In Situ Studies of TiC<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Hard Coating Tribology

TiC_1−x N _x hard coatings present time-dependent tribological behavior with an initial running-in period (500–2000 cycles) marked by an elevated friction coefficient, followed by >10000 cycles with low-friction and wear at room temperature (RT) in ambient air. The mechanisms behind this behavior are not completely understood. Tribological tests performed at RT and at different relative humidity (RH) levels revealed that a minimum value between 15 and 25% RH is needed to trigger the low-friction regime at a sliding speed of 100 mm s⁻¹. By in situ observations of transfer film growth, it could be observed that third body material is formed during this running-in period by plowing of the coating and shearing of the removed material. The appearance and thickening of the transfer film marks the beginning of the steady-state low-friction regime where the velocity is accommodated by interfacial sliding. At this stage in the tribological test, the recorded Raman spectra indicated the presence of C–H bonds in the wear track. Use of in situ analytical tools during wear tests provided insights with respect to tribological phenomena that were not available by conventional, post-mortem analysis methods.     

Design and evaluation of high-pressure nozzle assembly for laser cutting of thick carbon steel

Laser cutting of carbon steel is extensively used across a range of industries, due to its advantage of high speed, low kerf and high quality. Currently, a 1-kW carbon dioxide (CO₂) laser with its subsonic nozzle assembly can be used only to cut steel plates up to around 10 mm. This paper aims to design and evaluate a high-pressure supersonic laser cutting nozzle assembly, which can enable a 1-kW CO₂ laser to cut steel of up to 50 mm thickness. Basic gas dynamic and compressible flow equations were used to design the supersonic nozzle assembly. The flow of the high-pressure gas jet inside the nozzle assembly was investigated using computational fluid dynamics (CFD), and the structural integrity of the high-pressure nozzle assembly was ensured using finite element analysis (FEA). The gas flow pattern at the exit of the nozzle assembly was computed and compared with the experimental observation made through a shadowgraph technique. Laser cutting experiments were performed with the developed supersonic nozzle assembly to demonstrate cutting of 50-mm-thick low carbon steel with 1-kW CO₂ laser.     

The effects of the compressibility of the subsonic flow on heat transfer characteristics in a microscale impinging slot jet

We experimentally investigated the effects of both the compressibility and nozzle width on the local heat transfer distribution of microscale unconfmed slot jets impinging on a uniformly heated flat plate. We made heat transfer measurements under the following experimental conditions; Reynolds numbers of Re = 4000~10000, Mach numbers of Ma = 0.13~0.68, nozzle-to-plate distances of H/B = 3~25, lateral distances of x/B = 0~25, and nozzle widths of B = 300~700 μm having a nozzle aspect ratio of y/B = 30. A thermal infrared imaging technique was used to measure the impingement plate temperature. The experimental results show that for all tested Re and H/B values at a nozzle width of B = 300 μm, the Nusselt number maximum occurred nearly at the stagnation point and then monotonically decreased along the downstream. However, at B = 500 and 700 μm, the maximum Nusselt number point shifted toward x/B ≈ 1.5~2.0. And the Nusselt number increased, as x/B increased, from the stagnation point to the shifted maximum point and monotonically decreased afterward. This shifted maximum point may be attributable to vortex rings promoting sudden flow acceleration and entrainment of surrounding air moving along the jet axis. For the same Reynolds number, the Nusselt number in the stagnation region increased as the nozzle width increased due to a momentum increase of the jet flow caused by the formation of vortices. And, the Nusselt numbers for the smallest nozzle width of B = 300 μm (or highest Mach number at a given Reynolds number) at all H/B and Reynolds numbers tested significantly deviated from those for B = 500 and 700 μm in the downstream region corresponding to x/B > 5, suggesting that the compressibility, when it is high, can affect the heat transfer in the downstream region.

     

Numerical study on the low density gas flows in a plasma etch reactor

The direct simulation Monte Carlo method is employed to predict the etch rate distribution on Al wafer for a chlorine feed gas flow. The etching process of an Al wafer in a plasma etch reactor is examined by simulating molecular collisions of reactant and product. The surface reaction on the Al wafer is simply modelled by one-step reaction: 3Cl₂+2Al → 2AlCl₃. The gas flow inside the reactor is compared for six different nozzle locations. The present numerical results show that the etch rate increases with the mass flow rate of source gas Cl₂. It is also shown that the flow field inside the reactor is significantly affected by the nozzle locations.     

