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.     

Real-time control of reactive ion etching using neural networks

This paper explores the use of neural networks for real-time, model-based feedback control of reactive ion etching (RIE). This objective is accomplished in part by constructing a predictive model for the system that can be approximately inverted to achieve the desired control. An indirect adaptive control (IAC) strategy is pursued. The IAC structure includes a controller and plant emulator, which are implemented as two separate back-propagation neural networks. These components facilitate nonlinear system identification and control, respectively. The neural network controller is applied to controlling the etch rate of a GaAs/AlGaAs metal-semiconductor-metal (MSM) structure in a BCl₃/Cl₂ plasma using a Plasma Therm 700 SLR series RIE system. Results indicate that in the presence of disturbances and shifts in RIE performance, the IAC neural controller is able to adjust the recipe to match the etch rate to that of the target value in less than 5 s. These results are shown to be superior to those of a more conventional control scheme using the linear quadratic Gaussian method with loop-transfer recovery, which is based on a linearized transfer function model of the RIE system     

Fabrication of low-threshold InGaAs/GaAs ridge waveguide lasers by using in situ monitored reactive ion etching

In situ laser-monitored reactive ion etching is used to control ridge formation with 150-AA accuracy in fabricating double heterostructure InGaAs-GaAs strained layer single-quantum-well ridge waveguide lasers grown by molecular-beam epitaxy. Continuous-wave threshold current as low as 3.6 mA was obtained on devices with cleaved mirrors. High-reflectivity (96-70%) coated devices have the lowest threshold current at 2.1 mA.<>     

Time series modeling of reactive ion etching using neural networks

Neural networks have been used to model the behavior of real-time tool data in a reactive ion etch (RIE) process. An etch monitoring and data acquisition system for transferring data from the RIE chamber to a remote workstation was designed and implemented on a Plasma Therm Series 700 Dual Chamber etcher. This system monitors gas flow rates, RF power, temperature, pressure, and dc bias voltage. A neural network was trained on the monitored data using the feed-forward, error backpropagation algorithm. This network was used to perform three distinct modeling tasks. First, the network was trained on a subset of ten samples of the time series representing a single process run, and subsequently used to forecast the next data point. In the second task, the network was trained as in the first task, but used to predict the next ten values of the data sequence. In each of the first two tasks, the trained network yielded errors of less than 5%. In the final task, a neural net was used to generate a malfunction alarm when the sampled data did not conform to its previously established pattern     

Final polishing of Ga-polar GaN substrates using reactive ion etching

Reactive ion etching of {0001} oriented plate-like GaN single crystals has been investigated using SiCl₄:Ar:SF₆ chemistry. The reactive ion etching process is highly chemical. Large anisotropy of the etching rate and of the morphology has been established on (000 ) N-polar and (0001) Ga-polar sides of the GaN crystals, with remarkably higher rate on the N-polar side. Atomic force microscopy measurements have shown smooth surface and good polishing effect obtained on Ga-polar side, while N-polar surface exhibits an increased roughness of a factor of 10 after RIE.     

Via holes for GaAs MMICs fabricated using reactive ion etching

A dry etching process has been employed in the successful fabrication of through-substrate via holes for GaAs MMICs. The etching was carried out using Freon 12 (CCl2F2) as the etching gas. These vias have been shown to have low loss up to 12GHz.     

A novel in situ monitoring technique for reactive ion etching usinga surface micromachined sensor

