Plasma etching as a diagnostic technique in silicon surface studies

This paper describes a new application of plasma etching, namely as an aid to the characterization of specular semiconductor surfaces. The technique, which is simple and quick to perform, consists of subjecting the semiconductor slice to a brief etching treatment in a fluorocarbon plasma at low pressure, followed by inspection of the surface, using Nomarski microscopy. The whole operation is designated diagnostic plasma etching (DPE). Suitable etching times lie in the range 1 to 6 min and, under the operating conditions described, up to 3m silicon is removed, although generally the aim is to remove the minimum amount consistent with good image contrast under the microscope. When examined at high magnification, plasma-etched surfaces display a variety of artefacts, which can be related to features such as contamination and mechanical damage sites. The DPE technique possesses a high level of sensitivity and is capable of providing information on surface condition, not obtainable by existing wet chemical tests or high resolution microscopy, as exemplified by the detection of disturbance of surfaces cleaned by mechanical scrubbing techniques.     

Effect of bias in patterning diamond by a dual electron cyclotron resonance-radio-frequency oxygen plasma

Arrays of microhole patterns are fabricated on the surfaces of diamond films through a physical mask in a dual microwave electron cyclotron resonance/radio-frequency oxygen plasma. It is found that nanotips with high aspect ratio form in the microholes, and then through-holes are fabricated with a further increase of etching time. Optical emission spectroscopy was employed to calculate oxygen atom density and evaluate the variation of the plasma excitation temperature. The plasma excitation temperature and the O atom density present significant dependences on the voltage of rf bias V_b at a high frequency of 13.56 MHz, suggesting that the application of the rf bias not only strengthens ion bombardment on the material surface, but also induces the variations of the bulk plasmas including the increase of O atom density. Whereas, both the plasma excitation temperature and the O atom density remain nearly unchanged with V_b under the bias frequency of 400 kHz. The etching process depends on the rf-bias frequency and voltages, which are correlated with the measured plasma characteristics.     

Antireflective hydrophobic si subwavelength structures using thermally dewetted Ni/SiO2 nanomask patterns

We report the disordered silicon (Si) subwavelength structures (SWSs), which are fabricated with the use of inductively coupled plasma (ICP) etching in SiCl4 gas using nickel/silicon dioxide (Ni/SiO2) nanopattens as the etch mask, on Si substrates by varying the etching parameters for broadband antireflective and self-cleaning surfaces. For the fabricated Si SWSs, the antireflection characteristics are experimentally investigated and a theoretical analysis is made based on the rigorous coupled-wave analysis method. The desirable dot-like Ni nanoparticles on SiO2/Si substrates are formed by the thermal dewetting process of Ni films at 900 degrees C. The truncated cone shaped Si SWS with a high average height of 790 +/- 23 nm, which is fabricated by ICP etching with 5 sccm SiCl4 at 50 W RF power with additional 200 W ICP power under 10 mTorr process pressure, exhibits a low average reflectance of approximately 5% over a wide wavelength range of 450-1050 nm. The water contact angle of 110 degrees is obtained, indicating a hydrophobic surface. The calculated reflectance results are also reasonably consistent with the experimental data.     

表面预处理对钛合金表面低温等离子体氮化的影响

为提高TC4钛合金表面摩擦学性能,探究酸洗及等离子体预处理对TC4钛合金表面低温等离子体氮化进程的影响.首先采用热丝增强等离子体氮化系统分别对表面酸洗及未酸洗TC4钛合金在氩气气氛下进行等离子体预处理,然后对各种表面预处理的TC4钛合金实施低温(500℃)等离子体氮化.采用扫描电子显微镜、能谱仪及X射线衍射仪分别分析了...     

等离子体刻蚀处理对金刚石膜粘附性能的影响

采用直流等离子体射流ＣＶＤ法在ＹＧ８质合金基体上成功地合成了多晶金刚薄膜。通常基体表面经金刚石磨盘研磨、稀硝酸化学侵蚀脱钴预处理后，沉积的金刚石薄膜的的粘附性能仍不理想。本文首次采用原位的Ａｒ－Ｈ２等离子体射流对基体表面进行适当的轰击、刻蚀处理，显著粗化了基体表面，并使基体表面显微组织和化学成分发生重大变化，并且在合适的沉积工艺条件下，沉积的金刚石膜的粘附性能显著提高。借助ＸＲＤ、ＳＥＥＭ、ＴＥＭ     

