Solid Phase Epitaxial Growth Research Articles

Growth and structure of heteroepitaxial thin films of homologous compounds RAO 3( MO) m by reactive solid-phase epitaxy: Applicability to a variety of materials and epitaxial template layers

A reactive solid-phase epitaxy (R-SPE) method combines deposition of a thick amorphous or polycrystalline layer with a desired chemical composition and post-deposition solid-phase epitaxial growth. The solid-phase epitaxial growth is invoked by thermal annealing with an assistance of a sacrificial layer working as an epitaxial template. Thereby it enables us to grow high-quality epitaxial films of complex oxides whose epitaxial films are not grown by conventional high-temperature growth techniques. It was reported that 2-nm-thick ZnO layers worked as template for growing InGaO 3(ZnO) m ( m = integer) epitaxial films. The present study extended the R-SPE technique to growth of various complex oxides with chemical compositions of RAO 3( MO) m and to use of various epitaxial template layers. We found that mono oxide epitaxial layers such as In 2O 3 and Ga 2O 3 work as template layers as well. Alternatively, a ZnO epitaxial layer is also applicable to ZnO-free compounds. The films obtained were grown heteroepitaxially on YSZ(111) and single-crystalline when the fabrication conditions are optimized.

Ge diffusion and solid phase epitaxy growth to form Si 1 − xGe x/Si and Ge on insulator structure

We report growth of Si 1 − x Ge x /Si and Ge on insulator by Ge diffusion and SPE (solid phase epitaxy). Different annealing conditions were carried out and evaluated by X-ray diffraction. Ge diffusion and SPE growth of Ge on Si are observed after annealing at 800 °C. EDX (electron dispersive X-ray) composition analysis shows that the top 100 Å Si 1 − x Ge x layer is quite uniform with Ge content variation of less than 2%. TEM (transmission electron microscopy) picture shows no crystal orientation misalignment between the Si and the top Si 1 − x Ge x layer. This simple and cost-effective process can be used to make Si 1 − x Ge x /Si substrate for high-mobility metal oxide semiconductor field effect transistor application. In addition, Ge on insulator structure was achieved by SPE lateral growth on pre-patterned SiO 2.

Effect of substrate temperature on the radiation damage from MeV Si implantation in Si

We have investigated the radiation damage by MeV implantation of Si in Si and its evolution under thermal annealing. Si wafers were implanted with MeV Si at various substrate temperatures. Damages were characterized by Rutherford-backscattering (RBS) channeling and by transmission electron microscopy (TEM). Defect formation after post-implantation annealing is very sensitive to the substrate temperatures during implantation. When the substrate temperature was decreased to 200K, TEM revealed two distinct bands of damage after annealing: one around the mean projected ion range and another at half the projected range. Our study indicates that the formation of defects at half range results from the solid phase epitaxy growth of initial buried amorphous layers.

Deactivation of Solid Phase Epitaxy-Activated Boron Ultrashallow Junctions

The solid phase epitaxial growth technique appears to be a promising method for achieving junction depths and sheet resistance values low enough to meet the performance specifications of the 65 and 45 nm node for boron, , and doping profiles in amorphous silicon. Room-temperature implants of these three dopant species into Si(100) preamorphized by (30 keV, ) lead to boron concentration profiles that fulfill the technological requirements. It was found that even for ultrashallow junctions the time for the regrowth process at 650°C has to be optimized with regard to the implanted species in the range between 5 and 60 s, especially when fluorine is present. The thermal stability of the boron profile distribution that meets 65-nm-node requirements was evaluated by subsequent thermal anneals simulating the thermal effects expected for typical silicidation processes. For a more detailed investigation, the postannealing temperatures ranged from 250 to 1050°C with times from a few to several hundred seconds. All the junctions were analyzed by four-point probe and selected samples by secondary ion mass spectroscopy, transmission electron microscopy, and high-resolution electron microscopy.

Swift heavy ion beam induced recrystallization of amorphous Si layers

This paper focuses on the role of electronic energy loss in ion beam induced epitaxial crystallization for which swift heavy ions (100MeV Ag7+) have been used. We observed good epitaxial crystallization at 473–623K, which is a much lower temperature regime as compared to the one needed for conventional solid phase epitaxial growth. A systematic planar recrystallization has been observed as a function of temperature giving rise to an activation energy of 0.25±0.02eV. A possible mechanism of recrystallization is discussed on the basis of the production of vacancies along the track of the swift heavy ion and their migration at elevated temperatures.

