Metrology

Laser-based optical interferometry has long been playing a central role in the progress of dimensional metrology for precision manufacturing. Meanwhile, mode-locked lasers are nowadays available to facilitate the progress by responding to ever-growing industrial demands on the measurement precision and functionality beyond the capabilities of conventional lasers. The optical spectrum of mode-locked lasers, referred to as the frequency comb, acts as the ruler enabling ultra-stable wavelengths to be produced for precision interferometry with traceability to the atomic clock. In addition, mode-locked lasers are employed directly as the light source offering ultrashort pulses, of which the time-of-flight can be detected with unprecedented precision in implementing long distance measurement. Further, mode-locked lasers are able to provide well-controlled temporal coherence in combination with high spatial coherence, being suited to overcome the technical barriers long standing in 3-D profiling of rough surfaces. In summary, mode-locked lasers are now ready to lead the advance of dimensional metrology by providing unique temporal and spectral benefits over conventional continuous wave lasers or broad-spectrum light sources.

Continuing engineering progress in precision fabrication technologies, especially in the semiconductor industry, precision optics fabrication, and the diversified micro- and nanotechnologies, stimulates the advance in precision metrology. Fabricated structures reach atomic dimensions in ever-larger areas, thus becoming more and more complex, also in three dimensions. Consequently, measurements are made – to an increasing extent – of larger surface regions and sidewalls with higher aspect ratios as well as fully 3D micro- and nanostructures. Advanced high precision measurement technology is more and more an enabling technology for nanotechnologies. Today, nanopositioning and nanomeasuring machines provide high-precision measurements and the positioning of objects across different scales, from subnanometers up to several centimeters. This chapter deals with the requirements for highest measurement performance at the limits of physics and technology, resulting from the progress and the goals of modern high-tech fabrication technologies. The fundamentals of the nanopositioning and nanomeasuring machine, developed at the Institute of Process Measurement and Sensor Technology of the Ilmenau University of Technology and manufactured by the SIOS Meßtechnik GmbH Ilmenau, are described, and the measurement capabilities, potential applications, progress in research, and prospects of the device for the near future are pointed out.

The application of automated optical inspection (AOI) to advanced manufacturing processes with tight takt time and specifications is critical in winning today’s global competition. In the past decades, great effort had been devoted to developing novel solutions for in-line optical inspection of surfaces and the dynamic characteristics of tested components or devices. Conventional approaches to microscale 3D surface profilometry have adopted novel optics or concepts in confocal microscopy for measuring 3D surface characteristics with high speed and precision. One-shot measurement capability is demanded to minimize measured uncertainty from environmental vibration or system instability. Nevertheless, extremely high-speed microscopic 3D confocal profilometric methodologies for 100% full-field inspection are yet to be developed. This chapter intends to provide the measurement principle and development of confocal optical profilometry in overcoming bottlenecks and developing feasible solutions for novel manufacturing technologies, such as roll-to-roll nanoimprinting or semiconductor processes. It contains the basic optics, the measuring algorithms and industrial applications in optical confocal microscopy required for surface profilometry.

The development of smart machine tools will be the trend toward the worldwide need of intelligent manufacturing technology nowadays, which is the goal of industry 4.0 as well as cyber-physical system and China made 2025. Current techniques for machine tool metrology are implemented by measuring instruments mainly suggested by the ISO 230 series of international standard. Although these instruments are used to measure geometric errors of each axis of machine tool, they cannot be used as sensors for real-time detection since they are expensive and are in bulky sizes. In order to understand the functions of the optical sensors for machine tool metrology, this chapter firstly addresses the importance of geometric errors to the accuracy of machine tools. Abbe principle and Bryan principle are two important guidelines in machine design and measurement technology. The volumetric errors of machine tools are largely affected by these two principles. This is the second topic highlighted in this chapter. Some small and low-cost optical sensors for geometric error measurements are presented. These sensors can be portably mounted onto the machine frame for online measurement. They can also be embedded in the machine structure as feedback sensors for respective geometric errors. The integration of individual sensors into a multi-degree-of-freedom measuring (MDFM) module for volumetric error measurement and compensation is also introduced. Some applications of developed optical sensors to measure machine tool errors are described in the last part of this chapter. Experimental validation shows the feasibility of developed optical sensors for machine tool metrology and error compensation. This chapter neither includes the measuring instruments for ISO 230 series as these are the subject of other chapter nor those MDFM systems reported by many other researchers because those are mainly at the laboratory level and not ready for practice on machine tools.

