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  • 1.
    Daemi, Bita
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Advanced image analysis verifies geometry performance of micro-milling systems2017Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 56, nr 10, s. 2912-2921Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Accurate dimensional measurement of micro-milled items is a challenge and machine specifications do not include operational parameters in the workshop. Therefore, a verification test that shows the machine's overall geometrical performance over its working area would help machine users in the assessment and adjustment of their equipment. In this study, we present an optical technique capable of finding micro-milled features at submicron uncertainty over working areas > 10 cm(2). The technique relies on an ultra-precision measurement microscope combined with advanced image analysis to get the center of gravity of milled cross-shaped features at subpixel levels. Special algorithms had to be developed to handle the disturbing influence of burr and milling marks. The results show repeatability, reproducibility, and axis straightness for three micro-milling facilities and also discovered an unknown 2 mu m amplitude undulation in one of them.

  • 2.
    Daemi, Bita
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Lateral performance evaluation of laser micromachining by highprecision optical metrology and image analysis2017Ingår i: Precision engineering, ISSN 0141-6359, E-ISSN 1873-2372, ISSN 0141-6359Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Today several techniques are available for micro-manufacturing. Yet, it is difficult to assess the precisionand lateral X,Y accuracy of these techniques. The available accuracy information is usually based on spec-ifications given by machine suppliers. This information is based on in-house laboratory tests performedby dedicated machine operators and within an adapted environment. In practice, the accuracy is likelyto vary due to environmental conditions, materials and operator skills. In order to check the specifica-tions in realistic environments the EUMINAfab infrastructure consortium initiated a set of independenthigh precision onsite verification tests on different laser micromachining installations. In addition toproviding performance verification, it gave the participating partners real capability information of theirequipment and possibilities to improve machining performance to a higher level. In this study a compre-hensive verification test was designed and carried out by using a high precision metrology method for 2Dmeasurements based on subpixel resolution image analysis. This methodology improved our knowledgeof the capabilities of three laser micromachining installations, and showed that specifications at singlemicron levels are hard to obtain.

  • 3.
    Daemi, Bita
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Performance Evaluation of Micro Milling Installations2013Ingår i: Proceedings of the 10th International Conference on Multi-Material Micro Manufacture / [ed] Azcárate, S.; Dimov S., Singapore: Research Publishing Services, 2013, s. 213-216Konferensbidrag (Refereegranskat)
    Abstract [en]

    Micro manufacturing has developed into many areas over the past decade. Several manufacturing technologies are available but the precision and accuracy of the techniques are still difficult to get access to. Typically the capability information of micro milling equipment is based on specifications given by the machine deliverers. The specified high accuracy is likely to be altered in practice because of environmental conditions and operator skills. So in practice the absolute performances of micro milling/machining equipment may be far off from their listed specifications. When forming the EUMINAfab infrastructure consortium it was decided that independent high precision verification testsshould be made on different installations to help the micro-manufacturers to get the real capability information of their equipment and be able to improve performance to a higher EUMINAfab level. In this study a comprehensive verification test was designed and carried out by using an ultra-precision metrology method for 2D measurements in order to establish more knowledge about the capabilities of micro milling equipment. The measurement results show the machine’s X,Y positioning accuracy, pseudo-repeatability, reproducibility and axis straightness of two different micro milling installations.

  • 4.
    Ekberg, Lars Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Development of ultra-precision tools for metrology and lithography of large area photomasks and high definition displays2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Large area flat displays are nowadays considered being a commodity. After the era of bulky CRT TV technology, LCD and OLED have taken over as the most prevalent technologies for high quality image display devices. An important factor underlying the success of these technologies has been the development of high performance photomask writers in combination with a precise photomask process. Photomask manufacturing can be regarded as an art, highly dependent on qualified and skilled workers in a few companies located in Asia. The manufacturing yield in the photomask process depends to a great extent on several steps of measurements and inspections. Metrology, which is the focus of this thesis, is the science of measurement and is a prerequisite for maintaining high quality in all manufacturing processes. The details and challenges of performing critical measurements over large area photomasks of square meter sizes will be discussed. In particular the development of methods and algorithms related to the metrology system MMS15000, the world standard for large area photomask metrology today, will be presented.

    The most important quality of a metrology system is repeatability. Achieving good repeatability requires a stable environment, carefully selected materials, sophisticated mechanical solutions, precise optics and capable software. Attributes of the air including humidity, CO2 level, pressure and turbulence are other factors that can impact repeatability and accuracy if not handled properly. Besides the former qualities, there is also the behavior of the photomask itself that needs to be carefully handled in order to achieve a good correspondence to the Cartesian coordinate system. An uncertainty specification below 100 nm (3σ) over an area measured in square meters cannot be fulfilled unless special care is taken to compensate for gravity-induced errors from the photomask itself when it is resting on the metrology tool stage. Calibration is therefore a considerable challenge over these large areas. A novel method for self-calibration will be presented and discussed in the thesis. This is a general method that has proven to be highly robust even in cases when the self-calibration problem is close to being underdetermined.

