Top Si Layer Research Articles

Optical anisotropies of Si grown on step-graded SiGe(110) layers

Macroreflectance and microreflectance difference spectroscopies have been used to measure the strain induced optical anisotropies of semiconductor structures comprised of strained Si(110) thin films deposited on top of step-graded SiGe virtual substrates. The stress relaxation mechanism mainly occurs by the introduction of microtwin formation, whose fluctuation depends strongly on growth conditions. Correlations of such optical diagnostics with x-ray diffraction measurements and atomic force microscopy images, allow for the in situ study of the strain within both the top Si layer and the SiGe underneath with an spatial resolution of at least 5 μm.

Direct Observations of Relaxation of Si/SiGe/Si on Insulator

AbstractMicrostructural evolution is directly observed when the cross-sectional film specimen of Si/SiGe/Si on insulator (Si/SiGe/SOI) is heated from room temperature (R.T., 291 K) up to 1113 K in high voltage transmission electron microscope (HVEM). The misfit dislocation at the lower interface of the SiGe layer begins to extend downwards even at 913 K. The lower interface takes the lead in roughening against the upper interface of the SiGe layer. The roughened interface is ascribed to elastic relaxation. As misfit strain is partially transferred to SOI top Si layer and misfit dislocation is prolonged at the lower interface, the roughened interface turns smooth again. Thereafter, the misfit dislocations are introduced into the upper roughened interface of the SiGe layer to release the increased misfit strain. It is suggested that the microscopic relaxation of the SiGe layer is related to dislocation behavior and strain transfer.

Self-assembled Au nanoparticles in SiO2 by ion implantation and wet oxidation

Implantation, annealing, and oxidation processes have been used to form Au nanoparticles with a narrow size and depth distribution in a SiO2 layer. Different approaches have been attempted: in particular, the gettering of Au to fill preformed nanocavities (obtained by H-implantation and annealing) and thus overcome the broad particle size distribution that is normally associated with nanoparticles formed by implantation and annealing. The results suggest that nanocavities cannot be directly formed in SiO2 by H-implantation and a subsequent annealing due partly to the high mobility of H atoms in SiO2. However, cavities formed in Si are useful in obtaining a narrow size and depth distribution of Au precipitates: the Si substrate can then be oxidized to form Au nanoparticles in SiO2. Sequential wet oxidations of Si samples containing Au nanoparticles have revealed several interesting phenomena, namely, segregation of Au particles at a growing oxide interface, Au-enhanced oxidation, dissolution and reprecipitation of Au precipitates during oxidation, and preferential wetting of Au on the oxide layer. In particular, the Au dissolution and reprecipitation processes are Si interstitial mediated. By completely oxidizing the top Si layer, an array of Au precipitates can be confined at a precise depth within a SiO2 layer corresponding to the front interface of a buried oxide layer. The size distribution of the resulting Au precipitates in SiO2 is smallest when Au is first gettered to cavities and vacancies are subsequently introduced into the Si layer prior to oxidation.

Investigation on Silicon on Insulator Fabricated by Separation by Implanted Oxygen Layer Transfer

In this paper, two approaches combining the separation by implanted oxygen layer transfer (SLT) process with Si epitaxy are proposed to fabricate a silicon-on-insulator (SOI) wafer. Spectroscopic ellipsometry indicates that SOI wafers with the top Si layers of and are obtained. Defect-free top Si as well as atomic-scale sharp top Si/buried oxide interfaces are observed by transmission electron microscopy, indicating a high crystal quality and a perfect structure of the SLT SOI wafers. Using atomic force microscopy, the surface and top Si/buried oxide interface morphology of the SLT SOI wafers is also investigated.

Single-crystalline Si grown on single-crystalline Gd 2O 3 by modified solid-phase epitaxy

We investigate molecular beam epitaxial overgrowth of Si template layers produced by different approaches on single-crystalline oxide grown on Si(111). Three approaches based on modified solid-phase epitaxy were found to be suitable for the subsequent Si epitaxial overgrowth. The crystalline quality and interface properties of single-crystalline silicon on single-crystalline oxide grown on Si(111) make the obtained structures suitable for silicon-on-insulator applications. First measurements of electrical properties of p-type samples indicate good electrical properties of the top Si layer. Supplemental investigations demonstrate that Si layers with thickness in the range of 10 nm remain stable during thermal annealing up to 900 °C in an ultra-high vacuum.

