Anisotropy and texture in thin copper films—an elasto-plastic analysis

The role of elastic anisotropy on the stress inhomogeneity and effective behavior of columnar grained textured Cu thin films have been analyzed within a continuum framework. The analysis is based on a three-dimensional model of a film/substrate system. The film exhibits a fiber texture with (111), (001) and randomly oriented grains. Mainly two load cases have been considered. Biaxial loading of a film deposited on a silicon substrate and tensile loading of a film deposited on a polyimide substrate. The stress distributions in the (111) and (001) grains were generally found to be very different when subjected to biaxial loading and quite similar when subjected to tensile loading. When plastic behavior is invoked, a structural hardening effect is observed. The plastic behavior differs significantly between biaxial and tensile cyclic loading respectively. A new orientation dependent hardening law is proposed. This hardening law causes the plastic hardening behavior to be orientation dependent and scale with elastic anisotropy. The newly proposed hardening law is demonstrated on a film with small grain aspect ratio.     

Controlled biaxial deformation of nanostructured W/Cu thin films studied by X-ray diffraction

The deformation behaviour of 150 nm thick W/Cu nanocomposite deposited on polyimide substrates has been analysed under equi-biaxial tensile testing coupled to X-ray diffraction technique. The experiments were carried out using a biaxial device that has been developed for the DiffAbs beamline of SOLEIL synchrotron source. Finite element analysis has been performed to study the strain distribution into the cruciform shape substrate and define the homogeneous deformed volume. X-ray measured elastic strains in tungsten sub-layers could be carried out for both principal directions. The strain field was determined to be almost equi-biaxial as expected and compared to finite element calculations.     

Gliding at interface during thin film buckling: A coupled atomistic/elastic approach

The buckling of a Cu thin film deposited on a stiff W substrate is studied by means of molecular static simulations using interatomic potentials. The buckling of a preexisting delaminated part of the film is observed under a uniaxial strain without any further decohesion of the interface. A sliding phenomenon is also observed at the edges of the buckle which can be interpreted in terms of glide of misfit dislocations. Integrating this sliding effect in the Föppl-von Kármán theory of thin plates, a modified analytical expression for the deflection of the film has been derived which fits with the deflection obtained from the simulations.     

靶基距对Cu/Si(100)薄膜结构和残余应力的影响

采用高功率调制脉冲磁控溅射(MPPMS)技术在 Si(100)基体上沉积 Cu 薄膜,SEM 观察薄膜厚度及生长特征、XRD 分析薄膜晶体结构、nanoindentor 测量薄膜纳米硬度和弹性模量、Stoney 公式计算薄膜残余应力,研究沉积过程靶基距对 Cu / Si(100)薄膜沉积速率、微结构及残余应力的影响。 随着靶基距的增大,薄膜沉积速率降低,薄膜的生长结构由致密 T 区向 I 区转变,Cu(111)择优生长的晶粒逐渐减小,薄膜纳米硬度和弹性模量也相应降低,残余拉应力约为 400 MPa。 较小靶基距时增加的沉积离子通量和能量,决定了薄膜晶粒合并长大体积收缩过程的主要生长形式,导致了 Cu / Si(100)薄膜具有的残余拉应力状态。 MPPMS 工艺的高沉积通量和粒子能量可实现对 Cu / Si(100)薄膜残余应力的调控。     

磁控溅射Cu膜屈服强度的有限元计算

采用离子辅助轰击共溅射设备，在Si基体的(111)晶面上制得了所需的铜膜。采用纳米压入实验，获得不同退火温度下Cu膜的弹性模量和硬度。再在纳米压入实验的基础上，结合有限元模型计算不同退火温度下磁控溅射得到的Cu膜屈服强度。发现Cu膜的屈服强度远高于整体Cu材料的屈服强度，并且退火温度对薄膜的屈服强度影响很大。通过XRD测量发现其主要原因是退火改变了晶粒尺寸和多晶Cu膜的晶粒取向分布，而导致Cu膜屈服强度的降低。     

Enhanced adhesion of Cu-W thin films by ion beam assisting bombardment implanting

