SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing (ERC)

                                                          **  Bringing Sustainability to Semiconductor Manufacturing **

A multi-university research center leading the way to environmentally friendly semiconductor manufacturing, sponsored by the Semiconductor Research Corporation's Global Research Collaboration (GRC) Research Program



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- 2013 -
Jan. 10, 2013 No TeleSeminar--Holiday Schedule
Jan. 24 Host:  Duane Boning, Professor of Electrical Engineering and Computer Science, and Associate Head, EECS Department, MIT
Presented by
Sanha Kim, PhD candidate in Mechanical Engineering, MIT
Topic title
"Scratching by pad asperities in chemical-mechanical polishing"
Abstract:  Despite the universal usage of chemical-mechanical polishing (CMP) in the manufacture of Integrated Circuits (IC) and Micro Electro-Mechanical Systems (MEMS), one of the problems in CMP is the unintended scratching of the surface being polished. It has recently been shown that the primary sources of the scratches are not only due to the agglomerated, hard particles but also due to the soft pad asperities. In this talk, I will present the pad scratching models that are developed based on contact mechanics, and the experimental results on both monolithic and Cu/low-k patterned layers that validates the theoretical expectations.  (PDF)
Feb. 7 Host:  Rockford Draper, Department of Molecular and Cell Biology and Department of Chemistry, University of Texas-Dallas
Presented by:  Steven Nielsen, Department of Chemistry, University of Texas-Dallas
Topic title: 
"Carbon-based nanoparticle ESH : dispersibility and aggregation in lipid membranes"
Carbon-based nanoparticles (CNPs), such as spherical fullerenes and carbon nanotubes, have many potential applications but attention needs to be paid to their ESH impact. 
     The toxicity of CNPs remains disputable. This controversy is partly due to the variation of the CNP size, shape, functionalization, and aggregation state in different experiments.
     Some researchers have suggested that CNT aggregation is a key toxicity factor while others have made a link between CNT water dispersibility (through lipid bilayer vs. water partitioning) and toxicity.
     This seminar will focus on CNT dispersibility and aggregation in lipid membranes, which is a simple model system often used to investigate some of the above issues. However, as we will see, even results using this model system are contentious.  (PDF)
Feb. 21 Host:  Farhang Shadman, Chemical & Environmental Engineering, University of Arizona
Presented by:  Manish Keswani, Materials Science and Engineering, University of Arizona
Topic title: 
"Fundamentals of Megasonic Cleaning and Common Techniques Used for Measuring Acoustic Cavitation"
Megasonic cleaning is one of the common techniques used for removal of particles from wafer surfaces in semiconductor industry. With the advancement of technology node to 22 nm and lower, the feature size is becoming increasingly small and fragile while the requirements for cleaning are becoming more stringent. In order to be able to continue the use of megasonic technology for wafer cleaning, it is essential to understand the phenomena of acoustic cavitation which is known to play an important role in particle removal as well as feature damage. In the first part of the presentation, fundamentals of stable and transient cavitation pertinent to wafer cleaning will be discussed. The second part of the presentation will include discussion on use of acoustic emission and sonoluminescence based techniques for characterization of acoustic cavitation and correlation to particle removal and feature damage.  (PDF)
Mar. 7 No TeleSeminar--Annual Review Meeting-Preparation
Mar. 21 No TeleSeminar--Annual Review Meeting
April 4 No TeleSeminar -- Post-Annual Review Meeting
April 18 Host: Shyam Aravamudhan, Joint School of Nanoscience and Nanoengineering, North Carolina A&T State University
Presented by:  Jerzy Leszczynski, Professor and President's Distinguished Fellow, Dept. of Chemistry and Biochemistry, Jackson State University
Topic title
: "Toxicity of Nanomaterials - Development of New Theoretical Approaches at the JSU Interdisciplinary Nanotoxicity Center"
Nanotechnology is expanding rapidly, but development of novel materials synthesized at the ‘nano’ scale should be always accompanied by a comprehensive assessment of risk to human health and to environmental ecosystems. It is vital to be able to predict possible environmental impact of new nanomaterials before their mass production and application. This is one of the vital goals of the supported by the NSF for the last five years Interdisciplinary Nanotoxicity Center at the Jackson State University.
