Silicon Surface Topography Research Articles

Atomic Force Microscope Characterization of the Bending Stiffness and Surface Topography of Silicon and Polymeric Electrodes.

Implanted electrodes in the brain are increasingly used in research and clinical settings to understand and treat neurological conditions. However, a foreign body response typically occurs after implantation, and glial encapsulation of the device is a commonly observed. Multiple factors affect how gliosis surrounding the implantable electrodes evolves. Characterizing and measuring the surface features and mechanical properties of these devices may allow us to predict where gliosis will occur, and understanding how electrode design features may impact astrogliosis may give researchers a set of design guidelines to follow to maximize chronic performance. In this study, we used atomic force microscopy to measure surface roughness on parylene, polyimide, and silicon devices. Multiple features on microelectrode arrays were measured, including electrode sites, traces, and the bulk substrate. We found differences in surface roughness according to device material, but not device features. We also directly measured the bending stiffness of silicon devices, providing a more exact quantification of this property to corroborate calculated estimates.

空气中和水下激光等离子体冲击波对硅表面形貌的影响

空气中和水下激光等离子体冲击波对硅表面形貌的影响

Surface self-diffusion of silicon during high temperature annealing

The atomic-scale mechanisms driving thermally activated self-diffusion on silicon surfaces are investigated by atomic force microscopy. The evolution of surface topography is quantified over a large spatial bandwidth by means of the Power Spectral Density functions. We propose a parametric model, based on the Mullins-Herring (M-H) diffusion equation, to describe the evolution of the surface topography of silicon during thermal annealing. Usually, a stochastic term is introduced into the M-H model in order to describe intrinsic random fluctuations of the system. In this work, we add two stochastic terms describing the surface thermal fluctuations and the oxidation-evaporation phenomenon. Using this extended model, surface evolution during thermal annealing in reducing atmosphere can be predicted for temperatures above the roughening transition. A very good agreement between experimental and theoretical data describing roughness evolution and self-diffusion phenomenon is obtained. The physical origin and time-evolution of these stochastic terms are discussed. Finally, using this model, we explore the limitations of the smoothening of the silicon surfaces by rapid thermal annealing.

Investigating individual arsenic dopant atoms in silicon using low-temperature scanning tunnelling microscopy

We study subsurface arsenic dopants in a hydrogen-terminated Si(001) sample at 77 K, using scanning tunnelling microscopy and spectroscopy. We observe a number of different dopant-related features that fall into two classes, which we call As1 and As2. When imaged in occupied states, the As1 features appear as anisotropic protrusions superimposed on the silicon surface topography and have maximum intensities lying along particular crystallographic orientations. In empty-state images the features all exhibit long-range circular protrusions. The images are consistent with buried dopants that are in the electrically neutral (D0) charge state when imaged in filled states, but become positively charged (D+) through electrostatic ionization when imaged under empty-state conditions, similar to previous observations of acceptors in GaAs. Density functional theory calculations predict that As dopants in the third layer of the sample induce two states lying just below the conduction-band edge, which hybridize with the surface structure creating features with the surface symmetry consistent with our STM images. The As2 features have the surprising characteristic of appearing as a protrusion in filled-state images and an isotropic depression in empty-state images, suggesting they are negatively charged at all biases. We discuss the possible origins of this feature.

Transition from ripples to faceted structures under low-energy argon ion bombardment of silicon: understanding the role of shadowing and sputtering

In this study, we have investigated temporal evolution of silicon surface topography under 500-eV argon ion bombardment for two angles of incidence, namely 70° and 72.5°. For both angles, parallel-mode ripples are observed at low fluences (up to 2 × 1017 ions cm-2) which undergo a transition to faceted structures at a higher fluence of 5 × 1017 ions cm-2. Facet coarsening takes place at further higher fluences. This transition from ripples to faceted structures is attributed to the shadowing effect due to a height difference between peaks and valleys of the ripples. The observed facet coarsening is attributed to a mechanism based on reflection of primary ions from the facets. In addition, the role of sputtering is investigated (for both the angles) by computing the fractional change in sputtering yield and the evolution of surface roughness.PACS81.05.Cy, 81.16.Rf, 61.80.Jh, 87.64.Dz

