Intra-field Critical Dimension Uniformity Research Articles

EUV vote-taking lithography for mitigation of printing mask defects, CDU improvement, and stochastic failure reduction

Vote-taking lithography is a method for mitigating mask defects, which has been applied in the 1980s to enhance yield. Vote-taking sums up N different mask images with identical content, each at 1 / N dose, to mitigate the defects on each individual mask. The fundamental assumption is that the mask defects do not correlate in position from mask to mask, and so each individual defect will be blended with good images from the other N − 1 masks. Vote-taking has recently been reconsidered for extreme ultraviolet (EUV) lithography, where it might provide a temporary solution for situations in which the defectivity conditions are not yet meeting expectations. 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. We found additional benefits of blending different mask images, distinct from mask defect reduction. Experimental results will be shown that demonstrate improved critical dimension uniformity (CDU), both local CDU and intrafield CDU, reduced overlay errors, and smaller stochastic defect levels. 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. Although 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.

Mask characterization for critical dimension uniformity budget breakdown in advanced extreme ultraviolet lithography

As the International Technology Roadmap for Semiconductors critical dimension uniformity (CDU) specification shrinks, semiconductor companies need to maintain a high yield of good wafers per day and high performance (and hence market value) of finished products. This cannot be achieved without continuous analysis and improvement of on-product CDU as one of the main drivers for process control and optimization with better understanding of main contributors from the litho cluster: mask, process, metrology and scanner. We will demonstrate a study of mask CDU characterization and its impact on CDU Budget Breakdown (CDU BB) performed for advanced extreme ultraviolet (EUV) lithography with 1D (dense lines) and 2D (dense contacts) feature cases. We will show that this CDU contributor is one of the main differentiators between well-known ArFi and new EUV CDU budgeting principles. We found that reticle contribution to intrafield CDU should be characterized in a specific way: mask absorber thickness fingerprints play a role comparable with reticle CDU in the total reticle part of the CDU budget. Wafer CD fingerprints, introduced by this contributor, may or may not compensate variations of mask CDs and hence influence on total mask impact on intrafield CDU at the wafer level. This will be shown on 1D and 2D feature examples. Mask stack reflectivity variations should also be taken into account: these fingerprints have visible impact on intrafield CDs at the wafer level and should be considered as another contributor to the reticle part of EUV CDU budget. We also observed mask error enhancement factor (MEEF) through field fingerprints in the studied EUV cases. Variations of MEEF may play a role towards the total intrafield CDU and may need to be taken into account for EUV lithography. We characterized MEEF-through-field for the reviewed features, with results herein, but further analysis of this phenomenon is required. This comprehensive approach to quantifying the mask part of the overall EUV CDU contribution helps deliver an accurate and integral CDU BB per product/process and litho tool. The better understanding of the entire CDU budget for advanced EUVL nodes achieved by Samsung and ASML helps extend the limits of Moore’s Law and to deliver successful implementation of smaller, faster and smarter chips in semiconductor industry.

Toward 22 nm: fast and effective intrafield monitoring and optimization of process windows and critical dimension uniformity

ITRS lithography's stringent specifications for the 22 nm node are a major challenge for the semiconductor industry. With the EUV point insertion at 16 nm node, ArF lithography is expected to reach its fundamental limits. The prevailing view of holistic lithography methods, together with double patterning techniques, has targeted bringing lithography performance toward the 22 nm node (i.e., closer to the immersion scanner resolution limit) to an acceptable level. At this resolution limit, a mask is the primary contributor of systematic errors within the wafer intrafield domain. As the ITRS critical dimension uniformity (CDU) specification shrinks, it would be crucial to monitor the mask static and dynamic critical dimension (CD) changes in the fab, and use the data to control the intrafield CDU performance in a most efficient way. Furthermore, optimization and monitoring of process windows (PW) becomes more critical due to the presence of mask three-dimensional effects. This paper will present double patterning inter- and intrafield data, for CDU and PW monitoring and optimization, measured by Applied Materials' mask inspection and CD-SEM tools. Special emphasis was given to speed and effectiveness of the inspection for a production environment.