Masayasu Nishizawa

Controlled bond formation between chemical vapor deposition Si and ultrathin SiO2 layers

This article reports that chemically active sites on SiO2 surfaces can be either passivated or introduced intentionally by treating them in a proper chlorosilane gas, SiHnCl4−n (n=0,1,2). Our experiments of Si chemical vapor deposition on SiO2-covered Si have shown that Si deposition is suppressed on SiCl4- and SiHCl3-treated samples, while an SiH2Cl2 treatment drastically enhances Si nucleation. Thus, the chlorosilane treatment is a unique way for us to control the interface bonds between the SiO2 surface and the Si deposits on it. We also demonstrate resistless selective-area deposition using a SiHCl3-treated ultrathin SiO2 mask layer. Patterns are defined on the mask surface by direct electron-beam irradiation which induces Cl desorption thereby forming chemically reactive surface defects.

Scanning tunneling microscopy detection of individual dopant atoms on wet-prepared Si(111):H surfaces

We have performed scanning tunneling microscopy (STM) observation of individual acceptor and donor atoms on hydrogen-terminated Si(111)-1×1 surfaces prepared by wet etching in a NH4F aqueous solution. Separate measurements of p- and n-type substrates showed that acceptors appear as protrusions in filled-state images and as depressions in empty-state images, while for donors the topography is reversed in both filled- and empty-state images. The same relation between the bias polarity and the dopant appearance is preserved for codoped substrates. These results demonstrate that the STM on the Si(111):H surface can detect acceptors and donors distinguishably, enabling us to measure dopant profiles across codoped areas such as p-n junctions.

Chlorosilane adsorption on clean Si surfaces: Scanning tunneling microscopy and Fourier-transform infrared absorption spectroscopy studies

The initial adsorption processes of SiH2Cl2 on Si(111)-(7×7) and Si(100)-(2×1) surfaces have been investigated by using infrared absorption spectroscopy and scanning tunneling microscopy. We have found that dissociation reactions of SiH2Cl2 on these two surfaces are distinctively different. SiH2Cl2 adsorption on Si(111)-(7×7) takes place via Si–Cl bond breakage, while both Si–H and Si–Cl bonds of the SiH2Cl2 molecules are dissociated on Si(100)-(2×1).

Effects of Chemical Composition and Morphology of Substrate Surfaces on Crystallinity of Ultrathin Hydrogenated Microcrystalline Silicon Films

Hydrogenated microcrystalline silicon (?c-Si:H) films of 10 nm thickness were prepared by the plasma-enhanced chemical vapor deposition method on glass substrates that had been coated by a layer composed of Si, O, and N. The chemical composition of this layer was changed systematically, and the resultant changes in the crystallinity of the ?c-Si:H films were investigated using Raman scattering spectroscopy. We have found that SiNx layers inhibit nucleation of microcrystalline Si and the films deposited on them are dominated by an amorphous component, regardless of their stoichiometry. Substrate surfaces rich in Si?O bonds are preferable for the formation of high-quality ?c-Si:H films. It has been also found that the morphology of the coated layers does not affect the crystallinity of the ?c-Si:H films.

Scanning Tunneling Microscopy Observation of Individual Boron Dopant Atoms beneath Si(001)-2× 1 Surfaces

Individual B dopant atoms residing beneath Si(001)-2×1 surfaces have been detected by scanning tunneling microscopy (STM). A subsurface B atom appears as a broad protrusion in filled-state images, while it appears as either a broad depression or a localized protrusion in empty-state images depending on the STM tip condition. This variation in dopant appearance is attributed to the different work function (WF) of the tip, i.e., the amount of tip-induced band bending differs depending on the tip WF, resulting in a different tunneling path and an opposite dopant appearance under the same bias voltage.

