To simulate the heat and mass transfer in real heterogeneous systems, such as metal-production processes and lubrication, the point-contact condition with the formation of narrowly confined liquid film and its surrounding meniscus was constructed to study the classical microchannel boiling problem in this work. Specifically, the evaporation and diffusion of the superheated water meniscus and water/oil droplet in the point-contact geometry were investigated. The emphasis is put on the influence of the contact-line transport behaviors on nucleation and bubble dynamics in the confined meniscus. The observations suggested that superheat is the necessary condition for bubble formation, and enough vapor supply is the necessary condition for bubble growth in the confined liquid. The oil film could significantly inhibit the evaporation and diffusion of water molecules in the superheat geometry. The water/oil droplet can exist for a long time even in the hot contact region, which could have sustained damages to the mechanical system suffering from water pollution. This work is of great significance to better understand the damage mechanism of water pollution to the mechanical system.

•The starvation process was studied with initial amount of grease was strictly controlled.•The loss and reformation of lubricant reservoir around a grease lubricated contact was recorded.•The correlation between the reservoir loss/reformation process and the film thickness decay/recovery process was found for a grease lubricated point contact.•Greases with different chemical formulations were tested and compared.Six different types of greases were tested on the ball-on-disc test rig under starved condition. Both the central film thickness and the cross section film thickness profile were analyzed to better understand the mechanism of grease starvation. In-situ Monitoring of lubricant reservoir was achieved by using a high-resolution camera. Results showed that a new reservoir would re-form after a period of operation after the contact lost its initial grease reservoir under starved condition. The higher oil bleeding ratio of grease, the larger re-formed lubricant reservoir would be. A turning point on the central film thickness curve was found, which was due to the loss and re-formation of the lubricant reservoir.

Chemical mechanical polishing (CMP) is the most effective method for surface planarization in the semiconductor industry. Nanoparticles are significant for material removal and ultra-smooth surface formation. This research investigates the mechanical effects of the material removal in the CMP process. The various contact states of pad, individual particle, and wafer caused by the variations of working conditions and material properties are analyzed. Three different mechanical models for the material removal in the CMP process, i.e., abrasive wear, adhesive wear, and erosive wear are investigated, with a focus on the comparison of the results for different models. The conclusions and methods obtained could potentially contribute to the understanding and evaluation of the CMP process in further work.

This paper describes a study of point contact elastohydrodynamic (EHD) lubrication behavior at high speeds (up to 20 m s−1). Central film thicknesses were measured by optical interferometry device. The influence of slide-roll ratio and operating temperature on the central film thickness was determined. The influence of thermal effects on the reduction of film thickness was discussed via the analysis of numerical simulation method considering thermal effects. Subsequently, the experimental data was used to amend a set of unified parameters for the thermal corrections for different types of oil at high speeds.

Low dielectric constant (low-k) insulator films with outstanding mechanical strength and fracture resistance are needed urgently for the new generation of ultra-large-scale integrated circuits (ULSI). In this paper, the mechanical properties of low-k materials and the adhesion strengths between these materials with silica have been analyzed by using molecular dynamics (MD) simulations. Atomistic models of two kinds of representative low-k materials [nanoporous amorphous silica (n-a-SiO2) and SiOCH] and their contact models with silica have been constructed. The mechanical strength of the n-a-SiO2 film decreased with the increase of porosity, and the relationship between the normalized elastic modulus and porosity was modeled. The modulus of the SiOCH film with −CH2– groups was enhanced compared with that without −CH2– groups, and the mechanism was discussed. Through investigations of the adhesion strengths between n-a-SiO2, SiOCH, and silica, it was shown that the adhesion strengths of the n-a-SiO2/silica interfaces decreased with porosity. The adhesion strengths of the SiOCH films with both −CH2– groups and −CH3 groups were higher than that of the SiOCH film merely with −CH3 groups.Keywords: interface adhesion strength; low-k material; mechanical properties; nanoporous amorphous silica; porosities; SiOCH film

To simulate the interfacial behaviors in real heterogeneous systems, the point contact condition is constructed to study the classical immiscible displacement problem in this work. Specifically, the interfacial dynamics during the water droplet passing through the oil capillary bridge formed under the point contact condition is investigated. Emphasis is put on the influences of the wettabilities and the relative separation motion of the solid surfaces on the dynamic behavior of the droplets. The observations suggested that the capillary pressure had negligible effect on the movement of the water droplet when it was passing though the oil capillary bridge. The wettability and the relative separation of the disk and ball would influence the final adhesion behaviors of the water droplet after the droplet passed through the oil capillary bridge. Surface tension and adhesion energy were used to interpret these observations.

The interface adhesion of the Cu/Ta/Black Diamond™ (SiOC:H, BD, low-k)/Si substrate films stack structure was investigated. During the nanoindentation tests, a series of indentations under varied maximum normal loads of 1–120 mN were carried out. Regular triangular marks were formed on the surface, and the material pileup around the marks was clearly observed. The delamination occurred first at the Cu/Ta interface with the critical normal load of about 3.14 mN. As the normal load increased to about 63.71 mN, the BD layer began to delaminate from the Si substrate, resulted from the propagation of the cracking within BD layer along the BD/Si interface. The failure behaviors of the stack structure during the nanoscratch tests were similar to that during the nanoindentation tests. At the scratch velocity of 500 μm/min, the critical normal loads for Cu/Ta and BD/Si interfaces delamination were around 15.55 and 27.44 mN, respectively. Furthermore, the critical normal loads were decreased with the increase of the scratch velocity. Due to the similarity between the nanoscratch test and the chemical mechanical polishing (CMP) process, these results implied that lower polishing speed was preferred to avoid the interface delamination during the CMP of Cu/low-k interconnect structure.

