Embedded metal mask enhanced evanescent near field optical lithography

Simulation of evanescent optical lithography using an embedded metal mask (EMM) shows that resolution and throughput are significantly enhanced over conventional ENFOL, due to coupling between surface plasmons and cavity mode excitations. The key role played by surface plasmon polaritons and the effects of wave vector matching between the incoming photon and the EMM mask grating are clear from the simulation. In particular a double peaked resonant intensity distribution is revealed for the first time within the dielectric filled mask cavity, for the shorter wavelengths only. This effect is highly conducive to efficient sub wavelength lithography and has not been discovered by previous simulations. The EMM–ENFOL process has considerable potential for cheap, high throughput nanolithography with resolution well below diffraction limits.     

Binary and phase shifting mask design for optical lithography

The authors propose a number of pre-distorted mask design techniques for binary and phase-shifting masks. Their approach is based on modeling the imaging mechanism of a stepper by the Hopkins equations and taking advantage of the contrast-enhancement characteristics of photoresist. Optimization techniques such as the branch and bound algorithm and simulated annealing algorithm are used to systematically design pre-distorted masks under incoherent and partially coherent illumination. Computer simulations are used to show that the intensity contour shapes and developed resist shapes of their designed mask patterns are sharper than those of conventional masks. The designed phase-shifting masks are shown to result in higher contrast as well as sharper contours than binary masks. An example of phase conflicting masks designed with the algorithm is shown to outperform a simple intuitive design. This example indicates that a fairly general design procedure consisting of alternating phase shifts and their optimized phase-shift masks is a viable candidate for future phase-shifting mask design     

多层介质光学膜系的二阶膜厚误差因子分析

本文推导了多层介质光膜系的二阶膜相对误差因子表达式，以λ０／４高反射多层介质膜系为例对一阶和二阶误差因子进行了数值分析，比较了两者在不同波长区域对膜系光谱性能的影响，发现不应仅考虑一阶误差因子，而应同时考虑一阶和二阶误差因子的作用，才能较好地描述膜厚误差对膜系光谱性能的影响。     

光学光刻中的离轴照明技术

本文讨论了光学光刻中的离轴照明技术。主要从改善光刻分辨率、增大焦深、提高空间像对比度等方面对离轴照明与传统照明作了比较 ,并用Prolith仿真软件进行了模拟分析。研究表明 ,离轴照明是一种很有效的光刻分辨率增强技术。     

Substrate-tube lithography for optical fibres

We describe the first use of substrate-tube lithography to build complex structures into MCVD fibre preforms. While the basic process is illustrated with high-birefringence fibres of 1.9 and 3 mm beat lengths and a two-core fibre, the technique is more general and may lead to a new class of integrated optical devices.     

New effects of modified illumination in optical lithography

In optical lithography the most fine and isolated dark line is obtained at the phase-shifter edge of a chromeless phase-shifting mask, but only closed-loop patterns can be formed. An easy method for eliminating the useless dark line at the phase-shifter edge by combining modified illumination technologies is proposed. Using a modified light source, which is arranged along one axis (x or y) of the light source area, the resultant optical intensity is different in the x and y directions. A fine resist pattern of 0.15 μm produce along only one direction of the phase-shifter's edge is demonstrated     

Patterning characteristics under small vibrations of the mask and wafer in SR lithography

Patterning characteristics under mechanical vibrations between mask and wafer are investigated in terms of pattern profile deformation, linewidth change, and exposure dose margin by performing exposure experiments and using a Fresnel diffraction simulation. A small vibration works as a smoothing filter and provides a smooth profile in patterning. Stronger vibrations, generally, make the linewidth bigger, thereby reducing the dose margin. However, given vibrations of a particular amplitude, there is a certain range of doses in which the vibrations donot significantly affect the linewidth. Below the range, the linewidth becomes smaller; and above, it becomes larger. And it is possible to obtain the desired dimensions of delineated pattern even when the amplitude of the vibrations was a quarter of the minimum feature size.     

