氧分压对RF磁控溅射ZrO2薄膜生长特性的影响

采用反应射频(RF)磁控溅射法在n型(100)单晶S基片上沉积了ZrO2膜,研究了氧分压与ZrO：薄膜的表面粗糙度和沉积速率、SiO2中间界层的厚度以及ZrO2薄膜的折射率之间关系。结果表明：随着氧分压增高,薄膜的沉积速率降低,表面粗糙度线性地增加;在低的氧分压情况下,Si基片表面的本征SiO2层的厚度增加幅度较小,在高的氧分压情况下,Si基片表面的本征SiO2层的厚度有较大幅度地增加;在O2／Ar混和气氛下,溅射沉积的ZrO2薄膜的折射率受氧分压的影响不显著,而在纯氧气气氛环境下,ZrO2薄膜的折射率明显偏低,薄膜的致密性变差。     

Induced metal-dielectric selective reflecting filter for miniprojectors

Metal-dielectric multiple-band high-reflection coatings are designed as induced filters and fabricated by reactive deposition. Ta(2)O(5) and SiO(2) are used as high- and low-refractive-index layers, and Cr and Al are used as bonding and reflective layers, respectively, for constructing the filters. The metal-dielectric coatings are deposited on a light-shaping flexible plastic substrate for use as a screen with high-contrast enhancement performance. This screen was suitable for miniprojectors with red, green, and blue LEDs as light sources. Mechanical properties such as stress, hardness, and adhesive strength of these multilayer films are investigated also.     

On the Limiting Bandwidth of Interference Filters : Influence of Temperature during Production

Computer simulation of thin-film multilayer production has shown that the effects of errors in the layers on the performance of complete coatings depends strongly on the particular monitoring process used. Deposition of dielectric quarter-wave multilayers is usually controlled by a method which involves the detection of the maxima and minima of transmission for the centre wavelength of the filter, the turning value method, and we know that this technique profits from an exceptionally efficient error compensation. The true tolerances in stack production are much larger than we would calculate neglecting this compensation. However, the analysis of experimental results shows that we must consider other effects which have so far been neglected in the computer simulation and which affect the monitoring process enough to prevent the fabrication of interference filters with very narrow transmission bands. Here we describe how the computer simulation is modified to take account of the influence of temperature changes during filter manufacture. First, it is necessary, for each material used, to determine the dilatation coefficients of both refractive index and thickness; they may be deduced from measurements of shifts with temperature of the centre wavelength of narrow-band filters of two different designs. Then, as a first approximation, we assume in the simulation a gradual temperature change which is always proportional to the deposited thickness and which reaches a total of 60°C for the complete filter. The calculations show that the effects of such a temperature change cannot be neglected even if the actual monitoring is perfect, that is if the deposition is always terminated exactly at a turning value of transmittance. The optical characteristics of very narrow-band filters, and especially of double half-wave filters, are seriously degraded. If, in addition, errors in determination of the turning values are included, then the effects are considerably worse. This can explain why it is so difficult to make filters with passband width less than 8 Å. The results of this study can be used to choose optimal conditions for the production of narrow-band filters.     

Monitoring thin films of the fence post design and its advantages for narrow bandpass filters

A fence post design, when viewed on a plot of index of refraction versus film thickness, has thin (usually of equal thickness) high-index posts that stand above a broad low-index ground. Monitoring fence post and related posthole designs offers error compensation and error reduction. There tend to be two or more extrema within the optical monitoring trace of each layer between the fence posts that aid in the calibration and control of film thickness. This also leads to a potentially improved control during deposition of narrow bandpass filters that have been designed with nonquarterwaves at the passband wavelength.     

Narrow-band Resonant Grating Waveguide Filters Constructed with Azobenzene Polymers.

Resonant grating waveguide structures were used to fabricate narrow-bandwidth optical filters. Azopolymer films were deposited on top of slab waveguides, and surface relief gratings were optically inscribed on them to be used as couplers. This technique is a simple one-step process and produces efficient gratings with high accuracy. Sharp resonant peaks are observed in the transmission and the reflection spectra of these structures. The thickness and the index of refraction of the waveguide can be accurately determined from these resonances by use of modal theory. These parameters are then used in the design of an optical filter. Bandwidths of less than 1 nm and a decrease in transmitted signal of 60% are reported. Measurement of these values was limited by the divergence of the probe beam.     

