Buried Metal Layer Substrate Research Articles

Time-Resolved Surface Infrared Spectroscopy during Atomic Layer Deposition

This work presents a novel method for obtaining surface infrared spectra with sub-second time resolution during atomic layer deposition (ALD). Using a rapid-scan Fourier transform infrared (FT-IR) spectrometer, we obtain a series of synchronized interferograms (120 ms) during multiple ALD cycles to observe the dynamics of an average ALD cycle. We use a buried metal layer (BML) substrate to enhance absorption by the surface species. The surface selection rules of the BML allow us to determine the contribution from the substrate surface as opposed to that from gas-phase molecules and species adsorbed at the windows. In addition, we use simulation to examine the origins of increased reflectivity associated with phonon absorption by the oxide layers. The simulations are also used to determine the decay in enhancement by the buried metal layer substrate as the oxide layer grows during the experiment. These calculations are used to estimate the optimal number of ALD cycles for our experimental method.

Orientation of avidin molecules immobilized on COOH-modified SiO 2/Si(1 0 0) surfaces

Avidin molecules were immobilized on a COOH-modified SiO 2/Si(1 0 0) surface with subnano-level flatness (root-mean-square (rms) roughness ≈0.1 nm) forming covalent bonds between the COOH groups on the substrate surface and the NH 2 groups of avidin molecules. The structures of avidin-immobilized surfaces were investigated by atomic force microscopy (AFM), ellipsometry, and infrared (IR) reflection absorption spectroscopy using buried metal layer substrate (BML-IRRAS), and transmission IR absorption spectroscopy (TIRAS). These data have evidenced that the avidin molecules are immobilized with the 2-fold symmetry axis of the tetramer almost perpendicularly to the substrate surface.

Assignment of surface IR absorption spectra observed in the oxidation reactions: 2H + H 2O/Si(1 0 0) and H 2O + H/Si(1 0 0)

Infrared reflection absorption spectroscopy that used buried metal layer substrates (BML-IRRAS) and density functional cluster calculations were employed to investigate the water related oxidation reactions of 2H + H 2O/Si(1 0 0)-(2 × 1), 2D + H 2O/Si(1 0 0)-(2 × 1), and H 2O + H/Si(1 0 0)-(2 × 1). In addition to the oxygen inserted coupled monohydrides, which were previously reported in the former reaction system, we report several other oxidized Si hydride species in our BML-IRRAS experiments. Three new pairs of vibrational bands are identified between 900 and 1000 cm −1. These vibrational frequencies were calculated using Si9 and Si10 cluster models that included all possible structures from zero to five oxygen insertions into the top layer silicon atoms using a B3LYP gradient corrected density functional method with a polarized 6-31G** basis set for all atoms. The three pairs of vibrational modes are assigned to the scissoring modes of adjacent and isolated SiH 2 with zero, one, and two oxygen atoms inserted into the Si back bonds. All the other newly observed vibrational peaks related to Si oxidation are also assigned in this study. The Si–O stretching bands observed in the reaction 2D + H 2O/Si(1 0 0)-(2 × 1) show an isotope effect, which suggests that in the system 2H + H 2O/Si(1 0 0)-(2 × 1) also, hydrogen atom tunneling plays an important role for the insertion of oxygen atoms into Si back bonds that form oxidized adjacent dihydrides.

A theoretical investigation of the far-infrared RAIRS experiment applied to a buried metal layer substrate

In this paper we report a theoretical investigation of the reflection absorption infrared spectroscopy (RAIRS) experiment applied to non-metallic substrates incorporating a buried metal layer (BML). In particular we concentrate on the low wavenumber region (280–480 cm−1) typically studied using synchrotron based RAIRS experiments. To illustrate this study, an example system consisting of a hypothetical isotropic layer adsorbed on thin-films of tin(IV) oxide on tungsten has been used. Using a four-layer model, systematic wavenumber-dependent Greenler type calculations of ΔR/R (often taken as a measure of the sensitivity of the experiment) have been performed. The calculated spectra show the absorption band associated with the adsorbate but also reproduce an “inverse absorption” feature, which has been observed experimentally. The results show that the factors which influence the intensity of these adsorbate-induced inverse absorption bands are different from those that influence adsorbate bands and may therefore be used to discriminate between these two types of feature. A partial first order approximation of the full Greenler-type formula has then been used to rationalise the calculated dependences of the intensities of both absorption and inverse absorption bands and system parameters like layer thicknesses, incidence angles and optical characteristics of the adsorbate.