Predicting mask distortion, clogging and pattern transfer for stencil lithography

One of the ultimate tasks for stencil lithography is the ability to fabricate arrays of structures with controlled dimensions on the nanometer scale precisely positioned on a suitable surface. The race to shrink feature sizes requires the limits of conventional lithography to be extended to high-throughput, low cost, reliable and well-controlled processes of which stencilling is a promising candidate for nanoscale applications. Identifying, predicting and overcoming issues accompanying nanostencil lithography is critical to the successful and timely development of this technique for a wide range of potential applications. This paper addresses phenomena associated with stencil nanopatterning and presents the results of modelling and simulation studies for predicting the deleterious effects of mask distortion and clogging during pattern transfer. It is shown that degrading effects of stress-induced deformation of stencils can be dealt with via optimal design of corrugation structures which in turn reduce stencil deformation and significantly improves pattern definition. Modelling results are validated by comparison to experiment. The corrugation structures can be used to define practical design rules for fabrication of stable large area (“full scale”) purpose-designed stencil membranes. The accurate modelling of the clogging phenomenon combined with gradually evolving stencil deformation, also presented in the paper, can be used for prediction of pattern distortion, to calculate maximum thickness of a deposited layer and/or for prediction of the stencil lifetime.     

A simple mask aligner and printing frame for conformable photomask lithography

Conformable photomask lithography allows submicrometer lines to be replicated by contact printing. Surface acoustic wave devices with 0.4-µm lines have been produced using this technique. A mask aligner and printing frame have been designed which feature micrometer controlledXandYmotion, rotation about the center of the viewing field, and both top and bottom illumination of mask and substrate. The construction and use of the apparatus, which is based on a toolmaker's microscope, is fully described.     

Process extensions in optical lithography enabling 45-nm technologies

This work describes approaches in the field of process extensions, complementary to the more traditional optical extension techniques, to enable the extension of optical lithography to 45-nm technologies.     

光学光刻设备发展和展望

在半导体技术和制造的发展中,半导体加工技术中最为关键的光刻技术和光刻工艺设备,必将发生显著的变化,本文将对光刻技术和光刻设备的发展历史进行简述,并展望未来光刻技术的趋势.     

Influence of MEEF change on the mask shadowing effect in extreme ultraviolet lithography

The influence of mask error enhancement factor (MEEF) on the mask shadowing effect was investigated for extreme ultraviolet lithography. Imaging properties including horizontal-vertical (H-V) CD (critical dimension) bias and MEEF change through the pitch according to absorber thickness and process condition were studied using aerial image simulation. The mask structure used in this study consisted of tantalum nitride (TaN) absorber and 2 nm ruthenium (Ru) capping layer on the 40 pair of Mo-Si multilayer. As the absorber thickness increased and the pattern pitch decreased, both H-V CD bias and MEEF increased. At the illumination condition of 0.32 numerical aperture (NA), the H-V CD bias variation through the pitch was negligible and slightly increased at 1:1 pitch, while it steeply increased at 1:1.2 and 1:1 pitch for NA of 0.25. The MEEF value was below 1.5 for all calculated absorber thicknesses when the pitch was from 1:1.2 to 1:5, whereas it was 3 with 64 nm thick TaN for 1:1 pitch at vertical pattern. With the increment of absorber thickness, the MEEF difference between the horizontal and vertical pattern increased. We also calculated the H-V overlapping process window (PW) according to TaN thickness using 22 nm 1:1 line and space (L/S) pattern. As absorber thickness decreased, the overlapping zone in the EL of the focus-exposure plots between the horizontal and vertical features increased. Enough image contrast and H-V overlapping PW could be achieved by applying 38 nm thick TaN.     

A little light magic [optical lithography]

At first glance, it appears that optical lithography has hit a dead end. Wavelengths shorter than 193 nm can't be used without a drastic redesign of lithographic systems because the shorter wavelengths are simply absorbed by the quartz lenses that direct the light onto the wafer. So is this the end? Not quite. There are a few more tricks that IC manufacturers can play. Lumped together, they are called resolution enhancement techniques (RETs), and in one way or another, they all coax the light into resolving shapes much smaller than its wavelength. The main techniques are optical proximity correction, phase-shifting masks, and modified, or "off-axis," illumination. With these tricks, the existing-and already paid for-optical lithography equipment can create patterns much smaller than the wavelength of the light used to produce them, these techniques can be easily extended to one-eighth the wavelength of the light-that is, to less than 25 nm for 193 nm light. Using these techniques, scientists at the Massachusetts Institute of Technology's (MIT's) Lincoln Laboratory, in Lexington, have built prototype transistors with a gate length of only 9 run-smaller than the smallest virus. Other tricks can also come into play. For example, by immersing the focusing lenses in a liquid with an index of refraction greater than that of air, optical lithography may be extended indefinitely. Ever since the 180 nm generation of devices, in 1999, RETs are making advanced optical lithography possible.     

