MRS Online Proceedings Library (OPL)

CVD WSi, films produced by dichlorosilane reduction at 570°C and WSi, films sputter deposited at 50°C were characterized by in situ x-ray diffraction (IS-XRD), in situ resistivity (ISRes), in situ stress (IS-stress), ex situ/in situ transmission electron microscopy (EX/IS-TEM) and ex situ Auger electron spectrometry (EX-AES) over the temperature range 25–1100°C. The CVD films were crystalline after deposition, with columnar grains in the hexagonal phase and a Si:W atomic ratio of 2.6:1. The CVD films exhibited a sharp hexagonal to tetragonal phase transformation near 750°C. The final grain size was greater than the film thickness, with no evidence of voiding. Avrami analyses gave traditional curves with n values of 2 for the phase transition in the CVD films. In comparison, the sputtered films were amorphous as deposited (Si:W atomic ratio of 2.8:1 ) and crystallized to a different hexagonal phase microstructure than did the CVD films. The sputtered films showed a broad hexagonal to tetragonal phase transformation near 800°C, and a final grain size that was less than the fihn thickness with much voiding. A low Avrami exponent of 0.2 to 0.4 was obtained for the transformation of the sputtered films.

Due to its high near bandedge absorption, CuInSe2 is considered to be one of the most promising solar cell materials. As CuInSe2 films are usually grown by metastable processes, the Cu/In ratio often deviates from the ideal ratio of unity. To investigate the structural and morphological changes induced by such stoichiometric variations we have grown a series of epitaxial CuInSe2 epitaxial thin films with varying Cu/In ratios by molecular beam epitaxy on GaAs(001) substrates from elemental sources at a growth temperature of 450° C. Overall structural, microstructural and surface morphological changes were observed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy, respectively. It was observed that as films deviated from stoichiometry, twinning occurred preferentially on the anion {1 · 1 · 2} planes.

The early stages of the solid-state reaction between Ti and Al are characterized by a distinct phase selection in favor of TiAl3. In order to understand the selection mechanism which leads to the absence of phases other than TiAl3, trilayers were prepared by sputtering with a layer of α2-Ti3Al or γ-TiA1 being sandwiched between the Ti and Al layers. The growth of TiA13 in competition with α2 or γ was observed by transmission electron microscopy investigations. Upon annealing, the α2 and the γ layers were consumed by growth of TiA13.

The results indicate that the absence of phases other than TiAl3 is not due to the existence of nucleation barriers for α2 and γ, but is caused by a growth selection. A kinetic model is presented which quantitatively explains the observed phase selection on the basis of different growth velocities which result from different diffusion rates in the competing phases.

A Transmission Electron Microscopy (TEM), Photoluminescence (PL) and Photoluminescence Excitation Spectroscopy (PLE) investigation has been conducted on Ga0 52In0.48P epilayers, grown on GaAs(001) by Gas-Source Molecular Beam Epitaxy. Selected area diffraction in the TEM shows that epilayers grown at temperatures between 480°C and 535°C exhibit CuPt-type ordering with the antiphase domain size increasing with increasing growth temperature. PLE data shows that, in the temperature range 480°C to 535°C the band gap energy of Ga0.52In0-48P epilayers increases with increasing growth temperature from 1.971 to 2.003 (±0.001 eV). For high band gap optical data storage applications these values compare well with the highest band gap energies reported for epilayers grown by MOCVD.

Thin Nb films were grown by MBE in a UHV chamber at two different temperatures (50°C and 950°C) on the (110) surface of TiO2 (rutile).

At a growth temperature of 50°C, reflection high energy electron diffraction (RHEED) revealed epitaxial growth of Nb on rutile: (110)[001] TiO2 ¦¦ (100)[001] Nb. In addition, investigations with Auger electron spectroscopy (AES) revealed that a chemical reaction took place between the Nb overlayer and the TiO2 substrate at the initial growth stage. A 2 nm thick reaction layer at the Nb/TiO2 interface has been identified by means of conventional transmission electron microscopy (CTEM) and high-resolution transmission electron microscopy (HRTEM).

