Evolution Of Surface Topography Research Articles

A chemical mechanical planarization model for aluminum gate structures

In this work, we propose a new aluminum gate chemical mechanical planarization (CMP) model to describe the metal gate height variation in 32nm high-k metal gate (HKMG) process based on chemical kinetics and contact mechanics. The effects of mechanical abrasion, concentration of different types of chemical reagents and hydrogen ions, pattern geometry and pad elastic properties on surface profile are physically captured. In the process of constructing the model, the discrete convolution and fast Fourier transform (DC–FFT) technique is integrated with conjugated gradient method (CGM) for calculating the contact pressure between the wafer surface and the polishing pad. Then the computed pressure distribution is introduced into the new constructed chemical kinetics formula to determine the local removal rate of the underlying patterns and predict the evolution of the wafer surface topography. The detailed relationship between the metal gate dishing post-Al-CMP and the design pattern structures are systematically investigated. The model agrees reasonably well with the experimental data measured from the HKMG test structures. Therefore, it can be utilized for quantifying the effect of pattern geometry on dishing, predicting the wafer surface height evolution and optimizing some design rules for manufacturability to improve the surface planarization of HKMG structures.

Three-dimensional simulation of surface topography evolution in the Bosch process by a level set method

A deep reactive ion etching (DRIE) process (Bosch process) is used extensively in the fabrication of microelectromechanical systems (MEMS). Modeling and simulation studies have helped improve our understanding and process design. The Bosch process consists of multiple cycles of alternating etching and deposition steps. Based on a narrow band level set method, by integrating etching simulation and deposition simulation modules, a simulation system is proposed for three-dimensional (3-D) simulation of the Bosch process with arbitrarily complex mask shapes. To verify the simulation system, a series of simulations and experiments have been performed. The simulation results are in good agreement with the experiments. The method may be used to optimize the practical Bosch process and to design and control the profile of high-aspect ratio microstructures.

Electrolyte composition and removal mechanism of Cu electrochemical mechanical polishing

The optimization of electrolytes and the material removal mechanisms for Cu electrochemical mechanical planarization (ECMP) at different pH values including 5-methyl-1H-benzotriazole (TTA), hydroxyethylidenediphosphoric acid (HEDP), and tribasic ammonium citrate (TAC) were investigated by electrochemical techniques, X-ray photoelectron spectrometer (XPS) analysis, nano-scratch tests, AFM measurements, and polishing of Cu-coated blanket wafers. The experimental results show that the planarization efficiency and the surface quality after ECMP obtained in alkali-based solutions are superior to that in acidic-based solutions, especially at pH=8. The optimal electrolyte compositions (mass fraction) are 6% HEDP, 0.3% TTA and 3% TAC at pH=8. The main factor affecting the thickness of the oxide layer formed during ECMP process is the applied potential. The soft layer formation is a major mechanism for electrochemical enhanced mechanical abrasion. The surface topography evolution before and after electrochemical polishing (ECP) illustrates the mechanism of mechanical abrasion accelerating electrochemical dissolution, that is, the residual stress caused by the mechanical wear enhances the electrochemical dissolution rate. This understanding is beneficial for optimization of ECMP processes.

Surface and melt pond evolution on landfast first-year sea ice in the Canadian Arctic Archipelago

The evolution of landfast sea ice melt pond coverage, surface topography, and mass balance was studied in the Canadian Arctic during May–June 2011 and 2012, using a terrestrial laser scanner, snow and sea ice sampling, and surface meteorological characterization. Initial melt pond formation was not limited to low-lying areas, rather ponds formed at almost all premelt elevations. The subsequent evolution of melt pond coverage varied considerably between the 2 years owing to four principle, temporally variable factors. First, the range in premelt topographic relief was 0.5 m greater in 2011 (rougher surface) than in 2012 (smoother surface), such that a seasonal maximum pond coverage of 60% and maximum hydraulic head of 204 mm were reached in 2011, versus 78% and 138 mm in 2012. A change in the meltwater balance (production minus drainage) caused the ponds to spread or recede over an area that was almost 90% larger in 2012 than in 2011. Second, modification of the premelt topography was observed during mid-June, due to preferential melting under certain drainage channels. Some of the lowest-lying premelt areas were subsequently elevated above these deepening channels and unexpectedly became drained later in the season. Third, ice interior temperatures remained 1–2°C colder later into June in 2012 than in 2011, even though the ice was 0.35 m thinner at melt onset, thereby delaying permeability increases in the ice that would allow vertical meltwater drainage to the ocean. Finally, surface melt was estimated to account for approximately 62% of the net radiative flux to the sea ice cover during the melt season.

