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Residual stresses in PET preforms is thought to be an important cause in the stress cracking of blown bottles but there is no data yet that can be linked to stress and cracking. An important step i...

Polyethylene Terephthalate (PET) is used in many packaging applications. PET is especially important in the carbonated soft drink industry, where the pressure of carbonation and the imposed and residual stresses in the bottle bases can sometimes lead to cracking, and failures. In the process of bottle blowing, residual stresses are created and remain in the bottle base as a result of the uniaxial and biaxial stretching in these regions. It is advantageous to measure these residual stresses and the mode of stretching, which may be related to the failure characteristics of the bottle bases. Photoelasticity can be used to examine these residual stresses in the sidewalls and bases of bottles. This work reports on a residual stress measurement tool for the bottle blowing industry.

Near-infrared (NIR) polariscopy is a technique used for the non-destructive evaluation of the in-plane stresses in photovoltaic silicon wafers. Accurate evaluation of these stresses requires correct identification of the stress-optic coefficient, a material property which relates photoelastic parameters to physical stresses. The material stress-optic coefficient of silicon varies with crystallographic orientation. This variation poses a unique problem when measuring stresses in multicrystalline silicon (mc-Si) wafers. This paper concludes that the crystallographic orientation of silicon can be estimated by measuring the transmission of NIR light through the material. The transmission of NIR light through monocrystalline wafers of known orientation were compared with the transmission of NIR light through various grains in mc-Si wafers. X-ray diffraction was then used to verify the relationship by obtaining the crystallographic orientations of these assorted mc-Si grains. Variation of transmission intensity for different crystallographic orientations is further explained by using planar atomic density. The relationship between transmission intensity and planar atomic density appears to be linear.

This paper discusses the influence of tribology on the mechanical properties of cutting, shaping and forming silicon wafers. These processes, such as multi wire slurry sawing, diamond wire sawing, lapping and grinding, Chemical Mechanical Polishing (CMP), and dicing, utilize either a two-body or a three-body material removal, where the fundamental cutting process results from micro-fracturing of silicon by the hard abrasives. There are specific types of defects and related fracture strength characteristics for each process. The associated surface and subsurface damage, especially microcracks, have a dominant effect on the fracture strength of the silicon substrates, even playing a more significant role than edge chipping. There is a need to reduce the surface and subsurface damage, possibly through ductile regime machining/polishing, to improve the mechanical strength. KeywordsFracture Strength; Defects; Microcracks; Silicon

This paper reports on a comparison of the six- and ten-step phase shifting methods in digital transmission photoelasticity and the application of these methods to obtain the residual stresses in thin (200 μm), flat crystalline silicon wafers (156 mm square). The ten-step phase shifting technique is judged to be superior with reduced noise in the isoclinics and a resulting higher accuracy when dealing with the near-zero retardation prevalent in residual stress measurements of silicon wafers.

Single grit diamond scribing experiments were carried out to understand the effects of SiC and Si3N4 inclusions in diamond wire sawing or cutting of photovoltaic multicrystalline silicon (mc-Si) substrate material. Results show that hexagonal rod-type Si3N4 inclusions can significantly increase the cutting force and lead to large scale localized brittle fracture of the mc-Si substrate. In contrast, SiC filament-type inclusions do not affect the scribing/cutting process. Si3N4 fibers are found to be flexible and are not cut by diamond scribing. Explanations for the observations are given based on the material properties of mc-Si, diamond and inclusions. The detrimental effects of SiC and Si3N4 inclusions on diamond wire sawing are also discussed.

This paper presents an analysis of fracture strength of multicrystalline silicon (mc-Si) solar wafers produced by slurry and diamond wire sawing. The wafers were bent in two orthogonal orientations relative to the saw marks. The fracture strength of slurry sawn wafers increases gradually from wire entry to wire exit whereas the strength variation in the wire feed direction is small. The fracture strength of diamond wire sawn wafers is bi-directional, with a higher strength if bent perpendicular to the saw marks and a lower strength if bent parallel to the saw marks. The fracture strength variation is related to the microcracks generated in the vicinity of grit-induced surface damage.

In this study, silicon wafers were marked with four different kinds of laser marks. Initial characterization of the wafers was performed to measure various parameters such as minority lifetime, residual stress, wafer thickness, Photoluminescence, and Resonance Ultrasound Imaging. The wafers were consequently processed into solar cells. EL, PL and RUV measurements were also performed on solar cells, in addition to the flash I-V measurements to determine solar cell performance parameters. Cells were laminated into custom modules and the modules were passed through static and dynamic mechanical loading tests according to IEC 61215. A procedure to quantify the performance loss due to cell cracking for each cell was developed and applied for each cell that experienced significant cracking after mechanical loading tests. Following correlations were explored: (i) Propensity of power loss due to cell cracks and residual stress at wafer level (ii) Types of laser marks and their effects on parameters measured in various wafer and cell characterization techniques.