     We believe that the Computational Chemistry is able to provide various tools to evaluate interaction of nanomaterials with biomolecules, shed a light on mechanisms of such phenomena, and predict toxicity of nano sized species. We suppose that there is a strong need to develop “nano descriptors” i.e. novel and reproducible ways of representing the structures and/or physical properties of nanoparticles that are suitable for distinctive grouping these types of chemicals. This will facilitate development of QSARs that could reliable predict their characteristics and activities. A conceptual framework for grouping NPs should be considered as a first step in identifying QSARs that are applicable within each group. Due to high variability in the molecular structure and different mechanisms of action, individual groups of nanoparticles should be modeled separately. In each case, according to the general QSAR rules, the applicability domain of the models should be carefully validated.

     Our recent ab initio study reveals details of interactions of gold clusters, carbon nanotubes and fullerenes with DNA bases and base pairs. Direct prediction of toxicity of unknown nanomaterials could be done using QSAR models developed for a test set of compounds characterized experimentally. Based on experimental testing we developed and tested novel interpretative nano-QSAR model describing cytotoxicity of 17 nano-sized metal oxides to bacteria Escherichia coli. The proposed model allows us to formulate a hypothesis that mechanistically explains differences in toxicity between the individual oxides.
May 2 Host:  Alex Tropsha and Denis Fourches, Eshelman School of Pharmacy, University of North Carolina-Chapel Hill
Presented by:  Drs. Karmann Mills and Kimberly Guzan, RTI International, Center for Aerosol and Nanotechnology Engineering, Research Triangle Park, North Carolina
Topic title:  The Nanomaterial Registry: An growing data repository for well-characterized nanomaterials"
Abstract:   (No abstract)  (PDF)
May 16 Host Jane Chang, Professor and Associate Dean, Chemical and Biomolecular Engineering, University of California-Los Angeles.
Presented by: Jane Chang, Chemical and Biomolecular Engineering, University of California-Los Angeles
Topic title
:  “Assessment of etch chemistries for magnetic metal elements and alloys”
:  In this work, a thermodynamic approach is used to assess the feasibility of various etch chemistries, beginning with the consideration of reactions between the dominant vapor phase/condensed species and the surface at various temperatures and reactant partial pressures.  The volatility of etch product was determined to aid the selection of viable etch chemistry  leading to improved etch rate of reactive ion etching process. Specifically, a few important magnetic metals are considered along with various halogen and organometallic based chemistries.   In addition, the vapor pressure enhancement induced by adding secondary gas such as hydrogen has also been studied.  (PDF)
May 30 Host James Ranville, Department of Chemistry and Geochemistry, Center for Environmental Risk Assessment (CERA), Colorado School of Mines;  [Paul Westerhoff, ASU]
Presented by James Ranville, Colorado School of Mines
Topic title:  "Recent Advances in Nanoparticle Analysis Using ICPMS"
Abstract:  In recent years the array of techniques available for particle size analysis of nanoparticles (NPs) has grown and matured significantly.  For pristine NPs, dispersed in simple aqueous media, methods based on diffusion coefficient, particle mass, or optical properties all can give reliable size estimates, with fairly short analysis time.  A significant challenge arises when the NP characteristics, and/or the matrix in which the NP is dispersed becomes more complex.   If nanometrology is to inform investigations of nanosafety, where these more complex situations are likely to be the norm, these challenges must be addressed.  The presence of interfering background particles, changes in NP composition leading to uncertain bulk and surface properties, and both hetero- and homoaggregation all challenge our techniques.  A further challenge lies in the low concentrations expected in environmental and biological systems.
