Alignment Marks Research Articles

Design and Evaluation of Stamping Module to Pattern Alignment Marks for LED Post-Processing

LED (Light Emitting Device) is one of the most important and popular unit in display goods. Until now, the LED process could not make LED from broken substrates during production. This is because the damaged substrate cannot be post-processed by losing alignment mark on itself. After the substrate is pre-processed the substrate having LED dies are glued on blue tape. Therefore, if additional mark printed on the blue tape, it will be able to process the following post-process. In this paper, a precision stamping module to pattern the alignment mark on the blue tape is designed, fabricated and verified.

Process Feasibility and Reliability Performance of Fine Pitch Si Bare Chip Embedded in Through Cavity of Substrate Core

We demonstrate the concept and fabrication of through cavity core device-embedded substrate for fine-pitch Si bare chips with pad pitches down to 60 $\mu \text{m}$ . Instead of using a real active Si chip, we embedded a Si test element group inside a through cavity of the core. To adjust to the thickness of the passive device with a maximum thickness of 150 $\mu \text{m}$ , the Si chip was thinned to 120 $\mu \text{m}$ , not including bump height. After placing a chip, the cavity is filled by laminating a two-layer structure Ajinomoto build-up film from both sides of the substrate core. To accurately place the chip in the cavity, we strictly controlled the lamination conditions and curing temperature of the epoxy resin. Laser via drilling produced the best alignment for fine-pitch small pads using the local alignment marks of each test frame kit with overhead epoxy resin of the Cu mark pattern removed. To produce a high-quality microvia interconnection to the Al pad of the Si chip, we used a new, combined desmearing technique that included a plasma treatment with CF4 + O2 mixed gas. Finally, we discussed the production yield and reliability of the fine-pitch Si bare chip-embedded substrate using the daisy-chain structure consisted of Si chip pattern, microvia on Si pad, and substrate tracks.

The Construction of Finite Element Model of Invisible Appliance of Inhomogeneous Thickness by Reverse Engineering Technology

Reverse engineering technology and Laser scanning technology was used to obtain and establish the ideal digital dental mode and dental model with invisible appliance. To complete the Boolean subtraction between the dental model with invisible appliance and the ideal dental mode by the alignment marks designed in the guml, so that got the digital model of invisible appliance. Then the finite element model was established by the finite element analysis platform ANSYS. A more precise dentition finite element model of invisible appliance is established, which can reflect the real surface geometrical morphology of invisible appliance and its inhomogeneous thickness characteristics.

Binary matrices of optimal autocorrelations as alignment marks

The authors define a new class of binary matrices by maximizing the peak-sidelobe distances in the aperiodic autocorrelations. These matrices can be used as robust position marks for in-plane translational spatial alignment. The optimal square matrices of dimensions up to 7 × 7 and optimal diagonally symmetric matrices of 8 × 8 and 9 × 9 were found by exhaustive searches.

Adjustment Strategy for Inclination Moiré Fringes in Lithography by Spatial Frequency Decomposition

The recently proposed four-quadrant grating Moire fringe alignment scheme was demonstrated to have the potential of achieving nanometer alignment for proximity lithography. The mask-wafer misalignment was accurately detected by comparing the phase between two sets of Moire fringes averaged along with the fringe direction, making the inclination adjustment of Moire fringes highly imperative. The inclination closely related with the included angle between mask (alignment mark) and wafer (alignment mark) largely influences the alignment accuracy. To solve this issue, we present an adjustment strategy based on the spatial frequency decomposition of two sets of differential Moire fringes, by which the included angle can be accurately adjusted with an accuracy of better than 10 -5 rad. The subsequent discussion indicates that the position of imaging system can be responsible for the inclination but actually it would not affect the mask-wafer alignment, so that our proposed adjustment strategy can be operated simply and feasibly, which is validated by the theoretical analysis and experimental results.

