SiO2-coated Si Substrates Research Articles

Sensitivity enhancement in thermoreflectance microscopy of semiconductor devices using suitable probe wavelengths

In this paper we present an experimental and theoretical study of the thermoreflectance response as a function of the probe wavelength for layered microelectronics structures. The investigated sample consists of a polycrystalline silicon conducting track grown on a SiO2-coated Si substrate. Thermoreflectance measurements were carried out in the wavelength range from 450to750nm with the track biased in modulated regime. An oscillating pattern is observed in the spectral region where the upper layer is transparent. Such oscillations are due to the interference resulting from the multiple reflections at the interfaces. Using a thermo-optical model, we show that the optical constants (n and k) of the materials, which are wavelength dependent, as well as their temperature derivatives (dn∕dT and dk∕dT), strongly influence the thermoreflectance signal. The optical thicknesses of the layers, mainly determined by the real part of the refractive indices, define the period of oscillation. On the other hand, the imaginary part of the refractive indices establishes the cutoff wavelength of the oscillations. Below this cutoff wavelength, the probe light does not penetrate the material and the upper-surface reflectance dominates the signal.

Pt ∕ ZnO nanowire Schottky diodes

Pt Schottky diodes were formed on single ZnO nanowires grown by site-selective molecular-beam epitaxy and then transferred to SiO2-coated Si substrates. The diodes exhibit excellent ideality factors of 1.1 at 25 °C and very low (1.5×10−10A, equivalent to 2.35Acm−2, at −10V) reverse currents. The nanowire diodes show a strong photoresponse, with the current–voltage characteristics becoming ohmic under ultraviolet illumination (366 nm light). The on-off current ratio of the diodes at 0.15∕−5V was ∼6. These results show the ability to manipulate the electron transport in nanoscale ZnO devices.

Growth and properties of (0 0 1)-oriented Pb(Zr 0.52Ti 0.48)O 3/LaNiO 3 films on Si(0 0 1) substrates with TiN buffer layers

Pulsed laser deposition has been used to grow Pb(Zr 0.52Ti 0.48)O 3 (PZT)/LaNiO 3 (LNO) bilayer thin films on bare Si(0 0 1) and SiO 2-coated Si(0 0 1) substrates coated with TiN buffer layers. The effect of background gas pressure on the crystallographic texture of the polycrystalline thin films has been investigated in detail. XRD analysis shows that under optimized conditions, (0 0 1)-oriented PZT/LNO/TiN heterostructures can be grown on both Si(0 0 1) and SiO 2/Si substrates. SIMS measurement indicates that there is no inter-diffusion or chemical reaction at PZT/LNO interface, while La and Ni can inward diffuse into the TiN layers. The (0 0 1)-textured PZT films have remnant polarizations as high as 23 μC/cm 2 and low coercive fields. Up to 10 10 polarization switching cycles have been achieved in these PZT films.

Structure and growth of dotriacontane films on SiO2 and Ag(111) surfaces: synchrotron X-ray scattering and molecular dynamics simulations

We report synchrotron X-ray scattering experiments and molecular dynamics simulations of the structure and growth mode of dotriacontane (n-C32H66 or C32) films adsorbed on Ag(111) and SiO2-coated Si(100) substrates. On the SiO2 surface, the X-ray measurements confirm a structural model of the solid film inferred from high-resolution ellipsometry measurements in which one or two layers of C32 adsorb with the long axis of the molecule oriented parallel to the interface followed by a monolayer in which the molecules have a perpendicular orientation. At higher C32 coverages, preferentially oriented bulk particles nucleate consistent with a Stranski–Krastanov growth mode. On the Ag(111) surface, we again observe one or two layers of the “parallel” film but no evidence of the perpendicular monolayer before nucleation of the preferentially oriented bulk particles. We compare the experimentally observed structures with molecular dynamics simulations of a multilayer film of the homologous C24 molecule. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Room temperature self-assembly of CdSe nanocrystals on SiO 2-coated Si wafer

A simple method for deposition of CdSe nanocrystals to silicon surfaces using self-assembled monolayers is described. CdSe nanocrystals were first synthesized by using sodium dioctyl sulfosuccinate as surfactant in inverse micellar solution. An obvious 1s–1s absorption peak at 527 nm and narrow width of photoluminescence peak at 552 nm implied a narrow size distribution of CdSe nanocrystals. Then these nanocrystals were assembled on SiO 2-coated Si substrate by bifunctional linker molecule (3-mercaptopropyl)-trimethoxysilane (MPS). Auger electron spectroscopy showed that the MPS monolayer has been limited on SiO 2-coated Si substrate. The results of atomic force microscopy analysis and contact-angle measurements confirmed that nanocrystals with uniform sizes were bound to MPS-modified substrate through Cd–S covalent bounding.

