Influence of thermal annealing and ultraviolet light irradiation on LaF3 thin films at 193 nm

Lanthanum fluoride (LaF3) thin films were prepared by resistive heating evaporation and electron-beam gun evaporation under the same deposition rate, deposition substrate temperature, and vacuum pressure. The coated LaF3 films were then treated by heat annealing and UV light irradiation. The optical properties, microstructures, stress, and laser-induced damage threshold (LIDT) at a wavelength of 193 nm were investigated. The surface roughness, optical loss, stress, and LIDT of the films were improved after the annealing. The films had better properties when irradiated by UV light as compared with heat annealing.     

Annealing dependence of residual stress and optical properties of TiO2 thin film deposited by different deposition methods

Titanium oxide (TiO(2)) thin films were prepared by different deposition methods. The methods were E-gun evaporation with ion-assisted deposition (IAD), radio-frequency (RF) ion-beam sputtering, and direct current (DC) magnetron sputtering. Residual stress was released after annealing the films deposited by RF ion-beam or DC magnetron sputtering but not evaporation, and the extinction coefficient varied significantly. The surface roughness of the evaporated films exceeded that of both sputtered films. At the annealing temperature of 300 degrees C, anatase crystallization occurred in evaporated film but not in the RF ion-beam or DC magnetron-sputtered films. TiO(2) films deposited by sputtering were generally more stable during annealing than those deposited by evaporation.     

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)).     

Characterization of AlF3 thin films at 193 nm by thermal evaporation

Aluminum fluoride (AlF3) was deposited by a resistive heating boat. To obtain a low optical loss and high laser-induced damage threshold (LIDT) at 193 nm, the films were investigated under different substrate temperatures, deposition rates, and annealing after coating. The optical property (the transmittance, refractive index, extinction coefficient, and optical loss) at 193 nm, microstructure (the cross-sectional morphology, surface roughness, and crystalline structure), mechanical property (stress), and LIDT of AlF3 thin films have been studied. AlF3 thin films deposited at a high substrate temperature and low deposition rate showed a lower optical loss. The highest LIDT occurred at the substrate temperature of 150 degrees C. The LIDT of the films prepared at a deposition rate of 2 A/s was higher than that at other deposition rates. The annealing process did not influence the optical properties too much, but it did increase the LIDT and stress.     

Ultraviolet optical and microstructural properties of MgF2 and LaF3 coatings deposited by ion-beam sputtering and boat and electron-beam evaporation

Single layers of MgF2 and LaF3 were deposited upon superpolished fused-silica and CaF2 substrates by ion-beam sputtering (IBS) as well as by boat and electron beam (e-beam) evaporation and were characterized by a variety of complementary analytical techniques. Besides undergoing photometric and ellipsometric inspection, the samples were investigated at 193 and 633 nm by an optical scatter measurement facility. The structural properties were assessed with atomic-force microscopy, x-ray diffraction, TEM techniques that involved conventional thinning methods for the layers. For measurement of mechanical stress in the coatings, special silicon substrates were coated and analyzed. The dispersion behavior of both deposition materials, which was determined on the basis of various independent photometric measurements and data reduction techniques, is in good agreement with that published in the literature and with the bulk properties of the materials. The refractive indices of the MgF2 coatings ranged from 1.415 to 1.440 for the wavelength of the ArF excimer laser (193 nm) and from 1.435 to 1.465 for the wavelength of the F2 excimer laser (157 nm). For single layers of LaF3 the refractive indices extended from 1.67 to 1.70 at 193 nm to approximately 1.80 at 157 nm. The IBS process achieves the best homogeneity and the lowest surface roughness values (close to 1 nm(rms)) of the processes compared in the joint experiment. In contrast to MgF2 boat and e-beam evaporated coatings, which exhibit tensile mechanical stress ranging from 300 to 400 MPa, IBS coatings exhibit high compressive stress of as much as 910 MPa. A similar tendency was found for coating stress in LaF3 single layers. Experimental results are discussed with respect to the microstructural and compositional properties as well as to the surface topography of the coatings.     