Starved film thickness measurements are presented in grease-lubricated point contact under pure rolling condition. The starvation process of different types of greases is recorded and analysed in detail. Results show that the film decay rates for lithium greases and SiO2 greases are quite similar regardless of the rolling speed. Urea grease shows strong adsorbability to the metal surface, which can be clearly observed during the test. Oil separation tests and scanning electron microscopy observations proved the differences in structure and stability of the tested grease. A close relationship between starved film thickness and oil bleeding rate is found in the present research.

The film formation mechanism of lithium complex grease under starved condition was proposed based on the analysis of the relationship between grease reservoir and the finger-shaped lubricant along the rolling track using a laboratory built ball-on-disc test rig. Film thicknesses with rolling time at different slide/roll ratios were measured and discussed in detail. Experimental results showed that starvation occurred soon after the operation under pure rolling condition. In contrast, the contact remained fully flooded under slide–roll condition. The measurement of grease fingers proved that slide/roll ratio contributed to replenishing the contact by transferring more grease to the vicinity of the contact to form a lager lubricant reservoir. The volume of grease fingers, the inlet lubricant supply and the film thickness at different slide/roll ratios were found to be in good agreement.

The stresses of Cu/low-k interconnect structure during the whole Cu-CMP process were studied based on finite element method to analyze the interfacial delamination and fracture of the low-k layer. Effects of the polishing down pressure, low-k modulus, barrier modulus, Cu film thickness, and the coefficient of friction (COF) on the stress distribution were investigated. Simulation results revealed that the probabilities of both interfacial delamination and fracture of low-k layer during all three polishing steps were raised as increasing the polishing down pressure, barrier modulus, and the COF; while increase of low-k modulus made the probabilities decreased. The COF mainly affected interfacial delamination. During bulk Cu removal step, it can be seen that the decrease of Cu thickness made the probability of interfacial delamination increased, but had little effect on the fracture of low-k layer. Among three polishing steps, it was during the barrier polishing step that the risk of interfacial delamination between barrier layer and low-k layer was the largest, at the corner of interconnect structure interface; while the probability of fracture of low-k layer was the highest during overpolishing step, at the corner of low-k layer surface. Moreover, during the same polishing step, effects of the same parameter on interfacial delamination and on fracture of low-k layer were compared.

Microfluidic devices are of high efficiency for the coalescence and manipulation of monodispersed droplets. Numbers of microfluidic applications involve the control of droplets through networks of convergent or divergent junctions. The convergent microchannels are widely applied in transporting DNA and controlling other chemical and biological reactions. But there are still some problems unsolved such as that how to merge droplets more efficiently and how to guarantee the stability of the droplet in a convergent microchannel. In this work, numerical method is used to investigate the dynamic properties of the water microdroplets suspended in the convergent microchannel filled with oil. The moving of microdroplets in the convergent microchannel is driven by the initial droplet velocity. The surface tension is taken into account in the Navier-Stokes equations. The microchannel size parameter “Da” is firstly proposed to describe the convergent microchannel geometric characteristics and through which a regime map is created to classify droplets states into total coalescence regime, partial coalescence regime and no coalescence regime respectively. The dynamic behaviors of the droplets suspended in the convergent microchannel are discussed in detail. This work would contribute to the design of convergent microchannels for better biochemical analysis.

Investigations were performed to study the effects of H2O2 as oxidant, glycine as complexing agent, and benzotriazole (BTA) as inhibitor on surface mechanical characteristics and material removal of copper. Etch rates and surface roughness of Cu samples were measured in the presence of these chemicals at pH 4 or pH 10 under static conditions. Scanning electron microscopy images revealed that the surface of etched copper samples became layered and porous. Scratching experiments were carried out on the etched surface to investigate effects of these chemicals on mechanical removal of copper using atomic force microscopy. It was observed that the scratched depth of these etched Cu samples was higher than that of Cu metal. The addition of glycine enhanced chemical dissolution and mechanical removal greatly. However, the further addition of BTA made both of them decreased, suggesting BTA not only inhibitor of chemical dissolution, but also inhibitor of mechanical removal. In most cases, the measured hardness values of etched copper surface were slightly higher than that of Cu metal. These results indicated that changes of surface structure were the primary reason for increase of mechanical removal of copper, but not changes of copper surface nanohardness.

Ionic liquids are generally considered as environmentally friendly material. The film thicknesses of ionic liquids and silicone oils at high pressures up to 3 GPa are measured employing the relative optical interference intensity method. The results show that for the three ionic liquids the relative order of film thickness is 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM]PF6) > 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM]PF6) > 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6). In elastohydrodynamic lubrication the order of viscosity can simply account for this fact. In thin film lubrication condition the length of alkyl side chain and arrangement manner of cation are used to explain the experimental results. Another remarkable phenomenon is that even though the viscosities of silicone oils are close to those of ionic liquids, the measured film thicknesses of silicone oils are quite less than those of the ionic liquids. The results show that long alkyl chain ionic liquid can form rather thick films at high pressure.

A new test rig with an ability to obtain clear interference images at high pressure contacts has been developed. The technique of relative optical interference intensity has been used to obtain film thickness profiles and then lubrication properties of some base oils including six kinds of polyalphaolefin and four kinds of silicone oil have been studied at different pressures ranging from 1 to 3 GPa. The results show that viscosities of these lubricants have notable effect on slopes of film thickness curves (speed versus film thickness in log–log form), and the observed phenomenon is attributed to fluidity and molecular structure. A comparison of experimental central film thicknesses with computational work shows that at high loads the relationship between load and film thickness usually go against prediction given by Hamrock and Dowson. In addition, when more pressure is applied, the profiles of film thickness become more and more flat while rolling speed do little to change the shape of profiles.