Residual stress in obliquely deposited MgF2 thin films

MgF(2) films with a columnar microstructure are obliquely deposited on glass substrates by resistive heating evaporation. The columnar angles of the films increases with the deposition angle. Anisotropic stress does not develop in the films with tilted columns. The residual stresses in the films depend on the deposition and columnar angles in a columnar microstructure.     

氮化硅介质薄膜内应力的实验研究

研究了等离子体增强化学气相沉积氮化硅介质薄膜的内应力。采用钠光平面干涉测量了氮化硅薄膜内应力,通过改变薄膜沉积时的工艺参数,考察了反应气体流量比、沉积温度、射频功率密度等因素对氮化硅薄膜内应力的影响。在此基础上,对氮化硅介质薄膜本征应力的形成机制进行了分析讨论。     

液相基底上铝薄膜的开裂与折叠行为研究

利用真空蒸发方法在液相基底(硅油)上成功制备出具有自由支撑边界和界面条件的金属铝薄膜系统,研究了薄膜的开裂和折叠行为。结果表明:沉积过程中,硅油基底的受热膨胀使铝薄膜处于较大张应力状态,伴随着张应力的释放,薄膜中出现开裂形貌。沉积完成之后,系统的逐渐冷却促使硅油基底收缩,并使得铝薄膜处于较大压应力状态,伴随着压应力的释放,薄膜中出现特征的折叠形貌。基于液相基底上金属薄膜的特殊力学行为,对此类开裂和折叠形貌进行了深入阐述。     

Microstructure of magnesium fluoride films deposited by boat evaporation at 193 nm

Single layer magnesium fluoride (MgF2) was deposited on fused-silica substrates by a molybdenum boat evaporation process at 193 nm. The formation of various microstructures in relation to the different substrate temperatures and deposition rates were investigated. The relation between these microstructures (including cross-sectional morphology, surface roughness, and crystalline structures), the optical properties (including refractive index and optical loss) and stress, were all investigated. It was found that the laser-induced damage threshold (LIDT) would be affected by the microstructure, optical loss, and stress of the thin film. To obtain a larger LIDT value and better optical characteristics, MgF2 films should be deposited at a high substrate temperature (300 degrees C) and at a low deposition rate (0.05 nm s(-1)).     

The effect of grain size and film thickness on the thermal expansion coefficient of copper thin films

Cu thin films underwent thermal cycling to determine their coefficient of thermal expansion (CTE). The thermal stress of the Cu thin films with various microstructures (different grain size and film thickness) was measured using a curvature measurement system. The thermal expansion coefficients of the films were obtained from the slope of the stress-temperature curve with the knowledge of the Young's modulus and Poisson's ratio. The change in thermal stress with temperature of the Cu thin films tended to decrease with increasing grain size, resulting in an increase in the CTE. The thickness of Cu thin film had little effect on the thermal stress or the CTE.     

High-speed oxide coating by laser chemical vapor deposition and their nano-structure

Oxide thick films, partially yttria-stabilized zirconia (YSZ) and titania (TiO₂), were prepared by laser chemical vapor deposition (LCVD). The assistance of laser tremendously increased the deposition rate for YSZ and TiO₂ films up to 660 and 2500 μm/h, respectively. The increase in the deposition rate was accompanied by plasma formation around the deposition zone, and the plasma was observed over critical values of laser power and substrate pre-heating temperature. A wide variety of morphologies of films from feather-like columnar to dense microstructures were obtained depending on deposition conditions. The columnar structure contained a large amount of nano-pores at columnar boundary and inside grains. These columnar structure and nano-pores were advantageous for applying YSZ films to thermal barrier coatings.     