Surface cleaning and etching of 4H-SiC(0001) using high-density atmospheric pressure hydrogen plasma

We propose low-damage and high-efficiency treatment of 4H-SiC(0001) surfaces using atmospheric pressure (AP) hydrogen plasma. Hydrogen radicals generated by the AP plasma was found to effectively remove damaged layers on SiC wafers and improve surface morphology by isotropic etching. Localized high-density AP plasma generated with a cylindrical rotary electrode provides a high etching rate of 1.6 microm/min and yields smooth morphology by eliminating surface corrugation and scratches introduced by wafer slicing and lapping procedures. However, high-rate etching with localized plasma was found to cause an inhomogeneous etching profile depending on the plasma density and re-growth of the poly-Si layer at the downstream due to the decomposition of the vaporized SiH(x) products. On the other hand, for the purpose of achieving moderate etching and ideal cleaning of SiC surfaces, we demonstrated the application of a novel porous carbon electrode to form delocalized and uniform AP plasma over 4 inches in diameter. We obtained a reasonably moderate etching rate of 0.1 microm/min and succeeded in fabricating damage-free SiC surfaces.     

Thinning of multilayer graphene to monolayer graphene in a plasma environment

We present a facile approach to transform multilayer graphene to single-layer graphene in a gradual thinning process. Our technique is based upon gradual etching of multilayer graphene in a hydrogen and nitrogen plasma environment. High resolution transmission microscopy, selected area electron diffraction and Raman spectroscopy confirm the transformation of multilayer graphene to monolayer graphene at a substrate temperature of ～ 400?°C. The shift in the position of the G-band peak shows a perfect linear dependence with substrate temperature, which indicates a controlled gradual etching process. Selected area electron diffraction also confirmed the removal of functional groups from the graphene surface due to the plasma treatment. We also show that plasma treatment can be used to engineer graphene nanomesh structures.     

Formation and metrology of dual scale nano-morphology on SF(6) plasma etched silicon surfaces

Surface roughness and nano-morphology in SF(6) plasma etched silicon substrates are investigated in a helicon type plasma reactor as a function of etching time and process parameters. The plasma etched surfaces are analyzed by atomic force microscopy. It is found that dual scale nano-roughness is formatted on the silicon surface comprising an underlying nano-roughness and superimposed nano-mounds. Detailed metrological quantification is proposed for the characterization of dual scale surface morphology. As etching proceeds, the mounds become higher, fewer and wider, and the underlying nano-roughness also increases. Increase in wafer temperature leads to smoother surfaces with lower, fewer and wider nano-mounds. A mechanism based on the deposition of etch inhibiting particles during the etching process is proposed for the explanation of the experimental behavior. In addition, appropriately designed experiments are conducted, and they confirm the presence of this?mechanism.     

Thermal etching of GaAs (1 1 3) surfaces

We discuss scanning electron micrographs and atomic force microscope images of thermally etched GaAs(1 1 3) surfaces. The GaAs(1 1 3)A and GaAs(1 1 3)B surfaces are compared. The polarity of the surface leads to a different morphology for the two surfaces after thermal etching. It is found that the Ga-enriched droplets, which form under As-deficient conditions at higher temperatures, are sitting on characteristic pedestals, which are different for the two faces. The facets occurring after this thermal etching process are identified. They represent thermally favourable surfaces under the arsenic-deficient conditions of the thermal etching process. © 1998 Chapman & Hall     

Corrosion resistance studies on grain-boundary etched drug-eluting stents

In this paper we compare the influence of different microstructures on the corrosion resistance of new drug-eluting stainless steel stents, which have been produced by grain-boundary-selective electrochemical etching processes. The morphology of the stent surfaces was analysed by scanning electron microscopy (SEM), and the surface composition was investigated with Auger electron spectroscopy (AES) as well as with energy dispersive X-ray analysis (EDX). The passivity of the different microstructured stents was studied by cyclovoltammetry in Ringer solution. Release of nickel and chromium was assessed after potentiostatic experiments in Ringer solution by analysing the collected electrolyte with AAS. For stents produced by different two-step etching procedures bringing about ideal morphologies regarding the mechanical and biological properties of the surface, no significant differences in the passivation behaviour could be observed. A two-step process using first nitric acid and oxalic acid in a second step produces stent surfaces with very good corrosion properties: electrochemical analysis shows that the range of stable passivity is the same as for conventional stent surfaces, and low rates of nickel and chromium release are observed. The etching procedures do not seem to change the surface oxide layer composition.     

