High Alignment Accuracy Research Articles

Maskless Lithography Based on Digital Micro-Mirror Device (DMD) with Double Sided Microlens and Spatial Filter Array

A ultra-violet (UV) maskless lithography system is developed for arbitrary UV patterning. The system consists of an UV illumination system, a digital micro-mirror device (DMD), a projection system, and a double-sided microlens and spatial filter array (D-MSFA). The DMD acts as a virtual mask for generating arbitrary patterns by individually turning on or off of each micro-mirror. The projection lens projects the image of DMD onto the D-MSFA, which consists subsquently the fisrt microlens array (MLA1), the pinholes array, and the second microlens array (MLA2). The MLA1 focus the light from DMD to its corresponding pinhole, and the MLA2 projects the image of pinhole array onto a substrate to form a point array of UV light. The profiles of microlenses are designed optimized to chieve smallest focused spot size. A method has been developed to fabricate the D-MSFA and to ensure high microlens profile accuracy and excellent alignment between microlens arrays and pinhole array. The obatined UV spot sizze is 10 μm measured at FHMW level, and the system can generate arbitrary patterns with a minimum linewidth of 5.2 μm.

Self-Assembly and Electrostatic Carrier Technology for Via-Last TSV Formation Using Transfer Stacking-Based Chip-to-Wafer 3-D Integration

A self-assembly and electrostatic (SAE) carrier technology is developed for high-precision and high-throughput chip-to-wafer 3-D integration. In this paper, water surface tension-driven chip assembly is combined with electrostatic adhesion to keep high alignment accuracies obtained by the capillary self-assembly process. The self-assembled chips can be firmly fixed on an SAE carrier wafer by electrostatic adhesion, and then, the chips can be readily detached from the carrier by discharging and transferred to another carrier with a temporary adhesive. This paper describes the impact of chip clamping forces and electrical reliability of the SAE carrier on chips to be 3-D stacked in chip-to-wafer configuration. Through-Si via formation is demonstrated by using a via-last 3-D integration process based on the SAE carrier. The demonstration shows that the SAE carrier maintains higher chip alignment accuracies than does conventional carrier without electrostatic adhesion.

New solution for the high accuracy alignment of accelerator components

Several state-of-the-art metrology measurement methods have been investigated and combined for a fiducialization of accelerator components in the micrometric regime. The PACMAN project at CERN applied stretched-wire measurement methods to Compact Linear Collider quadrupole and cavity beam position monitor prototypes, to locate their magnetic, respectively, electromagnetic, axis using a dedicated test stand and to determine the position of the wire with respect to external alignment targets (fiducials) testing different methods, such as coordinate measuring machine measurements and microtriangulation. Further studies have been performed using a nanopositioning system, verifying the absolute accuracy and repeatability of the fiducialization method within a few micrometers.

Direct imaging exposure equipment with high overlay accuracy for flexible substrate in roll‐to‐roll method

AbstractIn order to fabricate thin‐film transistors on a flexible substrate, it is required to overlay patterns with high alignment accuracy. A polymer film can be deformed greatly and easily through thin‐film transistor fabrication processes because the glass transition point of a polymer film is below the maximum temperature of the processes. Furthermore, low stiffness of a polymer film can cause deformation when the polymer film is loaded on a working holder. These matters make it difficult to make patterns directly on a polymer film with high alignment accuracy. We proposed three concepts that solve three technical issues in order to directly make patterns with high overlay accuracy on a flexible film without a support substrate. We developed roll‐to‐roll exposure equipment with high overlay accuracy for a flexible substrate. Using this equipment, we succeeded to directly make patterns on a PET film, achieving a resolution of less than 6‐μm line and space pattern and an overlay accuracy of less than ±5 μm.

