High-throughput characterization of film thickness in thin film materials libraries by digital holographic microscopy

Abstract

A high-throughput characterization technique based on digital holography for mapping film thickness in thin-film materials libraries was developed. Digital holographic microscopy is used for fully automatic measurements of the thickness of patterned films with nanometer resolution. The method has several significant advantages over conventional stylus profilometry: it is contactless and fast, substrate bending is compensated, and the experimental setup is simple. Patterned films prepared by different combinatorial thin-film approaches were characterized to investigate and demonstrate this method. The results show that this technique is valuable for the quick, reliable and high-throughput determination of the film thickness distribution in combinatorial materials research. Importantly, it can also be applied to thin films that have been structured by shadow masking.     

High-throughput characterization of film thickness in thin film materials libraries by digital holographic microscopy

A high-throughput characterization technique based on digital holography for mapping film thickness in thin-film materials libraries was developed. Digital holographic microscopy is used for fully automatic measurements of the thickness of patterned films with nanometer resolution. The method has several significant advantages over conventional stylus profilometry: it is contactless and fast, substrate bending is compensated, and the experimental setup is simple. Patterned films prepared by different combinatorial thin-film approaches were characterized to investigate and demonstrate this method. The results show that this technique is valuable for the quick, reliable and high-throughput determination of the film thickness distribution in combinatorial materials research. Importantly, it can also be applied to thin films that have been structured by shadow masking.     

Model of holographic recording in thermoplastic materials

A method for the evaluation of images reconstructed from holograms recorded in thermoplastic materials is reported. The method is based on the use of the experimental modulation transfer function and nonlinear holographic characteristics of the recording material. Calculations have been carried out for high-numerical-aperture holograms of a five-element Ronchi ruling. The quality of the reconstructed image as a function of the recording parameters has been computed. The model predicts that it is possible to optimize holographic recording in these materials.     

用于全息记录的光致聚合物材料的研究进展

阐述了光致聚合物的反应原理、形成全息图的机理,讨论了影响光致聚合物全息存储性能的因素及其规律,同时还介绍了光致聚合物用于全息存储的最新进展,并对其发展趋势进行了展望.     

Modified holographic recording setup for photopolymerizable/flexible recording materials

An improvement in the conventional holographic recording setup has been done for liquid (photopolymerizable) or flexible recording materials. The new vertical recording setup that comprises a horizontal substrate holder permits holographic recording on such materials without positioning them between two substrates, as has been done until now. This setup can be conveniently used for the fabrication of transmission, reflection, Fourier transform, and computer-generated holograms with few simple modifications as indicated.     

Kinetic study of selenium used as optical data storage and holographic recording materials

A kinetic study has been performed on selenium for isothermal and continuous heating processes. The activation energy (E _a) and Avrami exponent (n) have been evaluated in the range 414 to 449 K for the isothermal process and at a heating rate of 5 to 40 K min^–1 for continuous heating. A new iterative calculation to give exact values ofE _a andn for a continuous heating process is also presented.     

Optimization of an acrylamide-based dry film used for holographic recording

A study of the optimization and the characteristics of a dry film photopolymerizable recording material is presented. The effects of intensity, the thickness, and the variation of the concentration of each component have been studied. Diffraction efficiencies of 80%, with energetic sensitivities of 40 mJ/cm(2), have been obtained in photosensitive films of a 35-mum thickness with a spatial frequency of 1000 lines/mm.     

Effect of the recording scheme parameters on the scattering characteristics of holographic diffusers

The influence of parameters of the recording scheme and the regime of photochemical processing on the scattering characteristics of holographic diffusers obtained using the Gabor on-axis scheme has been studied.     

A precision tester for studies of holographic optical storage materials and recording physics

The design and the realization of an advanced precision optical test stand for evaluating materials and developing tools and techniques for holographic digital data storage are described. This apparatus allows studies of holographic recording materials and recording physics to be performed in the context of practical data storage. The system concept, its implementation, and its performance are described, and examples of holographic storage in photorefractive materials are discussed.     