     Using techniques that are element specific, including inductively coupled plasma-mass spectrometry (ICP-MS) provides some assistance in meeting the challenge of working with NPs in “real-world” situations.  Its low detection limits, in addition to its elemental specificity, makes ICP-MS a powerful tool for detection, characterization, and quantification of metal-containing NPs. Important NP metrics including size and polydisersity can be examined if ICP-MS is coupled to field flow fractionation (FFF-ICPMS) or operated in a time-resolved (single particle) mode of data collection (spICPMS).  This talk will introduce the basic principles of these new methods and focus primarily on the challenges to nanometrology in working with “real-world” sample matrices. (PDF)
June 13 Host:  Farhang Shadman, Chemical and Environmental Engineering, University of Arizona
Presented by:  Armin Sorooshian, Asst. Professor, Chemical and Environmental Engineering/
Atmospheric Sciences, University of Arizona
Topic title:  "
Chasing Aerosol Particles Down to Nano Sizes"
Aerosol particles range in size from a few nanometers up to several micrometers in diameter and can consist of tens of thousands of species. Although they are so small, they have very important effects. For example, they directly interact with solar radiation and act as cloud condensation nuclei, which are the seeds of cloud droplets. Consequently, particles influence the earth’s radiation balance, atmospheric visibility, the hydrologic cycle, and the biogeochemical cycling and transport of nutrients and contaminants. Particles also negatively impact public health and can be a hazard in working environments such as with semiconductor manufacturing. This talk will report on the relevant aerosol properties that impact their transport, effects, and fate. Measurement capabilities will be introduced with examples from recent field projects in the atmosphere (PDF)
June 27 Host:  Kai Loon Chen, Department of Geography and Environmental Engineering, Johns Hopkins University
Presented by:
Khanh An Huynh, Department of Geography and Environmental Engineering, Johns Hopkins University
Topic title: "
Rates and Mechanisms of Heteroaggregation Between Carbon Nanotubes and Hematite Nanoparticles in Aquatic Environments"
Because carbon nanotubes (CNTs) have extraordinary physical, chemical, and electrical properties, they have been increasingly used in consumer products and industrial applications. During the manufacture, use, and disposal of CNT-containing products, these nanotubes could be released into aquatic environments and potentially cause adverse effects on microorganisms, ecology, and even human health. To understand the environmental fate and transport of CNTs, previous studies conducted ideal aggregation experiments between CNTs (homoaggregation) and reported that CNT homoaggregation depended on nanotube surface charge and solution chemistry, such as electrolyte concentrations, pH, and the presence of natural organic matter. However, in reality, the aggregation between naturally occurring colloids and CNTs (heteroaggregation) is expected to control the fate and transport of CNTs since the concentrations of naturally occurring colloids are much higher than that of CNTs. As a result, the understanding of CNT fate and transport in the environments is still very limited.
      Because of these reasons, the heteroaggregation between negatively charged CNTs and positively charged hematite nanoparticles (HemNPs, a naturally occurring colloid) was the main focus of this study. All the experiments were conducted at pH 5.2 and low ionic strength to obtain exclusive CNT-HemNP heteroaggregation. With a fixed HemNP concentration of 0.44 mg/L, the heteroaggregation rates over a broad range of CNT/HemNP mass concentration ratio (CNT/HemNP ratio) were determined using time-resolved dynamic light scattering. By observing actual heteroaggregate structures with cryogenic transmission electron microscopy technique, the mechanisms of heteroaggregation were then elucidated.
      The growth rate of CNT-HemNP heteroaggregates was initially found to increase with the increase in CNT/HemNP ratio until it reached the highest value at an optimal CNT/HemNP ratio of 0.0316. The maximum heteroaggregation rate was 3.3 times higher than the homoaggregation rate of HemNPs in the diffusion-limited regime. It was expected that the bridging of HemNPs by CNT strands was the mechanism of heteroaggregation at this stage. When the CNT/HemNPs ratio was further increased, a blocking mechanism was likely to occur as the heteroaggregation rates decreased significantly. In the presence of humic acid, similar dependency of heteroaggregation rates on CNT/HemNP ratios were also observed. However, the maximum heteroaggregation rates were smaller at higher humic acid concentrations, which could be explained by the decrease in available HemNP surface for CNT to attach to through favorable electrostatic interaction.