Synthesis of C-Axis-Oriented Aluminum Nitride Films by Reactive RF Magnetron Sputtering for Surface Acoustic Wave

C-axis-oriented aluminum nitride (AlN) films were deposited on SiO2-coated Si substrates by reactive rf magnetron sputtering. The crystallization of the AlN films, identified by X-ray diffraction (XRD) , was dependent on the deposition conditions. Highly c-axis-oriented AlN films, for fabricating AlN/SiO2/Si-based surface acoustic wave (SAW) devices, were obtained under an rf power of 300 W, substrate temperature of 350°C, sputtering pressure of 7.5 mTorr and N2 concentration of 75%. A dense pebblelike surface texture of the c-axis-oriented AlN films with an average grain size of about 100 nm was observed by scanning electron microscopy (SEM). The phase velocity showed a tendency to decrease with increasing kh, where k=2π/λ is the wavenumber and h is the AlN film thickness. In partucular, the phase velocity and the electromechanical coupling coefficient of the sample at kh=0.4 were calculated to be about 6080 m/s and 1.1%, respectively.

High mass positive ions and molecules in capacitively-coupled radio-frequency CF4 plasmas

The positive ions and neutral radicals arriving at the earthed walls of a capacitively-coupled radio-frequency pure CF4 plasma were analyzed using a quadrupole mass spectrometer adapted for high masses. Experiments were performed at 50 and 200 mTorr, in an empty reactor and with Si and SiO2-coated Si substrates on the powered electrode. High mass ions and neutrals were detected, up to 500 and 300 amu, respectively. The abundance of high-mass species was greatest in the presence of silicon wafers and at higher pressure. The observed ion masses can be separated into distinct series, originating from different initial bases to which successive CF2 units have been added. We, therefore, propose that these high-mass species are the result of a gas phase polymerization process consisting of CF2 addition reactions, in agreement with a model proposed recently by our group. The influence of a silicon substrate derives primarily from the strong decrease that it induces in the concentration of F atoms, which otherwise limit the concentration of CF2 and of chain initiating species.

Micro-patterning of 3-aminopropyltrimethoxy- silane self-assembled monolayers with colloidal gold

This paper provides a new method to the micro-patterning of 3-aminopropyl-trimethoxysilane (ATS) self-assembled monolayers by colloidal Au. Photolithographing of ATS self-assembled monolayers on SiO 2-coated Si substrates and subsequent assembly of colloidal Au to the amino terminal groups in the unirradiated regions lead to the formation of Au microstructures. As revealed by scanning electron microscopy, the colloidal Au closely replicates the mask patterns on the unirradiated regions. The present approach may be applicable to fabrication of microelectronic circuits and microbiosensors.

Ferroelectric Sr x Ba 1-x Nb 2 O 6 optical waveguiding thin films on SiO 2 -coated Si(100) substrates

Ba1-xNb2O6 (x=0.5) films (abbreviated as SBN:0.5) on SiO2-coated Si substrates are potential components for the application of integrated electro-optics devices. SBN:0.5 optical waveguiding thin films on SiO2-coated Si substrates with a very thin MgO diffusion buffer have been successfully prepared by pulsed laser deposition. The as-grown films have a refractive index of 2.28, which is close to that of bulk SBN. X-ray analysis showed that the as-grown films have a single-phase tetragonal tungsten bronze structure. The SBN:0.5 thin films prepared by PLD exhibit favorable ferroelectric and optical waveguiding properties. The composition and the morphology of the films were also examined by XPS and by SEM, respectively. Ferroelectric SBN:0.5 optical waveguiding thin films on SiO2-coated Si substrates are expected to be used in integrated electro-optic devices.

