Pupil wavefront manipulation for the compensation of mask topography effects in optical nanolithography

As semiconductor optical lithography is pushed to smaller dimensions, resolution enhancement techniques have been required to maintain process yields. For some time, the customization of illumination coherence at the source plane has allowed for the control of diffraction order distribution across the projection lens pupil. Phase shifting at the mask plane has allowed for some phase control as well. However, geometries smaller than the imaging wavelength introduce complex wavefront effects that cannot be corrected at source or mask planes. Three dimensional mask topography effects can cause a pitch dependent defocus (δBF), which can decrease the useable depth of focus (UDOF) across geometry of varying density. Wavefront manipulation at the lens pupil plane becomes necessary to provide the degrees of freedom needed to correct for such effects. The focus of this research is the compensation of such wavefront phase error realized through manipulation of the lens pupil plane, specifically in the form of spherical aberration. The research does not attempt to improve the process window for one particular feature, but rather improve the UDOF in order to make layouts with multiple pitches possible for advanced technology nodes. The research approach adopted in this dissertation includes rigorous simulation, analytical modeling, and experimental measurements. Due to the computational expense of rigorous calculations, a smart genetic algorithm is employed to optimize multiple spherical aberration coefficients. An analytical expression is formulated to predict the best focus shifts due to spherical aberration applied in the lens pupil domain. Rigorously simulated trends of best focus (BF) through pitch and orientation have been replicated by the analytical expression. Experimental validation of compensation using primary and secondary spherical aberration is performed using a high resolution wavefront manipulator. Subwavelength image exposures are performed on four different mask types and three different mask geometries. UDOF limiting δBF is observed on the thin masks for contact holes, and on thick masks for both one directional (1D) and two directional (2D) geometries. For the contact holes, the applied wavefront correction decreases the δBF from 44 nm to 7 nm and increases the UDOF to 109 nm, an 18% improvement. For the 1D geometries on a thick mask, the through pitch UDOF is increased from 59 nm to 108 nm, an 83% improvement. Experimental data also shows that an asymmetric wavefront can be tuned to particular geometries, providing a UDOF improvement for line ends under restricted processing conditions. The experimental data demonstrates that pupil wavefront manipulation has the capability to compensate for mask topography induced δBF. This dissertation recommends that corrective spherical aberration coefficients be used to decrease pitch dependent best focus, increase process yield, and ultimately expand the design domain over parameters such as mask materials and mask feature densities. The effect of spherical aberration applied in the pupil plane is to provide a wavefront solution that is equivalent to complex multiple-level mask compensation methods. This will allow the advantages of thicker masks to be explored for further applications in semiconductor optical lithography

Community Health Workers as Innovators: Methods and Results from a Tele-Education Pilot for Community Health Workers in Detroit, Michigan

Community health workers (CHWs) have played an important role in improving the health of underserved populations in resource-limited settings. CHWs are trusted in communities that they serve, and are often able to see solutions to community problems that outside persons cannot. Solutions need to be low cost and easily accessible, and address the knowledge gaps among CHWs through appropriate training. Utilizing information technology solutions can be key to increasing access to knowledge for these community agents. This paper outlines the methods and results from a pilot study of the Community Health Innovator Program performed in Detroit, Michigan with a group of community health workers in basic grant-writing training, utilizing an information technology platform. The results will be discussed as a larger response to growing issues in global health and how such platforms can be used and adapted in response to ever-evolving global health challenges

Mothers construct fathers: Destabilized patriarchy in La Leche League

This paper examines changing masculine ideals from the point of view of women homemakers through a case study of La Leche League, a maternalist organization dedicated to breastfeeding and mother primacy. We suggest two reasons for studying the League: first, an emerging literature suggests that changing norms are seeping into many such seemingly conservative groups, and second, the League continues to be highly successful among white, middle-class, married women. The paper looks at two aspects of masculinity, examining changes in the League through fieldwork, interviews, and content analysis, and finds that new norms of increased father involvement and decreased rights over women's bodies have both influenced League philosophy. We conclude that while in some respects a measure of the decline of men's patriarchal privileges, the League's changes also may contribute to a “restabilization” of male dominance in a modified, partial form.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43548/1/11133_2004_Article_BF00990071.pd

Creation of a Chloroplast Microsatellite Reporter for Detection of Replication Slippage in Chlamydomonas reinhardtii▿

Microsatellites are composed of short tandem direct repeats; deletions or duplications of those repeats through the process of replication slippage result in microsatellite instability relative to other genomic loci. Variation in repeat number occurs so frequently that microsatellites can be used for genotyping and forensic analysis. However, an accurate assessment of the rates of change can be difficult because the presence of many repeats makes it difficult to determine whether changes have occurred through single or multiple events. The current study was undertaken to experimentally assess the rates of replication slippage that occur in vivo in the chloroplast DNA of Chlamydomonas reinhardtii. A reporter construct was created in which a stretch of AAAG repeats was inserted into a functional gene to allow changes to be observed when they occurred at the synthetic microsatellite. Restoration of the reading frame occurred through replication slippage in 15 of every million viable cells. Since only one-third of the potential insertion/deletion events would restore the reading frame, the frequency of change could be deduced to be 4.5 × 10−5. Analysis of the slippage events showed that template slippage was the primary event, resulting in deletions rather than duplications. These findings contrasted with events observed in Escherichia coli during maintenance of the plasmid, where duplications were the rule

California condor poisoned by lead, not copper, when both are ingested: A case study

Abstract Lead poisoning from feeding on carcasses shot with lead‐based ammunition is a well‐known threat to wildlife. Thus, nonlead (e.g., copper‐based) ammunition is promoted as a safe alternative. We present a unique situation of a male California condor (Gymnogyps californianus) discovered with both a lead fragment and a copper bullet in his digestive tract simultaneously. We show that ingestion of a copper bullet did not result in elevated blood copper concentrations, while ingestion of a lead fragment contributed to lead toxicity. Our findings can inform nonlead ammunition outreach efforts by demonstrating that ingestion of a copper‐based bullet did not result in the poisoning of a California condor