Characterization of bromocresol green and resin as holographic film

We present a film composed by bromocresol green (BCG) dye and resin mixed with isopropyl alcohol as photosensitive emulsion. In this film, we have recorded phase gratings with the emission line λ = 457 nm of an argon laser. The characterization of this film indicates us a diffraction efficiency of 2.27%; and its simple fabrication and low cost make this film an attractive option for holographic elements.     

Co-doping with polysquaraine enhances the holographic optical data storage of PMMA/PQ photopolymers

In this study, we synthesised poly(3-octylpyrrole-co-squaric acid) (PSQ3), a polysquaraine, through the reaction of 3-octylpyrrole and squaric acid, and then co-doped it with phenanthrenequinone (PQ) into poly(methyl methacrylate) (PMMA) to improve the holographic data storage characteristics of the photopolymer. The photopolymers co-doped with relatively small amounts of PSQ3 exhibited greatly improved holographic recording characteristics, including superior diffraction efficiency and dynamic range (M#). Among the samples co-doped with PQ and PSQ3, the maximum diffraction efficiency reached 54.8% (cf. 9.0% for PMMA/PQ) without further downgrade and the value of M# reached 1.05 (cf. 0.46 for PMMA/PQ). Therefore, the holographic data storage characteristics of the photopolymer PMMA/PQ were improved through co-doping with PSQ3.     

Effect of the nanographite film thickness on the optical rectification pulse

The phenomenon of optical rectification during pulsed laser irradiation was studied in nanographite films of various thicknesses obtained by plasmachemical deposition on silicon substrates. The amplitude of the optical rectification pulse (ORP) strongly depends on the film thickness h and reaches a maximum at h ∼ 2.5 μm. At a smaller film thickness, the ORP is accompanied by a photoelectric signal of microsecond duration, which arises in the silicon substrate. For the nanographite films with h > 2.5 μm, the ORP is observed in the absence of any signal from the substrate, which allows such films to be used in fast-response detectors of pulsed laser radiation in a broad spectral range.     

Phase-conjugate holographic lithography based on micromirror array recording

We present phase-conjugate holographic lithography with a hologram recorded by a digital micromirror device (DMD) and a telecentric lens. In our lithography system, a phase-conjugate hologram is applied instead of conventional masks or reticles to form patterns. This method has the advantage of increasing focus range, and it is applicable to the formation of patterns on fairly uneven surfaces. The hologram pattern is dynamically generated by the DMD, and its resolution is mainly determined by the demagnification of the telecentric lens. We experimentally demonstrate that our holographic lithographic system has a large focus range, and it is feasible to make a large-area hologram by stitching each pattern generated by the DMD without a falling off in resolution.     

Metallized thiazolylazo dyes as optical recording materials

A series of metallized thiazolylazo dyes have been designed and synthesized. Smooth films on optical glass and single-crystal silicon were prepared using the spin-coated method. The UV-Vis absorption spectra of the dyes were measured in solution and in films. The optical constant (complex refractive index N=n+ik) of the films on single-crystal silicon has been determined using a scanning ellipsometer. The variation of the complex refractive index, N, with wavelength, λ, was obtained. From the value of n, k and the thickness of the dye films, the variation of the reflectance vs dye film thickness was then calculated. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) of the nickel thiazolylazo dye showed a clear threshold of thermal decomposition with a sharp exothermic park. Static optical recording tests were carried out. The results show that the nickel thiazolylazo dye is more suitable for use in short-wavelength diode-laser optical recording.     

Effect of re-evaporation on the uniformity of the thickness of a film

With complex kinematics characterizing the motion of the evaporator-substrate system, numerical modeling is used to study the effect of re-evaporation on the distribution of film thickness on the substrate.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 2, pp. 285–288, February, 1990.     