Fluoride antireflection coatings deposited at 193 nm

Antireflection coatings for 193 nm composed of low-index (MgF(2) and AlF(3)) and high-index (LaF(3) and GdF(3)) materials are deposited by the resistive heating boat method at a substrate temperature of 300 degrees C. The optical characteristics (reflectance and optical loss), microstructure (morphology and surface roughness), stress, and laser-induced damage threshold (LIDT) of the coatings are investigated and discussed. The related reflection at 193 nm of the four kinds of antireflection coatings is smaller than 0.2% and the optical loss is less than 0.15%. Of the fluoride antireflection coatings, AlF(3)/GdF(3) had the lowest stress value. Antireflection coatings with AlF(3) as the low-index material had higher LIDT values than when MgF(2) was used.     

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.     

Analysis of long-term internal stress and film structure of SiO2 optical thin films

Recently, the demand for durability of optical thin films, which have long been used, has been growing as the performance of optical components improves. The stress of a film is an important parameter that is related to its adhesion. The electron beam (EB) and ion-assisted deposition (IAD) methods are widely used to fabricate optical thin films. However, there are few reports on long-term internal stress, despite the importance of this issue. Here we discuss the time dependence of the stress of SiO2 optical thin films in terms of optical characteristics in the infrared region. It was found that SiO2 thin films prepared by the EB and IAD methods exhibited compression stress. The Si-OH molecular bond was observed at around 930?cm(-1) in the Fourier transform infrared spectroscopy spectrum of the sample prepared by the EB method, which exhibited a large change in internal stress after an elapsed time. It is considered that this change in bonding was related to the decrease in the stress of the films.     

Mechanical stress and thermal-elastic properties of oxide coatings for use in the deep-ultraviolet spectral region

Mechanical stress and the structures of SiO2, Al2O3, and HfO2 single oxide layers and of high-reflection multilayer coatings deposited by reactive evaporation, plasma ion-assisted deposition, and ion-beam sputtering have been studied. The stress was related to the microstructure and to the incorporation of water by means of infrared spectroscopy. From the slopes of measured stress-temperature curves of these coatings deposited onto two substrate materials (silicon and fused silica), the biaxial moduli and the thermal expansion coefficients of the films were estimated.     

Internal stress and optical properties of Nb2O5 thin films deposited by ion-beam sputtering

The influence on the internal stress and optical properties of Nb2O5 thin films with ion-beam energy was investigated. Nb2O5 thin films were deposited on unheated glass substrates by means of ion-beam sputtering with different ion-beam voltage, Vb. The refractive index, extinction coefficient, and surface roughness were found to depend on the ion-beam energy. The stresses in thin films were measured by the phase-shifting interferometry technique. The film stress was also found to be related to Vb, and a high compressive stress of -0.467 GPa was measured at Vb = 850 V. The Nb2O5-SiO2 multilayer coatings had smaller average compressive stress as compared with single-layer Nb2O5 film.     

A comparison of TiN films produced by reactive d.c. sputtering and ion-assisted deposition

The properties of TiN films produced by reactive d.c. sputtering have been compared with those formed by deposition during irradiation by 10 keV nitrogen ions. Films were deposited on aluminium, nickel, molybdenum, silicon and titanium substrates which were chosen because they have a range of mechanical properties. The composition of the films has been studied by Rutherford backscattering, nuclear reaction analysis and transmission electron microscopy and data concerning their hardness and adhesion are also presented. It was found that the films produced by ion-assisted deposition (IAD) were nearly stoichiometric TiN with a predominant (100) orientation while the reactively sputtered films were less crystalline and contained a significant amount of oxygen and carbon throughout the film. There was also considerable improvement in the adhesion of the IAD films but their hardness was only marginally improved.     

Material properties and growth control of undoped and Sn-doped In2O3 thin films prepared by using ion beam technologies

Undoped (IO) and Sn-doped In₂O₃ (ITO) films have been deposited on glass and polymer substrates by an advanced ion beam technologies including ion-assisted deposition (IAD), hybrid ion beam, ion beam sputter deposition (IBSD), and ion-assisted reaction (IAR). Physical and chemical properties of the oxide films and adhesion between films and substrates were improved significantly by these technologies. By using the IAD method, non-stoichiometry and microstructure of the films were controlled by changing assisted oxygen ion energy and arrival ratio of assisted oxygen ion to evaporated atoms. Relationships between structural and electrical properties in ITO films on glass substrates were intensively investigated by using the IBSD method with changing ion energy, reactive gas environment, and substrate temperature. Smooth-surface ITO films (R_rms ≤ 1 nm and R_p-v ≤ 10 nm) for organic light-emitting diodes were developed with a combination of deposition conditions with controlling microstructure of a seed layer on glass. IAR surface treatment enormously enhanced the adhesion of oxide films to polymer substrate. The different dependence of IO and ITO films' properties on the experimental parameters, such as ion energy and oxygen gas environment, will be intensively discussed.     

