原子光刻

与光子和电子不间,原子的激发亚稳态具有方便操作的内能态结构,这使利用内能态的光学淬灭原理实现光刻技术成为现实.基于原子光学的中性原子束光刻技术是下一代光刻技术(the next generation lithography,NGL)的一种,它可分两种途径实现:激光驻波原子直沉积技术和亚稳态中性原子光刻技术.前者可以实现图案的纳米尺度特征、大面积平行沉积和高分辨率;后者结合有效的抗蚀剂,同样可以实现纳米图形制造,在基板上获得的尖锐边缘分辨率目前可达40 nm.两种途径的原理相差甚远,但最终获得的结果相似.     

Atom lithography with ytterbium beam

We successfully produced periodic ytterbium (Yb) narrow lines on a substrate using near-resonant laser light and the direct-write atom-lithography technique. The Yb atom is a promising material for nanofabrication using atom optics due to its electrical conductivity, the laser wavelength required for handling the atoms, the vapor pressure of the fabrication process, etc. The ¹⁷⁴Yb atoms collimated by Doppler cooling were channeled by the dipole force of an optical standing wave and then deposited onto a substrate. We clearly observed a grating pattern of Yb atoms fabricated on the substrate with a line separation of approximately 200 nm after examining the surface of the substrate with atomic force microscope. This is the first demonstration of nanofabrication using the atom-optical approach with Yb atoms. PACS 32.80.-t; 32.80.-Pj     

Atom lithography with two-dimensional optical masks

With a two-dimensional (2D) optical mask at =1083 nm, nanoscale patterns are created for the first time in an atom lithography process using metastable helium atoms. The internal energy of the atoms is used to locally damage a hydrophobic resist layer, which is removed in a wet etching process. Experiments have been performed with several polarizations for the optical mask, resulting in different intensity patterns, and corresponding nanoscale structures. The results for a linear polarized light field show an array of holes with a diameter of 260 nm, in agreement with a computed pattern. With a circularly polarized light field a line pattern is observed with a spacing of /2^0.5=766 nm. Simulations taking into account many possible experimental imperfections can not explain this pattern. PACS 32.80.Lg; 39.25.+k; 81.16.Nd     

Photonic crystals with a chiral basis by holographic lithography

We demonstrate the use of holographic lithography to fabricate chiral photonic crystals. These structures are calculated to exhibit strong optical activity even though they are made from material that is not intrinsically optically active. By control of the polarizations of the interfering plane waves that are used to define the three-dimensional microstructure it is possible to create left- and right-handed and closely related non-chiral structures.     

Atom lithography with a cold, metastable neon beam

We study different aspects of atom lithography with metastable neon atoms. Proximity printing of stencil masks is used to test suitable resists that are sensitive to the internal energy of the atoms, including dodecanethiols on gold and octadecyltrichlorosilanes grown on a SiO₂ surface. As an example of patterning the atomic beam with laser light, we create parallel line structures on the surface with a periodicity of half the laser wavelength by locally de-exciting the atoms in a standing quenching wave. Received: 29 June 1999 / Revised version: 30 August 1999 / Published online: 10 November 1999     

Atom lithography without laser cooling

Using direct-write atom lithography, Fe nanolines are deposited with a pitch of 186 nm, a full width at half maximum (FWHM) of 50 nm, and a height of up to 6 nm. These values are achieved by relying on geometrical collimation of the atomic beam, thus without using laser collimation techniques. This opens the way for applying direct-write atom lithography to a wide variety of elements.     

Quantum lithography with classical light

We show how to achieve subwavelength diffraction and imaging with classical light, previously thought to require quantum fields. By correlating wave vector and frequency in a narrow band, multiphoton detection process that uses Doppleron-type resonances, we show how to achieve arbitrary focal and image plane patterning with classical laser light at submultiples of the Rayleigh limit, with high efficiency, visibility, and spatial coherence. A frequency-selective measurement process thus allows one to simulate, semiclassically, the path-number correlations that distinguish a quantum entangled field.     

3-D holographic lithography of organic-inorganic hybrids

Fabrications of ordered three-dimensional structures with submicron lattice constants were performed on organic-inorganic hybrids using a holographic lithography technique recently reported in the literature. The possibility of such a patterning has previously been demonstrated from single nanosecond laser pulse irradiation of thin films of epoxy photoresist and mixtures of methacrylate-alkoxy-silane with Zr or Ti alkoxides. In the present work, UV irradiation of similar hybrid resins were carried out through repeated laser pulses of low energy with a twofold objective: (i) to study the interference stability for future chemical gas phase decomposition experiments and (ii) to obtain patterning through large film thickness (e.g. 1 mm). The influence of several parameters on the structuration was examined from observations by scanning electron microscopy and optical diffraction. Many interdependent parameters were considered in different steps of the process, namely (i) hybrid resin preparations with required properties of stability, transparency and viscosity, (ii) film coating on different substrates, (iii) UV irradiation (energy and number of laser pulses), (iv) ultrasonic dissolution of monomer, and (v) sample drying. As results, different structuration resolutions were observed as a function of these parameters. But if the influence of a few parameters was easily understood and controlled, it has also appeared that it was not the case of all of them.     