A theoretical investigation of the far-infrared RAIRS experiment applied to a buried metal layer substrate

In this paper we report a theoretical investigation of the reflection absorption infrared spectroscopy (RAIRS) experiment applied to non-metallic substrates incorporating a buried metal layer (BML). In particular we concentrate on the low wavenumber region (280–480 cm −1 ) typically studied using synchrotron based RAIRS experiments. To illustrate this study, an example system consisting of a hypothetical isotropic layer adsorbed on thin-films of tin(IV) oxide on tungsten has been used. Using a four-layer model, systematic wavenumber-dependent Greenler type calculations of Δ R / R (often taken as a measure of the sensitivity of the experiment) have been performed. The calculated spectra show the absorption band associated with the adsorbate but also reproduce an “inverse absorption” feature, which has been observed experimentally. The results show that the factors which influence the intensity of these adsorbate-induced inverse absorption bands are different from those that influence adsorbate bands and may therefore be used to discriminate between these two types of feature. A partial first order approximation of the full Greenler-type formula has then been used to rationalise the calculated dependences of the intensities of both absorption and inverse absorption bands and system parameters like layer thicknesses, incidence angles and optical characteristics of the adsorbate.

Three-pairs of doublet bands assigned toSiH2scissoring modes observed inH2O-induced oxidation of Si(100) surfaces

Oxidation of Si(100) surfaces by H 2 O has been investigated on 2H+H 2 O/Si(100)-(2×1), H 2 O +Si(100)-(2×1), as well as H 2 O+H/Si(100)-(2×1) systems by infrared reflection absorption spectroscopy using CoSi 2 buried metal layer substrates (BML-IRRAS). Three pairs of doublet bands assigned to the scissoring modes of adjacent and isolated SiH 2 with zero, one, and two inserted back-bond oxygen atoms, respectively, have been reported. This report also has clearly shown the unique high sensitivity of BML-IRRAS for the perpendicular components in the fingerprint region, compared to the multiple internal reflection and the external transmission arrangements. Oxidation mechanisms have been proposed. In the 2H +H 2 O/Si(100)-(2×1) system, oxygen insertion into the back bond occurs easily. In the H 2 O+H/Si(100) system, however, the tunneling effect is important to reach the oxygen inserted state.

Fabrication of CoSi2-Buried-Metal-Layer Si Substrates for Infrared Reflection Absorption Spectroscopy by Wafer-Bonding

Infrared reflection absorption spectroscopy (IRRAS) using buried metal layer substrates (BML) is one of the high resolution and high sensitive surface vibration spectroscopy techniques. A unique characteristic is the wide frequency range including the so-called finger print region. The CoSi2 Si(100) BML substrates fabricated by Co ion implantation have been used to date. However, the technique has several problems such as the resultant surface roughness due to the ion implantation damage. To solve these problems, in this work, we have examined the fabrication of BML substrates with atomic-level flat surfaces by the wafer-bonding between a Co deposited Si(100) wafer and a Si on insulator (SOI) wafer. Self-assembled alkyl monolayers (SAMs) of octadecyltrichlorosilane and octenyltrichlorosilane were deposited on the fabricated BML substrate surface. Good BML-IRRAS spectra were observed in the wide frequency range from stretching to bending regions. It was also found that well-ordered SAMs were deposited.