    A random sampling method based on massive averaging in the time domain will be presented as the solution for achieving precise spatial measurements of the photomask patterns. This method has been used for detection of the position of chrome or glass edges on the photomask with a repeatability of 1.5 nm (3σ), using a measurement time of 250 ms. The method has also been used for verification of large area measurement repeatability of approximately 10 nm (3σ) when measuring several hundred measurement marks covering an area of 0.8 x 0.8 m2.

    The measurement of linewidths, referred to in the photomask industry as critical dimension (CD) measurements, is another important task for the MMS15000 system. A threshold-based inverse convolution method will be presented that enhances resolution down to 0.5 µm without requiring a change to the numerical aperture of the system.

    As already mentioned, metrology is very important for maintaining high quality in a manufacturing environment. In the mask manufacturing industry in particular, the cost of poor quality (CoPQ) is extremely high. Besides the high materials cost, there are also the stringent requirements placed on CD and mask overlay, along with the need for zero defects that make the photomask industry unique. This topic is discussed further, and is shown to be a strong motivation for the development of the ultra-precision metrology built into the MMS15000 system.

  • 5.
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Development of a state-of-the-art nm-measurement system for square meter sized lithography masks2012Ingår i: Proceedings of the 12th euspen International Conference 2012, 2012, s. 57-62Konferensbidrag (Refereegranskat)
    Abstract [en]

    The demands and solutions for ultra-precision metrology in the manufacturing of lithography masks for the display industry are indeed challenging. Specification demands to be overcome are a measurement repeatability of 10 nm (3 σ) and an absolute accuracy of better than 100 nm (3 σ) on a scale of more than 1.5 m in the X and Y directions. The design of a measurement system that meets these requirements calls for careful selections of materials such as metal, ceramic composites, quartz or glass as they at this precision level are highly affected by the surrounding temperature. Also the fact that the refractive index of air in the interferometers measuring absolute distances is affected by temperature, pressure, humidity and CO2 content make the reference measurements really challenging [1].

    As in many other areas in the industry high quality metrology is the key for success in developing high accuracy production tools. This paper will therefore start by introducing the metrology requirements of mask making for display screens and end with the state-of-the-art results we have achieved.

  • 6.
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Metrology: a forgotten added value maker that eliminates cost of poor qualityand supports a sustainable zero defect production2012Ingår i: The 5th International Swedish Production Symposium, 2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    The purpose of this paper is to highlight the importance of metrology in the industrial production process.

    Different kinds of processes, like mass production of parts and the very special photo mask process will be

    discussed. It will be shown how much impact metrology has on the added value of the product in the latter

    process. Proper inspection planning with feedbacks from the process at certain points is very important for

    both keeping up the yield and also keeping the process stable. In the example presented about the photo

    mask process bad inspection planning will have extreme consequences. Another aspect that will be

    discussed is the problem when metrology tools or production tools do not fulfil their intended specifications.

    In many cases the user is completely dependent on the tools without any chance to verify their performance.

    This will of course lead to poor quality. Solutions to these kinds of problems generate additional costs in

    investments but will in the long run pay off since quality can be assured.

  • 7.
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Ultra precision metrology: the key for mask lithography and manufacturing of high definition displays2011Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Metrology is the science of measurement. It is also a prerequisite for maintaining a high quality in all manufacturing processes. In this thesis we will present the demands and solutions for ultra-precision metrology in the manufacturing of lithography masks for the TV-display industry. The extreme challenge that needs to be overcome is a measurement uncertainty of 10 nm on an absolute scale of more that 2 meters in X and Y. Materials such as metal, ceramic composites, quartz or glass are highly affected by the surrounding temperature when tolerances are specified at nanometer levels. Also the fact that the refractive index of air in the interferometers measuring absolute distances is affected by temperature, pressure, humidity and CO2 contents makes the reference measurements really challenging. This goes hand in hand with the ability of how to design a mask writer, a pattern generator with a performance good enough for writing masks for the display industry with sub-micron accuracy over areas of square meters.

     As in many other areas in the industry high quality metrology is the key for success in developing high accuracy production tools. The aim of this thesis is therefore to discuss the metrology requirements of mask making for display screens. Defects that cause stripes in the image of a display, the so called “Mura” effect, are extremely difficult to measure as they are caused by spatially systematic errors in the mask writing process in the range of 10-20 nm. These errors may spatially extend in several hundreds of mm and are superposed by random noise with significantly higher amplitude compared to the 10-20 nm.

     A novel method for measuring chromium patterns on glass substrates will also be presented in this thesis. This method will be compared to methods based on CCD and CMOS images. Different methods have been implementedin the Micronic MMS1500 large area measuring machine, which is the metrology tool used by the mask industry, for verifying the masks made by the Micronic mask writers. Using alternative methods in the same system has been very efficient for handling different measurement situations. Some of  the discussed methods are also used by the writers for calibration purposes.

