KLA (Israel)

As semiconductor technology evolves and 3D integration rises, overlay metrology must evolve to meet tighter accuracy, precision, and sampling demands. Traditional overlay measurement techniques struggle with high topography and opacity in advanced packaging and SiC materials. This paper introduces a comprehensive solution combining advanced optics, intelligent run-to-run control, and predictive analytics to minimize rework, optimize exposure, and accelerate process development. Real-world case studies demonstrate how integrated metrology and analytics enhance overlay performance and reduce cycle time, enabling faster, first-pass success in high-yield manufacturing.

One key to managing the inaccuracy bias between optical overlay (OVL) at ADI and device overlay at AEI is to choose optical measurements with stable inaccuracy. The bias can then be managed as non-zero offsets (NZO) compared to an accurate e-beam OVL (eOVL) reference. High variability in the NZO, often driven by variations in the optical target asymmetries, can be a sizable portion of the on-product overlay budget. In this work, we break down the sources of NZO stability (sNZO) into target-to-device, litho-etch and optical inaccuracy variations by comparing the sNZO of optical image-based overlay (IBO) measurements to eOVL measurements on the same IBO targets. With all IBO targets measured by eOVL, compared to the standard pitch AIM® target, we show that the target-driven sNZO is reduced by almost 30% on small pitch AIM (sAIM™) IBO targets. We ascribe this effect to a reduction in intrinsic target asymmetry variability. Furthermore, we observe an even larger 50% reduction in sNZO moving from standard to small pitch targets when measuring optically. This complete breakdown of the sources of NZO variability highlights the relative contribution of the target itself to NZO control and the need for more process-robust targets like the sAIM design.

On-product overlay (OPO) control in the DRAM process has become a critical component from node to node to produce high device yield. To meet OPO node goals, Non-Zero Offset (NZO) and its stability across lots must be monitored and controlled. NZO is the bias between overlay (OVL) on-target measurement at After Development Inspection (ADI) vs. on-device measurement at After Etching Inspection (AEI). In this paper, we will present Imaging-Based Overlay (IBO) metrology data at ADI of two different marks, segmented AIM® with design rule patterns and robust AIM (rAIM®) with Moiré effect with a small pitch. NZO analysis will be presented for each target type including basic performance.

This paper will present a study about reducing on-product overlay (OPO) by optimizing imaging-based overlay (IBO) measurements utilizing newly developed extended wavelengths and optimal optical focus technologies on previous and current layers simultaneously in an advanced memory device process. Trends in memory device process variation using thicker/higher layer stacks along with more opaque process layers make this study especially crucial and topical to address these challenges.

On-product overlay (OPO) control is becoming more and more critical to successful 3D heterogeneous process integration which includes wafer-to-wafer (W2W) bonding. In this work, we will present novel overlay (OVL) methods and experimental metrology results on an advanced CMOS Image Sensor (CIS) W2W process. We will discuss metrology challenges such as thick wafer measurement, target design, precision, and accuracy. Different target designs will be presented and evaluated with the irArcher® 007 from KLA. We will demonstrate Total Measurement Uncertainty (TMU) of 1 nm on production wafers, with Tool-Induced Shift (TIS) values comparable to the current best-in-class metrology tool for single wafer OVL measurement and suitable throughput for High-Volume Manufacturing (HVM). We will highlight the importance of such precise OVL metrology tools to address the sub-50 nm OVL challenge in sub-micron pitch, wafer-to-wafer bonding applications. Inter-field and intra-field terms will be presented. Unexpected intra-field signatures will be discussed. Finally, the impact of bonding OVL on back-side lithography steps will be introduced opening interest for Advanced Process Control (APC) loops.

Numerical simulation of overlay metrology targets has become a de-facto standard in advanced technology nodes. While appropriate simulation software is widely available in the industry alongside with metrics that allow selection of the best performing targets, the model validation tools are less developed. We present an approach of numerical model validation based on the comparison between target simulation results and on-product overlay measurements. A “simulation-tomeasurement” software is used in this work to compare the performance metrics and accuracy flags of scatterometrybased overlay targets designed using KLA-Tencor AcuRate™ simulator for the critical layers of 12nm FD-SOI FEOL stack and 22nm FD-SOI BEOL stack. We demonstrate how simulation-to-measurement matching enabled us to verify the model, identify discrepancies between the model and the product stack and build an improved model that correctly describes the target. The refined target stack was used for image-based overlay target simulations that allowed us to obtain better performing optical overlay targets as well.

The gold-standard method for dermatophyte identification involves direct microscopy and culture, which have inherent shortcomings. Only few molecular methods have been standardised for routine clinical work. This study aimed to develop and test a platform for identifying the most common dermatophytes in Israel using multiplex real-time polymerase chain reaction (RT-PCR). Specific primers were designed for the multiplex system (LightCycler 480) according to known cultures and validated by reference isolates. The dermatophyte detection rate was compared to smear and culture in 223 clinical samples obtained from a tertiary medical centre. Inconsistencies between methods were evaluated by sequencing. The RT-PCR was further evaluated in 200 community-based samples obtained from a health maintenance organisation and 103 military-personnel-based samples analysed at a central laboratory. In hospital-based clinical samples, complete concordance between methods was observed in 190 samples (85%; Kappa=0.69). In most cases of non-concordance, sequencing was consistent with RT-PCR results. RT-PCR correctly identified all smear- and culture-positive cases in community and military-personnel samples. The results were available within 4hours. The multiplex RT-PCR platform is a rapid and efficient method for identifying dermatophyte species in clinical samples and may serve as a first step in the diagnostic algorithm of superficial fungal infections.

We present a novel metrology target design framework using the scanner exit pupil wavefront analysis together with Zernike sensitivity analysis (ZSA) based on the Monte-Carlo technique. The proposed method enables the design of robust metrology targets that maximize target process window (PW) while minimizing placement error discrepancies with device features in the presence of spatial and temporal variation of the aberration characteristics of an exposure tool. Knowing the limitations of lithography systems, design constraints, and detailed lithography information including illumination, mask type, etc., we can successfully design an optimal metrology target. We have validated our new metrology target design (MTD) method for one of the challenging DRAM active layer consisting of diagonal line and space patterns illuminated by a rotated extreme dipole source. We find that an optimal MTD target gives the maximized PW and the strong device correlation, resulting in the dramatic improvement of overall overlay performance. The proposed target design framework is completely general and can be used to optimize targets for different lithography conditions. The results from our analysis are both physically sensible and in good agreement with experimental results.

In order to fulfill the ever tightening requirements of advanced node overlay budgets, overlay metrology is becoming more and more sensitive to even the smallest imperfections in the metrology target. Under certain circumstances, inaccuracy due to such target imperfections can become the dominant contribution to the metrology uncertainty and cannot be quantified by the standard TMU contributors. In this paper we describe a calibration method that makes the overlay measurement robust to target imperfections without diminishing its sensitivity to the target overlay. The basic assumption of the method is that overlay measurement result can be approximated as the sum of two terms: the accurate overlay and the measurement inaccuracy (independently of the conventional contributors). While the first term (the “real overlay”) is robust it is known that the overlay target inaccuracy depends on the measurement conditions. This dependence on measurement conditions is used to estimate quantitative inaccuracy by means of the overlay quality merit which was described in previous publications. This paper includes the theoretical basis of the method as well as experimental validation.