This paper presents a novel technique for monitoring film thickness in reactive ion etching by incorporating a micromachined sensor. The prototype sensor correlates film thickness with the change in resonant frequency that occurs in a micromachined platform during etching. The platform is suspended over a drive electrode on the surface of the substrate and electrically excited into resonance. As material is etched from the platform, its resonant vibrational frequency shifts by an amount proportional to the amount of material etched, allowing etch rate to be inferred. As a proof-of-concept experiment, a platform made of DuPont 2611 polyimide has been fabricated. The sensor is driven into resonance electrostatically, and the shift in resonance is detected by monitoring the change in impedance between the drive electrode and platform as the drive frequency is swept. To enhance filtering of the sensor signal in the noisy plasma environment, the platform is designed so that the ratio of the plasma frequency to the fundamental mode of vibration is approximately 400:1. The prototype was etched in a Plasma Therm 700 series reactive ion etching (RIE) system in a CHF₃/O₂ plasma. Electrical contact was made with the sensor using a feedthrough attached to the vacuum line beneath the process chamber to facilitate in situ excitation and measurement. The sensor is shown to offer high resolution (approximately 1300 Hz/um), potentially permitting accurate in situ monitoring of etch rate and uniformity at a nominal cost     

Novel contact hole fabrication using selective liquid-phasedeposition instead of reactive ion etching

This work forms a contact hole utilizing the selectively liquid-phase deposited (S-LPD) silicon-oxide technique instead of the conventional reactive ion etching (RIE). The n⁺/p junction diode with contact hole formed by S-LPD exhibits an order of magnitude less reverse current, larger forward current, smaller ideality factor, and better thermal stability than that formed by RIE. A Schottky junction with S-LPD contact hole also possesses several excellent characteristics, including ideality factor, reverse current and barrier height, even without sintering treatment. These characteristics confirm the effectiveness of the S-LPD technique in replacing conventional RIE to form contact holes, particularly for future ultra-shallow junctions     

Characterization of GaN films etched using reactive ion etching technique by secondary ion mass spectrometry

We investigated GaN films etched by using reactive ion etching (RIE) technique to fabricate the GaN-based devices. The samples were grown on sapphire substrate by metal organic chemical vapor deposition (MOCVD), and Ti/Al contacts were formed on n-GaN surfaces after etching processes. The effects of the kinds of reactive gases were evaluated by secondary ion mass spectrometry (SIMS). The results showed that in the sample etched using BCl₃ gas, the signal from boron contaminations was strongly detected at the interface between the contact metal and n-GaN, and we found that additional etching in Cl₂ plasma after etching with BCl₃ gas was essential to make a good contact.     

基于神经网络的多电平逆变电路故障诊断

因含有大量的开关器件,多电平逆变器难以用基于模型的方法进行故障诊断。针对这一问题,提出了一种基于神经网络的故障识别和分类方法。采用载波相移脉冲宽度调制（PWM）策略搭建级联五电平逆变电路,对逆变器的输出电压信号进行快速傅里叶变换,获取其频谱并以此作为特征信息。利用反向传播算法（BP）神经网络对输出电压模式进行分类。Matlab仿真结果表明,本文设计的 BP神经网络有效地实现了对逆变器的故障诊断。     

Electron beam induced current investigations of active electrical defects in silicon due to reactive ion etching and reactive ion beam etching processes

Reactive ion etching and reactive ion beam etching are common tools for anisotropic etch processes in silicon microdevice fabrication; but, unfortunately, they also create radiation damage in the etched surface. We have studied the electrically active defects by measuring the recombination of carriers with the help of the electron beam induced current (EBIC) mode of a secondary electron microscope. We have measured the temperature behavior of the samples by annealing studies and the temperature dependent EBIC signal for several p-doped silicon wafers and obtained different shaped curves. Theoretical EBIC models developed with the assumption of a reduced net carrier concentration in the etched areas agree with our experimental results.     

High-power 0.98-μm strained quantum-well lasers fabricated usingin situ monitored reactive ion beam etching

0.98-μm wavelength InGaAs-AlGaAs strained quantum-well buried ridge lasers were fabricated using in situ monitored reactive ion beam etching (RIBE). This technique allowed a very accurate ridge geometry, resulting in high single transverse-mode power more than 250 mW and high-fiber coupled power more than 150 mW     

Damage-free reactive ion etching of GaAs FET gate recess

A GaAs reactive ion etching process is described which has good uniformity and causes no significant electrical damage to the underlying substrate. The process is shown to be suitable for forming the gate recess of a GaAs MESFET. FETs fabricated using the process exhibit DC and RF performance similar to equivalent wet etched devices.<>     

Fabrication of sharp silicon tips employing anisotropic wet etching and reactive ion etching

We developed a process to obtain sharper silicon tips by employing anisotropic etching in a KOH solution followed by SF₆ plasma etch. The tips were further sharpened using the established thermal oxidation technique to decrease the cone angle and, therefore, obtain smaller curvature radii. We have analyzed the impact of such changes in geometry on a figure of merit associated with the field emission characteristics. An increase in the figure of merit by a factor of three was found in relation to the tips before sharpening.     

