Printing of Contact Holes for the 45nm Generation using Immersion Interference Lithography

Interference lithography is a valuable tool for evaluating photoresist performance at the resolutions unattainable with conventional exposure tools. interference lithography is most commonly used to generate one dimensional patterns such as lines and spaces. however two dimensional patterns are of much greater interest to both the resist developers and the device manufacturers in microlithography. This paper presents a technique to produce two dimensional images of contact holes at the resolution of 45nm half pitch. To our knowledge this is the highest resolution contacts printed to date using 193nm radiation. Photoresist patterns with a half-pitch of 45 nm were formed with an effective NA of 1.05 utilizing the JUT Immersion Interference system [4]. The wafer was subsequently rotated and the same pattern was printed at an angle relative to the original pattern. This double exposure technique allowed the formation of the two dimensional features. The images formed were processed, and the scanning electron micrograph (SEM) images and analysis of the data will be presented

Development and Characterization of a GaAs nipi Superlattice Solar Cell

The development of photovoltaics as an energy source has been propelled by numerous technological advancements over the past 60 years to now enable the conversion of sunlight into power at an efficiency of 46%. This enables power production that is cleaner, and more transferrable to locations off the grid than ever before, however new technologies are required to further increase efficiency while driving down costs. Currently a large effort is being made to achieve intermediate band solar cells (IBSC) that more efficiently convert energy from the entire solar spectrum. This is enabled through multiple techniques, including quantum dots (QDs), and potentially through doping superlattice solar cells. Doping superlattices have been explored theoretically and some historic work has used these superlattices to form nipi solar cells with alternating n-type, intrinsic, p-type, intrinsic layers. Multiple purposes exist for evaluating nipi solar cells, which include radiation hardness, an electronically adjustable absorption edge, use with nanostructures, and the possibility of an IBSC. The primary motivation for this work is to develop the nipi solar cell for evaluation as an IBSC, while also evaluating the radiation tolerance of the design for potential use in space applications. This has been completed through a theoretical and experimental analysis of nipi superlattice layers, and an extensive evaluation of the fabrication and growth processes required to achieve a high efficiency solar cell. Additionally an improved model for nipi diodes and solar cells has been developed. Also a novel process for fabricating nipi solar cells through epitaxial regrowth and diffused junctions has been developed, where record efficiencies for nipi solar cells have been measured for devices fabricated via epitaxial regrowth at 12.5%. An understanding of the effect of adding QD into a nipi superlattice has been obtained. Finally a greater understanding of the intrinsic radiation hardness of the nipi design has been achieved and possible methods to improve it have been evaluated. The techniques and processes developed here have the possibility to be used to further the understanding of nipi devices, and lead to the potential development of an IBSC with a QD-nipi design

25nm Immersion Lithography at a 193nm Wavelength

The physical limitations of lithographic imaging are ultimately imposed by the refractive indices of the materials involved. At oblique collection angles, the numerical aperture of an optical system is determined by nsin(theta) , where n is the lowest material refractive index (in the absence of any refractive power through curvature). For 193nm water immersion lithography, the fluid is the limiting material, with a refractive index of near 1.44, followed by the lens material (if planar) with a refractive index near 1.56, and the photoresist, with a refractive index near 1.75. A critical goal for immersion imaging improvement is to first increase the refractive indices of the weakest link, namely the fluid or the lens material. This paper will present an approach to immersion lithography that will allow for the exploration into the extreme limits of immersion lithography by eliminating the fluid altogether. By using a solid immersion lithography (SIL) approach, we have developed a method to contact the last element of an imaging system directly to the photoresist. Furthermore, by fabricating this last element as an aluminum oxide (sapphire) prism, we can increase its refractive index to a value near 1.92. The photoresist becomes the material with the lowest refractive index and imaging becomes possible down to 28nm for a resist index of 1.75 (and 25nm for a photoresist with a refractive index of 1.93). Imaging is based on two-beam Talbot interference of a phase grating mask, illuminated with highly polarized 193nm ArF radiation. Additionally, a roadmap is presented to show the possible extension of 193nm lithography to the year 2020

Effects of Beam Pointing Instability on Two-Beam Interferometric Lithography

In a photolithographic system, the mask patterns are imaged through a set of lenses on a resist-coated wafer. The image of mask patterns physically can be viewed as the interference of the plane waves of the diffraction spectrum captured by the lens set incident on the wafer plane at a spectrum of angles. Two-beam interference fringe is the simplest format of the image. Consequently, two-beam interferometric lithography is often employed for photolithographic researches. For two-beam interferometric lithography, beam pointing instability of the illumination source can induce fringe displacement, which results in a loss of fringe contrast if it happens during the exposure. Since some extent of beam pointing instability is not avoidable, it is necessary to investigate its effects on the contrast of the interference fringe. In this paper, the effects of beam pointing instability associated with a two beam interferometric lithography setup are analyzed. Using geometrical ray tracing technique and basic interference theory, the relationship between the beam tilt angle and interference fringe displacement is established. For a beam pointing instability with random distribution, the resulted fringe contrast is directly proportional to the Fourier transform of the pointing distribution evaluated at 1/2(pi). The effect of a pointing instability with normal distribution on interference contrast is numerically investigated

