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Particulate and molecular contamination control in EUV-induced H2-plasma in EUV lithographic scanner
This paper presents several new diffuser concepts, both reflective as well as transmissive, with their respective key performance metrics for both NA=0.33 and NA=0.55 EUV projection optics. These concepts can be used for measuring wavefront quality from dedicated fiducial plates, or for measuring directly from the imaging reticle. The latter would enable a combination of reticle alignment with lens aberration control without throughput penalty.
It will be shown that with these diffuser concepts, we have a solution for in-situ aberration control for 5nm nodes and below.
This paper provides a thorough experimental assessment of the implementation of vote-taking, and discusses its pro’s and con’s. Based on N=4 vote-taking, we demonstrate the capability to mitigate different types of mask defects. Additionally, we found that blending different mask images brings clear benefit to the imaging, and provide experimental confirmation of improved local CDU and intra-field CDU, reduction of stochastic failures, improved overlay, ... Finally, we perform dedicated throughput calculations based on the qualification performance of ASML’s NXE:3400B scanner.
This work must be seen in the light of an open-minded search for options to optimally enable and implement EUV lithography. While defect-free masks and EUV pellicles are without argument essential for most of the applications, we investigate whether some applications could benefit from vote-taking.
Advances in source power have enabled a further increase of tool productivity requiring an associated increase of stage scan speeds. To maximize the number of yielding die per day a stringent Overlay, Focus, and Critical Dimension (CD) control is required. Tight CD control at improved resolution is obtained through a number of innovations: the NXE:3400B features lower aberration levels and a revolutionary new illumination system, offering improved pupil-fill ratio and larger sigma range. Overlay and Focus are further improved by implementation of a new wafer clamp and improved scanner controls.
The NXE:3400B also offers full support for reticle pellicles.
A novel optical technique uses a pulsed double cavity laser at 532 nm with beam-shaping optics that is fired at a synchronized time delay after the EUV burst. The light is converted to a thin light sheet that illuminates possible debris fragments in the direct region around the plasma.
Mie scattering theory is applied to convert the intensity of the incoming individual particles to an estimated diameter estimation and the two frames are correlated with advanced particle tracking algorithms to capture the velocity and direction of each individual particle. Because light intensity is used for particle sizing, small individual particles can be detected. The technique provides particle count, diameter, direction and velocity information.
This technique has successfully been applied on operating NXE test sources. It has proven to directly identify plasma conditions with significant debris reduction. Furthermore, it has potential to correlate the plasma settings to lifetime estimations and thus can be used for both source optimization and design.
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