Emerging Technologies for Advanced 3D Package Characterization to Enable the More-Than-Moore Era
Authors: Hartfield Cheryl , Harris Will , Gu Allen , Terada Masako , Viswanathan Vignesh , Jiao Longan , Rodgers Thomas 
Published: November 2022

To continue Moore’s Law, semiconductor packaging is adopting new architectures, materials, and structures. Package dimensions are becoming thinner and smaller while going 3D to enable higher performance in smaller footprints. New package technologies such as chiplets, hybrid bonding, TSV silicon interposers and silicon interconnect bridges enable heterogenous integration of diverse functions, such as RF and logic, into a single package. The advanced electrical systems known as system-in-package (SiP) are comprised of many components and materials, each offering unique failure modes and challenges for diagnosis and analysis.
The pace of materials and device development today, combined with the central role of IC packaging to meet the demands of system performance through More-than-Moore innovations, drives an urgent need for improved package characterization of structures and defects to aid fast development of reliable 3D packages. Traditional non-destructive techniques like 2D X-ray and scanning acoustic microscopy are hitting limits for 3D package analysis due to resolution and throughput limits. Focused ion beam scanning electron microscopes (FIB-SEM) enabled decades of technology advances for front-end-of-line (FEOL) and back-end-of-line (BEOL) processes, but their usefulness for packaging analysis is limited by slow FIB milling rates relative to the millimeter volumes of material that must be removed.
As the line between packaging and silicon interconnects blurs, it becomes more difficult to localize and image defects and structures throughout the package life cycle, starting from material selection through development and on to high volume production and field failure diagnostics. Characterization and failure analysis instruments must work synergistically to provide fast results for rapid package development of products meeting the required electrical and mechanical specifications with high yield, high quality and high reliability.
X-ray Computed Tomography (CT) has become a key enabler to solve 3D packaging challenges, because it can non-destructively image the interior of objects in 3D. X-ray Microscopy (XRM) extends this capability through higher resolution and increased versatility. Although 3D XRM achieves submicron resolution on full-sized intact packages, the trade-off for this performance is throughput. Traditional 3D XRM approaches can take many hours at the extreme end of highest resolution for largest package sizes. Meanwhile, the requirement for artifact-free cross sections of fast-shrinking package structures drives the use of ion beam technologies, such as broad Ar ion beams and Ga+ or Xe+ focused ion beams. Advances in packaging technology are pushing standard ion beam approaches beyond their limits, due to the combined need for precise end-pointing and rapid site-specific removal of millimeter volumes of material. Microbumps in 3D packages are 8,000 times smaller than solder balls, and 124 times smaller than C4 bumps [1], while I/O pitches are approaching 1 µm [Figure 1]. Broad Ar+ ion beams can be applied to large areas but lack the end-pointing specificity required by today’s advanced fine-pitch high density interconnect. While Ga+ FIB (used for semiconductor analysis) and Xe+ PFIB (used for far-BEOL structure analysis) deliver excellent end-pointing on the nanometer scale, both are unable to deliver the required milling rates to enable rapid site-specific cross-sectional analysis of structures deeply buried within 2.5/3D and other SiP packages.
We present advanced microscopy innovations for 3D package analysis. 3D XRM data acquisition speeds can be increased by 4X and sometimes more than 10X when using artificial intelligence for reconstruction of 3D XRM data [2,3] [Figure 2]. In addition, the recent integration of a fs-laser onto a FIB-SEM enables site-specific material removal rates that are orders of magnitude faster than a FIB alone [4] [Figure 3]. Enabled by the high-accuracy end-pointing and fast milling achievable with a 100nA Ga+ beam, the new laser-integrated FIB-SEM, or LaserFIB, enables site-specific cross sectioning for SiP and complex package structures with high throughput. We show that when combining the 3D XRM and LaserFIB advances into a package analysis workflow, unprecedented capability emerges for rapid, high-resolution characterization of large structures and deeply buried features. This supports fast development of reliable next-generation package technology by providing the combination of speed, site targeting, and end-pointing accuracy required to address increasingly complex devices with higher throughput and analysis success rates.

References

ASE Group; accessed April 8, 2022 from https://ase.aseglobal.com/en/technology/advanced_25dic

Harris et al., Putting AI to Work: A Practical and Simple Application to Improve 3D X-ray FA; International Reliability Physics Symposium (IRPS); Dallas, TX (2022).

Gu et al., Accelerate Your 3D X-ray Failure Analysis by Deep Learning High Resolution Reconstruction. ISTFA (2021). https://doi.org/10.31399/asm.cp.istfa2021p0291

Tordoff et al., The LaserFIB: new application opportunities combining a high-performance FIB-SEM with femtosecond laser processing in an integrated second chamber. Applied Microscopy. 50(1), 24 (2020)

Figure 1