Experimental Measurement of Photoresist Modulation Curves

An approach to measurement of resist CD response to image modulation and dose is presented. An empirical model with just three terms is used to describe this response, allowing for direct calculation of photoresist modulation curves. A thresholded latent image response model has been tested to describe CD response for both 90 nm and 45 nm geometry. An assumption of a linear optical image to photoresist latent image correlation is shown as adequate for the 90 nm case, while the 45 nm case demonstrates significant non-linear behavior. This failure indicates the inadequacy of a “resist blur” as a complete descriptive function and uncovers the need for an additional spread function in OPE-style resist models

Resist Process Window Characterization for the 45-nm Node Using an Interferometric Immersion microstepper

Projection and interference imaging modalities for application to IC microlithography were compared at the 90 nm imaging node. The basis for comparison included simulated two-dimensional image in resist, simulated resist linesize, as well as experimental resist linesize response through a wide range of dose and focus values. Using resist CD as the main response (both in simulation and experimental comparisons), the two imaging modes were found nearly equivalent, as long as a suitable Focus-Modulation conversion is used. A Focus-Modulation lookup table was generated for the 45 nm imaging node, and experimental resist response was measured using an interferometric tool. A process window was constructed to match a hypothetical projection tool, with an estimated error of prediction of 0.6 nm. A demodulated interferometric imaging technique was determined to be a viable method for experimental measurement of process window data. As long as accurate assumptions can be made about the optical performance of such projection tools, the response of photoresist to the delivered image can be studied experimentally using the demodulated interferometric imaging approach

CENTRIFUGAL LABTUBE FOR FULLY AUTOMATED DNA EXTRACTION & LAMP AMPLIFICATION BASED ON AN INTEGRATED, LOW-COST HEATING SYSTEM

In this paper, we introduce a disposable battery-driven heating system for loop-mediated isothermal DNA amplification (LAMP) inside a centrifugally-driven DNA-extraction platform (LabTube). We demonstrate fully automated, fully closed extraction of as little as 100 DNA copies of verotoxin-producing (VTEC) Escherichia coli lysate in water, milk and apple juice in a standard laboratory centrifuge, followed by subsequent automatic LAMP amplification with an overall time-to-result of 1.5hrs. The system is disposable, fully closed and automated, requiring only a single pipetting step. The microcontroller-driven heating system is low-cost (<1$) and it can be easily parallelized. Because the heated LabSystem runs within a standard laboratory centrifuge, it is suitable for DNA extraction and amplification in low-resource areas, at production sites or sales locations

An Empirical Assessment of Corporate Environmental Crime-Control Strategies

Corporate illegality is often attributed to greed by corporate managers and insufficient legal safeguards. Underlying this argument is an explicit critique of corporate crime regulatory systems. Yet there is little systematic investigation of the relative merits of different types or components of crime-control strategies; research comparing more punitive command-and-control strategies with self-regulatory approaches is particularly lacking. In this Article, we assess these crime prevention-and-control mechanisms in the context of individual and situational risk factors that may increase the likelihood of illegal behavior in the environmental arena. We use data drawn from two groups of business managers who participated in a factorial survey (using vignettes) measuring their intentions to participate in two types of environmental offenses. Generally, results show that the most effective regulatory levers are (1) credible legal sanctions and (2) the certainty and severity of informal discovery by significant others in the firm. We conclude by discussing the implications of our findings for regulatory policy and strategy, and for efforts to account for the role of social norms in corporate environmental compliance

GaSb on GaAs interfacial misfit solar cells

The GaAs/GaSb interface misfit design can achieve comparable efficiency to conventional inverted metamorphic multijunction cells at up to 30% cost reduction. In this pre-liminary work, GaSb single junctions were grown via molecular beam epitaxy on both GaSb and GaAs substrates to compare and fine tune the interfacial misfit growth process. Current vs voltage results show that the best homo-epitaxial cell achieved 5.2% under 35-sun concentration. TEM did not reveal any threading dislocations in the hetero-epitaxial cells, however, device results indicated higher non-radiative recombination than expected, likely due to unpassivated surface states. Improvements to cell processing will be explored and more characterization is planned to determine the cause of degraded hetero-epitaxial cell performance

Longitudinal Effects of a 2-Year Meditation and Buddhism Program on Well-being, Quality of Life, and Valued Living

Objectives: Most research on mindfulness and meditation has focused on structured therapeutic interventions, such as mindfulness-based stress reduction, or meditation retreats. Such programs have received moderate empirical support for improving psychological outcomes in clinical and nonclinical populations, but there remains a paucity of research on intensive or long-term mindfulness or meditation programs for experienced practitioners, especially those that incorporate Buddhist teachings. The purpose of the current study was to investigate the effects of a long-term integrated mindfulness/meditation and Buddhism program, Dharma in Daily Life (DIDL). Methods: Well-being, quality of life, valued living, and theorized processes of change were measured using a naturalistic, quasi-experimental design over the course of the 2-year program and 6-month follow-up. Participants included 17 individuals enrolled in the program and 14 individuals recruited from community meditation groups. Results: Participation in the program predicted increases in subjective well-being and mindfulness over time compared to the control group. Regardless of condition, frequency of meditation predicted lower psychological inflexibility and higher mindfulness, well-being, and progress toward values. Length of meditation session predicted a greater ability to observe experience, and prior meditation experience predicted greater non-reactivity to experience. Conclusions: Although preliminary, results suggest that participation in a long-term integrated mindfulness/meditation and Buddhism program may positively impact mindfulness and general well-being. Frequency of meditation sessions appears to be a particularly important variable. These findings warrant further investigation of such programs and practice parameters, as well as how each may affect key outcomes