Fabrication of colloidal gold micro-patterns using photolithographed self-assembled monolayers as templates

This paper provides a new method for the patterned metallization of self-assembled monolayers. Colloidal Au micropatterns were formed on photolithographed self-assembled monolayers (SAMs) of (3-mercaptopropyl)-trimethoxysilane (MTS) on SiO 2-coated Si substrates. As confirmed by scanning electron microscopy (SEM), the colloidal Au closely replicated the mask features. Atomic force microscopy (AFM)showed that the colloidal Au particles on the unirradiated monolayers of (3-mercaptopropyl)-trimethoxysilane were connected and an almost continuous monolayer of Au nanoparticles was formed. X-ray photoelectron microscopy (XPM) revealed that the -SH terminal groups of the MTS monolayer in the exposed region were oxidized and the self-assembly of colloidal Au onto the unexposed region were through Au–S covalent bounding. The present approach may be applicable to assembly of microelectronic circuits and microbiosensors.

A simple method for high-frequency characterization of (Ba,Sr)TiO3 thin film capacitors

We developed a simple method for characterizing high-frequency properties of (Ba,Sr)TiO3 thin film capacitors. This method includes a new fabrication process, a simple circuit model of measurement pattern and an easy procedure to de-embed parasitic components. In this study, we successfully fabricated BST capacitors of Pt/Ba0.7Sr0.3TiO3/Pt/Ti structure on the SiO2 coated Si substrate using a combination of lift-off process, wet etching and Au plating process. Also, we de-embedded parasitic components in the coplanar-type probing pad using two de-embedding patterns. As a result, it was found that the BST film had high dielectric property up to 5 GHz. This microwave property of the BST film is considered to be suitable for DRAM applications.

Optical Waveguiding (Pb, La)(Zr,Ti)O3 Thin Films Prepared by Pulsed Laser Deposition

AbstractThe ferroelectric (Pb, La) (Zr,Ti)03 (PLZT(9.4/65/35)) optical waveguiding thin films have been prepared on SiO2 coated Si and on silica glass substrates by pulsed laser deposition. X-ray θ–2θ scans revealed that the films are single-phase pseudo-cubic perovskite. The surface chemical composition of the as grown films were determined by XPS. The ferroelectric properties of the films as grown on Pt/Ti coated silicon were demonstrated by using a modified Sawyer-Tower circuit, and the optical waveguiding properties of the films were characterized by using a rutile prism coupling method. The as grown films have an average transmittance of 80% in the wavelength range of 400˜2000nm and a refractive index of 2.2 at 632.8mn close to the bulk PLZT. The distinct m-lines of the guided TM and TE modes of the films as grown on SiO2 coated Si substrates have been observed.

High-temperature interaction studies of C/Cu/SiO2/Si and related structures

Thermal stability of the C/Cu bilayer structure is studied up to 800 °C. Using electron-beam-evaporated Cu and amorphous C (700 Å) films on SiO2-coated Si substrates, no out-diffusion or oxidation of Cu is observed up to a heating of 72 h at 700 °C, or 6 h at 750 °C in a N2-H2 ambient. Reaction between Cu and the SiO2 layer is, however, observed under such conditions. Concerns such as adhesion are addressed by peeling the films at different stages of heat treatment and analyzing the surfaces exposed. Application of the carbon barrier to the reaction between Cu and other materials is studied using the Au/C/Cu structure. An enhanced out-diffusion of Cu through C is observed due to the presence of Au, which acts as a receiving layer for Cu. The out-diffused flux of Cu is enhanced by many orders of magnitude. The resulted dilution of the Au layer, however, is much less than that using Ni as a barrier in the Au/Ni/Cu structure. The mechanisms involved are discussed by considering the structural, chemical, and mechanical effects. Both the advantage and concerns using carbon as a barrier are also discussed.

Characterization of thin AlGaAs/InGaAs/GaAs quantum-well structures bonded directly to SiO2/Si and glass substrates

Strained GaAs/InGaAs/AlGaAs quantum-well structures grown on GaAs have been removed from their original substrates by a lift-off process and bonded directly to glass or SiO2-coated Si substrates. Both undoped and modulation-doped structures have been characterized before and after transfer by Hall measurements, variable temperature x-ray diffraction, and photoluminescence. The bonded structures retain the high quality of the as-grown layers.

Raman characterisation of stress in recrystallised silicon-on-insulator

Raman scattering measurements were carried out to characterise Si films deposited on SiO2-coated Si substrates and recrystallised by a graphite strip heater or Ar+ ion laser. The frequency downshifts of the Raman peaks demonstrate that the Si films are under tensile stress. The crystallinity of the recrystallised films is also discussed.