This paper describes a Kelvin probe based inspection technique which measures surface potentials (SP) at various illumination conditions and derives the delta surface potential (Δ V SP ) and surface band bending ( ϕ ) of photovoltaic (PV) cells. The Δ V SP is the difference of surface potential measured in light and dark conditions respectively. The delta surface potential (Δ V SP ) is related to charge injection and carrier lifetime, while the surface band bending ( ϕ ) is associated with the surface condition. A white light and short wavelength light illuminations are used to distinguish the bulk effects from that of the surface. A scanning vibrating Kelvin probe system was built to image PV cells with and without illumination. Experiments were performed on both single crystalline silicon (sc-Si) and multi-crystalline silicon (mc-Si) cells. It is found that the sc-Si cells possess a higher Δ V SP but a lower ϕ than that of mc-Si cells. The average Δ V SP and ϕ are 350 mV and 50 mV for the sc-Si cells, and 280 mV and 110 mV for the mc-Si cells. Process defects on a surface could affect both parameters, and it is found that the Δ V SP is not uniform and could be reduced to 170 mV at a defect on the mc-Si cells. The high Δ V SP and low ϕ s are expected to contribute to the high conversion efficiency on a cell.

Under certain conditions, the metals of some heavily loaded tribological units may slide against each other without the benefit of lubrication. In such cases, the heat or electrical conduction properties of the sliding materials are particularly important. Copper-based materials are relevant for such application. In this study, we investigated the wear and friction that occurs between copper-based composites and copper under dry sliding conditions. We varied the composition levels of molybdenum disulfide and molybdenum diselenite (from 1 to 15 percent) that were incorporated into a Cu-based substrate. The specimen composition (Cu+1; 5; 10 and 15 wt% MoS 2 and MoSe 2 ) was prepared by sintering powders with an average particle size of 35–40 μm into a hydrogen atmosphere at a temperature of 780 °C for 2 h. Pin-on-disk experiments were performed without any lubrication at a speed of 0.15 m/s while maintaining a contact pressure of 0.127–1 MPa. The prepared samples were used as flat-ended pins and slid against a copper plate to ensure contact conformability. The reference copper rapidly began scuffing and eventually experienced a catastrophic failure of the contact surfaces after a relatively short period of smooth sliding. Scuffing and catastrophic damage was prevented by using powder metallurgy technology to incorporate MoS 2 and MoSe 2 into the copper. Materials with MoS 2 and MoSe 2 had a coefficient of friction close to 0.2, undetectable linear wear under a contact pressure of less than 0.255 MPa, and an absence of material transfer between the pin and the copper plate. The solid lubricant embedded in the composite materials disintegrated and lubricated the surfaces; however, a protective layer did not form on the counterface. Heavier loads initiated substantial wear. Material removal resulted from adhesion between the sliding composite materials and the transferred material on the Cu counterface, which forms flaky debris. The mechanism of wear of the composite materials Cu–MoS 2 and Cu–MoSe 2 is consistent with the material removal process. As a function of composition, the lubricating effect is more pronounced at concentrations greater than 5 wt% of the solid lubricant.

This paper reports on the mechanical strength of polycrystalline silicon wafers cut by loose abrasive slurry and fixed abrasive diamond wire sawing processes. Four line bending and biaxial flexure tests are used to evaluate the fracture strength of the wafers. Fracture strength of the wafers depends on the location, size, and orientation of microcracks in the silicon wafer and the distribution and magnitude of applied stresses. Measurement of microcracks at the wafer edge and center shows that edge cracks are typically larger than center cracks. Fixed abrasive diamond wire sawn wafers are found to have a higher crack density but smaller average crack length. Wafer fracture in four line bending is found to be primarily due to the propagation of edge cracks while center cracks are found to be the primary cause of wafer failure in biaxial flexure tests. Fracture mechanics based analyses demonstrate that crack orientation plays a significant role in four line bending, but not in biaxial flexure. Correlations of the wafer fracture strength and critical crack length agree well with microcrack measurements. The fracture strength of diamond cut wafers is found to be comparable or superior to the strength of slurry cut wafers.

