Microcontact Mechanism Research Articles

The evolution and generation of nanosurfaces and their microcontact mechanism in glass‐embossing process

AbstractGlass‐embossing technology has attracted great attention due to its promise of low‐cost and environmentally conscious fabrication of well‐defined and controllable surfaces and nanostructured devices. The embossed surface quality of glass structures is a very important index for optics. However, the evolutions of nanosurfaces and their microcontact mechanism during glass‐embossing process have not been deeply and comprehensively investigated. Here, we studied the surface morphology evolution of optical glass under different processing conditions using a tungsten carbide surface plate with nanoscale roughness as the mold. The light transmittances of different embossed glasses were detected by an ultraviolet spectrophotometer. The flow deformation and microcontact mechanism of glass‐supercooled liquids were revealed during glass‐embossing process. The result showed that the rough optical glass can successfully replicate the nanoscale smoothness of the tungsten carbide template without grinding or polishing. On the basis of the previous study, the glass‐surfaced structures from nanoscale to macroscale are fabricated. This work provides better understanding for the evolution of nanosurfaces and the fabrication of nanostructured optics during glass‐embossing process.

Three-dimensional discrete element modeling of the irregularly shaped pebbles used in a truck escape ramp

The truck escape ramp is a clump of pebbles that is located alongside downgrades. As the pebbles are randomly placed in arrester beds, few studies have been conducted on simulation methods of the irregularly shaped pebbles. This paper proposed a pebble DEM model to analyze the micro-contact mechanism of the pebbles. Based on a polynomial algorithm, the 7th fit was selected and the coefficients of the edge curves were recorded. Second, the main view and left view were filled with preset numbers of ball elements. According to the ball element parameters, the ball elements were extended to three-dimensional models. Third, based on the edges of the main view and the top view, the ball element parameters were recalculated. Then, compression tests were conducted, and the key parameters of the pebble DEM model were calibrated. Based on the built pebble DEM model, compression tests were simulated with different pressing plate velocities and laying thicknesses. The results indicate that for increases in the pressing plate velocity, the contacting forces on the plate correspondingly increase, and this increase is linearly shaped. The results for different laying thicknesses indicate that for increases in the laying thickness, the contacting forces on the plate correspondingly decrease.

Microcontact mechanism in silicon wafer self-rotating grinding based on force decomposition

Carrying out silicon wafer self-rotating grinding using a cup-type diamond grinding wheel is a typical ultra-precision machining technique of silicon wafers. Studying the mechanism of the self-rotating grinding is the basis of the processing. The research takes the microcontact between the micro-element in the grinding wheel and the silicon wafer extracted during the steady ductile-regime grinding as the object and builds a mechanical model. On this basis, the research investigates the microscopic mechanism of the self-rotating grinding using the force decomposition method. The force decomposition in the normal direction using the Hertz theory in contact mechanics and the cavity model obtained the distributions of the load and stress on the silicon wafer in the elastic and plastic contact, as well as the corresponding stress distribution on the micro-element in the grinding wheel. The force decomposition in the tangential direction based on the microscopic friction theory yields the sliding friction. The superposition of normal and tangential forces reveals the overall distribution of microcontact stress. The analysis results are validated by comparing with corresponding experimental and simulation results.

Microcontact mechanism in silicon wafer self-rotating grinding based on force decomposition

Microcontact mechanism in silicon wafer self-rotating grinding based on force decomposition