New air speed calibration system at NMIJ for air speeds up to 90 m/s

National Metrology Institute of Japan (NMIJ) has established a high air speed standard facility and has been providing a calibration service since 2015. The facility has an air speed range of 40 m/s to 90 m/s with a relative expanded uncertainty (k = 2) of 0.63%. The purpose of this primary standard is mainly to contribute to the improvement of meteorological observation research and to the evaluation of flow field inside a turbo machine and around a high speed vehicle. The reference air speed is derived from the national primary gas flowrate standard of Japan. A conversion device from flowrate to air speed is installed in the test line of the closed-loop calibration facility. The reference air speed at the nozzle exit of the conversion device is obtained by comparing the integral of the air speed profiles and the reference volume flowrate. The total pressure tube used as a transfer standard is then calibrated against the reference air speed at the center of the nozzle exit. The Eiffel-type wind tunnel, which is a working standard for the daily calibration service, is calibrated using this total pressure tube. The present paper describes the calibration system, the traceability chain, and an uncertainty analysis using a validation method.     

Numerical study of air curtain systems for blocking smoke in tunnel fires

A tunnel fire is very dangerous to drivers because of generated poisonous gases. For dealing with this hazardous situation, ventilation systems for smoke control are installed so that drivers can be safely evacuated from the site of the fire. An air curtain system is one of these ventilation systems, and such a system in a tunnel generates an air wall to block the passage of poisonous gases. In this study, airflow discharge patterns of air curtain systems were analyzed using Computational fluid dynamics (CFD), with two design parameters—to predict the ability of the air curtain to block the contaminated adverse air-flow in the tunnel. The considered two design parameters were the installed angle of the slit nozzle (N_A) and the discharged air velocity at the slit nozzle outlet (N_V). The tunnel geometry for the CFD analysis was a two-lane type with a tunnel length of 100 m and an elliptical cross section. The height of the tunnel was approximately 7.3 m and the height of the installed air curtain was about 4.9 m from the road surface. In this study, the heat release rates of the fire, the distance from the fire site, and the temperature of the working fluid were respectively assumed to about 20 MW, 50 m and 473 K, on the basis of the NFPA 502. The CFD analysis demonstrated that an N_A of 0 deg could not block the adverse air flow due to a realistic tunnel inlet-outlet static pressure difference (ΔP_S). An N_A of 20 deg was required to effectively block the adverse flow. The blocking failure first formed at the sidewall of the tunnel, and it proceeded toward the center of the tunnel cross section when the adverse wind was strong. That aspect of the blocking failure was judged to be due to the fact that the tunnel cross section is elliptical. Anyway, when the tunnel ΔP_S was increased, that showed the need for a high N_V.     

Electro-magnetically actuated valveless micropump with two flexible diaphragms

We present a parallel dynamic passive valveless micropump, which consists of three layers-valve, diaphragm and electromagnetic coil. The valve is wetly etched in a silicon wafer, the diaphragm is a polydimethyl siloxane (PDMS) film spun on a silicon wafer with embedded permanent magnet posts, and the coil is electroplated on a silicon substrate. Under the actuation of the magnetic field of the coil, the flexible diaphragm can be displaced upwards and downwards. After analyzing magnetic and mechanical characteristic of the flexible membrane and direction-dependence of the nozzle, this paper designed a micropump. And the relative length (L/d) of the micropump's nozzle is 4. A 7×7 array of permanent magnetic posts is embedded in the PDMS film. Two diaphragms work in an anti-step mode, which can relieve the liquid shock and increase the discharge of the micropump. ANSYS and Matlab are adopted to analyze the actuation effect of the coil and the flow characteristic of the micropump. Results show that when actuated under a 0.3 A, 100 Hz current, the displacement of the diaphragm is more than 30 μm, and the discharge of the micropump is about 6 μL/s.     

