In-line Metrology Research Articles

Key Feature Identification for Monitoring Wafer-to-Wafer Variation in Semiconductor Manufacturing

To monitor process and identify the deviation as early as possible, data-driven methods have been applied for process monitoring and fault detection in semiconductor manufacturing. Although various fault detection and classification models had been discussed in the literature, however, little research has been devoted to feature selection from trace data that is important for process monitoring of natural variation. Additionally, the high-mix production mode with different recipes leads to process dynamic of wafer-to-wafer (W2W) variation which should also be identified for safeguarding false alarms and serving as a warning indicator. Therefore, this paper proposes a data-driven framework to identify the key features with respect to the W2W variation. In particular, the self-organizing map is used to annotate the grade of wafer variation among the in-line metrology data. Subsequently, the adaptive boosting (AdaBoost) is adopted to examine the effectiveness of every feature and its processing times, respectively. To validate the proposed framework, an empirical study from a semiconductor fabrication plant is conducted. The experimental results demonstrate that the key feature identification is of critical importance to build highly capable models for process monitoring. Through the dimensionality reduction technique, it has been illustrated that a smaller set of the identified key features are able to pinpoint the W2W variation of different wafer grades more clearly than the whole set of process features. <i>Note to Practitioners</i>&#x2014; Process monitoring has become more difficult with the shrinking linewidth in semiconductor manufacturing. The challenges of analyzing equipment sensor or raw trace data for process monitoring in high-mix manufacturing processes are to incorporate subject-matter expert knowledge for setting control limit meticulously, to detect the subtle changes by analyzing the whole trace data profile, and to identify W2W variation for reducing false alarms. This paper proposes a data-driven framework for process monitoring by adopting data-driven approaches without recourse to domain judgement. Experimental results demonstrate that the proposed data-driven framework can effectively identify the key features via sensor readings and corresponding processing times, respectively. The engineers can make use of the extracted features to perform a predictive monitoring on metrology data for detection of potential process deterioration.

(Digital Presentation) Advanced Process Control of Dual Patterns for FinFET Mass Production

Advanced Process Control (APC) has been widely applied in state-of-the-art semiconductor industries for the everlasting pursuit of cycle time reduction, higher yield, and zero scraps. Inline metrology is thus valuable input for the improvement of wafer-to-wafer and within-wafer CD variations originated from either abnormality or noise of different processes. Implementing a suitable APC scheme to process flow remains a challenging task for engineers. In most cases, it is enough to implement the APC to only one single pattern on Chip. However, for multi-purpose chip design, the CD control of multiple patterns is becoming important. In this paper, we presented an APC workflow to control the CD of two different patterns. It is shown that, with the same amount of APC process layers, we were able to improve from single pattern CD control to dual pattern CD control. The final process variations of two patterns can be controlled within ±0.5 nm.

(Digital Presentation) An Advanced Process Control Scheme for Fin Etching Process in Front-End-of-Line FinFET High Volume Production

As FinFET scales down to advanced technology nodes, Fin profile and Critical Dimension (CD) control are becoming a huge challenge due to the increased number of processes. For a stable wafer-to-wafer CD performance, Advanced Process Control (APC) system is widely deployed in high volume manufacturing production. In this work, we present a novel implementation of an APC-based fuzzy control system in the Fin etching process within the widely-used Self-aligned Quadruple Patterning (SaQP) scheme. Feed-forward APC is applied to the two processes: 1) Atomic Layer Deposition (ALD) process for fin hard-mask etching and 2) fin etching process with fuzzy control. With the deployment of the APC system, the inline metrology variation performance of Fin CD improved from ±3.5% to ±1.8%. The Cp and Cpk are increased by 29% and 32%, for various key inline parameters. The APC-based fuzzy control scheme shows great potential for the advanced nodes.

