Kevin D. Krenz

High-power extreme ultraviolet source based on gas jets

We report on the development of a high-power laser plasma extreme UV (EUV) source for EUV. The source is based on the plasma emission of a recycled jet beam of large Xe clusters and produces no particular debris. The source will be driven by a pulsed laser delivering 1500 W of focused average power to the cluster jet target. To develop condensers and to optimize source performance, a low-power laboratory cluster jet prototype has been used to study the spectroscopy, angular distributions, and EUV source images of the cluster jet plasma emission. In addition, methods to improve the reflectance lifetimes of nearby plasma-facing condenser mirrors have been developed. The resulting source yields EUV conversion efficiencies up to 3.8 percent and mirror lifetimes of approximately 109 plasma pulses, with further improvement anticipated.

Results With the Neutron Scatter Camera

We describe the design, calibration, and measurements made with the neutron scatter camera. Neutron scatter camera design allows for the determination of the direction and energy of incident neutrons by measuring the position, recoil energy, and time-of-flight (TOF) between elastic scatters in two liquid scintillator cells. The detector response and sensitive energy range (0.5-10 MeV) has been determined by detailed calibrations using a 252Cf neutron source over its field of view (FOV). We present results from several recent deployments. In a laboratory study we detected a 252Cf neutron source at a stand off distance of 30 m. A hidden neutron source was detected inside a large ocean tanker. We measured the integral flux density, differential energy distribution and angular distribution of cosmic neutron background in the fission energy range 0.5-10 MeV at Alameda, CA (sea level), Livermore, CA (174 m), Albuquerque, NM (1615 m) and Fenton Hill, NM (2630 m). The neutron backgrounds are relatively low, and non-isotropic. The camera has been ruggedized, deployed to various locations and has performed various measurements successfully. Our results show fast neutron imaging could be a useful tool for the detection of special nuclear material (SNM).

Scale-up of a cluster jet laser plasma source for extreme ultraviolet lithography

A high-average-power extreme UV (EUV) source based on a laser plasma cluster jet is being developed for EUV lithography. The source employs a cooled supersonic nozzle expansion to produce a dense beam of Xe clusters as the plasma source target. The cluster beam is irradiated with a pulsed laser to create a high-temperature plasma radiating efficiently in the EUV spectral region. To accommodate drive laser repetition rates of up to 6000 Hz, a continuous jet expansion with full Xe gas recycling is employed, rather than earlier pulsed jet expansions. The continuous jet employs an efficient high-throughput pumping scheme to minimize the ambient pressure highly-attenuating Xe gas. Source power scale-up is achieved by increasing laser repetition rate, keeping laser pulse parameters nominally fixed. In the first phase of EUV power scale-up, the continuous cluster jet source has been integrated with a 200 W laser driver operating at repetition rates up to 500 Hz. With this system, a laser-to-EUV conversion efficiency of 0.69 percent is achieved. In the second phase, the jet is being integrated with a 1700 W diode-pumped solid sate laser driver operating at repetition rates up to 6000 Hz. A brief description of the 1700 W laser system and its integration with the continuous cluster jet are discussed.

Results with the neutron scatter camera

We present results from recent deployments with the neutron scatter camera. We successfully detected and pinpointed a hidden 252Cf neutron source in a large ocean tanker at Alameda, CA. In a lab study we detected a 252Cf neutron source at a stand off distance of about 100 ft. We measured the integral flux, differential flux and angular distribution of cosmic neutron background in the fission energy range 0.5–10MeV at Alameda, CA (sea level), Livermore, CA (570 ft), Albuquerque, NM (5300 ft) and Fenton Hill, NM (8630 ft). The neutron backgrounds are relatively low, uniform and well understood. We recently increased the camera effective area 3x. The camera has been successfully ruggedized, deployed to various locations and has performed various measurements. Our results are encouraging and suggest fast neutron imaging could be a useful tool for the detection of special nuclear material (SNM).

