Ni-W-SiC纳米复合电镀工艺的研究

采用一种新型的分散方法促使纳米SiC在镀液中的均匀有效分布.初步探讨了工艺参数对复合镀层的影响,着重研究阴极电流密度对Ni-W-SiC纳米复合镀层表面形貌、断面形貌、n-SiC共析量和显微硬度的影响.结果表明:在其他工艺不变的条件下,选择适当的电流密度可制备出形貌良好、成分均匀、硬度较高的纳米复合镀层.     

Hybrid Anodic and Metal‐Assisted Chemical Etching Method Enabling Fabrication of Silicon Carbide Nanowires

Silicon carbide (SiC) is one of the most important third‐generation semiconductor materials. However, the chemical robustness of SiC makes it very difficult to process, and only very limited methods are available to fabricate nanostructures on SiC. In this work, a hybrid anodic and metal‐assisted chemical etching (MACE) method is proposed to fabricate SiC nanowires based on wet etching approaches at room temperature and under atmospheric pressure. Through investigations of the etching mechanism and optimal etching conditions, it is found that the metal component plays at least two key roles in the process, i.e., acting as a catalyst to produce hole carriers and introducing band bending in SiC to accumulate sufficient holes for etching. Through the combined anodic and MACE process the required electrical bias is greatly lowered (3.5 V for etching SiC and 7.5 V for creating SiC nanowires) while enhancing the etching efficiency. Furthermore, it is demonstrated that by tuning the etching electrical bias and time, various nanostructures can be obtained and the diameters of the obtained pores and nanowires can range from tens to hundreds of nanometers. This facile method may provide a feasible and economical way to fabricate SiC nanowires and nanostructures for broad applications.     

低热膨胀系数纳米碳化硅/聚酰亚胺复合薄膜的制备与性能

以原位分散聚合法制备出纳米碳化硅/聚酰亚胺(n-SiC/PI)复合薄膜, 采用SEM、热机械分析仪(TMA)、阻抗分析仪和热重分析(TG)研究了所制备薄膜的表面形貌、热膨胀、介电性能及热稳定性。结果表明: SiC粒子均匀分散在PI基体中, 复合薄膜的热膨胀系数(CTE)随着SiC含量的增加逐渐减小, SiC质量分数为15%时, CTE降低了11%, 且复合膜的热膨胀系数实验值比较接近于Kerner公式的计算值。复合膜的介电常数和介电损耗随着填料含量的变化而变化, 但始终维持在较低的范围内, 并在相当大的频率范围内保持稳定。      

Recent progress toward a manufacturable polycrystalline SiC surface micromachining technology

In this paper, we present results of recent research from our laboratory directed toward a manufacturable SiC surface micromachining technology for microelectromechanical systems (MEMS) applications. These include the development of a low-pressure chemical vapor deposition and in situ doping processes for silicon carbide (SiC) films at relatively low temperatures, as well as the development of selective dry etching processes for SiC using nonmetallic masking materials. Doped polycrystalline SiC films are deposited at 800/spl deg/C by using a precursor 1,3-disilabutane and dopant gas NH/sub 3/, with the minimum resistivity of 26 m/spl Omega//spl middot/cm. Dry etching for SiC and its selectivity toward silicon dioxide and silicon nitride masking materials are investigated using SF/sub 6//O/sub 2/, HBr, and HBr/Cl/sub 2/ transformer coupled plasmas. The etch rate, etch selectivity, and etch profile are characterized and compared for each etch chemistry. By combining the LPCVD and dry etching process with conventional microfabrication technologies, a multiuser SiC MEMS process is developed.     

Robust Free‐Standing Nano‐Thin SiC Membranes Enable Direct Photolithography for MEMS Sensing Applications

This work presents fabrication of micro structures on sub–100 nm SiC membranes with a large aspect ratio up to 1:3200. Unlike conventional processes, this approach starts with Si wet etching to form suspended SiC membranes, followed by micro‐machined processes to pattern free‐standing microstructures such as cantilevers and micro bridges. This technique eliminates the sticking or the under‐etching effects on free‐standing structures, enhancing mechanical performance which is favorable for MEMS applications. In addition, post‐Si‐etching photography also enables the formation of metal electrodes on free standing SiC membranes to develop electrically‐measurable devices. To proof this concept, the authors demonstrate a SiC pressure sensor by applying lithography and plasma etching on released ultrathin SiC films. The sensors exhibit excellent linear response to the applied pressure, as well as good repeatability. The proposed method opens a pathway for the development of self‐sensing free‐standing SiC sensors.     