Review of nanosheet metrology opportunities for technology readiness

Over the past several years, stacked nanosheet gate-all-around (GAA) transistors captured the focus of the semiconductor industry and have been identified as the lead architecture to continue logic complementary metal-oxide-semiconductor scaling beyond 5 nm node. The fabrication of GAA devices requires specific integration modules. From very early processing points, these structures require complex metrology to fully characterize the three-dimensional parameter set. As the technology progresses through research and development cycles and is poised to transition to manufacturing, there are many opportunities and challenges that still remain for in-line metrology. Especially valuable are measurement techniques that are non-destructive, fast, and provide multi-dimensional feedback, where reducing dependencies on offline techniques has a direct impact on the frequency of cycles of learning. More than previous technologies, then, nanosheet technology may be when some offline techniques transition from the lab to the fab, as certain critical measurements need to be monitored in real time. Thanks to the computing revolution the semiconductor industry enabled, machine learning has begun to permeate in-line disposition, and hybrid metrology systems continue to advance. Of course, metrology solutions and methodologies developed for prior technologies will also still have a large role in the characterization of these structures, as effects such as line edge roughness, pitch walk, and defectivity continue to be managed. We review related prior studies and advocate for future metrology development that ensures nanosheet technology has the in-line data necessary for success.

Development and evaluation of three-dimensional metrology of nanopatterns using electron microscopy

The semiconductor industry continuously moves toward smaller features and more complex, three-dimensional (3D) structures to enable next-generation devices. Thus there is a high need for 3D metrology techniques that would provide feedback to the advancing nanoscale fabrication processes. We introduce an approach for evaluating, calibrating, and developing new metrology of nanopatterns through comparing the new metrology data to 3D ground truth data, obtained by accurate scanning transmission electron microscopy (STEM) tomography 3D characterization. We demonstrate this approach by evaluating 3D height maps of sub-20-nm patterns obtained using multi-secondary electron detector scanning electron microscopy (multi-perspective SEM) and photometric stereo algorithm. We demonstrate the importance of full 3D characterization, including cross-sectional structure, height fluctuations, and line edge roughness to truly probe the pattern’s average structures and their 3D variations. Although STEM tomography is a high-resolution and accurate method, it is considered demanding in terms of sample preparation and cannot be used as an efficient in-line metrology method. However, we show that it can be used as a reliable 3D characterization technique to obtain the necessary 3D data for the development of new 3D metrology tools and demonstrate this approach by evaluating the accessible, in-line, multi-perspective SEM.

Connectivity as a Design Feature for Industry 4.0 Production Equipment: Application for the Development of an In-Line Metrology System

Industry 4.0 (I4.0) is built upon the capabilities of Internet of Things technologies that facilitate the recollection and processing of data. Originally conceived to improve the performance of manufacturing facilities, the field of application for I4.0 has expanded to reach most industrial sectors. To make the best use of the capabilities of I4.0, machine architectures and design paradigms have had to evolve. This is particularly important as the development of certain advanced manufacturing technologies has been passed from large companies to their subsidiaries and suppliers from around the world. This work discusses how design methodologies, such as those based on functional analysis, can incorporate new functions to enhance the architecture of machines. In particular, the article discusses how connectivity facilitates the development of smart manufacturing capabilities through the incorporation of I4.0 principles and resources that in turn improve the computing capacity available to machine controls and edge devices. These concepts are applied to the development of an in-line metrology station for automotive components. The impact on the design of the machine, particularly on the conception of the control, is analyzed. The resulting machine architecture allows for measurement of critical features of all parts as they are processed at the manufacturing floor, a critical operation in smart factories. Finally, this article discusses how the I4.0 infrastructure can be used to collect and process data to obtain useful information about the process.

In-line characterization of nanostructures produced by roll-to-roll nanoimprinting.

We present an in-line metrology solution for dimensional characterization of roll-to-roll imprinted nanostructures. The solution is based on a scatterometric analysis of optical data from a hyperspectral camera deployed at a production facility, where nanostructures are produced at speeds of 10m/min. The system combines the ease of use of a real-space imaging system with the spectral information used in scatterometry. We present nanoscale dimensional measurements on one-dimensional line gratings with various periods and orientations. The depths of the produced structures are accurately characterized with uncertainties on the scale of a few nanometers. The hyperspectral imaging capabilities of the system can also be used to avoid vibrational effects.

