The semiconductor manufacturing roadmap which generally follows Moore’s law requires smaller and smaller EPE (Edge Placement Error), and this places stricter requirements on OPC model accuracy, which is mainly limited by metrology errors, pattern coverage and model form. Current metrology errors are mainly related to SEM image noise and measurement difficulty in complex 2D patterns. And traditional model form improvement by adding empirical terms for PEB (Post Exposure Bake), NTD (Negative Tone Development) and PRS (Physical Resist Shrinkage) effects still cannot meet the accuracy spec because other physical and chemical effects are uncaptured. Fitting these effects also requires comprehensive pattern coverage during model calibration. Solely improving model form may overfit the metrology error, which is risky, while solely improving metrology ignores existing model errors: both factors are troublesome for OPC. In this paper, a new metrology (MXP, naming for Metrology of Extreme Performance) and deep learning (Newron, naming for a Deep Convolutional Neural Network model form) integrated solution is proposed, where MXP decreases the metrology errors and provides good pattern coverage with high-volume reliable CD and EP (Edge Placement) gauges, and Newron captures remaining complex physical and chemical effects embedded in high-volume gauges beyond the traditional model. This solution shows overall ~30% prediction accuracy improvement compared to baseline metrology and FEM+ (Focus Exposure Matrix) model flow in N14 NTD process, predicts SEM shape of critical weak points more accurately.
In recent years, compact modeling of negative tone development (NTD) resists has been extensively investigated. Specific terms have been developed to address typical NTD effects, such as aerial image intensity dependent resist shrinkage and development loading. The use of photo decomposable quencher (PDQ) in NTD resists, however, brings extra challenges arising from more complicated and mixed resist effect. Due to pronounced effect of photoacid and base diffusion, the NTD resist with PDQ may exhibit opposite iso-dense bias trend compared with normal NTD resist. In this paper, we present detailed analysis of physical effects in NTD resist with PDQ, and describe respective terms to address each effect. To decouple different effects and evaluate the impact of individual terms, we identify a certain group of patterns that are most sensitive to specific resist effect, and investigate the corresponding term response. The results indicate that all the major resist effect, including PDQ-enhanced acid/base diffusion, NTD resist shrinkage and NTD development loading can be well captured by relevant terms. Based on these results, a holistic approach for the compact model calibration of NTD resist with PDQ can be established.
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.
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