基于严格电磁场模型的光学光刻仿真

光学光刻技术已广泛应用于微电子机械系统（MEMS）以及集成电路（IC）领域。由于光刻工艺设备的价格十分昂贵,因此利用光刻仿真这一技术来预期工艺结果并优化工艺中存在的问题就显得很有必要。研究了一种基于严格电磁场模型的求解方法波导方法,并将此方法拓展应用于模拟MEMS领域中的厚胶曝光场景。通过这一模型,可以模拟光刻胶内部的光强分布,并进一步预测出显影后的光刻胶形貌。最后,针对某些特定掩模版结构,给出它们的仿真结果并验证其正确性。     

Coupled multiwave interactions in aperiodically poled nonlinear optical crystals

A new type of coupled nonlinear optical interactions that can be implemented in crystals with an aperiodic modulation of the nonlinear susceptibility is studied. The quasi-phase matching condition is satisfied simultaneously for several conventional three-frequency processes involved in the interaction due to the aperiodic variation of the nonlinearity in space. A simple method for designing aperiodically poled nonlinear optical crystals is proposed and analyzed. The method is based on the superposition of nonlinearity modulations produced by several periodic functions simultaneously so that each of these functions individually corresponds to its own quasi-phase-matched nonlinear process. The dynamics of energy exchange during interaction of five waves with different frequencies that involves three coupled three-frequency parametric interaction processes is investigated thoroughly. The ratio between the effective nonlinear wave coupling coefficients and the amplitudes of pump waves is determined for the case in which the initial stage of the interaction is characterized by the parametric instability. It is demonstrated that the secondary simplification of the coupled differential equations with spatially modulated nonlinear coefficients, which leads to the system of equations with constant nonlinear coefficients, correctly describes the dynamics of interaction of the waves at distances of the order of 50 characteristic nonlinear lengths.     

Research on the optical field distribution and micro-fabrication model in convex-surface laser lithography

A system of convex-surface laser lithography with diode laser is established in this paper. Based on this system, a mathematical model of optical field distribution and lithography on the photoresist layer of convex-surface substrate with diode laser is presented. According to the lithography system and model, some numerical simulations are carried out. The simulation result shows that lithographic lines on convex-surface lithography are not symmetric about the optical axis of incident laser beam. Axis of lines at different vector radius on convex-surface substrate will offset from the wavefront normal of incident laser beam. The offset distance depends on the slopes of different equivalent slants. The simulative results of lithographic model agree well with the lithographic experimental data.     

Direct observation of high-order optical susceptibilities via angularly-resolved multiwave mixing

A new method of monitoring specific high-order optical susceptibilities of nonlinear media via angularly-resolved emission in a phase-matched multiwave mixing configuration is presented. This technique, which can be viewed as the creation by two optical beams of a strongly anharmonic absorption or index grating, and the simultaneous exploration of higher Bragg-diffraction orders by a third wave, is demonstrated here in the case of gas media near optical resonance.     

Wave front transformation of optical vortices with multiwave interactions in resonant media

The transformation of singular light beams is analyzed theoretically for multiwave interactions on amplitude and phase dynamic holograms in media with a resonant nonlinearity. The possibility of multiplying topological charge using different diffraction orders is demonstrated and optimal conditions for parametric energy exchange are determined which ensure retention of the structure of the wave front of optical vortices. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 395–402, May–June, 2009.     

Frequency transformation of optical vortices upon nondegenerate multiwave interaction in dye solutions

A method for inverting the topological charge of singular light beams with their simultaneous frequency transformation under multiwave interaction in media with resonant and thermal nonlinearities is proposed. Frequency-nondegenerate four-wave and six-wave interactions of optical vortices are experimentally implemented using an ethanol solution of a polymethine dye 3274U as a nonlinear medium.     

Novel optical lithography using silver superlens

This work has demonstrated that with silver superlens,the resolution of conventional optical lithography can be improved significantly.Experimental and simulative results are given to verify the facts that the resolution and the pattern fidelity are sensitive to the contact tightness between layers.     