Metallic components in sliding contact are sometimes subjected to high-loads with little or no lubrication. Such starved conditions can lead to a phenomenon called scuffing. Various definitions exist for this term, but in the present case, three criteria were used to signal its onset: changes in friction, vibrations, and noise, coupled with surface examination. On this basis, scuffing initiation was determined for seven technically pure metals (Al, Mo, Nb, Ta, Ti, W, Cu) and stainless steel, all rubbing against Cu. A flat-ended pin-on-disk test configuration was used with normal loads of 1–3 N, and with step-wise increases in sliding speed from 0.16 to 2.56 m/s. Al was only weakly resistant to scuffing, presumably due to its solubility in Cu, its high ductility and its relatively low elastic modulus. Niobium provided satisfactory sliding behavior at low speeds and loads, presumably due to protective oxides; however, it scuffed at higher loads when the oxide broke through. Stainless steel, Mo, and Ta had higher friction coefficients than Al and Nb, presumably because the relatively high strengths of the former prevented severe wear even when their oxide films failed. Like Al, Ti scuffs on Cu, probably because of its high relative solubility; however, Ti's higher elastic modulus resists the more severe forms of surface damage than does Al. Of all the materials slid against Cu, W displayed the least scuffing, even under maximum speed and load. Tungsten's negligible solubility in Cu may have reduced its adhesion, and W's high elastic modulus resisted shear-deformation, even at high frictional heating. Self-mated Cu couple scuffed when the speed was increased. The oxides on the Cu surface serve as solid lubricant avoiding scuffing at lower speeds.

This paper discusses the application of an ionizing source coupled with galvanic differences between metals in a measure of the work function difference between the metal surfaces. The electrical field generated from the contact potential difference (CPD) between two electrodes will cause the gaseous ions to discharge at both surfaces, creating a measurable current. The current depends on the surface size, spacing, and ionizing source power. One of the surfaces (probe) can vary in shape and size, and if inert, can be used to obtain the work function or surface potential of the second surface. The ionic current is proportional to ion mobility, ion generation rate, CPD, and the probe size, but inversely proportional to the spacing between the probe and the sample. It is found, as expected, that there is an approximate linear relationship between the ionization probe signal and the work function of the surfaces of metals.

Recently, material removal utilising electrokinetic phenomenon was proposed as an alternative to create material removal at the nanometric level [1]. The concept of the introduced material removal process is to impinge particles contained in the slurry, under the influence of hydrodynamic and electrokinetic effects, onto the workpiece with a predetermined velocity to create material removal on the surface. The material removal process proved to be feasible where the material removal rate was reported to be in the range of a few hundred nm/hr with a surface roughness of a few nm (RMS). This paper aims to look into the effect of the electrochemical dissolution on the material removal process since high voltages are involved during the material removal process. During the experimental study, electrochemical dissolution was observed and it contributed a certain proportion of the material removal process. However, the main material removal mechanism still relies on the mechanical action of the abrasive particles on the surface of the workpiece to create material removal during the process.

This work reports on the subsurface plastic deformation depth (PDD) as a result of grinding of γ-TiAl, where the effects of grit size and shape, workpiece speed, and wheel depth of cut were studied. A grinding model based on a stochastic distribution of the chip thickness was used to estimate the expected maximum normal force per grit (\({F''_{n\:{\rm max}}}\)), which was correlated to the PDD. It was found that the PDD shows a linear correlation with \({F''_{n\:{\rm max}}}^{0.5}\). The results suggest that the indentation model is still valid for grinding if \({F''_{n\:{\rm max}}}^{0.5}\) is used as a PDD predictor variable instead of the total grinding force.

With the demand for precise nanometric material removal with minimal defects, several non-contact ultraprecision machining techniques were developed over recent decades. The electrokinetic material removal technique [1] is one such method that allows material to be removed without any physical contact between the tool and the workpiece. In this work, the influence of the slurry mixture on the material removal rate for the electrokinetic material removal process is studied. During the process, it was observed experimentally that the mixture of the slurry affected the material removal rate. The parameters varied in the slurry mixture experiments were the size and concentration of the particles. Explanations for the behaviour of the material removal rate were also suggested during the study to further understand the electrokinetic material removal technique.

Non-contact material removal processes offer numerous advantages over traditional machining approaches and nowhere is this more apparent than in the fabrication of micro devices. Current micromachining techniques such as microgrinding and micromilling have limitations with respect to their positioning accuracy and tool deflections. Electro thermal processes such as microEDM and laser machining usually result in a heat affected zone being produced. Other approaches such as etching and non-contact ultraprecision polishing are either costly or are not suitable for high throughput. In order to address these limitations, alternative micromachining techniques are required. In this paper, a non-contact material removal technique based on the electrokinetic phenomenon is proposed for precise material removal at rates in the order of nanometers/min. The aim of this research is to have a better understanding on the electrokinetic material removal technique by studying the trajectory of the particles and the influence of the frequency of the electric field on the material removal rate.