Model of noise-grating selectivity in volume holographic recording materials by use of Monte Carlo simulations

A model describing the angular selectivity of noise gratings in volume holographic recording materials is presented. The noise grating is treated as an ensemble of superimposed, statistically distributed planar gratings. Rigorous coupled-wave analysis is used to treat reconstruction with various polarization states. The model accounts for material properties such as thickness change, absorption, and the angular distribution of scattered light within the recording medium. Results show good agreement with noise gratings that are experimentally formed in a thick cationic ring-opening photopolymer material.     

热塑性共聚聚酰亚胺薄膜的合成及性能研究

以2,2′-二甲基-4,4′-二氨基联苯(m-TB)为二胺单体,均苯四甲酸二酐(PMDA)和3,3′,4,4′-联苯四甲酸二酐(BPDA)为二酐单体,N,N′-二甲基乙酰胺(DMAc)为溶剂,采用常规的两步法制备了一系列不同二酐比例的热塑性聚酰亚胺,并通过红外光谱仪、X-射线衍射仪、热重分析仪、紫外光谱仪、动态热分析仪、溶解性测试等对共聚聚酰亚胺的结构和性能进行表征.结果表明:在1 780、1 720、1 500、1 380、1 050和725 cm~(-1)处出现明显的吸收峰,说明成功制备了聚酰亚胺材料;共聚聚酰亚胺只在PMDA与BPDA物质的量比为0.2∶0.8时存在结晶峰,其他比例时均为非晶聚合物;亚胺化后的共聚聚酰亚胺在DMSO、DMAc、DMF、NMP和m-cresol中有溶解性,证明成功制备出热塑性聚酰亚胺薄膜;热塑性共聚PI起始分解温度大于500℃,800℃时的质量保持率在50%以上,具有良好的热稳定性;随着聚合物中BPDA含量的提高,热塑性聚酰亚胺薄膜的玻璃化转变温度呈现下降的趋势.当紫外光波长达到400 nm时,薄膜的透光率高达57.6%,当波长为760 nm时,薄膜透光率均达到100%,成功制备了透光率较高的聚酰亚胺薄膜.     

Effect of ramping-up rate on film thickness for spin-on processing

Spin-on processing is used in many industries to deposit very thin coatings on flat substrates, including silicon wafers, flat-panel displays, and precision optical components. A liquid precursor solution is first dispensed onto the surface of the substrate; this fluid then spreads out very evenly over the surface due to large rotational forces caused by spinning of the substrate. When looking for an optimum coating procedure process engineers can adjust many variables including the peak spin speed, the ramping rate to reach that speed, the spinning time, as well as allowing for dynamic solution dispense before ramping up, though most protocols focus on the peak spin speed as the primary controlling variable. Engineers often construct spin-speed versus thickness correlations that enable predictable adjustment of spin-speed to achieve a desired thickness. Yet, rather little attention has been paid to the importance of the acceleration rate used to reach the desired peak speed. We show here that ramping rate is also important in helping establish the final coating thickness. We present a numerical model of the fluid flow on a spinning wafer when the spin-speed is ramping linearly up to a desired peak speed and then held constant. It is shown that the coating may “set” into its final thickness before the spin-speed reaches its peak value. In these cases then the peak spin-speed parameter is no longer the primary variable that defines the final coating thickness. This also impacts the interpretation of critical exponents found when fitting spin-speed vs. thickness data. We perform parallel experimental measurements for different ramping-up times and confirm the results from the numerical model. Both experimental and theoretical results support use of the simplified model put forth by Meyerhofer over 25 years ago (J. Appl. Phys. 49 (1978) 3993–3997).     

不同厚度对分子束外延生长GaSb薄膜的影响

采用分子束外延(MBE)在GaAs衬底上生长GaSb薄膜,为了减小因晶格失配度较大所引起的位错密度,采用低温GaSb作为缓冲层.通过X射线双晶衍射仪和原子力显微镜分析得出,当低温GaSb缓冲层的厚度为20nm时,GaSb外延层中的位错密度最小,晶体质量最好.此外,缓冲层和外延层的厚度共同对GaSb薄膜晶体质量和表面形貌产生影响.