Tailoring the chemical behavior of aluminum for selective etching by laser interference metallurgy

The chemical behavior of aluminum modified by laser interference metallurgy (LIMET) is investigated. LIMET allows the single-step creation of periodic patterns with a well defined long-range order on material surfaces. This technique can also induce local and periodical oxidation on aluminum surfaces, which follows the ordered array imprinted by laser interference. The thin oxide layer built up during laser structuring enhances the chemical stability of the irradiated zones. Ordered local oxidation permits the selective etching of an exposed aluminum surface. The etch pits are generated preferentially at the interference minima positions. In comparison to conventional methods, this process significantly improves the homogeneity of the initiation sites of pits. Furthermore, LIMET not only influences the first stages of pits initiation, but also the final etch morphology formed during the total electrochemical etching of the surfaces.     

β-SiC薄膜在SF6和SF6+O2中的等离子体刻蚀研究

以SF₆和SF₆+O₂为刻蚀气体,采用等离子体刻蚀工艺成功地对化学气相淀积工艺制备的β-SiC单晶薄膜进行了有效的刻蚀去除.实验指出当气体混合比约为40%时,刻蚀速率达到最大值.俄歇能谱分析表明,在SF₆和SF₆+O₂气体中被刻蚀后的样品没有形成富C表面的SiC层.研究结果为各种SiC器件的研制奠定了必要的实验基础. 关键词：     

Tunable characteristic of phase-locked quantum cascade laser arrays

A multimode interference(MMI) structure is designed to simplify the fabrication of quantum cascade laser(QCL)phase-locked arrays. The MMI geometry is optimized with a sufficient output channel distance to accommodate conventional photolithography and wet etching process by which power amplifier array is fabricated without using the complicated two-step etching-regrowth or dry etching technique. The far-field pattern with periodically modulated peaks reveals that the beams from the arrays are phase-locked. Furthermore, the frequency tuning performance of the MMI-based phase-locked arrays is studied using the Littrow-configuration external cavity structure. A wavelength tuning range of more than 60 cm~(-1) is demonstrated, which will eventually realize the high power, frequency tunable, large-scale phase-locked arrays, and their application in spectroscopy.     

一种简单高效的制备硅纳米孔阵结构的方法

本文介绍了一种简单高效的制备硅纳米孔阵结构的方法. 利用激光干涉光刻技术, 结合干法和湿法刻蚀工艺, 直接将光刻胶点阵刻蚀为硅纳米孔阵结构, 省去了图形反转工艺中的金属蒸镀和光刻胶剥离等必要步骤, 在2英寸的硅 (001) 衬底上制备了高度有序的二维纳米孔阵结构. 利用干法刻蚀产生的氟碳有机聚合物作为湿法刻蚀的掩膜, 以及在干法刻蚀时对样品进行轻微的过刻蚀, 使SiO₂点阵图形下形成一层很薄的硅台面, 是本方法的两个关键工艺步骤. 扫描电子显微镜图片结果表明制备的孔阵图形大小均匀, 尺寸可控, 孔阵周期为450 nm, 方孔大小为200–280 nm. 关键词： 激光干涉光刻 纳米阵列 刻蚀 氟碳有机聚合物     

Formation of two-dimensional periodic nanostructures on fused quartz,polyimide, and polycrystalline diamond by pulsed four-wave interference laser modification

Atomic force microscopy is used to examine the topography of submicron periodic structures formed on the surfaces of synthetic polycrystalline diamond and polyimide films. The films are deposited on fused quartz substrates by four-wave interference modification using a pulsed 308-nm UV XeCl excimer laser. It is demonstrated that a two-dimensional periodic relief with a submicron period can be formed on the diamond surface directly by laser evaporation in the absence of a photoresist. Depending on the exposure, two mechanisms of polyimide film modification are observed. At exposures less than 100 mJ/cm², the relief is formed due to swelling at the positions of interference maxima. At exposures greater than 100 mJ/cm², holes are formed in the films. A periodic relief on the fused quartz surface is formed by using a UV photoresist exposed to pulsed interference laser radiation and subsequent Ar ion etching.     

Holographic control of surface modifications

The application of holographic interferometry to the control of surfaces, such as in processes of electro-deposition, vacuum deposition, and crystal etching is described. As examples, measurements concerning electro-deposition and crystal etching are reported. A double-exposure technique is used and both the thickness of deposited or etched material and the concentration gradient in the electrolyte give rise to interference fringes. From the reconstructed image it is then easy to evaluate the thickness and uniformity of deposition or etching. In the latter case, as is well known, etching figures give useful information about crystal structure and defects.     

