The stochastic effect in contact single patterning is one of the primary challenges in extending into sub-40nm pitch with 0.33NA EUV. EUV stochastic defects induced by EUV photon shot noise are known to strongly correlate to image contrast. Mitigation of Mask3D induced contrast fading is one of the key solutions to enable further shrink, while maintaining sufficient defect-free process latitude. Wavefront and pupil co-optimization is designed to compensate the Mask 3D phase error that leads to contrast fading. For application in HVM, the newly developed Pupil/Mask/Wavefront co-optimization gives the best imaging performance while maintaining the illumination efficiency and decreasing the rms wavefront for the final optimal wavefront to ensure there is no negative impact on the rest of the patterns that are not included in the optimization. In this paper, we investigate how to apply Pupil/Mask/Wavefront co-optimization to improve the image contrast of a sub-40nm pitch contact hole array, including in-resist verification. We will first explain the fundamentals of Mask 3D fading mitigation via phase injection for a 1D feature and how to extend this concept to 2D features. We will compare the effectiveness of new Pupil/Mask/Wavefront co-optimization versus Zernike Z5 or Z6 only phase injection method. Finally, we will show the potential benefit in combination with using a low-n phase shifting mask for which the optimum image contrast is achieved with the co-optimized wavefront, pupil and mask.
Dose and focus are both primary contributors to a change in feature size (critical dimension – CD). Within the context of this abstract, dose refers to all ‘apparent dose’ effects within the scanner and track combination. These dose-like effects can be an actual dose from the scanner and/or an apparent dose coming from process effects (i.e. resist/develop nonuniformity) that impact CD’s in a manner similar to scanner dose. Semiconductor manufacturers monitor CD over time for process control and can institute dose and/or focus changes in order to maintain CD performance and to optimize CD uniformity. This CD monitoring and control can be time consuming and a shift in CD does not directly indicate which has changed, dose or focus. Until now there is not a good alternate way to detect and monitor dose-related changes on product wafers. This paper will introduce a dual tone target concept for dose metrology to distinguish CD changes from dose and focus and demonstrate how the dual tone target concept is used to infer the apparent dose on a diffraction-based optical metrology system, like YieldStar. The concept is verified via experimental results showing accurate dose measurements with low focus cross talk. Additionally, correlation with CD-SEM measurements will be demonstrated which shows that apparent dose derived from this diffraction-based methodology matches well to the CD-SEM.
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