【作者】 金成刚；

【导师】 吴雪梅； 诸葛兰剑；

【作者基本信息】 苏州大学 ， 凝聚态物理， 2014， 博士

【摘要】 等离子体技术可以产生具有化学活性的基团,已被广泛用于材料特性的改变；可以制造出具有特殊结构和表面特性的材料,这种效果往往是无法用其他商业技术手段实现的。对世界主要的制造工业来说,等离子体处理技术起着极其重要的作用。低温等离子体应用已经成为一项具有全球影响力的重要科学工程,对高科技经济的发展及传统工业的改造有着巨大的影响。工业上低温等离子体放电大都由电磁场激发产生,如射频(RF)放电、微波放电等。RF(频率在1-500MHz)放电与直流放电相比,能够在较低的气压下工作(等离子体的阻抗随频率的增大而减小),有效的电离机制(电子能够在整个周期里获得能量),空间分布很均匀；与微波放电相比,RF电源价格更便宜且电源功率更大以上这些特点使得RF等离子体成为工业应用最普遍的选择。本论文依托现有等离子体放电系统,通过调研和材料表面处理特殊要求,分析,设计、搭建研制了新型RF等离子体放电系统,相关放电系统的研制,实现了设计思想,达到了预期目标。主要表现在：(1)搭建研制了中等磁场(～6300G)的螺旋波等离子体(HWP)放电系统,实现了连续稳态的HWP放电；通过等离子体诊断开展等离子体特性研究,推进了新型诊断技术——磁绝缘折流探针的研制,并取得了初步的实验结果；在此基础上,首次提出强磁场EAST的放电方案,成功实现EAST壁清洗实验。为具有自主知识产权的Tokamak壁处理提供了有价值的科学参考。(2)首次搭建研制了多频电感耦合／电容耦合等离子体(ICP/CCP)放电系统,实现了离子能量,离子通量以及等离子体均匀性的独立控制；通过碳氟等离子体对SiC材料的刻蚀／沉积研究,找到了刻蚀／沉积的动态平衡参数,为具有自主知识产权的可控半导体刻蚀／沉积技术发展提供借鉴。针对不同放电系统特性及材料处理特殊要求,分别选择对应于不同放电系统的材料,开展RF等离子体与材料相互作用的研究。得到一系列研究结果：1)开展新型磁化RF等离子体放电与处理材料研究：针对Tokamak上石墨(Ⅳ族)壁材料开展清洗实验,结果表明未经等离子体处理的样品表面疏松多孔,平均颗粒尺寸较大,且吸附有大量微小的颗粒状杂质,而经过HWP处理的样品的表面更加致密紧实,平均尺寸减小,颗粒状杂质吸附去除明显。在中科院等离子体物理研究所EAST装置上实现RF电源、真空电极、匹配网络和天线连接。在不同形状尺寸的5类天线、电源频率、功率、磁场和放电气压的条件下开展HWP放电实验。通过朗缪尔探针测量系统对HWP参数进行诊断分析,发现放电阈值功率较低(<50W),反射功率很小。5号天线比其他天线激发的等离子体亮度更高,更加均匀；增加极向场后,等离子体沿着磁力线更加容易到达壁,有望实现更高效率的清洗2)利用RF磁控等离子体技术,制备了具有c轴择优取向的、有序的Cr/Cu掺杂ZnO纳米棒阵列,纳米棒垂直于Si衬底并有序地排列。对于Zno.94Cro.06O纳米棒阵列,光致发光和X射线吸收近边结构(XANES)结果表明样品中存在大量的Zn空位。且样品在XANES和高分辨率电子透射显微镜的测量范围内没有发现二次相的存在。样品在650℃时的饱和磁化强度为1.16μB/Cr,且随着衬底温度的降低而减小。Zn0.94Cr0.06O纳米棒阵列表现出明显的稳定的铁磁性,认为这来源于以Zn空位为媒介的束缚磁极化子模型。从第一性原理计算中得出,可以通过控制Zn空位来调控Zn0.94Cr0.06O纳米棒阵列的铁磁性,与实验结果相吻合。对于Zn0.92Cu0.08O纳米棒阵列,实验结果表明样品中存在大量的O空位,且没有发现其它任何二次相的存在。样品在600℃时的饱和磁化强度为0.12μB/Cr,且随着衬底温度的降低而减小。Zn0.92Cu0.08O纳米棒阵列表现出明显而稳定的铁磁性,其来源于以O空位为媒介束缚磁极化子模型。3)开展复杂电磁场条件下非磁化等离子体处理材料研究：利用多频ICP/CCP氮等离子体对超薄Hf02薄膜掺氮处理,改善了薄膜的表面结构,使漏电流特性改善(从4.6×104降到2.1×10-7A cm-2),而其与表面形貌没有关联。通过改变ICP功率,调节电子能量概率分布函数,控制等离子体中N的性质,使得更多的N原子掺入HfO2薄膜中。通过增加ICP功率,获得较低的有效电子温度和离子能量,从而降低薄膜表面的损伤。N原子的掺杂减少了相关能隙的O空位,从而降低了通过HfO2电介质的漏电流。利用多频ICP/CCP碳氟等离子体处理SiC材料,通过改变多频功率,调制等离子体中各活性基团的浓度,从而调控碳氟等离子体的刻蚀／沉积过程。主要研究了不同等离子体参数对SiC材料表面质量的影响。同时研究了C4F8/Ar多频ICP/CCP对SiC基片表面粗糙度和化学成分的影响,并建立模型分析了多频ICP/CCP处理能有效抑制基片表面碳氟残留物的原因。4)低能离子束辅助沉积纳米薄膜材料,在石英衬底上制备了透明导电的AZO薄膜。AZO薄膜的结构、电学及光学性质和辅源离子束能量密切相关。在辅源离子束能量为200eV下得到的AZO薄膜,其电阻率最低,为4.9×10-3Ω cm,且可见光透光率最高,为85%以上,并且获得了绒面结构。利用N2/Ar离子束辅助溅射沉积高品质较厚的Hf1-xZrxO1-yNy栅极绝缘层薄膜。详细研究了低能离子束辅助轰击对Hf1-xZrxO1-yNy薄膜的化学组分,热稳定性,表面形貌和光学特性的影响。通过能谱分析,证实利用物理气相沉积法,成功将N掺入了Hf1-xZrxO2薄膜,使得其结晶温度超过1100℃更多还原

【Abstract】 Plasma technology has been widely used to modify the characteristics of materials asit can produce chemically active radicals. By means of plasma technology, materials withunique structures and surface characteristics can be fabricated, which can not be achievedby any other commercial technology. Plasma processing technology plays an extremelyimportant role in the world’s leading manufacturing industries. Application of lowtemperature plasmas has become one of the important scientific projects with globalinfluence, and has a huge impact on the development of high-tech economy as well as thetransformation of traditional industries.The low temperature plasma discharges used in industry are mostly produced by theelectromagnetic field excitation, such as Radio frequency (RF) discharge, microwavedischarge, etc. RF plasma discharges (frequency of1-500MHz) have the advantages overDC discharges of being able to work under low pressure (The plasma impedance decreaseswith the increase of frequency), effective ionization mechanism (The electrons can gainenergy in the whole cycle) and uniform spatial