AVS 71 Session TF2-MoM: Characterization of Thin Films

Understanding local crystallography – including local lattice parameters, interatomic spacings, and polarity – is key to understanding ferroelectricity, especially in systems with small domains, significant disorder, or interfacial features. Scanning nanobeam electron diffraction (NBED) combined with new high-speed, pixelated scanning transmission electron microscopy (STEM) detectors make it possible to measure a diffraction pattern (kx, ky) at every scan position (x, y). This opens doors to investigate crystalline properties such as lattice parameters, local fields, polarization directions, and charge densities with relatively low beam dose over large fields of view. However, extracting these signals of interest from confounding signals such as thickness or crystallographic mistilt effects remains challenging. Here, we combine a cepstral approach, which is similar to a 2D pair-correlation function, with precession electron diffraction (PED) to measure local polar displacements in non-centrosymmetric materials while suppressing artifacts from dynamical or mistilt effects. We first apply these techniques to a reference sample of GaN and demonstrate that the addition of PED reduces the standard deviation of the lattice parameter measurement 0.56 pm to 0.32 pm. We also measure the length of the vector associated with the non-centrosymmetric nature of the unit cell, and see that its standard deviation is reduced from 3.5 pm to 1.9 pm. Computational work shows that adding precession also increases the robustness of these measurements to specimen mistilt. We then apply these techniques to study polar domains in a sample of PMN-PT, and observe domains on the 100 nm length scale.

Extreme ultraviolet (EUV) and beyond extreme ultraviolet (BEUV) lithography can achieve sub-10 nm features in semiconductor manufacturing. These nanoscale patterns require photoresists to be highly sensitive to EUV and BEUV conditions. One of the photoresist candidates are polymethyl methacrylate (PMMA) based hybrid photoresists with vapor phase infiltrated (VPI) inorganic materials.

The sensitivity of the photoresists depends on photo absorption efficiency, secondary electron generation, and material degradation. Currently, sensitivity studies mainly focus on characterizing developed films, an approach that cannot decouple photoresist sensitivity and developer sensitivity. To isolate the photoresist sensitivity, a method to study these photoresists' in situ exposure behavior before development is needed.

This report presents a novel approach to studying photoresist sensitivity through in situ real-time low-energy electron/photoemission electron microscopy (LEEM/PEEM) and micro-spot X-ray photoelectron spectroscopy (μXPS). In particular, we model the time-dependent chemical change and the charging behavior of the photoresists under X-ray exposures at 92 eV and 400 eV. We show the approach is reliable in determining the PMMA and its VPI hybrids' sensitivity to EUV and BEUV conditions. This approach will allow the study of a broader range of EUV and BEUV photoresist candidates and assist in next-generation photoresist and developer selection.

Research is supported by the U.S. Department of Energy Office of Science Accelerate Initiative Award 2023-BNL-NC033-Fund and was carried out at the Center for Functional Nanomaterials and the National Synchrotron Light Source II at Brookhaven National Laboratory under Contract No. DE-SC0012704.

Thin films are essential in modern technology, providing unique properties for electronic, sensor, and optical applications. As more complex alloys and compounds are integrated onto devices, the need to effectively characterize material composition becomes increasingly important. To surmount this hurdle, many different methods are utilized throughout literature with XRF, XPS, and EDX being prime among the reported methods; however, it is common for there to be little to no discussion on the analysis, nuances, and accuracy of the technique used. These issues are further exacerbated by the common availability of black box analysis associated with each of these techniques leading to reports and conclusions based on imprecise analysis.

In this presentation we use BaTiO3 as a case study material to compare each of the common compositional methods. We report on the determination of the Ba/Ti atomic ratio in four thin films deposited by sputter deposition under conditions to produce a range of stoichiometries. We directly compare analysis produced from X-ray Fluorescence (XRF), Rutherford Backscatter Spectroscopy (RBS), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), X-ray Photoelectron Spectroscopy (XPS), and Wavelength Dispersive Spectroscopy (WDS). Discussion is focused on accuracy of each technique and nuances related to each method and the analysis.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC (NTESS), a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration (DOE/NNSA) under contract DE-NA0003525.