July 11 Host:  Paul Westerhoff, School of Sustainable Engineering and The Built Environment, Civil, Environmental and Sustainable Engineering Program, Arizona State University
Presented by
Kyle Doudrick, School of Sustainable Engineering and The Built Environment, Civil, Environmental and Sustainable Engineering Program, Arizona State University
Topic title
"Carbon Nanotube and Graphene Quantification"
Carbon nanotube (CNT) and graphene production is rapidly growing, and there is a need for robust analytical methods to quantify these in complex matrices. For this talk, I will discuss in detail our method for extraction and quantification of CNTs and graphene in complex matrices. Using a classical air pollution technique (thermal optical transmittance), we developed a thermal analysis quantification method specifically for CNTs and graphene termed programmed thermal analysis (PTA). This method operates on the basis that CNTs and graphene can be separated thermally from other forms of carbon because they are more thermodynamically stable. An evaluation of the thermal properties of CNTs and graphene revealed two classes: thermally “weak” and “strong.”  Some multi-walled CNTs (MWCNTs), single-walled CNTs (SWCNTs), and graphene oxide were classified as weak. All MWCNTs with a high crystallinity, graphene, and reduced graphene oxide were classified as strong. Most aqueous matrices (dispersants, surface water, wastewater, and urine) interfered some with the weak CNTs and none with the strong CNTs. CNTs and graphene embedded in solid matrices (e.g., rat lung tissue, composites) and those with large amounts of interfering background elemental carbon (e.g., sediment) were difficult to quantify with PTA alone and there was a need to develop extraction techniques. We demonstrate a procedure for developing such an extraction method using rat lung tissue as an example. The ability of various chemical treatment methods, including Solvable (2.5% sodium hydroxide/surfactant mixture), ammonium hydroxide, nitric acid, sulfuric acid, hydrochloric acid, hydrofluoric acid, hydrogen peroxide, and proteinase K, to extract CNTs from rat lung tissue was evaluated. The recovery efficiency of each of the eight chemical reagents studied was found to depend on the ability to (1) minimize oxidation of CNTs, (2) remove interfering background carbon from the rat lung tissue, and (3) separate the solid-phase CNTs from the liquid-phase dissolved tissue via centrifugation. A two-step extraction method using Solvable and proteinase K emerged as the optimal approach, enabling a recovery of 93 ± 15% of a 2.8 ± 0.44 µg CNT loading that was spiked into whole rat lungs. (PDF)
July 25 Host:  Shyam Aravamudhan, Joint School of Nanoscience and Nanoengineering, North Carolina A&T State University and The University of North Carolina at Greensboro
Presented by
Stacey Harper, Assistant Professor, ONAMI Signature Faculty Fellow, Department of Environmental and Molecular Toxicology, Oregon State University
Topic title:  "
Integrative Nanotoxicology:  Linking Rapid Assays and Informatics to Predict Nanomaterial –Biological Interactions"
This talk by an experimental toxicologist will address the challenges of capturing metrics of biological response from rapid-throughput systems and distilling response data down to statistically and biologically meaningful parameters.  Her research utilizes an integrative approach to strategically target structure-activity relationships by leveraging nanomaterial characterization and toxicity data using informatics. She will discuss the challenges in identifying the inherent material properties that govern nanomaterial-biological interactions and defining key drivers for nanomaterial toxicity.  She will also highlight some of the success stories that have resulted from community driven standardization efforts.  (PDF)
Aug. 8 Host:  Rocky Draper, Departments of Molecular & Cell Biology and Chemistry, University of Texas at Dallas 
Presented by
Donald R. Baer, Lead Scientist Interfacial Chemistry, EMSL Pacific Northwest National Laboratory, Richland WA
Topic title
Ceria Nanoparticles:  Environmental Impacts on Particle Properties and Potential Effects on Biological Systems”
Abstract:  Cerium oxide (ceria) nanoparticles are widely studied for their current and potential use in catalytic, energy, electronic materials, environmental protection and bio-medical applications. The performance of ceria in many of these applications depends on the ability of cerium to switch between +3 and +4 oxidation states. Our research involves examination of the properties of ceria nanoparticles as they apply to materials science research and impact biological systems. We have synthesized ceria nanoparticles by several solution growth processes as well as examined the impacts of the wide variety of other processes described in the literature. This paper summarizes some of our observations of the impact that synthesis route, processing conditions, storage and environmental conditions have on the properties of ceria nanoparticles.  An examination of the biological impacts of ceria nanoparticles indicates that larger faceted ceria particles that have been heated are more likely to have adverse consequences, while smaller particles synthesized at room temperature and never removed from solution often have anti-oxidative behaviors. Smaller particles are highly dynamic in nature changing their oxidation state not just as a function of size, but also as a function of aging (time) and environmental conditions.  During particle nucleation and growth in solution, both the particle size and oxidation state change with time. This type of observation suggests that interpretations of experimental results based primarily on particle size will be misleading at best.  It is possible to vary the rates of oxidation state change by varying the properties of the solution used for synthesis. We have also found that small variations in synthesis such as changing the source of chemicals, altering the water source or changing from clean glassware to sterilized plastic containers for biological studies can alter the character of particles formed as well as their stability.  Smaller particles are particularly susceptible to change and Raman and XRD studies suggest that these changes can be more complex than initially anticipated.   Because synthesis, analysis and relevant operational conditions often place particles in different environments, understanding how particles change as a function of time in different environments is essential to predicting their properties. In such cases, aging time and environmentally induced changes in particles may play a significant role in the results reported and hence lead to discrepancies reported in various studies.