Anisotropic optical properties of ZnS thin films with zigzag structure

ZnS sculptured thin films produced by thermal evaporation method using the glancing angle deposition technique at different deposition angles (0, 30, 60, 70 and 80\({^{\circ }}\)) are reported. The structural and optical properties of the prepared samples are investigated systematically using X-ray diffraction (XRD) and UV–VIS spectroscopy techniques. The XRD studies show cubic structure for the prepared films and deposition angle dependence of lattice constants, intrinsic stress, tensile stress and dislocation density. The obtained transmittance spectra in the range 380–850 nm for both s- and p-polarized light at normal incidence angle are used to study the s- and p-refractive indices and in-plane birefringence of the ZnS films. The maximum birefringence is evaluated at incident flux angle \(\alpha = 70{^{\circ }}\). Both the refractive index and packing density of the films decrease with increasing deposition angle, which confirm the structural inhomogeneity and porosity nature of the films.     

Porosity control in zig-zag vapor-deposited films

Many of the physical, chemical and mechanical properties of vapor-deposited films are strong functions of the volume fraction and morphology of pores that are entrained during film growth. It has recently been shown that by growing films under low surface mobility conditions (at homologous growth temperatures [T/T_m] of 0.5 or less) and alternating the inclination of a substrate to the vapor plume, it is possible to grow columnar zig-zag structures. Films with such a microstructure are of significant interest for thermal protection applications because they reduce the through-thickness thermal conductivity and the in-plane elastic modulus. They therefore provide a means for increasing the coating's thermal resistance while retaining its ability to accommodate thermal expansion mismatch with the underlying substrate during thermal cycling. A kinetic Monte Carlo (KMC) method has been utilized to simulate void evolution during physical vapor deposition of zig-zag microstructures and is used to explore methods for controlling pore morphology. The pore morphology of zig-zag coatings is found to depend strongly on the angular distribution of the incident flux. As the flux incidence angle changes from highly collimated to a cosine distribution, the coating changes from a uniform columnar to a hierarchical structure incorporating many length scales of porosity. The hierarchical nature of this structure is accentuated by increasing the substrate oscillation angle. A more narrowly distributed flux is found to result in denser films. Simulations have also revealed that the widely observed competitive growth phenomenon responsible for intercolumn porosity depends strongly on the incident flux distribution and is amplified by oblique deposition.     

Optical properties and residual stress of YbF3 thin films deposited at different temperatures

The influence of deposition temperature on the optical properties, microstructure, and residual stress of YbF(3) films, deposited by electron-beam evaporation, has been investigated. The increased refractive indices and surface roughness of YbF(3) films indicate that the film density and columnar structure size increase with deposition temperature. At the same time, higher packing density reduces absorption of moisture. The residual stress is related to deposition temperature and to substrate. For the samples deposited on BK7, the residual stress mainly comes from intrinsic stress, however, for those on fused silica, thermal stress is the dominant factor of total residual stress.     

Anisotropic scatter patterns and anomalous birefringence of obliquely deposited cerium oxide films

Cerium oxide films formed by electron-beam evaporation onto oblique substrates are shown to scatter light strongly into spatially anisotropic distributions and to exhibit large normal-incidence birefringence Δ n = n(s) - n(p). The apparatus for direct recording of a useful projection of the scatter distributions is described. Characteristic differences in scatter patterns recorded for cerium oxide, relative to those from tilted columnar titania and zirconia films, are believed to be associated with unusual microstructures recorded for cerium oxide films by scanning electron microscopy. With increasing angle of deposition, the microstructure of cerium oxide was observed to change from densely packed columns to partially isolated needlelike columns at angles that do not obey the tangent rule. In particular, deposition at 55° yielded columns nearly perpendicular to the substrate, yet the normal-incidence birefringence was large. The retardation of the films was recorded as a function of angle of incidence for propagation in the deposition plane. A turning point near 0° incidence for the 55° film confirmed that one principal axis is perpendicular to the substrate. Significant bunching of columns into rows running perpendicular to the deposition plane was recorded by scanning electron microscopy and may account for both the scatter and the birefringence.     