Effect of etching parameters on antireflection properties of Si subwavelength grating structures for solar cell applications

We fabricate the aluminum-doped zinc oxide (AZO) subwavelength gratings (SWG) on Si and glass substrates by holographic lithography and sequent CH₄/H₂/Ar reactive ion etching process. The etch selectivity of AZO over photoresist mask as well as the nano-scale shape is optimized for better antireflection performance. To analyze the antireflective properties of AZO SWG surface, the optical reflectivity is measured and then calculated together with a rigorous coupled-wave analysis. The reflectance spectrum can be considerably changed by incorporating the SWG into AZO film. As the SWG height of AZO on Si substrate increases, the magnitude of interference oscillations in the reflectance spectrum tends to be reduced with the larger difference between its maxima. The use of optimized SWG can significantly reduce the surface reflection of AZO film at the desired wavelengths. The measured reflectance data of AZO SWG are reasonably consistent with the simulation results. No considerable change in transmission characteristics is observed for AZO SWG structures.     

同步辐射Laminar光栅的研制

采用全息离子束刻蚀和反应离子刻蚀相结合的新工艺 ,在熔石英基片上成功地刻蚀出 2 0 0l/mm、线空比 4:6、槽深 70nm、刻划面积 60× 2 0mm2 的浅槽矩形Laminar光栅。对改进光栅线条粗糙度和线空比的方法进行了系统的研究。这一新工艺相对简单 ,降低了对干涉系统光学元件和全息曝光显影的严格要求     

Multimode interference wavelength multi/demultiplexer for 1310 and 1550 nm operation based on BCB 4024-40 photodefinable polymer

A 1310 and 1550 nm coarse wavelength multi/demultiplexer based on benzocyclobutene (BCB 4024-40) polymer is demonstrated for the first time. The device is designed based on a combination of general interference and paired interference mechanisms of multimode interference (MMI). It is fabricated on BK7 glass substrate with a thin layer of SiO₂ as cover. A cost effective chemical etching technique is used in the fabrication process to take advantage of the photosensitive nature of the polymer. The device length was significantly reduced by adopting the restricted multimode interference scheme, lower beat length ratio and cascaded MMI couplers. The measured crosstalk at 1310 nm was 14.4 dB and at 1550 nm was 20.6 dB. The measured insertion loss is around 3.2-3.5 dB for both ports.     

Antireflective properties of AZO subwavelength gratings patterned by holographic lithography

We fabricate the aluminum-doped zinc oxide (AZO) subwavelength gratings (SWG) on Si and glass substrates by holographic lithography and sequent CH₄/H₂/Ar reactive ion etching process. The etch selectivity of AZO over photoresist mask as well as the nano-scale shape is optimized for better antireflection performance. To analyze the antireflective properties of AZO SWG surface, the optical reflectivity is measured and then calculated together with a rigorous coupled-wave analysis. The reflectance spectrum can be considerably changed by incorporating the SWG into AZO film. As the SWG height of AZO on Si substrate increases, the magnitude of interference oscillations in the reflectance spectrum tends to be reduced with the larger difference between its maxima. The use of optimized SWG can significantly reduce the surface reflection of AZO film at the desired wavelengths. The measured reflectance data of AZO SWG are reasonably consistent with the simulation results. No considerable change in transmission characteristics is observed for AZO SWG structures.     

The study of the solution concentration influencing on laser-induced electrochemical etching silicon

The laser electrochemical etching process, which combines the laser direct etching process and the electrochemical etching process, is a compound etching technique. In order to further understand the solution concentration influencing on the laser-induced electrochemical etching of silicon; a 248 nm excimer laser as a light source and KOH solution as an electrolyte were adopted in this study. The experiments of micromachining silicon by laser-induced electrochemical etching were carried out. On the basis of the experiments results, the solution concentration influencing on the etching rates in the process of laser electrochemical etching of silicon was researched. The reasons of the etching phenomena were analyzed in detail. The experimental results indicate that the solution concentration influencing on the etching process is mainly rooted in the absorption of different concentration solutions to laser. In general, less absorption and low solution concentration are good for the etching role in the process of laser electrochemical etching.     

Subsurface quality of polished SiO2 surface evaluated by quasi-Brewster angle technique

As a surface-sensitive optical method, the quasi-Brewster angle technique is extended to evaluate the subsurface qualities of quartz crystal and fused silica. By measuring the ellipsometry parameters at λ = 900 nm with variable incidence angle, a fitting process is executed using a proper subsurface nanostructure with an exponential porosity distribution. The fitting results predict the surface and subsurface information which are in good agreement with that of the Zygo interference microscope measurements and etching methods. In addition, the shift characteristics of phase change at the Brewster angle of such crystal and non-crystal material are compared and demonstrated.     

Young-type interference in collisions between hydrogen molecular ions and helium

The dissociative electron transfer from He into 10 keV H2+ was measured in a kinematically complete experiment by using the cold target recoil ion momentum spectroscopy imaging technique in combination with a highly resolving molecular fragment imaging technique. The electron transfer into the dissociative b(3)Sigma+_(u) state of H2 could be selected by kinematic conditions. We find a striking double slit interference pattern in the transverse momentum transfer which we can modify by selecting different internuclear distances. Compared to an optical double slit, interference minima and maxima are interchanged. The latter is the result of a phase shift in the electronic part of the wave function.     

