Extreme ultraviolet microscope characterization using photomask surface roughness.

We demonstrate a method for characterizing the field-dependent aberrations of a full-field synchrotron-based extreme ultraviolet microscope. The statistical uniformity of the inherent, atomic-scale roughness of readily-available photomask blanks enables a self-calibrating computational procedure using images acquired under standard operation. We characterize the aberrations across a 30-um field-of-view, demonstrating a minimum aberration magnitude of smaller than [Formula: see text] averaged over the center 5-um area, with a measurement accuracy better than [Formula: see text].

Amplitude versus phase effects in extreme ultraviolet lithography mask scattering and imaging.

It is now well established that extreme ultraviolet (EUV) mask multilayer roughness leads to wafer-plane line-width roughness (LWR) in the lithography process. Analysis and modeling done to date has assumed, however, that the roughness leading to scatter is primarily a phase effect and that the amplitude can be ignored. Under this assumption, simple scattering measurements can be used to characterize the statistical properties of the mask roughness.

Quantitative phase retrieval with arbitrary pupil and illumination.

We present a general algorithm for combining measurements taken under various illumination and imaging conditions to quantitatively extract the amplitude and phase of an object wave. The algorithm uses the weak object transfer function, which incorporates arbitrary pupil functions and partially coherent illumination. The approach is extended beyond the weak object regime using an iterative algorithm.

Resist Materials for Extreme Ultraviolet Lithography: Toward Low-Cost Single-Digit-Nanometer Patterning.

Extreme ultraviolet lithography (EUVL) is the leading technology for enabling miniaturization of computational components over the next decade. Next-generation resists will need to meet demanding performance criteria of 10 nm critical dimension, 1.2 nm line-edge roughness, and 20 mJ cm(-2) exposure dose.

Biological soft X-ray tomography on beamline 2.1 at the Advanced Light Source.

Beamline 2.1 (XM-2) is a transmission soft X-ray microscope in sector 2 of the Advanced Light Source at Lawrence Berkeley National Laboratory. XM-2 was designed, built and is now operated by the National Center for X-ray Tomography as a National Institutes of Health Biomedical Technology Research Resource.

Electro-optical system for scanning microscopy of extreme ultraviolet masks with a high harmonic generation source.

A self-contained electro-optical module for scanning extreme ultraviolet (EUV) reflection microscopy at 13.5 nm wavelength has been developed. The system has been designed to work with stand-alone commercially available EUV high harmonic generation (HHG) sources through the implementation of narrowband harmonic selecting multilayers and off-axis elliptical short focal length zoneplates.

Optical modeling of Fresnel zoneplate microscopes.

Defect free masks remain one of the most significant challenges facing the commercialization of extreme ultraviolet (EUV) lithography. Progress on this front requires high-performance wavelength-specific metrology of EUV masks, including high-resolution and aerial-image microscopy performed near the 13.5 nm wavelength.

Validity of the thin mask approximation in extreme ultraviolet mask roughness simulations.

In the case of extreme ultraviolet (EUV) lithography, modeling has shown that reflector phase roughness on the lithographic mask is a significant concern due to the image plane speckle it causes and the resulting line-edge roughness on imaged features. Modeling results have recently been used to determine the requirements for future production worthy masks yielding the extremely stringent specification of 50 pm rms roughness. Owing to the scale of the problem in terms of memory requirements, past modeling results have been based on the thin mask approximation in this application.

Correlation method for the measure of mask-induced line-edge roughness in extreme ultraviolet lithography.

As critical dimensions for leading-edge semiconductor devices shrink, the line-edge roughness (LER) requirements are pushing well into the single digit nanometer regime. At these scales many new sources of LER must be considered. In the case of extreme ultraviolet (EUV) lithography, modeling has shown the lithographic mask to be a source of significant concern.

Tilt sensitivity of the two-grating interferometer.

Fringe formation in the two-grating interferometer is analyzed in the presence of a small parallelism error between the diffraction gratings assumed in the direction of grating shear. Our analysis shows that with partially coherent illumination, fringe contrast in the interference plane is reduced in the presence of nonzero grating tilt with the effect proportional to the grating tilt angle and the grating spatial frequencies. Our analysis also shows that for a given angle between the gratings there is an angle between the final grating and the interference plane that optimizes fringe contrast across the field.

Absolute sensitivity calibration of extreme ultraviolet photoresists.

One of the major challenges facing the commercialization of extreme ultraviolet (EUV) lithography remains simultaneously achieving resist sensitivity, line-edge roughness, and resolution requirement. Sensitivity is of particular concern owing to its direct impact on source power requirements. Most current EUV exposure tools have been calibrated against a resist standard with the actual calibration of the standard resist dating back to EUV exposures at Sandia National Laboratories in the mid 1990s.