Influence of the Chemical Composition and Topography of the Ti6Al7Nb Surface Etched in Fluorine Plasma on Its Selected Properties

Herein, a new way of the surface modification of Ti6Al7Nb alloy in fluorine plasma is presented using the mask made of stainless steel and its influence on the selected properties, including chemical composition, topography, and tribological ones. Depending on the etching process parameters, different characteristics of the surfaces are obtained. The higher is the value of the negative bias, the less fluorine concentration on the etched surface and higher etching rates. Etching using the SF₆ gas shows bigger etching rates in comparison to the etching using the CF₄ gas. Chemical composition of the modified surfaces shows greater impact on tribological characteristics than topography parameters. The lowest wear rate is observed for the sample modified using the CF₄ gas.     

Theory of plasma chemical transport etching of gold in a chlorine plasma

The behavior of the reactive ion etching of gold in a chlorine plasma reported earlier is shown in this paper to be interpretable in terms of a theory of chemical vapor transport, modified to account for the effect of species generated in the plasma and transported across the plasma sheaths to the reacting surfaces. The interpretation of the experiments in terms of such a theory is required because the volatile compound of gold generated at the etched surface must be transported to another surface where it is consumed by a reaction which is the reverse of etching, and gold is deposited. It is shown that the mass transport of the volatile product is not only due to the differences in temperature between the surfaces where the reactions occur, but is also driven by differences in the surface reaction effective free energy. These free energy differences arise from differences in the transport of the plasma-produced species across the plasma sheaths to the reacting surfaces. The dependences of the etch rate on the film area (the “loading”), on the gas flow and on the relative temperatures of the surfaces between which transport occurs also arise from these considerations and explain the salient features of the reactive ion etching of gold in a chlorine plasma.     

Argon plasma treatment of glass surfaces

The effect of argon plasma treatment of glass surfaces is studied by FTIR and SEM. The argon plasma on cleaned glass surfaces resulted in increased surface area due to microetching and surface rearrangement of the silicate network as indicated by the observed changes in the Si-O stretching infrared absorption. The result was a relative increase in surface hydrophilicity which could be optimized by the plasma reaction conditions. The etching action of the argon plasma on the substrate surfaces facilitated the removal of the micrometre thick sizing from the commercial fibres accompanied by little loss in tensile strength. Plasma was also used to graft selected monomers to the surface of glass fibres for enhancement of bond compatibility in a composite system. This grafting treatment was followed by an argon etching step. The argon plasma action on the coated surfaces improved the wettability further and increased the sur face area. Changes in surface chemistry that accompanied the argon etching treatment were very subtle in the case of the plasma polymer of allylamine, but proved significant in the case of the plasma polymer of hexamethyldisiloxane. On the latter surfaces, rearrangement of the siloxane (Si-O-Si) bonds to silylmethylene (Si-(CH₂) _n -Si) groups is suggested.     

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.     

Interlaminar fracture morphology of carbon fibre/PEEK composites

The interlaminar fracture morphology of a carbon fibre/poly(ether-ether-ketone) composite (Aromatic Polymer Composite, APC-2) has been examined. The techniques used included scanning electron microscopy on fracture surfaces and on polished and etched sections. Two types of interlaminar fracture are observed: stable and unstable fracture. Both fracture surfaces exhibit microductility but it is more extensive for stable fracture. The fracture surfaces are not planar but have surface roughness. Fibre breakage and peeling are also observed and a quantitative examination enables the fracture energy contributions from the various processes to be calculated. The use of an etching technique reveals the spherulite texture and the presence of a deformation zone which extends into the bulk of the composite from the fracture surface. The extent of this zone is greater in the stable fracture region than in the unstable region and its presence indicates that the volume of composite which can be brought into the energy absorbing process extends well beyond the interlaminar region. The size of the zone has also been calculated using the fracture energy contributions and there is moderate agreement between calculated and observed zone size. Patterns of microductility on the fracture surface are seen to be due to spherulite texture, however the spherulite boundaries do not influence the fracture path.     