Gap-optimized Moiré phase imaging alignment for proximity lithography

The proposed four-quadrant Moire alignment scheme to detect the misalignment between mask and wafer for proximity lithography can achieve the alignment accuracy with nanometer level. When implementing the scheme, however, the distribution of Moire fringes associated with the mask-wafer gap indeed goes against the alignment, making the gap optimization highly urgent. The optimization model is established, and numerical simulation as well as experimental verification is also provided. Furthermore, an alignment accuracy of similar to 3 nm with the illumination wavelength of 632.8 nm is experimentally attained. Simultaneously, the design mechanism of alignment marks for improving the availability of the alignment scheme is discussed. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Use of a Ball Alignment Mark Improves Putting Performance in Golf

Golfers place alignment marks on their balls in the belief that this improves the ability to align and hole more putts. The purpose of this study was to determine the effect of using an alignment mark on a golf ball on the number of putts holed. Twenty-nine amateur golfers (handicap 7.6 ± 4.06) performed 10 straight putts from a distance of 1.7m to ascertain putting ability. Based on putting ability they then performed 30 putts from a distance of 1.7m, 2.3m or 2.6m, with better putters putting further from the hole. Fifteen of the putts were performed using a ball with an alignment mark (AM) and 15 with no alignment mark (NAM). The order of putts with each ball was randomized. On average participants holed 17.1 ± 3.9 putts out of the 30 putts completed using both balls. The number of putts holed at each of the three distances from the hole did not differ (*p* = .60). More putts were holed with AM compared with NAM at a distance of 2.6m (AM 9.7 ± 2.4 putts, NAM 7.6 ± 2.8, *p* \< .01), but not at the shorter distances of 1.7m (*p* = .67) and 2.3m (*p* = .39). The use of an alignment mark on a golf ball improves putting success for straight putts from a distance of 2.6m.

Void-formation in uncured and partially-cured BCB bonding adhesive on patterned surfaces

A void-free bonding interface is critical to yield and reliability for high-quality wafer bonding. Although adhesive bonding using polymers as the bonding interface material is inherently able to restrain void-formation, for the wafers with uneven patterns like metal interconnects and alignment marks, void-free bonding is still challenging. This paper reports the void-formation in uncured and partially-cured benzocyclobutene (BCB) adhesive for bonding wafers with patterns. Experimental results show that uncured and partially-cured BCB has different behaviors in void-formation, and four types of voids, namely center voids, flower voids, micro voids, and floccules voids, are founded and their formation mechanisms are investigated. By optimizing bonding parameters for uncured BCB bonding, the center voids and flower voids are avoided and void-free bonding can be obtained. For partially-cured BCB, the micro voids and floccules voids tend to appear for uneven wafer surfaces. A reflow pretreatment at 140°C for 2h before curing process is beneficial to reducing the void areas.

Amorphous Si waveguides with high-quality stacked gratings for multi-layer Si optical circuits

To realize a stacked multi-layer silicon-based photonic device, a waveguide with a stacked grating was fabricated by using amorphous Si (a-Si) material, which is suitable for constructing layered structures. The fabrication method was based on forming a flat a-Si layer on a non-flat structure by using only spin-on-glass (SOG) coating technique. The a-Si grating was precisely constructed on the a-Si waveguide with gold alignment marks for electron beam lithography. Transmitted and reflected light power dependence on the grating period, wavelength, and polarization was systematically measured and compared with the designed dependence. As a result, the reflected light power exhibited a characteristic peak structure at a particular wavelength. Remarkable transverse electric/transverse magnetic (TE/TM) mode dependence was also observed. Furthermore, the measured and the designed properties were in excellent agreement with each other. Consequently, the designed structure was well reproduced in the actual stacked structure based on the a-Si material. These results pave the way for novel a-Si based integrated photonic devices such as polarization selectors and wavelength filters, indicating that a-Si is an excellent material for implementing Si-based multi-layer optical circuits.

A modified alignment method based on four-quadrant-grating moiré for proximity lithography

In this paper, we demonstrate a modified coarse-fine alignment scheme designed for proximity lithography. Both wafer alignment mark and mask alignment mark consists of linear grating arrays and “+” bar. Coarse alignment and fine alignment could work together to achieve the perfect alignment. Thereinto, coarse alignment, measured from two superposed “+” bars, guarantees the misalignment across wafer and mask within the measurement range of fine alignment, which is based on moiré fringes formed by the superposition of linear grating arrays. Then we conduct the experiments using a nanometer actuator to drive the wafer alignment mark meanwhile keeping the mask alignment mark motionless, which validates the feasibility and rationality of our designed scheme.