     

  • 8.
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik. Micronic Mydata AB,Täby, Sweden .
    Z-correction, a method for achieving ultra-high absolute pattern placement accuracy of large area photomasks2013Ingår i: Proceedings of the 13th International Conference of the European Society for Precision Engineering and Nanotechnology, EUSPEN 2013, euspen , 2013, Vol. 2, s. 253-256Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Photomasks are used in the production of LCD, OLED and other kinds of displays. For TV displays these photomasks, made of quartz glass with a Cr pattern, may have sizes up to 1.62 × 1.78 m2 and a thickness up to 16 mm. The absolute placement accuracy, i.e. ×,Y position of a pi×el or line in the mask pattern needs to be better than 150 nm (3s). The demand for higher resolution displays has led to tighter flatness requirements of the photomask, to secure that the chrome pattern is always in best focus. In contrast to small area semiconductor masks with dimensions up to 300 × 300 mm2and three point supports, the large area photomasks have to rest on a large stage in the mask writer. It is then unavoidable that distortions will be induced due to the fact that the glass backside or stage surface is not perfectly flat. If not corrected for, these distortions in Z direction can easily generate geometrical errors in the ×,Y plane corresponding to pattern displacements of several hundred nanometers. To avoid these ×,Y errors we have developed a technique called Z-correction. It is a function developed for correcting the mask pattern placement prior to the writing process in the pattern generator or in a verification measurement in the MMS15000 metrology tool [1]. This is the first time this method is used for improving the accuracy of photo masks. It is based on height measurements of the quartz glass when it is resting on the stage during the temperature stabilizing time. Without using Z-correction it is very challenging to achieve an absolute uncertainty better than ∼200 nm (3s) over an area of 0.8 × 0.8 m2. With Z-correction it is possible to enhance this number to < 100 nm (3s). In the MMS15000 metrology tool the performance is even better, ∼50 nm (3s) over a 0.8 × 0.8 m2 stage area when using Z-correction in the self-calibration process. [2] [3].

  • 9.
    Ekberg, Peter
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Daemi, Bita
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    3D precision measurements of meter sized surfaces using low cost illumination and camera techniques2017Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 28, nr 4, artikel-id 045403Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using dedicated stereo camera systems and structured light is a well-known method for measuring the 3D shape of large surfaces. However the problem is not trivial when high accuracy, in the range of few tens of microns, is needed. Many error sources need to be handled carefully in order to obtain high quality results. In this study, we present a measurement method based on low-cost camera and illumination solutions combined with high-precision image analysis and a new approach in camera calibration and 3D reconstruction. The setup consists of two ordinary digital cameras and a Gobo projector as a structured light source. A matrix of dots is projected onto the target area. The two cameras capture the images of the projected pattern on the object. The images are processed by advanced subpixel resolution algorithms prior to the application of the 3D reconstruction technique. The strength of the method lays in a different approach for calibration, 3D reconstruction, and high-precision image analysis algorithms. Using a 10 mm pitch pattern of the light dots, the method is capable of reconstructing the 3D shape of surfaces. The precision (1 sigma repeatability) in the measurements is < 10 mu m over a volume of 60 x 50 x 10 cm(3) at a hardware cost of similar to 2% of available advanced measurement techniques. The expanded uncertainty (95% confidence level) is estimated to be 83 mu m, with the largest uncertainty contribution coming from the absolute length of the metal ruler used as reference.

  • 10.
    Ekberg, Peter
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Mattson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    A new 2D-self-calibration method with large freedom and high-precision performance for imaging metrology devices2015Ingår i: Proceedings of the 15th International Conference of the European Society for Precision Engineering and Nanotechnology, EUSPEN 2015, Elsevier, 2015, s. 159-160Konferensbidrag (Refereegranskat)
    Abstract [en]

    When calibrating 2D (or 3D) metrology systems you need to rely on a traceable artefact for the calibration. However if the system you intend to calibrate has smaller uncertainties than the uncertainty of the reference artefact, the uncertainty of the instrument will be dominated by the artefact and not by the instrument. The only way to reveal the performance of the instrument is then to use self-calibration, i.e. a calibration without any externally verified references, except a 1D traceable measurement between two points on an artefact. Already in 1997, Mikael Raugh developed the rigorous mathematics for self-calibration of a 2D metrology stage, based on a lattice structured artefact. The original method and subsequent later improvements have in common that the problem is solved by using some assumptions regarding the artefact used in the calibration; like that the locations of the marks in the lattice are approximately known. There are also other constrains in the mathematical solution that limits its practical use in the industry. In this paper the application of a new general self-calibration algorithm is presented giving a large freedom to the positioning of the artefact, and also less demands on the 2D-structure on it. Rather than being based on rigorous mathematics requiring very exact positioning of the artefact, our algorithm is using a numerical iterative technique to minimize all overall errors. The algorithm is an enhancement of the self-calibration method already published by P. Ekberg et al. The algorithm has successfully been tested by simulations and by using real data from a white light interference microscope, yielding X, Y precision of few nm. The algorithm has also been used for separating distortions in ordinary low cost camera based systems opening up possibilities for accurate measurements in images. In the latter case the images can be compensated for most errors, like barrel or pin-cushion distortions, as well as perspective effects due to the angle of the camera relative the object.