Investigation of Fluoro-Carbon Layer on Dense Sicoh Formed during CF4 and CF4/C4F6 Based Continuous Wave Plasma Etch

Motivation: Plasma etching of low-k and ultra low-k (ULK) dielectric materials have seen a tremendous growth in deep nanoscale applications. Fluorocarbon based gases are the forerunners in etching low-k dielectrics as they are the F suppliers necessary to remove Si and C from SiCOH material. Different FC gases in combination with the additive gases contribute differently to the etch behavior of SiCOH due to differing reaction chemistry and formation of Fluorocarbon layer as an interfacial layer between plasma front and dielectric front [i]. Due to dynamic formation and etching of FC Layer happening at the dielectric surface, understanding FC layer properties in each gas plasma is the starting step to control etch rate and plasma induced damage in Low-k dielectrics. This paper aims to study and compare FC layer deposition by different gases grouped into CF4 and CF4/C4F6 family with N2, O2 and H2 as additive gases in each group. FC layer thickness, etch rate, optical properties of etched SiCOH and chemical composition of the FC layer by different plasma treatments have been presented in this work. Methodology: Dense SiCOH (k=2.75 and Open Porosity: 7%) with initial thickness of 157±3nm is deposited on 300mm Si Wafer with a thin SiO2 adhesion layer in between. These wafers are blanket etched in a commercial etch chamber with the given gas combinations (CF4, CF4/N2, CF4/O2, CF4/H2; CF4/C4F6, CF4/C4F6/N2, CF4/C4F6/O2, CF4/C4F6/H2) for same amount of time, total gas flow rate, similar power, pressure and temperature settings.Post Etch blanket wafers are subjected to various in-line and off-line metrology tools. In-line spectroscopic ellipsometer is used to model complex refractive index and thickness of individual layers. Tauc-Lorentz model best describes the FC layer whereas Cauchy model describes the dielectric [ii]. In-line XPS was carried out to probe the surface of FC layer and gain chemical information. Furthermore depth profile of etched layer is carried out by sputtering the surface with low power Ar ions to study variations in chemical composition with the layer depth. SEM is used to see the cross section profile and verify the results from above method Observation: Thickness evaluation from the dispersion models shows that the CF4 group has higher etch rate and lower FC layer thickness compared to CF4/C4F6 group. C4F6 has higher polymerization ability by the virtue of its lower F/C ratio. Amongst each group, Oxygen as additive gas shows the highest etch rate and least FC thickness followed by Nitrogen whereas Hydrogen has least etch rate but highest FC layer thickness. Under given etch conditions with CF4/C4F6/H2 plasma, deposition rate was higher than etching rate leading to stack growth (Fig.1a). Hydrogen supports polymerization by scavenging Fluorine away and aids in thicker FC films.XPS chemical composition shows Fluorine diffusion through FC layer into the dielectric layer bringing changes to its pristine structure. This affects Carbon% across the etched dielectric thickness (Fig.1b). Thicker the FC layer is, closer is the Carbon % to pristine SiCOH. Presence of surficial Nitrogen in the nitrogen containing plasmas shows nitrogen reacts with SiCOH Carbon, forms CN compounds and increases the etch rate. FC layer shows presence of CF3 radicals on the surface and decrease fast with the depth, followed by CF2 radicals. CF radicals are in larger quantity and are present deepest into the FC Layer. Presence of polymerized C-C and C-CFx bonds increases with the FC Layer depth and offset with increase of C-Si bond near the SiCOH interface. Conclusion: This paper shows comparison of Etch Rate and FC layer thickness during SiCOH etch using different gas combinations in the CCP plasma chamber. Thickness correlation between ellipsometric model data and XPS depth profile followed by SEM cross section measurement of layer thickness point towards the correctness of dispersion models for each layer. These models can be used for quick inline post etch metrology useful for process control. O2 containing plasmas are too aggressive on the dielectric with negligible FC layer formation, while H2 containing plasmas are less damaging but exhibit very small etch rate. CF4/C4F6/N2 plasma is the optimum combination for Low-k dielectric etch amongst other combinations in terms of desired etch rate and lower reduction in Carbon %. Relative concentration and penetration depth of different CFx radicals in FC film suggests its influence on film structure.