Rapid progress in microfabrication technology with great precision has been made owing to the miniaturization of complex product. However, no concomitant development has taken place in the evaluation technology for micro-components, particularly in three-dimensional metrology, which is still in development. The gap between the traditional CMM’s specification and the demand for geometric dimensioning and tolerancing of a micro-component with the basic size of less than several mm has been widening because a measuring accuracy of 100 to 10 nm is needed for the basic size of 10 to 1.0 mm. This situation has recently led to increased focus on the development of technology for practical micro-CMMs. The key – and hence the bottleneck – in realizing a micro-CMM system is the micro-probe system. This is because for features smaller than several dozen micrometers, the probing uncertainty is considerably exacerbated by scaling effects. Accordingly, the development of the probing system is attempted with a different approach from the traditional concept for the sake of scale effect that is remarkable with the use of a touch trigger probe. Therefore, the basic concept of the laser trapping micro-probe was proposed, whose principle is based on the single-beam gradient force optical trap of a micro-probe sphere in air. This probe can perform noncontact measurement of a position that is optically sensed based on the displacement of the micro-probe sphere given by dynamical interaction with the surface. Moreover, the improved circular motion probing technique enables to measure a surface position and a normal direction simultaneously. This probing system was integrated with a prototype micro-CMM that was specially designed for evaluating the performance of the probe system. The dynamic properties of the coordinate stage were evaluated by a heterodyne interferometer. The test results showed that the stage had a positioning accuracy of several dozen nanometers.

Machine tools produce parts by moving a tool relative to a workpiece. Any deviation from the command path may result in errors on the part thus degrading its quality. Machine tool calibration aims to quantify and compensate the machine errors in order to make better parts. This chapter reviews the definitions, nomenclature, and some principles associated with machine tool geometric errors. Forward mathematical models are also presented that calculates the volumetric errors at the tool tip as functions of the causal interaxis and intraaxis errors of the machine with examples covering three- and five-axis machines. Finally, measurement approaches and compensation schemes are briefly covered

The key to solve manufacturing quality and productivity problems in the machining of parts is to understand the physical attributes’ geometric/kinematic, static, dynamic, and thermal behavior of machine tools. In this chapter basic definitions, error sources, and instruments and methodologies for the identification and evaluation of machine tools’ physical attributes will be outlined.

The first section presents the background and answers “why” it is important to measure and evaluate machine tools under no-load and loaded condition. Basic concepts and definitions of metrological terms will be given. In the second part, error sources in machine tools are introduced, and in the third part, instruments and methodologies for the accuracy evaluation of machine tools will be given.

Increasing demand for precision-manufactured parts for high-tech applications in aerospace, nuclear power, transportation, etc. continually drives the advancement of precision manufacturing technologies. As the precision and quality of manufactured parts are significantly affected by the performance of the machine tools, accurate and reliable condition monitoring, performance prediction, and maintenance of machine tools become one important part of precision manufacturing. In this chapter, a stochastic modeling technique is presented for prediction of machine tool performance degradation based on sensing data from the tool wear. Specifically, to account for the nonlinear and non-Gaussian characteristic of operating and environmental conditions on the wear propagation and machine performance degradation, particle filter (PF) that approximates probability distributions through a set of weighted particles is investigated. To improve the reliability of time-varying degradation tracking and prediction, an adaptive resampling particle filter method is developed. Specifically, particles are recursively updated and resampled from the neighborhoods that are determined by particles’ estimation performance from the last iteration, to characterize the temporal variation in the tool degradation rates. This leads to improved tracking and prediction accuracy with progressively narrowed confidence interval. The developed method has been experimentally evaluated using a set of benchmark data that were measured on a high-speed CNC machine.

This chapter presents the basic principles and techniques for measuring the geometrical features of cylindrical gears. The mathematical models for nominal cylindrical gear geometry are given in a two-dimensional (2D) space and extended to a three-dimensional (3D) space. The geometric parameters for assessing the conformance of gear design and manufacturing are highlighted based on the current international standards. Conventional gear inspections by tactile measuring systems such as gear-measuring instruments (GMIs) and coordinate measuring machines (CMMs) are discussed in detail, including measuring strategies and evaluations of “raw” spatial data sets, methods of calibrating gear-measuring systems, and the estimation of measurement uncertainty. Emerging technologies including optical measuring systems and areal evaluation methods are introduced as part of future cylindrical gear metrology.