Development of a Neutron Scatter Camera for Fission Neutrons

Special nuclear material (SNM) emits high energy radiation during active and passive interrogation. This radiation can be imaged thus allowing visualization of shielded and/or smuggled SNM. Although gamma-ray imaging is appropriate for many cases, neutrons are much more penetrating through hi-Z materials, and are thus preferred in certain scenarios (e.g. weapons grade Pu or HEU smuggled inside a lead pig several inches thick). Techniques for thermal neutron imaging have already been developed, but these approaches only image the moderating material, not the true SNM source. Traditional neutron detectors such as He3 tubes and scintillators simply count neutrons. We are developing an instrument that will directly image the fast fission neutrons from an SNM source using a neutron scatter camera. This technique has been shown to be 10 times more sensitive for solar neutrons over traditional neutron counting techniques. In addition to being a 4pi neutron imager, this instrument will also be an excellent neutron spectrometer, and will be able to differentiate between different types of neutron sources (e.g. fission, gamma-n, cosmic ray, and dd or dt fusion). Our instrument will be able to pinpoint the source location. We will present results from a prototype detector and discuss key parameters that determine detector performance.

Advances in imaging fission neutrons with a neutron scatter camera

Special nuclear material (SNM) emits high energy radiation during active and passive interrogation. This radiation can be imaged thus allowing visualization of shielded and/or smuggled SNM. Lower backgrounds and higher penetration through hi-Z materials make neutrons the preferred detectable in many scenarios. We have developed a neutron scatter camera that directly images fast fission neutrons from SNM sources while simultaneously measuring energy spectra. We have made many significant advances in the design and implementation of such instruments leading to an over 30 fold improvement in sensitivity. We will present results from our detector including analysis techniques that we have developed for neutron imaging and particle discrimination techniques. We will discuss camera calibration and performance under realistic threat detection scenarios, and future prospects in this field.

High-power source and illumination system for extreme ultraviolet lithography

A clean, high-power Extreme Ultraviolet (EUV) light source is being developed for Extreme Ultraviolet Lithography (EUVL). The source is based on a continuous jet of condensable gas irradiated with a diode-pumped solid state laser producing a time-averaged output power of 1700 W at 5000 - 6000 Hz. An illumination system is being assembled to collect and deliver the EUV output from the source and deliver it to a reticle and projection optics box to achieve an EUV exposure rate equivalent to ten 300-mm wafers per hour.

Printability of substrate and absorber defects on extreme ultraviolet lithographic masks

Extreme ultraviolet lithography (EUVL) is a candidate for high‐volume production of integrated circuits with 0.1 μm design rules. As a reduction imaging technique with robust mask substrates, EUVL reduces the mask contribution to the critical dimension (CD) error budget. However, the ability to manufacture EUVL mask blanks that are free of printable defects remains an important challenge. Electromagnetic simulations and imaging experiments have suggested that defects in the substrates and reflective coatings, in particular, may be highly printable and difficult to detect. A defect printability study using programmed defects was performed in order to determine the printing behavior of mask defects of different sizes and locations with respect to absorber features. Imaging was performed using a 10× Schwarzschild camera operating at 13.4 nm with a numerical aperture of 0.08, corresponding to a Rayleigh resolution of 0.1 μm. This system has an effective exposure field of 0.4 mm diam. Measurements of the defec...

Recent advances in the Sandia EUV 10x microstepper

The Sandia EUV 10x microstepper system is the result of an evolutionary development process, starting with a simple 20x system, progressing through an earlier 10x system, to the current system that has full microstepper capabilities. The 10x microstepper prints 400-micrometers -diameter fields at sub- 0.10-micrometers resolution. Upgrades include the replacement of the copper wire target with a pulsed xenon jet target, construction of an improved projection optics system, the addition of a dose monitor a d an aerial image monitor, and the addition of a graphical user interface to the system operation software. This paper provides an up-to-date report on the status of the microstepper.

Mass-producible microscopic computer-generated holograms: microtags

We have developed a method for encoding phase and amplitude in microscopic computer-generated holograms (microtags) for security applications. An 8 x 8 cell phase-only and an 8 x 8 cell phase-and-amplitude microtag design has been exposed in photoresist by the extreme-ultraviolet (13.4-nm) lithography tool developed at Sandia National Laboratories. Each microtag measures 80 microm x 160 microm and contains features that are 0.2 microm wide. Fraunhofer zone diffraction patterns can be obtained from fabricated microtags without any intervening optics and compare favorably with predicted diffraction patterns.