At a substrate temperature of 950°C, during growth, the Nb film was oxidized completely, and NbO2 grew epitaxially on TiO2. The structure and the chemical composition of the overlayers have been investigated by RHEED, AES, CTEM and HRTEM. Furthermore, it was determined that the reaction of Nb with TiO2 is governed by the defect structure of the TiO2 and the relative oxygen affinities of Nb and TiO2.

Single domain InxGa(1-x)P (x=0.3) films were successfully grown on Si(001) misoriented substrates by molecular beam epitaxy with a solid phosphorous source. The effects of interfacial buffer layers such as InGaP (i.e. direct growth without buffer layer), GaP, AlP, and GaAs were examined. Also a Si epitaxial buffer layer was tried to control the Si surface structure. Mirror like surfaces were obtained for all films with RHEED patterns of (2×1) single domain surface structure. PL intensities for all films indicated almost the same values except for the films with a Si epitaxial buffer layer. The films with a Si epitaxial buffer layer had almost three times larger PL intensities than the films without Si epitaxial buffer layer. The results suggest incomplete cleaning of the Si surface by the high temperature (1000 °C) treatment and possibility of surface structure control for Si substrates by a Si epitaxial buffer layer.

The average optical properties of an ultra-thin surface reaction layer (SRL) during growth by pulsed chemical beam epitaxy (PCBE) can be quantitatively accessed by p-polarized reflectance spectroscopy (PRS), as demonstrated on the example of heteroepitaxial GaP growth. Under PCBE growth conditions, the surface of the substrate is exposed to pulsed ballistic beams of tertiarybutyl phosphine [TBP, (C4H9)PH2] and triethylgallium [TEG, Ga(C2H5)3]. The pulsed precursor supply causes a period in composition and thickness modulated SRL, monitored as a fine structure that is superimposed on interference oscillations, resulting from back reflection at the substratelayer interface with increasing layer thickness. The amplitude of this fine structure undergoes a period amplitude modulation and exhibits turning points at which the response to the first precursor pulse changes sign. The turning points can be characterized by the expression R4(Φmax)=R4(Φmin), which describes the maximal and minimal values of the temporally modulated phase factor in the SRL, using a four layer stack description. The positions of these turning points are not affected by the thickness of the SRL, which allows the computation of the average complex dielectric function of the SRL independent of its thickness. In the next step, the average thickness of the SRL can be extracted from the amplitude of the observed fine structure.

Magnesium is incorporated into the growth of Ca1-xMgxF2 to reduce the lattice constant of fluorite (CaF2) which is 0.6% larger than that of Si at room temperature. When grown epitaxially on Si(111) substrates at 300°C, the lattice constant of the alloy became smaller than that of Si by 1.5% when the Mg concentration was around 20%. At higher Mg concentrations, the lattice constant did not decrease any further. This invariability of the lattice constant was caused by a phase separation of the Ca1-xMgxF2 layer into a Mg-rich region and a Mg-deficient region. When the growth temperature was increased, the critical Mg concentration for the phase separation became smaller. When Ca1-xMgxF2 was grown on vicinal Si(111) substrates, the reflection high energy electron diffraction (RHEED) intensity oscillations reflected no change in the composition, suggesting segregation of a Mg-rich phase along the steps. Nevertheless, the oscillations in the intensity of the specular spot for Ca1-xMgxF2 lasted longer than those observed for pure CaF2, suggesting a flatter surface for the alloy. Scanning tunneling microscopy (STM) observations support this model.

RHEED intensity oscillations observed during MBE growth of CaF2 on Si(111) and PbSe on CaF2/Si(111) are presented. The effects of substrate temperature and initial nucleation procedure are investigated. Strong temporal oscillations of the specular beam intensity are found to be most readily observed at temperatures below 200°C for both CaF2 and PbSe. Growth rates measured as a function of cell temperatures exhibit Arrhenius behavior with activation energies of 5.0 eV and 1.93 eV for CaF2 and PbSe, respectively. The relatively high activation energy obtained for CaF2 is consistent with the high melting point and sublimation energy of ionic fluorides.