Study of Si Surface Reactions by Infrared Reflection Absorption Spectroscopy Using Buried Metal Layer Substrates

In order to obtain the infrared reflection absorption spectroscopy (IRRAS) on semiconductor or insulator surfaces, IRRAS using a buried metal layer substrate (BML) was proposed. Compared with attenuated total reflection (ATR) arrangement, sensitivity is low, but it is a favorable point that sensitivity exists at wide frequency ranges including the finger print regions. The transmission (TR) arrangement is also applicable for wide frequency ranges, but its sensitivity is slightly lower than that of the BML-IRRAS. The important difference between TR and BML-IRRAS is in the selection rule. TR is sensitive for parallel components, but on the other hand, BML-IRRAS is for perpendicular components. Some recent results about the reaction of hydrogen on the Si(100) surfaces and the IR spectra of self assembled alkyl monolayers (SAMs) investigated by BML-IRRAS are introduced.

Hydrogen Diffusion and Chemical Reactivity with Water on Nearly Ideally H-terminated Si(100) Surface

A nearly ideally H-terminated condition for a Si(100) 2×1 surface is determined from the dependence of the peak intensity and the linewidth of the coupled monohydride symmetric stretching vibration on the hydrogen exposure and exposure temperature, which has been investigated with infrared reflection absorption spectroscopy (IRRAS) using CoSi2 buried metal layer substrate. Even for nearly ideally H-terminated surfaces, the linewidth significantly changes depending on the hydrogen exposure and the exposure temperature. The concentration of deuterium atoms incorporated in the Si bulk is measured by temperature programmed desorption, and it is concluded that hydrogen diffusion into the subsurface of Si has a significant influence on the linewidth broadening. The chemical reactivity with water on the H-terminated Si surface is also investigated.

IR line width broadening at nearly ideal H-termination region on Si [formula omitted] surfaces

The dependence of the line width of the coupled monohydride symmetric stretching vibration of the H-terminated Si(1 0 0)-(2×1) surface on the exposure temperature and the hydrogen exposure has been investigated with infrared reflection absorption spectroscopy (IRRAS) using CoSi 2 buried metal layer substrate. Even for nearly ideally H-terminated Si(1 0 0) surface, the line width significantly changes depending on the exposure temperature and the hydrogen exposure. The reason of the line width broadening is discussed, and it is strongly suggested that hydrogen diffusion into the subsurface of Si has a significant influence on the line width broadening. Evidence of hydrogen (deuterium) diffusion into the subsurface is investigated for the first time using an IRRAS measurement.

Infrared Reflection Absorption Spectroscopy using Buried Metal Layer Substrates and Synchrotron Radiation Stimulated Surface Reaction.

Infrared reflection absorption spectroscopy (IRRAS) has been adopted for the high sensitive and high resolution vibrational spectrum measurements on the metal surfaces. In recent years, IRRAS using buried metal layer substrates (BML-IRRAS) has been developed. This technique provides sufficient sensitivity for the submonolayer adsorbates on the semiconductor and insulator surfaces. The synchrotron radiation stimulated process, which has characteristics of high spatial resolution, low damage, and unique reaction selectivities, is expected to realize a practical nano-process technique in future. We are developing the new BML-IRRAS technique and trying to apply it to the monitoring of the SR stimulated surface reactions. The BML-IRRAS technique is useful in the in-situ observations of the surface reaction, especially of the beam-induced reactions. In this report, our BML-IRRAS technique and recent results of our experiments using this technique with thermal and SR stimulated reaction on the hydrogen terminated Si(100) surfaces are introduced.

Infrared Reflection Absorption Spectroscopy of Selective Etching and Decomposition Stimulated by Synchrotron Radiation

The study of processing stimulated by synchrotron radiation (SR) started about 13 years ago. Unfortunately, for semiconductor processing, the reaction rate of this technique was considered to be too slow for practical applications. However the situation is rapidly changing as device dimensions shrink to the nanometer range, which requires high controllability and low defect densities, but is not so reliant on quick processing since much less material is involved. SR etching—which has a typical etching rate of 1–10 nm/min, capability of high-resolution etching due to the short wavelength of SR photons, high controllability, low damage production, and a clean reaction system—is considered to be extremely suitable for nanometer processing.The benefit of SR etching is that it has unique material selectivities. However the mechanisms for the selectivity are not yet clarified. Consideration of the future application of the SR process to nanometer structure fabrication is dependent upon the development of in situ observation techniques that can evaluate the reaction surface at an atomic or molecular level. Recently we have developed an in situ observation technique: infrared reflection absorption spectroscopy using buried metal layer substrates (BML-IRRAS), which is especially suitable for in situ monitoring of beam-induced reactions on the semiconductor surface in high vacuum.