High-accuracy alignment of the grating pattern along silicon 〈1 1 2〉 directions using a short rectangular array

A method for the accurate alignment of the grating pattern along silicon 〈1 1 2〉 directions is developed. A short rectangular array is fabricated as an alignment pattern in silicon wafer through quick pre-anisotropic wet etching. The short rectangles can locate the {1 1 1} planes with zero error without the need to determine the crystal directions manually. The grating pattern is aligned along 〈1 1 2〉 directions by using the diffraction characteristic of the short rectangular array without a superfluous process or equipment. The alignment pattern occupies an area of less than 4 mm2 and can be fabricated through one-time wet etching in any location on the silicon wafer. The alignment error of this method is up to 0.013°. The method is used to fabricate a silicon grating with a period of 220 nm and a groove depth of 1.8 µm. The sidewalls of the grating are atomically smooth {1 1 1} planes with an RMS roughness of 0.162 nm.

Scanning probe-based high-accuracy overlay alignment concept for lithography applications

Overlay alignment is a concern for nanolithography applications, in particular, for those using step and repeat techniques targeting next-generation lithographic applications. In this context, a new method and a proof of concept (POC) setup for accurately aligning a mask with a semiconductor wafer is presented. Utilizing active scanning probe technology, the method is employable for various lithographic techniques such as photolithography, electron- and ion-beam lithography, nanoimprint lithography (NIL). The developed method is demonstrated in the example of NIL. It employs compact highly integrated atomic force microscopes (mini-AFM), which are fixed on the lithographic template. The mini-AFM systems are applied for imaging of the surface relief marks on the semiconductor wafer to carry out the alignment process. In a next step, the obtained AFM section images are used to calculate the deviations and steer the bottom stage carrying the processed wafer in order to achieve the desired positioning accuracy. A POC test setup was built for emulation of the alignment procedure. Several measurement studies are addressed to evaluate the applicability of the overlay alignment method. As a result, it is shown that the implemented test setup is able to determine the positioning error of the bottom stage carrying the wafer with an accuracy of around 10 nm (without temperature compensation).

A new centering method of the measuring probe for spiral scanning-based surface profile measurement systems

Spiral scanning is a high-efficiency scanning mode for surface profile measurement systems. The most important priority to realize the spiral scanning mode is to accurately align the measuring probe with the rotational centre of the spindle. This paper proposes a novel centre alignment method of the measuring probe, which is considered to be suitable for any type of spiral scanning surface measurement systems. The proposed method, which only needs a tilted flat mirror as the artefact, makes the time-consuming centre alignment process of the measuring probe become much easier and faster. The operational steps of the proposed method are presented. Experiments have also been carried out based on a self-developed optical profiler with spiral scanning operation to verity the feasibility of the proposed method. The experimental results show that the proposed method is capable of conducting a fast alignment (only takes 3 min) while maintaining a high alignment accuracy. Evaluation of the alignment accuracy shows that the centering error is less than 10 µm on the mechanical guide rail stage and about 1.7 µm on the air-bearing stage.

A Semi-supervised manifold alignment algorithm and an evaluation method based on local structure preservation

Manifold alignment is the process of aligning the shared intrinsic structure extracted from multiple manifolds. The criteria of manifold alignment are 2-fold. First, the alignment should minimize the distance between manifolds, ensuring high alignment accuracy. Second, the original structure should be preserved. Currently, most alignment algorithms focus on alignment accuracy, whereas structure preservation has received little attention. This paper proposes a new semi-supervised alignment method that combines locally linear reconstructions in each manifold. The shared intrinsic structure is obtained by solving an optimization problem with a closed-form solution, which simultaneously matches the corresponding instances and preserves the local geometry of each manifold. Furthermore, a new method is presented to evaluate the local structure preservation. The structural stability is defined as a metric of the local structure preservation property. It is shown that the proposed method preserves the local geometry of the original dataset well. It is also found that better structural stability gives higher alignment accuracy, but the converse is not true. Experimental results on both synthetic and real datasets demonstrate the effectiveness and efficiency of our method.

Multi-modal automatic montaging of adaptive optics retinal images.

