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Figure 3: Overlay solution for AICS panels.
To improve process overlay, the substrates after the laser-drilled vias have costs. A comprehensive metrology and
lithography system, or stepper, must been created and before the stepper is lithography solution is required. This
analyze and compensate for CCL substrate involved. These are known as feedforward solution should be used in conjunction with
distortion errors. While this sounds simple corrections. Feedforward metrology advanced software that can automatically
in principle, the CCL distortion components requires a leap of faith, however, because it adjust models to compensate for the
are complex and extend beyond the depends on a laser-drilling tool and stepper dynamic substrate distortion components.
traditional six-parameter model supported working in concert to produce an accurate This approach could extend the roadmap
by most lithography steppers. This nonlinear and reliable dataset to create the stepper of CCL substrate manufacturing beyond
distortion requires additional higher order alignment solution (Figure 3). its current design limits, thereby reducing
lithography system corrections, thereby In principle, the ideal solution to solve costs and improving yields.
increasing the complexity of the model. the overlay problem would be to use a
The stepper’s ability to correct for the feedforward approach where X and Y Summary
substrate distortion is only part of the coordinate data from the laser-drilled With the AICS market forecast to reach
solution. We also need accurate metrology via holes are employed to generate an nearly $25 billion in 2027, according
data to generate optimum alignment alignment solution. The overlay metrology to Yole Group, there is little doubt that
solutions to compensate for distortion data will confirm if the feedforward AICS will be one of the chief drivers of
errors. Typically, this data is only available correction is accurate and will highlight innovation. However, AICS brings with
after the lithography process is finished the residual errors. If the residual errors it significant challenges, like total overlay
and overlay of the vias to the RDL landing are significant, the feedforward model shifts, yield loss and CCL substrate
pad is measured. The data is then analyzed likely needs to be adjusted. Ironically, distortion. And with the number of RDLs
and sent back to the stepper to correct post-exposure, final overlay metrology soaring to 24 with AICS, any unaddressed
panel distortion for future incoming panels could be used to optimize the feedforward errors in any single layer can ruin a
(a.k.a. feedback corrections). However, the model. With machine learning and substrate that otherwise would have been
feedback corrections are only relevant if continued iterations, the model could be used in a PLP. However, by applying the
the panel distortion remains constant for continuously adjusted to achieve good techniques in this article, manufacturing
incoming future panels. Sampling plans overlay with low residuals. teams can improve yield and throughput
and periodic metrology can help generate a The manufacturing of large packages and reduce costs in this emerging PLP
run-to-run solution. These steps, together requiring the heterogeneous integration segment of the semiconductor industry,
with artificial intelligence (AI) and of chiplets, high-bandwidth memory guiding manufacturers away from
machine-learning software, can correct (HBM) and GPU/CPU is only achievable turbulent waters and steering their ships
the dynamic distortion errors exhibited by using AICS processing. To deliver this toward smoother seas.
CCL substrates over time. capability, substrate distortion needs to be
An alternative approach could be characterized and compensation provided
to gather metrology data from the in order to maintain high yields and reduce

Biography
Keith Best is the Director of Product Marketing, Lithography, at Onto Innovation, Wilmington, MA. For
more than 35 years he has held a range of semiconductor processing and applications positions for both device
manufacturing and capital equipment companies. He also has numerous publications and holds 22 US patents
in the areas of photolithography and process integration. Email keith.Best@ontoinnovation.com

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