SrRuO3 (SRO) has recently found a number of applications in different fields, e. g. as a buffer layer for the growth of high temperature superconductor (HTS) YBa2Cu3O7-x films and as a bottom electrode for ferroelectric or high dielectric constant thin film capacitors and nonvolatile data storage. The growth of high crystallinity SRO films with good structural and electrical properties is the prerequisite for each of these applications. In this paper we describe the affect of one growth parameter, temperature (T), on the crystalline quality, epitaxial substrate relationship and resulting electrical properties. SRO films were deposited on LaAlO3 single crystal substrates by pulsed laser deposition at substrate temperatures (Ts) ranging from room temperature (RT) up to 800° C with a nominal film thickness of 150 nm range. The resulting films were characterized by x-ray diffraction, 4-point transport, and STM.

The films' microstructures, as revealed by STM, evolved from polygranular at RT to a layered plate-like structure at higher deposition temperatures, Ts. Increasing Ts was marked first by increasing grain size, then a stronger orientational relationship between film and substrate, finally followed by the development of increased connectivity between grains to an extended island or condensed layered state. The transition from polygranular to layered structure occurred at Ts > 650° C. Increased conductivity paralleled the changes in microstructure. The surfaces of all of the films were relatively smooth; the oriented films are suitable for use as conductive templates in multilayer structures.

The dielectric properties of Ba0.65Sr0.35TiO3(BST) films deposited by an electron beam assisted ionized cluster beam epitaxy (ICBE) technique were investigated. Highly (110) oriented BST films having a thickness up to 1, um have been successfully grown on a Si (100) substrate at 400°C using the electron beam assisted ICBE system with a plasma O2 source. It was found that the dielectric constant increases from 475 to 1191 with different process conditions. A BST film with a thickness of 500Å deposited at a substrate temperature of 400°C has a dielectric constant of 1191 and a leakage current of about 2.37×10-9 A/cm2. This shows the BST film can be applied to dielectrics of ULSI capacitors.

A method of studying thin film growth and materials processing using micromachined Si-based structures is presented. The microsubstrate platforms (called “microhotplates”) allow temperature control during deposition, and in situ monitoring of the electrical properties of connected coatings. The efficiency of the approach is amplified when multiple. Independentlyoperated elements are used in array configurations. Illustrations here involve chemical vapor deposition of semiconducting oxides, but the methodology can be employed to investigate the growth of other classes of materials as well.

We report preliminary in-situ time-resolved measurements of the effect of uniaxial stress on solid phase epitaxial growth in pure Si (001) for the case of stress applied parallel to the amorphous-crystal interface. The growth rate is reduced by the application of uniaxial compression, in agreement with previous results. Additionally, the velocity continues to decrease with time. This is consistent with interfacial roughening during growth under stress, and is supported by both reflectivity measurements and cross-sectional TEM observations. We present a new kinetically-driven interfacial roughening mechanism which is consistent with our observations.

In this contribution we report on the real-time monitoring of low temperature growth of epitaxial GaxIn1-xP/GaP heterostructures on Si(100) by pulse chemical beam epitaxy, using tertiary butylphosphine (TBP), triethylgallium (TEG), and trimethylindium (TMI) as source materials. Both step-graded and continuously graded heterostructures have been investigated. The composition of the GaxIn1-xP epilayers has been analyzed by various techniques including X-ray diffraction, Rutherford backscattering, Auger, and Raman spectroscopy. Good correlation has been found between X-ray diffraction, RBS, and Vegard's law compositional analysis. We used Ppolarized Reflectance Spectroscopy (PRS) and Laser Light Scattering (LLS) to monitor the growth rate and surface morphology during growth. The information gained by these techniques has been utilized in the improvement of the surface preconditioning as well as to optimize the initial heteroepitaxial nucleation and overgrowth process. We studied the optical response to the compositional changes in the surface reaction layer (SRL) during the exposure of the surface to either sequential or synchronous pulses of TEG and TMI. The cross sectional TEM analysis indicates that the synchronous exposure results in an abrupt GaxIn1-xP/GaP interface while the sequential exposure does not which may suggest a compositionally graded interlayer formation. For heteroepitaxial GaxIn1-xP films on Si, a buffer layer of GaP is found to be necessary for optimum uniformity of the GaxIn1-xP layer. The selective growth of GaxIn1-xP on Si(001) is accessed.