Ultrahigh-Vacuum Reaction Apparatus to Study Synchrotron-Radiation-Stimulated Processes

An ultrahigh-vacuum reaction apparatus to study synchrotron-radiation-stimulated processes has been constructed and placed on beamline 4B of the synchrotron radiation storage ring (UVSOR) at the Institute for Molecular Science. The apparatus is designed so that multiple synchrotron radiation processes such as etching and chemical vapour deposition can be carried out successively without breaking the high vacuum. It is equipped with IR reflection absorption spectroscopy (IRRAS) apparatus and reflective high-energy electron diffraction (RHEED) apparatus for in situ observations. The basic parameters of the apparatus including etching and deposition rates have been measured. IRRAS using buried metal layer substrates has been confirmed to be a very useful method of analyzing the reaction mechanisms of the synchrotron-radiation-stimulated processes.

Composition of dimers on Ge/Si(001)2×1 surfaces analyzed by infrared (IR) reflection spectroscopy of surface hydrogen vibration

The composition of dimer structures formed on a Ge/Si(001)2×1 surface was investigated under various conditions of Ge coverage and annealing temperature using surface infrared (IR) spectroscopy on Si substrates with a buried metal layer (BML). Dimer structures were modified by atomic hydrogen to visualize the surface species in the IR spectra, where the signals from the mixed Ge–Si and pure Si–Si/Ge–Ge dimers as well as the non-dimer structures have different frequencies and thus are distinguishable from each other. These surface modes can be assigned to specific dimer structures on the basis of the surface selection rule on the BML substrate. Ge grows as mixed Ge–Si dimers for 0.2 monolayer (ML) of initial Ge coverage, as a mixture of the mixed and pure dimers for 0.6 ML, and as the pure Ge–Ge dimers for 1.2 ML. On annealing, Ge in the Ge–Ge and Ge–Si dimers diffuses into the second or deeper layers of Si and the dimers converted into pure Si–Si dimers at 810°C, through the formation of the mixed dimer from the pure Ge–Ge dimer at medium annealing temperature. These results show the potential of IR spectroscopy as a sensitive probe for evaluating the composition of semiconductor surfaces.

Angle-variable infrared external reflection spectroscopy in UHV and its application to the observation of SiH vibrations on Si(001) substrates with a buried metal layer

We have constructed a system with a variable-angle mechanism for infrared (IR) reflection spectroscopy in UHV. Hydrogen-adsorbed Si(001) substrates with a buried metal layer (BML) are examined in vacuo to demonstrate the utility of this system for surface IR spectroscopy on semiconductors. The available range of the angle is between 60 and 85°, and the noise level of the 100% line after averaging 1000 scans on an Si BML substrate is <1 × 10 −4 at 2000 cm −1 and <5 × 10 −4 at 650 cm −1, which is sufficiently low to observe vibrations from surface species at submonolayer coverage. The results show that analysis of the spectral dependence on polarization, angle of incidence and Si overlayer thickness is very useful in examining the origin of the signals from surface species and their surface structures, including the orientation.

