Theodore G. Van Kessel

Use of scatterometric latent-image detector in closed-loop feedback control of linewidth

The use of a diffraction-based latent image detector during the post-exposure bake (PEB) step for a chemically amplified resist system was investigated and its use in a feedback control strategy was examined. A calibration between intensity of light diffracted from the wafers during PEB and the final post-develop linewidth was determined. Using this relationship, two feedback control strategies were tested. One method altered the PEB time to compensate for unmeasured process disturbances and drive the linewidth to its target. The other method involved altering of the develop time. We found that using the post-exposure bake monitor in a feedback control system can improve wafer-to-wafer and lot-to-lot variability to below that which has been possible through conventional SEM measurements.

Postexposure bake as a process-control parameter for chemically amplified photoresist

A new method is described for the real-time in-line control of critical dimensions for positive- tone chemically amplified resist systems. The technique relies on the generation of a diffraction grating in the resist film when a latent image appears during the post-exposure bake. A simple optical illumination/collection arrangement allows the diffracted signal to be measured during the post-exposure bake. This signal can be correlated to linewidths when measured by a non-destructive SEM. The result is a post-exposure bake time that can be used to correct for exposure-and-bake temperature variations to conveniently provide overall process control. Results generated by a prototype system are presented for a variety of 0.5- micrometers mask levels and process conditions.

Comparison of Experimental Temperature Results With Numerical Modeling Predictions of a Real-World Compact Data Center Facility

In this paper we address the high level of validation of commercially available numerical predictive tools, namely CFD models, for data center applications. Experimental data at a real world facility is compared with computational results. Specifically, a recently developed temperature measurement tool is used to capture three dimensional temperature profiles of the facility with very fine spatial granularity. These detailed contours based on actual measurements reveal hot air recirculation patterns in the room as well as variable utilization levels of the room air-conditioning units. We compare these experimental temperature distributions measured using a novel 3D mapping tool with CFD thermal modeling results. An algorithm for generating CFD models for real world systems is proposed and demonstrated. It is found that due to the extensive inaccuracies in rapidly gathered input data as well as inherent limitations of the model, there can be significant discrepancies between predicted and actual temperatures. In addition to steady state measurements, transient data was also collected and are presented. Knowledge of the transient temperature profiles at different parts of the room allows an estimation of the temporal behavior of the data center. Transient temperature fluctuations are presented which capture the real variations in the system boundary conditions, for example the temperature of the chilled water to the air conditioning units, or the power dissipation of the servers over time.Copyright

High-Concentration Photovoltaics—Effect of Inhomogeneous Spectral Irradiation

At high solar concentration, subtle optical and electrical effects in combination can have a substantial impact on photovoltaic power (PV) generation. We have identified such an effect through its clear signature: a “ripple” in the output current with respect to the pointing angle of the concentrated PV (CPV) system to sun direction. At small angular misalignment, this effect can lower cell current by as much as 15% at 1600x concentration in full sun. At medium concentration between 500 and 1000x, while not as clearly visible in single cells, the effect also reduces output by a smaller amount. The disappearance of the “ripple” signature at low concentrations below 300x indicates that the effect is not a linear effect, such as a light loss. We attribute the pronounced angular sensitivity of power output at high concentrations to a combination of inhomogeneous spectral irradiation incident on the multijunction solar cell and of the impact of the finite lateral resistance of the cell.

Exploring the limits of concentration for UHCPV

Practical multi receiver ultra high (1000+ Suns) concentration photovoltaic (UHCPV) systems experience large radiation, thermal and electrical loads in addition to large power density transients under routine operation. This report is a summary of the issues involved in determining the practical limits to concentration. How high is too high? Explorations into UHCPV have both theoretical and experimental aspects. Understanding the theoretical device physics and circuit limitations is often essential to determining which experiments to do and in interpreting results. On the experimental side the work can be divided into two fields depending on the type of light source. The first is artificial or simulated sources and the second is working in the field with direct solar irradiation. Both fields have advantages and disadvantages. Direct solar radiation was selected for the current experiments due to the low cost and ability to produce ultra high concentrations (4000+) over relatively large areas (25+ mm2). Several experimental examples from these direct solar measurements shed light on some of the basic theories of how concentrated light affects the performance of multi junction photovoltaic cells. Out of these examples and theoretical foundations we conclude that for practical devices the first order constraint to optimum efficiency at ultra high concentrations is the series resistance. We also present a simple model based on published data and our results that can be used to predict the total system series resistance needed to optimize a system for a particular concentration.