  • 11.
    Ekberg, Peter
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Traceable X,Y self-calibration at single nm level of an optical microscope used for coherence scanning interferometry2018Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 29, nr 3, artikel-id 035005Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Coherence scanning interferometry used in optical profilers are typically good for Z-calibration at nm-levels, but the X,Y accuracy is often left without further notice than typical resolution limits of the optics, i.e. of the order of similar to 1 mu m. For the calibration of metrology tools we rely on traceable artefacts, e.g. gauge blocks for traditional coordinate measurement machines, and lithographically mask made artefacts for microscope calibrations. In situations where the repeatability and accuracy of the measurement tool is much better than the uncertainty of the traceable artefact, we are bound to specify the uncertainty based on the calibration artefact rather than on the measurement tool. This is a big drawback as the specified uncertainty of a calibrated measurement may shrink the available manufacturing tolerance. To improve the uncertainty in X, Y we can use self-calibration. Then, we do not need to know anything more than that the artefact contains a pattern with some nominal grid. This also gives the opportunity to manufacture the artefact in-house, rather than buying a calibrated and expensive artefact. The self-calibration approach we present here is based on an iteration algorithm, rather than the traditional mathematical inversion, and it leads to much more relaxed constrains on the input measurements. In this paper we show how the X, Y errors, primarily optical distortions, within the field of view (FOV) of an optical coherence scanning interferometry microscope, can be reduced with a large factor. By self-calibration we achieve an X, Y consistency in the 175 x 175 mu m(2) FOV of similar to 2.3 nm (1 sigma) using the 50x objective. Besides the calibrated coordinate X, Y system of the microscope we also receive, as a bonus, the absolute positions of the pattern in the artefact with a combined uncertainty of 6 nm (1s) by relying on a traceable 1D linear measurement of a twin artefact at NIST.

  • 12.
    Ekberg, Peter
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik. Micronic Laser Systems, Stockholm, Sweden.
    Stiblert, Lars
    Micronic Laser Systems, Stockholm, Sweden.
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    A Large-area ultra-precision 2D geometrical measurement technique based on statistical random phase detection2012Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 23, nr 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The manufacturing of high-quality chrome masks used in the display industry for the manufacturing of liquid crystals, organic light emission diodes and other display devices would not be possible without high-precision large-area metrology. In contrast to the semiconductor industry where 6' masks are most common, the quartz glass masks for the manufacturing of large area TVs can have sizes of up to 1.6 x 1.8 m(2). Besides the large area, there are demands of sub-micrometer accuracy in 'registration', i.e. absolute dimensional measurements and nanometer requirements for 'overlay', i.e. repeatability. The technique for making such precise measurements on large masks is one of the most challenging tasks in dimensional metrology today. This paper presents a new approach to two-dimensional (2D) ultra-precision measurements based on random sampling. The technique was recently presented for ultra-precise one-dimensional (1D) measurement. The 1D method relies on timing the scanning of a focused laser beam 200 mu m in the Y-direction from an interferometrically determined reference position. This microsweep is controlled by an acousto-optical deflector. By letting the microsweep scan from random X-positions, we can build XY-recordings through a time-to-space conversion that gives very precise maps of the feature edges of the masks. The method differs a lot from ordinary image processing methods using CCD or CMOS sensors for capturing images in the spatial domain. We use events grabbed by a single detector in the time domain in both the X-and Y-directions. After a simple scaling, we get precise and repeatable spatial information. Thanks to the extremely linear microsweep and its precise power control, spatial and intensity distortions, common in ordinary image processing systems using 2D optics and 2D sensors, can be practically eliminated. Our 2D method has proved to give a standard deviation in repeatability of less than 4 nm (1 sigma) in both the X-and Y-directions over an area of approximately 0.8 x 0.8 m(2). Only feature edges are recorded, so all irrelevant information in areas containing constant intensity are filtered out already by the hardware. This relaxes the demands and complexity of the data channel dramatically compared to conventional imaging systems.