Eccentricity estimation with error modeling in dynamic wafer handling

Wafer-handling robots are used to transfer wafers in semiconductor manufacturing. Typically, a pick–measure–place method is used to transfer wafers accurately between stations. The measurement step is performed using an aligner, which is time-consuming. To increase the wafer transfer efficiency, it is desirable to speed up the measurement process or place it in parallel with other operations. Hence, optic sensors are installed at each station to estimate the wafer eccentricity on the fly. The eccentricity values are then used to control the robot to place the wafer directly onto another station accurately without using the aligner. In this paper, the kinematic model of a wafer-handling robot is developed. The errors in the kinematics model are analyzed. A model parameter identification method is proposed to obtain the parameters. A wafer eccentricity identification method is derived to calculate the eccentricity values on the fly. Experiments were performed to validate the proposed methods. The computed eccentricity errors are compared with those obtained by other researchers. The results demonstrated that the kinematics error modeling method can increase the wafer eccentricity identification accuracy. Hence, the developed methods can be applied to estimate the wafer eccentricity on the fly to reduce the wafer transfer cycle time and increase wafer-handling efficiency.     

Design and application of an efficient scheme for wafer transfer procedure during ion implantation process

Ion implantation is widely used in semiconductor manufacturing to modify electrical properties of the near-surface region of silicon wafers. The efficiency of ion implantation process deeply relies on wafer transfer procedure. Increasing wafer transfer speed is one of the most efficient ways to accelerate the ion implantation process for higher productivity of silicon chips. This study focuses on developing an efficient scheme for wafer transfer procedure to acquire higher transfer speed and reduce cycle time during ion implantation process. The scheme we proposed improves the layout of the vacuum chamber in currently used ion implanter by introducing an additional wafer transfer robot inside while placing the alignment station outside, planning optimal motion sequence of three wafer transfer robots in order to make all of them keep working without spending a long time waiting for other robots. Experimental platform has been established and the results show that wafer transfer speed based on the proposed scheme is over three times faster than the commonly used apparatus.     

Analysis of contoured holes produced using STED process

Recent developments in air engines call for more efficient means of turbine blade cooling to have higher power generation for the same unit size with increased inlet air temperature. To allow the turbine to operate at higher temperature, thousands of cooling holes are drilled in turbine blades. In order to increase heat transfer in cooling holes, the present design demands the wall of the cooling passage should be provided with contoured ribs. These irregularities help in inducing turbulence in the flow of cooling air, thereby increasing the rate of heat transfer. For drilling these kinds of contoured deep holes in a turbine blade made of material such as Inconel, the conventional drilling techniques are not suitable. The shaped tube electrolytic drilling (STED) is used to perform the task of drilling contoured holes in difficult-to-machine materials. In the present case, contoured holes are drilled by using two distinct feed rates f ₁ and f ₂ alternately (f ₁ > f ₂) and two types of workpiece materials, namely stainless steel and Inconel superalloy. Experimentally obtained profiles are compared with the profiles derived theoretically from the basic electrochemical machining equations. Quality performance factor is evaluated for the machined holes to find the best hole profile. From the present study, it has been observed that by varying the process parameters (viz., voltage (V), faster feed rate (f ₁), and slower feed rate (f ₂)) during drilling and fixing different step lengths, various types of hole profiles can be generated using STED process.     

The influence of water vapour in air on the friction behaviour of pure metals during fretting

An investigation was conducted to determine the effect of water vapour content in air on the frictional behaviour during fretting of pure metals: iron, aluminium, copper, silver, chromium, titanium and nickel. The fretting experiments were carried out under various humidity levels, ranging from dry air to 50% relative humidity at 23°C. During the experiment the frictional force between fretting surfaces was measured. Pure metals, except iron, were found to have a maximum value of the coefficient of friction during the steady-fretting stage (μ_s) at a specific humidity (RH_max). Iron showed a rapid decrease in μ_s with increasing humidity at RH_max. Each pure metal also exhibited maximum fretting wear at RH_max. The value of μ_s at RH_max for each metal was strongly related to the heat of formation of the lower metal oxide, indicating that the adhesive contact area was larger at RH_max for the fretting of metals with less chemical activity. At high humidity levels water vapour generally reduced the coefficient of friction, μ_s.     

Modelling and diagnostics of multiple cathodes plasma torch system for plasma spraying

Usage of a multiple-arcs system has significantly improved process stability and coating properties in air plasma spraying. However, there are still demands on understanding and controlling the physical process to determine process conditions for reproducible coating quality and homogeneity of coating microstructure. The main goal of this work is the application of numerical simulation for the prediction of the temperature profiles at the torch outlet for real process conditions. Behaviour of the gas flow and electric arcs were described in a three-dimensional numerical model. The calculated results showed the characteristic triangular temperature distribution at the torch nozzle outlet caused by three electric arcs. These results were compared with experimentally determined temperature distributions, which were obtained with specially developed computed tomography equipment for reconstructing the emissivity and temperature distribution of the plasma jet close to the torch exit. The calculated results related to temperature values and contours were verified for the most process parameters with experimental ones.     

