Deposition Of Optical Thin Films Research Articles

Atomistic Simulation of Physical Vapor Deposition of Optical Thin Films.

A review of the methods and results of atomistic modeling of the deposition of thin optical films and a calculation of their characteristics is presented. The simulation of various processes in a vacuum chamber, including target sputtering and the formation of film layers, is considered. Methods for calculating the structural, mechanical, optical, and electronic properties of thin optical films and film-forming materials are discussed. The application of these methods to studying the dependences of the characteristics of thin optical films on the main deposition parameters is considered. The simulation results are compared with experimental data.

In-situ interferometric monitoring of optical coatings.

We present a new method for the in situ measurement of the amplitude and phase of the reflection coefficient of a plane substrate installed in a mechanical holder rotating at high speed (120 turns per minute) during the deposition of optical thin films. Our method is based on digital holography and uses a self-referenced scheme to cancel the effects of the severe constraints generated by the vibrational and thermal environment of the deposition machine.

Report on the 11th Seminar on Techniques for Manufacturing, “Fundamentals and Applications of Optical Thin Film Deposition”

Report on the 11th Seminar on Techniques for Manufacturing, “Fundamentals and Applications of Optical Thin Film Deposition”

근적외선 반사 박막 특성 연구

Abstract Near infrared blocking function in energy saving window glass is required. The design, deposition and characteristics of optical thin films for reflection of near-infrared light were studied. The optical thin film is designedas laminated film structure with low refractive index film and high index film. Deposition experiments of SiO 2 and TiO 2 thin films with designed structure using the RF sputtering method were carried out. The characteristics of thethin film with deposition conditions were analyzed. High-refractive-index thin film of TiO 2 /low refractive-index thinfilm of SiO 2 and high-refractive-index thin film of TiO 2 structure for reflection of near-infrared light was designed to be simulated. Results of simulation showed reflectance of 30% or more in the range from 930nm to 1682nm. Triplelayer thin films fabricated with simulated results showed wavelength bands from 930nm to 1525nm for the reflectanceof 33% or more. Key Words : Near infrared, Reflection, Thin film 본 연구는 한경대학교 2014년도 학술연구조성비의 지원에 의한 것임 (This work was supported by a research grant from Hankyong National University in the year of 2014.)

Patterning of multilayer dielectric optical filters using metal masks fabricated by electroforming and photolithography

Ni films, replacing photoresists, serve as masks in the selective deposition of optical thin films by electron-beam gun evaporation at a substrate temperature of 300°C. Photolithography is adopted herein to define the growth of Ni films by electroforming. Mosaic patterns with a width of 20 µm are employed as red color filters, which are longwave pass. These red filters are formed from alternate SiO2 and TiO2 layers and have a mean transmittance of >90%. The experimental results show that the combined use of photolithography, electroforming, and electron-beam gun evaporation can deposit miniaturized multilayer dielectric coatings with high light transmittance in a hot process.

Using fence post designs to speed the atomic layer deposition of optical thin films

Atomic layer deposition (ALD) at this time is much slower than conventional optical thin-film deposition techniques. A more rapid ALD process for SiO(2) has been developed than for other ALD materials. A fence post design for optical thin films has thin layers of high-index posts standing above a broad low-index ground. If a design for ALD can be predominantly composed of SiO(2) layers with thin high-index layers, the deposition times can be correspondingly shortened, and it is shown that the required performance can still be nearly that of more conventional designs with high- and low-index layers of equal thickness. This combination makes the ALD benefits of conformal coating and precise thickness control more practical for optical thin-film applications.

Variation of the deposition rate during ion beam sputter deposition of optical thin films

Time–power monitoring technique was used for monitoring the thickness of optical films during ion beam sputter deposition. For Ta 2O 5, in the initial stage of coating, the growth rate increases with deposition time. While for SiO 2, the rate increases first and then decreases. Both growth rates eventually stabilize when a proper ratio of atoms are sputtered from target materials. Finally, the mismatch of optical thickness and the inhomogeneity of film layers that affect substantially the optical performance of the samples were discussed.

Pulsed laser deposition of optical waveguide Nd-doped gadolinium vanadate thin films

High-quality Nd-doped gadolinium vanadate thin films on silica glass substrates were fabricated successfully by using a pulsed laser deposition technique. The properties of the samples were characterized by using X-ray diffraction, Rutherford backscattering, atomic force microscopy (AFM), and prism-coupling measurements. The RBS shows no obvious evidence for interdiffusion between the film and the substrate. The ratio of Gd/V in the film is 0.995. X-ray diffraction results show that the as-deposited Nd:GdVO 4 film is basically oriented polycrystalline, and strong (2 0 0) peak was revealed. The refractive indices of the films determined with dark-mode prism coupling measurements are slightly smaller than that of the bulk crystal.

