Micro and Nano Technology (MNT) Measurement Club Workshop
Critical Dimension Metrology using SPM, SEM and Related Techniques
Venue: National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW Date: Wednesday 20 September 2006 Overview of Meeting Following rapid developments in industries involving semiconductor processing, precision engineering, microsystems and materials science, there is an increasing need for accurate quantitative dimensional measurements of micro- and nanostructures. The aim of this meeting is to raise awareness of and discuss the measurement and characterisation issues surrounding critical dimension metrology In MNT, focussing on the implementation of Scanning Probe Microscopy (SPM), Scanning Electron Microscopy (SEM) and related techniques beyond their use as only visual tools. Areas where there are outstanding measurement issues and needs, not fully addressed by existing measurement techniques, will be highlighted. This meeting will be of interest to researchers, engineers, scientists and technical/quality control managers in R&D and manufacturing organisations who would like to find out more about measurement and characterisation issues, techniques, tools and facilities in order to improve their products and processes and to network with others working in this field.
PROGRAMME 09.45 – 10.30 REGISTRATION, COFFEE 10.30–10.35 Introduction to meeting – Chairman: Dr Richard Leach, NPL 10.35–11:05 New developments in AFM – Dr Shelley Wilkins, Asylum Research 11.05–11.35 Issues and approaches in CD metrology with AFM and SEM – Dr John
Villarrubia, NIST 11.35–12.05 Metrological atomic force microscopy at NPL – Dr Andrew Yacoot, NPL 12.05–12.35 Dimensional metrology at the micro- and nanoscale – Dr Gaoliang Dai, PTB 12.35–13.40 LUNCH 13.40–14.00 CD Measurements from a MEMS development perspective – Dr Allen Pidduck,
Qinetiq 14:00-14:30 Three dimensional metrology in the SEM – Dr Manfred Prantl, Alicona Imaging 14:30-15:00 Optical track width measurements below 50nm using artificial neural
networks – Dr Chung See, University of Nottingham 15.00–15.30 Metrological enabling tools for practical micro-sytems and nanotechnology –
Professor Derek Chetwynd, University of Warwick 15.30–16.00 Low energy scanning analytical microscopy (LeSAM) – Professor Mohamed El-
Gomati, University of York 16.00–16.30 Discussion
16.30 COFFEE and MEETING CLOSE
PRESENTATION ABSTRACTS AND PRESENTER BIOGRAPIES Title: New developments in AFM Presenter: Dr Shelley Wilkins Asylum Research Abstract: Not available Biography: Not available Title: Issues and approaches in CD metrology with AFM and SEM Presenter: Dr John Villarrubia NIST Abstract: In integrated circuits the transistor gate width is a "critical dimension" (CD). The gate is typically the smallest printed feature in a circuit, and circuit performance is linked to its size. For this reason it is closely monitored. Semiconductor electronics manufacturers wish to measure the CD with nanometer accuracy and subnanometer repeatability. What are the obstacles to doing so? Some error sources (e.g., measurement noise, scanner motion errors, length scale miscalibration) apply to all dimensional measurements, including pitch, height, and roughness in addition to CD. I will not concentrate on these, but instead focus on the error arising from the measuring instrument's finite spatial resolution. CD measurement is uniquely sensitive to this error, and it typically contributes most of the measurement uncertainty. The source of the problem is fundamental; it is rooted in symmetry considerations. Consequently all CD measurement techniques are subject to it, to one extent or another. The solution involves developing accurate physical models of the probe/sample interaction. These necessarily depend upon the details of the individual techniques. I will illustrate by reviewing our model-based metrology efforts for atomic force microscopy (AFM) and scanning electron microscopy (SEM). Biography: John Villarrubia received his Ph.D. in physics from Cornell University in 1987. He spent two years as a visiting scientist at IBM's Thomas Watson Research Laboratory, where he used STM to obtain the first atomic resolution images of silicon's (111) surface rest-atom layer (the layer beneath the usually outermost adatom layer). He moved to the National Institute of Standards and Technology's Nano-Scale Metrology group in 1989. His interests there are primarily in CD and roughness metrology using SPM and SEM. His papers at the SPIE Microlithography meeting were given the "Metrology Best Paper" award in 2003 and again in 2005. He was the recipient of a U.S. Dept. of Commerce gold medal in 1995 for development of the Molecular Measuring Machine and a silver medal in 2005 for the development of the model-based library method that will be discussed in this talk. Title: Metrolological atomic force microscopy at NPL Presenter: Dr Andrew Yacoot NPL Abstract: The talk will give an overview of the metrological atomic force microscope (MAFM) at NPL and the design of the tip-sample interaction AFM (WW-AFM) developed jointly with German national standards laboratory, Physikalisch-Technische Bundesanstalt (PTB). The MAFM is used for
