Geometric analysis algorithm based on a neural network with localized simulation data for nano-grating structure using Mueller matrix spectroscopic ellipsometry.

Mueller matrix spectroscopic ellipsometry (MMSE) is a nondestructive tool for nanostructure analysis, and recently the enhanced computational power, combining neural networks and simulation data, enhance its analysis ability on more complex geometries. This study introduces a deep learning method to realize fast and accurate analysis; predicting nanostructure parameters by pairing Mueller matrices with relatively limited library data and then applying neural network algorithm. Thus, it was realized to predict the width and height of 1D grating structure with an accuracy of MAE below 0.1 nm through the proposed two-step prediction algorithm. Finally, experimental validation on SiO2 grating of 38 nm width and 100 nm height showed a good agreement in the dimensions with reasonable range compared to those measured by scanning electron microscopy.

Measurement uncertainty evaluation procedures and applications for various types of multichannel rotating-element spectroscopic ellipsometers.

A universal measurement uncertainty evaluation procedure is required for different types of multichannel rotating-element spectroscopic ellipsometers (RE-SEs) used in modern semiconductor industry. Herein, an improved uncertainty evaluation procedure, based on the universal measurement model functions and implicit function theorem, is introduced for unknown optical parameters of a sample. In addition, we develop a measurement standard instrument that can solve the error problems related to the basic principles of the multichannel RE-SEs used in the industrial field and present an example of applying the proposed uncertainty evaluation method to this standard instrument. Accordingly, the measurement performance for several types of real-time RE-SEs can be quantitatively compared. It can also be used for standardization, instrumentation, and measurement optimization.

Normal-incidence type solution immersed silicon (SIS) biosensor for ultra-sensitive, label-free detection of cardiac troponin I.

Early diagnosis of acute myocardial infarction (AMI) significantly reduce the mortality rate and can be achieved via high-sensitive detection of AMI specific cardiac troponin I (cTnI) biomarker. Here, we present normal-incident type solution-immersed silicon (NI-SIS) ellipsometric biosensor, designed for ultra-high sensitive, high-throughput, label-free detection of the target protein. The NI-SIS sensors are equipped with a specially designed prism that maintains the angle of incidence close to the Brewster angle during operation, which significantly reduces SIS noise signals induced by the refractive index fluctuations of the surrounding medium, improves the signal-to-noise ratio, in-results lowers the detection limit. We applied NI-SIS biosensor for ultra-sensitive detection of cTnI biomarkers in human serum. The optimized sensor chip fabrication and detection operation procedures are proposed. The wide linear concentration ranges of fg/mL to ng/mL is achieved with the detection limit of 22.0 fg/mL of cTnI. The analytical correlation was assessed by linear regression analysis with the results of the Pathfast reference system. These impressive biosensing capabilities of NI-SIS technology have huge potentials for accurate detection of target species in different application areas, such as diagnosis, drug discovery, and food contaminations.

Label-free detection of hepatitis B virus using solution immersed silicon sensors.

Highly sensitive solution immersed silicon (SIS) biosensors were developed for detection of hepatitis B virus (HBV) infection in the early stage. The ultrasensitivity for overlayer thickness at the nonreflecting condition for the p-polarized wave is the basis of SIS sensing technology. The change in thickness due to biomolecular interactions and change in refractive index of the surrounding buffer medium were assessed simultaneously using two separate ellipsometric parameters (Ψ and Δ), respectively, from a single sensing spot. A direct antigen-antibody affinity assay was used to detect and quantify hepatitis B surface antigen (HBsAg), which is the early stage biomarker for HBV infection. The detection limit of 10 pg/ml was achieved for HBsAg in the human blood serum, which is comparable with the results of enzyme-linked immunosorbent assay and other hybrid assays. The SIS sensor's response time was less than 10 min. The SIS sensors exhibit excellent stability and high signal-to-noise ratio, and are cost-effective, which makes them a suitable candidate for point-of-care applications.

Ultrasensitive, label-free detection of cardiac biomarkers with optical SIS sensor.

Acute myocardial infarction (MI) is the leading cause of high mortality and morbidity rate worldwide, early and accurate diagnosis can increase the chances of survival. In this work, we report a simple, ultrasensitive, label-free, and high-throughput solution immersed silicon (SIS) immunosensor based on non-reflection condition (NRC) for p-polarized wave for early diagnosis of MI. SIS sensor chips are just a thin dielectric polymer layer on the silicon surface, which can be functionalized for specific application. At NRC, SIS sensors are extremely sensitive to the growing thickness of a bio-layer on the sensor surface while independent of refractive index change of the surrounding medium. Therefore, SIS signal is free from thermal noise, unlike surface plasmon resonance based sensor. Also, there is no need of reference signal which facilitates fast and accurate interaction measurement. Here, SIS technology is applied to tackle two issues in MI diagnosis: high sensitivity with the direct assay and the ability to measure in human serum. Myoglobin, creatine kinase-MB, and cardiac troponin I (cTnI) proteins were used as the MI biomarkers. We were able to measure over a broad concentration range with the detection limit of 5 and 10pg/ml for cTnI in PBS and blood serum, respectively. The response time is about 5min. This novel technique is a suitable candidate for cost effective point-of-care application.

Universal evaluation of combined standard uncertainty for rotating-element spectroscopic ellipsometers.

We present for the first time a universal expression for the combined standard uncertainty for all types of rotating-element spectroscopic ellipsometers (RE-SEs). Specifically, we introduce general model functions as universal analytic expressions for the combined standard uncertainties of the ellipsometric sample parameters. The model functions are expressed as functions of influencing quantities that are not known exactly. The detailed expressions for the model functions are provided for the common RE-SEs. Our approach can be used for instrumentation, standardization, simulation, metrology, optimization of measurement conditions, and performance comparison between RE-SEs.