Simple fabrication process for UV nanoimprint mold with embedded metal alignment marks for in-liquid alignment

In-liquid alignment is expected to be applied to UV nanoimprint lithography (UV-NIL) for the fabrication of integrated circuits that requires high-precision multilayer processes. It is not very easy to perform in-liquid alignment using quartz molds commonly used in UV-NIL, since alignment marks on the molds become invisible owing to the refractive index matching of quartz and UV-curable resin when alignment marks of a mold are filled with UV-curable resin. In this paper, we developed a simple fabrication process for quartz molds without the mentioned problem. We successfully fabricated Ti patterns, which served as high-contrast alignment marks, exclusively in the recess part of the mold mark. We also performed in-liquid alignment process using a mold with the marks and demonstrated less than sub-100-nm alignment accuracy.

Multi-Height Precision Alignment With Selectively Developed Alignment Marks

The alignment step in fabricating multi-height photoresist masters is a critical and time-consuming process. SU8 masters that combine very thin and thick layers can be difficult to align because of low contrast visibility. We increase visual contrast by selectively developing alignment marks to ease fabrication of masters with thick resist layers deposited on much thinner ones. In addition, we use a vernier calliper based alignment mark to achieve high precision alignment.

Experimental study of Talbot imaging moiré-based lithography alignment method

A four-quadrant gratings alignment method was presented for proximity lithography, which experimentally achieved the alignment accuracy of nanometer level. The alignment marks consist of gratings with slightly different periods, leading to different Talbot distances with the same monochromatic planar wave. The contrast of moiré fringe varies with the gap between mask (alignment mark) and wafer (alignment mark), which will affect the phase comparison, and induce more errors as well. This paper concentrates on the optimization of parameters of alignment marks to achieve the resulting moiré fringes with an optimum contrast. By simulation and experiment, we investigate effects of the gap on the contrast, based on which, the design principle of alignment marks is concluded, and it is helpful to the practicability with our proposed alignment method.

Automated long-term monitoring of parallel microfluidic operations applying a machine vision-assisted positioning method.

As microfluidics has been applied extensively in many cell and biochemical applications, monitoring the related processes is an important requirement. In this work, we design and fabricate a high-throughput microfluidic device which contains 32 microchambers to perform automated parallel microfluidic operations and monitoring on an automated stage of a microscope. Images are captured at multiple spots on the device during the operations for monitoring samples in microchambers in parallel; yet the device positions may vary at different time points throughout operations as the device moves back and forth on a motorized microscopic stage. Here, we report an image-based positioning strategy to realign the chamber position before every recording of microscopic image. We fabricate alignment marks at defined locations next to the chambers in the microfluidic device as reference positions. We also develop image processing algorithms to recognize the chamber positions in real-time, followed by realigning the chambers to their preset positions in the captured images. We perform experiments to validate and characterize the device functionality and the automated realignment operation. Together, this microfluidic realignment strategy can be a platform technology to achieve precise positioning of multiple chambers for general microfluidic applications requiring long-term parallel monitoring of cell and biochemical activities.

Mask Design and Fabrication of Micro/Nanowire Biochip for Reliable and Repeatability Pattern Transfer

In Micro/Nanowire fabrication, the alignment and exposure process are the most critical steps in photolithography process, and indeed for the whole biochip processing. This process determines the success of transferring the Micro/Nanowire design pattern on the mask to the photoresists on the wafer surface. Hence, the resolution requirementsand precise alignment are vital; each mask needs to be precisely aligned with original alignment mark in order to transfer the original pattern from mask onto photoresist layer. Otherwise, itcant successfully transfer the original pattern to the wafer surface causing device and circuit failure. Therefore, the UniMAPs Second Generation Mask Aligner is used for precise alignment and pattern transfer process. Thus, the paper present a preliminary study on fundamentals of resist exposure and development mechanisms for fabrication of Micro/Nanowire, We demonstrated significance of considering process parameters such as mask aligner, quality of resist, soft bake, exposure time and intensity, and development time. There was a very little room for alignment error; we were able to achieved error free design to the criticaldimension.

