Semiconductor manufacturing is a highly intricate process involving multiple stages, each requiring stringent quality control to ensure defect-free devices. From wafer fabrication to wafer-level packaging, even microscopic defects can lead to significant yield loss and reliability concerns.
Microscopy plays a crucial role in defect detection, failure analysis (FA), and process optimization. This article explores the different stages of fabrication and packaging, highlighting how various microscopy techniques help detect and analyze defects at each step.
Before the lithography process creates a pattern on a prepared wafer, a layer of photoresist is applied to the wafer's surface. This photoresist layer serves as a component in the patterning process, acting as a light-sensitive material that will define the intricate designs necessary for semiconductor devices. Once the photoresist is in place, a photomask is positioned over it.
The photomask contains the desired pattern, which will be transferred onto the wafer during the lithography process. This step is critical as it determines the precision and accuracy of the patterning, which directly impacts the performance and functionality of the final semiconductor devices.
In the pursuit of enhancing node yield and new process research with the introduction of cutting-edge equipment, scientists and failure analysis engineers must sometimes go beyond examining patterns of post-lithography or in the Back-End-of-Line (BEOL) stages.
They are often required to conduct comprehensive evaluations of the photoresist development and the lithography processes. This thorough examination is essential to identify and understand the root causes of failures that may arise during semiconductor manufacturing. By delving into these preliminary stages, researchers can uncover potential issues that might affect the overall yield and reliability of the devices.
To achieve this, it is imperative to first explore the methods used to evaluate photoresist. This involves a detailed analysis of the photoresist's properties, its interaction with the photomask, and its behavior during the lithography process. Understanding these factors is crucial for optimizing the patterning process and ensuring that the final semiconductor devices meet the required specifications and performance standards.
Moreover, photoresist has a characteristic of shrinking when exposed to an electron beam (E-beam). This shrinkage can lead to inaccuracies in the patterning process, as the dimensions of the photoresist may change, affecting the precision of the final semiconductor device.
Due to this issue, the evaluation of photoresist primarily relies on optical microscopy, which does not involve the use of E-beams. This reliance on optical microscopy presents its own set of challenges, as it may not always provide the level of detail required for certain analyses. The limitations of using E-beam for photoresist evaluation stem from the potential for distortion and the difficulty in obtaining accurate measurements, which can hinder the ability to conduct thorough assessments of the photoresist's properties and performance. Consequently, researchers and engineers must navigate these constraints to ensure that the photoresist meets the necessary standards for successful semiconductor manufacturing.
During lithography, circuit patterns from the photomask are transferred onto a wafer coated with photoresist. Defects such as line edge roughness, incomplete pattern transfer, and misalignment can occur.
This technique expand the region of interest (ROI) of an optical microscope by integrating it with a low-resolution Scanning Electron Microscope (SEM). The primary objective of this approach is to prevent the photoresist on the semiconductor chip from undergoing shrinkage, which can occur when exposed to high-energy electron beams. To achieve this, the method focuses on magnifying only the specific area that requires confirmation, utilizing a low voltage electron beam. This careful targeting ensures that the rest of the photoresist remains unaffected, thereby maintaining the integrity and precision of the patterning process. By combining the strengths of optical microscopy with the detailed imaging capabilities of SEM, this technique provides a balanced solution that enhances inspection accuracy while minimizing potential distortions in the photoresist layer.
Confocal Microscopy: Provides depth profiling of photoresist layers, detecting irregularities in resist thickness.
High-precision microscopy at this stage ensures accurate pattern replication and minimizes defect propagation in subsequent steps.
The key to lithography lies in the precise creation of gates, which are fundamental components in semiconductor devices. These gates control the flow of electrical current, acting as switches that turn the current on or off, thereby playing a crucial role in the functionality of integrated circuits.
Recently, Atomic Layer Deposition (ALD) technology has been introduced for the fabrication of these gates, particularly due to the advent of Gate-All-Around (GAA) transistors and other advanced gate architectures. ALD is a highly controlled process that allows for the deposition of ultra-thin films, which are essential for creating the structures required in modern semiconductor devices.
However, the challenge in gate fabrication is ensuring that the material used for the gate is of exceptional purity. Any impurities can lead to defects that compromise the performance and reliability of the semiconductor device. In the case of GAA transistors, the fabrication process requires that the atomic-level buffer layer or the very thin film, along with the lattice constant of several layers, must be similar and change gradually.
This gradual transition is crucial to prevent lattice mismatches, which can lead to defects such as dislocations or voids. These defects can cause significant issues, including the breaking of the chip or the inability to manage heat effectively, which can lead to device failure.
Even when expensive optical inspection tools are employed to detect the presence of defects, they often fall short in providing detailed information about the nature or root cause of these defects. This limitation necessitates the continued reliance on electron microscopes, which offer high-resolution imaging capabilities. Electron microscopy allows engineers and researchers to analyze the morphology of defects in great detail, enabling them to determine the underlying causes of these issues.
Transmission Electron Microscopy with Selected Area Electron Diffraction (TEM with SAED): Tools for epitaxy and lattice constant evaluation
STEM: The highest resolution microscope for atomic-level gate structure and epitaxy analysis
Metallization is a phase in semiconductor manufacturing that involves the deposition of conductive layers, which are essential for forming interconnects between transistors. These interconnects serve as the pathways for electrical signals, enabling communication between different components of the semiconductor device.
The process of metallization must be executed with precision to ensure the integrity and functionality of the device. However, several issues can arise during this stage, such as metal voids, which are small gaps or cavities that can disrupt the continuity of the conductive path. Contamination, which refers to the presence of unwanted materials or particles, can also occur, potentially leading to short circuits or other electrical malfunctions. Additionally, adhesion failures, where the metal layer does not properly bond to the underlying surface, can compromise the structural stability and reliability of the interconnects.
