Treated Si Substrates Research Articles

Electron trapping in HfO2 layer deposited over a HF last treated silicon substrate

Electron trapping in HfO2-based MOS structures was studied through pulsed capacitance-voltage (C-V) technique. 10 nm HfO2 layer was deposited by atomic layer deposition over a HF last treated Si substrate. The C-V curves were observed to shift to positive voltages driven by the positive applied voltage along the pulses, consistent with electron trapping due to tunneling transitions between the substrate and pre-existing defects within the oxide and the subsequent lattice relaxation through electron-phonon interaction. The dependences of the voltage shift for a given capacitance value (ΔVC) with stress bias and time, allowed to distinguish two mechanisms. An initial trapping process occurs for times shorter than the microsecond, probably associated with a thin non-stoichiometric SiOx interfacial layer, which is followed by a trapping process that starts after tens of μs and progressively slowed down, associated with traps within the HfO2 layer. Numerical simulations yield for the HfO2 traps an energy of 1.3 eV below the conduction band edge, decreasing exponentially with the distance from the Si interface with a characteristic length of 1.7 nm; and phonon and relaxation energies of 50 meV and 1 eV, respectively. These physical parameters are consistent with previous reports of electron trapping in HfO2 layers deposited on a controlled interfacial layer, suggesting that trapping properties of defects inside the HfO2 layer are insensitive to the treatment of the Si surface before HfO2 deposition. On the other hand, the observed large initial trapping suggests that the non-controlled SiOx interfacial region is more defective than a controlled one.

Fabrication of Zinc Oxide Nanoparticles Deposited on (3-Aminopropyl) Triethoxysilane-Treated Silicon Substrates by an Optimized Voltage-Controlled Electrophoretic Deposition and Their Application as Fluorescence-Based Sensors

In this study, a voltage controlled, reproducible, scalable, and cost-effective approach for depositing zinc oxide (ZnO) nanoparticles (NPs), using electrophoretic deposition (EPD) onto p-type silicon (Si) substrates, has been researched and analyzed for its feasibility with respect to electronic device fabrication and fluorescence-based sensors. Our work presents a detailed investigation to evaluate the influence of ZnO morphology, ZnO concentration, and the method of surface treatment applied to the underlying Si substrates, because these pertain to an optimized EPD system. It has been noted that the ZnO NP structures formed directly atop the (3-aminopropyl) triethoxysilane (APTES)-treated Si substrates were more adhesive, thus resulting in a higher yield of NPs over that of comparable depositions on bare silicon. Our observation is that smaller particle sizes of ZnO will increase the energy emission for fluorescence transmission, eliminate several peak emissions, obtain higher fluorescence quantum yield (FQY) efficiency, and require less excitation energy. The results obtained are promising in relation to the integration of EPD in the fabrication of nano biosensors, PV solar cells, nano electronic devices, and thin film transistors (TFTs), where ZnO improves the reliability, affordability, and increased sensitivity needed for the next generation of nanoscale devices and systems.

Smoothness improvement of micrometer- and submicrometer-thick nanocrystalline diamond films produced by MWPECVD

Thick (around 3 μm) and thin (48–310 nm) nanocrystalline diamond (NCD) films have been produced from Ar-rich CH4/Ar/H2 (1/89/10 %) and H2-rich CH4/H2 (1/99 %) microwave plasmas, respectively. The deposition rate and the nucleation enhancement have been monitored in situ and in real time by pyrometric and laser reflectance interferometry for micrometer- and nanometer-thick films. For thick films, an improvement of the NCD films’ smoothness has been obtained by a buffer layer between the films and the treated Si substrate. For thin films, a combinatorial approach, i.e., a treatment of the Si substrate in a suspension of mixed diamond powders of 250 nm and 40–60 μm, has been utilized. The present experimental results show that the buffer layer procedure allows good preservation of the surface of the treated Si substrate and the combinatorial approach promotes effectively the seeding of the Si surface.

Interfacial structure of ferromagnetic Fe-Pt thin films grown on a Si substrate

In order to understand the Fe-Pt phase transformation, Fe-Pt films were sputtered on HF-treated, untreated Si substrates, and SiO 2 substrates and the magnetic and structural properties were analyzed by XRD, VSM, and XPS. The formation of Pt 2Si on the interface between Fe-Pt films and a Si substrate could be clearly observed with a shift of Pt4f 7/2 binding energy. Native oxide on the surface of Si substrate slowed the transformation of the disordered Fe-Pt phase to the ordered phase. The Pt 2Si phase was easily formed during sputtering on an HF treated Si substrate; moreover, a formation of a very small amount of Pt 2Si phase could be observed on the interface of Fe-Pt films and a SiO 2 substrate. Thus, the formation of Pt silicide assumes an important role in the transformation of Fe-Pt films grown on Si substrates.