Novel process for integration of optoelectronic devices using reactive ion etching without chlorinated gas

A new process for RIE of III?V compound semiconductors using mixtures of CH4, Ar and H2 as the etching gas is presented. This process can be successfully applied to most III-V materials used in micro-optoelectronic technology     

In situ and real-time metrology during rinsing of micro- and nano-structures

A new technology, called electro-chemical residue sensor (ECRS), has been developed for the in situ and real-time measurement of the residual impurities left on the wafer surface and in the fine structures of patterned wafers during typical rinse processes. The key components of this technology, which consist of the sensor hardware and a process model, are described. The testing results of the ECRS show that the residual impurity concentration is significantly different from what is typically provided by the bulk water resistivity, which is usually employed for determining the progress of the rinse. As a case study, the new metrology method has been applied to the removal of sulfate ions from patterned wafers; the importance of various surface interactions, charge effects, and transport processes is determined. Two examples of the use of the ECRS for the development of novel rinse recipes to reduce water usage are also discussed.     

硅传感器反应离子刻蚀的观察

六十年代发展起来的微电子技术,已大大影响了人类社会的面貌,而由微电子技术与机械学相互交叉而诞生的微机械技术,正成为一项新的产业。微电子技术以硅的平面加工技术为主,其制造工艺一般在表面几十微米以内。而微机械的厚度(或深度)往往达到几百微米,因此,必须研究硅的深加工技术以适应微机械的需求。本文以制作一种以玻璃为衬底的单晶硅叉指电容式加速度传感器为目的,开展了离子刻蚀技术的研究[1]。硅的反应离子刻蚀是一个复杂的辉光放电等离子体物理一化学作用过程。该技术早期存在刻蚀速率低,不能获得高的深宽比,掩膜选择比不高等技术障…     

反应离子刻蚀InSb芯片引入的损伤研究

应用CH₄/H₂/Ar作为刻蚀气源对InSb微台面阵列进行了反应离子刻蚀,并对刻蚀后引入的损伤进行了分析。实验证实利用干法刻蚀与湿法腐蚀相结合的方法能有效地减少刻蚀引入的缺陷和损伤,获得较好的电学特性,达到低损伤刻蚀InSb材料的目的。     

Uniformity in HgCdTe diode arrays fabricated by reactive ion etching

Two-dimensional, midwavelength infrared (MWIR) HgCdTe detector arrays have been fabricated using reactive ion etching (RIE). Detector-to-detector uniformity has been studied in the devices fabricated with CdTe- and ZnS-passivation layers. Mapping of the doping profile, passivant/HgCdTe interface electrical properties, and diode impedance-area product (R₀A_j) in a two-dimensional array of diodes has been carried out. Temperature and perimeter/area dependence of the dark current are studied to identify the bulk and surface current components. Maximum R₀A_j=2×10⁷ Θcm² was achieved in CdTe-passivated, 200×200 μm² diode arrays. It demonstrates that CdTe-passivated, RIE-processed HgCdTe is a feasible technology.     

GaInAsP/InP mass transport laser monolithically integrated with photodetector using reactive ion etching

A 1.5 mu m GaInAsP/InP laser is monolithically integrated with a photodiode. The laser is isolated from the photodiode by an etched groove formed by reactive ion etching. Ethane and hydrogen gases are used as an etchant of reactive ion etching instead of chlorinated gas. The threshold current of the laser under CW operation and the sensitivity of the monitor photodiode are 57 mA and 0.24 A/W, respectively.<>