William P. Ballard

Comprehensive approach for diagnosing intense single‐pulse microwave sources

A comprehensive approach to developing intense pulse microwave diagnostics for measuring the performance of a high‐power microwave source is presented. Both conventional and new diagnostic techniques were used. Hence all measurements were made in a redundant fashion allowing small error bars in the measured data. The output power was diagnosed using four methods: two transmitting–receiving systems, two circular waveguide directional couplers, calorimetry, and gaseous breakdown. The operating frequency was measured using three methods: bandpass filters, a heterodyne receiver, and a homodyne receiver. The diagnostics were evaluated by using a 12‐vane S‐band inverted relativistic magnetron operating at 1 MV, 0.31 T, and 5 kA which reliably produced 3.15‐GHz microwaves at powers of approximately 100 MW for pulse lengths variable from 5 to 70 ns. The microwave power pulse had a rise time of approximately 2 ns.

Ku‐band radiation produced by a relativistic backward wave oscillator

Reported in this paper are the results of an experiment to produce high‐power Ku‐band (12–18 GHz) microwave radiation from a backward wave oscillator (BWO) driven by a relativistic electron beam. Experimentally measured output power was about 250 MW at 12.5 GHz and 100 MW at 14 GHz. A description of the slow wave structure is given along with theoretical predictions of the vacuum waveguide dispersion relations. The diagnostics to determine the frequency and power of the device are described. Finally, comparisons between the experimentally measured frequency and power, and the analytic and numerical simulations of the BWO are made.

Initial results from the EUV engineering test stand

The Engineering Test Stand (ETS) is an EUV lithography tool designed to demonstrate full-field EUV imaging and provide data required to accelerate production-tool development. Early lithographic results and progress on continuing functional upgrades are presented and discussed. In the ETS a source of 13.4 nm radiation is provided by a laser plasma source in which a Nd:YAG laser beam is focused onto a xenon- cluster target. A condenser system, comprised of multilayer-coated and grazing incidence mirrors, collects the EUV radiation and directs it onto a reflecting reticle. The resulting EUV illumination at the reticle and pupil has been measured and meets requirements for acquisition of first images. Tool setup experiments have been completed using a developmental projection system with (lambda) /14 wavefront error (WFE), while the assembly and alignment of the final projection system with (lambda) /24 WFE progresses in parallel. These experiments included identification of best focus at the central field point and characterization of imaging performance in static imaging mode. A small amount of astigmatism was observed and corrected in situ, as is routinely done in advanced optical lithographic tools. Pitch and roll corrections were made to achieve focus throughout the arc-shaped field of view. Scan parameters were identified by printing dense features with varying amounts of magnification and skew correction. Through-focus scanned imaging results, showing 100 nm isolated and dense features, will be presented. Phase 2 implementation goals for the ETS will also be discussed.

Calorimetric measurements of single‐pulse high‐power microwaves in oversized waveguides

A method for measuring the peak power of a single microwave pulse in an oversized circular waveguide is presented. This measurement technique uses a new circular waveguide calorimeter to measure the total energy of the microwave pulse. The peak power is determined from the total energy and by measuring the pulse shape with a fast diode detector connected to a circular waveguide directional coupler. Measurements have been made at 3.15 GHz for power levels up to 200 MW. Pulse widths were varied between 5 and 50 ns giving pulse energies between 1 and 10 J.

New Directional Couplers for Multimode Circujlar Waveguides Applied to Intense Pulsed Microwave Systems

Three new types of directional couplers are described for use in overmoded circular waveguide operating in the TM0 1 mode. The types are (1) circular/rectangular waveguide multihole couplers, (2) circular waveguide/coaxial multihole couplers, and (3) circular waveguide loop couplers. These directional couplers are designed to diagnose intense pulsed microwave systems in the frequency range 3 - 18 GHz. Coupling coefficients vary between 50 dB and 70 dB with directivities between 13 dB and 20 dB. These devices have been used to measure the output powers of relativistic magnetrons and backward wave oscillators (BWOs) in the power range 100 MW to 300 MW.

An electro‐optical technique for intense microwave measurements

An electro‐optical technique has been developed to measure high‐frequency electric fields in free space. Electrically induced birefringence in an electro‐optical crystal is used to modulate a linearly polarized continuous‐wave laser beam. The modulation impressed on the laser beam contains both frequency and field intensity information. A way to use this technique as both a frequency and power meter is discussed. A proof‐of‐principle experiment has been carried out with a 3.1‐GHz magnetron source.

