With EUV attenuated phase shift absorbers rapidly approaching maturity, actinic metrology soon will be required to ensure phase accuracy, uniformity, and stability. The target phase shift for these absorbers is carefully optimized to a value typically around 1.2pi for optimal printing. The additional 0.2pi is necessary due to mask 3D effects (M3D), which increasingly distort the near-field scattering and phase as the feature size is reduced. Therefore, EUV attenuated phase shift masks require phase metrology not only for large-area multilayer and absorber, but also for feature-dependent in-pattern phase. We demonstrate in-pattern phase measurement using spectroscopic variable angle scatterometry with the commercially available EUV Tech ENK (EUV n/k tool). We describe experiments validating the accuracy and precision of actinic scatterometry-based pattern phase measurements conducted on the ENK platform through direct comparison to synchrotron reference scattering measurements.
With EUV Attenuated Phase Shift Masks (aPSMs) rapidly approaching maturity, actinic metrology soon will be required to ensure phase accuracy, uniformity, and stability. The target phase shift is carefully designed to an optimized value, which is not 𝜋, but typically around 1.2𝜋 for optimal printing at critical feature sizes. The additional 0.2𝜋 phase shift is necessary due to mask 3D effects (M3D), which increasingly distort the nearfield scattering and phase as the feature size is reduced. Therefore, EUV attenuated phase shift masks require metrology, not only for the relative Fresnel phase shift between large-area multilayer and absorber regions, but also for the feature-dependent pattern phase shift in the near-field scattering. We demonstrate a metrology solution for measuring the in-pattern phase shift using spectroscopic variable angle scatterometry. The measurements are performed using the commercially available EUV Tech ENK (EUV n/k tool), based on a compact continuously tunable laser-produced plasma light source. In this presentation we describe experiments validating the accuracy and precision of actinic scatterometry-based pattern phase measurements conducted on the ENK platform on seven samples of EUV attenuated phase shift absorbers of varying thickness. We demonstrate good agreement with simulation on measurements of phase vs absorber thickness and phase vs grating pitch, validating the suitability of this measurement for measuring the actinic phase shift of an EUV mask.
With the coming adoption of EUV phase shift absorbers in high-volume manufacturing, it soon will be critical to ensure phase uniformity across the mask and stability over time. Synchrotron-based EUV variable angle spectroscopic reflectometry has been demonstrated to be a highly sensitive metrology technique for the measurement of phase. More recently, this phase measurement technique has been successfully implemented as a fab-scale tool based on a laser produced plasma source. The metrology enabled by this tool supports the continual monitoring of phase stability in a manufacturing environment, which can provide invaluable knowledge about best practices for mitigating or reversing phase drift resulting from effects such as contamination and mask aging. In this presentation we report on such phase drift measurements on real EUV masks looking at various sources of phase change on the mask.
This conference presentation was prepared for Photomask Japan 2022: XXVIII Symposium on Photomask and Next-Generation Lithography Mask Technology, 2022.
Since the beginning of lithography using a reticle, defects have been one of the key factors in determining reticle quality and wafer yields. With the rapid adoption to EUV Lithography and the high cost of existing EUV mask defect review systems there is an industry need for an alternative defect review and dispositioning system. To meet this need Micron Mask Technology Center, the supplier of state-of-the-art mask technology, has partnered with EUV Tech, the world’s leading supplier of EUV Metrology equipment, to develop a standalone Zoneplate-based EUV wavelength microscope.
EUV Tech has introduced and delivered the AIRES (Actinic Image REview System), an at-wavelength EUV Mask Defect Review Tool for EUV photomasks. The tool features EUV Tech’s patented zone plate imaging system equipped with the EUV Tech’s automated mask transfer system to the process chamber.
AIRES is based on the successful Zoneplate EUV Microscope at Lawrence Berkeley Lab called SHARP which has been used to support semiconductor development for over a decade. AIRES is the first commercial standalone EUV projection imaging zoneplate microscope supporting photomask defect review and dispositioning to support EUV high volume manufacturing. In this paper, we introduce the tool and its performance with defect cases and pattern imaging application on EUV production reticles.