  • 13.
    Ekberg, Peter
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Stiblert, Lars
    Micronic Laser Systems, Stockholm, Sweden.
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    A new general approach for solving the self-calibration problem on large area 2D ultra-precision coordinate measurement machines2014Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 25, nr 5, s. 055001-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The manufacturing of flat panel displays requires a number of photomasks for the placement of pixel patterns and supporting transistor arrays. For large area photomasks, dedicated ultra-precision writers have been developed for the production of these chromium patterns on glass or quartz plates. The dimensional tolerances in X and Y for absolute pattern placement on these plates, with areas measured in square meters, are in the range of 200-300 nm (3 sigma). To verify these photomasks, 2D ultra-precision coordinate measurement machines are used having even tighter tolerance requirements. This paper will present how the world standard metrology tool used for verifying large masks, the Micronic Mydata MMS15000, is calibrated without any other references than the wavelength of the interferometers in an extremely well-controlled temperature environment. This process is called self-calibration and is the only way to calibrate the metrology tool, as no square-meter-sized large area 2D traceable artifact is available. The only parameter that cannot be found using self-calibration is the absolute length scale. To make the MMS15000 traceable, a 1D reference rod, calibrated at a national metrology lab, is used. The reference plates used in the calibration of the MMS15000 may have sizes up to 1 m(2) and a weight of 50 kg. Therefore, standard methods for self-calibration on a small scale with exact placements cannot be used in the large area case. A new, more general method had to be developed for the purpose of calibrating the MMS15000. Using this method, it is possible to calibrate the measurement tool down to an uncertainty level of <90 nm (3 sigma) over an area of (0.8 x 0.8) m(2). The method used, which is based on the concept of iteration, does not introduce any more noise than the random noise introduced by the measurements, resulting in the lowest possible noise level that can be achieved by any self-calibration method.

  • 14.
    Ekberg, Peter
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Stiblert, Lars
    Micronic Laser Systems, Stockholm, Sweden.
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Ultra-precision geometrical measurement technique based on a statistical random phase clock combined with acoustic-optical deflection2010Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 21, nr 12, s. 125103-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mask writers and large area measurements systems are key systems for production of large liquid crystal displays (LCD) and image devices. With position tolerances in the sub-mu m range over square meter sized masks, the metrology challenges are indeed demanding. Most systems used for this type of measurement rely on a microscope camera imaging system, provided with a charge coupled device, a complementary metal-oxide-semiconductor sensor or a time delay and integration sensor to transform the optical image to a digital gray-level image. From this image, processing algorithms are used to extract information such as location of edges. The drawback of this technique is the vast amount of data captured but never used. This paper presents a new approach for ultra-high-precision lateral measurement at nm-levels of chrome/glass patterns separated by centimeters, so called registration marks, on masks used for the LCD manufacturing. Registration specifications demand a positioning accuracy <200 nm and critical dimensions, i.e. chrome line widths, which need to be accurate in the 80 nm range. This accuracy has to be achieved on glass masks of 2.4 x 1.6 m(2) size. Our new measurement method is based on nm-precise lateral scanning of a focused laser beam combined with statistical random phase sampling of the reflected signal. The precise scanning is based on an extremely accurate time measuring device controlling an acousto optic deflector crystal. The method has been successfully applied in measuring the 4 mu m pitch of reference gratings at standard deviations sigma of 0.5 nm and registration marks separated by several cm at standard deviations of 23 nm.

  • 15.
    Ekberg, Peter
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Stiblert, Lars
    Micronic Laser Systems, Stockholm, Sweden.
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Z-correction, a method for achieving ultraprecise self-calibration on large area coordinate measurement machines for photomasks2014Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 25, nr 5, s. 055002-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-quality photomasks are a prerequisite for the production of flat panel TVs, tablets and other kinds of high-resolution displays. During the past years, the resolution demand has become more and more accelerated, and today, the high-definition standard HD, 1920 x 1080 pixels(2), is well established, and already the next-generation so-called ultra-high-definition UHD or 4K display is entering the market. Highly advanced mask writers are used to produce the photomasks needed for the production of such displays. The dimensional tolerance in X and Y on absolute pattern placement on these photomasks, with sizes of square meters, has been in the range of 200-300 nm (3 sigma), but is now on the way to be <150 nm (3 sigma). To verify these photomasks, 2D ultra-precision coordinate measurement machines are used with even tighter tolerance requirements. The metrology tool MMS15000 is today the world standard tool used for the verification of large area photomasks. This paper will present a method called Z-correction that has been developed for the purpose of improving the absolute X, Y placement accuracy of features on the photomask in the writing process. However, Z-correction is also a prerequisite for achieving X and Y uncertainty levels <90 nm (3 sigma) in the self-calibration process of the MMS15000 stage area of 1.4 x 1.5 m(2). When talking of uncertainty specifications below 200 nm (3 sigma) of such a large area, the calibration object used, here an 8-16 mmthick quartz plate of size approximately a square meter, cannot be treated as a rigid body. The reason for this is that the absolute shape of the plate will be affected by gravity and will therefore not be the same at different places on the measurement machine stage when it is used in the self-calibration process. This mechanical deformation will stretch or compress the top surface (i.e. the image side) of the plate where the pattern resides, and therefore spatially deform the mask pattern in the X- and Y-directions. Errors due to this deformation can easily be several hundred nanometers. When Z-correction is used in the writer, it is also possible to relax the flatness demand of the photomask backside, leading to reduced manufacturing costs of the plates.