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.

Evolution of slip surface roughness through shear

AbstractA significant part of displacement in fault zones occurs along discrete shear surfaces. The evolution of fault surface topography is studied here in direct shear laboratory experiments. Matching tensile fracture surfaces were sheared under imposed constant normal stress and sliding velocity. The roughness evolution was analyzed using measurements of surface topography before and after slip. We show that shearing reduces the initial surface roughness at all measurement scales. At all wavelengths, the roughness ratio between initial and final roughness increases as a function of the slip distance. For a given test, the roughness ratio increases with wavelength up to a few millimeters, beyond which the ratio becomes wavelength independent. At this region the roughness measured after slip follows a power law similar to that of the initial tensile fracture surface. We interpret this geometrical evolution as a consequence of the deformation stage of interlocked asperities which is followed by shear‐induced dilation.

Laser Machining of Structural Alumina: Influence of Moving Laser Beam on the Evolution of Surface Topography

Laser machining technique has emerged as an innovative tool to effectively machine the structural ceramics, which previously was nearly impossible using various conventional machining techniques. However, obtaining a desired surface finish via laser machining is still a critical issue. As many physical phenomena act simultaneously during laser machining, it is very difficult to understand their influence in real time and predict the surface topography. To address this issue, a multiphysics‐based finite‐element modeling approach was implemented to understand the influence of moving laser beam (with lateral overlap) on the generation of corresponding surface topography/profile/roughness during laser machining of structural alumina. A computation model that coupled heat transfer and computational fluid dynamics was designed to understand the combined influence of Marangoni convection, recoil pressure, cooling rates, and surface tension on the evolving surface topography during laser machining of structural alumina under various machining conditions. Both computational and experimental results evidently showed the systematic increase in surface roughness parameters with the increase in lateral overlap (0, 17, 33, 50, 67, and 83%). The results of the computational model are also validated by experimental observations with reasonably close agreement (±3.5%).

Three-dimensional simulations of the surface topography evolution of niobium superconducting radio frequency cavities

This paper contains results of the three-dimensional simulations of the surface topography evolution of the niobium superconducting radio frequency cavities during isotropic and anisotropic etching modes. The initial rough surface is determined from the experimental power spectral density. The simulation results based on the level set method reveal that the time dependence of the root mean square roughness obeys Family-Viscek scaling law. The growth exponential factors b are determined for both etching modes. Exponential factor for the isotropic etching is 100 times lower than that for the anisotropic etching mode reviling that the isotropic etching is very useful mechanism of the smoothing. [Projekat Ministarstva nauke Republike Srbije, br. O171037 i br. III45006

Effect of thermal annealing on the surface of sol-gel prepared oxide film studied by atomic force microscopy and Raman spectroscopy

In this work, we have investigated the surface topography evolution of sol-gel deposited SiO2-SnO2 nanocomposite films annealed in the temperature range 200–600°C. The fractal dimension of atomic force microscopy images of the films was determined by the cube counting method and the triangulation method. The fractal dimension was shown to be an appropriate and easy to use tool for the characterization of nanosized thin film structures. Raman spectroscopy revealed the formation of a SiO2 cage-like structure at 400°C and SnO2 crystallization above 500°C.