Behavior of microcontacts in rock joints under direct shear creep loading

Two types of fractures were induced in sandstone by means of modified shear and indirect tension. The fractured rock samples were assembled following their initial formation and direct shear tests were performed under a constant normal force and stepwise increased shear creep loadings. Using computerized tomography (CT) and laser scanning, the micro-contact mechanism of the fractured rock surfaces were observed and measured before, during, and after the shear tests. Under a moderate normal force, dilation tends to occur in the shear fractured rocks; with the increase of normal force, the peak shear strength of tensile fractured rocks grows faster than that of shear fractured rocks and eventually gives rise to a higher value. A few micro-contact modes and fracture phenomena of the rough surfaces in contact are recognized through CT and laser scanning images, such as shear-off of micro-asperities, friction between macrowaved rough surfaces, migration of worn debris, propagation and healing up of hybrid cracks in subsurface. The long-term shear strength of fractured rocks is mainly composed of two mechanisms: one is the shear resistance raised from interlocked microasperities in the scale of roughness in tensile fractured rocks, the other is the frictional resistance produced between macroasperities in the scale of waviness on the shear fractured rocks. The microcontact configuration and contact area are observed and measured by slice cutting of the mated rough surfaces in contact. Two distinct patterns of contacts in rock joints are recognized, term as coastline pattern and islands pattern. The shear strength of fractured rocks is closely related to the maximum contact area and the surface roughness.

Materials removal principle in nano-precision wafer polishing based on probability theory and micro-contact mechanism

Based on assumptions of micro-contact over wafer-abrasive and pad-abrasive interfaces, the Gaussian distribution of abrasive size and an assumed normal distribution of pad surface, a novel model for material removal in chemical mechanical polishing is developed. The chemical effect is taken into account by parameter Hw (the hardness of the chemically modified surface layer on wafer). The model proposed integrates process parameter, wafer harness, pad topography, pad properties and abrasive distribution into the model to predict the material removal rate (MRR). Based on the deformation of hyper-elastic asperities attached to a liner-elastic pad, asperity scale MRR is introduced. Active particles is calculated by probability theory and the wafer scale MRR is proposed. Compared with the experimental results, the model accurately predicts MRR.

A Material Removal Modeling of Chemical Mechanical Polishing Based on Micro-Contact Mechanism

The model proposed integrates process parameters including pressure and velocity and other important input parameters including the wafer hardness, pad roughness, abrasive size, and abrasive geometry into the formulation to predict the material removal rate. Based on the deformation of hyper-elastic asperities attached to a linear-elastic pad, contact mechanism between the asperities and the wafer is analyzed. Micro-contact mechanism between the particle and wafer is proposed on the basis of elastic-plastic deformation theory. Material removal rate of single abrasive particle is calculated by the abrasive wear theory. The fluid effect in the current model is attributed to the number of active abrasives. Wafer scale material removal rate is analyzed in detail, which is agreed with the experimental results. The Preston’s coefficient, which has been determined empirically, is now given as a function of various processing variables, pad roughness, wafer material properties and slurry status.

Study of Contact Temperature in Polishing Surfaces

Based on a three-body micro-contact mechanism and contact temperature theory, a micro-contact temperature model was developed to investigate the effect of particle size, particle density, and rotational speed on temperature rise between particles and workpieces. The experiments with different particle sizes and rotational speeds verified the feasibility of the micro-contact temperature analysis. The results indicate that contact temperature between particles and workpieces linear increases as particle size and rotational speed increase. The particle density has a negligible effect on maximum contact temperature between particles and workpieces.

Chemical Mechanical Polishing in Elastic Contact and Partial Hydrodynamic Lubrication: Modeling and Experiments

Chemical mechanical polishing (CMP) has become a primary technique for planarization of semiconductor wafers in submicro device fabrication. Increasing demands for high uniformity and dimensional precision make previously discountable levels of asperity, powder slurry, and wafer-pad contact significant. In this study, a CMP model considering both the elastic microcontact mechanism and the grain flow with roughness effects is presented. The model applies the average lubrication equation with partial hydrodynamic lubrication theory and elastic microcontact theory proposed by Greenwood and Williamson. In experiments, a test rig is used to simulate the CMP process and acquire the signals of polishing. The shear force is measured by a load transducer mounted on the lever and connected with the polishing head during CMP process. Furthermore, the theoretical results are compared with the experimental data. The theoretical and experimental results increase the understanding of CMP process.