  • 16.
    Ekberg, Peter
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Su, Rong
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Chang, Ernest W.
    Yun, Seok Hyun
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Fast and accurate metrology of multi-layered ceramic materials by an automated boundary detection algorithm developed for optical coherence tomography data2014Ingår i: Optical Society of America. Journal A: Optics, Image Science, and Vision, ISSN 1084-7529, E-ISSN 1520-8532, Vol. 31, nr 2, s. 217-226Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Optical coherence tomography (OCT) is useful for materials defect analysis and inspection with the additional possibility of quantitative dimensional metrology. Here, we present an automated image-processing algorithm for OCT analysis of roll-to-roll multilayers in 3D manufacturing of advanced ceramics. It has the advantage of avoiding filtering and preset modeling, and will, thus, introduce a simplification. The algorithm is validated for its capability of measuring the thickness of ceramic layers, extracting the boundaries of embedded features with irregular shapes, and detecting the geometric deformations. The accuracy of the algorithm is very high, and the reliability is better than 1 mu m when evaluating with the OCT images using the same gauge block step height reference. The method may be suitable for industrial applications to the rapid inspection of manufactured samples with high accuracy and robustness.

  • 17.
    Ekberg, Peter
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Su, Rong
    Leach, Richard
    High-precision lateral distortion measurement and correction in coherence scanning interferometry using an arbitrary surface2017Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 25, nr 16, s. 18703-18712Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lateral optical distortion is present in most optical imaging systems. In coherence scanning interferometry, distortion may cause field-dependent systematic errors in the measurement of surface topography. These errors become critical when high-precision surfaces, e.g. precision optics, are measured. Current calibration and correction methods for distortion require some form of calibration artefact that has a smooth local surface and a grid of high-precision manufactured features. Moreover, to ensure high accuracy and precision of the absolute and relative locations of the features of these artefacts, requires their positions to be determined using a traceable measuring instrument, e.g. a metrological atomic force microscope. Thus, the manufacturing and calibration processes for calibration artefacts are often expensive and complex. In this paper, we demonstrate for the first time the calibration and correction of optical distortion in a coherence scanning interferometer system by using an arbitrary surface that contains some deviations from flat and has some features (possibly just contamination), such that feature detection is possible. By using image processing and a self-calibration technique, a precision of a few nanometres is achieved for the distortion correction. An inexpensive metal surface, e.g. the surface of a coin, or a scratched and defected mirror, which can be easily found in a laboratory or workshop, may be used. The cost of the distortion correction with nanometre level precision is reduced to almost zero if the absolute scale is not required. Although an absolute scale is still needed to make the calibration traceable, the problem of obtaining the traceability is simplified as only a traceable measure of the distance between two arbitrary points is needed. Thus, the total cost of transferring the traceability may also be reduced significantly using the proposed method. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.

  • 18.
    Ekberg, Peter
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik. Micronic Mydata AB, Sweden .
    Von Sydow, A.
    Past and future challenges from a display mask writer perspective2012Ingår i: Photomask and Next-Generation Lithography Mask Technology XIX, SPIE - International Society for Optical Engineering, 2012, Vol. 8441, s. 84410N-Konferensbidrag (Refereegranskat)
    Abstract [en]

    Since its breakthrough, the liquid crystal technology has continued to gain momentum and the LCD is today the dominating display type used in desktop monitors, television sets, mobile phones as well as other mobile devices. To improve production efficiency and enable larger screen sizes, the LCD industry has step by step increased the size of the mother glass used in the LCD manufacturing process. Initially the mother glass was only around 0.1 m 2 large, but with each generation the size has increased and with generation 10 the area reaches close to 10 m2. The increase in mother glass size has in turn led to an increase in the size of the photomasks used - currently the largest masks are around 1.6 &amp;times; 1.8 meters. A key mask performance criterion is the absence of "mura" - small systematic errors captured only by the very sensitive human eye. To eliminate such systematic errors, special techniques have been developed by Micronic Mydata. Some mura suppressing techniques are described in this paper. Today, the race towards larger glass sizes has come to a halt and a new race - towards higher resolution and better image quality - is ongoing. The display mask is therefore going through a change that resembles what the semiconductor mask went through some time ago: OPC features are introduced, CD requirements are increasing sharply and multi tone masks (MTMs) are widely used. Supporting this development, Micronic Mydata has introduced a number of compensation methods in the writer, such as Z-correction, CD map and distortion control. In addition, Micronic Mydata MMS15000, the world's most precise large area metrology tool, has played an important role in improving mask placement quality and is briefly described in this paper. Furthermore, proposed specifications and system architecture concept for a new generation mask writers - able to fulfill future image quality requirements - is presented in this paper. This new system would use an AOD/AOM writing engine and be capable of resolving 0.6 micron features.

