Pragmatic Micrometre to Millimetre Calibration Using Multiple Methods for Low-Coherence Interferometer in Embedded Metrology Applications

In-situ metrology utilised for surface topography, texture and form analysis along with quality control processes requires a high-level of reliability. Hence, a traceable method for calibrating the measurement system’s transfer function is required at regular intervals. This paper compares three methods of dimensional calibration for a spectral domain low coherence interferometer using a reference laser interferometer versus two types of single material measure. Additionally, the impact of dataset sparsity is shown along with the effect of using a singular calibration dataset for system performance when operating across different media.

In Situ Metrology for Pad Surface Monitoring in CMP Using a Common-Path Phase-Shifting Interferometry: A Feasibility Study

In the fabrication of semiconductors, chemical mechanical polishing (CMP) is an essential wafer-planarization process. For optimal CMP, it is crucial to monitor the texture of the polishing pad; this leads to homogenous planarization of wafers. Hence, we present a new interferometric approach for in situ evaluation of the CMP pad surface based on a common-path phase-shifting interferometry, with which a series of phase-modulated interference signals immune to external perturbation can be recorded. A nanoscopic surface topology can then be reconstructed to estimate surface roughness using the recorded interference images. The surface mapping performance of the proposed method was tested by retrieving a topology of a vibrating nanostructure in immersion, of which height profiles were consistent with the result from atomic force microscopy (AFM). The method was also validated by examining the surface of a used CMP pad in simulated conditions.

From Light to Displacement: A Design Framework for Optimising Spectral-Domain Low-Coherence Interferometric Sensors for In Situ Measurement

Growing requirements for in situ metrology during manufacturing have led to an increased interest in optical coherence tomography (OCT) configurations of low coherence interferometry (LCI) for industrial domains. This paper investigates the optimisation of spectral domain OCT hardware and signal processing for such implementations. A collation of the underlying theory of OCT configured LCI systems from disparate sources linking the journey of the light reflected from the object surface to the definition of the measurand is presented. This is portrayed in an applicable, comprehensible design framework through its application to profilometry measurements for optimising system performance.

Exclusive solution discharge in Li-O2 batteries

<b>Electrodepositing insulating and insoluble Li2O2 is the key process during discharge of aprotic Li-O2 batteries and determines rate, capacity, and reversibility. Current understanding states that the partition between surface adsorbed and solvated LiO2 governs whether Li2O2 grows as surface film or particles, leading to low or high capacities, respectively. Here we show that Li2O2 forms exclusively as particles via solution mediated LiO2 disproportionation. We describe a unified O2 reduction mechanism that conclusively explains capacity limitations across the whole range of electrolytes. Low-donor-number electrolytes are shown to accelerate disproportionation rather than slowing it down. Deciding for particle morphology and achievable capacities are species mobilities, true areal rate and the rate at which associated LiO2 forms in solution. Provided that species mobilities and surface are high, this allows for high capacities even with low-donor-number electrolytes, previously considered prototypical for low capacity via surface growth. The tools for these insights include microscopy, hydrodynamic voltammetry, a numerical reaction model, and in situ small/wide angle X-ray scattering (SAXS/WAXS). Combined with sophisticated data analysis, SAXS allows retrieving rich quantitative information from complex multi-phase systems. On a wider perspective, this SAXS method is a powerful in situ metrology with atomic to sub-micron resolution to study mechanisms in complex electrochemical systems and beyond.<br></b>