EUV Lithography (EUVL) is poised to enter High Volume Lithography (HVM) in the near future. One of the principal challenges in the EUVL implementation for HVM is the availability of necessary clean at wavelength metrology tools. Since the company’s inception in 1997, EUV Tech has pioneered the development of EUV Metrology tools.
EUV Tech recently delivered the world’s first EUV Pellicle inspection tool to measure EUV pellicle transmission. This tool provides key measurement information for the qualification of a EUV Pellicle for use in a EUV Scanner. Recent results from measuring a variety of candidate EUV pellicles will be shown to highlight the measurement performance of the tool. This paper will show the measurement performance and data output of the tool, the uses within the photomask development lifecycle,
This paper will also discuss our R&D program including new novel tools for accelerated EUV Exposure testing of samples, an EUV Microscope for actinic defect printability review, and scatterometry for mask phase roughness.
The improvements in reflectivity and wavelength precision and accuracy of our EUV Reflectometer to meet the requirements of future processing nodes will also be discussed.
Key words: EUV, Mask, Pellicle, Metrology tools, Inspection tools, Reflectometer.
KEYWORDS: Metrology, Line width roughness, Scanning electron microscopy, Digital filtering, Atomic force microscopy, Standards development, Semiconductors, Image acquisition, Image quality, Electron microscopes
As semiconductor technology keeps moving forward, undeterred by the many challenges ahead, one specific deliverable is capturing the attention of many experts in the field: line width roughness (LWR) specifications are expected to be <2 nm in the near term, and to drop below 1 nm in just a few years. This is a daunting challenge and engineers throughout the industry are trying to meet these targets using every means at their disposal. However, although current efforts are surely admirable, we believe they are not enough. The fact is that a specification has a meaning only if there is an agreed methodology to verify if the criterion is met or not. Such standardization is critical in any field of science and technology and the question that we need to ask ourselves today is whether we have a standardized LWR metrology or not. In other words, if a single reference sample were provided, would everyone measuring it get reasonably comparable results? We came to realize that this is not the case and that the observed spread in the results throughout the industry is quite large. In our opinion, this makes the comparison of LWR data among institutions, or to a specification, very difficult. We report the spread of measured LWR data across the semiconductor industry. We investigate the impact of image acquisition, measurement algorithm, and frequency analysis parameters on LWR metrology. We review critically some of the International Technology Roadmap for Semiconductors (ITRS) metrology guidelines [such as measurement box length >2 μm and the need to correct for scanning electron microscope (SEM) noise]. We compare the SEM roughness results to AFM measurements. Finally, we propose a standardized LWR measurement protocol—the imec roughness protocol—intended to ensure that every time LWR measurements are compared (from various sources or to specifications), the comparison is sensible and sound. We deeply believe that the industry is at a point where it is imperative to guarantee that when talking about a critical parameter such as LWR, everyone speaks the same language, which is not currently the case.
Extreme Ultraviolet (EUV) Lithography is still viewed as the most promising approach for maintaining the pace of
Moore's Law. Recent real achievements in EUV Lithography (EUVL) have encouraged semiconductor manufacturers to
reconsider their road maps. One of the principal challenges in the ongoing EUVL implementation for high volume
manufacturing (HVM) is the availability of necessary clean at wavelength metrology tools.
EUV Tech is the world's leading manufacturer of at-wavelength EUV metrology equipment. Founded in 1997, EUV
Tech has pioneered the development of several stand-alone inspection, metrology, and calibration tools for EUV
lithographic applications that can be operated in a clean room environment on the floor of a fab.
In this paper, EUV Tech’s R&D program to minimize particle adders in our EUV Reflectometer along with the ongoing
effort to enhance the reflectivity and wavelength, precision and accuracy required to qualify the EUV masks for HVM.
In addition to preliminary results from our stand alone EUV Scatterometer developed to characterize the phase roughness
of a EUV mask and the introduction of EUV Tech’s Pellicle test suite for testing EUV pellicles.
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