Nanoplate field-effect capacitive (bio-)chemical sensor array based on SOI structure

An array of individually addressable nanoplate field-effect capacitive (bio-)chemical sensors based on an SOI (silicon-on-insulator) structure has been developed for multi-parameter detection. An isolation of the individual capacitors was achieved by forming a trench in the top Si layer with various thicknesses of 30-350 nm. The feasibility of the proposed approach has been demonstrated by realising sensors for the detection of pH as well as for the label-free electrical monitoring of adsorption and binding of charged macromolecules.

Effect of residual stress on nanoindented property of <inline-formula><math display="inline" overflow="scroll"><mrow><mi mathvariant="normal">Si</mi><mo>∕</mo><mi mathvariant="normal">C</mi><mo>∕</mo><mi mathvariant="normal">Si</mi></mrow></math></inline-formula> multilayers

The effect of residual stress on the nanoindentation property of Si/C/Si multilayers has been investigated. Sandwiched Si/C/Si multilayers were deposited on Si(100) substrates by means of ultrahigh-vacuum ion-beam sputtering at room temperature (RT). Four structures with different Si top-layer thickness of 5, 10, 25, and 50 nm and the constant thickness of C/Si underlayer at 100/50 nm were investigated in this study. The residual stress of the Si/C/Si (5/100/50 nm/nm/nm thick) film was about −17.76 GPa under compression, and its hardness was 20.39 GPa at RT. The compressive residual stress was decreased to −5.54 GPa with the increased thickness of Si toplayer up to 50 nm, and its hardness was reduced to ~16.22 GPa at RT. The effect of Si top-layer thickness (5-50 nm) on Si/C/Si residual stress on the nanoindentation property were also discussed. The results showed that the thicker was the Si toplayer, the lower was the residual stress and hardness, which was good for the suppression of the buckling or wrinkling in the C/Si-nanocomposite film.

Fabrication of Thick-film Silicon-on-Insulator by Separation by Implanted Oxygen Layer Transfer

In this paper, two approaches combined the Separation by IMplanted OXygen (SIMOX) layer transfer (SLT) process with Si epitaxy are proposed to fabricate thick-film Silicon-on-Insulator (SOI). Spectroscopic ellipsometry indicates thick-film SOI wafers with the top Si layers of 1430.86 {plus minus} 19.8 nm and 1476.44 {plus minus} 18.5 nm are achieved. Atomic-scale sharp interfaces between the top Si layer and buried oxide layers are observed by high-resolution transmission electron microscopy. Using atomic force microscopy, surface morphology of the SOI wafer is also investigated.

Growth of ZnO Epitaxial Films Using 3C-SiC Substrate with Buried Insulating Layer

ZnO epitaxial films were grown by metal organic chemical vapor deposition (MOCVD) on novel large-diameter or 8-in. 3C-SiC substrate with a buried insulating layer whose structure is 3C-SiC/SiO2/Si. The substrate is fabricated by thinning the top Si layer of a silicon-on-insulator (SOI) substrate, and then carbonizing the ultrathin top Si layer of the SOI substrate. X-ray diffraction (XRD) and photoluminescence (PL) of the ZnO epitaxial films on a 3C-SiC substrate with a buried insulating layer revealed excellent characteristics of crystalline structure and luminescence. These results can be attributed not only to the 3C-SiC layer with a small lattice mismatch for ZnO but also to the buried insulating layer working as a compliant buffer layer. Thus, the 3C-SiC substrate with a buried insulating layer has advantages for growing high-quality ZnO epitaxial films owing to the small lattice mismatch and for fabricating ZnO epitaxial films inexpensively owing to Si technology.

Investigation of an ion-milled Si/Cr multilayer using micro-RBS, ellipsometry and AES depth profiling techniques

To investigate the details of the ion beam induced mixing and validate the Auger electron spectroscopy depth profiling technique, sputter-deposited Si 40 nm/Cr 40 nm multilayer samples were irradiated with a 20 keV CF 4 + ion beam. Due to the ion bombardment the top Si layer was damaged and a crater was created. Elemental depth profiles and layer thicknesses together with surface topography were measured with Rutherford backscattering spectrometry by applying a focussed 2 MeV He + beam. The thickness of the top Si layer was also determined from ellipsometry measurements. The results are compared to that of obtained from Auger electron spectroscopy depth profiling.

