Spatial characterization of wafer state using principal componentanalysis of optical emission spectra in plasma etch

Optical emission spectroscopy (OES) is often used to obtain in-situ estimates of process parameters and conditions in plasma etch processes. Two barriers must be overcome to enable the use of such information for real-time process diagnosis and control. The first barrier is the large number of measurements in wide-spectrum scans, which hinders real-time processing. The second barrier is the need to understand and estimate not only process conditions, but also what is happening on the surface of wafer, particularly the spatial uniformity of the etch. This paper presents a diagnostic method that utilizes multivariable OES data collected during plasma etch to estimate spatial asymmetries in commercially available reactor technology. Key elements of this method are: first, the use of principal component analysis (PCA) for dimensionality reduction, and second, regression and function approximation to correlate observed spatial wafer information (i.e., line width reduction) with these reduced measurements. Here we compare principal component regression (PCR), partial least squares (PLS), and principal components combined with multilayer perceptron neural networks (PCA/MLP) for this in-situ estimation of spatial uniformity. This approach has been verified for a 0.35-μm aluminum etch process using a Lam 9600 TCP etcher. Models of metal line width reduction across the wafer are constructed and compared: the root mean square prediction errors on a test set withheld from training are 0.0134 μm for PCR, 0.014 μm for PLS, and 0.016 μm for PCA/MLP. These results demonstrate that in-situ spatially resolved OES in conjunction with principal component analysis and linear or nonlinear function approximation can be effective in predicting important product characteristics across the wafer     

Fault detection technique for wavelength division multiplexing passive optical network using chaotic fiber laser

We propose a fault localization method for wavelength division multiplexing passive optical network (WDM-PON). A proof-of-concept experiment was demonstrated by utilizing the wavelength tunable chaotic laser generated from an erbium-doped fiber ring laser with a manual tunable fiber Bragg grating (TFBG) filter. The range of the chaotic lasing wavelength can cover the C-band. Basing on the TFBG filter, we can adjust the wavelength of the chaotic laser to match the WDM-PON channel with identical wavelength. We determined the fault location by calculating the cross-correlation between the reference and return signals. Analysis of the characteristics of the wavelength tunable chaotic laser showed that the breakpoint, the loose connector, and the mismatch connector could be precisely located. A dynamic range of approximately 23.8 dB and a spatial resolution of 4 cm, which was independent of the measuring range, were obtained.     

Fault location in optical fibers using optical frequency domain reflectometry

This paper describes the experimental and analytical investigations performed on another backscattering technique named "Optical Frequency Domain Reflectometry" (OFDR). In this approach the temporal signatures of graded-index multimode fibers are obtained as the inverse Fourier transform of the OFDR data. In the employed OFDR system the entire process is automated, and the modulation frequency is changed stepwise to obtain an exact inverse Fourier transform. The effects of starting frequency, frequency increment, and highest modulation frequency on OFDR temporal response are considered. The experimental results are in good agreement with those obtained by computer simulations. Also, a synchronous detection type of filtering process is suggested for signal-to-noise ratio improvement in OFDR technique.     

Combined optical fiber interferometric sensors for the detection of acoustic emission

A type of combined optical fiber interferometric acoustic emission sensor is proposed. The sensor can be independent on the laser source and make light interference by matching the lengths of two arms, so it can be used to monitor the health of large structure. Theoretical analyses indicate that the system can be equivalent to the Michelson interferometer with two optical fiber loop reflectors, and its sensitivity has been remarkably increased because of the decrease of the losses of light energy. PZT is powered by DC regulator to control the operating point of the system, so the system can accurately detect feeble vibration which is generated by ultrasonic waves propagating on the surface of solid. The amplitude and the fre- quency of feeble vibration signal are obtained by detecting the output light intensity of interferometer and using Fourier transform technique. The results indicate that the system can be used to detect the acoustic emission signals by the fre-quency characteristics.     

Combined optical fiber interferometric sensors for the detection of acoustic emission

A type of combined optical fiber interferometric acoustic emission sensor is proposed. The sensor can be independent on the laser source and make light interference by matching the lengths of two arms,so it can be used to monitor the health of large structure. Theoretical analyses indicate that the system can be equivalent to the Michelson interferometer with two optical fiber loop reflectors,and its sensitivity has been remarkably increased because of the decrease of the losses of light energy. PZT is powered by DC regulator to control the operating point of the system,so the system can accurately detect feeble vibration which is generated by ultrasonic waves propagating on the surface of solid. The amplitude and the frequency of feeble vibration signal are obtained by detecting the output light intensity of interferometer and using Fourier transform technique. The results indicate that the system can be used to detect the acoustic emission signals by the frequency characteristics.     

