Subsurface optical microscopy of semiconductor integrated circuits

Thesis (Ph.D.)--Boston UniversityThe semiconductor industry continues to scale integrated circuits (ICs) in accordance with Moore's Law, and is currently developing the processing infrastructure at the 14nm technology node and smaller. In the wake of such rapid progress, a number of challenges have arisen for the optical failure analysis methods to meet the requirements of the advancing process technology. Most notably, complex circuits with shrinking critical dimensions will demand higher resolution signal localization currently beyond the capability of the existing optical techniques. This dissertation aims to develop novel optical systems to address the challenges of non-destructive circuit diagnostics at the 14nm technology node and beyond. Backside imaging through the silicon substrate has become an industry standard due to the dense multi-level metal wiring and the packaging requirements. The solid immersion lens is a plano-convex lens placed on the planar silicon substrate to enhance the subsurface focusing and collection of light in back-side imaging of ICs. The silicon and gallium-arsenide aplanatic solid immersion lenses (aSILs) were investigated in detail for the subsurface laser-scanning, voltage modulation, photon emission and dark-field IC imaging applications. Wave-front sensing and shaping techniques were developed to evaluate and mitigate optical aberrations originating from practical issues. Furthermore, the method of pupil function tailoring was explored for sub-diffraction spatial resolution. Super-resolving annular phase and amplitude pupil masks were developed and experimentally implemented. A record-breaking light confinement of 0.02 λ2 0(λ 0 refers to the free-space wavelength) was demonstrated using the vortex beams. The beam invasiveness is a critical issue in the optical circuit probing as the localized heat due to the absorption of the focused beams may unwittingly interfere with the circuit operation in the course of a measurement. A dual-phase interferometry assisted circuit probing was developed to enhance the signal extraction sensitivity by as much as an order of magnitude. Thus, the power requirement of the probe beam is significantly reduced to avert the consequences of the beam invasiveness. The optical systems and methods developed in this dissertation were successfully demonstrated using a number of modern ICs including devices of 14nm, 22nm, 28nm and 32nm technology nodes

Polarization enhanced interferometric imaging

https://patentimages.storage.googleapis.com/1e/21/aa/dee6cbdf9a3542/US11428626.pdfPublished versio

Fibre Bragg Grating Based Strain Sensors: Review of Technology and Applications

Fibre Bragg grating (FBG) strain sensors are not only a very well-established research field, but they are also acquiring a bigger market share due to their sensitivity and low costs. In this paper we review FBG strain sensors with high focus on the underlying physical principles, the interrogation, and the read-out techniques. Particular emphasis is given to recent advances in highly-performing, single head FBG, a category FBG strain sensors belong to. Different sensing schemes are described, including FBG strain sensors based on mode splitting. Their operation principle and performance are reported and compared with the conventional architectures. In conclusion, some advanced applications and key sectors the global fibre-optic strain sensors market are envisaged, as well as the main market players acting in this field

Fast compressive lens-free tomography for 3D biological cell culture imaging

We present a compressive lens-free technique that performs tomographic imaging across a cubic millimeter-scale volume from highly sparse data. Compared with existing lens-free 3D microscopy systems, our method requires an order of magnitude fewer multi-angle illuminations for tomographic reconstruction, leading to a compact, cost-effective and scanningfree setup with a reduced data acquisition time to enable high-throughput 3D imaging of dynamic biological processes. We apply a fast proximal gradient algorithm with composite regularization to address the ill-posed tomographic inverse problem. Using simulated data, we show that the proposed method can achieve a reconstruction speed 10 faster than the state-of-the-art inverse problem approach in 3D lens-free microscopy. We experimentally validate the effectiveness of our method by imaging a resolution test chart and polystyrene beads, demonstrating its capability to resolve micron-size features in both lateral and axial directions. Furthermore, tomographic reconstruction results of neuronspheres and intestinal organoids reveal the potential of this 3D imaging technique for high-resolution and high-throughput biological applications.status: Published onlin

Low-temperature Synthesis of Eu2+ and Dy3+ Doped Strontium Dialuminate (SrAl4O7: Eu2+, Dy3+) Scintillator Materials

Although single crystals are widely used as scintillator materials, the use of polycrystalline powder ones is being proposed as a low-cost alternative. In this report, the synthesis of single phase, highly crystalline divalent europium and trivalent dysprosium doped strontium dialuminate (SrAl4O7: Eu2+, Dy3+) was investigated by modifying the Pechini process, which can be conducted at much lower temperatures compared to the conventional solid state diffusion process. These modifications were necessary due to strontium being one of the host elements in the crystal lattice. Because Sr has a high oxygen affinity, the conventional Pechini process promoted the formation of SrCO3, which hindered the material’s ability to form single phase and highly crystalline SrAl4O7. These are the key requirements for the material, when doped with Eu2+, Dy3+, to serve as a model system for studying the luminescence mechanisms. TG/DTA, XRD, and STEM characterizations were used to explore the region of phase stability of doped dialuminate in the SrO-Al2O3 system, between 700-1300°C. The reduction atmosphere and time were carefully controlled in order to achieve fully reduced samples. Oxygen content analysis performed on the samples revealed interesting reduction behavior in the strontium dialuminates not previously reported in the literature. When unreduced, crystalline, doped strontium dialuminate contained 60% oxygen, while after reduction for 4 hours, this amount decreased to and remained at 35%, independent of the reduction time. However, the glow intensity continued to increase in proportion to the change in the reduction time. The luminescence behavior of these compounds would also be presented in order to investigate the evolving electronic structure in the doped dialuminate

Development of an integrated breath analysis technology for on-chip aerosol capture and molecular analysis

As proven early on in the pandemic, SARS-CoV-2 is mainly transmitted by aerosols. This urged us to develop a silicon impactor that collects the virus particles directly from breath. Performing PCR on these breath samples proved equally sensitive as nasopharyngeal swabs during the first week of an infection [Stakenborg et al., 2022], yet it remained a mostly manual process and PCR turn-around-time was still long. To overcome these drawbacks, we developed a fast and sensitive, fully integrated point-of-need breath test, comprising a novel breath sampler device and PCR instrument. The breath sampler combines virus collection and in-situ RNA amplification. The PCR instrument performs very fast amplification of the released viral RNA. Sample-to-result time was reduced to <20 min with an equal performance as the original manual procedure