Silicon nanotips formed by self-assembled Au nanoparticle mask

The Au nanoparticle monolayer is formed by self-assembly technology on the Si substrates terminated with different functional groups. Silicon nanotips were fabricated by a self-assembled gold colloidal particle monolayer as an etch mask. The silicon nanotips with high density and uniformity in height and shape were obtained using reactive ion etching (RIE). The Si nanotips on the surface of the 3-aminopropyltrimethoxysilane (APTMS)-treated Si substrate are less-ordered array and uniformity than 3-mercaptopropyltrimethoxysilane (MPTMS)-treated Si substrate at the same etching conditions. The ordered array and uniformity of Si nanotips on the APTMS-modified Si substrate was improved through heat-treatment. This result is implied the different functional groups on the Si surfaces could affect the formation of the Si nanostructures during RIE process. The uniformly nanotip pattern with height of >20 nm is obtained on the etched nanoparticle-coated Si substrate. This method can be applied to patterning a wide variety of thin film materials into tip arrays.

Sputter Deposition of CuInSe2 and CuGaSe2 from Composite Targets on (100) Si

AbstractThin films of CuInSe2 (CIS) and CuGaSe2 (CGS) were deposited on (100) Si substrates by RF magnetron sputtering using stoichiometric targets, at various substrate temperatures. Prior to film deposition, the Si substrates were cleaned using the RCA cleaning procedure and treated in a buffered oxide etch (BOE) solution. Deposited films were characterized using Rutherford backscattering spectroscopy (RBS), transmission electron microscopy (TEM) of cross-sectional samples and Hall measurements. Rutherford backscattering analysis indicated that the CIS films had a composition of Cu0.8In1.1Se1.9, whereas CGS films were Cu-poor and Ga-rich with a composition of Cu0.3Ga1.5Se1.5. Clean Cu-chalcopyrite/Si interfaces were obtained using BOE treated Si substrates. Transmission electron micrographs of cross-sectional samples indicated a polycrystalline film structure and that the native oxide on the Si substrate was eliminated. Energy dispersive X-ray spectroscopy (EDS) conducted in the TEM showed that contamination levels in the films were low. The Hall-mobility experiments performed the CIS film indicated that the material was of p-type conductivity with a carrier concentration of 9.6 x 1020/cm3 and a Hall mobility of 390 cm2V-1s-1.

Packing structure of MPS SAMs and its influence on oriented deposition of SnO2 crystal films

AbstractThe (110) crystal plane of SnO2 was found by X‐ray diffraction, atomic force microscopy and X‐ray photoelectron spectroscopy to grow preferentially in the direction of short‐chain sulfonate self‐assembled monolayer (SAM) formed from in situ oxidation of 3‐mercaptopropyltrimethoxysilane (MPS) treated Si substrates. Molecular simulations were performed to study the optimal packing structure of MPS SAMs on Si (100) surface as well as its induced deposition mechanism to the SnO2 crystal. Molecular mechanics calculations showed that the MPS molecules self‐assembled on Si (100) surfaces with a coverage ratio of 50% and a zigzag‐like packing pattern. Molecular dynamics calculations reflected that oxidation of the SH of MPS contributed to uniform SO3H‐terminated SAMs with narrower distribution of dihedral angles. Density functional theory calculations suggested the existence of strong interactions between the SO3H groups of SAMs and SnO2 (110) plane, which was due to the structural and electrical match between the SO3H group and the unsaturated atoms on SnO2 (110) plane. These results consistently confirmed that the ordered SAMs with SO3H terminal group are beneficial to the epitaxial growth of crystal SnO2. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Spectroscopic Ellipsometry of Porphyrin Adsorbed in Porous Silicon

Aqueous solution of meso-tetra(4-sulfonatophenyl)porphine was deposited on electrochemically etched n-Si wafers. The morphology of the hybrid systems was investigated by scanning electron microscope and atomic force microscope techniques. The optical response of the hybrid systems was studied by spectroscopic ellipsometry in the range of 1–5 eV. Particular features in adsorption process were revealed for meso-tetra(4-sulfonatophenyl)porphine deposited on variously chemically treated Si substrates. It was found that porphyrin J-aggregates can be intercalated into large pores formed in a bulk n-Si as well as into nanopores of luminescent oxide layer.