These problems can significantly impact the electrical performance of the semiconductor device, leading to reduced efficiency, increased power consumption, or even complete device failure. Therefore, meticulous attention to detail and rigorous quality control measures are imperative during the metallization process to mitigate these risks and ensure optimal device performance.
As wafers transition into wafer-level packaging, a critical phase in semiconductor manufacturing, new failure modes emerge that can significantly impact the performance and reliability of the final product. These failure modes include delamination, which occurs when layers within the package separate, potentially leading to electrical disconnections or mechanical instability.
Voids, or small air pockets, can form within the material, disrupting the continuity of electrical pathways and causing potential short circuits or open circuits. Solder joint defects, another common issue, can result from improper bonding or thermal stress, leading to weak connections that may fail under operational conditions.
Each packaging method—flip-chip, fan-out wafer-level packaging (WLP), and through-silicon via (TSV)—introduces its own set of unique challenges. Flip-chip packaging, for instance, requires precise alignment and bonding of the chip to the substrate, while fan-out WLP involves redistributing the chip's connections to a larger area, which can introduce warpage or misalignment.
TSV, on the other hand, involves creating vertical interconnects through the silicon wafer, which can be prone to voids and cracks if not properly fabricated. Addressing these challenges requires meticulous attention to detail and the use of advanced inspection techniques to ensure the integrity and functionality of the packaged semiconductor devices.
In addition to the techniques already mentioned, Scanning Electron Microscopy (SEM) and Emission Microscopy (EMMI) can also be effectively utilized in the evaluation of packaging and global interconnects.
SEM provides high-resolution imaging that is crucial for analyzing the surface morphology and structural integrity of packaging materials, allowing engineers to detect and assess defects such as cracks, voids, and delamination.
EMMI, on the other hand, is particularly useful for identifying electrical failures by detecting emissions from semiconductor devices under stress conditions.
This technique helps in pinpointing the exact location of defects within the interconnects, which is essential for ensuring the reliability and performance of the semiconductor devices. By employing these advanced microscopy techniques, researchers and engineers can gain a comprehensive understanding of the challenges associated with packaging and interconnects, ultimately leading to improved design and manufacturing processes.
Deep Block is an advanced AI model development tool and image analysis software capable of processing any type of micrographs. This innovative software provides users with a comprehensive AI toolbox that allows them to perform a wide range of computer vision routines, such as image segmentation, polygon morphology analysis, and defect detection, all without the need for coding.
The software is designed with a user-friendly interface that enables users to rapidly analyze large-area micrographs through a graphical user interface (GUI), making it accessible even to those without extensive technical expertise. By leveraging this software, users can conduct various failure analyses across all stages of semiconductor fabrication, ensuring thorough and efficient inspection processes.
While large companies like TSMC and Samsung have the financial resources to employ numerous high-cost equipment such as KLA's Surfscan or AMAT's E-beam equipments for their chip manufacturing processes, many MEMS manufacturers and smaller fabs face significant challenges in acquiring and maintaining such expensive equipment.
To address this issue, we offer a tool that is not only easy to use but also versatile enough to be applied in various contexts. Our product supports not only TEM and SEM images with a narrow field of view but also a wide array of stitched micrograph files.
It facilitates training data annotation for AI model development, rapid analysis of large-area images, and extraction of polygon information, such as defects, in JSON format.
In addition to these capabilities, we provide customization services for the product and support its operation in on-premise environments. This ensures that users can protect their AI technologies and models from external threats while receiving comprehensive customer support and consulting services to assist with their diverse computer vision tasks. Over the years, we have developed various microscopy image analysis and large-scale image processing technologies, enabling us to inspect massive chips quickly and help users automate metrology and inspection tasks without relying on optical inspection equipment.
Failure analysis is not limited to large companies; it is also conducted by failure analysis service providers and research organizations within IDMs. A significant challenge is that even large fabs' departments often cannot operate expensive inspection equipments unless they are in the mass production stage.
Furthermore, nano-device fabrication does not rely on a single type of microscope; instead, multiple types are used, and users require different AI models and objects to be identified at each stage. However, rest assured, we support all micrographs and can seamlessly process large-area micrographs. For innovation in your failure analysis, large-area inspection, and various AI technology research, contact us at DeepBlock.net/contact for the ideal partnership!
Small companies, developing countries, various research institutions, and university researchers often face significant financial constraints, making it challenging for them to afford and operate expensive inspection equipment. These entities typically rely on outdated equipment or microscopes, which limits their ability to conduct advanced analyses or in-situ inspection.
The situation is further exacerbated by the fact that inspection equipment companies like KLA continue to increase the prices of their equipment, making it even more difficult for smaller research institutions and departments involved in failure analysis and process research to access the necessary tools. These departments often depend heavily on human labor to analyze the LARGE surfaces and cross-sections of large chips and wafers, which is both time-consuming and labor-intensive.
Researchers, for instance, may spend sleepless nights painstakingly examining chip cross-sections extracted with Focused Ion Beam (FIB) to identify even the smallest defects.
In emerging semiconductor manufacturing countries like India, the combination of Deep Block and microscopes offers a promising solution for this financial huddle. Deep Block allows users to automate of failure analysis at a cost significantly lower than that of expensive software like Carl Zeiss's Zen.
By automating these processes, researchers can conduct a variety of process experiments and ultimately achieve improvements in yield.
Despite being a small company, we are fully committed to working diligently for our clients. We continuously study various technologies and strive for excellence in product development and company growth. We eagerly await your interest and inquiries, as we are ready to assist you in overcoming these challenges and achieving your research and manufacturing goals.