Ahmed A. Busnaina

Thermal conductivity of bovine serum albumin: a tool to probe denaturation of protein

Byoung Kyoo Park et al. — Wed, 18 Apr 2012 10:16:33 PDT

We demonstrate a strong correlation between denaturation of bovine serum albumin (BSA) and the thermal conductivity k of aqueous solutions of BSA. When denaturation of BSA began, k dropped significantly. These results suggest that k, i.e., the ability of a protein to transport passively applied thermal energy, can be exploited to probe the conformational dynamics of BSA and potentially of other proteins. The technique of protein analysis demonstrated in this work is expected to be useful in micro-total-analysis systems because it is easier to miniaturize and to integrate into a device than is conventional differential scanning calorimetry analysis.

Analysis of scratches formed on oxide surface during chemical mechanical planarization

Jae-Gon Choi et al. — Wed, 29 Jun 2011 09:42:39 PDT

Scratch formation on patterned oxide wafers during the chemical mechanical planarization process was investigated. Silica and ceria slurries were used for polishing the experiments to observe the effect of abrasives on the scratch formation. Interlevel dielectric patterned wafers were used to study the scratch dimensions, and shallow trench isolation patterned wafers were used to study the effect of polishing parameters, such as pressure and rotational speed (head/platen). Similar shapes of scratches (chatter type) were observed with both types of slurries. The length of the scratch formed might be related to the period of contact between the wafer and the pad. Large particles would play a significant role in increasing the number of scratches. The probability of scratch generation is more at higher pressures due to higher friction force and removal rate. The optimization of the head to platen velocity could decrease the number of scratches.

Parylene-C passivated carbon nanotube flexible transistors

Selvapraba Selvarasah et al. — Wed, 29 Jun 2011 09:42:32 PDT

Carbon nanotubes are extremely sensitive to the molecular species in the environment and hence require a proper passivation technique to isolate them against environmental variations for the realization of reliable nanoelectronic devices. In this paper, we demonstrate a parylene-C passivation approach for CNT thin film transistors fabricated on a flexible substrate. The CNT transistors are encapsulated with 1 and 3 μm thick parylene-C coatings, and the transistor characteristics are investigated before and after passivation. Our findings indicate that thin parylene-C films can be utilized as passivation layers for CNT transistors and this versatile technique can be readily applied for the encapsulation of CNT devices such as field effect transistors, p-n diodes, and logic circuits fabricated on flexible substrates.

Effect of different deposition mediums on the adhesion and removal of particles

S. Hu et al. — Wed, 29 Jun 2011 09:42:25 PDT

The purpose of this study is to investigate the effect of the different deposition mediums on the adhesion and removal of particles. Polystyrene latex (PSL) particles (50 µm) are deposited on thermal oxide and silicon nitride coated silicon wafers using different suspension mediums: air, isopropyl alcohol (IPA), and deionized water and then removed in a dry environment. The results show that PSL particles deposited on oxide are easier to remove than those on nitride due to a higher van der Waals force in all deposition mediums. In addition, dry particles deposited in air are much easier to remove than those desposited in a liquid medium. When particles are deposited from a liquid suspension, a liquid meniscus is formed between the particle and the substrate, resulting in a capillary force. The capillary force induces a plastic deformation for soft particles such as PSL, which increases the contact area between the particle and the substrate, making them more difficult to remove. The liquid meniscus evaporates shortly after it is exposed to either a dry air environment or vacuum; however, the plastic deformation of particles would take place mainly due to the initial adhesion force in addition to the short time exposure of the capillary force.

Interfacial and electrokinetic characterization of IPA solutions related to semiconductor wafer drying and cleaning

Jin-Goo Park et al. — Thu, 02 Jun 2011 09:31:18 PDT

In this study, the interfacial and electrokinetic phenomena of mixtures of isopropyl alcohol (IPA) and deionized (DI) water in relation to semiconductor wafer drying is investigated. The dielectric constant of an IPA solution linearly decreased from 78 to 18 with the addition of IPA to DI water. The viscosity of IPA solutions increased as the volume percentage of IPA in DI water increased. The zeta potentials of silica particles and silicon wafers were also measured in IPA solutions. The zeta potential approached neutral values as the volume ratio of IPA in DI water increased. A surface tension decrease from 72 to 23 dynes/cm was measured when the IPA concentration increased to 30 vol %. The surface excess of IPA at the air–liquid interface reached a maximum at around 20 vol % IPA. The adhesion forces of silica particles on silicon wafers were measured using atomic force microscopy in IPA solutions. The adhesion force increased as the volume percent of IPA in water increased. Lower particulate contamination was observed when the wafers were immersed and withdrawn from solutions containing less than 25 vol % IPA.

The effect of frictional and adhesion forces attributed to slurry particles on the surface quality of polished copper

Yi-Koan Hong et al. — Thu, 02 Jun 2011 09:31:16 PDT

The effect of frictional and adhesion forces attributed to slurry particles on the quality of copper surfaces was experimentally investigated during copper chemical mechanical planarization process. The highest frictional force of 9 Kgf and adhesion force of 5.83 nN were observed in a deionized water-based alumina slurry. On the other hand, the smallest frictional force of 4 Kgf and adhesion force of 0.38 nN were measured in an alumina slurry containing citric acid. However, frictional (6 Kgf) and adhesion (1 nN) forces of silica particles in the slurry were not significantly changed regardless of the addition of citric acid. These differences were explained by the strong adsorption of citric ions on alumina but not on silica, which was verified by the charge reversal of alumina in zeta potential measurements. Higher particle adhesion forces resulted in higher friction. A higher magnitude of particle contamination and scratches was observed on polished copper surface in slurry condition with higher adhesion and friction forces.

