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1-13 of 13
Christopher H. Kang
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Proceedings Papers
ISTFA2024, ISTFA 2024: Conference Proceedings from the 50th International Symposium for Testing and Failure Analysis, 221-226, October 28–November 1, 2024,
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Photoresist (PR) profiles tend to have deformation and shrinkage with typical transmission electron microscopy (TEM) analysis method using a focused ion beam scanning electron microscope (FIB-SEM) and TEM. The elevated temperatures during sample preparation and TEM analysis are believed to contribute to these issues. This study evaluates the effectiveness of cryogenic workflow in mitigating PR profile shrinkage by employing cryo-focused ion beam (Cryo-FIB) and cryo-transmission electron microscopy (Cryo-TEM). Comparative experiments were conducted at room temperature and cryogenic conditions, demonstrating that full cryogenic workflow reduces the shrinkage of PR, bottom anti-reflective coating (BARC), and line critical dimension (CD). Our findings indicate that both the sample preparation and analysis temperatures influence PR profiles. This study highlights how the full cryogenic workflow significantly minimizes shrinkage, providing more accurate PR profile measurements.
Proceedings Papers
ISTFA2024, ISTFA 2024: Conference Proceedings from the 50th International Symposium for Testing and Failure Analysis, 266-272, October 28–November 1, 2024,
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In this paper, we approach three Nanoprobing EBAC (Electron Beam Absorbed Current) applications for DRAM metal lines. Typically, more than 70-80% of metal lines in DRAM devices experienced invisible EBAC imaging, due to high-gain EBAC amplifier becoming saturated. This overloaded case typically occurs when the signal probe lands on a contact connected to the well, source, or drain of the substrate. One of the ways to overcome this limit, a new EBAC analysis approach on lamella-like sample, is introduced in this paper. We introduce a large lamella-like sample by using Xe + PFIB for EBAC analysis technique on DRAM metal line as well as to compare it with the conventional EBAC technique. Delayering technique also used by plasma FIB for uniform sample surface to target metal layer.
Proceedings Papers
ISTFA2023, ISTFA 2023: Conference Proceedings from the 49th International Symposium for Testing and Failure Analysis, 224-227, November 12–16, 2023,
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As semiconductor devices continue to decrease in size and pitch, demands for accurate microstructural analysis have increased to enable downward scaling. Critical dimension (CD) metrology is key to delivering process insights, but at such scales, rigorous metrology analysis providing high precision data may lack desired throughput. CD measurement using the scanning electron microscope (SEM) is a widely used technique, however, to acquire large area SEM images with high precision, multiple image stitching is currently required. In this paper, a new method for precise and efficient metrology analysis is introduced. This study demonstrates that large area imaging with ultra-high pixel resolution can deliver better throughput while maintaining the same level of precision that can be achieved by the traditional method.
Proceedings Papers
ISTFA2023, ISTFA 2023: Conference Proceedings from the 49th International Symposium for Testing and Failure Analysis, 228-232, November 12–16, 2023,
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Scanning Electron Microscope (SEM) is a valuable tool for measuring Critical Dimensions (CD) of semiconductor devices at the nanometer scale. Vertical SEM application is one of the applications for high accurate CD measurement on cross-sectional surface. Even a slight stage tilt angle change of the vertical sample can impact CD values in nanometer scales of the sample surface features. For accurate CD measurements, it is essential to ensure the sample is positioned correctly to acquire the sample image. However, it is challenging to achieve a perfect alignment with the incident beam direction and the accurate perpendicular direction on the cross-sectional surface on SEM tool. To achieve an ideal vertical positioning of the sample, the combination of the stage tilt axis and stage rotation axis can be used. Exact calculation is required to achieve an accurate CD measurement. In this paper, a calculation method of the tilt angle correction to achieve a perpendicular angle to the surface and its verification method are described. Reliable measurement can be achieved by employing an automated script for compensation. We also demonstrate an approach for highly reliable angle correction and improved metrology results in this paper.
Proceedings Papers
ISTFA2023, ISTFA 2023: Conference Proceedings from the 49th International Symposium for Testing and Failure Analysis, 233-237, November 12–16, 2023,
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Photoresist (PR) profiles tend to have deformation and shrinkage with typical transmission electron microscopy (TEM) sample preparation methods using a focused ion beam scanning electron microscope (FIB-SEM). As the temperature increases during the TEM sample preparation, it may lead to deformation and shrinkage in PR profiles. In this study, we analyze the impact when performing the sample preparation at a cold temperature using a cryo-FIB to minimize deformation and shrinkage issues. To test this methodology, the TEM sample preparation process was performed under different conditions. From these experiments, the TEM results with full cryo conditions showed that the PR line to space ratio was closest to the target, which is the sample’s real line to space ratio (1:1), and the bottom anti-reflective coating (BARC) shrinkage was minimized.
Proceedings Papers
ISTFA2023, ISTFA 2023: Conference Proceedings from the 49th International Symposium for Testing and Failure Analysis, 279-281, November 12–16, 2023,
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In this paper, we propose a method to get more accurate metrology data using the tilt-axis on a transmission electron microscope (TEM) to compensate for microscopic tilt-axis changes that occur during focused ion beam (FIB) sample preparation processing. This method was developed using V-NAND plan-view samples which require channel hole measurements for each layer to support process monitoring. To test this method, we obtained the same image by progressively tilting the alpha and beta axes one degree in the positive and negative direction using a V-NAND planar sample. The strongest contrast edge was found by contrast profile analysis of each edge of the V-NAND channel using automated software. Through this method, we were able to optimize the sample position and automate the process to capture high quality images to accurately measure V-NAND channel holes. The details are discussed in this paper.
