Aerial image formation of quantum lithography for diffraction limit

Since the diffraction limit of Rayleigh criterion hardly creates finer features, the development for the quantum lithography of entangled photons, one of technologies beyond the diffraction limit, is a key merit without the shorter wavelength source tool. In the arbitrary pattern formation for the commercialization of this lithography, however, this quantum lithography is required to implement mask patterns and the conventional optical lithography. In this paper, for the quantum lithography of entangled photons, collective behavior of N-photon entangled states is modeled and simulated to show the effect of photon entangled states for 3-dimensional arbitrary pattern formation by using the rigorous coupled wave analysis (RCWA) and Kirchhoff analysis. For the enhanced resolution from the point of view that the de Broglie wavelength of a quantum state comprised of two entangled photons is half the classical wavelength associated with either photon, simulation results of entangled photons are similar to those of short wavelengths. However, both of simulation results show that the resolution of entangled photons is better than those of the shorter wavelengths. Simulation results can predict realistic better performance of entangled photons.     

Three‐dimensional optical laser lithography beyond the diffraction limit

Direct laser writing has become a versatile and routine tool for the mask‐free fabrication of polymer structures with lateral linewidths down to less than 100 nm. In contrast to its planar counterpart, electron‐beam lithography, direct laser writing also allows for the making of three‐dimensional structures. However, its spatial resolution has been restricted by diffraction. Clearly, linewidths and resolutions on the scale of few tens of nanometers and below are highly desirable for various applications in nanotechnology. In visible‐light far‐field fluorescence microscopy, the concept of stimulated emission depletion (STED) introduced in 1994 has led to spectacular record resolutions down to 5.6 nm in 2009. This review addresses approaches aiming at translating this success in optical microscopy to optical lithography. After explaining basic principles and limitations, possible depletion mechanisms and recent lithography experiments by various groups are summarized. Today, Abbe's diffraction barrier as well as the generalized two‐photon Sparrow criterion have been broken in far‐field optical lithography. For further future progress in resolution, the development of novel tailored photoresists in combination with attractive laser sources is of utmost importance.     

Quantum interferometric optical lithography: exploiting entanglement to beat the diffraction limit

Classical optical lithography is diffraction limited to writing features of a size lambda/2 or greater, where lambda is the optical wavelength. Using nonclassical photon-number states, entangled N at a time, we show that it is possible to write features of minimum size lambda/(2N) in an N-photon absorbing substrate. This result allows one to write a factor of N2 more elements on a semiconductor chip. A factor of N = 2 can be achieved easily with entangled photon pairs generated from optical parametric down-conversion. It is shown how to write arbitrary 2D patterns by using this method.     

Recent developments in nanofabrication using scanning near-field optical microscope lithography

In addition to its well-known capabilities in imaging and spectroscopy, scanning near-field optical microscopy (SNOM) has recently shown its great potentials for fabricating various structures at the nanoscale. A variety of SNOM-based fabrication techniques have been developed for different applications. In this paper, the SNOM-based techniques involving three major functions: material modification, addition, and removal, are examined with emphasis on their abilities and reliability to make structures with resolutions at the nanometer level. The principles and procedures underlying each technique are presented, and the differences and uniqueness among them are subsequently discussed. Finally, concluding remarks are provided to summarize the major techniques studied and to recommend the scopes for technology improvement and future research.     

Example of a rigorous solution for the gravitational field of a hollow,rotating cylinder

A class of exact solutions-depending upon two dimensionless parameters-to the gravitational field equations is obtained, where the source of the field is a rotating, hollow cylinder of infinite length. The material properties, although highly idealised, nevertheless are not unrealistic and chosen in such a way as to allow elementary integration. The solutions show how the inertial frame inside the cylinder is dragged by the rotating material, and also how the drag continues inside the material and in the outside region. They are exact examples for the Lense-Thirring effect.     

Investigation of a slot nanoantenna in optical frequency range

Following the analogy of radio frequency slot antenna and its complementary dipole, we propose the implementation of a slot nanoantenna (SNA) in the optical frequency range. Using finite-difference time-domain (FDTD) method, we investigate the electromagnetic (EM) properties of a SNA formed in a thin gold film and compare the results with the properties of a gold dipole nanoantenna (DNA) of the same dimension as the slot. It is found that the response of the SNA is very similar to the DNA, like their counterparts in the radio frequency (RF) range. The SNA can enhance the near field intensity of incident field which strongly depends on its feedgap dimension. The resonance of the SNA is influenced by its slot length; for the increasing slot length, resonant frequency decreases whereas the sharpness of resonance increases. Besides, the resonance of the SNA is found sensitive to the thickness of metal film, when the latter is smaller than the skin depth. The effect of polarization of incident field on the EM response of the SNA was examined; the field enhancement is optimum when polarization is parallel to the feedgap. Finally, we calculate the radiation patterns of the DNA and SNA and compare them with those of the RF dipole antenna. The radiation pattern of the SNA is found to be independent of its slot length when excited at resonant frequency. To the best of our knowledge, this is the first study on a slot antenna in the optical frequency.     

The rigorous electromagnetic theory of the diffraction of vector beams by a circular aperture

The rigorous electromagnetic theory of the diffraction of vector beams by an aperture is proposed and numerically evaluated by the diffraction of vector Gaussian beams by a circular aperture. The results are compared with those, by using the vector Rayleigh–Sommerfeld diffraction integrals and angular-spectrum expression theory, showing a good consistency. The numerical calculation shows that the result calculated by the rigorous theory is much more precise than those calculated by the integral method in diffraction near field, and a highly consistency reaches by the three methods in diffraction far field. A further extension of the theory is discussed.     