SiC陶瓷表面处理工艺对SiC-AFRP界面粘接性能的影响

为提高SiC陶瓷-芳纶纤维增强树脂基复合材料(SiC-AFRP)的界面粘接性能,研究了陶瓷腐蚀工艺、偶联剂处理工艺、粘接剂种类对SiC-AFRP界面剥离强度的影响。结果表明:SiC陶瓷表面腐蚀工艺和偶联剂处理工艺能有效提高SiC-AFRP界面粘接性能。陶瓷经K3Fe(CN)6与KOH混合腐蚀液浸泡2h,使用乙烯基三乙氧基硅烷偶联剂偶联化处理后,SiC-AFRP的界面剥离强度由0.45kN/m提高至2.20kN/m;VA含量15%(质量分数)的EVA热熔胶膜是理想的界面胶黏剂。     

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。     

A combined etching process toward robust superhydrophobic SiC surfaces

Large-scale porous SiC was fabricated by a combination of Pt-assisted etching and reactive ion etching. It was found that the surface roughness of combined etchings increased dramatically in comparison with metal-assisted etching or reactive ion etching only. To reduce the surface energy, the porous SiC surface was functionalized with perfluorooctyl trichlorosilane, resulting in a superhydrophobic SiC surface with a contact angle of 169.2°?and a hysteresis of 2.4°. The superhydrophobicity of the SiC surface showed a good long-term stability in an 85?°C/85% humidity chamber. Such superhydrophobicity was also stable in acidic or basic solutions, and the pH values showed little or no effect on the SiC surface status. In addition, enhancement of porosity-induced photoluminescence intensity was found in the superhydrophobic SiC samples. The robust superhydrophobic SiC surfaces may have a great potential for microfluid device, thermal ground plane, and biosensor applications.     

SiC材料的低速率浅刻蚀工艺研究

对比研究了SiC材料在CF4+O2混合气体中的ICP刻蚀和RIE刻蚀,获得了刻蚀速率、刻蚀表面粗糙度随刻蚀功率、偏置功率、工作真空、氧含量等工艺条件的变化规律,研究结果表明,通过牺牲一定的刻蚀速率可以获得原子量级的刻蚀表面粗糙度,能够满足SiC微波功率器件研制的要求.     

Lapping assisted dissolved wafer process of silicon for MEMS structures

Dissolved wafer process (DWP) is being extensively used to fabricate complex micro-electro-mechanical system (MEMS) structures. Etching non-uniformity, increased surface roughness and duration of DWP is often influence MEMS devices yields. This paper presents a modified DWP involving lapping and polishing followed by chemical etching of silicon to release MEMS based structure. The lapping experiments are performed using silicon-carbide (SiC) and alumina (Al₂O₃) abrasive. The polishing of the silicon samples is also done. The lapped and polished surfaces are compared with etched silicon surfaces in KOH and EDP solutions. The lapping-polishing process is found to be 2.5 (Al₂O₃)–3 (SiC) times faster than a standard etching processes based on KOH and EDP solutions. The average roughness (R_a) of the lapped–polished silicon surfaces are found to be 19.2 and 32.9 nm corresponding to SiC and Al₂O₃ abrasive respectively. The R_a value of EDP and KOH etched silicon surfaces are found to be 16.2 and 238.3 nm respectively. Based on the lapping—polishing results, SiC based lapping followed by polishing of silicon surface can be used as an alternate of etching of silicon during DWP. In this paper, a two-step DWP, involving lapping-polishing followed by EDP chemical etching of silicon, is used to fabricate suspended comb-type microaccelerometer structure.     

Molecular dynamics simulations of CF3 etching of SiC

Molecular dynamics simulations were performed to investigate CF₃ continuously bombarding SiC surfaces with energies of 100, 150 and 200 eV at normal incidence and room temperature. The simulated results show that the etching rates of Si and C atoms increase linearly with the incident energy. The etch rate of Si atoms is much more than that of C atoms. A carbon-rich surface layer is observed which is in good agreement with experiments. Under bombarding by CF₃, an F-containing reaction layer is formed through which Si and C atoms are removed. In reaction layer, SiF and CF species are dominant. The formation mechanisms of ejected products are discussed. In etching products, SiF₃ is dominant. It is found that etching of C atoms in SiC is controlled by physical sputtering, while etching of Si atoms in SiC is controlled by chemical sputtering.     

Wet etching of GaN,AlN, and SiC: a review

The wet etching of GaN, AlN, and SiC is reviewed including conventional etching in aqueous solutions, electrochemical etching in electrolytes and defect-selective chemical etching in molten salts. The mechanism of each etching process is discussed. Etching parameters leading to highly anisotropic etching, dopant-type/bandgap selective etching, defect-selective etching, as well as isotropic etching are discussed. The etch pit shapes and their origins are discussed. The applications of wet etching techniques to characterize crystal polarity and defect density/distribution are reviewed. Additional applications of wet etching for device fabrication, such as producing crystallographic etch profiles, are also reviewed.     

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.     

Multi-scale hybrid eco-nanocomposites: synthesis and characterization of nano-SiC-reinforced vinyl-ester eco-composites

Polymer eco-nanocomposites based on vinyl-ester, recycled cellulose fibre and nano-silicon carbide (n-SiC) have been synthesized and characterized in terms of porosity, water-absorption behaviour, thermal and mechanical properties. The addition of n-SiC led to reduced porosity and water uptake because of enhanced fibre–matrix adhesion which permitted efficient load transfer and thus strength improvement. However, n-SiC addition reduced the prevalence of fibre debonding and pull-outs, thus causing sample brittleness and inferior fracture toughness. In terms of thermal properties, n-SiC addition facilitated improved mass transport and heat barriers, thus improving thermal stability and fire resistance.     