Measurement of complex shaped parts is of interest in many applications. Complex functional freeform surfaces may have a great influence on the performances of a product. Geometrical deviations in manufacturing can cause waste of large quantities of energy. Testing of parts having freeform surfaces is a key activity during the development of products with better performances. Depending on the workpiece shape, its manufacturing process, and tolerance limits, it is required to measure freeforms densely, for sufficiently high probability to capture crucial regions. This often requires fast measurement processes to keep measurement time feasible low. Fast measurements can be obtained by increasing the speed of acquiring a single point and/or parallelizing this process by acquiring multiple points at the same time. A brief overview of methods with high measurement speed is given. The concept of optical triangulation is discussed in detail, and case study is presented to illustrate an implementation in industry of a dedicated measuring system for high-speed measurement of complex shapes.

Micro-probing system has become a remarkable technique for the dimensional measurement of complex micrometric features on the micro-parts and precision tools. In especial, the tactile micro-probes are one of the most effective micro-probing systems since the miniaturized micro-stylus and high-sensitive probing sensor of the micro-probing systems allows both the capability of three-dimensional accessibility and nanometric resolution for the complex micrometric features. Therefore, there have been many efforts for the miniaturization of the stylus size with high-accuracy tip shape. In addition, since high sensitivity of the tactile micro-probing system is influenced by the external interaction force which has been ignored in the previous probing systems, new principle of the probing sensor and novel calibration method of the micro-probing system have been required.

On the other hand, the probe tip ball of the micro-probing systems is composed with the high-accuracy microsphere, so that their diameter is smaller than the micrometric features of the measuring workpiece generally in order to realize good accessibility for complex features. Therefore, precise qualification of the probe tip dimension is also important issues for the calibration of the micro-probing system because the uncertainty of the dimensional measurement is also affected by the geometrical tolerance of the probe tip shape. The uncertainty of the micro-dimensional measurement is dominated not only by the reliability of the micro-probe and the probe positioning instruments as well as the conventional probing system but also by the nanometer-scale deformation of the surface and the nanometric dimension of probe tip. In this chapter, a high-sensitive micro-probing system utilizing the local interaction force has been described. With respect to the compensation of the geometrical tolerance of the tip of the micro-probing system, an online qualification method has been introduced. Finally, dimensional measurement of micrometric feature by a micro-probing system is described, and its measurement results are investigated according to the uncertainty analysis.

The increasing adoption of additive manufacturing (AM) within the manufacturing industry is pushing companies to rethink how components and integrated component assemblies can be manufactured and not least how to ensure that manufacturing quality is met. This chapter is an enchiridion that details the most commonly applied AM technologies, their existing standards, and what measurements and quality assurance methods that are most relevant for each technology. The chapter is commenced by introducing the principles of vat photopolymerization and powder-bed fusion, after which the intrinsic of each process is linked to what geometrical, surface, and internal characteristics can be expected. This is followed by a deliberation of what measurement methods are applicable and relevant for each process.

In-line quality control is able to provide direct feedback with regard to quality deviations in production systems. Thus, it is a crucial enabler to guarantee high-quality standards and prohibit waste within production. As an enabler for this, in-line measurement technology is to be implemented and applied in the production system in an effective manner. In this chapter, different types of in-line measurement technology are explained and structured. Based on this, a framework is introduced to systematically implement in-line metrology in production systems in order to realize suitable quality control cycles. Finally, the application of the framework is demonstrated in various industrial use cases.

This chapter describes in-process measurement of subwavelength structures. Especially, from the viewpoint of affinity with in-process measurement, this chapter focuses on optical measurement, which provides in-process evaluation of engineering microstructure surfaces beyond the diffraction limit. First, application of optical super-resolution using structured light illumination to semiconductor patterns inspection is shown. Second, a new type of optical depth measurement of subwavelength microgrooves using an interference measuring method, which can measure the depth of microgrooves, with widths less than the diffraction limit, is described. Third, as an example of application of near-field optics for in-process measurement for quality of subwavelength structures, nano-thickness inspection of residual layer thickness during nanoimprint lithography is demonstrated. Through concrete examples, the possibility of an optical measurement method for the in-process measurement of subwavelength structures is discussed.