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

Pattern transfer during deposition and fixation of oligomeric bisphenol A on pre-structured copper surfaces

Pattern transfer during deposition of oligomeric bisphenol A (OBA) on pre-structured Cu surfaces is investigated by means of a combined experimental-computational approach. Aiming for quantitative prediction of experiments, as characterized by atomic force microscopy (AFM), we explore the capabilities of stochastic rate equations to quantitatively account for the spatio-temporal evolution of surface topography. While surface diffusion and deposition noise constitute the main mechanisms, pattern transfer is affected by the inclusion of retardation in the interface potential, which appears to be necessary beyond a critical initial surface slope. In addition, routes for successful surface fixation by cross-linking are also demonstrated, which may pave the way for further technological use.

Surface Topography Characterization in Steel Running-in Process of Dry Sliding Friction

Running-in is an important and inevitable wear process for machine system, and it plays an indispensable role in extending service life and improving operating performance. Surface topography appears as a significant feature of friction pairs. Therefore, study on modification of surface topography in running-in is crucial to control surface quality and then achieve improvement of machine system. In this paper, to understand the evolution of surface topography in running-in process, steel dry sliding running-in experiments were conducted, and surface topographies in running-in were evaluated with the areal surface evaluation parameters. The results reveal that surface topography evaluation could provide valuable information about wear status of steel running-in process of dry sliding friction, amplitude parameters, area and volume parameters, and hybrid parameters play different and important roles in characterization of surface topography modification in running-in.

Experimental methods for the characterization of fatigue in microstructures

The mechanical fatigue behavior of gold microbeams is analyzed. Dedicated devices have been designed and built able to produce alternate loading on gold specimens; the electrostatic actuation is used as driving force. Gold beams are tested under both bending and tensile alternate loadings. Results were used to plot S-N curves and fatigue Goodman-Smith diagram in order to estimate the fatigue limit of the material in presence of mean and alternate stress conditions. The surface topography evolution is studied and failure modes are discussed.

The role of confinement on stress-driven grain boundary motion in nanocrystalline aluminum thin films

3D molecular dynamics simulations are performed to investigate the role of microstructural confinement on room temperature stress-driven grain boundary (GB) motion for a general population of GBs in nanocrystalline Al thin films. Detailed analysis and comparison with experimental results reveal how coupled GB migration and GB sliding are manifested in realistic nanoscale networks of GBs. The proximity of free surfaces to GBs plays a significant role in their mobility and results in unique surface topography evolution. We highlight the effects of microstructural features, such as triple junctions, as constraints to otherwise uninhibited GB motion. We also study the pinning effects of impurities segregated to GBs that hinder their motion. Finally, the implications of GB motion as a deformation mechanism governing the mechanical behavior of nanocrystalline materials are discussed.

Nanoscale surface pattern formation kinetics on germanium irradiated by Kr+ions

Nanoscale surface topography evolution on Ge surfaces irradiated by 1 keV Kr+ ions is examined in both directions perpendicular and parallel to the projection of the ion beam on the surface. Grazing incidence small angle x-ray scattering is used to measure in situ the evolution of surface morphology via the linear dispersion relation. A transition from smoothing (stability) to pattern-forming instability is observed at a critical ion incidence angle of approximately 62◦ with respect to the surface normal. The linear theory quadratic coefficients which determine the surface stability/instability are determined as a function of bombardment angle. The Ge surface evolution during Kr+ irradiation is qualitatively similar to that observed for Ar+ irradiation of Si. However, in contrast to the case of Si under Ar+ irradiation, the critical angle separating stability and instability for Ge under Kr+ irradiation cannot be quantitatively reproduced by the simple Carter-Vishnyakov mass redistribution model.