Lithographic characterization of improved projection optics in the EUVL engineering test stand

Static and scanned images of 100nm dense features for a developmental set of l/14 optics (projection optics box # 1, POB 1) in the Engineering Test Stand (ETS) were successfully obtained with various LPP source powers last year. The ETS with POB1 has been used to understand initial system performance and lithographic learning. Since then, numerous system upgrades have been made to improve ETS lithographic performance to meet or exceed the original design objectives. The most important upgrade is the replacement of POB 1 with an improved projection optics system, POB2, having lower figure error (l/20 rms wavefront error) and lower flare. Both projection optics boxes are a four-mirror design with a 0.1 numerical aperture. Scanned 70-nm dense features have been successfully printed using POB2. Aerial image contrast measurements have been made using the resist clearing method. The results are in good agreement to previous POB2 aerial image contrast measurements at the subfield exposure station (SES) at Lawrence Berkeley National Laboratory. For small features the results deviate from the modeling predictions due to the inherent resolution limit of the resist. The intrinsic flare of POB2 was also characterized. The experimental results were in excellent agreement with modeling predictions. As predicted, the flare in POB2 is less than 20% for 2μm features, which is two times lower than the flare in POB1. EUV flare is much easier to compensate for than its DUV counterpart due to its greater degree of uniformity and predictability. The lithographic learning obtained from the ETS will be used in the development of EUV High Volume Manufacturing tools. This paper describes the ETS tool ETS tool setup, both static and scanned, that was required after the installation of POB2. The paper will also describe the lithographic characterization of POB2 in the ETS and cmpare those results to the lithographic results obtained last year with POB1.

System and process learning in a full-field, high-power EUVL alpha tool

Full-field imaging with a developmental projection optic box (POB 1) was successfully demonstrated in the alpha tool Engineering Test Stand (ETS) last year. Since then, numerous improvements, including laser power for the laser-produced plasma (LPP) source, stages, sensors, and control system have been made. The LPP has been upgraded from the 40 W LPP cluster jet source used for initial demonstration of full-field imaging to a high-power (1500 W) LPP source with a liquid Xe spray jet. Scanned lithography at various laser drive powers of >500 W has been demonstrated with virtually identical lithographic performance.

Performance upgrades in the EUV Engineering Test Stand

The EUV Engineering Test Stand (ETS) has demonstrated the printing of 100-nm-resolution scanned images. This milestone was first achieved while the ETS operated in an initial configuration using a low power laser and a developmental projection system, PO Box 1. The drive laser has ben upgraded to a single chain of the three-chain Nd:YAG laser developed by TRW. The result in exposure time is approximately 4 seconds for static exposures. One hundred nanometer dense features have been printed in step-and-scan operation with the same image quality obtained in static printing. These experiments are the first steps toward achieving operation using all three laser chains for a total drive laser power of 1500 watts. In a second major upgrade the developmental wafer stage platen, used to demonstrate initial full-field imaging, has been replaced with the final low-expansion platen made of Zerodur. Additional improvements in the hardware and control software have demonstrated combined x and jitter from 2 to 4 nm RMS Over most of the wafer stage travel range, while scanning at the design scan speed of 10 mm/s at the wafer. This value, less than half of the originally specified jitter, provides sufficient stability to support printing of 70 nm features as planned, when the upgraded projection system is installed. The third major upgrade will replace PO Box 1 with an improved projection system, PO Box 2, having lower figure error and lower flare. In addition to these upgrades, dose sensors at the reticle and wafer planes and an EUV- sensitive aerial image monitor have been integrated into the ETS. This paper reports on ETS system upgrades and the impact on system performance.

Rectangular waveguide calorimeter for single intense microwave pulses

A new calorimeter for single intense microwave pulses has been designed and tested. The device was constructed in WR284 rectangular waveguide and was operated at frequencies from 2.5 to 4.3 GHz with a tunable instantaneous bandwidth of approximately 500 MHz. The calorimeter used a single thermistor to measure the energy deposited on a carbon absorber having a microwave power absorbance of 90%. The calorimeter was tested at power levels from 100 to 1000 MW for pulse lengths of 12–6 ns, respectively. The sensitivity of the device was 200–300 mV/J.