Using calibration tests for adjusting target uniformity masks

An important problem in optical multilayer thin film deposition is the adjusting of target uniformity masks to reach the desired film uniformity distribution over the substrate. Calibration tests, that is, special multilayer optical designs, are a widely used tool to determine deposition rates for deposited materials at different substrate points; these rates are used to identify the trim pattern for the target mask. I show that using calibration tests along with special fit algorithms for measured optical spectra provide the relative deposition rates for deposited materials at different substrate points with precision significantly exceeding the error in layer thicknesses of deposited film structure. The proposed method is an excellent tool to trim target uniformity masks.

Table-top 50-W laser system for ultra-fast laser ablation

We have built a mode-locked Nd:YVO4 laser with a very long resonator which produces an average power of 50 W in 13-ps pulses at 1064 nm and was designed for applications in micro-machining, the deposition of optical thin films, and the growth of nano-clusters in the laser-ablated plumes. By operating the laser at very low mode-locking repetition rates (1.5 MHz, 2.6 MHz, and 4.1 MHz), high pulse power is available in a near diffraction limited beam, allowing focused intensities to exceed 1012 W/cm2 and permitting efficient evaporation of difficult materials such as Si. The high power also allows conversion into the second harmonic at 532 nm with an efficiency exceeding 80%. Measurements of the ablation mass in experiments with metals show a 30–100 times increase in the ablation rate compared to the conventional low-repetition-rate ns-range lasers.

High density plasma enhanced chemical vapor deposition of optical thin films

Deposition of pure and Ge-doped silica as well as silicon oxynitride films has been studied in a recently developed matrix distributed electron cyclotron resonance (MDECR) reactor. Process parameters were optimized in order to obtain optical quality thin films at low substrate temperatures and high deposition rates without post-deposition treatment. The choice of injection system is shown to be of crucial importance for the deposition of high quality materials in low pressure PECVD. It has been found that injecting silane near the surface allows to obtain films with a low OH absorption independently of silane flow i.e. growth rate in a certain range of process parameters. On the contrary, in the case of uniform distribution of silane in the reactor volume the hydrogen content increases with silane flow, which affects the quality of films deposited at higher rates. With the optimized injection system, stress-free silica films with a low absorption have been deposited at the rates up to 70 nm/min at temperatures lower than 150 °C. Non-absorbing oxynitride films with a controllable refractive index ranging from 1.46 to 1.86 have been obtained from SiH 4 /O 2 /N 2 mixtures. Ge-doped silica films with a Ge content of up to 4% has been deposited using a mixture GeH 4 in H 2 as a dopant. The properties of deposited films have been studied as a function of process parameters. The results show that the MDECR concept, that permits, in principle, unlimited scaling of substrate size, can be technology of choice for the deposition of optical thin films and functional coatings.

Optical multilayers for ultra-narrow bandpass filters fabricated by PICVD

We report on the deposition of high quality optical thin films by a plasma enhanced chemical vapor deposition (PECVD) method. Especially in telecom applications, drag-and-drop filters for dense wavelength division multiplexing (DWDM) systems require ‘high-quality’ films with performance close to the technical limits, particularly regarding absorption and scattering. Schott has developed a pulsed microwave-induced plasma CVD-technology (PICVD) for the deposition of such films. In this study, optical properties of niobia and tantala films are compared. Refractive indices at 1550 nm reach 2.27 for niobia and 2.10 for tantala. Furthermore, physical properties of Nb 2O 5/SiO 2 multilayer coatings are discussed. The films are synthesized from metal-organic and halide precursors like hexamethyldisiloxane and tantalum chloride or niobium chloride, respectively. The optical performance of narrow bandpass filters made by the PICVD process complies with conventional DWDM requirements.

Stable optical thin film deposition with O 2 cluster ion beam assisted deposition

O 2 gas cluster ion beam (O 2-GCIB) assisted depositions were studied to deposit high-quality Ta 2O 5, Nb 2O 5 and SiO 2 films. The optimum irradiation conditions of O 2-GCIB were the acceleration energy of 5–9 keV and the cluster ion current density over 0.5 μA/cm 2, respectively. Nb 2O 5/SiO 2 films deposited with O 2-GCIB assist showed very uniform and dense structures without columnar or porous structures. Due to the significant surface smoothing effect of GCIB, the interface and top surface of Nb 2O 5/SiO 2 multi-layer were quite flat. The interference filter deposited with O 2-GCIB assist deposition was very stable and there was no shift of wavelength before and after environmental tests. As O 2-GCIB is equivalently very low-energy ion beam and is able to deposit flat and dense amorphous films, it is suited to deposit multi-layered films where low-energy assisting ions are required.

Optical spectroscopy diagnostics and thin film deposition of laser ablated rare earth–Ni 2B 2C plasma plumes

We describe optical spectroscopy diagnostics of UV laser ablated rare earth–Ni 2–B 2–C superconducting targets. In the light of this characterization, we have optimized the parameters for high-quality thin film deposition of borocarbide compounds. Our measurements have evidenced relevant differences in the flow velocity as well as in the spatial divergence of different plasma components. This is related to the influence of the different masses of the atoms of the multicomponent target during plume expansion. These results have led us to identify the target-to-substrate distance and substrate temperature as the critical parameters for the deposition of high-quality thin films, as clearly evidenced by residual resistivity ratio measurements.