A comparative study of the UV optical and structural properties of SiO2, Al2O3, and HfO2 single layers deposited by reactive evaporation, ion-assisted deposition and plasma ion-assisted deposition

Growing requirements for the optical and environmental stability, as well as the radiation resistance against high-power laser radiation, especially for optical interference coatings used in the ultraviolet spectral range, have to be met by new, optimised, thin-film deposition technologies. For applications in the UV spectral range, the number of useful oxide thin film materials is very limited due to the higher absorption at wavelengths near to the electronic bandgap of the materials. Applying ion-assisted processes offers the ability to grow dense and stable films, but in each case careful optimisation of the deposition process (evaporation rate, substrate temperature, bombarding gas, ion energy and ion current density) has to achieve a balance between densification of the layers and the absorption. High-quality coatings and multilayer interference systems with SiO₂ as the low-index material can be deposited by various physical vapour deposition technologies, including reactive e-beam evaporation, ion-assisted deposition and plasma ion-assisted deposition. In order to improve the degradation stability of dielectric mirrors for use in UV free-electron laser optical cavities, a comparative study of the properties of SiO₂, Al₂O₃ and HfO₂ single layers was performed, and was addressed to grow very dense films with minimum absorption in the spectral range from 200 to 300 nm. The films were deposited by low-loss reactive electron-beam evaporation, by ion-assisted deposition using a ‘Mark II’ ion source, and by plasma ion-assisted deposition using the advanced plasma source. Optical and structural properties of the samples were studied by spectral photometry, infrared spectroscopy, X-ray diffraction and reflectometry, as well as by investigation of the surface morphology. The interaction of UV radiation with photon energy values close to the bandgap was studied. For HfO₂ single layers, laser-induced damage thresholds at 248 nm were determined in the 1-on-1 and 1000-on-1 test modes as a function of the deposition technology and film thickness.     

Ion-assisted sputtering deposition of antireflection film coating for flexible liquid-crystal display applications

The optical properties and surface morphologies of sputtering films both without and with use of the ion-assisted deposition (IAD) technique are investigated and compared. Optimal antireflection (AR) coating films with SiO2/Nb2O5 layers, which are grown at 80 degrees C with a 15 cm distance between target and substrate, 55 SCCM oxygen flow (SCCM denotes cubic centimeters per minute at STP), and 1250 W magnetron sputtering power with use of the IAD technique, are used to study the optical performance. By using an atomic force microscope to investigate the surface of the sputtered Nb2O5 films, we find that the films' roughness is 0.185 nm. On a flexible hardness polycarbonate (HPC) substrate with the multilayer AR films, the peak transmittances measured in the visible range are 95.89% and 93.40%, respectively, for coatings with and without use of the IAD sputtering technology. These results are better than those measured with a bare HPC substrate (91.25%) and are well above the commercial liquid-crystal display standard (90%) and flexible application.     

单层二氧化铪（HfO2）薄膜的特性研究

利用电子束蒸发、离子束辅助沉积和离子束反应溅射三种制备方法制备了单层HfO2薄膜,对薄膜样品的晶体结构、光学特性、表面形貌以及吸收特性进行了研究。实验结果表明,薄膜特性与制备工艺有着密切的关系。电子束蒸发和离子束反应溅射制备的薄膜为非晶结构,而离子束辅助制备的薄膜为多晶结构。电子束蒸发制备的薄膜折射率较低,薄膜比较疏松,表面粗糙度较小,吸收相对较小,而离子束辅助以及离子束反应溅射制备的薄膜折射率较高,薄膜的结构比较致密,但表面粗糙度较大,吸收相对较大。不同制备工艺条件下薄膜的光学能隙范围为5.30～5.43eV,对应的吸收边的范围为228.4～234.0nm。     

