Papers by Author: Chao Hui Zhang

Abstract: Composite coatings of PTFE/PEEK (Polytetrafluoroethylene/Polyetheretherketone) were prepared by electrostatic powder spraying method. The factors were investigated on the preheating temperature and working temperature by the orthogonal experimental method. The results show that 250°C preheating temperature and 100°C working temperature are better conditions for playing good performance of PTFE/PEEK coatings.

Abstract: The relationship between the wettability and the roughness structure on silicon surface is studied. The unitary microscale square pillar arrays are fabricated by the way of inductively coupled plasma (ICP). The wettability of water droplets on the silicon surface is changed from hydrophilic to hydrophobic only by introducing microscale pillarlike structure. Furthermore, the scale effects of the unitary rough structure on hydrophobicity are investigated. For those silicon surfaces with a fixed pillar height, the relatively larger scale of grooves leads the droplets wettability state to unstable Cassie state and the contact angle will initially get larger and then decrease with the increase of groove width. The research could provide further insights into the design of functional surface with controllable roughness-induced hydrophobic.

Abstract: Aqueous solutions have found broad usages as lubricants, in conjunction with other possible utilizations, such as in metal working and other industries. Due to the inferior lubricity, functional additives are needed to improve their tribological performances among which aqueous surfactants are exclusively included. The film forming property of aqueous solution with polyethoxylated ether added (PEOE) is measured, taking consideration of the influences of the temperature and the concentration. The addition of PEOEs into aqueous solutions will largely increase the film forming capacity. But the concentration has only a minor influence on the lubrication property of the aqueous solutions with PEOEs. The cloud point will strongly alter the film forming characteristics.

Abstract: When two surfaces are brought into contact or at small separations, the liquid between them forms meniscus, which contributes to adhesion and friction. The increased adhesive force and friction are always the substantial cause leading to micro/nanodevices’s failure. In this study, a dynamic contact model of sphere-on-sphere surfaces during nanoscale separation is presented. A numerical analysis of meniscus and viscous forces based on the dynamic contact model has been carried out. During the separation process, the effects of separation distance, initial meniscus height, surface wettability and separating time on meniscus and viscous forces between the contact surfaces are investigated. The results of numerical solution revealed the adhesion mechanism of sphere-on-sphere surfaces during the separation with liquid mediated. The analyses provide a fundamental understanding of the separating process of two sphere surfaces. It is also useful for the design of the de-wetting and antisticking micro/nanoscale surfaces in various devices.

Abstract: Slurry preparation is of paramount importance in chemical mechanical planarization (CMP) process. It couples the combination effects of chemical and mechanical ones. In this paper, the characteristics of the slurry particles used in CMP are firstly modeled, which includes the size and the concentration with primary priority. And then, the model is validated by experiments during hard disk wafer polishing. The slurry prepared contributes to a high quality hard disk surface processed with CMP, which leads to low waviness Wa and roughness Ra with suitable material removal rate (MRR) as well. The study will surely lay a feasible foundation to the CMP mechanism.

Abstract: Chemical mechanical polishing (CMP) has been widely accepted in modern integrated circuit (IC) industries and hard disk manufacturing processes, to insure wafer surface with high level of global and local planarity required. In CMP process, temperature rise has two-edged influences: temperature-rise accelerates the chemical activity and the motion of nano-particles contained in the slurry through which material removal ratio (MRR) is enhanced; the other side of the same coin is, however, that it will soften the pad surface and subsequently reduce the MRR. Furthermore, it is found that temperature-rise would cause agglomeration of nano-particles, which would cause the wafer surface defect. The net effects of temperature thus should be under investigation with scrutiny. In an attempt to study the temperature variation and influencing rule, in this paper we firstly establish the flow equation considering pad roughness, coupling the energy equation on the basis of thermodynamics. Then, by taking numerical simulation which is carried out to give out the temperature distribution of conventional CMP process. The results show that temperature-rise in the CMP process is very minor. The research will surely shed some lights on the mechanism of CMP and lay a feasible foundation for possible future utilization.

Abstract: Chemical mechanical polishing (CMP) is a widely adopted technique to achieve high level of global and local planarity required in modern integrate circuit (IC) industries, wherein the pad properties weigh heavily on the final performance. A preliminary two-dimensional wafer-scale flow model for CMP is presented considering the roughness, the elasticity, as well as the porosity of the pad. Numerical simulations were conducted to show the slurry flow features’ variations due to pad parameters change. The results show that the porosity of the pad is conducive to slurry delivering, and small porous parameter will lead to prominent increase of load capability, accounting for larger material removal rate (MRR) whilst the elasticity of the pad has a more complex influence. The rough surface carries additional fluid in the valleys of the polishing pad thereby provide some chemical reactions. The model will shed lights on the mechanism of CMP process, which is for a long time considered as a difficult circle to square.

Abstract: A bimetal composite material is a variant of the typical composite that is composed of two materials joined at their interface surface. The advantage of clad material is that the combination of different properties of materials can satisfy both the need of good mechanical properties and the demand of user such as electrical properties simultaneously. This paper is concerned with the hydrostatic extrusion process of copper-clad aluminum rod. The commercially available finite element program ANSYS was used to simulate the process of hydrostatic extrusion for Cu/Al bimetal composite through the equal-strain contour concave dies. The relative slippage between the inner and outer metals under the condition of different friction factors is studied, and the stress-strain distribution in the billet was analyzed. Experiment test was carried out; it was found that the experimental result has good agreement with relative slippage from the finite element analysis.

Abstract: Temperature rise has two-edged influences on chemical mechanical polishing (CMP) process: temperature-rise facilitates the chemical activity and the motion of the nano particles contained in the slurry through which material removal ratio (MRR) is enhanced; to the other side of the same coin, however, it will soften the pad surface and subsequently reduce the MRR. Thus the research on temperature distribution of CMP process will be conducive to discovering the mechanism of polishing, and acquiring stable MRR and improving surface quality. With the help of the knowledge of tribology, hydrodynamics, and thermodynamics, flow equation considering the temperature variation in the fine step of CMP process, wherein high surface quality is the main concern and usually operates in contact free state, is set up, based on which the temperature field in contact is investigated in detail by taking advantage of the simulation technique, and the heat energy production and transition relations are obtained. Due to the slurry used, a small viscous heating effect is acknowledged by simulated results, and the temperature rise is negligible in contact-free flows, which is very conducive to the promotion of the final polished wafer/disk surfaces. The research will surely shed some lights in the mechanism of CMP and lay a feasible foundation for possible future utilization.

Abstract: Chemical mechanical polishing (CMP) is a widely used technique to achieve high level of global and local planarity required in modern integrate circuit (IC) industries and hard disk manufacturing process, etc., which pleas for concentrate researches. The main purpose of the present research is in an attempt to express the counterintuitive experimental aftermath: the ‘negative’ pressure, i.e., a suction force occurred in conventional commercial CMP process. A preliminary two tiers wafer-scale flow model for CMP is presented considering the roughness as well as the elasticity of the bulk pad substrate. Numerical simulations were conducted to elucidate the contact pressure and flow pressure distributions. The results show that a divergence region appears near the leading edge, which contributes to the suction pressure. A stress-richened area near the edges will give rise to over polishing. The research aftermaths agree well with the experiments, that validate the proposed analysis to some extend. This will shed lights on the mechanism of CMP process, which for a long time is considered as a black art where empirical or semi-empirical data are dependent upon to optimize the CMP parameters.