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.