This paper describes a mechanical mechanism of chemical mechanical polishing (CMP) and the model is applied to the polishing of silicon substrates by polyurethane pads and slurries containing fumed silica as is typically done in the manufacture of integrated circuits. The model utilizes the concept that the polishing pad surface contains asperities that support the normal load on the wafer, and that friction and hydrodynamic forces influence wear. The interfacial fluid pressure can significantly influence the normal pressures on the wafers and its effects modify the wear rate predictions.

A lattice Boltzmann method-based single-phase free surface model is developed to study the interfacial dynamics of coalescence, droplet formation and detachment phenomena related to surface tension and wetting effects. Compared with the conventional multiphase models, the lattice Boltzmann-based single-phase model has a higher computational efficiency since it is not necessary to simulate the motion of the gas phase. A perturbation, which is given in the same fashion as the perturbation step in Gunstensen's color model, is added to the distribution functions of the interface cells for incorporating the surface tension into the single-phase model. The assignment of different mass gradients along the fluid-wall interface is used to model the wetting properties of the solid surface. Implementations of the model are demonstrated for simulating the processes of the droplet coalescence, the droplet formation and detachment from ceiling and from nozzles with different shapes and different wall wetting properties.

Pressure and shear flow factors (Patir and Cheng, 1978) were used to take into account the roughness of the pad surface in the modeling of the interfacial fluid pressure during chemical mechanical polishing. An attempt was made to explain the physical meaning of the flow factors in this particular application. Additionally, a parametric study was carried out to see the effect on the model after the incorporation of the flow factors. The pressure and shear flow factors were found to have a competing effect on the magnitude of the sub-ambient fluid pressure.

Previous experimental work has shown that negative fluid pressure does develop at the disk/pad interface during chemical mechanical polishing. However, these studies dealt with one-dimensional measurement and modeling. To better understand the problem, two-dimensional pressure mapping is carried out. In addition, the orientation of the disk is measured with a capacitive sensing technique. Results reveal a large negative pressure region at the disk/pad interface that is skewed toward the leading edge of the disk. The disk is also found to be leaning down toward the leading edge and toward the center of the pad. A mixed-lubrication model based on the Reynolds equation and taking into account the disk orientation angles has been developed. Modeling and experimental results show similar trends, indicating the tilting of the disk as a dominant factor in causing the negative pressure phenomenon.

A novel, non-vibrating, micro-contact potential difference (CPD) probe fabricated by micromachining has been tested for measurements on a magnetic hard disk drive. The 50 μm diameter probe, with integrated shielding, provides high-resolution surface images as the probe is scanned over the surface of interest. The probe utilizes Parylene as a flexible substrate material that allows it to be bent away from the integrated electronics and closely approach the surface under study. A four-mask process was used to create the micro-CPD probe, including a 500 μm radius, annulus of SU-8 that provides mechanical support for the gold electroplated probe and sputtered shielding. Defects, such as scratches and adhesive tape placed on a magnetic hard disk, were measured at a height of 0.5 mm and rotation speed of 1000–3600 rpm. From these signals the features, were reconstructed from the CPD signal, to determine the feature size.

Pad Soaking Effect on Interfacial Fluid Pressure Measurements During CMP Prior work has shown that there exist a sub-ambient fluid pressure at the interface between a rigid flat and the polishing pad during chemical mechanical polishing (CMP). This sub-ambient fluid pressure can have a significant impact on the polishing process since its magnitude may be similar to the applied load, depending on conditions. Further results have shown that there is a relationship between pad soaking time and the magnitude of this sub-ambient fluid pressure. This paper addresses measurements of the pad soaking time versus the magnitude of the sub-ambient interfacial fluid pressure. Experiments utilized a Rodel IC1000 polishing pad made of foamed polyurethane with average void size of 30 to 50 microns. Pad soaking tests indicated that the weight of the pad increased with soaking time due to water absorption. There is a high rate of water absorption initially before the pad becomes saturated and the mass of the pad stabilizes. It is also observed that the pad material is impermeable to water and most of the water penetrated only the topmost layer of voids in the material. These experiments suggest that the water progressively softens the top layers of the pad during the soaking and causes the sub-ambient fluid pressure to increase in magnitude. A model of the sub-ambient fluid pressure increasing as the elastic modulus of the pad decreases is also suggested.