Anisotropic etching of SiC whiskers

We have demonstrated a method of producing nanoplatelets or complex well-ordered nanostructures from silicon carbide (SiC) whiskers. Preferential etching of SiC whiskers in a mixture of hydrofluoric and nitric acids (3:1 ratio) at 100 degrees C results in the selective removal of cubic SiC and the formation of complex structures resembling a pagoda architecture. Possible mechanisms governing selective etching are discussed. Reproducible results on SiC whiskers manufactured in different laboratories suggest that the self-patterning phenomena are common in SiC whiskers, and the same electroless etching procedure can be used to synthesize various complex nanostructures from more conventional nano- and microscale objects for use as building blocks in the fabrication of sensors, cellular probes, and electronic, optoelectronic, electromechanical, and other devices.     

Investigation of micropipe defect terminating during SiC crystal growth

Abstract

Micropipe is a vital defect for fabricating SiC based devices. In order to understand the evolution of micropipe during growth process, the authors studied axial cuts sliced from different parts of the sublimation grown SiC single crystals. The cuts have been characterised using optical microscopy, etching in molten mixed KOH and K₂CO₃, scanning electron microscope and X-ray photoelectron spectroscopy. It is found that second phase inclusion (silicon droplet) is contributing not only to the formation of micropipe defect but also to its termination during SiC growth process. And X-ray photoelectron spectroscopy measurement result shows that growth interface can be demarcated obviously without intentionally doping any other impurity, which offers a good and simple method for observing crystal growth process.     

n—SiC在聚四氟乙烯（PTFE）复合材料中的行为研究

质量分数为3．0%的n-SiC的多元聚四氟乙烯（PTFE）复合材料具有优良的摩擦因数和耐磨性。论文主要研究了n-SiC对复合材料摩擦磨损过程中的膜转移与磨损形貌的影响。研究认为,n-SiC的主要作用机理是：促进了PTFE转移膜的形成,获得了低而稳定的摩擦因数;提高了复合材料的耐热性与承载能力,减少了粘着磨损量,提高了复合材料的抗微切削能力;促进了复合材料的磨损机制由粘着磨损为主向微切削磨损为主转变。     

铝合金表面耐磨复合膜的制备及其性能

针对在特殊场合对铝合金耐磨性、耐腐蚀性的高要求,结合铝合金阳极氧化工艺以及阳极氧化膜多孔的特点,在阳极氧化电解液中添加耐磨性物质n-SiC,使之进入到多孔铝合金阳极氧化膜中,达到提高耐磨性和耐腐蚀性的要求;运用正交试验法得到了添加n-SiC复合阳极氧化最佳工艺方案为:温度20℃,n-SiC添加量20mg/L,电流密度2A/dm2,氧化总时间40min。扫描电镜和X射线能谱分析结果证实n-SiC进入了氧化膜中;通过磨损试验机、盐雾腐蚀试验箱对复合阳极氧化膜的性能进行了检测,表明添加n-SiC可以提高复合阳极氧化膜的耐磨性。     

Black SiC formation induced by Si overlayer deposition and subsequent plasma etching

Black SiC formation by plasma etching with SF₆/O₂ chemistry is reported. Black SiC was produced by depositing Si overlayer on SiC and then etching the Si/SiC stack sequentially, thus replicating the black Si morphology to SiC. Black SiC is obtained with almost zero reflectance over the wavelengths from 300 nm to 1050 nm. Thicker Si film was advantageous, and it was important to optimize the etch condition considering both the black Si morphology and the flattening effect of SiC.     

先驱体浸渍-裂解SiC界面改性涂层对气相渗硅3D-C_f/SiC复合材料力学性能的影响

界面改性涂层对调节复合材料的力学性能起到重要作用。特别是在气相渗硅(GSI)制备C_f/SiC复合材料时,合适的界面改性涂层一方面保护C纤维不受Si反应侵蚀,另一方面调节C纤维和SiC基体的界面结合状况。通过在3D-C纤维预制件中制备先驱体浸渍-裂解(PIP)SiC涂层来进行界面改性,研究了PIP-SiC涂层对GSI C_f/SiC复合材料力学性能的影响。结果表明:无涂层改性的GSI C_f/SiC复合材料力学性能较差,呈现脆性断裂特征,其弯曲强度、弯曲模量和断裂韧性分别为87.6 MPa、56.9GPa和2.1 MPa·m~(1/2)。具有PIP-SiC界面改性涂层的C_f/SiC复合材料力学性能得到改善,PIP-SiC涂层改性后,GSI C_f/SiC复合材料的弯曲强度、弯曲模量和断裂韧性随着PIP-SiC周期数的增加而降低,PIP-SiC为1个周期制备的GSI C_f/SiC复合材料的力学性能最高,其弯曲强度、弯曲模量、断裂韧性分别为185.2 MPa、91.1GPa和5.5 MPa·m~(1/2)。PIP-SiC界面改性涂层的作用机制主要体现在载荷传递和"阻挡"Si的侵蚀2个方面。