Enhancement of LED light extraction via diffraction of hexagonal lattice fabricated in ITO layer with holographic lithography and wet etching

A novel method for enhancing light extraction efficiency of LEDs via diffraction of the lattice fabricated in ITO layers of LEDs is proposed. The lattice fabrication process includes holographic lithography and wet etching. 3-beam interference holographic approach was used to fabricate large-area hexagonal lattice mask which can cover 2-inch semiconductor wafer, and acid etching was used to transfer the lattice structure into p-contact ITO layer. 1.4 fold enhancement of light output at 20 mA injection current was obtained from GaN-based LEDs in the primary experiment. The lattice fabrication process is rapid and cost-effective thus enabling industrial mass production of high brightness LEDs.     

The pore opening process and its influence on conductivity measurements of irradiated polymer films by application of the electrochemical etching method

The technique of the electrochemical etching of irradiated polymer films is an useful method to investigate structures of the track cores.

The transversale etching rate as a function of the radius, derived from the time-dependence of the radius of the etching pore, can be interpreted as a corresponding magnitude of the degree of the damage within the track core.

In the case of polymer films irradiated by a high track density, the influence of the time distribution of the breakthroughs (pore opening process) of the etching microchannels on the conductivity changes during the etching process is to be discussed. First represented results lead to statements about the statistical nature of the pore opening process.     

Acoustic monitoring of frontal zone

A new method for detecting frequency shifts of acoustic field interference maxima is proposed. The method is based on the cross-correlation processing of frequency-swept signals. Perturbations of medium are modeled as variations in the frontal zone width. The potential of this method is analyzed in comparison with the known methods for measuring frequency shifts of interference maxima. A model reconstruction of the frontal zone variability is performed.     

The pore opening process of etching polymer films irradiated by single and multiple heavy ions. The etching process in the range of the track core radius (10 nm)

The technique of electrochemical etching of irradiated polymer films is an useful method to investigate structures of the track cores. In the case of the investigation of multiple track foils, the mean effective radius corresponds to the average of all synchron etching pores. On the other hand, the etching cones of all tracks do not break through to conducting micro channels coincidentally. The statistical character of this pore opening (break through) process is still unexplained, although several effects concerning this topic have been observed in the past. Another computer program simulates by way of the Monte Carlo Method the etching process of an ensemble of tracks within a thin polymer film. The conductivity of the multiple track etching foil can be described by the convolution between the conductivity of a single pore and the time dependent breakthrough rate. By way of the Laplace Transforms the measurements of the multiple and single track etching polymer films can be deconvoluted and yield the statistical nature of the pore opening process.     

Optical properties of one-dimensional photonic crystals fabricated by photo-electrochemical etching of silicon

The optical properties of one-dimensional photonic crystals (1D PCs), fabricated by electrochemical etching of periodic wall arrays on n-type (100) Si substrates, are investigated in this study. Several 1D PCs were fabricated with lattice periods varying from 4 to 7 μm and with trench depths in the range 160–210 μm. In-plane reflection spectra of the photonic structures at different depths were registered over a wide spectral range of 1.5–15 μm using Fourier Transform Infra-Red (FTIR) micro-spectroscopy. Some of the features observed in the reflection spectra of the structures investigated are believed to be as a result of interface roughness. A corrugated side-wall surface, an artifact of the fabrication technique, results in the degradation of optical reflection characteristics, principally mainly in the near IR spectral range, and the emergence of optical anisotropy. As a result of the periodicity, modulation of the reflection spectra, that is, the difference between the maxima and minima of the interference fringes, reached a value of 95% in the mid-infrared. The optical properties of the structures investigated indicate that they show promise for microphotonics applications.     

Fabrication of three-dimensional crystalline microstructures by selective ion implantation and chemical etching

We present a new fabrication technique to produce three-dimensional (3D) microstructures on crystalline substrate using selective ion implantation and chemical etching. Localized lattice-damage layers at the specified depth beneath the substrate surface are formed by selective ion implantation. After etching out the partial surface regions and the buried lattice-damage layers by chemical etching, the 3D crystalline microstructures are produced. This technique is demonstrated on LiNbO₃ crystal to produce undercutting and free-standing microstructures, including microwire, microring, and microdisk. The measurement results of micro-Raman spectra show that the used fabrication process does not affect the original crystalline structure. The features of this technique include smooth structure surface, large undercutting range, and auto-etching stop. By using multiple implantations or repeating the proposed process several times, versatile 3D crystalline microstructures can be produced.     

Methods of measuring frequency shifts in the interference structure of the sound field in oceanic waveguides

The efficiency of the correlation method is considered as applied to measuring frequency shifts of maxima in the interference structure of the sound speed under the influence of distortions of the sound-speed profile. The method is based on tracing the position of the maximum of the cross-correlation function corresponding to the spectrum of the transmitted signal in the frequency domain. The distortion is modeled by seasonal variations of the hydrological environment. The noise immunity of the method is analyzed. The correlation method is compared with other known methods of tracing frequency shifts of the interference maxima.