This paper addresses the grinding of ordered intermetallic compounds and their brittleness at ambient temperature. The depth of plastic deformation is supposed as the measure of surface integrity. The current paper expands the work of a previously reported indentation model that correlated the depth of plastic deformation and the normal component of the grinding force. This paper studies the indentation model using force control grinding of gamma titanium aluminide (TiAl-γ). Reciprocating surface grinding is carried out for a range of normal force 15–90 N, a cutting depth of 20–40 μm and removal rate of 1–9 mm3/sec using diamond, cubic boron nitride (CBN) and aluminum oxide (Al2O3) abrasives. The measured depths of plastic deformation are in the range of 150–300 μm. The deviations from the indentation model are explained by changes in the ductility during the grinding process. Furthermore, a force-based model for specific energy is developed and evaluated. The measured specific energies are in the range of 40 J/mm3 (diamond) to 400 J/mm3 (CBN).

The experimental results of interfacial fluid pressure and friction measurements during polishing are presented, as well as their dependence on some major process variables. Under simulated conditions, a sub-ambient fluid pressure was observed, and its magnitude was of the same order of magnitude as the applied polishing load. Since this fluid pressure is non-uniformly distributed, the contact stress, obtained by combining the effects of both applied load and the fluid pressure, is not uniform across the wafer and will result in non-uniform material removal. The mechanism of the presence of the fluid pressure was investigated, and an analytical model was developed to predict the magnitude and distribution of this fluid pressure. The effects of the sub-ambient fluid pressure on material removal rate and profile were tested with thermally grown silicon dioxide on 100 mm diameter, p-type (1 0 0), single-crystal silicon wafers. The polishing experiments show the effect of sub-ambient fluid pressure on polishing rate and profile.

This paper reports on a study of stress in thin silicon plates sectioned from wafers by a near-infrared transmission technique. Phase stepping was incorporated to determine the magnitude and orientation of stress from fractional birefringence fringe images. The anisotropic relative optic-stress coefficient of (100) silicon was determined and the limitation of the stress orientation measurement is discussed.

This paper addresses the influence of nano-scale abrasive particle size in the polishing of thermally-grown silicon dioxide on 100 mm diameter, p-type, (100), single crystal silicon wafers. The abrasive particles are incorporated in a chemical slurry, which is used in chemical mechanical polishing (CMP). Polishing (material removal) rate was measured with six (6) slurries, each with a different mean abrasive particle diameter of 10, 20, 50, 80, 110 and 140 nm. The experimental results indicate that the material removal rate (MRR) is related to the particle size. Results confirm that there exists an optimum abrasive size (80 nm) with respect to material removal rate and surface finish, for a given set of experimental conditions. The variation of the MRR vs. particle size (on a log-log plot) varies as d3.4. In addition, the surface polished with 10 nm and 20 nm abrasives was stained by the slurries. For a pad surface roughness of 5.2 μm (Ra), the slurry containing the 80 nm particles resulted in the highest...

This paper presents the results of an experiment designed to understand the effect of manufacturing-induced residual stress on photoluminescence (PL) in multi-crystalline silicon (mc-Si) wafers used for photovoltaic applications. The experiment relies on the use of near-infrared birefringence polariscopy and polarized micro-Raman spectroscopy to measure casting-induced residual stress present in mc-Si wafers. High temperature annealing was used to relieve the residual stress in the mc-Si wafers, and photoluminescence was used to evaluate the electrical performance to provide a correlation of residual stress to electrical activity. High temperature annealing produced a drastic improvement in photoluminescence. A decrease in the number of points of highest maximum shear stress correlated with an increase in photoluminescence. Additionally, a direct correlation was found between higher tensile residual stress and increased PL.

The effect of dc electric fields on material removal rates of single crystal langasite during the chemical mechanical polishing process was investigated. The removal rate of the langasite in the commercial silica slurry was increased by up to 30% with a dc electric field ranging from −300 to +300 V/mm. The motion of slurry particles by surface charge was responsible for the electrical field-assisted chemical mechanical polishing (EFACMP) of langasite observed in this study. The effect of electric fields on chemical mechanical polishing is explained by the variation of the particle concentration due to the attraction to either the langasite surface or the pad by surface charge. The variation of the slurry particles near the langasite surface due to the electric field was confirmed experimentally by hardness variation in the slurry.

Mechanical interactions, such as contact stress and fluid pressure are of extreme importance in silicon wafer polishing, especially for the wafer-scale planarity of the finished surfaces. In this paper, the measurements of interfacial fluid pressure and friction, as well as their dependence on some major process variables, are presented. A nonuniform subambient fluid pressure was measured, and the resulting wafer/pad contact stress, obtained by combining the effects of both applied normal load and interfacial fluid pressure, is determined. An analytical model was developed to predict the magnitude and distribution of the interfacial fluid pressure. The results of polishing experiments show good evidence of the effects of this subambient fluid pressure on with in-wafer nonuniformity (WIWNU). By properly designing the polishing process variables, the fluid pressure may be tailored, and a relatively uniform material removal can be achieved.