Electrical characterization of 5 keV phosphorous implants in silicon

Si(100) wafers were implanted with 5-keV phosphorous (fluences of 1×1014–1×1016cm−2) and then annealed at 600–1000 °C, for 30 s or for 5 mins, to study shallow junction formation. Carrier densities were obtained by Van de Pauw Hall measurements, and carrier concentrations were depth profiled via a native-oxide stripping, differential Hall technique. For implanted fluences ⩾5×1014cm−2, an amorphous silicon surface layer is created. This results in solid-phase epitaxial growth at low annealing temperatures (600 °C), with reverse annealing upon dissolution of end-of-range interstitial clusters at higher temperatures (>700°C). Sheet resistances as low as 20Ω∕sq with electrical activation approaching 100% were achieved after annealing at 1000 °C.

Swift heavy-ion-induced epitaxial crystallization of buried Si3N4 layer

We report on swift heavy-ion-beam-induced epitaxial crystallization of a buried Si3N4 layer. We observe good epitaxial crystallization at 200 °C, which is a much lower temperature than that required for the conventional solid phase epitaxial growth. High-resolution transmission electron microscopy and selected area diffraction patterns have been used to study the 100-MeV Ag8+-ion-beam-induced epitaxial growth of the Si3N4 layer. A possible mechanism of recrystallization is discussed on the basis of synergetic effects of electronic and nuclear energy-loss processes along the trajectory of the swift heavy ions at elevated temperatures.

Low-Temperature Formation of Epitaxial NiSi2 Layers with Solid-Phase Reaction in Ni/Ti/Si(001) Systems

The solid-phase epitaxial growth of NiSi2 in Ni/Ti/Si systems has been investigated. Continuous epitaxial NiSi2 layers consisting of pyramidal domains with {111} facets at the Ni-silicide/Si interface can be formed by annealing at a temperature (350°C) lower than that for conventional Ni/Si systems. This NiSi2 layer is transformed to a uniform epitaxial NiSi2 layer with an atomically flat silicide/Si interface by additional annealing at 850°C, while the {111} facets at the NiSi2/Si interface remains in the Ni/Si system under the same annealing conditions. Moreover, the epitaxial NiSi2 layer formed at 350°C exhibits a high thermal robustness even after annealing at higher than 750°C, in contrast to the polycrystalline NiSi layer.

Two-step growth of SrTiO3 films on Sr-modulated Si(001) substrates

Perovskite-type SrTiO3 (STO) films have been grown on the Sr-modulated Si(001) substrates using “two-step growth method” with a molecular beam epitaxy technique. About 6 A Sr was deposited on the surface of chemically formed SiO2/Si at 800 ∘C, which resulted in the formation of Si(001)-Sr(2 × 1) surface. About 250-A-thick STO films have been deposited on the Si(001)-Sr(2 × 1) surface at 350 ∘C in the O2 partial pressure of approximately 3 × 10−7 Torr (first step), followed by an annealing at 600 ∘C in a pressure of 3 × 10−9 Torr (second step). Reflection high-energy electron diffraction patterns of grown films become elongated streaky features after the annealing, suggesting the solid-phase epitaxial growth of STO. The presence of strong STO(001) and STO(002) diffraction peaks in X-ray diffraction measurements suggests that the high-quality crystalline STO films grow on the Sr-modulated Si(001) substrates by the two-step growth method. Atomic force microscopy image shows the smooth surface with root mean square roughness of about 18 A.

Structure of NiO and Li-doped NiO single crystalline thin layers with atomically flat surface

Crystalline thin films of NiO and nominally 20 at.% Li-doped NiO were deposited at room temperature by pulsed laser deposition on the lattice matched MgO (100) substrate. As-deposited films were annealed at various temperatures to promote a solid phase epitaxial growth and control the surface morphology. Films were characterized by AFM and RHEED measurements. AFM images of the NiO film annealed at 1200 °C for 30 min showed an atomically flat surface and an excellent step-terrace morphology with a step height corresponding to one unit cell of NiO over a wide range of 2 μm×2 μm. Formation of atomically smooth surface in a range of annealing temperatures is highlighted and a temperature of 1200 °C is identified as being the most suitable in the solid phase epitaxy for single crystalline growth and a smooth surface of the films deposited by PLD.

Interfacial roughening during solid phase epitaxy: Interaction of dopant, stress, and anisotropy effects

The effects of externally applied stress and rate-enhancing dopants on interfacial roughness during the solid phase epitaxial growth of ion-implantation-doped Si are investigated using cross-sectional transmission electron microscopy and time-resolved reflectivity. We find long-wavelength roughness in the absence of an applied stress that arises solely from the dopant-gradient. With the addition of a compressive stress, the interface roughens further with an enhanced magnitude and a dramatically reduced wavelength. We discuss the experimental results in the context of a simulation that includes our current understanding of stress, dopant-gradient, and interface anisotropy effects. We find a rich interplay between these effects in determining growth morphology evolution, and demonstrate the successes and current limitations of the model.