Defect Structure of Heteroepitaxial Zn2-2xCuxInxS2 Layers Grown by Pulsed Laser Deposition on (111) Si, (001) Si and (001) GaP Substrates

Zn2-2xCuxInxS2 (ZCIS) films might be attractive for absorbers in solar cells (band gap variation from Eg(ZnS) = 3.67 eV to Eg(CuInS2) = 1.53 eV at room temperature). Therefore, we have grown ZCIS on (001)GaP, (001)Si and (111)Si substrates at 500°C by pulsed laser deposition (PLD). Epitaxial growth on (001) GaP substrates could be proved for all compositions between ZnS and CuInS2. However, there is a striking asymmetry in twin nucleation that occurs for cubic ZCIS (CuInS2 content less than 22 mol-%) preferably on the (1̄1̄1) and (111) planes of the [1̄10] zone. In addition, beside the dislocations lying in-clined to the interface, perfect 60° misfit dislocations coexist that align parallel to [110] and [1̄10] , having b=1/2<011> and {111} slip planes inclined to the interface. Additional Cu- and/or In-sulfides could not be detected in the monocrystalline films. CuAu-I type ordering was observed for CuInS2-rich compositions as Zn0.22Cu0.46In0.32S, Zn0.044Cu0.544In0.412S and pure CuInS2 only. On (001) Si the films appear to be polycrystalline for all compositions between Zn0.2Cu0.4In0.4S and Zn0.62Cu0.19In0.19S. At Zn0.7Cu0.15In0.15S there is the transition between poly- and monocrystalline growth, i.e. the range of monocrystalline growth is strongly restricted to the lattice matched position. In these layers twins have been nucleated on all four inclined {111} planes. On chemically treated (111) Si the films grew epitaxially for compositions 0.1 ≤ x ≤ 0.7. They are monocrystalline, but consist of polysynthetically twinned column-like grains which are precisely oriented to the (111) Si sub-strate. Coherent Σ=3{111} twin boundaries exist parallel to the interface and incoherent Σ=3{112} grain boundaries are for-med perpendicular to it. Perfect dislocations that lie along <110> directions and parallel to the interface envelop the colums to form a dislocation network like a honeycomb. The films become polycrystalline for compositions x > 0.7. On non-treated (111) Si substrates, similar to the deposition on molybdenum-coated glass, the ZCIS films are polycrystalline, but a distinct <111> texture exists. Extended defects have been produced inside both the GaP and chemically treated Si substrates due to the preferred Cu out-diffusion from the layer. In the GaP substrates a Cu3P phase is formed but within the Si substrates amor-phisized regions occur exclusively. With increasing ZnS content the propensity to form these defects decreases appreciably.

Structural properties of thin Zn 0.62Cu 0.19In 0.19S alloy films grown on Si(111) substrates by pulsed laser deposition

Alloys of Zn 2−2 x Cu x In x S 2 (ZCIS) have been grown on Si(111) substrates by pulsed laser deposition (PLD). The thin films grew epitaxially on chemically treated Si(111) regardless of an about 2–5 nm thick interfacial amorphous layer between the ZCIS and the Si substrate. The particular Zn 0.62Cu 0.19In 0.19S layers under investigation consist of column-like grains propagating from the interface to the layer surface. Despite of the existence of the amorphous layer in the interfacial region each ZCIS grain is precisely oriented to the structure of the underlying silicon substrate and to the neighboring ZCIS grains without any azimuthal misorientation. Each individual column-like grain contains many twin lamellae of various thickness that lie parallel to the interface and, therefore, coherent Σ3{111} twin boundaries occur. Σ3{112} grain boundaries are formed perpendicular to the interface during the intergrowth of the individual columns. Perfect dislocations with their lines parallel to the interface envelop the columns and finally, a dislocation network like a honeycomb can be observed during TEM plane-view observation. However, polycrystalline ZCIS layers exhibiting a distinct 〈111〉 texture have been formed on untreated Si(111) substrates, where the 2–2.5 nm thick intermediate native layer consists of amorphous SiO x . The individual ZCIS grains were found to be polysynthetically twinned too. Amorphisized regions have always been produced inside the chemically treated Si substrates due to the out-diffusion of copper from the layer into the Si substrate that seems to be favored against that of Zn. However, the amorphous native SiO x layer which covers the untreated silicon substrates prevents substantially the out-diffusion of metal atoms from the layer into the substrate and, therefore, no diffusion-induced defects have been generated inside the untreated Si substrate.

Oxidation of rf plasma: hydrogenated crystalline Si

The growth kinetics of thermal oxidation of H-plasma hydrogenated (100) and (111)Si surfaces is studied and is compared with that of most used so far wet chemical cleaning. Prior oxidation the silicon surface was hydrogenated by exposure to hydrogen plasma in an rf planar unit. The substrates were kept at the lower electrode without heating or at temperature of 100°C. The oxidation was performed at 800°C in dry O 2. Oxide thickness and refractive index were measured by ellipsometry. In the investigated thickness range of up to about 200 Å the growth rate was linear with time. The growth rate constant was smaller as compared to the case of Si surface with wet RCA preoxidation clean only. In spite of this, for the same time periods thicker oxides were grown on plasma treated Si substrates. Possible explanations of the experimental observations are discussed. An estimation of the film stress from variation of the refractive index over the oxide thickness is used to infer the role of the stress for the oxidation kinetics.