The inhomogeneous slab,a rigorous solution to the propagation problem

A rigorous solution based on an integral equation to investigate the propagation in an inhomogeneous slab of arbitratry index profile is given.     

模拟光刻中双层衰减相移接触孔衍射的理论公式

为了仿真光刻中接触孔掩模的衍射,建立了严格的三维(3D)掩模模型。采用法向矢量法(NV)改善了接触孔掩模耦合波方程的收敛性。利用S矩阵求解线性方程组避免了数值不稳定问题。对于双吸收层衰减相移接触孔掩模,当有效的截断级次达到1225级以上时,(0,0)级次能得到更好的收敛结果。当有效的截断级次分别为1225级,1369级,1521级及1681级时,衍射效率分别为23.64%,23.67%,23.63%及23.66%。利用建立的模型,研究了偏振态随着掩模、入射光参数的变化关系。当线宽小于25nm时,掩模主要透过TM偏振光。     

A new generation optical lithography using a third harmonic pulse generated by micro-ring resonators

We first propose a new system of a third harmonic generation by using a soliton pulse circulating in the integrated micro-ring devices. By using this system, the ultra-short pulse in the attosecond (as) and beyond can be easily generated. In principle, light pulse known as a soliton pulse is input into a design system. It consist the three-stage micro-ring resonators, where the ring radii are within the range between 5 and 35 μm. With the appropriate parameters such as ring radius, coupling ratio and nonlinear refractive index, the attosecond pulse is generated by filtering the chaotic signals within the micro-ring devices. One of the results obtained has shown that the generation of the ultra narrow pulse (spectral width) and sharp tip is achieved. The potential of using such a pulse for picometer (pm)-scale lithography is plausible.     

Freeform lens for off-axis illumination in optical lithography system

A method of designing a freeform lens for off-axis illumination (OAI) in an optical lithography system is proposed in this paper. Based on the Snell's law and conservation law of energy, a series of first-order partial differential equations are deduced. Coordinate relations are established with the energy mapping relations by the characteristics of the incident beam and the predetermined irradiance distribution on the target plane. The contours of the freeform lens are calculated by solving partial differential equations numerically. Moreover, the optical performance for OAI is simulated and analyzed. Simulation results show that the irradiance distributions can be well controlled with a maximum uniformity of 95.71% and a maximum efficiency of 99.04%. Tolerance analysis shows that the angular errors of the freeform lens are more sensitive than the coordinate errors.     

优化抗蚀剂的预烘工艺减小衍射对X射线光刻的影响

讨论了衍射效应在微米 /纳米X射线光刻中对分辨率的影响和抗蚀剂的预烘温度与其衬度的关系。分析发现增加抗蚀剂的衬度能有效地提高工艺的容裕度 ,减小衍射作用。实验表明 ,在预烘温度为 170℃时 ,正性抗蚀剂PMMA有最高的衬度为 4 46 ,负性抗蚀剂PN 114在预烘温度为 115℃时有最高的衬度为 8 40。给出了最佳预烘温度下使用两种抗蚀剂的X射线光刻的实验结果     

Phase optical elements for widening a minimum diffraction spot

An iterative technique has been developed for calculating phase radial optical elements characterized by a small number of phase gradations and aimed at stretching a minimum diffraction spot. The proof of the algorithm convergence is given and the results of computer simulation are reported.     

Adaptive synthesis of optical pattern for photonic crystal lithography

The two-photon absorption spectrum and cross-section (δ) for ruby (Cr³⁺:sapphire) have been measured over the 0.8–1.2 μm wavelength range at 25°C. Absolute values of δ were obtained by comparing the fluorescence yield for two-photon excitation with that for single-photon excitation of the same ionic transition under identical illumination conditions. The maximum values of δ are 4.6×10⁻³ GM for o-polarisation and 5.9×10⁻³ GM for e-polarisation at 840 nm. The relevance of these measurements to distributed optical fibre sensing is briefly discussed.     

Electromagnetic-wave diffraction by slot in faster-than-light flow of nondispersive medium

Plane-wave diffraction by a slot in an ideally conducting shield in a moving nondispersive medium is examined. The main diffraction characteristics are determined for the case of faster-than-light motion of the medium. The particular cases of narrow and wide slots are analyzed.St. Petersburg State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 8, pp. 678–687, August, 1992.     

像质检测用光学窗口的温度适应性设计与实验北大核心CSCD

为了在温度变化条件下对光电成像系统进行像质检测与评价,设计一种具有温度自适应功能的光学窗口。分析了温度变化对光学玻璃面形的影响,进行光学窗口的温度适应性光机结构设计,通过有限元分析与实测实验相结合的方法分析了温度变化对光学窗口面形的影响,验证了温度适应性设计的有效性。实验结果表明:常温20℃条件下,光学窗口波像差的PV值和RMS值分别为82.90 nm和6.96 nm;高温50℃条件下,波像差的PV值和RMS值分别为136.68 nm和14.55 nm;低温−40℃条件下,波像差的PV值和RMS值分别为183.51 nm和28.48 nm;高、低温环境下光学窗口的波像差与常温环境下结果对比的数值变化趋势与有限元分析结果具有较好的吻合性;在3种温度条件下光学窗口波像差的PV值均小于或接近(1/4)λ,且由于温度变化引起的光学窗口面形变化很小,设计的光学窗口具有较好的温度适应性。