Characterization of wafer geometry and overlay error on silicon wafers with nonuniform stress

Process-induced overlay errors are a growing problem in meeting the ever-tightening overlay requirements for integrated circuit production. Although uniform process-induced stress is easily corrected, nonuniform stress across the wafer is much more problematic, often resulting in noncorrectable overlay errors. Measurements of the wafer geometry of free, unchucked wafers give a powerful method for characterization of such nonuniform stress-induced wafer distortions. Wafer geometry data can be related to in-plane distortion of the wafer pulled flat by an exposure tool vacuum chuck, which in turn relates to overlay error. This paper will explore the relationship between wafer geometry and overlay error by the use of silicon test wafers with deliberate stress variations, i.e., engineered stress monitor (ESM) wafers. A process will be described that allows the creation of ESM wafers with nonuniform stress and includes many thousands of overlay targets for a detailed characterization of each wafer. Because the spatial character of the stress variation is easily changed, ESM wafers constitute a versatile platform for exploring nonuniform stress. We have fabricated ESM wafers of several different types, e.g., wafers where the center area has much higher stress than the outside area. Wafer geometry is measured with an optical metrology tool. After fabrication of the ESM wafers including alignment marks and first level overlay targets etched into the wafer, we expose a second level resist pattern designed to overlay with the etched targets. After resist patterning, relative overlay error is measured using standard optical methods. An innovative metric from the wafer geometry measurements is able to predict the process-induced overlay error. We conclude that appropriate wafer geometry measurements of in-process wafers have strong potential to characterize and reduce process-induced overlay errors.

Chrome Mask Design for Microfluidic Fabrication

This paper presents a simple and effective method to design chrome mask for microfludic fabrication. Microfluidic fabrication involves 9 major step and mainly depends on the master mold template formation by SU-8 photoresists using conventional photolithography process The chrome mask was design using AutoCAD software. Essentially, mask is a crucial element in a microfluidic fabrication in which resolution requirements and precise alignment are vital, each mask needs to be precisely aligned with original alignment mark. Otherwise, it cant successfully transfer the original pattern to the wafer surface causing microchannel formation failure. Thus, the initial design is compared with the fabricated chrome mask to achieved a better result during device fabrication.

Thick Epitaxy Stepper Method for Special-Type Device

A stepper lithography method for thick epitaxy of special-type device was proposed. In this method, a mask with both alignment mark for proximity lithography and identification mark for stepper equipment was designed to solve the problem of precise alignment to patterns before thick-layer epitaxy and stepper lithography after thick-layer epitaxy. Using this method, the accuracy for alignment of patterns before and after thick-layer epitaxy reached 0.5 μm. This pattern alignment method special for thick-layer epitaxy is also applicable for stepper lithography of VDMOS with NBL, super-junction VDMOS, high-voltage complementary bipolar device and high-voltage BCD device.

Multifunctional bowtie-shaped ridge aperture for overlay alignment in plasmonic direct writing lithography using a contact probe

We propose a scheme of overlay alignment for plasmonic lithography using a scanning contact probe. Using two resonances of a ridge aperture in a metal film, we introduce the aperture's multifunctional characteristics for patterning and alignment at different wavelengths. To verify this idea, we measure an image of an alignment mark using a scanning ridge aperture and determine the reference point for the alignment. We then analyze the uncertainty of the alignment method with respect to the image data noise and compare the numerical results with the experimental results. The uncertainty of the overlay alignment method is shown to be less than approximately 2nm.

Four-quadrant gratings moiré fringe alignment measurement in proximity lithography

This paper aims to deal with a four-quadrant gratings alignment method benefiting from phase demodulation for proximity lithography, which combines the advantages of interferometry with image processing. Both the mask alignment mark and the wafer alignment mark consist of four sets of gratings, which bring the convenience and simplification of realization for coarse alignment and fine alignment. Four sets of moiré fringes created by superposing the mask alignment mark and the wafer alignment mark are highly sensitive to the misalignment between them. And the misalignment can be easily determined through demodulating the phase of moiré fringe without any external reference. Especially, the period and phase distribution of moiré fringes are unaffected by the gap between the mask and the wafer, not excepting the wavelength of alignment illumination. Disturbance from the illumination can also be negligible, which enhances the technological adaptability. The experimental results bear out the feasibility and rationality of our designed approach.