Solid-Phase Epitaxial Growth of SrTiO3 Thin Films on Si(001) Substrates at Low Temperature

The solid-phase epitaxial growth of perovskite-type SrTiO3 films on Sr-deposited Si(001) substrates has been studied. Sr deposition on the Si oxide substrate reduces the thickness of the oxide layer and leads to the formation of a Si(001)-Sr(2×1) reconstructed surface. Reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) analyses, and atomic force microscopy (AFM) show that the SrTiO3 film grown at 80°C is amorphous and after postgrowth annealing at an elevated temperature the SrTiO3 film changes to a crystalline phase and has a smooth surface.

Thermal stability of boron electrical activation in preamorphised ultra-shallow junctions

We present a detailed study of the thermal stability of activated junctions as a function of the post-annealing conditions. p +/n junctions were formed by implanting 500 eV boron (1 × 10 15 cm −2) into Ge + preamorphised Si followed by solid phase epitaxial growth (SPEG) at 650 °C. Post-annealing temperatures ranged from 250 to 950 °C, with times ranging from 3 to 1800 s. Four point probe (4PP), secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) analysis were then used to investigate the evolution of boron activation, boron diffusion and of the implantation induced extended defects. During isothermal anneals in the 750–900 °C range, it is found that the sheet resistance initially increases (deactivation) and then decreases (reactivation) with rates proportional to the temperature itself. TEM results elucidate the crucial role of the extended defects in the deactivation process. On the other hand, the combination of 4PP and SIMS measurements allows to separate the respective contribution of both cluster dissolution and dopant in-diffusion to the reactivation process.

New approach to remove crystal originated pits in Czochralski-grown silicon: combination of germanium ion implantation with solid-phase epitaxy

A two-step process is designed for removing crystal-originated pits (COPs) in the near-surface region of the Czochralski-grown silicon wafers. Firstly, Ge-ion implantation is used to acquire amorphous layer and thus disrupt COPs in the near-surface region. Following that, the annealing process is performed to boost solid-phase epitaxial growth (SPEG) and remove the implant damage. It is verified by cross-sectional transmission electron microscopy (XTEM), Rutherford backscattering spectroscopy (RBS), Raman spectroscopy and laser scattering technique that a refinement epitaxial layer of fewer COPs and excellent crystalline properties can be acquired by our method. Additionally, it is found that appropriate Ge-implant dose may be around 6×10 14/cm 2 and the corresponding annealing temperature should be above 600 °C. The two-step process may have some advantages, including relaxed conditions for pulling crystals, over previous methods.

Modeling the effect of hydrogen infiltration on the asymmetry in arsenic-enhanced solid phase epitaxy in silicon

The kinetics of solid phase epitaxy (SPE) in surface amorphous silicon layers doped with a single arsenic profile have been examined in relation to the generalized Fermi level shifting model of the SPE growth process. The model has been extended to include passivation by hydrogen of the defects responsible for SPE and∕or passivation of dopant atoms. A previous study has suggested that the asymmetry between the dopant-enhanced SPE rate and the arsenic concentration profile is due to the infiltration of hydrogen from the surface oxide. Theoretical calculations of the dopant-enhanced SPE rate compare well with experiment if it is assumed that the indiffusing hydrogen passivates some of the SPE defects and∕or some of the dopant atoms.

Solid phase epitaxy of amorphous silicon carbide: Ion fluence dependence

We have investigated the effect of radiation damage and impurity concentration on solid phase epitaxial growth of amorphous silicon carbide (SiC) as well as microstructures of recrystallized layer using transmission electron microscopy. Single crystals of 6H-SiC with (0001) orientation were irradiated with 150keV Xe ions to fluences of 1015 and 1016∕cm2, followed by annealing at 890°C. Full epitaxial recrystallization took place in a specimen implanted with 1015 Xe ions, while retardation of recrystallization was observed in a specimen implanted with 1016∕cm2 Xe ions. Atomic pair-distribution function analyses and energy dispersive x-ray spectroscopy results suggested that the retardation of recrystallization of the 1016Xe∕cm2 implanted sample is attributed to the difference in amorphous structures between the 1015 and 1016Xe∕cm2 implanted samples, i.e., more chemically disordered atomistic structure and higher Xe impurity concentration in the 1016Xe∕cm2 implanted sample.

