrates with atomically flat terraces are a request for growing high-quality epitaxial thin films. In this paper results on chemical etching of some substrates with perovskite, ABO3, structure (e.g., SrTiO3, LSAT - the (LaAlO3)0.3(Sr2AlTaO6)0.35 solid solution, and NdGaO3) are presented. In order to obtain high quality substrates, different etchants (NH4F + HF, HCl + NH4Cl, and HCl + HNO3) with various pH values have been studied. From Atomic Force Microscopy (AFM), in air, we conclude that, irrespective of the etchant that has been used, a substrate surface with a BOx terminated layer and atomically flat terraces without etch pits could be obtained. The pH-value and temperature of the etchant and the etching time, however, influence significantly the surface quality. Reflection high energy electron diffraction (RHEED) patterns confirmed the AFM results.

We have been using the low-cost method of fabrication of epitaxial wafer for discrete devices for many years. This low-cost operation is done by eliminating the conventional but costly polishing procedure, instead of using grinding, cleaning and etching processes prior to epitaxy growth. The etching step is needed to remove any residual grinding scratches and possible remaining contamination. In this study, etching is accomplished with HCl gas at a temperature range from 1120 to 1150 °C, at atmospheric pressure. The surface analysis and inspection techniques were used to test residual grinding scratch removal and point defect density. It is found that the temperature effect on the etch rate is small, but the surface morphology with ground pattern is very sensitive to the etching temperature. The study revealed the presence of regions of temperature which the silicon surface has a minimum of grinding scratches and little etch pits. The etching temperature has strong effect on the substrate surface thereby strongly impacting subsequent epitaxial layer morphology. The different morphologies and their temperature dependence can be explained on the basis of the thermodynamics of the surface and role of surface diffusion and evaporation.

Variation of surface steps on sapphire (0001) and (1120) substrates processed with thermal annealing in air or a reducing environment at 1000 to 1400°C for 1 to 10 hours were investigated with an atomic force microscope (AFM). The annealed (0001) surfaces consist of atomically smooth and large terraces and atomic-height steps, whose configurations strongly depend on annealing conditions. On the (1120) surfaces, where crystallographic misorientation is almost an order of magnitude larger than that of the (0001) surfaces, step height and terraces increase in size with the longer annealing time and higher annealing temperature. Characteristic step figures due to the symmetry of atomic arrangement were observed on the (0001) surface.

The lack of a suitable, lattice matched substrate for the growth of the group III nitrides typically restricts GaN film growth to substrates such as sapphire or SiC, despite the large lattice and thermal mismatch. With the use of AlN or GaN nucleation layers (NL), GaN films of sufficient quality have been produced for blue LEDs. However, for laser and large-area microwave device applications, the large number of dislocations (> 108 cm−2) limit device performance, and techniques are desired to reduce dislocation density during the growth process. Here, we demonstrate how low temperature AlN interlayers (IL) sandwiched between high temperature (HT) GaN layers can be used to improve the electrical, optical, and structural properties of Si doped GaN films. A nearly two-fold increase in mobility is observed in Si doped GaN grown using 5 AlN IL compared to GaN grown on a single AlN NL. For GaN films grown on multiple AlN IL, cross-sectional transmission electron microscopy images reveal a significant reduction in the screw dislocation density and photoluminescence spectra reveal a reduction in yellow band intensity. An analysis of the electrical data based on a single donor/single acceptor model suggests that the improved electron mobility is the result of a reduced acceptor concentration in the top GaN film. The reduction in the calculated acceptor concentration may be associated with the reduction of the screw dislocation density.

Large grain (> 10 um) poly-Si film has been formed from nickel Metal Induced Lateral Crystallization (MILC) and subsequent high temperature annealing. The fabricated thin film transistors (TFT) have near SOI performance. The new technology has good potential to provide low cost SOI substrates, multi-layer devices and other novel applications.

We investigated the formation of large-grain polycrystalline silicon films on glass substrates for application in low-cost thin film crystalline silicon solar cells. Since use of glass substrates constrains process temperatures, our approach to form large-grain polycrystalline silicon templates is selective nucleation and solid phase epitaxy (SNSPE). In this process, selective crystallization of an initially amorphous silicon film, at lithographically predetermined sites, enables grain sizes larger than those observed via random crystallization. Selective heterogeneous nucleation centers were created on undoped, 75 nm thick, amorphous silicon films, by masked implantation of Ni islands, followed by annealing at temperatures below 600 °. At this temperature, the Ni precipitates into NiSi2 particles that catalyze the transition from the amorphous to the crystalline Si phase. Seeded crystallization begins at the metal islands and continues via lateral solid phase epitaxy (SPE), thus obtaining crystallized regions of several tens of square microns in one hour. We have studied the dependence of the crystallization rate on the Ni-implanted dose in the seed, in the 5×1015/cm3 - 1016/cm3range. The large grained polycrystalline Si films were then used as a substrate for molecular beam epitaxy (MBE) depositions of 1 [.proportional]m thick Si layers. Transmission electron microscopy (TEM) analysis showed a strong correlation between the substrate morphology and the deposited layer. The layer presented a large grain morphology, with sizes of about 4 [.proportional]m.