Cu-W thin film with high W content was deposited by dual-target DC-magnetron co-sputtering technology. Effects of the substrates surface treating technique on the adhesive strength of Cu-W thin films were studied. It is found that the technique of ion beam assisting bombardment implanting of W particles can remarkably improve the adhesive property of Cu-W thin films. Indentation and scratching test show that, the critical load is doubled over than the sample only sputter-cleaned by ion beam. The enhancing mechanism of ion beam assisting bombardment implanting of Cu-W thin films was analyzed. With the help of mid-energy Ar^＋ ion beam, W atoms can diffuse into the Fe-substrate surface layer; Fe atoms in the substrate surface layer and W atoms interlace with one another; and microcosmic mechanical meshing and diffusing combination on atom-scale among the Fe and W atoms through the film/substrate interface can be formed. The wettability and thermal expansion properties of the W atoms diffusion zone containing plentiful W atoms are close to those of pure W or W-based Cu-W film.     

Multilayer thin films/substrate system with variable film thickness subjected to non-uniform misfit strains

Current methodologies used to infer thin-film stress from curvature measurements are strictly restricted to stress and curvature states that are assumed to remain uniform over the entire film/substrate system. These methodologies have recently been extended to a single thin film of non-uniform thickness deposited on a substrate and subjected to the non-uniform misfit strain. Such methodologies are extended to multilayer thin films of non-uniform thickness deposited on a substrate in the present study. Each thin film may have its own non-uniform misfit strain and non-uniform thickness. We obtain the film stresses and system curvatures in terms of the misfit strains and thickness in thin films. We derive the film stresses and interface shear stresses in terms of system curvatures and film thicknesses. They all feature a “non-local” dependence on curvatures, which make full-field measurement a necessity for the experimental inference of such stresses.     

基片负偏压对Cu膜纳米压入硬度及微观结构的影响

测试了不同溅射偏压下Cu膜的纳米压入硬度，探讨了溅射偏压、残余应力及压痕尺寸效应对Cu膜硬度的影响。结果表明，随着溅射偏压的增大，薄膜晶粒尺寸及残余压应力均减小，导致薄膜的硬度增大，并在-80V达到最大值，随后有所降低。同时薄膜中的压痕尺寸效应对薄膜硬度随压入深度的分布有很大的影响。     

磁控溅射法制备W-Cu薄膜的研究

采用W70Cu30单靶磁控溅射与纯W、纯Cu双靶磁控共溅两种工艺,在多种基材上制备W-Cu薄膜,分析了薄膜的宏观形貌和组织结构.分析结果表明:单靶磁控溅射时,控制靶电压520 V,溅射电流0.8～1.2A,Ar气流量25 mL/min(标准状态),可在玻璃基体上镀得W-Cu薄膜,但退火时如温度过高,会使W和Cu两种元素原子偏聚加重;双靶磁控溅射时,控制Ar气流量20 mL/min(标准状态),Cu靶电流0.7A,W靶电流1.2A,溅射时间3600 s,可在硅基和玻璃基上镀得W-Cu薄膜,但在石墨基体、陶瓷基体及45钢基体上的镀膜效果不理想.     

Effect of substrate bias voltage on the texture and microstructure of Cu thin films deposited by ion beam deposition

Cu thin films deposited by non-mass separated ion beam deposition under various substrate bias voltages were investigated. The film textures and microstructure were analyzed by X-ray diffraction and field emission scanning electron microscopy, and the resistivity of the film was measured with the Van der Pauw method. It was found that the optimum negative substrate bias voltage for Cu films was −50 V. The Cu films deposited without substrate bias voltage showed a columnar grain structure with small grains and random orientation. However, when a substrate bias voltage of −50 V was applied, the Cu films had a non-columnar structure with a strong (111) texture and large grains. The electrical resistivity of the Cu films decreased remarkably with increasing negative substrate bias voltage, and reaching a minimum value of 1.8±0.13 μΩ cm at the substrate bias voltage of −50V.     