distribution. Meanwhile, RF plasmadischarges have the advantage over microwave discharges of possessing a cheap RF powersupply with a large power. The above characteristics make RF plasma become the mostpopular choice in industrial applications.In this thesis, depending on the existing plasma discharge systems, novel RF plasmadischarge system has been analyzed, designed and constructed. Meanwhile, relevantdischarge systems have been developed. The design concept has been realized and theexpected objectives have been achieved mainly in the following areas.(1) We have constructed and studied the Helicon Wave Plasma (HWP) dischargesystem with moderate magnetic fields (6300G), by which continuous and steady HWP discharge has been realized. The research of plasma characteristics has been carried outthrough diagnostic analysis, and further promotes the development of a novel plasmadiagnostic technique (magnetically insulated baffled probe). Preliminary experimentalresults have been obtained. Based on these researches, the discharge scheme on EAST withstrong magnetic field has been proposed, and the wall cleaning experiment on EAST hasbeen successfully carried out. Our research can provide valuable scientific reference forTokamak wall treatment with independent intellectual property rights.(2) For the first time, we have constructed and studied the multi-frequencycapacitively-combined inductively-coupled plasmas (ICP/CCP) discharge system, bywhich the ion energy, ionic flux and uniformity of the plasma can be manipulatedindependently. Parameters of dynamic balance in etching/deposition have been acquiredthrough research on fluorocarbon plasma etching/deposition on SiC, thus providingreference for the development of controllable etching/deposition techniques insemiconductors.Research on interactions between RF plasma and materials has been carried out, byselecting the materials corresponding to different discharge systems according to thecharacteristics of different discharge systems as well as particular requirements of materialprocessing. A series of research results has been obtained.1) Research on plasma discharge and material processing of novel magnetization RFplasmas has been carried out. Cleaning experiments aimed at wall materials graphite IVgroup has been conducted. The results show that the sruface of the samples withoutplasma treatment is of porous structure, large average size, and is adsorbed by a largenumber of small granular impurities. However, the sruface of the samples with HWPtreatment is of compact and tight structure, smaller average size, and is obvious inelimination of adsorbed granular impurities.The RF power supply, vacuum electrodes, matching network and antenna have beensuccessfully connected on EAST in Institute of Plasma Physics, Chinese Academy ofSciences. HWP discharge experiment has been carried out with antennas in various shapesand sizes, under different frequencies, powers, magnetic field and discharge pressures. Parameters of HWP have been diagnostic analyzed by Langmuir probe measurementsystem. The results show that the discharge threshold power is very low (<50W), andreflection power is zero. The plasmas excited by antenna5is of higher brightness anduniformity than the plasmas excited by other antennas. Moreover, the plasmas arrive thewall along the lines of magnetic force more easily after adding the poloidal field.2) Well-aligned Cr/Cu doped ZnO nanorod arrays were synthesized by the RF