Epitaxial Growth of Active Si on Top of SiGe Etch Stop Layer in View of 3D Device Integration

Three-dimensional System-On-Chip (3D-SoC) technology schemes require wafer-to-wafer bonding combined with good control of the Si thickness and the Si within wafer uniformity [1,2]. As a result, there is a renewed interest in epitaxial strained Si1-xGex as etch stop layer [3]. Epitaxial growth by means of Chemical Vapor Deposition (CVD) offers excellent control of layer thickness and material composition. If needed, the Si cap layer can be in-situ doped. The challenge is to develop low cost epitaxial growth processes without compromising the material quality. Indeed, relaxation of the Si1-xGex layer must be avoided as the presence of threading dislocations in the Si-cap has a detrimental effect on electrical properties and the yield of the devices fabricated afterwards. On the other hand, the Ge concentration in the Si1-xGex layer should be sufficiently high to guarantee etch selectivity with respect to the underlying Si substrate [4]. The Si1-xGex layer also needs to be relatively thick as some material loss cannot be avoided. Etching of the Si-cap layer during wafer back-side thinning must be prevented.In this contribution, we discuss the different challenges for the epitaxial growth of such Si-cap / Si1-xGex // Si-substrate layer stacks, with Si-cap layer thicknesses ranging from 20 to 500 nm and a targeted Ge content in the Si1-xGex layer of 25%. All epi-layers discussed in this work were grown in an ASM Intrepid RP-CVD cluster tool, aiming the highest possible process throughput. To control the epitaxial material quality, fast and reliable in-line metrology and inspection techniques are required. For instance, Wostyn et al. recently reported on inline light scattering measurements, commonly used to determine wafer quality and cleanliness, and have shown that the technique is also suitable to study the crystalline quality after hetero epitaxy [5].Standard deviations in thickness below 1.5% as measured for both the Si0.74Ge0.26 and the Si-cap layers by means of Spectroscopic Ellipsometry illustrate the within wafer uniformity of the epitaxially grown layer stacks. The Si0.74Ge0.26 material quality is confirmed by the presence of well-defined Kiessig fringes on the (004) XRD spectrum. The lack of a surface crosshatch pattern in AFM and the very low haze values as obtained from light scattering measurements using the KLA Surfscan® SP3 indicate the absence of misfit dislocations in uncapped Si0.74Ge0.26 layers for thicknesses up to 100 nm. After Si capping, RSM measurements still indicate that the layer is fully strained (Fig. 1a). Moreover, no defects were detected by commercial in-line defect inspection systems such as the KLA Electron-Beam Wafer Defect Review (EDRT M) System and the automated optical inspection system. However, depending on the process conditions, enhanced haze values might be measured. This enhanced surface roughness is due to the presence of misfit dislocations as evidenced by AFM (Fig. 1b). A careful process optimization enables the deposition of Si-cap / Si0.75Ge0.25 // Si-substrate bilayers with low haze values which are completely free of misfit dislocations, still allowing a Si-cap thickness of up to 500 nm and a relative high processing throughput (Fig. 1d). Still, it is striking that in case of 300 mm substrates, layer relaxation, if present, starts at the edge of the wafer (Fig. 1c) [6]. Therefore, special care needs to be taken to ensure that no relaxation is initiated at wafer edges. Extremely sensitive characterization methods are mandatory to detect the onset of relaxation and to ensure the fabrication of defect-free epi stacks. The developed epi process was successfully implemented in 3D device integration schemes to fabricate stacked Gate All Around devices and to demonstrate functional backside integration.