The effect of mineral oil on surface potentials of copper and aluminum coated with a perfluoropolyether (PFPE) film is studied with a non-vibrating Kelvin probe. The probe measures the contact potential difference (CPD) between the probe surface and the coated copper and aluminum surfaces. The PFPE film was applied to the Cu and Al surfaces by a dip-coating technique. The Kelvin probe signals are especially sensitive to the interface between the coated and uncoated regions of the metal surfaces. It is found that the PFPE film causes the surface potentials of Cu and Al to drop by 150 and 98 mV, respectively. Immersion of the PFPE-coated surfaces in mineral oil causes the surface potential difference of the PFPE/Cu and PFPE/Al to increase, and removing the mineral oil re-establishes the surface potential.

This paper reports on the roller skew in tapered roller bearings monitored by contact potential difference probes. The effect of the load, rotational speed, and viscosity of lubricant on roller skew angle, along with the variation of bearing torque with the running conditions, were measured on a LM501300 bearing. Two greases (SHC15 and SHC460) were used to lubricate the bearing. The skew angles were found to vary from 0.15° to 0.6°. The results indicate that the skew angle depends on the friction force at the roller-rib interface. An empirical equation is derived which relates the skew angle to the bearing operational parameters. Presented at the 55th Annual Meeting Nashville, Tennessee May 7–11, 2000

This paper reports on a feasibility study in the detection of nanometer thick lubricated regions on a hard disk by a novel use of a Kelvin probe. A nonvibrating Kelvin probe was constructed and used to measure the voltages between the copper surface of the probe and a hard disk partially-lubricated with a perfluoropolyether. The probe, constructed of a shielded 1.6 mm diameter gold-coated copper wire, was fixed above the hard disk and the probe voltage was obtained as a function of the speed of the disk and lubricant thickness. The probe generates an electrical signal as the interface between the lubricated and unlubricated regions is crossed. Results show that the probe can distinguish between regions on the hard disk that contain 3 and 10 nm thick lubricant films.

This paper reports on roller skew in tapered roller bearings. The roller skewing of a tapered roller bearing is experimentally measured with a specialized capacitance probe (Kelvin contact potential difference, CPD, probe). The probe measures the electro-chemical potential difference between the probe and roller surfaces. Two probes are inserted through holes in the housing and bearing outer race. The electrical signals from both ends of a roller are used to determine the skewing. The technique, as well as the effect of lubrication and rotational speed on the roller skewing, is presented. It is shown that the skewing increases with an increase in rotational speed, and the lubrication of the large end of the roller. A theoretical analysis has been developed to account for the experimental results. [S0742-4787(00)01803-8]

This paper reports the results of a model for predicting the development of subambient pressures during the polishing of flat hard substrates by sliding against a compliant pad in the presence of a slurry (liquid). This work is an extension of our prior experimental work on the polishing of single crystal silicon wafers with polyurethane pads and high pH slurries containing silica particles. Subambient pressures have important implications in the polishing rate and uniformity of silicon and, therefore, in the manufacture of large-scale integrated circuits. The subambient pressure is the result of pad asperity compression at the wafer leading edge followed by elastic reexpansion beneath the wafer due to the nonuniform wafer/pad contact stress. Liquid is expelled from interasperity voids where high leading edge contact stress causes asperities to be compressed. Lower contact stress behind the leading edge causes asperity reexpansion leading to recreation of interasperity voids and subambient liquid pressures. A Poiseuille like in-flow of liquid from the sides of the wafer limits the value of the subambient pressure. Numerical simulations predict subambient pressures as a function of liquid viscosity and relative velocity of the pad and wafer and the pad and wafer mechanics which follow the same trend as the experimental data. [S0742-4787(00)01702-1]

This paper reports on the measurement of fluid (water) pressure distribution at a soft (polyurethane) pad/steel interface. The distribution of the interfacial fluid pressure has been measured with a specially-designed fixture over the typical range of normal loads and velocities used in the chemical mechanical polishing/planarization of silicon wafers. The results show that, for most cases, the leading two-thirds of the fixture exhibits a subambient pressure, and the trailing third a positive pressure. The average pressure is sub-ambient and may be of the order of 50∼100% of the normal load applied. An analytical model has been developed to predict the magnitude and distribution of the interfacial fluid pressure. The predictions of this model fit the experimental results reasonably well, especially for low sliding velocities. [S0742-4787(00)00902-4]

A preliminary model for the contact mechanics and fluid mechanics of the chemical mechanical polishing process is presented. Only the basic equations of elastic contact surface mechanics and hydrodynamic lubrication are required. Although the model is highly idealized, no ad hoc assumptions or adjustable parameters are required. Some new experimental results are presented, reinforcing the counterintuitive experimental determination of suction fluid pressure below the pad. The model correctly predicts the magnitude of the suction pressure and the effect of load, speed, and roughness. © 1999 The Electrochemical Society. All rights reserved.