We present a fully automated adaptive optics (AO) retinal image montaging algorithm using classic scale invariant feature transform with random sample consensus for outlier removal. Our approach is capable of using information from multiple AO modalities (confocal, split detection, and dark field) and can accurately detect discontinuities in the montage. The algorithm output is compared to manual montaging by evaluating the similarity of the overlapping regions after montaging, and calculating the detection rate of discontinuities in the montage. Our results show that the proposed algorithm has high alignment accuracy and a discontinuity detection rate that is comparable (and often superior) to manual montaging. In addition, we analyze and show the benefits of using multiple modalities in the montaging process. We provide the algorithm presented in this paper as open-source and freely available to download.

Face Alignment With Deep Regression.

In this paper, we present a deep regression approach for face alignment. The deep regressor is a neural network that consists of a global layer and multistage local layers. The global layer estimates the initial face shape from the whole image, while the following local layers iteratively update the shape with local image observations. Combining standard derivations and numerical approximations, we make all layers able to backpropagate error differentials, so that we can apply the standard backpropagation to jointly learn the parameters from all layers. We show that the resulting deep regressor gradually and evenly approaches the true facial landmarks stage by stage, avoiding the tendency that often occurs in the cascaded regression methods and deteriorates the overall performance: yielding early stage regressors with high alignment accuracy gains but later stage regressors with low alignment accuracy gains. Experimental results on standard benchmarks demonstrate that our approach brings significant improvements over previous cascaded regression algorithms.

All‐solution‐printed oxide thin‐film transistors by direct thermal nanoimprinting for use in active‐matrix arrays

All‐solution‐printed oxide thin‐film transistors (TFTs) were fabricated using a direct thermal nanoimprinting technique termed nanorheology printing (n‐RP). n‐RP is a printing technology that utilizes the thermoplastic properties of oxide gels. We prepared such thermoplastic oxide gels and developed a suitable alignment system. Using this system, TFTs designed for use in active‐matrix arrays were fabricated with a high alignment accuracy of less than 5 µm. We succeeded in incorporating these TFTs into all‐solution‐printed oxide TFT arrays, and the operation of the transistors in the arrays was confirmed.

MSAProbs-MPI: parallel multiple sequence aligner for distributed-memory systems.

Source code in C ++ and MPI running on Linux systems as well as a reference manual are available at http://msaprobs.sourceforge.net CONTACT: jgonzalezd@udc.esSupplementary information: Supplementary data are available at Bioinformatics online.

Conductive Semiconductor Interfaces Fabricated by Room Temperature Covalent Wafer Bonding

Low temperature direct bonding in the range of maximum 400°C opened an entirely new applications field as it allowed for the direct bonding of wafers with metallization (e.g CMOS) while maintaining a high alignment accuracy as well as bonding of thermally mismatched materials. Despite the clear benefits of the low temperature direct bonding process, the requirements of some categories of applications in terms of allowing for room temperature covalent bonding or oxide-free, electrically conductive interfaces fabrication cannot be fulfilled. A new technology was developed to address these types of applications: EVG®580 Combond®. This paper reports on fabrication of oxide-free, electrically conductive Si-Si and Si-GaAs bonded interfaces based on the newly developed technology. Experimental results on bonding quality and electrical performance of the bonded interfaces are presented.

High Precision Low Temperature Direct Wafer Bonding Technology for Wafer-Level 3D ICs Manufacturing

The development of low temperature direct wafer bonding processes paved the way for new categories of applications based on semiconductor devices. Precise optical alignment of wafers prior wafer bonding plays a key role in manufacturing of current and future applications based on wafers stacking. In order to address the continuous feature size shrinking and increasing integration levels the need for high alignment accuracy imposed significant hardware and process improvements. The future microelectronics applications are foreseen to require wafer-to-wafer alignment accuracy as low as ±100 nm and better. This work reviews the main contributors to the misalignment budget and presents experimental alignment results for alignment accuracy in the range of 50 – 100 nm.