光纤光谱结合模式识别无损检测苹果表面疤痕

为了实现基于光纤光谱技术结合模式识别无损检测苹果表面疤痕, 利用光纤光谱采集系统采集了完好无损和表面有疤痕苹果的光谱数据, 采用标准正态变换(SNV)和1阶导数对原始光谱数据进行预处理; 利用主成分分析方法对预处理后的光谱数据进行降维, 以提取能反映苹果表面疤痕的特征光谱; 利用k最近邻(KNN)模式识别方法和偏最小二乘判别分析方法, 建立了苹果表面疤痕的识别模型。结果表明, 采用主成分分析法选择了累计贡献率超过99%的前8个主成分作为样本集特征光谱数据, 很好地实现了光谱数据的降维; 利用1阶导数+KNN识别模型对校正集以及SNV+KNN识别模型对预测集中正常果和疤痕果的正确率识别均高达96.0%。验证了基于光纤光谱技术结合模式识别方法无损检测苹果表面疤痕的可行性。     

Digital fibre transmission using optical homodyne detection

Homodyne detection of a 140 Mbit/s PSK signal transmitted over 30 km of cabled fibre has been achieved using a balanced optical phase-locked-loop receiver. System phase error was dominated by the laser frequency instability and not the cabled fibre.     

Evanescent wave methane detection using optical fibres

The optical detection of methane gas usually requires an open cell with light propagating through it as the detection system. This implies the need for precise and, therefore, often expensive and delicate alignment optics. The Letter reports, for the first time, the use of a continuous optical fibre link as the absorption system, thereby obviating the need entirely for precision optics. The system uses a suitably designed section of D-fibre as the interaction mechanism. Initial experimental results indicate that resolutions in the region of 100 parts per million of methane should be achievable.<>     

Optical preamplifier using optical modulation of amplified spontaneous emission in saturated semiconductor optical amplifier

This paper demonstrates a novel optical preamplifier using optical modulation of amplified spontaneous emission (ASE) emitted from a saturated semiconductor optical amplifier (SOA). Requirements on optical alignments and antireflection coating for SOAs can be relaxed and the elimination of an optical filter gives us a large tolerance of an input light wavelength in the proposed optical preamplifier. A small-signal gain of a fabricated preamplifier was over 13.5 dB for an input power of below -20 dBm. An optical gain bandwidth was over 60 nm. We measured the small-signal response of the optically modulated ASE. The 3 dB bandwidths at SOA bias currents of 200, 300, and 400 mA were 5.8, 12.6, and 16.5 GHz, respectively. We also investigated improvements in receiver sensitivities with the proposed optical preamplifier. Our calculation shows a possibility of 10 dB improvement in receiver sensitivities by using the optical preamplifier at 10 Gb/s. The measured receiver sensitivity was -22.7 dBm at 10 Gb/s with the optical preamplifier, which is corresponding to an improvement of 2.5 dB in the receiver sensitivity. Further improvements of the receiver sensitivity can be expected by optimizing the structure of SOAs for saturating ASE.     

Spectroscopic detection of gastrointestinal dysplasia using optical microsensors

The detection of dysplasia in the gastrointestinal tract can be performed using optical microsensors based on thin-film optical filters and silicon photodiodes. This paper describes two optical microsensors that can be used for spectroscopy data collection in two different spectral bands (one in the violet/blue region and the other in the green region) for which two optical filters were designed and fabricated. An empirical analysis of gastrointestinal spectroscopic data using these specific spectral bands is performed. The obtained results show that it is possible to accurately differentiate dysplastic lesions from normal tissue, with a sensitivity and specificity of 77.8% and 97.6%, respectively. Therefore, the developed filters can be used as a tool to aid in diagnosis. The small size of the optical microsensors can enable, in the future, integration in endoscopic capsules.     

激光辐照GaAs膜的光透射谱实验研究

GaAs薄膜材料生长技术的迅速发展和成熟及其广泛应用,该材料性质及其在外部电磁场等条件下的变化的广泛研究,促使以GaAs多层膜为结构的光电子元器件和集成光学元件以及相关的集成光电子技术和光计算技术等高科技研究和实用化的飞速进展,其中GaAs膜材料的光学性质,尤其是激光与GaAs膜的相互作用,影响其光学性质的研究是极其有用的。本文报道He-Ne激光辐照金属有机氧化物气相外延(MOVPE)技术生长的不掺杂GaAs膜,其光透射性质发生变化的实验研究结果。     

Low open-area endpoint detection using a PCA-based T2statistic and Q statistic on optical emission spectroscopy measurements