Analysis of the early growth mechanisms during the chemical deposition of CdS thin films by spectroscopic ellipsometry

Chemically deposited CdS thin films were analyzed in this work by means of the spectroscopic ellipsometry technique. The CdS thin films were deposited from an ammonia-free process at short durations in order to obtain information about the layer microstructure and kinetic growth process. We found that the conditions of the ammonia-free reaction solution promote the ion-by-ion deposition process at the early growth stages yielding a compact, high refraction index and highly crystalline oriented CdS layers. Using a concentration of 1.82 mg/ml of cadmium in the reaction solution, the resulting films possess a double layer microstructure which consists of an inner compact layer and an external porous one. The inner layer is developed during the first 15 min of deposition time and it reaches a thickness around of 80 nm. After this time and on this inner layer of CdS, it grows an external porous layer whose thickness increases with the deposition time. The formation of the CdS compact layer at the early stages is related with the ion-by-ion growth mechanism. The subsequent CdS porous layer is formed during the cluster-by-cluster growth stage at longer deposition times. By reducing the cadmium concentration in reaction solution down to 0.76 mg/ml, maintaining constant molar ratio concentrations of Cd/complexing and Cd/thiourea, the chemically deposited CdS films develop only the inner compact layer with a thickness of about 80 nm after 35 min of deposition time.     

R.F. sputtering system for the preparation of multilayer optical filters

Thin film multilayer optical filters are usually prepared by vacuum evaporation of successive layers. The deposition of thin films by sputtering has many advantages over the vacuum evaporation technique and hence it is employed for the fabrication of better quality optical filters. However, the filters may be more time consuming to prepare if a single-target sputtering system is used because two different materials are required for alternate layers. For the preparation of multilayer optical filters, a special r.f. sputtering jig arrangement with two target holders is fabricated. Using this the successive layers can be deposited in one pumpdown. A simple coupling arrangement used to match the r.f. generator output impedance to the load is explained. With all the sputtering parameters such as the pressure, the temperature and the power maintained constant except the time, control of the thickness of the multilayers is achieved. A calibration chart of sputtering time versus thickness of the materials to be deposited is prepared for TiO₂ and SiO₂ for the above purpose. Using this calibration chart, the deposition time of different layers of any optical filters based on these dielectric materials can be fixed to obtain optical filters of acceptable quality and reproducibility.     

Elastic and plastic relaxation of densified SiO2 films

Ion- and plasma-assisted deposition has been extensively used for the fabrication of high-performance optical films with dense and smooth microstructures that are essential for applications such as low-loss and environmentally stable optics. SiO(2) is a well-known amorphous material suitable for energetic deposition. SiO(2) single layers and SiO(2)-based single-cavity narrow-bandpass filters were prepared by plasma-ion-assisted deposition. The refractive index and film thickness were determined by variable-angle spectroscopic ellipsometry. The high compressive stress of the densified film was correlated to increased packing density. The center wavelength shift of the narrow-bandpass filters as a function of sample-temperature as well as high-temperature annealing was determined via spectral transmission measurement. Structural relaxation of the densified SiO(2) films was observed from the variation of the refractive index and physical thickness for the single layers and the center wavelength shift for the narrow-bandpass filters, suggesting elastic and plastic deformation of the densified films corresponding to a reversible and an irreversible center wavelength shift, respectively.     

Robust optical coating design with evolutionary strategies

The optical performance of interference filters depends on systematic and statistical variations of the thicknesses and indices of refraction of the layers that occur during production and use. Assuming that their distributions are known, the expected performance can be optimized as a function of the nominal layer thicknesses with the help of strategies that mimic biological evolution. This results in filter designs that are easier to manufacture and more robust to use. The method is illustrated for color shifts that are rather sensitive to layer thickness variations. Its scope is entirely general, and it could be applied to other tolerancing problems that arise in optical design.     

Dispersion implementation in optical filter design by the Fourier transform method using correction factors

The Fourier transform method to design graded-index optical filters, that relates the desired reflection spectrum and the index profile through the use of a Q function, has two important drawbacks: (1) It relies on approximate Q functions, and (2) it does not account for the dispersion of the index of refraction. The former is usually addressed by an iterative correction process. We propose to address the latter by scaling the wavelength in the Fourier transform by the optical thickness of the filter and to multiply the Q function by a wavelength-dependent correction factor. We demonstrate the high effectiveness of this approach by the performance of optical filters designed with such correction factors using the optical properties of SiO2/TiO2 mixtures.     

On-line reoptimization of filter designs for multivariate optical elements

An automated method for producing multivariate optical element (MOE) interference filters that are robust to errors in the reactive magnetron sputtering process is described. Reactive magnetron sputtering produces films of excellent thickness and uniformity. However, small changes in the thickness of individual layers can have severe adverse effects on the predictive ability of the MOE. Adaptive reoptimization of the filter design during the deposition process can maintain the predictive ability of the final filter by changing the thickness of the undeposited layers to compensate for the errors in deposition. The merit function used, the standard error of calibration, is fundamentally different from the standard spectrum matching. This new merit function allows large changes in the transmission spectrum of the filter to maintain performance.     

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.     