Aug. 22 Host:  Ara Philipossian, Chemical and Environmental Engineering, University of Arizona
Presented by
Xiaoyan Liao, PhD candidate in Chemical Engineering, University of Arizona
Topic title:  "
Analysis of Large Pad Surface Contact Area in Copper Chemical Mechanical Planarization"
The large pad surface contact area and its role in copper CMP were investigated. Scanning Electron Microscope (SEM) analysis showed that the individual large pad surface contact areas were induced by fractured pore walls and loosely attached pad debris. Simulation results indicated that individual large contact areas corresponded to very low values of the Young’s modulus (about 50 MPa). A case study was presented to illustrate the role of the individual large contact area of IC1000 K-groove pad in copper CMP. Results confirmed that the individual large contact area had minimal contribution to removal rate and indicated that the removal rate was mainly caused by small individual contact areas. In our case, small contact areas corresponded to those smaller than 9 square microns. We believe that this methodology can be also applied for other kinds of pad, although the threshold values that may define ‘SMALL’ and ‘LARGE’ individual contact areas for different pads and processes need to be further investigated.  (PDF)
Sept. 5 No TeleSeminar
Sept. 19 No TeleSeminar
Oct. 3 Host:  Paul Westerhoff, School of Sustainable Engineering and the Built Environment, Ira A. Fulton Schools of Engineering, Arizona State University
Presented by:  Yu Yang, Postdoc Research Associate, School of Sustainable Engineering and the Built Environment, Ira A. Fulton Schools of Engineering, Arizona State University
Topic title:  "Cloud-Point Extraction and Characterization of Nanomaterials from Water"
Abstract:  Increasing application of engineered nanomaterials (ENMs) in industry and consumer products will inevitably lead to the release of them to water environment. To characterize the nanomaterials efficiently in water, a fast and simple method is needed to enrich nanomaterials from water without altering their shape and size. Cloud-point extraction (CPE) by Triton 114 demonstrated the ability to enrich gold nanoparticle from nanopure water about 18 times while preserving the size and shape. A series of CPEs were conducted to extract nanomaterials from diversity sources of water, including Salt River, Verde River, influent and effluent from a local water and wastewater treatment plant, and Saguaro Lake. Transmission electron microscopy coupled with energy dispersive X-ray spectroscopy was applied to characterize the nanoparticles enriched in organic phase. The most abundant nanoparticles identified so far were silica and titanium containing particles with diameter in the range 4-99 nm. Other nanoparticles ranged from 30-65 nm contained a list of major elements, including calcium, magnesium, aluminum, iron, oxygen, sulfur, carbon, and chloride. Further research is needed to track the sources of nanoparticles identified and justify their potential eco-toxicity on aqueous environment.  (PDF)
Oct. 17 HostKai Loon Chen, Asst. Professor, Department of Geography and Environmental Engineering, Johns Hopkins University
Presented by
:  Peng Yi, Ph.D., Postdoctoral Research Fellow, Department of Geography and Environmental Engineering, Johns Hopkins University
Topic title
:  "Release of Multiwalled Carbon Nanotubes from Silica Surfaces”
:   Deposition and remobilization (or release) of carbon nanotube (CNTs) on natural solid surfaces are two key processes that control the fate and transport of CNTs in surface and ground water systems.  While the mechanisms for the deposition of CNTs on environmental surfaces have been investigated, the influence of solution chemistry on the remobilization of CNTs from environmental surfaces is still not well understood.  In this study, the remobilization of deposited multiwalled CNTs (MWNTs) from silica surfaces was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D).  MWNTs were deposited on silica surfaces under favorable deposition conditions and then exposed to different solution chemistries to induce the remobilization of MWNTs.  