Raman and luminescence probes for the study of compound semiconductors

Optical characterization using local probes with submicrometric spatial resolution is very useful for many problems concerning compound semiconductors and devices. In particular, micro-Raman spectroscopy and cathodoluminescence spectrum imaging are very powerful analytical techniques that manage good signal/noise ratios allowing to acquire images including spectral information and slightly submicrometric spatial resolution in a short time. The main analytical and spatial resolution aspects concerning both techniques are addressed. Several examples are presented in order to illustrate the capabilities of micro-Raman and cathodoluminescence spectrum imaging for the characterization of compound semiconductors and the devices based on them.     

Basic study of a glass substrate in dry etching system

Electrostatic Chucks (ESCs) in the dry etchers for the TFT-LCD fabrications have been investigated briefly. The behaviors of glass encountering electric fields in the presence of plasma were studied. In some conditions, it has been shown that the electric force and the pressure by He backside cooling acting on the glass might be larger than the gravitational force. With a simple model, the stability condition of glass substrate was obtained.     

Lattice thermal expansion for normal tetrahedral compound semiconductors

The cubic root of the deviation of the lattice thermal expansion from that of the expected value of diamond for group IV semiconductors, binary compounds of III-V and II-VI, as well as several ternary compounds from groups I-III-VI₂, II-IV-V₂ and I-IV₂V₃ semiconductors versus their bonding length are given straight lines. Their slopes were found to be 0.0256, 0.0210, 0.0170, 0.0259, 0.0196, and 0.02840 for the groups above, respectively. Depending on the valence electrons of the elements forming these groups, a formula was found to correlate all the values of the slopes mentioned above to that of group IV. This new formula which depends on the melting point and the bonding length as well as the number of valence electrons for the elements forming the compounds, will gives best calculated values for lattice thermal expansion for all compounds forming the groups mentioned above. An empirical relation is also found between the mean ionicity of the compounds forming the groups and their slopes mentioned above and that gave the mean ionicity for the compound CuGe₂P₃ in the range of 0.442.     

Nanopillars by calcium chloride self-assembly and dry etching

Some applications of nanopillars (solar cell, Li ion battery, etc.) require neither long range order nor strict uniformity but more practicality of fabrication methods. Thin film of deliquescent salts may aggregate into nanodots (dry etch mask) by interaction with absorbed water, with enhanced practicalities such as easy mask removing, covering uneven surface, wide tunability and compatibility. However, only cesium chloride succeeded in last decade, based on diffusion. Herein, a new material calcium chloride (CaCl₂) is reported to self-assemble into nanodots for the first time, based on the reaction of crystalline hydrate. Their diameters could vary at least from 100 nm to 1.5 μm with coverage ratio above 35% by the control of film thickness and substrate moisture content. The formed dihydrate dots can keep integrity for more than 1 month in general environments, stable enough for practical use. The whole process flow is possibly controlled within 20 min, due to the fast forming and removing of CaCl₂ dots. Besides, the dots have been made on Si and PMMA substrates and transferred into pillars by dry etch, during which enough etch resistance and good coverage over rough surface are revealed.     

反应离子刻蚀工艺仿真模型的研究

以ＳＦ６／Ｎ２混合气体对Ｓｉ反应离子刻蚀工艺研究为例提出干法刻蚀计算机工艺模拟的方法：在分段拟合优化工艺条件下采用人工神经网络该当建立干法刻蚀仿真模型,可以预测绘定射频功率、总气流量下刻蚀速率和纵横比,并且以仿真实验数据训练模型学习,模型具有通用性,与设备无关。     

等离子体微细加工技术的新进展

在大规模集成电路制造中常用反应离子刻蚀 ,但对于加工 2 0 0mm以上直径的片子和 0 2 5 μm的线宽及孔洞 ,它的能力已达到极限。低压等离子刻蚀设备 (ECR ,ICP ,HWP)和高浓度等离子体可以解决这一问题。已经在整个片子上均匀地获得高的刻蚀速率。剖面控制精确 ,可改善图形的保真度。本文介绍了干法刻蚀技术的这一最新进展 ,阐述了电子回旋共振等离子体源、感应耦合等离子体源、螺旋波等离子体源的工作原理和干法刻蚀的关键技术问题。     

Laser etching and dry processing

Controlled, anisotropic etching of different materials commonly used in microelectronics is an important processing step in microfabrications. During recent years it has been demonstrated that lasers can be used for initiating and enhancing the etching process in many gas-solid (dry processing) and liquid-solid (wet processing) systems. The laser-induced reaction could be either photochemical or thermochemical. Using laser etching technique a variety of materials such as Al, Ta, Ni/Fe, GaAs, InP, Si, SiO₂ mylar, different polymers and superconducting materials have been processed. In this paper we briefly review these laser etching experiments.     

