Advanced technology nodes require a thinner photoresist layer for patterning to prevent pattern collapse as feature sizes are tighter. Within this study, we delve into the impact of photoresist thickness thinning on metrology performance utilizing ASML's eP5 scanning electron microscope (SEM). A variety of eP5 SEM configurations and scanning methodologies were employed to assess SEM image quality and metrology precision. Additionally, the efficacy of line-space programmed defect (PD) detection was evaluated using distinct eP5 SEM settings. We note that achieving optimal metrology performance for distinct features might require to use of different SEM settings and scanning configurations. For instance, eP5 Quad-directional scan technique offers superior metrological results when compared to the unidirectional scan for the tip-to-tip (T2T) features. In the context of line-space PD inspection, lower e-beam landing energy is found to increase the sensitivity of bridge defect detection.
In this work, the measurement of local variables such as Line Edge Roughness (LER) and Line Width Roughness (LWR) in large field of view (FoV) Scanning Electron Microscopic (SEM) images is demonstrated. We show that larger FoV images include more of the lower frequency components in the roughness profile and hence these variables are measured more accurately. We also show that larger FoV images provide a better statistics which improves the precision of the measurement significantly. We also address the impact of image distortion on LER as the main challenge of large FoVs. The study is performed on large FoV 8µm×8µm images with line/space features, acquired by massive metrology capability of a high throughput eP5 SEM. We crop the images to smaller ones and compare the results measured for different FoVs, with and without distortion correction. We see that by the distortion correction, especially in low frequency, we can calculate the local variables accurately.
In this paper we show experimental verification of the feasibility of printing pitch 40x70nm hexagonal holes using EUV single patterning. We show that at a local CDU (LCDU) of 2.7nm and an exposure dose of 54 mJ/cm2 a defect rate smaller than 7x10-9 is observed. This result was enabled by optimization of the illumination source and improvements in the resist. Resist selection identified multiple candidates that show a promising LCDU performance and optimization of the processing conditions resulted in improved performance. Experimental validation of the defect performance was done using HMI eP5 on the baseline process. Assessment of the LCDU performance for EUV single expose at pitches beyond 40x70nm, showed promising results.
Introduction and problem statement
Given that EUV lithography allows printing smaller Critical Dimension (CD) features, it can result in non-normal distributed CD populations on ADI wafers [Civay SPIE AL 2014], leading to errors in predicted failure rates [Bristol SPIE AL 2017]. As a result, there is a need to quantify the actual behavior of the CD population extremes by means of massive metrology [Dillen EUVL 2018]. Not only allows this to study the CD distribution, we can in parallel also evaluate pattern quality and the failure mechanisms leading to defects. This massive metrology method provides an accurate failure rate based on CD, and enables new possibilities to define a failure rate based on different metrics in a single measurement.
Method
We analyze the CD uniformity of pillars in polar coordinates using a global waveform based thresholding strategy. In conjunction with this CD information, we also evaluated the print quality of each individual measured feature.
Fig 1. In line detected anomalies and failure definitions
As we gather this information during the measurement of CD, we can limit the additional measurement overhead to neglectable levels.
Application and outlook
We will show how we can leverage this to determine a defect based process window and relations of failure mechanisms through process conditions (see figure 2). When we take failures in a CH dataset into account, we illustrate the effect on the shape of a large dataset distribution in figure 3.
Fig 2. Defect identification for a through exposure dose experiment of pillars. For each condition >13k pillars where measured. The plot clearly shows an asymmetric behavior due to different failure mechanisms at low and high energy. The 2 vertical lines at relative energies 0.93 and 1.05 times nominal indicate the low defect process window.
Fig 3. A distribution of measured regular grid dense CH. The red line is the unfiltered CD data, the blue line is the shape of the distribution after filtering individual CH measurements that have a much lower contrast than expected.
Scanner induced pattern shifts between layers are a large contributor to DRAM Bitline to Active overlay. One of the main root causes for this Pattern Shift non-Uniformity are lens aberrations. Currently measuring the Bitline to Active overlay requires a decap CDSEM method1. In this paper, an in-resist pattern shift uniformity metrology method is proposed which quantifies the main DRAM Bitline to Active overlay without the necessity to decap. We have designed a high transmission reticle (≥ 60%) to measure the pattern shift non-uniformity between two dense gratings under the rotation angle of the Active layer in both cold and hot lens states. Each module on the reticle contains product-like features and a variety of metrology targets, i.e. alignment and overlay, such that the product-to-product and the productto- metrology pattern shift fingerprints can be measured. OPC is applied to enlarge the overlapping process windows of the metrology targets with respect to the product-like features.
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