Formation of Optical Thin Films by Ion and Plasma Assisted Techniques

An overview of ion and plasma assisted techniques for optical thin films is given. The individual deposition methods are described and their specific advantages and drawbacks with respect to optical thin film deposition presented. It is shown that ion and plasma assistance can have also unwelcome side effects. As far as possible the physical mechanisms governing the film formation are identified and used for interpretation of the experimental results.

Large area glass coating

Abstract Since the end of the seventies vacuum coating technology for the deposition of optical thin films on large area glass substrates has enjoyed a steady growth. Nowadays, the main applications are low emissivity and solar control thin film systems on architectural glass as well as transparent electrodes for flat panel displays. Future markets like electrochromic or anti-reflective coatings appear on the horizon; the latter covering a wide range of products like picture frames, show-cases, shop windows, and all kinds of data and TV screens. The paper gives an introduction into the above-mentioned applications and outlines the present state of sputtering technology for large area glass coating.

Laser induced chemical vapor deposition of optical thin films on curved surfaces

Laser induced chemical vapor deposition (LCVD) of silicon nitride and silicon dioxide single and double layers has been investigated using excimer laser operating at a wavelength of 193 nm. Single layers of silicon nitride were formed from SiH4/NH3 gas mixture with Si/N atomic ratio of 0.6–0.7. The layers that contained a small amount of hydrogen had a refractive index and extinction coefficient of n=2, k=0015 at 600 nm. Deposition of silicon dioxide was investigated using SiH4/N2O. Using this gas mixture the film composition depended strongly upon the SiH4/N2O ratio. At high ratio the film formed was silicon oxynitride, which contained both SiN and SiO bonds. The film also contained small a amount of SiH bonds. Decreasing the SiH4/N2O ratio led to the formation of pure silicon dioxide with a refractive index of 1.45. A two layer coating of silicon nitride and silicon dioxide resulted in the formation of an antireflection coating with a reflectivity of about 0.5% at 750 nm.

Optical and compositional study of silicon oxide thin films deposited in a dual-mode (microwave/radiofrequency) plasma-enhanced chemical vapor deposition reactor

This study is focused on the deposition and growth of amorphous silicon oxide optical thin films in a dual-mode (microwave/rf) reactor. The optical, chemical, and structural properties of a-SiOx:H films have been studied as a function of different parameters (substrate temperature, microwave power, gas flow, dilution, addition of rf plasma) by in situ UV-visible and in situ infrared (IR) ellipsometry, Fourier transform IR transmission spectroscopy, nuclear analysis, and VUV absorption spectroscopy. We have shown that it is possible to increase the density of the films and decrease their hydrogen content by depositing at higher temperature (T⩾200 °C) and/or using a helium dilution and/or using the ion bombardment effect of the rf plasma. In situ IR ellipsometry has revealed water absorption on the as-deposited silicon oxide films, just after exposing them to the ambient atmosphere. The lower is the film density and the higher is the water absorption. UV absorption spectroscopy has evidenced an absorption peak at 6.3 eV, with an amplitude dependent on the hydrogen content. Since the films are interesting for optical multilayers, we have also studied the effect of UV irradiation, showing the decrease of O–H groups (reduction of the hydrogen content) and a reoxydation of the silicon oxide films. The thermal stability studies reveal an effusion of H2 and H2O molecules for temperatures above 300 °C.

Low emissivity coatings on architectural glass

New energy conservation regulations became effective in Germany by the beginning of 1995. These regulations contain stringent instructions on the thermal insulation of buildings, and thus imply the use of so-called “low emissivity” coatings for nearly any kind of architectural glazing. As a consequence, the new law has significant impact on the market for vacuum coating equipment, which nowadays plays a key role in manufacturing low emissivity thin film systems. Modern vacuum coaters handling panes of glass with dimensions of up to 3.21 m × 6.00 m operate at cycle times less than 1 min and provide uptimes that exceed 90% Novel solutions for high rate magnetron sputtering, the key process for large area coating, are presently under laboratory investigation or already successfully implemented into industrial coaters. AC powered magnetron systems permit the deposition of optical thin films with high rates and an outstanding process stability. Current development work on the design of low-e film stacks is aiming in highly transparent and chemically stable coatings permitting a heat transfer coefficient k of 1.0 W/m 2K and less. The present paper tries to give an overview on the state-of-the-art related to vacuum coating of glass as well as low-e film designs and their properties.

Optical Scattering and Surface Microstructure of Thin Films for Laser Application.

Experimental studies are described of the problem of scattering and roughness modification after deposition of optical thin films as used for application in laser components. BK7 substrates with different surface finish have been coated with MgF2, LaF3, Si02 and Nb2O5 films as representatives of low index/ high index columnar structured and structureless films, respectively. Total integrated scattering (TIS) and angle resolved scattering (ARS) measurements at 632.8 nm and 325 nm as well as atomic force microscopy (AFM) investigations demonstrate that coating can result not only in roughness and scattering enhancement but also in its reduction.