Universal evaluations and expressions of measuring uncertainty for rotating-element spectroscopic ellipsometers.

We obtain the universal evaluations and expressions of measuring uncertainty for all types of rotating-element spectroscopic ellipsometers. We introduce a general data-reduction process to represent the universal analytic functions of the combined standard uncertainties of the ellipsometric sample parameters. To solve the incompleteness of the analytic expressions, we formulate the estimated covariance for the Fourier coefficient means extracted from the radiant flux waveform using a new Fourier analysis. Our approach can be used for optimization of measurement conditions, instrumentation, simulation, standardization, laboratory accreditation, and metrology.

Optimizing the precision of a multichannel three-polarizer spectroscopic ellipsometer.

We developed a multichannel three-polarizer spectroscopic ellipsometer based on a data acquisition algorithm for achieving optimized precision. This algorithm measures unnormalized Fourier coefficients accurately and precisely. Offset angles for optical elements were obtained as wavelength-independent values using regression calibration. Derived subsets of data reduction functions were used to calculate sample parameters. Correlation coefficients of Fourier coefficients were used to calculate errors in the sample parameters. Mean standard deviations of the sample parameters for each data reduction method were compared to identify the best method. This approach could be used to identify suitable precision optimization methods for other rotating-element ellipsometers.

In situ control of oxygen vacancies in TiO2 by atomic layer deposition for resistive switching devices.

Oxygen vacancies (V(O)) have profound effects on the physical and chemical performance of devices based on oxide materials. This is particularly true in the case of oxide-based resistive random access memories, in which memory switching operation under an external electrical stimulus is closely associated with the migration and ordering of the oxygen vacancies in the oxide material. In this paper, we report on a reliable approach to in situ control of the oxygen vacancies in TiOx films. Our strategy for tight control of the oxygen vacancy is based on the utilization of plasma-enhanced atomic layer deposition of titanium oxide under precisely regulated decomposition of the precursor molecules (titanium (IV) tetraisopropoxide, Ti[OCH(CH3)2]4) by plasma-activated reactant mixture (N2+O2). From the various spectroscopic and microstructural analyses by using Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, confocal Raman spectroscopy, and spectroscopic ellipsometry, we found that the precursor decomposition power (R(F)) of plasma-activated reactant mixture determines not only the oxygen vacancy concentration but also the crystallinity of the resulting TiO(x) film: nanocrystalline anatase TiO(x) with fewer oxygen vacancies under high R(F), while amorphous TiOx with more oxygen vacancies under low RF. Enabled by our controlling capability over the oxygen vacancy concentration, we were able to thoroughly elucidate the effect of oxygen vacancies on the resistive switching behavior of TiO(x)-based memory capacitors (Pt/TiO(x)/Pt). The electrical conduction behavior at the high resistance state could be explained within the framework of the trap-controlled space-charge-limited conduction with two characteristic transition voltages. One is the voltage (V(SCL)) for the transition from Ohmic conduction to space-charge-limited conduction, and the other is the voltage (V(TFL)) for transition from space-charge-limited conduction to trap-filled-limited conduction. In this work, we have disclosed for the first time the dependence of these two characteristic transition voltages (i.e., V(SCL) and V(TFL)) on the oxygen vacancy concentration.

Snapshot phase sensitive scatterometry based on double-channel spectral carrier frequency concept.

Spectroscopic ellipsometry is one of the most important measurement schemes used in the optical nano-metrology for not only thin film measurement but also nano pattern 3D structure measurement. In this paper, we propose a novel snap shot phase sensitive normal incidence spectroscopic ellipsometic scheme based on a double-channel spectral carrier frequency concept. The proposed method can provide both Ψ(λ) and Δ(λ) only by using two spectra acquired simultaneously through the double spectroscopic channels. We show that the proposed scheme works well experimentally by measuring a binary grating with nano size 3D structure. We claim that the proposed scheme can provide a snapshot spectroscopic ellipsometric parameter measurement capability with moderate accuracy.

Fourier analysis for rotating-element ellipsometers.

We introduce a Fourier analysis of the waveform of periodic light-irradiance variation to capture Fourier coefficients for multichannel rotating-element ellipsometers. In this analysis, the Fourier coefficients for a sample are obtained using a discrete Fourier transform on the exposures. The analysis gives a generic function that encompasses the discrete Fourier transform or the Hadamard transform, depending on the specific conditions. Unlike the Hadamard transform, a well-known data acquisition method that is used only for conventional multichannel rotating-element ellipsometers with line arrays with specific readout-mode timing, this Fourier analysis is applicable to various line arrays with either nonoverlap or overlap readout-mode timing. To assess the effects of the novel Fourier analysis, the Fourier coefficients for a sample were measured with a custom-built rotating-polarizer ellipsometer, using this Fourier analysis with various numbers of scans, integration times, and rotational speeds of the polarizer.

Angle-resolved annular data acquisition method for microellipsometry.

An ellipsometric data acquisition method is introduced to measure the optical properties of sample. It is based on a microellipsometer hardware layout integrated a high numerical aperture objective lens, which is aligned in the normal direction of sample surface. This technique enables to achieve ellipsometric data at multiple incident angle with a sub-mum probe beam size, moreover real-time measurement is possible due to no moving parts. The experimental results of different SiO(2) thin film are demonstrated, also calibration technique is described.