Three dimensional controlled assembly of gold nanoparticles using a micromachined platform

Nishant Khanduja et al. — Thu, 02 Jun 2011 09:31:13 PDT

By using optical lithographic procedures, the authors present a micromachined platform for large scale three dimensional (3D) assembly of gold nanoparticles with diameters of ∼ 50 nm. The gold nanoparticles are formed into 3D low resistance bridges (two terminal resistance of ∼ 40 Ω) interconnecting the two microelectrodes using ac dielectrophoresis. The thickness of the parylene interlevel dielectric can be adjusted to vary the height of the 3D platform for meeting different application requirements. This research represents a step towards realizing high density, three dimensional structures and devices for applications such as nanosensors, vertical integration of nanosystems, and characterization of nanomaterials.

Scalable nanotemplate assisted directed assembly of single walled carbon nanotubes for nanoscale devices

Prashanth Makaram et al. — Thu, 02 Jun 2011 09:31:11 PDT

The authors demonstrate precise alignment and controlled assembly of single wall nanotube (SWNT) bundles at a fast rate over large areas by combining electrophoresis and dip coating processes. SWNTs in solution are assembled on prepatterned features that are 80 nm wide and separated by 200 nm. The results show that the direction of substrate withdrawal significantly affects the orientation and alignment of the assembled SWNT bundles. I-V characterization is carried out to demonstrate electrical continuity of these assembled SWNT bundles.

Experimental and analytical study of submicrometer particle removal from deep trenches

Kaveh Bakhtari et al. — Thu, 02 Jun 2011 09:31:09 PDT

Particle removal from patterned wafers and trenches presents a tremendous challenge in semiconductor manufacturing. In this paper, the removal of 0.3 and 0.8 µm polystyrene latex (PSL) particles from high-aspect-ratio 500 µm deep trenches is investigated. An experimental, analytical, and computational study of the removal of submicrometer particles at different depths inside the trench is presented. Red fluorescent polystyrene latex (PSL) particles were used to verify particle removal. The particles are counted using scanning fluorescent microscopy. A single-wafer megasonic tank is used for the particle removal. The results show that once a particle is removed from the walls or the bottom of a trench, the vortices and circulation zones keep the particles in the trench for a few minutes before eventually moving the particle out of the trench. The experimental results show that the time required for complete removal of particles from the bottom of the trench takes a much longer time than particles on the surface. This has been also verified and explained by physical modeling of the cleaning process. The removal efficiency and cleaning time are reported at different trench depths.

Experimental and numerical investigation of nanoparticle removal using acoustic streaming and the effect of time

Kaveh Bakhtari et al. — Thu, 02 Jun 2011 09:31:07 PDT

Theremoval of nanoparticles is becoming increasingly challenging as the minimumlinewidth continues to decrease in semiconductor manufacturing. In this paper,the removal of nanoparticles from flat substrates using acoustic streamingis investigated. Bare silicon wafers and masks with a 4 nmsilicon cap layer are cleaned. The silicon-cap films are usedin extreme ultraviolet masks to protect Mo–Si reflective multilayers. Theremoval of 63 nm polystyrene latex (PSL) particles from these substratesis conducted using single-wafer megasonic cleaning. The results show higherthan 99% removal of PSL nanoparticles. The results also showthat dilute SC1 provides faster removal of particles, which isalso verified by the analytical analysis. Particle removal from the4 nm Si-cap substrate is slightly more difficult as compared tobare silicon wafers. The experimental results show that the removalof nanoparticles takes a relatively long removal time. Numerical simulationsshowed that the long time is due to particle oscillatorymotion and redeposition, and that this phenomenon is not observedin the removal of sub-µm or larger size particles.

Directed assembly of gold nanoparticle nanowires and networks for nanodevices

Xugang Xiong et al. — Thu, 02 Jun 2011 09:31:04 PDT

Alternating electric field is used to assemble gold nanoparticle nanowires from liquid suspensions. The effects of electrode geometry and the dielectrophoresis force on the chaining and branching of nanowire formation are investigated. The nanowire assembly processes are modeled using finite element calculations, and the particle trajectories under the combined influence of dielectrophoresis force and viscous drag are simulated. Nanoparticle nanowires with 10 nm resolution are fabricated. The wires can be further oriented along an externally introduced flow. This work provides an approach towards rapid assembly and organization of ultrasmall nanoparticle networks.

High-throughput assembly of nanoelements in nanoporous alumina templates

Evin Gultepe et al. — Thu, 02 Jun 2011 09:31:01 PDT

The authors demonstrate a nanofabrication method utilizing nanoporous alumina templates which involves directed three dimensional assembly of nanoparticles inside the pores by means of an electrophoretic technique. In their demonstration, they have assembled polystyrene nanobeads with diameter of 50 nm inside nanopore arrays of height of 250 nm and diameter of 80 nm. Such a technique is particularly useful for large-scale, rapid assembly of nanoelements for potential device applications.