【作者】 文懋；

【导师】 于文学； 郑伟涛；

【作者基本信息】 吉林大学 ， 材料物理与化学， 2010， 博士

【摘要】 过渡族金属氮化物具有优异的物理性能,如高硬度、高熔点、高电导率及高化学稳定性等,使其广泛应用于微电子器件、微电子机械系统和切削刀具的硬质保护涂层。过渡族金属氮化物薄膜的各种性能强烈依赖于薄膜的择优取向和相结构,因此为了获得理想的薄膜性能,控制薄膜的择优取向和相结构十分必要。尤其随着工业的发展,从对单一性能薄膜到对力、热、光或电复合性能薄膜的需求日益扩大,要求薄膜的微观结构具有较高的可控性和可重复性,同时也对过渡族金属氮化物薄膜的生长机制的研究提出了更高的要求。此外,过渡族金属氮化物构成的纳米多层膜通常表现出超硬效应,其优异的力学性能和广泛的工业应用,引起了人们的普遍关注。然而目前对多层膜中硬度增强机制的理解仍然有限,对新多层膜体系的开发和研究有重大需求。本论文立足于前人的研究成果,系统地研究了沉积条件对NbN和WNx单层膜的结构和力学性能的影响,重点探讨了NbN和WNx单层膜中织构行为、相变机制及其与力学性能之间的关系;通过对单层膜的优化,设计并制备了NbN/WNx、NbN/SiNx和NbN/AlN三种体系的纳米多层膜,对比研究了三种多层膜的界面特点和硬度增强效应。本论文的研究对单层膜的结构控制和多层膜中材料的选择、界面结构和硬度增强机制的理解提供了很好的借鉴作用。更多还原

【Abstract】 A considerable number of industrial applications are based on the use of thin films. To deposit these films, magnetron sputter deposition is a widely accepted and trusted technique. The magnetron sputtered transition metal nitrides thin films have attracted numerous attentions due to their exotic properties such as excellent hardness, the chemical inertness, high melting point, good chemical stability and high conductivity, and these properties are favorable for applications in microelectronic devices, microelectromechanical systems, and hard protective coatings for cutting tools. Despite the success of sputter deposited transition metal nitrides thin films, the understanding of the deposition method itself and the fundamental aspects of the growth of these films are still living and challenging topics in research. The properties depemicrtings based on transition metal nd strongly on the deposition conditions used because the deposition conditions influence the microstructure, the crystallographic orientation and also phase configuration of the transition metal nitrides films. This means that control of the functional properties of the deposited films calls for an understanding of the relationship between the deposition conditions and the resulting orientation, phase and ostructure. Therefore, the effects of deposition parameters on the preferred orientation, phase transition, and mechanical properties for the NbN and WN thin films have been explored.In addition, significant improvements in terms of the strength, hardness and toughness of coatings as well as wear, oxidation and corrosion resistance have been extensively reported in nanostructured multilayer coa nitrides as compared to those of monolithic coating tts for understanding the mechanisms of hardness enhancement for multilayer are needed. In is dissertation, NbN/WNx, NbN/SiNx, and NbN/AlN nanostructured multilayer oatings are deposited, and the dependence of mechanical properties on modulation eriodicity (Λ) is explored.The main results of this thesis are summarized as following:1.δ- andδ′-NbN thin films can be deposited via DC reactive magnetron sputtering in discharging a mixture of N2 and Ar gas. The deposition rate, intrinsic stress, preferred orientation, phase structure, and hardness for the obtained films are influenced significantly by nitrogen flow rate (FN2), substrate bias (Vb), and deposition pressure. A phase transition fromδ- NbN toδ′-NbN occurs when increasing nitrogen flow or substrate bias, or when decreasing deposition pressure, whose driving force is provided by strain energy minimization. The preferred orientation inδ- orδ′-NbN phase is dependent on the competition between the strain and surface energy. The higher intrinsic hardness forδ′-NbN, compared toδ-NbN, is attributed to its larger shear modulus and higher ideal strength, which was calculated using density functional theory. For ?-NbN film, as the deposition time (thinckness) increases, the alternating texture occurs. In addition, theδ-NbN andδ′-NbN films deposited at Vb= -40 and -200 V, respectively, have been subjected to annealing treatment at 900°C for 2 hr, in which no phase transition takes place.2. The influence of FN2 and Vb on the composition, phase structure, intrinsic stress and hardness for the obtained WNx films has been studied. It is difficult to obtain the WNx with a high nitrogen concentration duo to its low heat of formation. As proper Vb is applied on the substrate, the implantation of N2+ species and backscattered N species at subsurface sites plays an important role in increasing the nitrogen concentration in WNx films. Keeping Vb at -40 V, as FN2 increases, the N/W atomic ratio gradually increases, accompanying by a phase transition fromβ-W to s of the consti uent materials. However, because the crystalline structure and he interface of multilayered film are very complicated, the investigation of the hardening mechanism is still at a stage for data accumulation. Hence, further investigations on other new systemthcp hexagonal WN through fcc-W2N. On the other hand, the N/W atomic ratio gradually decreases with increasing the absolute value of Vb, resulting in an evolution from centration and a high density of defects, created by ion esponsible for the stress evolution with FN2. For the tween the defects creation and defect ssive stress with increasing the bsolute value of Vb from 80 to 200 V. Furthermore, the maximum hardness of 38.9 GPaardness enhancement can be observed in multilayer films, comofδ-NbN is coherent with (0002) of AlN, i.e., fcc-W2N structure toβ-W(N) through a mixture of fcc-W2N+β-W(N). As FN2 varies, an increase in the nitrogen conbombarding, are rwell-crystallized film, the competition berelaxation determines the evolution of the comprea is obtained for the film deposited at Vb=-120 V, which is attributed to the formation of mixed structure of fcc-W2N+β-W(N).3. The investigations on the NbN/WN multilayers indicate that NbN layer grow coherently with WN layer when modulation periodicity is less than 11 nm, accompanied by a remarkable increase in hardess and a decrease in stress. With further increasing modulation periodicity, W phase is observed at WN layer, resulting in a quick decline in hardness. Forδ′-NbN/W(N) multilayers, the W(N) (210)/δ′-NbN(101) strong texture is present, indicating that the lattice plane (210) of W(N) is coherent with (101) ofδ′-NbN. The maximum hardness of 42 GPa is obtained for theδ′-NbN/W(N) multilayers with modulation periodicity ?= 15.5nm.4. Forδ-NbN/SiNx multilayers, as SiNx layer thickness is smaller than or equal to 0.4 nm, the SiNx layers epitaxially grow on the crystalline NbN layers. Correspondingly, the multilayer films exhibit a significant hardness enhancement with a maximum hardness of 31.4 GPa. As SiNx layer thickness is larger than or equal to 0.6 nm, SiNx layers become amorphous, accompanied by the presence of (111) preferred orientation and decrease in hardness for the multilayer films. Forδ′-NbN/SiNx multilayer films, both the stress and hardness decrease with increasing SiNx layer thickness. No hpared toδ′-NbN single layer film.5. Forδ-NbN/AlN multilayers, the crystal structures ofδ-NbN layer and AlN layer are face-centered cubic and hexagonal, respectively, and the lattice plane (111) . The superhardness effects ofδ-NbN/AlN multilayers exist in a wide range of modulation periods due to the structural barriers (fcc/hexagonal) to dislocation motion betweenδ-NbN and AlN layers.更多还原