  • 19.
    Li, Yujiang
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Datorsystem för konstruktion och tillverkning.
    Su, Rong
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Hedlind, Mikael
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Datorsystem för konstruktion och tillverkning.
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Kjellberg, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Datorsystem för konstruktion och tillverkning.
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Model based in-process monitoring with optical coherence tomography2012Ingår i: Procedia CIRP: 1st CIRP Global Web Conference: Interdisciplinary Research in Production Engineering (CIRPE2012),, Elsevier, 2012, s. 70-73Konferensbidrag (Refereegranskat)
    Abstract [en]

    The demands on in-process 3D monitoring in ceramic micromanufacturing industry require a high-precision, non-destructive, rapid and automated inspection technique for measuring the thickness of component layer, determining the shape and dimensions of the embedded 3D structures, and detecting the de-bonding, cracks, warping and deformation. One of the promising metrology techniques is optical coherence tomography (OCT). With the dedicated image processing algorithm and the industrial product data exchange standard, the model-based integration of OCT as a new metrology tool is demonstrated. As a generic standard for any product or manufacturing information, ISO 10303 STEP AP242 is employed for the measured data model. Unambiguous data representation is achieved by integrating additional modelling constraints. The proposed framework allows fully using the technical advantages of OCT to in-process 3D monitoring.

  • 20. Su, R.
    et al.
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Leach, R.
    High-precision lateral distortion correction in coherence scanning interferometry using an arbitrary surface2017Ingår i: Proceedings - ASPE 2017 Spring Topical Meeting - Precision Engineering and Optics: What are the Limits of Precision, and How to Characterize Them?, American Society for Precision Engineering, ASPE , 2017, s. 84-89Konferensbidrag (Refereegranskat)
  • 21.
    Su, Rong
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Chang, Ernest
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Yun, Seok
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Enhancement of probing depth and measurement accuracy of optical coherence tomography for metrology of multi-layered ceramics2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    Light scattering strongly limits the probing depth and speckles degrade the image quality in optical coherence tomography (OCT) detection of embedded features in high-scattering ceramics. For high-precision metrology application we evaluated an OCT system working at a centre wavelength of 1.7μm in order to improve the probing depth, and developed a dedicated image processing algorithm for improving the measurement accuracy and speed. The results are demonstrated for 3D OCT measurement of embedded laser-machined pattern in ceramics.

  • 22.
    Su, Rong
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Leitner, Michael
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Accurate and automated image segmentation of 3D optical coherence tomography data suffering from low signal to noise levelsIngår i: IEEE Transactions on Image Processing, ISSN 1057-7149, E-ISSN 1941-0042Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Optical coherence tomography (OCT) has proven to be a useful tool for investigating internal structures in ceramic tapes and the technique is expected to be important for roll-to-roll manufacturing. However, because of high scattering in ceramic materials, noise and speckles deteriorate the image quality which makes automated quantitative measurements of internal interfaces difficult. To overcome this difficulty we present in this paper a new image analysis approach based on volumetric OCT data. The engine in the analysis is a 3D image processing and analysis algorithm. It is dedicated for boundary segmentation and dimensional measurement in volumetric OCT images, and offers high accuracy, efficiency, robustness, sub-pixel resolution and a fully automated operation. The method relies on the correlation property of a physical interface and eliminates effectively pixels caused by noise and speckles. The remaining pixels being stored are the ones confirmed to be related to the target interfaces. Segmentation of tilted and curved internal interfaces separated by ~10 μm in z-direction is demonstrated. The algorithm also extracts full-field top-view intensity maps of the target interfaces for high-accuracy measurements in x- and y- directions. The methodology developed here may also be adopted in other similar 3D imaging and measurement technologies, e.g. ultrasound imaging, and for various materials.

  • 23.
    Su, Rong
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Leitner, Michael
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Accurate and automated image segmentation of 3D optical coherence tomography data suffering from low signal-to-noise levels2014Ingår i: Journal of the Optical Society of America A, ISSN 0740-3232, Vol. 31, nr 12, s. 2551-2560Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Optical coherence tomography (OCT) has proven to be a useful tool for investigating internal structures in ceramic tapes, and the technique is expected to be important for roll-to-roll manufacturing. However, because of high scattering in ceramic materials, noise and speckles deteriorate the image quality, which makes automated quantitative measurements of internal interfaces difficult. To overcome this difficulty we present in this paper an innovative image analysis approach based on volumetric OCT data. The engine in the analysis is a 3D image processing and analysis algorithm. It is dedicated to boundary segmentation and dimensional measurement in volumetric OCT images, and offers high accuracy, efficiency, robustness, subpixel resolution, and a fully automated operation. The method relies on the correlation property of a physical interface and effectively eliminates pixels caused by noise and speckles. The remaining pixels being stored are the ones confirmed to be related to the target interfaces. Segmentation of tilted and curved internal interfaces separated by similar to 10 mu m in the Z direction is demonstrated. The algorithm also extracts full-field top-view intensity maps of the target interfaces for high-accuracy measurements in the X and Y directions. The methodology developed here may also be adopted in other similar 3D imaging and measurement technologies, e.g., ultrasound imaging, and for various materials.