Diffusion profiles of high dosage Cr and V ions implanted into silicon

The depth profiles of high dosage Cr+52 and V+51 ions implanted in (100) crystalline silicon after thermal anneal at temperatures between 300 °C and 1000 °C are studied by secondary ion mass spectrometry and cross-sectional transmission electron microscopy. At dosages of 1×1015 ions/cm2 and above, the surface layer of silicon substrate is amorphorized. During the subsequent thermal annealing, the depth profiles of the implanted ions are strongly coupled with the solid phase epitaxial growth of amorphous silicon. Silicide precipitate formation is important to understand the differences between Cr and V diffusion. After anneal of the 1×1015 ions/cm2 implanted samples at 900 °C and 1000 °C, most of the Cr has left the silicon, but only 10% of the V has escaped. The 1×1014 ions/cm2 Cr-implanted sample shows Cr ions exist only near the surface after 1000 °C anneal. The V-implanted sample, on the other hand, only shows a narrowing of the V profile after 1000 °C anneal.

Buried contact solar cells with innovative rear localised contacts

AbstractA new rear contacting scheme using low‐temperature processes to form localised contacts without the use of photolithography has been developed. It uses randomly nucleated, aluminium‐induced, localised regions of solid phase epitaxial growth of p+ silicon onto the rear surface of a wafer through a thick rear surface passivating oxide. This rear contacting technique has been applied on solar cells with front buried contacts and results have shown that a suitable ohmic contact to the rear can be formed through oxide as thick as 3000 Å and using only low temperature sintering below the eutectic temperature of silicon and aluminium. This low‐temperature sintering avoids the destruction of the interfacial oxide which has been shown to provide good surface passivation for the rear of the solar cells. Microscopic images indicate the possibility of forming p+ rear contacts with aluminium‐induced crystallisation, but without requiring any additional deposition of silicon. The source of silicon for the latter appears to be from the reduction of the silicon dioxide by the aluminium. Copyright © 2004 John Wiley & Sons, Ltd.

Activation, Diffusion and Defect Analysis of a Spike Anneal Thermal Cycle

ABSTRACTIn this paper, the evolution of sheet resistance, junction depth and defects during the whole thermal cycle of a typical spike anneal with a peak temperature of 1050°C was investigated in detail. To this purpose, spike anneals were performed at peak temperatures ranging from 800°C up to 1050°C in temperature steps of 50°C. These experiments were done both on B+ (500 eV, 1.1015 cm−2) and BF2+ (2.2 keV, 1.1015 cm−2) implanted wafers. It is found that for temperatures below 850°C BF2+ implanted wafers exhibit a much better electrical activation, resulting in a lower sheet resistance, than B+ implanted ones, due to the amorphisation process occurring during the BF2+ implant and the subsequent solid phase epitaxial growth. In this low temperature regime, boron clustering takes place very rapidly in B+ implanted wafers, as confirmed by both SIMS and TEM analysis. In particular, “large” clusters, i.e. with diameter above the TEM detection limit (∼2 nm), undergo a classical Ostwald ripening process (increase in size, decrease in density). SRP measurements indicate that boron activation in this low temperature regime is not related to cluster dissolution. On the other hand, after the initial solid phase epitaxial regrowth, BF2+ implanted wafers exhibit a slight increase in sheet resistance, due to boron clustering induced by the dissolution of end of range defects. Finally, it is found that at higher spike anneal temperatures (above 850°C), both B+ and BF2+ implanted wafers exhibit a similar behaviour, with a progressive decrease in sheet resistance due to boron cluster dissolution and dopant diffusion.

Surface and Interface Smoothing of Epitaxial CoSi2 Films by Solid-Phase Epitaxy Using Adsorbed Oxygen Layers and Two-Step Growth on Si(001) Surfaces

The oxygen-mediated two-step growth of high-quality CoSi2(001) films on Si(001) is demonstrated. In the first-step growth, uniform 6-monolayers (ML)-thick CoSi2(001) films with atomically flat surfaces and interfaces are grown by solid-phase epitaxy (SPE) at 470°C of 3 ML Co on O-adsorbed Si and O-covered 3 ML Co on clean Si. In both cases, O atoms improve the surface and interface flatness in SPE growth. In the second-step growth, 5.6 nm Co is solely deposited at 470°C on the O-covered CoSi2 template. We successfully achieve the growth of 20-nm-thick CoSi2(001) films with smooth surfaces and abrupt interfaces. In the O-mediated two-step growth, O atoms segregating to the film growth front suppress the lateral migration of Co atoms. Furthermore, in the second-step growth, the uniform template promotes homogeneous growth and keeps the surfaces and interfaces of CoSi2 films smooth. This novel technique, applicable to salicide processes, is highly suitable for the formation of epitaxial CoSi2 contacts in future ULSI devices.