Unusual pattern formation on Si(1 0 0) due to low energy ion bombardment

In this paper evolution of silicon surface topography, under low energy ion bombardment, is investigated at higher oblique incident angles in the range of 63–83°. Si(100) substrates were exposed to 500eV argon ions. Different surface morphologies evolve with increasing angle of incidence. Parallel-mode ripples are observed up to 67° which undergo a transition to perpendicular-mode ripples at 80°. However, this transition is not a sharp one since it undergoes a series of unusual pattern formation at intermediate angles. For instance, mounds, cone-, and needle-like structures appear at intermediate angles, viz. in the angular range of 70–78°. Complete smoothening of the silicon surface is observed at incident angles beyond 80°. The observed patterns are attributed to surface confined viscous flow and sputter erosion under ion bombardment.

Nanorelief formation under ion irradiation of germanium and silicon surfaces

The surface topography of silicon and germanium single crystals formed under 10-keV Ar+ and Ne+ irradiation was studied experimentally. A relief with typical nanometer-scale dimensions is detected using atomic-force microscopy. It is established that the average height of the nanorelief formed depends on the silicon doping levels. It is also shown that the average height is determined by the parameters of ion irradiation.

Nanoscale self-affine surface smoothing by ion bombardment

The topography of silicon surfaces irradiated by a 2-MeV ${\mathrm{Si}}^{+}$ ion beam at normal incidence and ion fluences in the range ${10}^{15}--{10}^{16}{\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{s}/\mathrm{c}\mathrm{m}}^{2}$ has been investigated using scanning tunneling microscopy. At length scales below \ensuremath{\sim}50 nm, surface smoothing is observed; the smoothing is more prominent at smaller length scales. The smoothed surface is self-affine with a scaling exponent \ensuremath{\alpha}=0.53\ifmmode\pm\else\textpm\fi{}0.03.

Room Temperature Wafer Bonding Using Oxygen Plasma Treatment in Reactive Ion Etchers With and Without Inductively Coupled Plasma

The effects of oxygen plasma treatment on silicon surface topography and the properties of bonded interfaces formed using the oxygen plasma pretreatment were investigated. Bonded samples of silicon or oxidized silicon wafers using oxygen plasma pretreatment in reactive ion etchers with and without inductively coupled plasma were characterized in terms of surface energies obtained at room temperature. Annealing experiments at 1000°C were made to study the origin of thermally generated voids. Atomic force microscopy was used to study how the surface roughness of plasma-treated silicon wafers evolved over time. Furthermore, the influence of water dipping on the roughness of plasma-treated silicon surfaces was investigated. The results showed that plasma treatment of one wafer results in a surface energy of approximately at room temperature. The role of water in the increase of surface energy was found to be crucial. From annealing experiments it is concluded that water present at the wafer surfaces before bonding has a pronounced influence on void generation upon annealing. A dramatic change in the topography of silicon surfaces treated in oxygen plasma was observed during storage at room temperature, while water dipping the wafers after plasma treatment appeared to stabilize the surface topography. © 2003 The Electrochemical Society. All rights reserved.

Atomic force microscopy (AFM) of the topography of silicon surfaces exposed to ion beams

Reactive ion beams such as O2+and Cs+are used in Secondary Ion Mass Spectrometry (SIMS) to analyze solids for trace impurities. Primary beam properties such as energy, dose, and incidence angle can be systematically varied to optimize depth resolution versus sensitivity tradeoffs for a given SIMS depth profiling application. However, it is generally observed that the sputtering process causes surface roughening, typically represented by nanometer-sized features such as cones, pits, pyramids, and ripples. A roughened surface will degrade the depth resolution of the SIMS data. The purpose of this study is to examine the relationship of the roughness of the surface to the primary ion beam energy, dose, and incidence angle. AFM offers the ability to quantitatively probe this surface roughness. For the initial investigations, the sample chosen was <100> silicon, and the ion beam was O2+.Work to date by other researchers typically employed Scanning Tunneling Microscopy (STM) to probe the surface topography.