Photonic band gap architectures for holographic lithography

Using symmetry considerations, we identify three families of large photonic band-gap (PBG) architectures defined by the isointensity surfaces of four beam laser interference. For particular choices of beam intensities, directions, and polarizations, we obtain a diamondlike crystal, a novel body-centered cubic architecture, and a simple cubic structure with PBG to center frequency ratios of 25%, 21%, and 11%, respectively, when the isointensity surface defines a silicon (dielectric constant of 11.9) to air boundary.     

Three-dimensional holographic lithography by an iterative algorithm

We have applied an iterative algorithm for hologram design with multiple output image planes arranged in close proximity to create continuous patterns within an imaging volume. These holograms have been designed for photolithography on three-dimensional surfaces. The influence of simulated image plane separation on the final image, and its suitability for lithography, is assessed. Results are presented and the most suitable case is demonstrated experimentally.     

Subnanometer-accuracy z-position monitor mask for optical lithography

A lithographic test pattern, the phase shift grating (PSG) z monitor, is introduced. Through the use of phase shift techniques, position errors of images in the z-direction translate into lateral shifts in the printed pattern. The lateral shifts are easily measurable using an overlay metrology tool. Each z monitor pattern in a test mask can be directly read for the sign and magnitude of the z error. When the experimental conditions, namely, the period of a PSG and a coherent factor of the lithography tool simultaneously satisfies a criterion of the asymmetric two-beam interference between the zeroth-order ray and either of the two first-order rays of diffraction, the linearity of a z-vs-overlay curve is always complete and the slope of the curve is constant everywhere in the image field. Using state-of-the-art overlay metrology tools, we realized subnanometer-order accuracy in the z measurement.     

Atom funnel running with evanescent light generated by a thick hollow light beam

The use of a hollow light beam reduces the loss of atoms inside and outside an evanescent-light funnel. Therefore, we superimpose an LG₀₁ beam with a small hole onto a doughnut beam with a large outer diameter and couple the resultant hollow light beam to the 240-μm-wide outlet of an inverted trigonal-pyramidal funnel. Compared to the case where a Gaussian light beam is employed for generation of evanescent light, the flux intensity of the output cold ⁸⁷Rb atoms rises 13-fold when the inner diameter of the 4.5-mm wide hollow light beam is 1.7 times as large as the size of the outlet under optimal blue-detuning conditions.     

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 new method of fabrication of submicron structures by optical lithography with mask shifting and mask rotation

This paper presents the methods of fabricating narrow parallel submicrometric stripes in silicon dioxide and a resist layer. The experiments were conducted by two techniques: double patterning lithography and double exposure lithography. In addition to the above mentioned processes, mask translation was applied. For all conducted experiments, chrome masks and a 405 nm line of the high pressure mercury lamp of an MA-56 Mask Aligner System were used. The main aim of the performed tests was to establish the utility and the possible applications of the methods used.     

Photonic crystals for the visible spectrum by holographic lithography

We describe a general and flexible technique for the fabrication of three-dimensional photonic crystals that is particularly well adapted to the production of structures with the sub-micron periodicity required for applications in the visible optical spectrum. Three-dimensional microstructure is generated by using a four-beam laser interference pattern to expose a thick layer of photoresist. Exposed areas are rendered insoluble; unexposed areas are dissolved away leaving a three-dimensional photonic crystal formed of cross-linked polymer with air-filled voids. The polymeric structure may be used as a template for the production of photonic crystals with higher refractive index contrast. Photonic crystals made of polymer and of TiO₂ have been characterized by scanning electron microscopy and by optical diffraction measurements.     

Reflective mask for projection lithography operating at a wavelength of 13.5 nm

This work is devoted to the technology of mask manufacturing and investigation of the characteristics of the reflective mask employed in the extreme ultraviolet lithography test bench designed at the Institute for Physics of Microstructures, Russian Academy of Sciences. The mask??s structure and composition have been optimized. The antireflecting (absorbing) coating and stop-layer materials that are used to etch the mask structure and the multilayer interference system, which reflects radiation at the operating wavelength, have been selected. The mask manufacturing technology is described. The measured reflective and geometrical characteristics of a mask (absorbing layer thicknesses, line widths, and line-edge roughnesses) are presented. A new direct method for certifying mask defects of 30 nm or more is proposed.     

Extending standard mask lithography exposure technique to spherical surfaces

Similar to planar lithography, the use of a mask to produce multiple copies of a binary master sample is also possible in the case of spherical surfaces. Evidently, the spherical mask needs to have the opposite radius of curvature of the desired substrate, and additional problems arising from the curved geometry have to be taken into consideration. Inhomogeneities of the illumination impinging on the resist-coated surface negatively influence the exposure result. Ways of overcoming these difficulties to obtain satisfactory results for the implementation of the exposure in a conventional mask aligner are shown. Despite a lowered contrast due to back reflections and a varying distance between mask and substrate, exposure results of sufficient quality are achieved with the help of an adapted aperture and the use of water as an immersion fluid.     

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.