Lina Si

Monoatomic layer removal mechanism in chemical mechanical polishing process: A molecular dynamics study

Molecular dynamics simulations of nanoscratching processes were used to study the atomic-scale removal mechanism of single crystalline silicon in chemical mechanical polishing (CMP) process and particular attention was paid to the effect of scratching depth. The simulation results under a scratching depth of 1 nm showed that a thick layer of silicon material was removed by chip formation and an amorphous layer was formed on the silicon surface after nanoscratching. By contrast, the simulation results with a depth of 0.1 nm indicated that just one monoatomic layer of workpiece was removed and a well ordered crystalline surface was obtained, which is quite consistent with previous CMP experimental results. Therefore, monoatomic layer removal mechanism was presented, by which it is considered that during CMP process the material was removed by one monoatomic layer after another, and the mechanism could provide a reasonable understanding on how the high precision surface was obtained. Also, the effects of the...

Abrasive rolling effects on material removal and surface finish in chemical mechanical polishing analyzed by molecular dynamics simulation

In an abrasive chemical mechanical polishing (CMP) process, materials were considered to be removed by abrasive sliding and rolling. Abrasive sliding has been investigated by many molecular dynamics (MD) studies; while abrasive rolling was usually considered to be negligible and therefore was rarely investigated. In this paper, an MD simulation was used to study the effects of abrasive rolling on material removal and surface finish in the CMP process. As the silica particle rolled across the silicon substrate, some atoms of the substrate were dragged out from their original positions and adhered to the silica particle, leaving some atomic vacancies on the substrate surface. Meanwhile, a high quality surface could be obtained. During the abrasive rolling process, the influencing factors of material removal, e.g., external down force and driving force, were also discussed. Finally, MD simulations were carried out to examine the effects of abrasive sliding on material removal under the same external down force as abrasive rolling. The results showed that the ability of abrasive rolling to remove material on the atomic scale was not notably inferior to that of abrasive sliding. Therefore, it can be proposed that both abrasive sliding and rolling play important roles in material removal in the abrasive CMP of the silicon substrate.

Electrospreading of dielectric liquid menisci on the small scale

The effects of an external electric field (EEF) on dielectric liquid menisci formed in a small gap between a smooth plate and a high precision steel ball have been investigated. It was found that thin spreading films were pulled out and moved away from the menisci of low permittivity dielectric liquids after exposure to the EEF. During the initial period of spreading, a strong “electric wind” due to the gas discharge in the vicinity of the three-phase contact line (TCL) of the liquid meniscus was observed. However, such electrospreading phenomena were absent for the menisci of conductive liquids which were commonly used in classical electrowetting studies. It is deduced that the spreading of liquid menisci under EEFs is driven by the thermocapillary force near the TCL.

Mechanical properties and interface characteristics of nanoporous low-k materials.

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.

Sessile multidroplets and salt droplets under high tangential electric fields

Understanding the interaction behaviors between sessile droplets under imposed high voltages is very important in many practical situations, e.g., microfluidic devices and the degradation/aging problems of outdoor high-power applications. In the present work, the droplet coalescence, the discharge activity and the surface thermal distribution response between sessile multidroplets and chloride salt droplets under high tangential electric fields have been investigated with infrared thermography, high-speed photography and pulse current measurement. Obvious polarity effects on the discharge path direction and the temperature change in the droplets in the initial stage after discharge initiation were observed due to the anodic dissolution of metal ions from the electrode. In the case of sessile aligned multidroplets, the discharge path direction could affect the location of initial droplet coalescence. The smaller unmerged droplet would be drained into the merged large droplet as a result from the pressure difference inside the droplets rather than the asymmetric temperature change due to discharge. The discharge inception voltages and the temperature variations for two salt droplets closely correlated with the ionization degree of the salt, as well as the interfacial electrochemical reactions near the electrodes. Mechanisms of these observed phenomena were discussed.

Water droplets on a hydrophobic insulator surface under high voltages: A thermal perspective

The thermal characteristics in the interaction process between water droplets on a hydrophobic insulator surface under high direct current voltages have been investigated with the infrared thermography. Discharge inception under a sufficiently high electric field resulted in the temperature rise between droplets and the formation of a liquid channel. The channel was transient for low conductivity droplets followed by their coalescence while stable for highly conductive ones. Asymmetric temperature distributions in the associated droplets appeared, and localized drying in the low conductivity droplet near the higher potential electrode initiated intermittent discharge. Mechanisms of these experimental phenomena have been discussed.

Ultralow Friction Self-Lubricating Nanocomposites with Mesoporous Metal–Organic Frameworks as Smart Nanocontainers for Lubricants

Smart nanocontainers with stimuli-responsive property can be used to fabricate a new kind of self-lubricating nanocomposite, while the practical potential of the metal-organic frameworks (MOFs) as nanocontainers for lubricants has not been realized. In this work, mesoporous Cu-BTC MOFs storing oleylamine nanocomposites were explored from synthesis and microstructure to self-lubricating characterization. The stress stimuli-responsiveness behavior of the Cu-BTC storing oleylamine (Cu-BTCO) for lubrication has been investigated by subjecting it to macroscopic ball-on-disc friction tests. The steady-state coefficients of friction (COFs) of the Cu-BTC nanocomposites without lubricants were ca. 0.5. In contrast, after oleylamine as the lubricant was incorporated into the Cu-BTC container in the nanocomposite, ultralow friction (COF, ca. 0.03) was achieved. It has been demonstrated that the improved lubricating performance was associated with the lubricating film which was in situ produced by the chemical reaction between the oleylamine released from the nanocontainer and the friction pairs. Therefore, the nanocomposite with smart Cu-BTC container holds the promise of realizing extraordinary self-lubricating properties under stress stimuli.

AC Pulse Dielectric Barrier Corona Discharge Over Oil Surfaces: Effect of Oil Temperature

The oil temperature effect on the interaction between plasma caused by high ac pulse barrier corona discharge and dielectric oil film is investigated. The results showed that funnels due to the impact of electric wind or the shock wave generated by streamer discharge occurred more easily under asymmetric negative ac pulse voltages at low oil temperatures but more difficult at high oil temperatures compared with those under asymmetric positive ac pulse voltages. The variation of the funnel diameter with voltage was more obvious under asymmetric positive ac pulse voltages. Oil boiling appeared in the funnel induced by discharge under asymmetric negative ac pulse voltages with high temperatures; thermal flow manifested by localized material transfer existed, and finally, a viscous layer formed in the funnel for oils with elevated temperatures under asymmetric positive ac pulse voltages.