Characterization of Light Element Impurities in Ultrathin Silicon-on-Insulator Layers by Luminescence Activation Using Electron Irradiation

We analyzed light element impurities in ultrathin top Si layers of silicon-on-insulator (SOI) wafers by luminescence activation using electron irradiation. Photoluminescence (PL) analysis under ultraviolet (UV) light excitation was performed on various commercial SOI wafers after the irradiation. We detected the C-line related to a complex of interstitial carbon and oxygen impurities and the G-line related to a complex of interstitial and substitutional carbon impurities in the top Si layer with a thickness down to 62 nm after electron irradiation. We showed that there were differences in the impurity concentration depending on the wafer fabrication methods and also that there were variations in these concentrations in the respective wafers. Xenon ion implantation was used to activate top Si layers selectively so that we could confirm that the PL signal under the UV light excitation comes not from substrates but from top Si layers. The present method is a very promising tool to evaluate the light element impurities in top Si layers.

未退火硅基锗光电二极管反向电流的降低

A new approach to reduce the reverse current of Ge pin photodiodes on Si is presented, in which an i-Si layer is inserted between Ge and top Si layers to reduce the electric field in the Ge layer. Without post-growth annealing, the reverse current density is reduced to ~10 mA/cm2 at -1 V, i.e., over one order of magnitude lower than that of the reference photodiode without i-Si layer. However, the responsivity of the photodiodes is not severely compromised. This lowered-reverse-current is explained by band-pinning at the i-Si/i-Ge interface. Barrier lowering mechanism induced by E-field is also discussed. The presented non-thermal approach to reduce reverse current should accelerate electronics-photonics convergence by using Ge on the Si complementary metal oxide semiconductor (CMOS) platform.

Surface Inspection of Silicon-on-Insulator Wafers with Ultrathin Top-Si Layer by Laser Scattering: Numerical Analysis of Light Scattering by Voids

The dependences of the scattering of laser light on the size and shape of voids, which are known as “killer” defects of silicon-on-insulator (SOI) wafers in the fabrication of transistors, were investigated. Forward scattering dominated in the higher reflectance films at a wavelength of 488 nm and in all cases of a wavelength of 355 nm. Side scattering dominated in the lower reflectance films at a wavelength of 488 nm. These results indicated that the scattering properties of voids in the SOI wafers with various reflectance values depending on the thicknesses must change using an inspection tool with a laser wavelength of 488 nm. This characteristic is unsuitable in the detection of voids. The dependence of light scattering at a wavelength of 355 nm was not observed with void sizes of 240 or 500 nm. Circular and square-shaped voids showed similar scattering patterns. Therefore, an inspection tool with a wavelength of 355 nm is superior for detecting not only particles but also voids.

Optical properties of ion-implanted silicon and separation by implantation of oxygen silicon-on-insulator substrates in the infrared: Study of B + and P 2+ implantation doping

The optical properties of ion implanted silicon and silicon-on-insulator substrates have been studied by Fourier transform infrared spectroscopy. The influence of the implanted-ion mass in changing the refractive index of a silicon target has been examined by implanting 80 keV 11B + and 62P 2 + ions respectively. A refractive index rise not exceeding 2% and total amorphization were observed respectively in the vicinity of the Si surface after boron and phosphorous implantations. Free carrier profiles generated after thermal annealing at 950 °C/30 min and 1150 °C/120 min were modeled by Pearson and half-Gaussian distributions respectively. The phosphorous implantation was also performed in silicon-on-insulator substrates, yielding after annealing nearly homogeneous free-carrier profiles in the top-Si layer and optical mobility values comparable to those of bulk-Si.

