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.
The semiconductor industry is moving toward 20nm nodes and below. As the Overlay (OVL) budget is getting tighter at these advanced nodes, the importance in the accuracy in each nanometer of OVL error is critical. When process owners select OVL targets and methods for their process, they must do it wisely; otherwise the reported OVL could be inaccurate, resulting in yield loss. The same problem can occur when the target sampling map is chosen incorrectly, consisting of asymmetric targets that will cause biased correctable terms and a corrupted wafer. Total measurement uncertainty (TMU) is the main parameter that process owners use when choosing an OVL target per layer. Going towards the 20nm nodes and below, TMU will not be enough for accurate OVL control. KLA-Tencor has introduced a quality score named ‘Qmerit’ for its imaging based OVL (IBO) targets, which is obtained on the-fly for each OVL measurement point in X & Y. This Qmerit score will enable the process owners to select compatible targets which provide accurate OVL values for their process and thereby improve their yield. Together with K-T Analyzer’s ability to detect the symmetric targets across the wafer and within the field, the Archer tools will continue to provide an independent, reliable measurement of OVL error into the next advanced nodes, enabling fabs to manufacture devices that meet their tight OVL error budgets.
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.
Magneto-resistive Random Access Memory (MRAM), considered the leading candidate for the next generation of universal memory, has moved from research to pilot production. Commercialization of the MRAM devices in mobile computing, cell phones, portable recording and other playback devices, home computing, consumer electronics, enterprise computing and telecommunications, promise to bring in annual revenues exceeding $50 billion during the coming years. CD-SEM correlation of contact physical Critical Dimension to Magnetic Tunneling Junction (MTJ) resistance is critical for MRAM device performance. This paper focuses on a new two-dimensional metric that more accurately characterizes MTJ resistance by calculating total contact area of unique and complex structures. We consider the advantages of the Contact Area metric for measurement of complicated shapes. We illustrate that introduction of the new metric allows for improvement in process control for critical contacts.
Downscaling of semiconductor fabrication technology requires an ever-tighter control of the production process. CD-SEM, being the major image-based critical dimension metrology tool, is constantly being improved in order to fulfill these requirements. One of the methods used for increasing precision is averaging over several or many (ideally identical) features, usually referred to as "Macro CD". In this paper, we show that there is much more to Macro CD technology- metrics characterizing an arbitrary array of similar features within a single SEM image-than just the average. A large amount of data is accumulated from a single scan of a SEM image, providing informative and statistically valid local process characterization. As opposed to other technologies, Macro CD not only provides extremely precise average metrics, but also allows for the reporting of full information on each of the measured features and of various statistics (such as the variability) on all currently reported CD SEM metrics. We present the mathematical background behind Macro CD technology and the opportunity for reducing number of sites for SPC, along with providing enhanced-sensitivity CD metrics.
The edge roughness of straight lines has received intense focus in the past, whereas the edge roughness of contact holes has been relatively unexplored. Reductions in contact hole roughness can be shown to offer improvements in electrical breakdown voltages, or potentially the opportunity for reduced cellsize. This paper introduces two CD-SEM algorithms for characterizing the amplitude and frequency of contact hole edge roughness. When combined, these two metrics proved capable of detecting differences within four wafer pairs with varying dimension and processing. Increased roughness amplitude was shown to correlate to electrical breakdown failures.
The paper presents results of a thorough study using the UV- based die-to-database mask inspection system ARIS100i for the inspection of alternating phase shifting masks (AAPSM) designed for KrF (248nm) technology. A specifically designed test mask was used to investigate sensitivity limitations of the i-line tool. Main focus is on phase errors, which were treated as a function of defect size, phase, and mask location.
The paper presents the use of the Linewidth Bias Monitor (LBM), the critical dimension (CD) uniformity mapping option of the ARIS 2li die-to-database mask inspection system, for incoming quality control (IQC) in the wafer fab. LBM is qualified for this purposes by comparing it's quantitative results with CD measurements. Masks, provided by different commercial vendors, are evaluated based on the LBM maps obtained during mask inspection. Mean-to-target and 3-sigma values are evaluated and compared.
The paper presents the use of the Linewidth Bias Monitor (LBM), the critical dimension (CD) uniformity mapping option of the ArisTM21i die-to-database mask inspection system, for mask process control and incoming quality control (IQC) in the wafer fab. LBM is qualified for this purposes by baselining it with CD measurements. Masks, provided by different commercial vendors, are evaluated based on the LBM maps obtained during mask inspection. Mean-to-target and 3-sigma values are evaluated and compared. The results are presented. In addition, a case, where LBM identified a killer CD variation during IQC is presented.
The paper presents results of a thorough study using the UV-based die-to-database mask inspection system ARISTM100i for the inspection of alternating phase shifting masks (AAPSM) designed for ArF (193nm) technology. Specially designed test masks were used to investigate sensitivity limitations of the i-line tool. Main focus is on phase errors, which were treated as a function of defect size, phase, and mask location. In addition, production reticles were inspected using a specially developed sensitivity AAPSM. Production issues like false defect rate and data preparation were addressed. The paper is concluded with a short printability analysis of different phase defects detected during the experiment.
The paper presents the inspection of embedded attenuated phase shift masks for the 193nm lithography generation using UV-based mask inspection systems. Production issues like light calibration due to the existence of different transmissions on the mask and halftone-specific inspection sensitivity settings are discussed. A mask inspection example is presented and the most severe defect types are analyzed. In addition, the mask is investigated using the Linewidth Bias Monitor (LBM) option of the inspection system used, which provides a critical dimension (CD) uniformity map of the entire mask.
With the advance of photolithography technology into the super-resolution regime, reticle features are becoming denser and their dimensions are shrinking. This leads to much stricter design rules, which include a decrease in the dimensions of the critical defects needed to be detected. Orbot-Applied's new Improved Image Acquisition module has been developed as a means of meeting the rising demand in defect detection capability and integrated into RT-8000ES Die-to-Database reticle inspection system. The main purpose of this evaluation was to test the system's performance under difficult production conditions in its highest defect detection sensitivities.
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