基体脉冲偏压对TiN/Cu纳米复合薄膜组织结构、力学及耐磨性能的影响

本文采用轴向磁场增强电弧离子镀在高速钢基体上沉积了TiN/Cu纳米复合薄膜,研究了基体脉冲偏压幅值对薄膜成分、结构、力学性能及耐磨性能的影响。结果表明,薄膜中铜含量随着脉冲偏压幅值的增加先增加而后降低,在一个较低的范围内(1.3-2.1at.%)。X射线衍射结果表明所有的薄膜均出现TiN相,并未观察到Cu相。薄膜的择优取向随着脉冲偏压幅值的增加而改变。薄膜的最高硬度为36GPa,是在脉冲偏压幅值为-200V时得到的,对应了1.6at.%的Cu含量。与纯的TiN薄膜相比,Cu的添加明显增强了薄膜的耐磨性能。     

Growth of highly oriented Pt(100) thin films on a MgO(100) seed layer deposited on Si(100) substrates by rf magnetron sputtering

The growth of highly oriented Pt(100) thin films on Si(100) substrates deposited by rf magnetron sputtering was studied using a MgO(100) seed layer. The effects of the sputtering parameters on the growth of the MgO(100) seed layer were investigated in order to obtain the deposition condition which gives the best crystalline quality of (100) oriented MgO thin films. A highly crystallized MgO(100) film was obtained at a substrate temperature of 425°C, a rf power of 4.4W/cm² and a pressure of 12.5 mTorr. The crystalline quality of the MgO film was greatly decreased when the Si substrate was oxidized. The degree of (100) preferred orientation of the Pt film deposited on a MgO(100)//Si(100) substrate was found to be sensitive to the thickness of the MgO(100) seed layer, which is explained by the thickness dependence of the crystalline quality and the surface roughness of the MgO seed layer. A highly oriented Pt(100) film, for which the I₂₀₀/(_I200+I₁₁₁) ratio was about 0.8, was obtained at 550°C on a 50 nm thick MgO seed layer.     

Effect of capping layer on hillock formation in thin Al films

The effect of capping layers on hillock formation has been studied in pure aluminum films. For this purpose, different capping materials (Ti, Mo, SiO₂) of various thicknesses (from 200 Å to 1000 Å) were deposited on an Al/glass substrate. The density, diameter and height of hillocks were analyzed after annealing for 400 min at 280 °C. As the thickness of the capping layer increases, the hillock density, diameter and height decreases. The total volume of hillocks per unit area of the film decreases while both the thickness and the biaxial modulus of the capping layers increases. Using a spherical cap model of the bulge test, a simple equation which can predict the total volume of hillocks per unit area of the film is suggested. The comparison shows excellent agreement between the modeled and experimental profiles.     

Microstructure and mechanical properties of pulsed DC magnetron sputtered nanocomposite Cr-Cu-N thin films

The nanocomposite Cr-Cu-N thin films have been deposited at a substrate temperature of 250 °C by a bipolar asymmetric pulsed DC reactive magnetron sputtering process. Different Cu contents ranging from 0.4 to 14.9 at.% were achieved. The structures of Cr-Cu-N thin films were analyzed by XRD. The surface and cross sectional morphologies of thin films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The nanoindentation and scratch tests were adopted to evaluate the mechanical and tribological properties of Cr-Cu-N coatings. The influences of Cu content on the structure, mechanical and tribological properties of Cr-Cu-N coatings were explored. It is observed that the columnar structure no longer exists when the Cu content exceeds 10.9 at.%. The stability of CrN phase in the coating is influenced by the Cu content. The scratching coefficient of thin films decreases with increasing Cu content. Sufficient adhesion and tribological properties of Cr-Cu-N coatings are achieved. The maximum average hardness around 20 GPa and scratching coefficient around 0.1 are found in the coatings with around 2.1 to 2.6 at.% Cu in this work.     

Mechanical properties and microstructures of Al-Cu Thin films with various heat treatments

The relationship between microstructure and mechanical properties has been investigated in Al-Cu thin films. The Cu content in Al-Cu samples used in this study ranges from 0 to 2 wt.% and substrate curvature measurement was used to measure film stress. In thin films, the constraints on the film by the substrate influence the microstructure and mechanical properties. Al-Cu thin films cooled from high temperatures have a large density of dislocations due to the plastic deformation caused by the thermal mismatch between the film and substrate. The high density of dislocations in the thin film enables precipitates to form inside the grain even during a very rapid quenching. The presence of a large density of dislocations and precipitates will in turn cause precipitation hardening of the Al-Cu films. The precipitation hardening is dominant at lower temperatures, and solid solution hardening is observed at higher temperatures in the tensile regime. Pure Al films showed the same values of tensile and compressive yield stresses at a given temperature during stress-temperature cycling.     