Radiation-Hardened JFET Devices and CMOS Circuits Fabricated in SOI Films

The effects of total-dose radiation have been investigated for the first complementary JFETs fabricated in zone-melting-recrystallized (ZMR) Si films on SiO2-coated Si substrates. With a -5 V bias applied to the Si substrate during irradiation and device operation, both n- and p-channel devices show low threshold-voltage shift, low leakage currents and small transconductance degradation for total doses up to 108 rad(Si). Fully functional CMOS 1K static RAMs and 1.2K gate arrays have been fabricated in both ZMR and oxygen-implanted (SIMOX) SOI films. The ZMR circuits are superior in speed performance to the SIMOX circuits because parasitics are smaller for the ZMR structure. Excellent transient-radiation hardness has been demonstrated for both ZMR and SIMOX SRAMs, which showed no logic upset for dose rates up to 7 × 1010 rad(Si)/s.

Raman microprobe analysis of stress in Ge and GaAs/Ge on SiO2-coated Si substrates

Stress and strain in single-crystal Ge and GaAs/Ge films grown on SiO2-coated Si substrates have been investigated through the Raman microprobe analysis. The Ge film is found to be subject to a tensile stress of (3.4–6.1)×109 dyne/cm2 and a strain of (2.4–4.3)×10−3 without distinguished spatial variation within a SiO2 island. The stress agrees well with that evaluated from the GaAs electroluminescence spectral shift with the deformation-potential model. The strain can be attributed dominantly to the thermal expansion difference between the Ge and the substrate Si. A large Raman spectral shift to the lower frequency side and a large linewidth for Ge have been observed in the seeding opening region, which represents Ge lattice disorder in this region.

Microsecond carrier lifetimes in Si films prepared on SiO2-coated Si substrates by zone-melting recrystallization and by subsequent epitaxial growth

The generation lifetimes in zone-melting-recrystallized Si films on SiO2-coated Si substrates and in epitaxial Si layers grown by chemical vapor deposition on the recrystallized films have been determined by pulsed metal-oxide-semiconductor (MOS) capacitor and p-n junction leakage current measurements. For recrystallized Si films that are 1×1017 cm−3 n type and 1×1016 cm−3 p type, respectively, the lifetimes are 0.2–0.5 μs and ∼1 μs. For epitaxial Si layers that are 2×1015 cm−3 n type, lifetimes are 0.8–1.3 μs, compared to ∼2 μs for control layers grown on single- crystal Si 〈100〉 wafers. The relatively high lifetimes suggest the possibility of fabricating bipolar devices utilizing Si-on-insulator structures prepared by the present techniques.

Stress-enhanced carrier mobility in zone melting recrystallized polycrystalline Si films on SiO2-coated substrates

Thermal stress is found to have a significant influence on the carrier mobilities in Si films prepared by zone melting recrystallization of polycrystalline Si on SiO2-coated substrates. Films recrystallized on SiO2-coated fused quartz substrates exhibit a large tensile stress, which enhances the electron mobility by ∼75% compared to the stress-free Si films recrystallized on SiO2-coated Si substrates. In contrast, Si films recrystallized on SiO2-coated sapphire substrates are under a large compressive stress, which yields an increase of ∼10% in hole mobility compared to the stress-free films.

Silicon-On-Insulator Mosfets Fabricated in Zone-Melting-Recrystallized Poly-Si Films on SiO2

ABSTRACTN- and p-channel enhancement-mode MOSFETs have been fabricated in Si films prepared by zone-melting recrystallization of poly-Si deposited on SiO2-coated Si substrates. The transistors exhibit high surface mobilities, in the range of 560–620 cm2/V−s for electrons and 200–240 cm2/V−s for holes, and low leakage currents of the order of 0.1 pA/μm (channel width). Uniform device performance with a yield exceeding 90% has been measured in tests of more than 100 devices. The interface between the Si film and the SiO2 layer on the substrate is characterized by an oxide charge density of 1–2 × 1011 cm−2 and a high surface carrier mobility. N-channel MOSFETs fabricated inSi films recrystallized on SiO2-coated fused quartz subtrates exhibit surface electron mobilities substantially higher than those of single-crystal Si devices because the films are under a large tensile stress.