Polishing tool with phyllotactic distributed through-holes for photochemically combined mechanical polishing of N-type gallium nitride wafers

In this work, we further developed the photochemically combined mechanical polishing (PCMP) method for finishing N-type gallium nitride (GaN) wafers. A core improvement is to design a novel polishing tool with phyllotactic distributed through-holes, through which the wafer surface underneath through-holes can receive ultraviolet (UV)-light for the photochemical oxidation, while the rest parts undergo mechanical polishing. During PCMP, the co-rotation of the wafer and polishing tool allows the wafer surface to undergo the uniform and high-frequency conversion of oxidation and polishing. Based on the designed PCMP system and apparatus, the fundamental issues arising from such an alternate processing mode, which is different from the parallel mode of conventional chemical mechanical polishing (CMP), were investigated. Results show that the technical features of PCMP depend on the nature of the photochemical oxidation of wafers themselves if the mechanical polishing procedure can sufficiently remove oxides in time. The material removal rate (MRR) is inversely proportional to the dislocation density of wafers. Under acidic conditions, the oxidation proceeds by the GaN monocrystal step orientation, allowing PCMP to clear surface/subsurface damages (SSDs) and to prepare step-terrace structures on the wafer surface. When the polishing solution (pH = 1.5) includes 0.1 M K₂S₂O₈ oxidants and 10 wt% SiO₂ abrasives, the surface roughness Sa attains 0.21 nm in 10 × 10 μm², and the MRR reaches 275.3 nm/h. The present study shows that the phyllotactic distributed through-hole array structure designed for polishing tools offers rich possibilities for the innovation of polishing technologies combining with various oxidation approaches.     

In Situ Analysis of Third Body Contributions to Sliding Friction of a Pb–Mo–S Coating in Dry and Humid Air

Reciprocating sliding tests of ion-beam deposited (IBD) Pb–Mo–S coatings were performed with an in situ tribometer that allows real-time visualization and Raman analysis of the sliding contact through a transparent hemisphere. Experiments were performed in dry air, ambient air (∼50% RH) and mixtures of dry and humid air cycled between low and high humidity. Third bodies formed in the sliding contact were monitored through an optical microscope and analyzed by Raman Spectroscopy. Third body velocity accommodation modes were identified and correlated with friction behavior in dry and ambient air. The dominant velocity accommodation mode in both dry and humid air was interfacial sliding between the outer surface of the transfer film and the wear track; this interface, based on present and earlier studies, is crystalline MoS₂. Therefore, the friction coefficient was controlled by the interfacial shear strength of MoS₂ sliding against MoS₂. Humid air sliding was accompanied by a rise in the friction coefficient and a small but observable second velocity accommodation mode: shear/extrusion of the transfer film. It is concluded that the friction rise in humid air was due to an increase in the interfacial shear strength, and that the rise in friction caused the third body to deform rather than the deformation causing the friction to rise.     

Investigation of turbulent spray disintegration characteristics depending on the nozzle configuration

The experimental measurements were carried out to examine turbulent disintegration characteristics ejecting from a counter-flowing internal mixing pneumatic nozzle under variable conditions of swirl angles and air pressures. The air injection pressure was varied from 60 kPa to 180 kPa and four counter-flowing internal mixing nozzles with axi-symmetric tangential-drilled holes at swirl angle of 15°, 30°, 45°, and 60° to the central axis have been specially designed. The experimental results were quantitatively analyzed, focusing mainly on the comparison of turbulent atomization characteristics issuing from an internal mixing swirl nozzle. To illustrate the swirl phenomena, the distributions of mean velocities, turbulence intensities, volume flux, and SMD (Sauter Mean Diameter, or D₃₂) were comparatively analyzed.     