Step method: a new synthesis method for the design of optical filters with intermediate refractive indices

We propose a new synthesis method for the design of multilayer optical filters with intermediate refractive indices, the step method. This method consists in adding infinitesimally small index steps in the index profile at optimal positions and then reoptimizing the thickness and the refractive index of the layers. Application of the method to the design of an antireflective coating, a low-pass edge filter, and an immersed polarizing beam splitter shows that it provides interesting solutions, even in the absence of a proper starting design. The formalism developed for the method also serves to demonstrate that the optimal filter consists of either homogeneous layers that maximize the effective refractive index contrast, or of graded-index layers.     

界面梯度对TiN／不锈钢涂层应力的影响

气相沉积表面涂层在科学技术各领域得到广泛应用，然而，由于涂层与基体在化学和物理性质上的差异，使得涂层与基体在界面两侧产生结构和性能上的突变，影响了涂层功能的充分发挥。为此，采用多靶磁控溅射技术制备了具有梯度过渡层的ＴｉＮ／不多靶磁控溅射技术制备了具有梯度过渡层的ＴｉＮ／不锈钢涂层，并研究了梯度层对涂层内应力的影响。研究结果表明：采用多靶磁控溅射技术，分别控制各靶的功率，能够精确控制梯度层的成份变化     

Spectroscopic and kinetic ellipsometry studies of hot-wire deposited polycrystalline silicon on glass

In order to get more insight into the growth mechanism of polycrystalline silicon deposited by hot-wire chemical vapor deposition on Corning glass, spectroscopic and kinetic ellipsometry studies have been performed. Spectroscopic ellipsometry measurements have been performed on layers, deposited using different levels of hydrogen dilution. From this study, it followed that the crystallinity of the films becomes higher with higher hydrogen dilution. Kinetic ellipsometry measurements have been performed during the deposition of profiled layers, starting with a seed layer deposited at high hydrogen dilution. This study showed that by using a seed layer, highly crystalline layers could be deposited using a lower hydrogen dilution. Without the use of the seed layer, this lower hydrogen dilution yields amorphous silicon layers.     

Stress control of a-SiC films deposited by dual source dc magnetron sputtering

In the present paper, we show that a-SiC films deposited from two independent Si and graphite magnetron sputtering sources have small tensile stress of ∼100 MPa without post-deposition annealing. Our sputtering apparatus has a rotation substrate holder that is designed to move to the front of individual targets alternately. In this experimental geometry, the relaxation period, when no deposition is made, must be present during sputtering. The presence of this relaxation period is found to be effective to change the compressive internal stress of deposited films into tensile direction. We have also succeeded to fabricate free-standing a-SiC soft X-ray filter with the thickness of 100-600 nm. The transmission spectra of these filters for soft X-ray beam showed good agreement with calculated ones.     

高隔离度干涉截止滤光片的设计与制备

根据光通讯无源器件和激光探测仪器对光学薄膜的特殊需求，采用解析法和自动优化法综合设计了高隔离度的干涉截止滤光片，分析了膜厚改变2％对设计膜系的透过率曲线的影响，通过莱宝APS1104镀膜机对所设计的膜系进行了实际镀制，获得了性能优良的高隔离度截止滤光片．     

Effect of stress on performance of dense wavelength division multiplexing filters: optical properties

Thin-film filters used for dense wavelength division multiplexing (DWDM) applications are processed by a variety of deposition techniques, including ion-beam sputtering. Ion-beam sputtering produces high-quality coatings and provides flexibility of coating materials. However, DWDM filters consisting of oxide films that are reactively deposited by ion-beam sputtering, as in most sputter techniques, typically exhibit high levels of compressive stress. This affects the optical characteristics of the filters. Details of the filter passband characteristics and wave-front distortion illustrate the influence of the stress. Spatial variation of the stress on the filter surface causes the filter center wavelength to have spatial variation, and it causes the filter to have an asymmetric passband characteristic.     

Reliable deposition of induced transmission filters with a single metal layer

The sensitivity of an induced transmission filter (ITF) design to deposition errors is analyzed for the case of a single metal layer ITF. Theoretical knowledge of the least and most sensitive layers within the ITF design improves deposition reliability when using broadband optical monitoring of only the dielectric part of such metal-dielectric filters. Linearly variable ITFs have been successfully fabricated using this developed approach for error compensation.     

Study of the delamination of diamond coatings under thermal stress

The influence of the thickness of CVD diamond coatings on the adhesion to a substrate, after cooling down from deposition temperature to room temperature, has been studied experimentally and theoretically. Diamond layers have been deposited at 850°C on W substrates by microwave plasma enhanced CVD. Cooling down of the substrate-diamond coating system to room temperature induces thermal stresses, due to different thermal expansion coefficients of coating and substrate. For thick diamond coatings a total and sudden delamination could be observed as a consequence of these stresses. On the contrary thin coatings, produced under identical circumstances, adhered well. These phenomena have been modelled and explained by the use of an energetic criterion for the delamination of a two-layer system under thermal stress. From the model a critical thickness of the coating can be calculated. Above this critical thickness, delamination will suddenly occur. The calculations also predict that for intermediate coating thicknesses delamination can easily be induced by external causes.