Analysis based on microcontact mechanism for the roughness dependent stick–slip motion

The stick–slip behavior occurring between an indenter with its round tip treated as a rigid sphere with a radius of 300 nm and the (1 0 0) Si specimen was considered. The characteristic slip distances were observed in the stick–slip behavior under small normal loads. A statistical evaluation of microcontact on the basis of Fourier cosine series was proposed to evaluate the dominant scales of roughness under different normal loads. The experimental results showed the elastic deformation exhibited in the contact between the indenter and the specimen when the contact load was smaller than 40 μN. The characteristic scales of roughness obtained by the proposed method revealed good agreement with the experimental results of slip distance under different contact loads. Through the proposed method, the roughness dependence of the stick–slip behavior can be further understood quantitatively.

An improved model considering elastic—plastic contact and partial hydrodynamic lubrication for chemical mechanical polishing

Chemical mechanical polishing (CMP) has become a primary technique for planarization of semiconductor wafers in sub-micro device fabrication. A physical CMP model combines the effects of grain flow hydrodynamic lubrication, pad roughness, and asperity contact between wafer and pad. In this study, an improved CMP model, considering both the grain flow with roughness effects and the micro-contact mechanism, is proposed. The model applies the average lubrication equation with partial hydrodynamic lubrication theory and considers the elastic—plastic micro-contact theory. The applied load acting on the wafer is balanced by the slurry pressure in the non-contact area, and the surface asperity contact force in the contact area. The effects of the CMP parameters including applied load, rotation speed, particle size, and pad roughness are studied and discussed. The simulation results compare well with experimental data in the literature and contribute to further understanding in wafer—pad contact mechanism.

Elasto-Partial Hydrodynamic Contact Model for Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) has become a primary technique for the planarization of semiconductor wafers in submicrometer device fabrication. Increasing demands for high uniformity and dimensional precision make previously discountable levels of asperity, powder slurry, and wafer-pad contact significant. In this study, an improved model considering both the elastic microcontact mechanism and the grain flow with roughness effects is proposed. The model applies the average lubrication equation with the partial hydrodynamic lubrication theory and elastic microcontact theory proposed by Greenwood and Williamson. The external force acting on the wafer is supported by the partial hydrodynamic slurry pressure in the noncontact area and the surface asperity contact force in the contact area. This model predicts slurry flow film thickness under a variety of the CMP parameters, including applied load, rotation speed, particle size, and pad roughness. The results compare well with experimental data in the literature. Furthermore, the contact ratio of area and removal rate are studied and discussed.

On the Microcontact Mechanism of Thermosonic Wire Bonding in Microelectronics: Saturation of Interfacial Phenomena

Thermosonic ball bonding is widely used in interconnections to integrated circuits. This work used a thermosonic bonding machine and a shear tester to study the effects of preload, preheat temperature, ultrasonic power, welding time, and wire diameters on shear force. The results reveal that shear force of thermosonic wire bonding can be elucidated from the viewpoint of interfacial microcontact phenomena such as energy intensity, interfacial temperature, and real contact area. As the energy intensity is increased, the shear force increases, reaches a maximum, and then decreases. The energy intensity at which the shear force reaches maximum is called the saturated energy intensity. After saturation (that is, the establishment of maximum atomic bonds), any additional energy input will damage the bonding, decreasing the shear force. The saturated energy phenomenon can be further confirmed by using wires with different diameters. It is also observed that the saturation phenomena, and thereby the optimal shear force, occurs under a certain range of interfacial temperature.

Tribological Analysis of CMP with Partial Asperity Contact

Chemical mechanical polishing (CMP) is the most effective technology for global planarization in submicrometer device fabrication. Therefore, much research has been conducted to understand the basic mechanisms of the CMP process. In this study, a model that considers the microcontact mechanism and the grain flow is proposed. The down force acting on the wafer is supported by both the slurry pressure in the noncontact area and the surface asperity contact force in the contact area. The operation parameter effects on the force distribution, separation distance, and real contact area were investigated. The results show that larger down force and lower relative speed between the wafer and the polishing pad lead to increased contact ratio between the polishing interfaces. Larger slurry particle size can decrease the contact ratio. © 2003 The Electrochemical Society. All rights reserved.