traceable calibration of artefacts. The WW-AFM will be used for the examination of tip sample interactions and their effects on dimensional metrology. Biography: Andrew Yacoot received his PhD in Physics from London University in 1990. His research topic was x-ray diffraction topography of defects in natural and synthetic diamonds. He worked at King’s College London developing an x-ray microscope before coming to NPL. He spent several years working in the area of combined optical and x-ray interferometry measuring non-linearity in optical interferometry and more recently has been collaborating with scientists at the PTB in the area of atomic force microscopy. Title: Dimensional metrology at the micro- and nano-scale Presenter: Dr Gaoliang Dai PTB Abstract: More and more nano and micro technologies are being transferred from research laboratories into industry. To establish a quality assurance system in this field, accurate and traceable dimensional measurements of micro and nano structures are widely and urgently demanded. In this talk, dimensional metrology at micro- and nanoscale by means of stylus profilometer, optical and scanning force microscopes will be focused. Calibrations of various structures with feature sizes spaning from a few nanometres to over millietres, for instance the step height, groove, layer thickness, 1D & 2D gratings, micro roughness, geometry of hardness indenters and others will be introduced. In addition, to address the challenging measurement tasks, for example, at sidewalls of nano and micro structures, a kind of novel probing method will also be presented. Biography: Dr.Gaoliang Dai is currently a principal research scientist at Physikalisch-Technische Bundesanstalt (PTB). His main areas of research have been the measurements of nano- and microscale structures by means of stylus profilometer, optical and scanning force microscopes (SFM). He is responsible for developing the high accurate metrological SFM and metrological large range SFM at PTB. Gaoliang gained a BSc, an MSc and a PhD in optical engineering from the Tsinghua University, P. R. China. He was a R&D engineer in the Physik Instrument (PI) GmbH & Co till the year 2001. He has authored over 50 technical publications in the field of micro- and nanometrology. Title: CD measurements from a MEMS development perspective Presenter: Dr Allan Pidduck Qinetiq Abstract: Not available Biography: Not available Title: Three dimensional metrology in the SEM Presenter: Dr Manfred Prantl Alicona Imaging Abstract: Not available Biography: Not available
Title: Optical track width measurements below 50nm using artificial neural networks Presenter: Dr Chung See University of Nottingham Abstract: In a recent publication1, we have demonstrated optical line width measurement in the range of 50nm, with a precision better than 2nm. The line width is less than 1/50th of the diameter of the point spread function, and is well beyond the conventional resolution of the optical system. The measurement is performed by using an ultrastable optical interferometer together with artificial neural networks. We estimate that the technique has the ability to measure down to 10nm. In this talk, we will demonstrate the characteristics and the ability of the technique by using results obtained both experimentally and through computer simulations. Our current research is concentrated on extending the application areas of the technique, so that it can be used to measure samples of more general types. We will discuss the importance of signal classification, and the crucial role it will have on increasing the measurement capability of the system when applied to different sample/structure types. We will consider the potential of several methods in performing signal classification, and will present simulation results to support their cases. 1. Smith RJ, See CW, Somekh MG, Yacoot A, Choi E, “Optical track width measurements
below 100 nm using artificial neural networks”, MEASUREMENT SCIENCE & TECHNOLOGY 16 (12): 2397-2404, 2005.