Preparation and characterization of a well-ordered surface on a Si(001) substrate with a buried metal layer for application of infrared reflection spectroscopy

The preparation and characterization of an atomically flat and well-ordered surface on the Si(001) substrate with a buried metal layer (BML) are reported. The BML substrate was formed by implantation of Co+ ion and subsequent annealing. After molecular beam epitaxy growth of the Si overlayer on the cleaned BML sample in ultrahigh vacuum, clear 2×1 patterned and ordered steps with regular terrace width were observed by reflection high energy electron diffraction and atomic force microscopy. No contamination, including Co, was observed in the spectra of Auger electron spectroscopy and x-ray photoelectron spectroscopy. Ultraviolet photoelectron spectra showed a distinct surface peak that originated from surface dangling bonds and is characteristic of a clean and ordered surface. The surface atomic structure, including stress and damage caused by ion implantation, was characterized by medium energy ion scattering (MEIS). Very low χmin (1.7% with 300 keV H+) and a dip pattern in blocking profile in the MEIS spectra indicate that surface crystal quality is comparable to that of a homoepitaxially grown Si layer on normal Si substrate without BML. These results show that the BML substrate obtained by the procedure is quite useful for the structural investigation of surface species on Si by infrared (IR) reflection spectroscopy. Typical examples of IR spectra qualifying the BML substrate for surface studies are also presented.

埋め込み金属層基板を用いた赤外反射吸収スペクトル法による放射光励起半導体プロセス反応のその場観察

埋め込み金属層基板を用いた赤外反射吸収スペクトル法による放射光励起半導体プロセス反応のその場観察

Synchrotron Radiation Irradiation Effects for S i H n on Si(100) Surface in the Synchrotron Radiation Stimulated Si Gas Source Molecular Beam Epitaxy

SiH n on Si (100) surfaces during synchrotron radiation (SR) stimulated gas source molecular beam epitaxy (SR-GSMBE) using Si2H6 gas (1.0×10-3 Torr) are investigated in situ by means of infrared reflection absorption spectroscopy using CoSi2 buried metal layer substrates (BML-IRAS) in the low substrate temperature region (400° C-140° C). It has been found that SiH2 and SiH3 on the surface are easily decomposed by SR to SiH and the decomposition rate of SiH is extremely slow. The decomposition reaction cross sections for SiH2 and SiH3 for the total irradiating photon flux have been evaluated to be 5.7×10-20 cm2 and 1.7×10-19 cm2, respectively. Experimental results are discussed, considering the model of the localized multihole excitation and its quenching.

In situ observation of silicon hydrides on Si(100) surfaces during synchrotron-radiation-stimulated Si2H6 gas source molecular beam epitaxy

Silicon hydrides (SiHn) on the Si(100) surface during synchrotron-radiation (SR) stimulated Si2H6 gas source molecular beam epitaxy has been observed in situ at low temperatures (≤400 °C), by means of infrared reflection absorption spectroscopy using CoSi2 buried metal layer substrates. At high temperatures (400 °C, 370 °C), SiH is a dominant surface species, while with temperature decrease from 275 to 50 °C, the number of SiH decreases, and, on the other hand, SiH2 and SiH3 appear and increase. This result explains the change of reflection high-energy diffraction pattern from 2×1 to 1×1. The SiH in the bulk network has not been observed. SR irradiation on the film at 140 °C after deposition shows that SiH2 and SiH3 are easily decomposed to SiH and that SiH decomposes much more slowly than SiH2 and SiH3.

Infrared reflection absorption spectra of trimethylaluminum and dimethylaluminum hydride condensed layers on an SiO 2 surface with a buried metal layer substrate

Infrared reflection absorption spectroscopy (IRAS) of trimethylaluminum (TMA) and dimethylaluminum hydride (DMAH) layers condensed on an SiO 2 surface was carried out by using a buried metal layer (BML) substrate. TMA was a dimer in the experimental temperature range of 110 K < T < 160 K. The molecular orientation varied depending on the deposition temperature. The condensed layer of DMAH as-deposited at the temperature ranging from 110 to 130 K was a mixture of trimers and dimers. The dimers changed to trimers as the temperature increased, practically disappearing above 130 K. This temperature dependence was not reversible. The trimers did not change to dimers below 130 K. The ordered orientation of the trimer molecules was a stable DMAH condensed layer structure on the SiO 2 surface. The usefulness of BML-IRAS for studying the structure and molecular orientation of adsorbed layers on semiconductor materials is discussed.