Multi receiver concentrator photovoltaic testing at extreme concentrations

Practical multi receiver concentrator photovoltaic systems operating at high solar concentration levels up to 2000 suns experience large radiation, thermal and electrical loads in addition to large power density transients under routine operation. These systems require efficient cooling to manage the associated incident power densities between 100 to 200 W/cm2. Photovoltaic cells and thermal interface materials experience considerable stress under these load conditions. Their assembly is sensitive to contamination and process optimization. Efficient optical coupling of light at high concentration requires precise component alignment and tracking. We will discuss high power testing of single and multi receiver, high concentration systems comprising commercial triple junction cells, Fresnel optics, electric actuators, and cooled through a metal thermal interface using active and passive cooling methods.

Concentrator photovoltaic reliability testing at extreme concentrations up to 2000 suns

Practical concentrator photovoltaic systems operating at high solar concentration levels up to 2000 suns experience large thermal and electrical loads in addition to large power density transients under routine operation. These systems require efficient cooling systems to manage the associated incident power densities up to 200 W/cm2. Photovoltaic cells and thermal interface materials experience considerable stress under these load conditions. Reliability data is sparse for operation above 500 suns. We present high power test results for a commercial triple junction cell cooled through a high performance metal thermal interface using active liquid cooling methods for power densities up to 200 W/cm2.

Extending photovoltaic operation beyond 2000 suns using a liquid metal thermal interface with passive cooling

Photovoltaic systems operating at solar concentration levels in excess of 500 suns require efficient cooling systems to manage the associated high incident power densities above 50 W/cm2. We present results for a liquid metal thermal interface with a 2–5 mm2C/W thermal resistance used in conjunction with a 1 cm2 commercial triple junction concentrator cell to produce up to 75 W of electrical power. We show that the liquid metal interface can be used to extend the limits of passive cooling relative to polymer thermal interface materials for solar photovoltaic concentrator systems. We will discuss the operation of triple junction photovoltaic cells above the 2000 sun level employing the liquid metal thermal interface and passive cooling.

A testing platform for on-drone computation

This paper describes the development of a test bed for an on-drone computation system, in which the drone plays the game of ping-pong competitively (YCCD: The Yorktown Cognitive Competition Drone). Unlike other drone systems and demonstrators YCCD will be completely autonomous with no external support from cameras, servers, GPS etc. YCCD will have ultra-low power computation capabilities including on-drone real-time processing for vision and localization (non-GPS based). Architectural design and processing algorithms of the system are discussed in detail.

Localization and quantification of trace-gas fugitive emissions using a portable optical spectrometer

We present a portable optical spectrometer for fugitive emissions monitoring of methane (CH4). The sensor operation is based on tunable diode laser absorption spectroscopy (TDLAS), using a 5 cm open path design, and targets the 2ν3 R(4) CH4 transition at 6057.1 cm-1 (1651 nm) to avoid cross-talk with common interfering atmospheric constituents. Sensitivity analysis indicates a normalized precision of 2.0 ppmv·Hz-1/2, corresponding to a noise-equivalent absorbance (NEA) of 4.4×10-6 Hz-1/2 and minimum detectible absorption (MDA) coefficient of αmin = 8.8×10-7 cm-1·Hz-1/2. Our TDLAS sensor is deployed at the Methane Emissions Technology Evaluation Center (METEC) at Colorado State University (CSU) for initial demonstration of single-sensor based source localization and quantification of CH4 fugitive emissions. The TDLAS sensor is concurrently deployed with a customized chemi-resistive metal-oxide (MOX) sensor for accuracy benchmarking, demonstrating good visual correlation of the concentration time-series. Initial angle-ofarrival (AOA) results will be shown, and development towards source magnitude estimation will be described.