plasmadeposition method. The Zn0.94Cr0.06O nanorod arrays were aligned perpendicular to the Sisubstrate. The PL and O K-edge XANES analyses indicate the existence of numerous Znvacancies. No secondary phase in the sample is found within the XANES and HRTEMdetection limits. The saturated magnetization is1.16μBper Cr ion at650oC and decreaseswith decreasing substrate temperature. The Zn0.94Cr0.06O nanorod arrays exhibit obviousstable RT ferromagnetic ordering, which is believed to originate from the Zn vacancymediated BMP model. From first-principles calculations, we conclude that the Zn vacancycan be controlled to tune the ferromagnetism of the Zn0.94Cr0.06O nanorod arrays.The experimental results indicate the existence of numerous O vacancies and provideevidence for absence of any secondary phase or nanoclusters in Zn0.92Cu0.08O nanorods.The saturated magnetization was0.12μB/Cu at600oC and de-creases with decreasing thesubstrate temperature. Our results revealed that the interactions between substitutionalCuZnin a divalent charge and oxygen vacacy played an important role in the ferromagneticorigin of Zn0.92Cu0.08O nanorods.3) ICP/CCP nitrogen (N) plasma discharges were investigated to nitridize ultrathinHfO2films for leakage improvement. In terms of the plasma chemical and surfaceprocesses, nitridation samples show great improvements in surface structure and theleakage current property (it decreases from4.6×104to2.1×107A cm2), while theleakage current is independent of the morphology. By modulating the EEPFs depending onthe power levels of CCP and ICP, the radical concentration of the N atom increases by theelectron–neutrals collision dependence on the high-energy electron, resulting in more Natoms incorporated in HfO2films. The lower effective electron temperature and ion energywere obtained with ICP power, causing less film surface damage. Therefore, N atoms possess intrinsic effects that drastically reduce the electron leakage current through HfO2dielectrics by deactivating the oxygen vacancy related gap states.C4F8-based ICP/CCP was used to process6H-SiC substrates. By modulating themulti-frequency powers, the concentrations of F and fluorocarbon radicals are increased bythe collisions of electron-neutrals, which depend on high-energy electrons, resulting in ahigh Si selectively etching rate and a low fluorocarbon film deposition rate. The effects ofplasma parameters on the chemical compositions, and surface morphology properties ofSiC substrates are discussed in detail.4) Transparent conductive AZO films are prepared on quartz substrates bydual-ion-beam sputtering deposition at room temperature. The structural, electrical andoptical properties of AZO films are closely related to the assisting-ion beam energy. Withincreasing assisting-ion beam bombardment, AZO films have a strong improved crystallinequality and increased radiation damage such as oxygen vacancies and zinc interstitials. Thelowest resistivity of4.9×103Ω cm and highest transmittance of above85%in the visibleregion were obtained under the assisting-ion beam energy200eV.High-quality Hf1-xZrxO1-yNygate dielectric thin films are deposited by ion beamassisted deposition. The chemical compositions, thermal stability, surface morphology andoptical properties of Hf1-xZrxO1-yNyfilms are discussed in detail. EDS analyses confirmthat nitrogen is incorporated into Hf1-xZrxO1-yNyfilms effectively, the crystallizationtemperature of Hf1-xZrxO1-yNyfilms is above1100oC.更多还原