Nanoimprint of a 3D structure on an optical fiber for light wavefront manipulation

Integration of complex photonic structures onto optical fiber facets enables powerful platforms with unprecedented optical functionalities. Conventional nanofabrication technologies, however, do not permit viable integration of complex photonic devices onto optical fibers owing to their low throughput and high cost. In this paper we report the fabrication of a three-dimensional structure achieved by direct nanoimprint lithography on the facet of an optical fiber. Nanoimprint processes and tools were specifically developed to enable a high lithographic accuracy and coaxial alignment of the optical device with respect to the fiber core. To demonstrate the capability of this new approach, a 3D beam splitter has been designed, imprinted and optically characterized. Scanning electron microscopy and optical measurements confirmed the good lithographic capabilities of the proposed approach as well as the desired optical performance of the imprinted structure. The inexpensive solution presented here should enable advancements in areas such as integrated optics and sensing, achieving enhanced portability and versatility of fiber optic components.

Capillary Self-Assembly for 3D Heterogeneous System Integration and Packaging

ABSTRACTThe self-assembly of known good dies (KGDs) on substrates using the liquid capillary method is shown to be a promising technology to achieve three-dimensional (3D) heterogeneous system integration and packaging. Firstly, the effects of the edge structures of self-assembled substrates and chips on alignment accuracies were investigated. When hydrophobic sidewalls with 10-µm-height steps were applied to both chips and assembly sites formed on substrates, the alignment accuracy within 1.0 µm was realized. The alignment accuracies were within 2.0 µm using either substrates or chips having 10-µm-height step structures with hydrophobic sidewalls. Self-assembly of 12-ch vertical-cavity surface-emitting lasers (VCSELs) with a long rectangle shape on glass substrates were also demonstrated. Separation of assembly sites into twelve areas enhanced the resultant force acting on the VCSEL short edge. The enhanced resultant force provided the high alignment accuracies within 2.0 μm. After the self-assembly of the VCSEL and the subsequent thermal compression, the chips successfully exhibited no degradation of their current–voltage (I–V) characteristics and appropriate 850-nm light emission. We demonstrated self-assembly and microbump bonding using non-conductive film (NCF)-covered dies with Cu/Sn microbumps for high-throughput and high-yield multichip-to-wafer 3D integration. The self-assembly of the NCF-covered dies provided high alignment accuracy within 1.1 μm on average. After the self-assembly of NCF-coved dies and thermal compression, microbump chains composed of 7396 bump joints were successfully obtained, resulting in good electrical properties of 32 mΩ/joint without any bridge shorts and failures. The variations of microbump joint resistance were maintained within 5% of the initial value after thermal cycle testing of even 1000 cycles.

A local alignment approach to similarity analysis of industrial alarm flood sequences

Similar alarm sequence alignment algorithms have been used to find similar alarm floods in the historical database for the prediction and prevention of alarm floods. However, the existing modified Smith–Waterman (SW) algorithm has a high computation complexity, preventing its online applications within a tolerable computation time period. This paper proposes a new local alignment algorithm, based on the basic local alignment search tool (BLAST). The novelty of the proposed algorithm is three-fold. First, a priority-based similarity scoring strategy makes the proposed algorithm more sensitive to alarms having higher alarm priorities. Second, a set-based pre-matching mechanism avoids unnecessary computations by excluding all irrelevant alarm floods and alarm tags. Third, the seeding and extending steps of the conventional BLAST are adapted for alarm floods, which reduce the searching space significantly. Owing to the novelties, the proposed algorithm is much faster in computation and provides a higher alignment accuracy than the SW algorithm. The efficiency of the proposed algorithm is demonstrated by industrial case studies based on the historical alarm floods from an oil conversion plant.