High ion density dry etching of compound semiconductors

The use of plasma sources that generate high ion densities (> 10¹¹ cm⁻³) enables dry etching of compound semiconductors at high rates with anisotropic sidewalls. In this paper we review the use of several types of electron cyclotron resonance (ECR) plasma sources and contrast the result with those obtained under reactive ion etching conditions. Various problems occurring in dry etching will be discussed, including aspect ratio dependent etch rates, mask erosion, sidewall roughening and damage introduction into the semiconductor. This damage may consist of point and line defect creation, non-stoichiometric surfaces, resputtering of mask materials or deposition of contaminating films. The use of low or high substrate temperatures to control the desorption kinetics of etch products is also discussed; at low temperatures problems can occur with condensation of the etch gases onto the substrate, while at elevated temperatures it is necessary to thermally bond the sample to the r.f. powered electrode to obtain reproducibility. Etch selectivity between the components of heterostructure systems such as GaAs/AlGaAs, GaAs/InGaP, InGaAs/AlInAs and GaN/AlN is usually much worse under high ion density conditions because of the high rates and large physical component.     

Plasma‐Induced Hetero‐Nanostructures on a Polymer with Selective Metal Co‐Deposition

Plasma‐induced pattern formation is explored on polyethylene terephthalate (PET) using an oxygen plasma glow discharge. The nanostructures on PET are formed through preferential etching directed by the co‐deposition of metallic elements, such as Cr or Fe, sputtered from a stainless‐steel cathode. The local islands formed by metal co‐deposition have significantly slower etching rates than those of the pristine regions on PET, generating anisotropic nanostructures in pillar‐ or hair‐like form during plasma etching. By covering the cathode with the appropriate material, the desired metallic or polymeric elements can be co‐deposited onto the target surfaces. When the cathode is covered by a relatively soft material composed of only carbon and hydrogen, such as polystyrene, nanostructures typically induced by preferential etching are not observed on the PET surface, and the surfaces are uniformly etched. A variety of metals, such as Ag, Cu, Pt, or Si, can be successfully co‐deposited onto the PET surfaces by simply using a cathode covered in the desired metal; high‐aspect‐ratio nanostructures coated with the co‐deposited metal are subsequently formed. Therefore this simple single‐step method for forming hetero‐nanostructures—that is, nanoscale hair‐like polymer structures decorated with metals—can be used to produce nanostructures for various applications, such as catalysts, sensors, or energy devices.     

碳化硅颗粒增强复合材料超疏水表面的制备

采用电化学蚀刻方法在碳化硅颗粒增强复合材料(SiC/Al)表面构筑了微纳结构, 重点分析了蚀刻电流密度和蚀刻时间等关键操作参数对所得表面微观形貌及润湿特性的影响。研究发现, 较高电流密度(6 A/dm²)下刻蚀的SiC/Al复合材料表面可形成由微米级“粒状”结构和纳米级结构(颗粒状和波鳞状)复合而成的微-纳双层结构, 且这种特殊结构不因后续刻蚀时间延长而改变; 优化条件形成的SiC/Al复合材料刻蚀表面呈现出静态接触角高达160.7°、滚动角低至4°的超疏水特性。本研究结果说明SiC/Al复合材料可用于制备自清洁表面。     

射频等离子体放电的宏观参数与PET表面改性的关系

通过射频等离子体放电，采用O2，CF4及CH4／CF4混合气体等离子体对PET表面进行处理。改变射频等离子体放电的宏观参数，如放电时间、放电功率、电极间距离和复合参数，详细地研究了这些参数对PET表面改性的影响。结果表明：碳氟混合气体等离子体在PET表面的沉积速率为正值，在PET表面形成了聚合物；而O2和纯CF4气体的沉积速率为负值，两者在PET表面产生刻蚀效应。增加等离子体放电功率和放电时间，聚合或刻蚀效果更明显；而增加电极间距离和复合参数，聚合或刻蚀效果明显减弱。     

Prozesse mit hoher Plasmastromdichte und unterschiedlichen Verdampfungsquellen

The hot filament supported high current discharge can be used with various process steps. During the heating cycle, intense electron bombardment provides a soft and efficient energy source. In triode etching the high plasma density improves the throwing power and reduces the arcing problem on oxide inclusions from preceding grinding steps. For the coating cycle the high current density can be fitted into different deposition processes. Activated reactive ion plating is done with a high voltage electron beam gun. But one can also combine the high current density plasma with a magnetron to produce a high plasma density on the substrate and solve the problems of reactivity of this vapor source. Alternatively the high current density plasma can also be used to drive a CVD-reaction. Several of these processes can be combined to hybrid deposition technologies. A few examples of coating realisations and performance in the different processes will be given.