In situ accelerated micro-wear — A new technique to fill the measurement gap

A novel accelerated microtribological capability was implemented on a commercial ultra-low drift nanomechanical test system (NanoTest) by modification of the instrument's hardware. 10 and 25 μm spheroconical and Berkovich diamond probes were used in this study. To compare the accelerated micro-wear capability with existing nano-scratch tests, a range of thin film samples previously characterised were evaluated, including 80 nm ta-C film deposited on Si, 150 nm a-C:H thin film deposited on Si, metal-containing molybdenum disulphide (MoST) 70-150 nm, 70 nm a-C:H and 1 μm a-C films deposited on Si, multilayered 20 nm Si3N4/20 nm NiCr/80 nm Si3N4 multilayer coating deposited on float glass and additionally bulk Cu sample. Operational principles of the experimental setup are explained and reliability of the method is validated with a number of experiments. Results are presented and discussed following four experimental sections of this paper: (i) constant load micro-wear of various films on Si, (ii) constant load micro-wear kinetics of bulk Cu, (iii) ramped load micro-wear of thin films and (iv) tangential force calibration.     

Zn靶与掺铝ZnO靶共溅射制备ZnO:Al薄膜及其性能

采用Zn靶和ZnO(掺2%Al2O3(质量分数))陶瓷靶在玻璃衬底上共溅射沉积Al掺杂ZnO薄膜,即ZnO:Al透明导电薄膜,研究Zn靶溅射功率(0～90 W)和衬底温度(室温、100℃和200℃)对薄膜结构、形貌、光学和电学性能的影响。结果表明:按双靶共溅射工艺制备的ZnO:Al薄膜的晶体结构均为六角纤锌矿结构,且随着Zn靶溅射功率的增加,薄膜的结晶质量呈现出先改善后变差的规律,薄膜中的载流子浓度逐渐升高,电阻率逐渐降低,而薄膜的光学性能受其影响不大;随着衬底温度的升高,薄膜的结晶性能得到改善,薄膜的可见光透过率增强,电阻率降低。     

溅射功率对射频磁控溅射Al掺杂ZnO（ZAO）薄膜性能的影响

用射频磁控溅射技术,在纯氩气氛中不同溅射功率（120 W~210 W）下于玻璃衬底上制备了Al掺杂ZnO（ZAO）薄膜。利用X射线衍射仪（XRD）、扫描电子显微镜（SEM）、光谱仪和四探针测试仪等对所制备的薄膜进行了晶体结构、光学和电学性能分析。结果表明,纯氩气氛中不同溅射功率下玻璃衬底上原位沉积的ZAO薄膜具有明显的c轴择优取向性,它没有改变ZnO的六角纤锌矿结构;ZAO薄膜的可见光区平均透光率不强烈依赖于溅射功率,为75%左右;原位沉积ZAO薄膜的电阻率达到102Ω.cm数量级范围,随溅射功率由120 W增大到210 W时,薄膜电阻率从132.67Ω.cm降低到21.08Ω.cm。     

Multi-walled carbon nanotube-reinforced copper nanocomposite coating fabricated by low-pressure cold spray process

Multi-walled carbon nanotube (MWCNT)-reinforced copper (Cu) nanocomposite coatings were successfully deposited on aluminum (Al) substrate by a cold spraying process at a low pressure. The microstructure and the Raman spectrum of the low-pressure-cold-sprayed MWCNT–Cu nanocomposite coating showed that the MWCNTs maintained their tube structure in the Cu matrix, even though structural damage to the MWCNTs increased slightly. MWCNT–Cu nanocomposite-coated Al exhibits higher thermal diffusivity than pure-Cu-coated Al with a comparable hardness. The higher thermal diffusivity of the MWCNT–Cu coating could be explained by the dispersion of MWCNTs within the clean and closed CNT/Cu interfaces, which were achieved with the aid of compressive stress during the cold spraying.