Design of a motorised plasma delivery system for ultra-precision large optical fabrication

A unique plasma figuring (PF) process was created and demonstrated at Cranfield University for manufacturing extremely large telescopes. The atmospheric pressure processing is faster and more cost-effective than other finishing processes; thus, providing an important alternative for large optical surfaces. The industrial scale manufacturing of thousands of ultra-precision metre-scale optics requires a robust PF machine: this requirement is achieved by making the plasma delivery system (PDS) performance repeatable. In this study, a dedicated PDS for large optical manufacturing was proposed to meet the industrial requirement. The PDS is based on an L-type radiofrequency (RF) network, a power supply, and an inductively coupled plasma torch. However, the complexities of these technologies require an in depth understanding of the integrated components that from the PDS. A smart control system for the modified PDS was created. This novel control system aims to make the characterization process deterministic: by automating the tuning of critical electrical components in the RF network, which is achieved by the use of in-line metrology. This paper describes the main design aspects. The PDS was tested with a good correlation between capacitance and RF frequencies. The robust PDS design enables a stable discharge of plasma with a low deviation of RF signals during the total 15 hours’ test.

High-voltage CD-SEM-based application to monitor 3D profile of high-aspect-ratio features

Background: In-line metrology for three-dimensional (3D) profiling high-aspect-ratio (HAR) features is highly important for manufacturing semiconductor devices, particularly for memory devices, such as 3D NAND and DRAM. Aim: Our purpose was to obtain the cross-sectional profiles of the HAR features from top-view critical dimension scanning electron microscopy (CD-SEM) images. Approach: Based on Monte Carlo simulation results, we proposed a method for 3D profiling of HAR features using backscattered electron (BSE) signal intensities. Several kinds of HAR holes with different taper angles and bowing geometries were fabricated. High-voltage CD-SEM was used for experiments to determine the feasibility of our approach. Results: Using the BSE line-profile, we constructed cross sections of the taper holes and estimated sidewall angles (SWAs), which were approximately the same as those observed using field-emission scanning electron microscopy (FE-SEM). The constructed cross sections of the bowing holes and the trends of the geometric variance, which were estimated by the middle CD and its depth, were consistent with the cross sections observed by FE-SEM. Conclusions: The results demonstrate that the variation in the HAR holes, such as SWA and bowing geometry, can be measured and monitored using the BSE images.

Suspended Nanochannel Resonator Arrays with Piezoresistive Sensors for High-Throughput Weighing of Nanoparticles in Solution.

As the use of nanoparticles is expanding in many industrial sectors, pharmaceuticals, cosmetics among others, flow-through characterization techniques are often required for in-line metrology. Among the parameters of interest, the concentration and mass of nanoparticles can be informative for yield, aggregates formation or even compliance with regulation. The Suspended Nanochannel Resonator (SNR) can offer mass resolution down to the attogram scale precision in a flow-through format. However, since the readout has been based on the optical lever, operating more than a single resonator at a time has been challenging. Here we present a new architecture of SNR devices with piezoresistive sensors that allows simultaneous readout from multiple resonators. To enable this architecture, we push the limits of nanofabrication to create implanted piezoresistors of nanoscale thickness (∼100 nm) and implement an algorithm for designing SNRs with dimensions optimized for maintaining attogram scale precision. Using 8-in. processing technology, we fabricate parallel array SNR devices which contain ten resonators. While maintaining a precision similar to that of the optical lever, we demonstrate a throughput of 40 000 particles per hour-an order of magnitude improvement over a single device with an analogous flow rate. Finally, we show the capability of the SNR array device for measuring polydisperse solutions of gold particles ranging from 20 to 80 nm in diameter. We envision that SNR array devices will open up new possibilities for nanoscale metrology by measuring not only synthetic but also biological nanoparticles such as exosomes and viruses.

