[NanoIC] Metrology and Defectivity Study in 3D Patterning Processes

The continued scaling of semiconductor technology is leading to increasingly complex three-dimensional (3D) structures with smaller dimensions and higher aspect ratios (HAR). These structures often contain multiple materials, buried features, and mechanically fragile patterns, making precise and uniform fabrication increasingly challenging. Small variations during patterning processes can result in non-uniform structural dimensions, incomplete or excessive material removal, surface damage, residues, or structural deformation and collapse. For example, post-etch residues or heterogenous surface chemistry on HAR structures can promote air trapping and potentially lead to non-uniform wet etching  [1,2]. Likewise, sub-nanometer variations in structural dimensions or profiles can significantly alter the mechanical stability of nanostructures, increasing their susceptibility to capillary force induced deformation and pattern collapse during drying  [3,4]. Although such defects may originate locally or during a specific process step, their effects can propagate through subsequent fabrication steps and ultimately impact device performance, variability and reliability. Understanding how these defects originate and evolve, and how they relate to process conditions and material properties, is therefore essential for the development of robust patterning processes.

Charactering such defects in complex 3D structures remains a critical challenge for conventional metrology. Many established techniques primarily probe patterned substrates from the top surface and therefore provide limited information on sidewalls, buried interfaces, or defects located deep within HAR structures. Cross-sectional SEM or TEM can reveal these features with high spatial resolution, but they are often destructive and provide limited statistical information due to their low throughput. Furthermore, there is a lack of in-situ metrology capable of capturing dynamic material and surface changes under actual process conditions, particularly during liquid-phase processes such as wet etching and cleaning. This PhD project aims to address these challenges by combining dedicated advanced patterning test structures fabricated using imec’s state-of-the-art nanofabrication facilities with complementary optical and electron-beam based characterization techniques  [2,3,5–8]. The project will explore and develop advanced metrology approaches to probe structural, material and surface changes in patterned HAR structures and establish quantitative and statistical correlations with defect formation.

Candidates should hold a master’s degree in Applied or Experimental Physics, Physical or Materials Chemistry, Semiconductor Engineering, or a closely related discipline. A strong interest in experimental metrology and quantitative data interpretation is essential. Experience with optical modelling, image processing, statistical data analysis, or semiconductor characterization techniques, such as ellipsometry/scatterometry, XRR/XRD, XPS, SEM, ATR-FTIR, or in-situ flow cell characterization is a plus.

Contact: XiuMei Xu (xiumei@imec.be), Harold Philipsen (Harold.Philipsen@imec.be)

[1]      X. Xu et al., Capturing Wetting States in Nanopatterned Silicon, ACS Nano 8, 885 (2014).

[2]      N. Vrancken et al., Superhydrophobic Breakdown of Nanostructured Surfaces Characterized in Situ Using ATR-FTIR, Langmuir 33, 3601 (2017).

[3]      N. Vrancken et al., Nanoscale Elastocapillary Effect Induced by Thin-Liquid-Film Instability, J. Phys. Chem. Lett. 11, 2751 (2020).

[4]      T. Ghosh et al., Preventing the Capillary-Induced Collapse of Vertical Nanostructures, ACS Appl. Mater. \& Interfaces 14, 5537 (2022).

[5]      N. Vrancken et al., In-situ ATR-FTIR for Dynamic Analysis of Superhydrophobic Breakdown on Nanostructured Silicon Surfaces, Sci. Rep. 8, (2018).

[6]      U. Anand et al., Dynamics of Thin Precursor Film in Wetting of Nanopatterned Surfaces, Proc. Natl. Acad. Sci. U. S. A. 118, 6 (2021).

[7]      Z. Aabdin et al., Transient Clustering of Reaction Intermediates During Wet Etching of Silicon Nanostructures, Nano Lett. 17, 2953 (2017).

[8]      X. Xu and G. F. Lorusso, A Method for Evaluating the Bending Stiffness of High Aspect Ratio Nanosized Structures. European Patent EP 4 509 825 and U.S. Patent US 2025/0052703, 2025.