Poly-Si films with the preferential orientation to a random, a (100) and a (110) texture were annealed using a flat gas flame. Remarkable lateral grain growth of (111) grains was observed for poly-Si films with a random and a (110) texture, while in (100) texture films the growth of (100) grains predominated over other grains. There existed tensile stress in as-prepared films. Grains with different orientation were under a different tensile stresses, and such stress distributions on the orientation of grains were different for different textures. The tensile stress was found to become larger in grown grains after high temperature annealing, while the stress on shrunken grains decreased or turned to compressive stress after annealing. These results indicate that strain energy stored in grains is one of the important driving forces in secondary grain growth.

During annealing of a polycrystalline thin film, grain-boundaries and film surfaces move. If the grain-boundaries move faster, the grains having the lowest free energy grow at the expense of others, resulting in a continuous film with large grains. If the film surfaces move faster, they groove along their junctions with the grain-boundaries, breaking the film to islands. This paper describes analytic solutions for steady surface motions, and discusses the morphology selection.

Basic mechanisms for both Ni- and Pd-metal induced lateral crystallization (MILC) are investigated. For both cases, tiny silicides were formed under the metal deposited area, and propagated toward amorphous Si films leaving crystallized Si behind at temperatures as low as 500 °C. Ni-MILC was influenced by Pd such that the lateral crystallization rate was enhanced, and the temperature for the lateral crystallization was lowered to 450 °C. Through TEM analysis and external stress experiments, it was found that the enhancement of the lateral crystallization rate was closely related to the compressive stress generated by the formation of nearby Pd2Si.

The addition of Ho or Er to Al thin films markedly suppresses the grain growth at high temperature (350 °C – 450 °C). However, different from the effect of adding elements of Y, La, Pr, Nd, Sm, Gd, and Dy, thermal defects of hillocks or whiskers start to appear on the film surface after annealing at 300 °C ( though depending on the content of added elements). It has been revealed that small amounts of metallic compounds of Al3RE (RE = Ho and Er) have been segregated in a supersaturated solid solution of the Al phase after annealing at 300 °C, and that a large amount of added impurities still remained in the Al matrix. The resistivity of Al1−xREx alloy thin films (RE = Ho or Er, x = 2 – 7 atomic %) was 5 – 7 μΩcm after annealing at 450 °C.

The photoluminescence (PL) measurement of unstrained and compressive strained InxGa1−xAs quantum wells (QWs) demonstrated that the interfaces had a roughness of 1 to 2.5 monolayers (ML). The spacer layers of tensile strained InyGa1−yAs were inserted between a compressive strained In0.7Ga0.3As QW and the InP barrier layers. PL spectra of the In0.7Ga0.3As/InyGa1−yAs/InP structures grown at 605°C became significantly narrower with increasing Ga content in the spacer layers above (1−y)=0.6. The PL line width of the In0.7Ga0.3As/In0.3Ga0.7As alternatingly strained multiple quantum well (MQW) structures gradually decreased when the number of periods and the deposition temperature increased. The structure, consisting of 4 periods grown at 635°C, exhibited a PL line width of about 4 meV which corresponded to the QW thickness fluctuation of 0.5 ML. The superlattice satellites of X-ray rocking curves of MQW structures were better defined under an envelope corresponding to the tensile strained layers.

A novel structure, based upon phosphorus-implanted poly-Si films treated with phosphoric acid (H3P 4) and the standard RCA cleaning process, has been demonstrated as the bottom electrodes of DRAMs' stacked capacitors. After the H3PO4 treatment and the RCA cleaning process, micro-islands are formed on the poly-Si surface of the electrodes. For the capacitors with this novel structure, the capacitance value is 18.17 fF/μm2 and the effective oxide thickness is 18.9 Å in comparison with conventional capacitors of 5.77 fFW/μm2 and 59.5 Å. The roughened poly-Si electrode can achieve a surface enlargement of 3.15 times. The leakage current density at +1.65V and −1.65V are 7.24 × 10−8 A/cm2 and −3.31 × 10−8 A/cm2, respectively, fulfilling the requirements of 256Mb DRAMs. Weibull plots of time-zero-dielectric-breakdown (TZDB) characteristics under ramping voltage test also show tight distribution and good electrical properties. It indicates that the phosphorus-implanted poly-Si films etched by H3PO4 and then cleaned with the standard RCA process can easily and simply increase the surface area and have good electrical properties fulfilling the requirements of 256Mb DRAMs and beyond.