Nucleation enhancement behavior of diamond on Si substrate according to surface treatment materials

The dependence of diamond nucleation on pretreatment materials was investigated. Diamond, cubic boron nitride (c-BN), silicon carbide (SiC) and alumina (Al 2 O 3 ) powders with an average particle size of 3 μm were used for surface treatment. Si substrates are vibrated ultrasonically in a powder-acetone mixture and then cleaned in acetone. Diamond was deposited on the treated Si substrate by a tungsten filament CVD (HFCVD) method under the following conditions: 40 mbar of pressure, 1% of methane in hydrogen, 800 °C substrate temperature. The nucleation density was decreased until saturated as the substrate cleaning time increased regardless of the substrate treatment material. However, the saturated nucleation density decreased in the order of diamond, c-BN, SiC and finally Al 2 O 3 . The residue of the treatment material on Si surface was detected after cleaning for a long period of time. The measured density of residue decreased in the same order to that of the diamond nucleation density. Furthermore, the ratio of the density of nucleated diamond to that of the residue decreased in the order of diamond, c-BN, SiC and lastly Al 2 O 3 . The larger the lattice difference between the residue material and diamond, the smaller the nucleation density. This result suggests that the residue of the treatment powder plays a significant role as a site for the diamond nucleation. The possibility of surface shape and defects as a nucleation site is also discussed.

The Reduction of The Defect Density in CdTe Buffer Layers for The Growth of HgCdTe Infrared Photodiodes on Si (211) Substrates

CdTe epilayers were grown by molecular beam epitaxy on As-passivated nominal (211) Si substrates using thin interfacial ZnTe layers. By using thin recrystallized (initially amorphous) ZnTe buffei layers, we utilized migration enhanced epitaxy (MEE) in the ZnTe layer and overcome the tendency toward three dimensional nucleation. The threading dislocation densities in 8–9 tm thick CdTe films deposited on the recrystallized amorphous ZnTe films were in the range of 2 to 5 × 105 cm−2. In addition to the reduction of threading dislocation density, the interface between the ZnTe layers and the Si substrate is much smoother and the microtwin density is an order of magnitude lower than in regular MEE growth. In order to understand the initial nucleation mechanism of the ZnTe on the As precursor Si surface, we also grew ZnTe epilayers on Te precursor treated Si substrates. The growth mode, microtwin density, and threading dislocation density are compared for films grown on Si substrates with different surface precursors and grown by different growth methods.

The Reduction of The Defect Density in CdTe Buffer Layers for The Growth of HgCdTe Infrared Photodiodes on Si (211) Substrates

CdTe epilayers were grown by molecular beam epitaxy on As-passivated nominal (211) Si substrates using thin interfacial ZnTe layers. By using thin recrystallized (initially amorphous) ZnTe buffer layers, we utilized migration enhanced epitaxy (MEE) in the ZnTe layer and overcome the tendency toward three dimensional nucleation. The threading dislocation densities in 8–9 μm thick CdTe films deposited on the recrystallized amorphous ZnTe films were in the range of 2 to 5 × 105cm−2. In addition to the reduction of threading dislocation density, the interface between the ZnTe layers and the Si substrate is much smoother and the microtwin density is an order of magnitude lower than in regular MEE growth. In order to understand the initial nucleation mechanism of the ZnTe on the As precursor Si surface, we also grew ZnTe epilayers on Te precursor treated Si substrates. The growth mode, microtwin density, and threading dislocation density are compared for films grown on Si substrates with different surface precursors and grown by different growth methods.

Growth of GaAs on hydrogen-fluoride treated Si (100) surfaces using migration-enhanced epitaxy

Heteroepitaxial growth of GaAs has been successfully achieved for the first time using migration-enhanced epitaxy (300 °C) on HF treated Si substrates which have been subjected to an initial in situ pre-heat treatment in the range of 350–620 °C and without the customary high-temperature Si oxide desorption step. High quality GaAs on Si exhibiting double-crystal x-ray rocking curve full-width at half-maximum value of 280 arcsec was obtained by using two-step growth technique MEE(300 °C)/MBE (580 °C). Secondary-ion mass spectrometry studies indicated 0.05 (monolayer) ML of oxygen at the interface of GaAs and HF treated Si substrate. The photoluminescence spectra at 10 K for GaAs grown on HF treated Si substrates was dominated by sharp excitonic related peaks and no carbon acceptor related emission could be detected.