  • 24.
    Su, Rong
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Kirillin, Mikhail
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Three-dimensional metrology of embedded microfeatures in ceramics by infrared optical coherence tomography – advantages and limitations2015Ingår i: The Proceedings of the 11th International Conference and Exhibition on Laser Metrology, Coordinate Measuring Machine and Machine Tool Performance, European society for precision engineering & nanotechnology , 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    Advanced printing, structuring, and lamination technologies allow for large-scale and cost-effective manufacturing of multi-layered ceramic micro devices with complex three-dimensional (3D) structures. Infrared (IR) optical coherence tomography (OCT) is a promising technology for rapid, non-contact, high-resolution, and 3D inspection of the microchannels, metal prints, defects, and delaminations embedded in alumina and zirconia ceramic layers at hundreds of micrometres beneath surfaces. In this study the recent progresses of OCT technology for ceramic materials are reviewed, and its advantages and limitations as a metrology tool are evaluated through experiments and Monte Carlo simulations. Several measurement errors of OCT are revealed and the measurement in lateral directions is significantly affected by scattering in the ceramics. Besides of that, two types of image artefacts are found to be present in OCT images due to multiple reflections between neighbouring boundaries and inhomogeneity of refractive index. A wavefront aberration exists in the OCT system with a scanning scheme of two galvo mirrors.

  • 25.
    Su, Rong
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Kirillin, Mikhail
    Laboratory of Biophotonics, Institute of Applied Physics RAS, Russia.
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Roos, Arne
    The Ångstrom Laboratory, Uppsala University, Sweden.
    Sergeeva, Ekaterina
    Laboratory of Biophotonics, Institute of Applied Physics RAS, Russia.
    Mattsson, Lars
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Optical coherence tomography for quality assessment of embedded microchannels in alumina ceramic2012Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, nr 4, s. 4603-4618Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Large-scale and cost-effective manufacturing of ceramic micro devices based on tape stacking requires the development of inspection systems to perform high-resolution in-process quality control of embedded manufactured cavities, metal structures and defects. With an optical coherence tomography (OCT) system operating at 1.3 mu m and a dedicated automated line segmentation algorithm, layer thicknesses can be measured and laser-machined channels can be verified in alumina ceramics embedded at around 100 mu m depth. Monte Carlo simulations are employed to analyze the abilities of OCT in imaging of the embedded channels. The light scattering parameters required as input data for simulations are evaluated from the integrating sphere measurements of collimated and diffuse transmittance spectra using a reconstruction algorithm based on refined diffusion approximation approach.

  • 26.
    Åman, Johan
    et al.
    KTH, Skolan för industriell teknik och management (ITM).
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Leonardsson, Lars
    Micronic Laser Systems, Stockholm, Sweden.
    Edgren, Klas
    KTH, Skolan för industriell teknik och management (ITM).
    Sandström, Torbjörn
    Micronic Laser Systems, Stockholm, Sweden.
    Stiblert, Lars
    Micronic Laser Systems, Stockholm, Sweden.
    Recent developments in large-area photomasks for display applications2001Ingår i: Journal of the Society for Information Display, ISSN 1071-0922, Vol. 9, nr 1, s. 3-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    One of the most critical areas in the manufacturing process for FPD panels or shadow masks for CRTs is lithography. Most existing lithography technologies require high-quality large-area photomasks. The requirements on these photomasks include positioning accuracy (registration) and repeatability (overlay), systematic image quality errors ("mura" or display quality), and resolution (minimum feature size). The general trend toward higher resolution and improved performance, e.g., for TFT desktop monitors, has put a strong focus on the specifications for large-area-display photomasks. This article intends to give an overview of the dominant issues for large-area-display photomasks, and illustrates differences compared with other applications. The article will also present state-of-the-art methods and trends. In particular, the aspects of positioning accuracy over large areas and systematic image-quality errors will be described. New qualitative and objective methods have been developed as means to capture systematic image-quality errors. Results indicating that errors below 25 nm can be found early in the manufacturing process is presented, thus allowing inspection for visual effects before the actual display is completed. Positioning accuracy below 400 nm (3 sigma) over 720 × 560 mm have been achieved. These results will in the future be extended up toward 1 × 1 m for generation 4 in TFT-LCD production.

1 - 26 av 26
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