This paper reports on the potential of a new, non-contact sensor for the detection of defects in rotating systems. Proof-of-concept experiments have been performed with measurement of two gross `defects': a missing roller of a taper roller bearing, and an electrical discharge machined (EDM) line on a single taper roller. The probe used is based on the Contact Potential Difference (CPD) method, which measures the work function of dissimilar metals without physical contact. The work function is strongly influenced by the physical and chemical conditions of the surface, so the probe can be used to detect the geometrical features of a surface if the chemical conditions are fixed. The probe was inserted into a tapered roller bearing assembly via a hole in the cup to detect the signals from bearing rollers, without contacting the rollers. Individual rollers passing by the probe produce a repeatable electrical signal, and this signal can be used to monitor the surface condition of the rollers via the signal strength and frequency. The peak-to-peak voltage (ΔVcpd) of the probe increases with increasing rotational speed of a shaft and a decrease in spacing between the probe head and roller surface. Normal, undamaged bearing rollers generate a stable, steady state CPD signal with two main spikes. The defects on the roller surface cause the magnitude of the spikes of the CPD signal to decrease.

Rolling element bearing failure is a major factor in the failure of rotating machinery. Current methods of bearing condition monitoring focus on determining any existing fault presence on a bearing as early as possible. Although a defect can be detected when it is well below the industry standard of a fatal size of 6.25 mm2 (0.01 in2), the remaining life of a bearing (the time it takes to reach the final failure size) from the point where a defect can be detected can vary substantially. As a fatal defect is detected, it is common to shut down machinery as soon as possible to avoid catastrophic consequences. Performing such an action, which usually occurs at inconvenient times, typically results in substantial time and economics losses. It is, therefore, important that the bearing's remaining life be more precisely forecasted, in a prognostic rather than diagnostic manner, so that maintenance can be optimally scheduled. Unfortunately, current bearing remaining life prediction methods have not been well dev...

This paper describes the results of measurements of the vertical displacement between a polishing pad and a sapphire disk surface. Those experiments were intended to simulate silicon/pad interaction as it occurs in the chemical-mechanical polishing of integrated circuits. Results show that the pad is suctioned into the sapphire surface so that the measured displacement is negative by up to 7 μm. Capillarity associated with the surface roughness of the pad is able to account for approximately 4 μm of this negative displacement.

The influence of grinding geometry and damage depth on the fracture strength of 100 mm diameter (1 1 1) p-type silicon wafers has been studied. The fracture strengths were measured in a biaxial flexure test after the wafers were ground to 0.36 mm from 0.53 mm thick, in a grinding apparatus that produces a swath of swirls on the silicon wafer surfaces. Analysis of orientations of the swirl geometries and fracture probability was used to deduce the fracture strength relative to the crystallographic orientation of the wafers. Optical and scanning electron microscopy of bevelled, and cleaved and etched samples was used to measure the damage depths from selected locations on the wafers. The depth of damage and fracture strengths were correlated to the geometry of the backgrind swirl pattern and the relative position of the orientation flat. The damage depth was smaller when the swirl path was parallel or at 45° to the orientation flat as compared to the swirl paths at 90° and 135° orientations. As a result, the wafers ground in the former orientations had a higher fracture strength than those of the latter orientations (136 and 124 MPa versus 100 and 103 MPa, for the four orientations, respectively).

Near-infrared (NIR) Polariscopy has been used to find residual stresses in thin silicon wafers using phase shifting techniques. This paper describes the usage of the ten-step phase shifting method to measure the in-plane residual stresses in single- and multi-crystalline silicon wafers. We show how this technique can be applied to wafers without the application of external loading. The system is calibrated with a beam of monocrystalline CZ silicon loaded in an in-plane four-point bending fixture. The residual maximum shear stresses of the unloaded wafers are then determined. The shear difference technique is used for obtaining the normal stress values. Results are compared before and after smoothing of the isoclinic parameter, and its impact on the separated stress values is explained.

