Transmission measurements of niobium and zirconium at both extreme-ultraviolet (EUV) and ultraviolet, visible, and near infrared (UV/Vis/NIR) wavelengths are presented. Thin foils of various thicknesses mounted on nickel mesh substrates were measured, and these data were used to calculate the optical constants delta and beta of the complex refractive index n = 1- δ + iβ. β values were calculated directly from the measured transmittance of the foils after normalizing for the nickel mesh. The average beta values for each set of foils are presented as a function of wavelength. The real (dispersive) part of the refractive index, delta was then calculated from Kramers-Kronig analysis by combining these beta values with those from previous experimental data and the atomic tables.
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.
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.
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.
Static and scanned images of 100 nm dense features were successfully obtained with a developmental set of projection optics and a 500W drive laser laser-produced-plasma (LPP) source in the Engineering Test Stand (ETS). The ETS, configured with POB1, has been used to understand system performance and acquire lithographic learning which will be used in the development of EUV high volume manufacturing tools. The printed static images for dense features below 100 nm with the improved LPP source are comparable to those obtained with the low power LPP source, while the exposure time was decreased by more than 30x. Image quality comparisons between the static and scanned images with the improved LPP source are also presented. Lithographic evaluation of the ETS includes flare and contrast measurements. By using a resist clearing method, the flare and aerial image contrast of POB1 have been measured, and the results have been compared to analytical calculations and computer simulations.
Extreme-ultraviolet (EUV) lithography based on reflective optics is expected to require at least one filter window to 1) reduce out-of-band radiation in the ultraviolet, visible and infrared, 2) partially protect the optics from debris from the radiation source and any outgassing from the resist on the wafer, and 3) perhaps to serve as a barrier for EUV absorbing gasses. To maximize wafer throughput, the filter window or windows will need to provide the highest possible transmittance at 13.4 nm. EUV filters must operate in a harsh vacuum environment. They will be irradiated with high energy EUV light and will absorb out-of-band radiation that will cause temperature increases of greater than 100 degree(s)C. Outgassing from the filters must be minimal, and they must survive handling as well as pressure differentials during pump-down operation, and return-to-atmospheric pressure. Prototype filters were fabricated for Sandia's Engineering Test Stand (ETS) and are being utilized in on-going EUV lithography demonstrations. Their in and out-of-band transmittance has been measured and found to meet Sandia's performance specifications, and they have been exposed to various environments with good results.