Accuracy of Computed Tomography–Based Navigation-Assisted Total Knee Arthroplasty: Outlier Analysis

BackgroundAchieving neutral limb alignment during total knee arthroplasty (TKA) has been identified as a potential factor in long-term prosthesis survival. This study aimed to analyze the accuracy of component orientation and postoperative alignment of the leg after computed tomography (CT)–based navigation-assisted TKA, compare these parameters with those of a conventional technique, and analyze differences in the data of outliers. MethodsWe retrospectively compared the alignment of 130 TKAs performed with a CT-based navigation system with that of 67 arthroplasties done with a conventional system. The knee joints were evaluated using radiographs. ResultsMean hip–knee–ankle (HKA) angle, frontal femoral component angle, and frontal tibial component angle were 180.7°, 88.8°, and 90.6°, respectively, for the navigation-assisted arthroplasties and 181.1°, 88.7°, and 90.2°, respectively, for the conventional arthroplasties. All preoperative leg axes of 10 outliers in the navigation group were >193°, whereas the data of 17 outliers in the conventional group were scattered. ConclusionThis study demonstrates significant improvements in component positioning with the CT-based navigation system. Furthermore, when analyzing cases with preoperative HKA angles ≤192°, no outliers were found in the navigation group, indicating high alignment accuracy. However, in cases with preoperative HKA angles ≥193°, outliers were found in both groups, and no significant difference between the groups was observed (P = .08). Detailed analysis of the outlier cases in the navigation group revealed that the femoral component was placed in the varus position. These findings indicate that the varus knee is an important factor influencing accurate positioning of the femoral component and the postoperative leg axis.

Fine Pitch Rapid Heat Self-Aligned Assembly and Liquid-Mediated Direct Bonding of Si Chips

3-D stacking with vertical interconnection of thinned microelectronic silicon chips is a novel approach to achieve the enhanced performance, higher density, and smaller size of integrated circuits with a better multifunctionality than the traditional 2-D chip packaging. To achieve this, high alignment accuracy is required between the top chip and the bottom substrate along with good bonding between the two intermediate surfaces. In this paper, a novel approach to stacking is proposed: rapid heating self-aligned assembly. Using this approach, fast and good intermediate dielectric bonding is realized along with high alignment accuracy between the top chip and the bottom substrate compared with the similar process at room temperature. This approach can be used for die-to-die bonding and die-to-wafer bonding for 3-D and MEMS applications.

The effect of mold materials on the overlay accuracy of a roll-to-roll imprinting system using UV LED illumination within a transparent mold

Although several studies on the roll-to-roll (R2R) imprinting process have reported achieving flexible electronics, improving the alignment accuracy in the overlay process of R2R imprinting is recognized as the biggest problem for the commercialization of this technology. For an overlay technique with high alignment accuracy, it is essential to develop a roll mold with high positional accuracy. In this study, a method for fabricating a roll mold with high positional accuracy is proposed by wrapping a thin glass substrate flexible mold around the transparent roll base, because it can provide higher mechanical strength and thermal stability than a conventional polymer substrate. To confirm the usability of the proposed process, the prepared roll mold was used to fabricate a test pattern of thin-film transistor backplane for a rollable display. The positional and overlay accuracy of the roll mold with the proposed thin glass substrate flexible mold were compared with the roll mold with a conventional polymer substrate flexible mold. Large-area transparent flexible molds with a size of 470 × 370 mm were fabricated by an ultraviolet (UV) imprinting process on thin glass and polyethylene terephthalate substrates, and these flexible molds were wrapped around a roll base of 125 mm radius through a precision alignment process. After an anti-adhesion treatment and the wrapping process, the roll mold with the polymer substrate showed a ~180 μm positional error, whereas the thin glass substrate showed a ~30 μm positional error. After the overlay process using the R2R imprinting system with the alignment system, an average overlay error of ~3 μm was obtained when the thin glass flexible wrapped roll mold was used, whereas a ~22 μm overlay error was obtained when the polymer substrate flexible wrapped roll mold was used.