Atomization characteristics in pneumatic counterfiowing internal mixing nozzle

In an effort to illustrate the global variation of SMD (Sauter mean diameter, orD ₃₂) and AMD (Arithmetic mean diameter, orD ₁₀) at five axial downstream locations (i. e., at Z=30, 50, 80, 120, and 170 mm) under the different experimental conditions, the radial coordinate is normalized by the spray half-width. Experimental data to analyze the atomization characteristics concerning with an internal mixing type have been obtained using a PDPA (Phase Doppler Particle Analyzer). The air injection pressure was varied from 40 kPa to 120 kPa. In this study, counterfiowing internal mixing nozzles manufactured at an angle of l5^o with axi-symmetric tangential-drilled four holes have been considered. By comparing the results, it is clearly possible to discern the effects of increasing air pressure, suggesting that the disintegration process is enhanced and finer spray droplets can be obtained under higher air assist. The variations inD ₃₂ are attributed to the characteristic feature of internal mixing nozzle in which the droplets are preferentially ejected downward with strong axial momentum, and dispersed with the larger droplets which are detected in the spray centerline at the near stations and smaller ones are generated due to further subsequent breakup by higher shear stresses at farther axial locations. The poor atomization around the centre close to the nozzle exit is attributed to the fact that the relatively lower rates of spherical particles are detected and these drops are not subject to instantaneous breakup in spite of the strong axial momentum. However, substantial increases in SMD from the central part toward the edge of the spray as they go farther downstream are mainly due to the fact that the relative velocity of droplet is too low to cause any subsequent disintegration.     

微磨料气射流成形加工表面粗糙度的研究

通过微磨料气射流成形加工玻璃试验,研究了工艺参数及其交互作用对加工表面粗糙度的影响,建立了表面粗糙度的回归模型。结果表明,气压对表面粗糙度的影响最显著,其次是靶距和喷嘴横移速度的交互作用、气压和靶距的交互作用以及靶距,而气压和喷嘴横移速度的交互作用、喷嘴横移速度对表面粗糙度的影响相对较小。表面粗糙度随着气压的增加而增大,随着靶距和喷嘴横移速度的增加先减小后增大。选用中低气压和较大靶距的组合有利于降低表面粗糙度。方差分析和残差检验的结果表明回归模型可以有效地预测表面粗糙度。     

Active wafer shape modulation using a multi-actuator chucking system

Jet and Flash Imprint Lithography has proven to be a viable alternative to optical lithography for fabrication of sub 30 nm nanostructures for large volume semiconductor manufacturing. Machine throughput, overlay and process defectivity that meet and exceed the International Technology Roadmap for Semiconductors (ITRS) are essential for commercial viability of any new lithography technology. Jet and Flash Imprint Lithography uses an inkjet head to dispense a grid of liquid drops on the wafer surface to match the volume requirements of the pattern being imprinted. Wafer shape modulation has been shown to increase imprinting speed significantly by reducing air bubble trapping in the drop interstitial sites. A wafer shape modulation chuck that can address arbitrary field locations and sizes on a wafer with a novel actuation scheme that minimizes the number of actuators while increasing imprinting speed and reducing process defects significantly is presented.     

Optimization of P-type poly-Si thermoelectric films design

In this study, a polycrystalline silicon (poly-Si) film layer for micro thermoelectric generators (TEGs) was optimized by using Taguchi methods. An experimental plan using an orthogonal array L₉ (3⁴) is described. The fabrication process of the thermoelectric poly-Si films layer is presented in detail. The P-type poly-Si films were fabricated on a tetra ethoxy silane (TEOS) layer with a supporting Si wafer. The thermoelectric properties, Seebeck coefficient and electrical conductivity were measured, including the transport properties such as the hall coefficient, hall mobility and carrier concentration. The design parameters were optimized based on the experimental results. Using the optimum values, a p-type poly-Si films layer was fabricated and its power factor was measured. The measured power factor was 541 μWm⁻¹K⁻², which was better than the predicted value of 221 μWm⁻1K⁻².     

利用拉伐尔管技术提高气体轴承实验台主轴转速

为了提高气体动静压径向轴承实验台主轴转速.根据气体动力学理论,建立了气体在喷管中流动的基本微分方程组,并分析了在不同音速下的截面变化规律.以马赫数为主要设计参数,建立了拉伐尔管内部曲线方程,并利用VB6.0对其内部曲线和压力进行了辅助设计,仿真结果显示当拉伐尔管中喉部压强为0.21MPa时,从拉伐尔管中喷出的气体流速的马赫数可达1.6.把实际加工的拉伐尔管应用到气体轴承实验台主轴上,使实验台主轴转速由原来的最高转速3495 r/min提高到5000 r/min左右.