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.
We report on the development of an electric capillary discharge source that radiates with comparable efficiency at both 13.5 nm and 11.4 nm, two wavelengths of interest for EUV lithography. The discharge source is comprised of a low- pressure, xenon-filled, small diameter capillary tube with electrodes attached to both ends. A high-voltage electric pulse applied across the capillary tube generates an intense plasma that radiates in the EUV. This source is capable of producing 7 mJ/steradian per pulse in a 0.3 nm bandwidth centered at 13.4 nm. In this paper we will address three significant issues related to the successful development of this source: minimization of debris generation, thermal management, and imaging quality.
We report on the comparison of defect printability experimental results with at-wavelength defect inspection and printability modeling at extreme ultraviolet (EUV) wavelengths. Two sets of EUV masks were fabricated with nm- scale substrate defect topographies patterned using a sacrificial layer and dry-etch process, while the absorber pattern was defined using a subtractive metal process. One set of masks employed a silicon dioxide film to produce the programmed defects, whereas the other set used chromium films. Line-, proximity- and point-defects were patterned and had lateral dimensions in the range of 0.2 micrometer X 0.2 micrometer to 8.0 micrometer X 1.5 micrometer on the EUV reticle, and a topography in the range of 8 nm - 45 nm. Substrate defect topographies were measured by atomic force microscopy (AFM) before and after deposition of EUV-reflective Mo/Si multilayers. The programmed defect masks were then characterized using an actinic inspection tool. All EUVL printing experiments were performed using Sandia's 10x- reduction EUV Microstepper, which has a projection optics system with a wavefront error less than 1 nm, and a numerical aperture of 0.088. Defect dimensions and exposure conditions were entered into a defect printability model. In this investigation, we compare the simulation predictions with experimental results.
The capabilities of the EUV 10x microstepper have been substantially improved over the past year. The key enhancement was the development of a new projection optics system with reduced wavefront error, reduced flare, and increased numerical aperture. These optics and concomitant developments in EUV reticles and photoresists have enabled dramatic improvements in EUV imaging, illustrated by resolution of 70 nm dense lines and spaces (L/S). CD linearity has been demonstrated for dense L/S over the range 100 nm to 80 nm, both for the imaging layer and for subsequent pattern transfer. For a +/- 10 percent CD specification, we have demonstrated a process latitude of +/- micrometers depth of focus and 10 percent dose range for dense 100 nm L/S.
Recent experiments with four 10x EUV imaging systems provide the first direct comparisons of visible-light and at- wavelength EUV interferometers performed using the state-of- the-art measurement tools that will be used to assemble and align the next generation of EUV imaging systems. Measurements from four individual multilayer-coated Schwarzschild objectives are discussed. Favorable agreement has been achieved between EUV and visible-light system wavefront measurements in all four optical systems. Measurements made in the presence of surface contamination and multilayer thickness variation, however, do show expected localized differences between the two measurements.
Two new Schwarzschild cameras have been fabricated for the EUV 10x microstepper. The surface topography of the mirrors was characterized over the full range of spatial frequencies both before and after multilayer coating. EUV scattering from the individual mirrors was measured and compared with the surface profilometry. A knife-edge test was used to directly measure the flare of the assembled cameras. The flare measured in this way is in excellent agreement with the contrast of isolated printed lines and with the point spread function of the camera as determined by EUV interferometry. The measured flare of the camera is also in good agreement with the flare calculated from the combined surface profile measurements of the individual mirrors. Consistent with the improvements made in the surface finish of the mirror substrates, a significant reduction in the flare is observed as compared with previously existing cameras.
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.
The strong attenuation of extreme UV (EUV) radiation by organic materials necessities the use of a thin layer imaging (TLI) process for EUV lithography. Several TLI processes have been identified for potential use for EUVL, and the common theme in these approaches is the transfer of the aerial image to a thin layer of refractory-containing material, which is then used as a dry O2 etch mask during a subsequent pattern transfer to the device layer. One TLI process that has been extensively examined for EUVL is the silylated top-surface imaging (TSI) technology, which is discussed in this paper. Using a new disilane silylation reagent, dimethylaminodimethyldisilane (DMDS) and 13.4 nm exposure, the TSI process has been sued to print 100 nm lines and spaces at equal pitch and 70 nm lines and spaces at a higher 1:2 pitch. The line edge roughness for the printed lines has been determined using a custom image analysis program and, as expected, varies with the particular EUV exposure system and numerical aperture. Exposures done with 193 nm lithography and the TSI process using DMDS are also shown for comparison to the EUV results.