Laser processing of III–V compound semiconductors

Lasers have found an increasingly important role in semiconductor processing technology. While they are now widely used in some of the silicon-based device fabrication processes, their applications in III–V compound semiconductor processing are not equally well established. Considerable research work has been carried out to find ways to overcome some of the technical difficulties in their usage in technologies based mainly on GaAs. In this paper, we review these developments and mention possible future directions that will help establish the use of lasers in this very active field. Based on the talk given at the Winter School of Laser Material Processing, University of Poona, November 16–25, 1987.     

Inductively coupled plasma reactive ion etching of ZnO films in HBr/Ar plasma

The etching characteristics of ZnO thin films were examined in an HBr/Ar gas mix using an inductively coupled plasma reactive ion etching system. The etch rate and etch profile were systematically investigated as a function of gas concentration. In addition, the effects of etch parameters such as coil rf power, dc-bias voltage, and gas pressure were studied. As the HBr concentration increased, the etch rate of the ZnO films gradually decreased while the etch profile was improved. Surface analyses including X-ray photoelectron spectroscopy and atomic force microscopy were employed to elucidate the etch mechanism of ZnO in an HBr/Ar chemistry.     

Fabrication and characterization of large-core Yb/Al-codoped fused silica waveguides using dry etching

A deep inductively coupled plasma etching process was developed as a part of a continuous effort to develop an all-silica on-chip platform for high-power optical devices. Combined F and Cl based etching chemistry was found most suitable since silica matrix and Al doping are generally etched using different chemistries. First large-core (∼20 × 20 μm) Yb/Al-codoped fused silica waveguides on pure silica substrate were successfully fabricated, featuring ∼1 dB/cm optical propagation loss.     

Hydrogen bromide plasma-copper reaction in a new copper etching process

The hydrogen bromide (HBr) plasma-copper reaction, which is the base of a new copper etching process, has been studied. A high etch rate has been obtained with the reaction. Influences of process parameters, such as plasma exposure time, pressure, plasma power and substrate temperature, to the reaction process were explored. In addition to the reaction rate, we also investigated the relationship between the morphology and structure of the reaction product layer and the process condition. The results show that both the plasma-phase chemistry and the ion bombardment energy are important to the reaction. Mechanism for the HBr plasma-Cu reaction process was compared with that for the HCl or Cl₂ plasma-Cu reaction. The reaction product was characterized with X-ray photoemission spectroscopy and X-ray diffraction. These results are critical to the understanding of this new copper dry etching process.     

High density plasma etching of amorphous CoZrNb films for thin film magnetic devices

Inductively coupled plasma reactive ion etching of CoZrNb magnetic thin films was studied using a TiN hard mask in a Cl₂/O₂/Ar gas mix. The etch rates of CoZrNb films and TiN hard mask gradually decreased with increasing Cl₂ or O₂ gas concentrations. When O₂ gas was added in the Cl₂/Ar gas mix, the etch rate of TiN hard mask was suppressed effectively so that the etch selectivity of CoZrNb film to TiN hard mask was enhanced. The addition of O₂ into the gas mix also led to the anisotropic etching of the CoZrNb films and it was confirmed by Auger electron spectroscopy that there were no redeposited materials on the sidewall of the etched films. Highly anisotropic etching of CoZrNb films was achieved at room temperature under the optimized etching conditions.     

Evolution of etch profile in etching of CoFeB thin films using high density plasma reactive ion etching

Inductively coupled plasma reactive ion etching of CoFeB magnetic thin films patterned with Ti hard mask was studied in a CH₃OH/Ar gas mix. As the CH₃OH concentration increased, the etch rates of CoFeB thin films and Ti hard mask decreased but the etch profiles improved with high degree of anisotropy. The effects of coil rf power, dc-bias voltage and gas pressure on the etch characteristics were investigated. The etch rate increased with increasing coil rf power, dc-bias voltage and decreasing gas pressure. The degree of anisotropy in the etch profile of CoFeB films improved with increasing coil rf power and dc-bias voltage. X-ray photoelectron spectroscopy revealed that the chemical compounds containing Co and Fe components were formed during the etching. However, it was expected that the formation of these compounds could not increase the etch rates of the films due to low volatile compounds despite the improvement in etch profile.     