Fabrication of thin-film silicon on insulator by separation by implanted oxygen layer transfer

In this article, the authors propose an improved approach—separation by implanted oxygen (SIMOX) layer transfer process—to fabricate thin-film silicon on insulator (SOI). The top Si layer, a low-dose SIMOX wafer, was transferred upside down onto a thermally oxidized Si handle wafer by a bonding technique and etch-stop thinning process. Spectroscopic ellipsometry indicated a thin-film SOI with the device layer of 147.5±3.1nm. An atomic-scale sharp interface between the device layer and buried oxide layer was observed by high-resolution transmission electron microscopy.

Fabrication Process for Double Barrier Si-Based Quantum Well Resonant Tunneling Diodes (RTD) by UHV Wafer Bonding

Double barrier Si-based Resonant Tunneling Diode (RTD) structures were fabricated by ultra high vacuum (UHV) wafer bonding. 300 mm ultra thin body silicon-on-insulator (SOI) wafers with 10 nm top Si layers were developed and used for the integration of Si/SiO2((<3nm)/Si(<10nm)/SiO2(<3nm)/Si RTD structures. The dielectric oxide/Si interfaces characterized by Capacitance-Voltage (C-V) measurements were of good quality. The bonded oxide/Si interfaces characterized by high resolution transmission electron microscopy (HRTEM) were atomically sharp.

Role of Strontium in Oxide Epitaxy on Silicon (001)

Epitaxial oxide-Si heterostructures, which integrate the functionality of crystalline oxides with Si technology, are made possible by a submonolayer of Sr deposited on Si (001). We find by electron diffraction studies using single termination Si wafers that this Sr submonolayer replaces the top layer of Si when deposited at 650 degrees C. Supported by first-principles calculations, we propose a model for the reaction dynamics of Sr on the Si surface and its effect on oxide epitaxy. This model predicts, and we experimentally confirm, an unexplored 25 degrees C pathway to crystalline oxide epitaxy on Si.

Pseudomorphic SiGe∕Si(001) layers synthesized by gas immersion laser doping

We report on the synthesis of SiGe layers on silicon by gas immersion laser doping. GeCl4 molecules are adsorbed on the surface and further incorporated into the Si top layer by a pulsed laser induced melt/regrowth process. Structural and chemical characterizations of the SiGe layers have been performed by using complementarily Rutherford backscattering spectrometry and x-ray Diffraction which indicate that Ge incorporation in the Si matrix results in a fully strained SiGe layer with gradual Ge concentrations reaching up to 18.5% near the surface.

Characterization of bonded silicon-on-aluminum-nitride wafers with RBS, TEM and HRXRD techniques

Bonded silicon-on-insulator (SOI) materials via the Smart-cut TM (or ion-cut) process attract increasing interests due to their great capability and versatility in fabricating novel virtual substrates. Previously we reported the successful fabrication of silicon-on-aluminum-nitride (SOAN) structure with smart-cut process [C.L. Men, Z. Xu, Z. An, X.Y. Xie, M. Zhang, C.L. Lin, Physica B 324 (2002) 229]. In this work, we characterize the bonded SOAN structure with Rutherford backscattering spectroscopy (RBS), transmission electron microscopy (TEM) together with Kikuchi line diffraction patterns, and high resolution X-ray diffraction (HRXRD) techniques. It is found that, after smart-cut process, the top Si layer preserves a rather good single crystalline quality, while strain is induced in top Si and can be altered in the annealing step. The rotational misalignment during bonding step can be evaluated by Kikuchi line patterns. Our discussions here may be common for all bonded virtual substrates via smart-cut technology.

Dielectric constant reduction in silicon nanostructures

We performed a systematic measurement of the dielectric function of Si nanoslabs as a function of their thickness using spectroscopic ellipsometry from $0.73\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ $(1700\phantom{\rule{0.3em}{0ex}}\mathrm{nm})\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}4.58\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ $(270\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$. The Si nanoslabs were obtained by repeatedly thinning down the top Si layer in silicon-on-insulator wafers by successive oxidation and HF etching. As predicted by the theories, both real and imaginary parts of the dielectric function are reduced as the thickness decreases. The dielectric constant of $3.3\text{\ensuremath{-}}\mathrm{nm}$-thick nanoslabs measured at $0.73\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, below the band gap energy of bulk Si, is reduced by $\ensuremath{\sim}13%$ (from 12 to 10.4) compared to the bulk value. The measured size dependence is in qualitative but not quantitative agreement with the most applicable theory.