Effect of thermal annealing on the microstructure and morphology of erbium films

The effects of thermal annealing on the microstructure and morphology of erbium films were investigated by X-ray diffraction and scanning electron microscopy. All the erbium films were fabricated by electron-beam vapor deposition. The columnar grain sizes of as-received erbium films increased with the substrate temperatures and were enlarged by the coalescence and migration of grains during the high temperature annealing. The intrinsic stresses of erbium films, fabricated at a low substrate temperature (200 °C), were relaxed accompanied with the appearance of cracks on the films surface. The films deposited at 200 °C had (002) preferred orientation, and the film deposited at 450 °C had mixed (100) and (101) texture. The peak positions and the full width at half maximum of (100), (002), and (101) diffraction lines of erbium shift towards higher angles and sharply decrease during the annealing process, indicating that the stress inside the film was relaxed.     

Comparing internal stress in diamond-like carbon films with different structure

Diamond-like carbon (DLC) films with different structures were deposited on Si (100) and stainless steel substrates in a hybrid deposition system with Ar and CH₄ as the feedstocks. The effects of the bias voltage, Ti-interlayer, Ti functional gradient layer and Ti-doping on the internal stress in DLC films were investigated. The results show that the internal stress in DLC films arises from both the intrinsic stress generated during the film growth and the thermal stress generated due to the mismatching of the thermal expansion coefficient between the DLC films and the substrate materials. The intrinsic stress can be released through doping titanium element at the expense of reducing the sp³/sp² ratio. The thermal stress in DLC films can be decreased through introducing Ti-interlayer or Ti functional gradient layer. Noticeably, DLC films with very low internal stress deposited on stainless steel can be obtained through the combination of Ti-doping and Ti functional gradient layer.     

Film morphology modification in ion-assisted glancing angle deposition

Porous structured films grown with the glancing angle deposition technique have been widely studied for thin film optical device applications. We report the use of ion assistance to modify the structural and optical properties of porous silicon dioxide and titanium dioxide columnar thin films grown at deposition angles of 70° and 85°. Optical characterization studies show that tilted columnar structures will undergo an increase in tilt angle and film density with increasing ion dose. These two trends contrast with unassisted films where film density and column tilt angle are primarily controlled by the deposition angle. Thus, a regime of film structures simultaneously exhibiting high film density and large column tilt angle is enabled by incorporating an ion-assisted process. The phisweep substrate motion algorithm for minimizing columnar anisotropy used in conjunction with ion-assisted deposition provides additional control over film morphology and expands the utility of this modified fabrication process.     

Microstructure-related properties at 193 nm of MgF2 and GdF3 films deposited by a resistive-heating boat

MgF2 and GdF3 materials, used for a single-layer coating at 193 nm, are deposited by a resistive-heating boat at specific substrate temperatures. Optical characteristics (transmittance, refractive index, extinction coefficient, and optical loss) and microstructures (morphology and crystalline structure) are investigated and discussed. Furthermore, MgF2 is used as a low-index material, and GdF3 is used as a high-index material for multilayer coatings. Reflectance, stress, and the laser-induced damage threshold (LIDT) are studied. It is shown that MgF2 and GdF3 thin films, deposited on the substrate at a temperature of 300 degrees C, obtain good quality thin films with high transmittance and little optical loss at 193 nm. For multilayer coatings, the stress mainly comes from MgF2, and the absorption comes from GdF3. Among those coatings, the sixteen-layer design, sub/(1.4L 0.6H)8/air, shows the largest LIDT.     

Growth and characterisation of SiC films deposited on a-SiO2/Si (100) substrates

Abstract

The growth of polycrystalline SiC films has been carried out by low pressure chemical vapour deposition in a horizontal quartz reaction chamber using tetramethylsilane and H2 as the precursor gas mixture. Silicon (100) wafers were used as substrates. A thin Si O₂ amorphous layer of ~6 nm was formed before SiC deposition to reduce the strain induced by the 8% difference in thermal expansion coefficients between SiC and Si. Samples were. analysed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and infrared reflectivity. The structure of films grown at temperatures between 950 and 1150°C varies from amorphous to polycrystalline SiC. Preferential [111] orientation and columnar growth of polycrystalline films develops with increasing temperature.