Throughout the deposition and remobilization processes, the mass of the deposited MWNTs was monitored and obtained through Voigt-based modeling.  Our results show that deposited MWNTs were released when the electrolyte concentrations (either CaCl2 or NaCl) were decreased under neutral pH conditions.  The release of MWNTs was attributed to an increase in electrostatic repulsion between MWNTs and silica surfaces which in turn resulted in a decrease in the depth of the primary energy minimum.  The fraction of deposited MWNTs that were remobilized increased stepwise when the electrolyte concentrations of the elution solutions were sequentially decreased, which was likely due to the heterogeneity in surface charge densities of MWNTs.  The degrees of MWNT remobilization resulting from a sequential decrease in NaCl concentration were lower at pH 4.0 than at 7.1 due to the smaller electrostatic repulsion experienced between MWNTs and silica surfaces at pH 4.0.  Decreasing pH from 7.1 to 4.0 in the presence of 1.5 mM CaCl2 resulted in significant MWNT remobilization, possibly due to the elimination of calcium bridging between the carboxyl groups on MWNTs and the silanol groups on silica surfaces with the decrease in pH.  In addition to the degree of MWNT release, the kinetics of MWNT release was also investigated.  Both the fraction of deposited MWNTs that could be released and the release rate coefficient of releasable MWNTs are important parameters for describing the first-order release kinetics of MWNTs.  The release rate coefficient of releasable MWNTs increased with decreasing CaCl2 concentration probably due to the decrease in the height of energy barrier for releasable MWNTs.  Moreover, the release rate coefficient decreased when the surface concentration of deposited MWNTs was over 1000 ng/cm2, probably due to the formation of surface-bound MWNT aggregates which have lower diffusion coefficients than individual MWNT strands.  (PDF)
Oct. 31 No TeleSeminar--Holiday Schedule
Nov. 14 HostPaul Pantano, Department of Chemistry, Bionanosciences Group, and Alan G. MacDiarmid NanoTech Institute, The University of Texas at Dallas
Presented by:
  Michael Yukica, Research Chemist, The University of Texas at Dallas
Topic title:
  "Differentiation of Carbon Nanotube and Particulate Matter Contamination on Workplace Surfaces using microProbe Raman Spectroscopy"
  Carbon nanotubes (CNTs) have unique electrical, optical, thermal, and mechanical properties with applications in the electronics, defense, automotive, and aerospace industries.  Driven by these applications, the global production capacity of CNTs is expected to exceed 12,800 metric tons by 2016 (source:  Nanowerk Spotlight, October 2011).  The large-scale synthesis of CNTs generates a fine powder, or soot, and it is this dry soot that causes the greatest concerns with respect to occupational exposure.  Potential workplace contamination by CNT soot comes from a variety of possible sources including the cleaning of CNT reactor ovens, packaging, and end point usage.  A major concern in a research laboratory setting is contamination when the soot is being weighed since this operation can introduce CNTs into the air.  Our group has been refining standard operating protocols (SOPs) for the safe handling and disposal of CNTs, but still, the question remains if this training is effective.  Therefore, the goal of my research project has been to develop a rapid, sensitive, and selective method to sample and test for the presence of CNTs on workplace surfaces where CNT soot has been handled.  Raman spectroscopy was chosen for this endeavor since there are a number of characteristic CNT Raman peaks that can be used to differentiate CNTs from other particulate matter.  Findings and recommendations will be presented following the analysis of an analytical balance workstation where a number of researchers weigh a variety of carbon nanomaterial powders (e.g., CNTs, fullerenes, graphite, graphene, and graphene oxide).  (PDF)
Nov. 28 No TeleSeminar--Holiday Schedule
Dec. 12 No TeleSeminar--Holiday Schedule
Dec. 26 No TeleSeminar--Holiday Schedule

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