Relationships between landslide types and topographic attributes in a loess catchment, China

Topographic attributes have been identified as the most important factor in controlling the initiation and distribution of shallow landslides triggered by rainfall. As a result, these landslides influence the evolution of local surface topography. In this research, an area of 2.6 km2 loess catchment in the Huachi County was selected as the study area locating in the Chinese Loess Plateau. The landslides inventory and landslide types were mapped using global position system (GPS) and field mapping. The landslide inventory shows that these shallow landslides involve different movement types including slide, creep and fall. Meanwhile, main topographic attributes were generated based on a high resolution digital terrain model (5 m × 5 m), including aspect, slope shape, elevation, slope angle and contributing area. These maps were overlaid with the spatial distributions of total landslides and each type of landslides in a geographic information system (GIS), respectively, to assess their spatial frequency distributions and relative failure potentials related to these selected topographic attributes. The spatial analysis results revealed that there is a close relation between the topographic attributes of the post-landsliding local surface and the types of landslide movement. Meanwhile, the types of landslide movement have some obvious differences in local topographic attributes, which can influence the relative failure potential of different types of landslides. These results have practical significance to mitigate natural hazard and understand geomorphologic process in thick loess area.

Evolution of coefficient of friction with deposition temperature in diamond like carbon thin films

Diamond like carbon (DLC) thin films, used as excellent solid lubricant, are grown on Si substrates at temperatures in the range of 100–600 °C using pulsed direct current magnetron sputtering to understand the role of substrate temperature on the tribological properties. Friction tests have been carried out using a micro-tribometer at a load of 2 N. Phase evolution in the films with temperature is studied using micro-Raman spectroscopy. Lateral force microscopy is employed to study the evolution of surface and friction topography in the films. We have observed an increase in the coefficient of friction (μ) from 0.05 to 0.30 with increase in deposition temperature. The films deposited below 400 °C exhibited excellent tribological properties with film deposited at 100 °C depicting the lowest value of μ (approx. 0.05). The films deposited above 400 °C have been found to wear out at early stages. The degradation in tribological properties of DLC films deposited at high temperatures is explained on the basis of structural transformation taking place during the film deposition.

Evolution of surface topography in one-dimensional laser machining of structural alumina

High energy lasers are an emerging industrial tool to fabricate complex shapes on hard and brittle structural ceramics such as alumina. The selection of laser processing parameters and the prediction of material removal rates during the laser machining are the critical issues. This paper was attempted to present the state of the art of laser machining of alumina using an integrated experimental and computational approach. A multistep computational model based on COMSOL™ Multiphysics was developed to study the influence of various single-pulse laser energy densities and associated physical phenomena (recoil pressure, Marangoni convection, and surface tension) on the temperature history, fluid velocity, crater size, and surface topography. A pulsed Nd:YAG laser was employed to machine alumina under different processing conditions. The surface topography of laser machined alumina was measured by an optical profilometer and the results were compared with the computationally predicted topographic parameters with reasonably close agreement.

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.

Models of nanoparticles movement, collision, and friction in chemical mechanical polishing (CMP)

Nanoparticles have been widely used in polishing slurry such as chemical mechanical polishing (CMP) process. The movement of nanoparticles in polishing slurry and the interaction between nanoparticles and solid surface are very important to obtain an atomic smooth surface in CMP process. Polishing slurry contains abrasive nanoparticles (with the size range of about 10–100 nm) and chemical reagents. Abrasive nanoparticles and hydrodynamic pressure are considered to cause the polishing effect. Nanoparticles behavior in the slurry with power-law viscosity shows great effect on the wafer surface in polishing process. CMP is now a standard process of integrated circuit manufacturing at nanoscale. Various models can dynamically predict the evolution of surface topography for any time point during CMP. To research, using a combination of individual nanoscale friction measurements for CMP of SiO2, in an analytical model, to sum these effects, and the results scale CMP experiments, can guide the research and validate the model. CMP endpoint measurements, such as those from motor current traces, enable verification of model predictions, relating to friction and wear in CMP and surface topography evolution for different types of CMP processes and patterned chips. In this article, we explore models of the microscopic frictional force based on the surface topography and present both experimental and theoretical studies on the movement of nanoparticles in polishing slurry and collision between nanoparticles, as well as between the particles and solid surfaces in time of process CMP. Experimental results have proved that the nanoparticle size and slurry properties have great effects on the polishing results. The effects of the nanoparticle size and the slurry film thickness are also discussed.