MST/3317     

High-rate deposition of nanostructured SiC films by thermal plasma PVD

With ultrafine SiC powder as starting material, thermal plasma physical vapor deposition has been applied successfully to the deposition of SiC films on Si substrates. The control of processing parameters such as substrate temperature, powder feeding rate and composition of plasma gases, permits the deposition of SiC films on a wide area of around 400 cm² with a variety of microstructures from amorphous to nanostructured and with various morphologies from dense to columnar. For the nanostructured case, the crystallite size was between 3 and 15 nm and the maximum deposition rate calculated based on the actual deposition duty time reached 200 nm/s. The deposition mechanism is discussed briefly.     

High-rate deposition of nanostructured SiC films by thermal plasma PVD

With ultrafine SiC powder as starting material, thermal plasma physical vapor deposition has been applied successfully to the deposition of SiC films on Si substrates. The control of processing parameters such as substrate temperature, powder feeding rate and composition of plasma gases, permits the deposition of SiCfilms on a wide area of around 400 cm² with a variety of microstructures fromamorphous to nanostructured and with various morphologies from dense to columnar. For the nanostructured case, the crystallite size was between 3 and 15 nm and the maximum deposition rate calculated based on the actual deposition duty time reached 200 nm/s. The deposition mechanism is discussed briefly.     

Ag-MgF2金属陶瓷薄膜的制备及其微观结构研究

用真空双蒸发源交替蒸发法和单蒸发源混合瞬时蒸发法制备了Ag-MgF2金属陶瓷薄膜。透射电镜、电子衍射、X射线衍射以及X射线光电子能谱分析结果表明，薄膜由晶态超微粒Ag镶嵌于主要为非晶态的MgF2中构成。Ag-MgF2形成的金属陶瓷复合晶体结构所对应的主要谱峰为d=0．26102，0．23540，0．20393nm。用真空单蒸发源混合瞬时蒸发法制备的Ag-MgF2薄膜表面元素的结合能大于双蒸发源交替蒸发法制备的薄膜表面元素的结合能。     

Effects of annealing on the optical, structural, and chemical properties of TiO2 and MgF2 thin films prepared by plasma ion-assisted deposition

Effects of thermal annealing at 400 degrees C on the optical, structural, and chemical properties of TiO2 single-layer, MgF2 single-layer, and TiO2/MgF2 narrow-bandpass filters deposited by conventional electron-beam evaporation (CE) and plasma ion-assisted deposition (PIAD) were investigated. In the case of TiO2 films, the results show that the annealing of both CE and PIAD TiO2 films increases the refractive index slightly and the extinction coefficient and surface roughness greatly. Annealing decreases the thickness of CE TiO2 films drastically, whereas it does not vary that of PIAD TiO2 films. For PIAD MgF2 films, annealing increases the refractive index and decreases the extinction coefficient drastically. An x-ray photoelectron spectroscopy analysis suggests that an increase in the refractive index and a decrease in the extinction coefficient for PIAD MgF2 films after annealing may be related to the enhanced concentration of MgO in the annealed PIAD MgF2 films and the changes in the chemical bonding states of Mg 2p, F 1s, and O is. It is found that (TiO2/MgF2) multilayer filters, consisting of PIAD TiO2 and CE MgF2 films, are as deposited without microcracks and are also thermally stable after annealing.     

Al+MgF2作为真空紫外傅立叶变换光谱仪分束膜之光谱特性研究

根据在研VUV FTS分束器的技术要求 ,进行采用Al MgF2 材料制作紫外 真空紫外波段分束膜的实验研究。理论上通过数据计算分析了膜层选材及设计的可行性 ,制备了Al MgF2 分束膜 ,建立了以Seya Namioka单色仪为主体的实验装置 ,测量了紫外熔石英基底上镀制分束膜 5°入射的光谱特性 ,给出结果分析。扩大了Al MgF2 膜的应用范围