Biography: Not available Title: Metrological enabling tools for practical micro-systems and nanotechnology Presenter: Professor Derek Chetwynd University of Warwick
Abstract: The successful exploitation of nanoscience through nanotechnology, MEMS, etc. throws us large challenges that are only now being properly addressed in a relatively orderly way. While many of the early attempts resemble methods used in microelectronics, different design, production and assurance methods become essential because of the different sized production batches and much wider range of materials. This talk offers some thoughts about the emerging enabling technologies, aiming to promote discussion in areas where there are not yet solutions that could be strongly recommended. It starts with a few observations, drawn together from various recent reports, about the size and international competitiveness of research and development in MNT and on the types of International Standards that may be necessary and appropriate if the sector is to develop commercially. It then introduces a few examples of where new metrology is required as an enabling technology for MEMS applications, drawing on topics under study at the University of Warwick. Much of it relates to the use of functionally-active polymers within complex devices. With materials that may have morphologies and anisotropy at a scale not that much smaller than the devices, there are important questions about how we should reliably measure both the basic properties to enable designs and to check production quality to ensure reliable products. . Biography: Derek Chetwynd is a Professor of Engineering at the University of Warwick and leader of its Precision Engineering and Materials Research Group. His early career at Rank Taylor Hobson involved developing of optical and mechanical measuring instruments and, especially, commercially viable computer-aided metrology. He moved to Warwick to help found the Centre for Microengineering and Metrology, and has subsequently spent periods as Director of its descendents. His international reputation covers areas of interest in ultra-precision mechanisms, instrument systems, nanometrology and microsystems characterization. He has over 80 major publications and many conference papers and has been investigator on about 40 grants awarded by research councils, industry, charities and the EU.
Title: Low energy scanning analytical microscopy (LeSAM) Presenter: Professor Mohamed El-Gomati University of York Abstract: The desire to maintain Moore’s Law, where the number of transistors per chip is predicted to double every couple of years, has provided instrument developers with the goals to aim for. The samples provided by the electronics industry have formed the toys in this playground of instrument development. However, the newly defined goals from the Semiconductor Industry Association (SIA) (i.e. features to be analysed) are posing a problem or two. SIA’s need is for technology which is fast with non-destructive 2-D profiling at sub-10 nm spatial resolution and detection sensitivity for dopants in the range of 1016 cm-3 to 1020 cm-3. In addition, there is a need to chemically identify features (defects) with dimensions of the order of 10-20 nm, with the same speed and benign impact upon the specimen. In my talk, I will review progress of two techniques which are being developed to meet the above stringent “metrology” criteria, and which could equally be used in other fields. The first is detecting dopants in semiconductors using low and ultra-low energy electron microscopy using secondary electrons. Incident electron energies in the range 1-5000 eV is used. The second technique is the development of parallel detection in Auger electron spectroscopy and microscopy, where a complete spectrum in the range 1-2000 eV is collected in one second. Both techniques can be combined in one instrument, the low energy scanning analytical microscope (LeSAM). M. El-Gomati et al, Surface and Interface Anal, 37, (2005) 901-911. M. Jacka, M. Kirk, M. El-Gomati and M. Prutton, Rev. Sci. Inst. 70, (5) (1999)2282-7. Biography: Mohamed El-Gomati is the Professor of Electron Optics and Surface analysis at the University of York, Department of Electronics. His main interest is in the development and use of novel electron based instrumentation for nanolithography and analysis, with particular emphasis in the use and development of Schottky and field electron emitter sources. He received his BSc from Tripoli, Libya, an MSc from California (LA) and DPhil from York. He is the author and co-author of more than 150 papers in the above fields, as well as a number of patents related to his research.