Measurement of in-plane residual stresses in photovoltaic Si wafers with NIR polariscopy requires the knowledge of the stress-optic coefficient of the silicon, which varies with local crystallographic orientation. We have found that, all other variables being equal, the transmission of light through crystals will vary with crystallographic orientation. After measuring transmitted light intensities through monocrystalline CZ wafers of known thickness and orientation, we have created a calibration scale by which the orientation of grains in a random multicrystalline wafer may be obtained. A stereoscopic light setup was also used to compare the same grains in reflection.

Contact potential difference (CPD) experiments were conducted by the vibrating probe (Kelvin) method on humidity‐exposed hard disk drive surfaces. The measurements were made at various locations along the circumference of a wear track caused by the sliding contact with a spherical silicon pin, operated in a pin‐on‐disk configuration. The load on the pin, rotational speed of the disk, and the humidity were controlled. The CPD signals varied along the wear track and the magnitude of the CPD change increased with the load from 29 to 98 mN at a fixed relative humidity. The CPD signals also increased linearly with relative humidity ranging from 30% to 70% as the normal load was fixed at 29 and 49 mN. The CPD signal appears to saturate at a load of 98 mN where the relative humidity is 50% and higher.

The effect of partial cracking on critical current density ( J c ) has been modelled for Ag-sheathed superconductor tapes. Effects of crack length and density on current-voltage characteristics and J c were evaluated for monofilament and multifilament tapes. The results show that a single long crack is more harmful than numerous small cracks. Multiple small partial cracks (less than 20% of core dimension) can be present in the Bi 2 Sr 2 Ca n − 1 Cu n O 2 n +4 (BSCCO) before J c degradation is observed. In general, a multifilament tape can withstand cracks better than a monofilament tape.

Various MoS2 compositions of hot-pressed, sintered Ni/MoS2 composites were made and tested in a ball-on-disk wear test machine. The friction and wear of the composites with reciprocating sliding were measured at elevated temperatures, as well as at room temperature. Stepwise loading test results at room temperature and 25 percent relative humidity showed that as the MoS2 content increased, the friction and wear of the composite decreased up to 60 wt % MOS2 and then increased. However, at elevated temperatures, the friction and wear properties of the composite with 80 wt % MoS2 were better than that with 60 wt % MoS2. The worn surfaces of the composites have been analyzed by electron microscopy techniques. Scanning electron microscope analysis showed that friction and wear are related to the formation of solid films formed on the sliding surfaces. The more cohesive the films, the lower the friction and wear, and this can be used as a criterion of the tribological behavior of the composite. Transmission ele...

Tribological rolls, composed of amorphous silica, were produced by the ball-on-flat linear reciprocating sliding of self-mated silicon at elevated temperatures (200, 400, 500 and 600°C) and humid conditions (PH20=0.034, 0.064 and 0.085 MPa). Normal loads of 2.04, 3.59, 4.73 and 5.80 N were used in the tests. The changes in the coefficient of friction at various loads and environmental conditions were identical. The coefficients of friction were initially between 0.45 and 0.65 and then rapidly decreased to a steady value of about 0.13. The present study describes a model where the steady state coefficient of friction is a function of the length, diameter and population density of the rolls (number of rolls per unit area). The roll length and diameter increase, and the population density decreases with temperature. The roll length increases with load, whereas the other parameters are nearly independent of load. Humidity does not affect these parameters. The compensating effects of the variation in length, diameter and population density lead to the uniformity in the steady state coefficient of friction with the applied load and environment.

The present study investigates the mechanics of roll formation between sliding bodies at elevated temperatures and humid conditions. Silicon is used as the model material for reciprocating linear sliding tests. The evolution of tribological rolls initially involves the rapid oxidation of silicon wear debris by water, the deformation of SiO2 particles into platelets, and then the compaction of these particles into a film deposited on the wear surface. The formation of compacted silica film requires minimum adsorption of water which enhances the adhesion between silica platelets. The stress cycle imposed on the film leads to the delamination of platelets near the sliding surface. The delaminated debris cluster into multiple aggregates that are subsequently rolled into dense cylindrical particles so as to relieve the interfacial shear stress. When the film and rolls are formed, the friction and wear rate is maintained at low steady state values.

This paper describes a PV wafer scanning system that can perform multiple measurements on one platform. The scanning system consists of two probes (a Kelvin probe and a fiber optic probe), a light source, and a monochromator. The Kelvin probe is used to measure the surface potential at different illumination conditions. Surface uniformity and defects, particularly shunting, can be identified from various types of surface potential maps. A monochromator is incorporated with the Kelvin probe to yield the spectral response of solar cells. The fiber optic probe is used to measure the crystalline orientation - related reflectivity and stress-induced wafer curvature. Applications for the scanning system in PV wafer and cell inspections are discussed.