DUV-E-beam Mix and Match lithography in a single mask for fabricating a multi-terminal SQUID device

A new kind of superconducting device has been fabricated, which is recently predicted to show tunable macroscopic quantum behaviour. As such it is a nonlinear element highly sensitive to the action of electromagnetic fields. The device is a multi-terminal SQUID (MTS), consisting of a superconducting ring interrupted by a Josephson multi-terminal junction, which in our case is a 4-terminal nanocross, 240 nm long and 40 nm wide. In this work we present the fabrication process and some preliminary measurement results.     

Automated electrical measurements of registration errors in step-and-repeat optical lithography systems

An automated electrical measurement technique for evaluating registration errors in step-and-repeat optical lithography systems is discussed, with emphasis on the ability of such equipment to meet the manufacturing requirements of very-large-scale integration (VLSI). Sources of registration error are outlined, and the relative contributions of these errors for a group of wafers stepped on a commercial 10:1 reduction system are reported. The components of registration error obtained from specially designed resistor structures are displayed using computer-drawn vector displacement maps and frequency plots. The data are analyzed using a six-parameter model which determines the extent to which level-to-level translation, rotation, and linear dimensional changes are present. Estimates ofxandystage-stepping precision are made by determining the residual errors in both the registration data and the data obtained from specially designed control structures.     

Resolution and linewidth tolerances in electron beam and optical projection lithography

In order to understand the practical limits of electron beam direct-write and optical projection lithography techniques in device fabrication with micrometer and submicrometer geometries, we have exercised two computer simulation programs to estimate resolution limits and linewidth control. Latent image contrast and developed resist thickness contrast were calculated as a function of line-array spatial frequency. The linewidth tolerances were calculated by varying exposure, development time, focusing, line/space Pattern, resist thickness, etc. These simulation results indicate that the lithographic performance of the two techniques using state-of-the-art exposure tools are comparable at 1-µm dimensions. Some relevant experimental data also are presented.     

Nanoimprint lithography fabrication of waveguide-integrated optical gratings with inexpensive stamps

We demonstrate that a replica grating can be effectively used as an inexpensive stamp for nanoimprint lithography to pattern diffractive optical couplers integrated with planar optical waveguides. Imprinted grating patterns were integrated with silicon oxynitride waveguide films to be used as an evanescent wave sensor in the input grating-coupler configuration. An anti-adhesion layer using an inexpensive, two-step chemical functionalization was developed for the stamps. The stamps were able to withstand imprint temperatures ranging from 140 to 190 °C and high fidelity imprints were obtained. The groove pattern was integrated in waveguide films by etch transfer and light-coupling properties of gratings with 1.2 μm pitch were tested using a λ = 1.55 μm laser. Compared to etched silicon masters, replica optical gratings provide uniform pattern density over their entire surface with no unstructured regions, are inexpensive, and readily available for R&D use.     

Enhancement of submicron optical lithography performance using phase-only pupil filters

We present a pupil filter design method based on iterative optimisation of the intensity point spread function (PSF) of a binary phase-only diffractive optical element, for use in a lens, diffractive element combination. Increase in the depth of focus and control over the sidelobe levels in the PSF is shown. The favourable performance is retained in simulated aerial images when the pupil filter is incorporated into a typical photolithography system.     

A novel method for submicron structurization using optical projection lithography

A novel method to delineate submicrometer structures using optical projection lithography is described. These structures are useful in gate design for micro-wave FETs. Dimensions ranging from 0.7 μm down to 0.1 μm are achievable using this double exposure technique.     

New approach to resolution limit and advanced image formationtechniques in optical lithography

Practical resolution, the minimum feature size with a depth of focus (DOF) required for LSI fabrication process, is analyzed. Dependence of practical resolution on various factors, such as optical system parameters (exposure wavelength λ, and numerical aperture NA), resist processes, and required DOF, is investigated. It is shown that practical resolution in the sub-halfmicrometer region is not improved, and may even be degraded, with increasing NA. Furthermore, resolution improvement by increasing NA becomes less effective as λ becomes shorter. This means that the high-resolution capability of high-NA/short-wavelength optics cannot be utilized to create fine-pattern LSIs. In order to overcome this limitation, the effectiveness of advanced image formation techniques, the phase-shifting method and the FLEX method, in practical resolution enhancement is investigated. It is experimentally verified, using a phase-shifting mask and the excimer laser stepper, that a pattern feature size less than 0.2 μm can be clearly delineated with sufficient focus latitude. These advanced techniques make it possible to overcome the resolution limitation of conventional optical lithography