Observation of two multiwave mixing processes via dual optical pumping channels

Based on double optical pumping channels,we experimentally study the competition between two coexistent six-wave mixing(SWM) processes falling into two electromagnetically induced transparency windows by scanning the frequency of the probe field in two similar five-level atomic systems of 85Rb.By blocking one optical pumping channel unrelated to the four-wave mixing(FWM) process,one SWM process,together with the FWM process,generated by a conjugated small-angle static grating could be observed in the spectrum.Moreover,the other SWM process obtained by blocking the first SWM channel is also observed together with the FWM process in a lower N-type four-level subsystem.These experimental results agree well with theoretical predictions.     

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     

High-resolution capability of optical near-field imprint lithography

We propose a novel method to increase the resolution of imprint lithography by introducing strong localization of the optical near-field intensity, depending on the mold structure. By optimizing the thickness of the metallic film on a SiO₂ line-and-space (LS) mold without a sidewall coating, we confirmed that the optical near-field strongly localizes at the edge of the mold, using a finite-difference time-domain calculation method. Based on the calculated results, we performed optical near-field imprint lithography using a mold with metallized (20-nm-thick Al without a sidewall coating) SiO₂ LS with a 300-nm half-pitch that was 200-nm deep with illumination using the g-line (λ=436 nm), and obtained features as narrow as 50 nm wide. PACS 81.16.Nd; 81.16.Rf     

Rigorous model of classical spacetime foam

If in the gravity quantization process one changes from the smooth manifold category to a more general category, qualitatively new features can appear. To illustrate this, we construct a geometrically precise but physically naive model of a classical “spacetime foam” and discuss the consequences of the principle of general covariance and the equivalence principle in this more general setting. We also show how Einstein's equations can be defined on this “spacetime foam”.     

Resolution enhancement techniques for optical lithography and optical imaging theory

Production of a fine pattern is necessary to get a high integration degree of integrated circuits. The conventional methods which utilize high numerical aperture and short wavelength exposure are limited by designing and manufacturing of a practical lens and make the focus depth narrow. Resolution enhancement techniques (RETs) have, therefore, been required and proposed. This paper introduces a phase-shifting mask, a typical RET, points out the problems and inconsistencies of conventional optical imaging theory and explains the image formation concept of expansion of plane waves. Essentially using this concept, an attempt is also made to describe some other typical RETs with potential.     

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.     

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.     

Dye assisted enhanced transmission in near field optical lithography

Surface plasmon lithography using embedded-amplitude masks has received considerable attention in recent times for its ability to produce high density features with resolution beyond diffraction limit. However plasmon damping caused due to intrinsic metal absorption restricts the achievable aspect ratio of the fabricated features. One possible way to rectify this issue is to use a gain medium to amplify the surface plasmons and thereby increase their propagation length. In this context this paper proposes a novel concept of employing dye medium to enhance plasmon propagation in mask based surface plasmon lithography, so as to obtain higher transmission depth in the writing medium. The proposed concept is supported by numerical simulations and the results obtained indicate a 14.5 fold field enhancement in presence of dye (gain) medium.     

All-reflective optical system design for extreme ultraviolet lithography

All-reflective optical systems,due to their material absorption and low refractive index,are used to create the most suitable devices in extreme ultraviolet lithography （EUVL）.In this letter,we present a design for an all-reflective lithographic projection lens.We also discuss its design idea and structural system.After analysis of the four-mirror optical system,the initial structural parameters are determined,the optical system is optimized,and the tolerances of the system are analyzed.We also show the implementation of optimal layout and desired imaging performance.     

Pump-probe spectroscopy on photoinitiators for stimulated-emission-depletion optical lithography

We report on femtosecond pump-probe experiments on two different photoinitiators in solution. These two molecules have recently appeared as attractive candidates for far-field optical lithography based on stimulated-emission-depletion (STED) inspired approaches aiming at beating Abbe's diffraction limit. For the case of 7-diethylamino-3-thenoylcoumarin (DETC), we find that stimulated emission clearly dominates over excited-state absorption, whereas the opposite holds true for the case of isopropylthioxanthone. We argue that it is desirable that stimulated emission dominates over excited-state absorption as depletion mechanism in STED photoresists. Thus, DETC is an attractive corresponding photoinitiator.     

Design procedure using coupled multiwave efficiency analysis for wavelength shifted holographic optical elements

A design procedure uses coupled multiwave efficiency analysis in wavelength shifted holographic optical elements. The procedure is adapted for producing 488 nm holographic lenses for use at 628 nm.     

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.