Prediction of silicon dry etching using a piecewise linear algorithm

A piecewise linear algorithm for predicting silicon etch rates in fluorine-based plasmas is shown. Discrete experimental data of pressure and RF power in reactive ion etching are used to construct a set of local two-dimensional etching functions that serve as a basis for computing numerical solutions (pressure and power values for a specific predicted silicon etch rate). It must be pointed out that, although the algorithm scans the entire data domain, a testing procedure is applied to ensure that the computing task will be invoked only when a solution exists, and otherwise it will be discarded (this avoids brute force methods). In the last step of the algorithm, all solutions are collected and interpolated to construct a solution path. In order to verify the match between the experimental etching results and numerical predictions, the algorithm has been coded and tested using Maple® Release 13.0, showing a successful validation with a difference between experimental data and computed numerical solutions as low as 1% for SF₆, and 4% for SF₆/O₂ in the best case and a root-mean squared error of 0.03.     

Dry etching of AlN films using the plasma generated by fluoride

The plasma produced by the mixture of fluoride and argon (SF₆/Ar) was applied for the dry etching of AlN films. Very high etching rate up to 140 nm/min have been observed. The effects of the bias voltage and the plasma component on the etching results were investigated. It shows that AlN can be effectively etched by the plasma with the moderate SF₆ concentration and the etching rate varies linearly with the bias voltage. The FTIR spectra confirm that AlF₃ is formed due to the chemical reaction of Al and F atoms. The mechanism of AlN etching in F-based plasma is probably a combination between physical sputtering and chemical etching and can be briefly outlined: (i) F⁻ ions reacts with Al atoms to form low volatile product AlF₃ and passivate the surface, and (ii) at the same time the Ar⁺ ions sputter the reaction product from the surface and keep it fluoride free to initiate further reaction. AlF₃ formed on the patterned sidewall play a passivation role during the etching process. The etching process is highly anisotropic with quite smooth surface and vertical sidewalls.     

电子回旋共振CF4+O2等离子体中Si3N4刻蚀工艺研究

在一台自行研制的电子回旋共振 (ECR)刻蚀系统中用CF4、O2 气体实现了Si3 N4材料的微细图形刻蚀。获得了气体流量、气体混合比、微波功率等因素对刻蚀速率的影响。结果表明刻蚀速率在O2 含量为 0 %时最慢 ,然后随着气体混合比的增加而增大 ,当气体中O2 含量为 2 0 %时达到最大 ,然后随着气体混合比的增加而缓慢降低。保持气体混合比为 2 0 % ,刻蚀速率随气体流量增加而增大 ;同时 ,微波功率越大 ,刻蚀速率也越高。     

离子束刻蚀工艺误差对DOE器件的影响

针对衍射光学元件(DOE)的离子束刻蚀工艺,结合掩模套刻过程实例,本文提出了刻蚀误差面形分布的概念.在标量衍射的夫琅和费原理上,进行了误差数值模拟分析及讨论.模拟分析和实验数据结果表明,误差的面形分布在DOE器件的衍射焦斑中心会产生一个明显的光强畸变毛刺亮点,严重破坏了靶场照明的均匀性.     

Comparative study on dry etching of polycrystalline diamond thin films

The reactive ion etching (RIE) technique was used to etch polycrystalline diamond thin films. In this study we investigate the influence of process parameters (total pressure, rf power, gas composition) of standard capacitively coupled plasma RIE system on the etching rate of diamond films. The surface morphology of etched diamond films was characterized by Scanning Electron Microscopy and the chemical composition of the etched film part was investigated by Raman Spectroscopy.We found that the gas composition had a crucial effect on the diamond film morphology. The use of CF₄ gas resulted in flatter surfaces and lateral-like etching, while the use of pure O₂ gas resulted in needle-like structures. Addition of argon to the reactant precursors increased the ion bombardment, which in turn increased the formation of non-diamond phases. Next, increasing the rf power from 100 to 500 W increased the etching rate from 5.4 to 8.6 μm/h. In contrast to this observation, the rise of process pressure from 80 to 150 mTorr lowered the etching rate from 5.6 down to 3.6 μm/h.