Advancing technology nodes in DRAM continues to drive the reduction of on-product overlay (OV) budget. This gives rise to the need for OV metrology with greater accuracy. However, the ever increasing process complexity brings additional challenges related to metrology target deformation, which could contribute to a metrology error. Typically, an accurate OV measurement involves several engineering cycles for target and recipe optimization. In particular, process optimization in either technology development (TD) phase or high volume manufacturing (HVM) phase might influence metrology performance, which requires re-optimization. Therefore, a comprehensive solution providing accuracy and process robustness hereby minimizing the cycle time is highly desirable. In this work, we report multi-wavelength µDBO enhanced with accuracy aware pixel selection as a solution for robust OV measurement against process changes as well as improved accuracy in HVM. Accuracy aware pixel selection is capable of tackling intra-target processing variations and is established on a multi-wavelength algorithm with immunity to target asymmetry impact. DRAM use cases in FEOL critical layers will be discussed in this paper. Superior robustness and accuracy will be demonstrated together with improved on-product OV performance, promising a process of record metrology solution in specific applications throughout the TD and HVM.
KEYWORDS: Metrology, Optical proximity correction, Data modeling, Optical lithography, Signal to noise ratio, OLE for process control, Instrument modeling, Image analysis, Calibration, Metals
In the course of assessing OPC compact modeling capabilities and future requirements, we chose to investigate the interface between CD-SEM metrology methods and OPC modeling in some detail. Two linked observations motivated our study:
1) OPC modeling is, in principle, agnostic of metrology methods and best practice implementation.
2) Metrology teams across the industry use a wide variety of equipment, hardware settings, and image/data analysis methods to generate the large volumes of CD-SEM measurement data that are required for OPC in advanced technology nodes.
Initial analyses led to the conclusion that many independent best practice metrology choices based on systematic study as well as accumulated institutional knowledge and experience can be reasonably made. Furthermore, these choices can result in substantial variations in measurement of otherwise identical model calibration and verification patterns.
We will describe several experimental 2D test cases (i.e., metal, via/cut layers) that examine how systematic changes in metrology practice impact both the metrology data itself and the resulting full chip compact model behavior. Assessment of specific methodology choices will include:
• CD-SEM hardware configurations and settings: these may range from SEM beam conditions (voltage, current, etc.,) to magnification, to frame integration optimizations that balance signal-to-noise vs. resist damage.
• Image and measurement optimization: these may include choice of smoothing filters for noise suppression, threshold settings, etc.
• Pattern measurement methodologies: these may include sampling strategies, CD- and contour- based approaches, and various strategies to optimize the measurement of complex 2D shapes.
In addition, we will present conceptual frameworks and experimental methods that allow practitioners of OPC metrology to assess impacts of metrology best practice choices on model behavior.
Finally, we will also assess requirements posed by node scaling on OPC model accuracy, and evaluate potential consequences for CD-SEM metrology capabilities and practices.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.