Process control in microelectronic manufacturing requires real-time monitoring techniques. Optical scatterometry, also referred to as optical critical dimension metrology, has become one of the most important techniques for critical dimension (CD) and overlay metrology in semiconductor manufacturing over the past decades due to its inherent noncontact, nondestructive, time-effective, and relatively inexpensive merits over other metrology techniques, such as scanning electron microscopy (SEM) and atomic force microscopy (AFM). As a kind of model-based optical metrology, the measurement in optical scatterometry is not straightforward and typically involves solving a complicated inverse diffraction problem. However, it is not restricted by the well-known Abbe diffraction limit as usually encountered in the image-based metrology techniques and thus has become a good alternative to SEM and AFM in addressing devices with sub-wavelength feature sizes in semiconductor industry. This chapter aims to give the engineers and the graduates working in relevant fields some basic knowledge in optical scatterometry. Emphasis will be given to the two basic steps involved in the implementation of optical scatterometry, including the measurement of the optical response of a nanostructure under test by a scatterometer and the modeling of the light-nanostructure interaction and the extraction of the parameters under measurement from the measured optical response by solving an inverse diffraction problem. Some examples on the measurement of CD, overlay, and line roughness will also be presented to demonstrate the specific applications of optical scatterometry.

Surface defect detection, which is carried out in advance of defect review process during surface defect inspection of products having smoothly finished surfaces such as bare semiconductor wafers, magnetic disks, and optical components, is important process to assure the quality of products. In this chapter, a surface defect detection method, in which defect detection is carried out in such a way that the existence of a surface defect on a target of interest is verified by detecting frictional heat induced by a collision between a micro thermal sensor and a surface defect, is described. Although the frictional heat to be generated by a collision between the micro thermal sensor and a surface defect is expected to be small since surface defects required to be verified during the inspection are quite small, the micro thermal sensor designed to have a micrometric sensor element is expected to carry out highly sensitive detection of the frictional heat and thus realize high-resolution surface defect detection. A principle of the surface defect detection method based on the micro thermal sensor is at first described. After that, design and fabrication of the micro thermal sensor based on photolithography process are presented. In addition, by using the developed micro thermal sensor, some experiments have been carried out to demonstrate the feasibility of the defect detection method. An example of the application of micro thermal sensor for surface defect detection in the hard disk drive industry is also introduced.

X-ray computed tomography (CT) has emerged over the last years as an innovative dimensional measuring technique and has been increasingly applied in industry. This chapter describes the state of the art, the main technical characteristics, and examples of applications of CT in industrial dimensional metrology. Although still in its youth, metrological CT offers unique solutions and provides several advantages in comparison to other coordinate measuring systems such as tactile coordinate measuring machines. In particular, CT systems allow reconstructing holistic three-dimensional models of the scanned workpieces, which are then used to obtain nondestructive and noncontact measurements of outer as well as inner features. However, important drawbacks still limit a wider acceptance of CT in industrial metrology. One of the most critical aspects is the establishment of metrological traceability, which is often challenging due to many and complex error sources that affect CT measurements and complicate the evaluation of metrological performances and of task-specific uncertainties

In the new digital environment of Industry 4.0 for Germany, Innovation 25 program for Japan, Advanced Manufacturing for USA, Intelligent Manufacturing or Made in China 2025 for China, Factories of the Future for France, etc., the measurement uncertainty needs a specific management in order to control the quality of the manufactured part. In this future digital world, where the software will have a central position in the verification of a specification, it is necessary to provide to the metrologist data with uncertainty in real time. The aim of this chapter is to present the uncertainty calculation methodologies. The common analytical and numerical methods to estimate uncertainty will be presented.

Establishment of the tool-workpiece contact, in which the diamond tool is set on the workpiece surface with a small contact force, determines the depth of cut accuracy in a force sensor-integrated fast tool servo (FS-FTS) for single point diamond microcutting and the scan force and scan depth in the following step of on-machine surface metrology. Molecular dynamics (MD) simulations are carried out to characterize the tool-workpiece contact process. It is clarified that even a small instability induced by the vibration of the workpiece atoms can generate large uncertainties in the subnanometric MD simulation results. Based on the vibration of the workpiece, atoms have a certain period determined by the MD model size; a multi-relaxation time method is proposed for reduction of the atom vibrations and stabilization of the MD model. It is confirmed that the proposed multi-relaxation time method is effective to eliminate the instability over a wide temperature range up to room temperature under which a practical microcutting or surface metrology process is carried out. An accurate elastic-plastic transition contact depth is then evaluated by observing the residual defects on the workpiece surface after the diamond tool is retracted back to its initial position.