Proceedings Papers
ISTFA2022, ISTFA 2022: Conference Proceedings from the 48th International Symposium for Testing and Failure Analysis, 269-276, October 30–November 3, 2022,
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As advanced device technologies scale to 5nm with dimensions getting smaller and materials change, it is difficult to control the sample preparation delayering end pointing by polishing. Therefore, it requires an alternative solution such as Xe+ PFIB (Plasma Focused Ion beam) Microscopy for accurate delayering control. PFIB can be used for planar Failure Analysis (FA) delayering but also for nanoprobing sample preparation. This paper introduces the detail of nanoprobing sample preparation by PFIB and discusses nanoprobing results on 5nm FinFET technology.
Proceedings Papers
ISTFA2021, ISTFA 2021: Conference Proceedings from the 47th International Symposium for Testing and Failure Analysis, 274-278, October 31–November 4, 2021,
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Convention hand polishing, which is widely used for delayering, is becoming increasingly difficult as metal lines and stacks in semiconductor devices get thinner. For one thing, endpointing at the exact targeted layer and region of interest is a major challenge. The presence of cobalt and its propensity to oxidize, thus complicating electrical measurements, is another challenge. In this study, the authors demonstrate an alternative delayering method based on plasma focused ion beam (PFIB) milling aided by DX gas. The workflow associated with the new method is more efficient than that of conventional hand polishing and can help prevent cobalt oxidation.
Proceedings Papers
ISTFA2021, ISTFA 2021: Conference Proceedings from the 47th International Symposium for Testing and Failure Analysis, 313-315, October 31–November 4, 2021,
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This paper describes the development and implementation of a TEM-based measurement procedure and shows how it is used to determine the verticality or etching angle of channel holes in V-NAND flash with more than 200 layers of memory cells. Despite the high aspect ratio of the region of interest, the method can resolve offsets down to a few nm. Such precision is critical, as the paper explains, because the radius and thus electrical characteristics of each memory cell is determined by the etching angle.
Proceedings Papers
Automated Cell Layer Counting and Marking at Target Layer of 3D NAND TEM Samples by Focused Ion Beam
ISTFA2021, ISTFA 2021: Conference Proceedings from the 47th International Symposium for Testing and Failure Analysis, 347-351, October 31–November 4, 2021,
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This paper discusses the development of an automated cell layer counting process for preparing 3D NAND flash memory samples for TEM analysis. In an initial proof-of-concept, several line markings were inscribed on the test device in evenly spaced intervals in order to evaluate its helpfulness for a human operator. A more automated procedure was then developed in which cell layers were counted to a desired target layer starting from a reference layer set by the operator. At that point, the operator could begin preparing the TEM sample.
Proceedings Papers
ISTFA2020, ISTFA 2020: Papers Accepted for the Planned 46th International Symposium for Testing and Failure Analysis, 299-304, November 15–19, 2020,
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Focused ion beam (FIB) microscopy is an essential technique for the site-specific sample preparation of atom probe tomography (APT). The site specific APT and automated APT sample preparation by FIB have allowed increased APT sample volume. In the workflow of APT sampling, it is very critical to control depth of the sample where exact region of interest (ROI) for accurate APT analysis. Very precise depth control is required at low kV cleaning process in order to remove the damaged layer by previous high kV FIB process steps. We found low kV cleaning process with 5 kV and followed by 2kV beam conditions delivers better control to reached exact ROI on Z direction. This understanding is key to make APT sample with fully automated fashion.
Proceedings Papers
ISTFA2020, ISTFA 2020: Papers Accepted for the Planned 46th International Symposium for Testing and Failure Analysis, 12-16, November 15–19, 2020,
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Correlation across applications and imaging platforms is essential and brings increased insurance for fault isolation in advance of destructive imaging. This paper demonstrates an approach for a detailed advanced packaging defect isolation and analysis workflow. To determine the effectiveness of the proposed workflow, a 28nm flip-chip was used as a test vehicle. By using this workflow, the yield in determining the fault location has increased from 60% to over 85%. To further improve the result, a surface charging mitigation scheme was used and the resulting measured correlative offset between the two systems was found to be less than 10um. This creates novel opportunities in reducing the size of the cross-section and increasing the overall throughput to find the defect, with high confidence. This workflow creates unique abilities in fault localization and analysis as it can detect both opens and shorts between the different techniques that are employed.
Proceedings Papers
ISTFA2020, ISTFA 2020: Papers Accepted for the Planned 46th International Symposium for Testing and Failure Analysis, 325-329, November 15–19, 2020,
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In semiconductor manufacturing technology, copper has been widely used for BEOL process due to better conductivity than aluminum. TEM (Transmission Electron Microscopy) characterization has been played in key role to understand the process of semiconductor manufacturing. Gallium base Focused Ion Beam (FIB) is widely used on TEM sample preparation. The experiment to understand the impact of gallium which is from sample preparation process on Cu layer was performed. In-situ TEM studies have shown real time material characteristic of Cu at various temperature [1]. We observed the gallium aggregation phenomenon on Cu layer at round the temperature of 400°C. This thermal aggregation of gallium on Cu layer has been confirmed by EDS analysis in the study. Detectable amount of gallium was found in whole area in the sample before heating the sample at in-situ TEM work. This paper also introduces alternative solutions to resolve this gallium aggregation in copper layer including the sample preparation technique using Xe Plasma Focused Ion Beam (PFIB) [2]. This Xe PFIB showed the substantial improvement of specimen quality for the in-situ TEM experiment of sample preparation.