Examines an approach for automatically identifying endpoint (the completion in etch of a thin film) during plasma etching of low open area wafers. Because many end-pointing techniques use a few manually selected wavelengths or simply time the etch, the resulting endpoint detection determination may only be valid for a very short number of runs before process drift and noise render them ineffective. Only recently have researchers begun to examine methods to automatically select and weight spectral channels for estimation and diagnosis of process behavior. This paper will explore the use of principal component analysis (PCA)-based T² formulation to filter out noisy spectral channels and characterize spectral variation of optical emission spectroscopy (OES) correlated with endpoint. This approach is applied and demonstrated for patterned contact and via etching using digital semiconductor's CMOS6 (0.35-μm) production process     

Neural network modeling of reactive ion etching using optical emission spectroscopy data

Neural networks are employed to model reactive ion etching (RIE) using optical emission spectroscopy (OES) data. While OES is an excellent tool for monitoring plasma emission intensity, a primary issue with its use is the large dimensionality of the spectroscopic data. To alleviate this concern, principal component analysis (PCA) and autoencoder neural networks (AENNs) are implemented as mechanisms for feature extraction to reduce the dimensionality of the OES data. OES data are generated from a 2/sup 4/ factorial experiment designed to characterize RIE process variation during the etching of benzocyclobutene (BCB) in a SF/sub 6//O/sub 2/ plasma, with controllable input factors consisting of the two gas flows, RF power, and chamber pressure. The OES data, consisting of 226 wavelengths sampled every 20 s, are compressed into five principal components using PCA and seven features using AENNs. Each method is subsequently used to establish multilayer perceptron neural networks trained using error back-propagation to model etch rate, uniformity, selectivity, and anisotropy. The neural network models of the etch responses using both methods show excellent agreement, with root-mean-squared errors as low as 0.215% between model predictions and measured data.     

Label-free quantitative detection using porous silicon as optical biosensor

The single-layer porous silicon is prepared by electrochemistry etching method,which is used as an immunosensor for determining recombinant mouse zona pellucida 3 fusion protein(r-mZP3) by Raman spectroscopy analysis at room temperature.The molecule binding increases the effective optical thickness(EOT),and thus the Raman spectrum intensity decreases.The concentration and variation of Raman intensity show a good linear quantitative relation.The excellent sensing performance could open the way to a new family of optical sensors for biological standardization.     

Waveguide-type optical passive ring-resonator gyro using time-division detection scheme

An optical passive ring-resonator gyro is demonstrated using a waveguide ring-resonator and a conventional distributed feedback laser diode. A novel detection technique for the Sagnac effect based on a time-division switching scheme is also proposed.<>     

Motion detection using block based bi-directional optical flow method

Detecting moving objects from video frame sequences has a lot of useful applications in computer vision. This proposed method of moving object detection first estimates the bi-directional optical flow fields between (i) the current frame and the previous frame and between (ii) the current frame and the next frame. The bi-directional optical flow field is then subjected to normalization and enhancement. Each normalized and enhanced optical flow field is then divided into non-overlapping blocks. The moving objects are finally detected in the form of binary blobs by examining the histogram based thresholded values of such optical flow field of each block as well as the optical flow field of the candidate flow value. Our technique has been conceptualized, implemented and tested on real video data sets with complex background environment. The experimental results and quantitative evaluation establish that our technique achieves effective and efficient results than other existing methods.     

A novel method of optical detection using a capacitive device

This paper describes a new method of optical detection, which essentially involves the measurement of the change in charge spectrum of MOS capacitors with incident light. It also suggests a symmetric insulator-semiconductor-insulator (ISI) structure for an efficient optical detector     

In-process detection of microscratching during CMP using acoustic emission sensing technology

An experimental investigation on the correlation between the microscratches and the signal characteristics of acoustic emission (AE) generated during chemical mechanical planarization (CMP) has been performed. CMP experimental results from both laboratory and production line CMP machines have clearly showed that AE rms voltage in the time domain has distinctive features relating to scratching. The sensitivity of AE signals to the CMP process state change was also investigated. The results show that this AE sensing technology can be used as a tool for in-situ microscratch detection and process monitoring in CMP.     

Fault detection in combinational circuits using a compressed fault table

A method is developed for obtaining a highly compressed fault table for two-level combinational circuits. A set of operations is defined through which the minimal test set for detecting stuck-at faults is obtained from the compressed fault table. The method is equally suitable for sum of products form or product of sums form realization of logic functions and generates the test set directly from the algebraic expression of the logic function.     

Fault detection in combinational circuits using Gunn effect logic devices

It is shown that certain realisations of combinational switching functions using Gunn effect logic gates can be tested for single or multiple stuck-type faults by using two tests only. This result is achieved by exploiting the fact that the function of Gunn effect logic gates is sensitive to bias voltage