Design and testing of a positioning system based on a quasi kinematic guide and a clamp plate suspended by compliant straps for in-line metrology systems

Full inspection of parts in production lines has emerged as an alternative to validate compliance of products with target specifications. Quick and accurate workpiece setup is critical for reliable measuring operations. This article introduces a design for quick, accurate fixturing of parts for in-line metrology. The design includes quasi-kinematic couplings that direct and position parts at the end of the stroke of a linear actuator, and a set of compliant straps to hold parts in place. Tests show the system is capable of positioning parts with excellent repeatabilities, at rates that allow the measuring process to keep up with production.

Nondestructive characterization of nanoscale subsurface features fabricated by selective etching of multilayered nanowire test structures using Mueller matrix spectroscopic ellipsometry based scatterometry

Nondestructive measurement of three-dimensional subsurface features remains one of the most difficult and unmet challenges faced during the fabrication of three-dimensional transistor architectures, especially nanosheet and nanowire based field effect transistors. The most critical fabrication step is the selective etching of silicon-germanium subsurface layers. The resulting shape and dimensions of the remaining Si(1 − x)Gex structure strongly impacts further processing steps and ultimately the electrical performance of gate-all-around transistors, thus creating the need for accurate inline metrology. In order to demonstrate the ability to characterize this etch, nanowire test structures made from Si(1 − x)Gex/Si/Si(1 − x)Gex/Si/Si(1 − x)Gex/Si multilayers have been characterized using Mueller matrix spectroscopic ellipsometry based scatterometry. Transmission electron microscopy images were used to corroborate the authors’ scatterometry measurements. Here, they successfully demonstrate the ability to measure the Si(1 − x)Gex etch, providing an industrially viable technique for inline three-dimensional metrology.

Nanoscale limits of angular optical scatterometry

Angular scatterometry is a fast, in-line, noncontact, and nondestructive nanoscale metrology tool that is widely used in manufacturing processes. As scatterometry is a potential metrology technique for next generation semiconductor manufacturing and for other emerging large-area (roll-to-roll) nanotechnology products such as wire grid polarizers (WGPs) and nanostructured metamaterials, it is necessary to study its fundamental sensitivity and accuracy limitations. Two different samples are simulated using rigorous coupled-wave analysis. One is a high index contrast aluminum WGP structure, and the other is a low-index contrast resist grating on a polycarbonate substrate. During modeling, the sample structure is scaled by simultaneously scaling both the line width and the height of the grating with a fixed pitch and all linear dimensions, including pitch, line width, and grating height, of the structure. Two metrics are chosen to define the limits: the first is the comparison with experimental limits, that is, if the reflection difference for a 5% scaling variation is larger than the experimental noise floor, scatterometry has sufficient resolution to recover the metrology information; the second is the comparison with effective medium models, that is, if the simulated angular scatterometry signature differs from an effective medium model signature, again within experimental noise limits, scatterometry is judged to have sufficient resolution to determine the feature parameters. Using a 405 nm source, scatterometry provides sufficient information to analyze a 20 nm pitch WGP structure using a 405 nm laser source (wavelength/pitch = 20), while the minimum pitch resist grating is ∼24 nm (wavelength/pitch = 16.8).

Statistical Behavioral Models of Silicon Ring Resonators at a Commercial CMOS Foundry

We reported on statistical behavioral models of silicon ring resonators at a commercial CMOS foundry. The ring resonators were fabricated on 300 mm silicon-on-insulator wafers using the DAPHNE technology at STMicroelectronics. Process variability, including lot-to-lot, wafer-to-wafer, and field-to-field variation, is inferred from optical test results, and cross validated by inline metrology data. Significant amount of reflection is observed in many ring designs, and the impacts of reflection on system integration are discussed.