Fluoride antireflection coatings for deep ultraviolet optics deposited by ion-beam sputtering

Optically high quality coatings of fluoride materials are required in deep ultraviolet (DUV) lithography. We have applied ion-beam sputtering (IBS) to obtain fluoride films with smooth surfaces. The extinction coefficients were of the order of 10(-4) at the wavelength of 193 nm due to the reduction of their absorption loss. The transmittance of the MgF2/GdF3 antireflection coating was as high as 99.7% at the wavelength of 193 nm. The surfaces of the IBS deposited films were so smooth that the surface roughness of the A1F3/GdF3 film was comparable with that of the CaF2 substrate. The MgF2/GdF3 coating fulfilled the temperature and humidity requirements of military specification. Thus, the IBS deposited fluoride films are promising candidate for use in the DUV lithography optics.     

Effects of ion energy on internal stress and optical properties of ion-beam sputtering Ta2O5 films

Abstract

The effects of ion-beam energy on the internal stress and optical properties of tantalum pentoxide (Ta₂O₅) thin film have been investigated. Ta₂O₅ thin films were deposited on unheated glass substrates by ion-beam sputter deposition (IBSD) with different ion-beam voltage V _b. The mechanical properties, internal stress and surface roughness, and the optical properties, refractive index and absorption, were studied directly after deposition. The refractive index, extinction coefficient and surface roughness were found to depend on the ion-beam energy. The internal stresses were measured by the phase-shifting interferometry technique. The film stress was also found to be related to V _b, and a high compressive stress of -0.560 GPa was measured at V _b = 750 V. Ta₂O₅/SiO₂ multilayer coatings had smaller average compressive stress than single-layer Ta₂O₅ film.     

Properties of indium tin oxide films prepared by ion-assisted deposition

Conducting transparent films of indium tin oxide were deposited by 100 eV oxygen-ion-assisted deposition. A refractive index of 2.13 at 550 nm was obtained for films deposited onto ambient temperature substrates. The refractive index decreased with increasing substrate temperature to a value of 2.0 at 400°C. The sheet resistance of films 135 nm thick decreased from 800 Ω/□ for layers deposited onto room temperature substrates to around 25 Ω/□ at 400°C. Structural studies revealed that ion-assisted deposition onto ambient temperature substrates produced amorphous films, and that at temperatures above 100°C the films exhibit In₂O₃ crystallinity. In addition, it was found that the number of voids in the ion-bombarded films was reduced relative to that in films produced by conventional reactive evaporation.     

Effect of the working gas of the ion-assisted source on the optical and mechanical properties of SiO2 films deposited by dual ion beam sputtering with Si and SiO2 as the starting materials

Silicon and fused-silica targets are used as the starting materials for depositing silicon oxide (SiO2) films. The SiO2 films are prepared by a dual ion beam sputtering deposition system with a main ion source and an ion-assisted source with different working gases. The films deposited are then examined and compared by using a visible spectrophotometer, a Fourier-transform IR spectrophotometer, an atomic force microscope, and contact angle instruments. A Twyman-Green interferometer is employed to study the film stress by phase-shift interferometry. All the SiO2 films show excellent optical properties with extra-low extinction coefficients (below 2x10(-5)) and have no water absorption. When the working gas is O2 for the ion-assisted source, the deposited SiO2 films show good properties in terms of stress and roughness and with a good molecular bonding structure order for both targets. However, SiO2 films deposited from the fused-silica target had a larger contact angle, while those deposited from the silicon target had 2.5 times the deposition rate.     

离子辅助蒸发TixOy制备氧化钛薄膜及特性

采用离子辅助沉积的方法,分别以TiO2和Ti3O5为初始膜料在K9玻璃上制备了氧化钛薄膜,并研究了离子束流密度对以Ti3O5为膜料制备的薄膜透射性能的影响.实验结果表明,热处理前薄膜都为无定形结构;热处理后有明显的锐钛矿结构(101)择优取向,以Ti3O5为初始膜料制备的薄膜吸收优于以TiO2为膜料制备的薄膜;薄膜透射率极值随束流密度增大有临界值.