SAND2025-04533A

Electronic packaging technology is evolving towards advanced substrates, including glass, to overcome limitations posed by traditional organic substrates. Glass packaging offers low dielectric loss, high modulus, low and tunable coefficient of thermal expansion (CTE), enhanced thermal stability, high I/O density, and reduced warpage. However, fully adopting glass packaging technology still faces several hurdles, including metal adhesion, stress management, and a full understanding of long-term reliability. The CTE mismatch between glass and copper (5 to 15 ppm/°C) leads to reliability issues such as glass and through-glass via (TGV) cracking, copper via protrusion, and delamination. We aim to address the glass and TGV cracking by introducing an organic or inorganic liner inside the TGV to act as a stress buffer, lowering the propensity for TGV electrode failure. In this study, we will describe TGV substrates coated with different liners – Parylene C, SiO₂N, SiO₃N, AZO (Aluminium-Zinc oxide), and Parylene C+AZO, obtained through different methods of deposition. The foremost step is to characterize if the liner is conformally coating the 100 µm diameter via. Conformal coating is essential to mechanical performance and even electroplating through the entire depth of the TGVs. A non-uniform liner coating will lead to an uneven Ti-Cu seed layer prior to electroplating of copper. Since the liner can be 0.1 to 5 µm thick, cross-sectioning is inadequate for post-plating liner inspection. Non-destructive methods for evaluating these coatings would also be of value to research and development, as well as in-line process monitoring. We have evaluated the effectiveness of several methods. In this work, two advanced techniques—two-photon imaging and micro-computed tomography (microCT)—are used to assess liner uniformity and measure thickness. Two-photon imaging is particularly effective for fluorescent materials like Parylene C and SiO2N, enabling visualization and thickness measurement within TGVs. The thickness of Parylene C is measured to be 5.6 µm (expanding to 8.7 µm near the surface), and Parylene C+AZO is measured to be 1.87 µm (expanding to 2.8 µm near the surface). Although AZO and SiO₂N are fluorescent, the nanoscale thickness (< 100 nm) is challenging to measure due to the resolution of the tools. The paper will propose additional metrology tools and show preliminary attempts to measure such nanoscale thicknesses. We will also show preliminary results on plating the liner-coated TGVs to assess their performance in mitigating crack formation upon thermal cycling.

Surface passivation of n-type InP was evaluated by X-ray Photoelectron Spectroscopy (XPS) depth-profile analysis after depositing an Al₂O₃ layer [1] with and without plasma treatments (oxidation (O2), nitriding (N2), oxidation followed by nitriding (O2N2), and nitriding followed by oxidation (N2O2)). To compare samples, we use the atomic fractions of Al2p, In3d, P2p, O1s, N1s, and C1s and two metrics [2]: top-film O/Al ratio at the first depth, with values near 1.5 indicating stoichiometric Al₂O₃; (ii) interface depth, the etch time where the sum of In+P≥20%.

The data show that O2 yields a stoichiometric surface (O/Al = 1.37) and the deepest interface (75s), consistent with a thicker interfacial oxide. N2 presents a very low O/Al (0.12) with detectable N and no interface onset within 120s, indicating a dense nitride/oxynitride barrier. N2O2 is intermediate (O/Al=1.42; interface 50s) with no residual N, suggesting oxidation of the nitride. The control sample shows oxidation (O/Al=0.51; interface 45s), while O2+sputtering produces the lowest O/Al (0.14) and the shallowest interface (35s), indicative of a less oxidized/less dense film.

Electrical C-V corroborates the chemical trends: the O2 sample exhibits a median flat-band voltage Vfb=0.00V (-0.30V for the control) and a donor density of the same order (2×10¹⁹ vs 1×10¹⁹ cm⁻³), indicating a flatter band alignment without doping degradation. Altogether, O2 delivers the most stoichiometric Al₂O₃, a thicker/interfacial oxide and superior C-V metrics, pointing to improved passivation of InP compared with ALD on untreated surfaces; N2 forms a robust nitride that retards sputter breakthrough; and ALD delivers denser, more stoichiometric Al₂O₃ than sputtering.

References

[1] X. Liu et all, “Interface optimization and performance enhancement of InP MOS capacitors with Sm₂O₃/Al₂O₃ gate stacks,” Semicond. Sci. Technol., vol. 36, n. 10, p. 105013, 2021.

[2] A. G. Shard, “A step-by-step guide to X-ray photoelectron spectroscopy (XPS),” J. Appl. Phys., vol. 131, no. 6, p. 061101, 2022.

Acknowledgments