Measurements of Electrostatic Potential Across p--n Junctions on Oxidized Si Surfaces by Scanning Multimode Tunneling Spectroscopy

We investigated the variation in contact potential difference (CPD) voltage across p–n junctions on oxygen-passivated Si(110) surfaces by scanning multimode tunneling spectroscopy, which detects probe–sample interaction force simultaneously with tunneling current. The enhancement of sensitivity to electrostatic force was achieved with a small amplitude of probe vibration (0.3 nm) when the tip–sample gap was adjusted to reduce short-range interactions by maintaining the tunneling current at a specified bias voltage. At the optimal tip–sample gap, the CPD voltage, derived from force gradient spectra, agrees with the expected built-in potential across the p–n junction. The CPD voltage showed a standard deviation of ~30 mV on atomically flat terraces. Larger fluctuations were ascribed to structural and charge variations on the oxidized surfaces.

Direct imaging of the evolving Au/InSb(111) B interface

In situ high-resolution transmission electron microscopy in the profile geometry has been used to observe the evolving features of the Au/InSb(111) B-(2×2) interface. During Au deposition in the range between 0 monolayer (ML) and ∼1 ML coverage, the outermost Sb-trimer layer of the InSb(111) B-(2×2) substrate changes in contrast, presumably revealing that deposited Au atoms are partially captured into it. At ∼2 ML coverage, an unknown phase emerges on the outermost layer, beyond which it continues to grow epitaxially in an island state, causing partial disruption of the substrate. The phase is identified as Au9In4 alloy with a γ-brass structure determined from a digital Fourier transform diffractogram and a transmission electron diffraction pattern. The epitaxial relationship of Au9In4 with the substrate is given by (111) InSb∥(111) Au9In4 and [110] InSb∥[110] Au9In4. The high resolution-profile transmission electron microscopy images of this alloy agree well wITH the results calculated by the multislic...

Carrier concentration profiling on oxidized surfaces of Si device cross sections by resonant electron tunneling scanning probe spectroscopy

Quantitative carrier concentration profiles of super-junction power metal-oxide-semiconductor field-effect transistor devices were obtained by resonant electron tunneling (RET) scanning probe spectroscopy making use of a discrete energy level of adsorbed C60 molecules. RET voltage profiles measured on oxidized (100) surfaces of fine-polished cross sections revealed the presence of separated p-type islands in the n-type epitaxial layer and agreed well with the profiles obtained by local work function spectroscopy, although fluctuations were observed owing to surface defects and variations in the oxide and C60 film thickness. The derived boron concentration coincides with the implanted boron density obtained by numerical simulations. These results verify that the C60 RET scanning probe spectroscopy on oxidized surfaces has the ability of quantitative carrier concentration profiling of Si device cross sections, if flat surfaces with good quality are prepared.

In situ electron spin resonance of initial oxidation processes of Si surfaces

Abstract We have made for the first time electron spin resonance (ESR) measurements on Si(111)7×7 and Si(100)2×1 surfaces during the initial oxidation processes at room temperature. The present results clearly show that, at a very initial stage of oxidation of Si surfaces where only a few surface layers were oxidized, a variety of defects are formed that have not been seen in ex situ ESR studies of SiO 2 /Si structures.

Chemical bonding features for faultily stacked interfaces of GaAs{111}

The electronic states for normally stacked and faultily stacked layers on the GaAs{111} A, B surfaces are calculated by use of the discrete variational X α cluster method and the plane wave nonlocal pseudopotential method. The results show that chemical bondings between atoms are not as ionic in the faultily stacked layer of (111) B as they are in the (111) A case, and that on the (111) A surface more attractive Coulomb interaction energy is gained in the faulty stacking layer than in the normal stacking one. These results explain well the more frequent emergence of in-plane faults in the (111) A surface, which is well known in GaAs{111} A, B growth experiments. The total energy calculations also provide quantitative interpretation of such growth features.The electronic states for normally stacked and faultily stacked layers on the GaAs{111} A, B surfaces are calculated by use of the discrete variational X α cluster method and the plane wave nonlocal pseudopotential method. The results show that chemical bondings between atoms are not as ionic in the faultily stacked layer of (111) B as they are in the (111) A case, and that on the (111) A surface more attractive Coulomb interaction energy is gained in the faulty stacking layer than in the normal stacking one. These results explain well the more frequent emergence of in-plane faults in the (111) A surface, which is well known in GaAs{111} A, B growth experiments. The total energy calculations also provide quantitative interpretation of such growth features.