In recent years, Deep Learning (DL) algorithms employing artificial neural networks (NN) have been shown to be a powerful tool for the classification and quantification of images including intensity data from various x-ray scattering techniques. These algorithms generally require massive, labeled datasets for training and validating the NNs. Such datasets can be extremely difficult to obtain from measurements for several reasons. The size of the dataset is limited by the variation in available samples and the time available to measure the samples. The labels are limited by both the number and quality of available reference measurements. In this work we will discuss the use of DL for the analysis of critical dimension small angle x-ray scattering (CD-SAXS) data from high-aspect ratio (HAR) structures encountered in 3D NAND and DRAM memories. We have developed a novel solution for the automatic generation and labeling of large synthetic datasets using “realistic simulations” of the x-ray scattering data. Our solution includes instrumental artifacts such as background scattering and Poisson noise normally found in real x-ray images. Additionally, we have included structural variations based on parameters obtained from limited reference data, e.g., cross-section SEM images, which are critical to prevent overfitting of the DL model and improve the accuracy of the analysis. The realistic simulations are generated automatically using the NanoDiffract for XCD (NDX) software. The synthetic data are then used to train a convolutional neural network (CNN) that can be deployed and used for real-time inference. We demonstrate this approach by evaluating single-shot alignment and tilt of HAR memory hole structures. The CNN was validated with experimental data collected and analyzed using a Sirius-XCD® tool. Validation with reference data from production quality wafers resulted in an R2 > 0.95 and precision 3σ < 0.02 degree with a significant reduction in measurement time per site.
High aspect ratio (HAR) structures found in three-dimensional nand memory structures have unique process control challenges. The etch used to fabricate channel holes several microns deep with aspect ratios beyond 50:1 is a particularly challenging process that requires exquisitely accurate and precise control. It is critical to carefully analyze multiple aspects of the etch process, such as hole profile, tilt, uniformity, and quality during development and production. X-ray critical dimension (XCD) metrology, which is also known as critical dimension small-angle x-ray scattering, is a powerful technique that can provide valuable insights on the arrangement, shape, and size of periodic arrays of HAR features. XCD is capable of fast, non-destructive measurements in the cell-area of production wafers, making XCD ideal for in-line metrology. Through several case studies, we will show that XCD can be used to accurately and precisely determine key properties of holes etched into hard mask, multilayer oxide/nitride film stacks and slit trenches. We show that the measurement of hole and slit tilt can be achieved without the aid of a structural model using a Fast Tilt methodology that provides sub-nanometer precision. Measurements were performed across several production wafers to determine the etch uniformity and quality. Particular attention was given at the edge of the wafers to account for large variations observed. In addition, we used a detailed physical model to characterize the HAR structures beyond linear tilt. This approach provides a more complete picture of the etch quality.
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