Sensitivity study of two high-throughput resolution metrics for photoresists.

The resolution of chemically amplified resists is becoming an increasing concern, especially for lithography in the extreme ultraviolet (EUV) regime. Large-scale screening is currently under way to identify resist platforms that can support the demanding specifications required for EUV lithography. Current screening processes would benefit from the development of metrics that can objectively quantify resist resolution in a high-throughput fashion.

Design and fabrication of a high-efficiency extreme-ultraviolet binary phase-only computer-generated hologram.

As the development of extreme-ultraviolet (EUV) lithography progresses, interest grows in the extension of traditional optical components to the EUV regime. The strong absorption of EUV by most materials and its extremely short wavelength, however, make it very difficult to implement many components that are commonplace in the longer wavelength regimes. One such component is the diffractive optical element used, for example, in illumination systems to efficiently generate modified pupil fills.

Spin-on-glass coatings for the generation of superpolished substrates for use in the extreme-ultraviolet region.

Substrates intended for use as extreme-ultraviolet (EUV) optics have extremely stringent requirements in terms of finish. These requirements can dramatically increase the cost and fabrication time, especially when nonconventional shapes, such as toroids, are required. Here we present a spin-on-glass resist process capable of generating superpolished parts from inexpensive substrates.

Lithographic characterization of the spherical error in an extreme-ultraviolet optic by use of a programmable pupil-fill illuminator.

Extreme-ultraviolet (EUV) lithography remains a leading contender for use in the mass production of nanoelectronics at the 32 nm node. Great progress has been made in all areas of EUV lithography, including the crucial issue of fabrication of diffraction-limited optics. To gain an accurate understanding of the projection optic wavefront error in a completed lithography tool requires lithography-based aberration measurements; however, making such measurements in EUV systems can be challenging.

Effect of mask-roughness on printed contact-size variation in extreme-ultraviolet lithography.

Relying on reflective mask technology, extreme-ultraviolet (EUV) lithography is particularly vulnerable to mask substrate roughness. Previous research has shown mask roughness to play a significant role in printed line-edge roughness (LER). Here the analysis of mask-roughness effects is extended to printed contact-size variations.

Design, fabrication, and characterization of high-efficiency extreme-ultraviolet diffusers.

As the development of extreme-ultraviolet (EUV) lithography progresses, interest grows in the extension of traditional optical components to the EUV regime. Because of the strong absorption of EUV by most materials and because of its extremely short wavelength, however, it is difficult to implement many components that are commonplace in the longer-wavelength regimes. One such example is the diffuser that is often implemented with ordinary ground glass in the visible light regime.

Relevance of mask-roughness-induced printed line-edge roughness in recent and future extreme-ultraviolet lithography tests.

The control of line-edge roughness (LER) of features printed in photoresist poses significant challenges to next-generation lithography techniques such as extreme-ultraviolet (EUV) lithography. Achieving adequately low LER levels requires accurate resist characterization as well as the ability to separate resist effects from other potential contributors to LER. One potentially significant contributor to LER arises from roughness on the mask coupling to speckle in the aerial image and consequently to LER in the printed image.

Verification of point-spread-function-based modeling of an extreme-ultraviolet photoresist.

A crucial component of lithographic modeling is the resist. Resists typically used at extreme-ultraviolet (EUV) wavelengths are derivatives of deep-ultraviolet chemically amplified resists. Models that describe these resists are often very complicated and are dependent on a large number of free parameters.

Hartmann wave-front measurement at 13.4 nm with lambdaEUV/120 accuracy.

We report, for the first time to our knowledge, experimental demonstration of wave-front analysis via the Hartmann technique in the extreme ultraviolet range. The reference wave front needed to calibrate the sensor was generated by spatially filtering a focused undulator beam with 1.7- and 0.

Line-edge roughness transfer function and its application to determining mask effects in EUV resist characterization.

The control of line-edge roughness (LER) of features printed in photoresist poses significant challenges to next-generation lithography techniques such as extreme-ultraviolet (EUV) lithography. Achieving adequately low LER levels will require accurate resist characterization as well as the ability to separate resist effects from other potential contributors to LER. One significant potential contributor is LER on the mask.

Fourier-synthesis custom-coherence illuminator for extreme ultraviolet microfield lithography.

Scanning illumination systems provide for a powerful and flexible means for controlling illumination coherence properties. Here we present a scanning Fourier synthesis illuminator that enables microfield extreme ultraviolet lithography to be performed on an intrinsically coherent synchrotron undulator beamline. The effectiveness of the system is demonstrated through a variety of print experiments, including the use of resolution enhancing coherence functions that enable the printing of 50-nm line-space features by use of a lithographic optic with a numerical aperture of 0.