KEYWORDS: Extreme ultraviolet lithography, Metrology, 3D metrology, Nondestructive evaluation, Line width roughness, Atomic force microscopy, Surface roughness, Photoresist materials, Line edge roughness, Algorithm development
EUV lithography enables continued scaling beyond 5nm nodes and allows the employment of single patterning methods with improved resolution. Thinner photo-resist layers with shrinking feature sizes consequently make stochastic errors worse during the lithography step and require a metrology solution with sub-nanometer resolution and information in the third dimension (depth and full profile shape). Atomic force microscopy (AFM), a topography imaging technique, can achieve the required precision to capture critical dimensions of photoresist patterns in 3 dimensions, but it is generally limited by the ability to fully resolve deep and narrow structures, can be destructive and suffer from low throughput. Here, we show validation of a novel fully automated in-line AFM system, QUADRA, that overcomes these challenges. Details relevant for use in HVM are reported on line and space EUV photoresist patterns after development (ADI).
Pitch scaling of interconnects is required for 3D system integration with the industry shifting to bumpless bonding technology. However, hybrid metal/dielectric bonding requires tight process control of planarity after chemical mechanical polishing (CMP) to avoid bonding voids. Due to its sub-angstrom resolution, atomic force microscopy (AFM) is typically used to assess the nano-topography but conventional systems suffer from increased noise floor at high scanning speeds making it unsuitable for high-volume manufacturing (HVM). Here, we validate a novel in-line high-throughput AFM system (QUADRA) by reporting the topographical parameters of 250 nm and 1 μm size copper nano-pads at high scanning speeds that reach tens of wafers per hour throughput.
High-NA EUV technology enables cost-effective patterning below the 5nm node. The integration is simpler but still requires multiple innovations. Thinner resists are needed for single-patterning enablement. The decrease in thickness poses a challenge for traditional metrology and inspection systems like OCD or CD-SEM, which lose sensitivity due to diminishing interaction volume. The reverse is true for Scanning Probe Microscopy, which excels in the low-height patterning regime. Here we discuss patterning metrology and introduce defect inspection / review applications for High-NA EUV patterning using a high-throughput SPM.
Improved resolution of the High-NA EUV technology comes with thinner photoresist and smaller aspect-ratio requirements. Trade-offs include more stringent process control needs for resist loss and line roughness. Traditional metrologies like OCD or CD-SEM lose sensitivity due to diminishing interaction volume. A metrology technique that thrives in this regime is Scanning Probe Microscopy: thinner resist allows for higher scanning speed, and smaller aspect ratio for higher measurement accuracy. Here we propose a High-Throughput SPM technique as key enabler for High-NA EUV process control. Detailed, high-density full wafer measurements of resist loss, CD and roughness are enabled by a high-throughput, 4-head SPM toolset, and compared for different resist thicknesses down to 10nm. Sampling schemes consistent with scanner throughput are considered.
Atomic Force Microscopy (AFM) topographic imaging has enabled semiconductor manufacturing research and development since early '90s. Unique strength over competing metrology techniques includes the potential for undistorted, local high resolution information. Comparatively slow throughput has traditionally limited high volume manufacturing (HVM) deployment. Here, we discuss the advantages of a multi-head AFM system with miniaturized high-speed SPMs working in parallel. In addition, we extend traditional AFM techniques to selective imaging and metrology of subsurface 3D structures and show a path to enabling Overlay metrology through opaque hard mask layers.
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