Measurement of the stress-strain behavior of freestanding ultra-thin films

The stress-strain behavior of freestanding ultra-thin films (<100 nm) is characterized using residual-stress-driven structures. The proposed technique does not require an external sample loading setup and uses standard fabrication and metrology techniques that are available in the clean-room. A uniaxial load is applied to the freestanding test films using the residual stress of a well-characterized reference material. Highly cross-linked SU-8, a negative photoresist, is proposed as the reference loading material. The test wafer includes structures for in-situ calibration of the properties of the loading material. The geometry of the structures is varied to measure strains as high as 3.7%. The displacements of the freestanding test films are measured using digital image processing and used to measure the stress-strain response. Measurements on 63 nm thick passivated copper film stack show a slightly lower elastic modulus and a much higher yield strength than observed in bulk materials, and are in-line with the expectations from a nanocrystalline film with passivation. The properties of SU-8 and copper measured here are in good agreement with those measured using an alternate technique by the authors. As such, the proposed technique of residual-stress-driven structures is easy-to-replicate and serves as a useful in-line metrology tool that can be seamlessly implemented on coatings used in a semiconductor device production line.

Optical angular scatterometry: In-line metrology approach for roll-to-roll and nanoimprint fabrication

Metrology is an essential aspect of nanomanufacturing. Increasingly, nanoscale three-dimensional features are demanded for advanced applications, increasing the demands on metrology. New fabrication techniques such as roll-to-roll (R2R) processes are being developed for manufacturing large-area nanotechnology products such as wire-grid polarizers (WGP), metal-mesh grids, and metamaterials. Angular scatterometry has demonstrated noncontact, optical capabilities for characterizing WGP and photoresist structures with sub-100 nm dimensions. However, existing implementations are not applicable to real-time R2R nanofabrication due to both a requirement of rotating a small sample over a range of angles and measurement times that are incompatible with a moving R2R web. This work demonstrates a high-speed approach (2.5 kHz scanning) to angular scatterometry where the optical beam is scanned rather than the sample mount. The design uses a scanning mirror and high numerical aperture (NA) optics to vary the incident angle over a range from ∼29° to ∼59°. Approaches to increase the angular range are discussed. The scatterometry results are in good agreement with off-line scatterometry results for plane surface, 1D, and 2D patterned samples.

Depth-correlated backscattered electron signal intensity for 3D-profile measurement of high aspect ratio holes.

In-line metrology for measuring 3D features of the high aspect ratio (HAR) holes is becoming more challenging due to the progressing semiconductor technology, particularly in memory devices. Measurements of the bottom critical dimension (CD), taper angles and 3D profiles of the HAR holes require new imaging capabilities. In this work, we explored the characteristics of high-energy backscattered electron (BSE) signals and demonstrated their promising application to 3D metrology. From Monte Carlo simulation results, it is worth noting that BSE signal intensity emitted from an irradiated location in the depth of the hole decreases exponentially with the increase of the depth from the top surface (perpendicular depth) of the hole. Furthermore, the influences of various factors including the electron energy, the depth and the sidewall angle (SWA) of the hole on the attenuation of the BSE signal intensity were investigated. The simulation results show that the attenuation of the BSE signal intensity depends on the electron energy, the depth and the density of the hole but is independent of the SWA and the incident angle of the primary electron beam. Based on the characteristics of the BSE signal intensity, an algorithm was proposed for the 3D metrology of the HAR holes. Finally, the differences in CDs between the measured value and the target value of HAR holes with various geometries were examined. A maximum measurement bias within ±2.0nm for various holes with different depths, densities and SWA values shows great potential of depth-correlated BSE signals in 3D metrology.

Effect of Defects in Silicon Carbide Epitaxial Layers on Yield and Reliability

Inline metrology tools are widely used to detect defects in SiC epitaxial layers. The defect statistics are used in a variety of ways to determine quality, pass/fail and screen affected die. In this work, we document the automated detection and classification of various epitaxial defects based on type and origin. We further classify these categories into killer and non-killer defects and compare them to the electrical yield of Schottky Diodes. The origins of these defects are determined in broad categories, resulting in a clustering and yield-scaling model, which agrees very closely to experimental data. Further, we look at on-wafer screening techniques of potential weak die by both defect tagging and unclamped inductive switching (UIS) stress testing. Successful 1000-hr reliability tests show the robustness of our detection and screening methods.