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The term acronym is the name for a word made from the first letters of each word in a series of words. Some distinguish an acronym (such as NATO), which is pronounced as a word, from an initialism (such as FBI), which is pronounced by saying each letter separately. Most people, however, ignore such distinctions. The more general term abbreviation includes acronyms but also abbreviations that use letters other than the first letters of a word (such as nm for "nanometers" or Mr. for "mister"). Here, "acronym" will be used loosely to mean any abbreviation.

The spectral properties of LaN/B and LaN/B₄C multilayer mirrors have been investigated in the 6.5 to 6.9 nm wavelength range, based on measured B and B₄C optical constants. We show that the wavelength of optimal reflectance for boron-based optics is between 6.63 and 6.65 nm, depending on the boron chemical state. The wavelength of the maximum reflectance of the LaN/B₄C multilayer system is confirmed experimentally. Calculations of the wavelength-integrated reflectance for perfect ten-multilayer-mirror stacks show that a B-based optical column can be optimized for a wavelength larger than 6.65 nm.

An electrostatic compensation method is proposed to realize the frequency robustness of a capacitive accelerometer by taking advantage of the electromechanical coupling characteristics, rather than mechanical structure alone. The limitations of microfabrication on structural configuration are overcome by an efficient adjustment of circuit parameters, which have equivalent contributions on the natural frequency as mechanical structures. The results of theoretical analysis and experiments indicate that this design method is practical for different microprocessing conditions, and the robustness of a mechanical structure to error can be achieved by a reasonable electrostatic compensation in electromechanical coupling microdevices. The test results have shown that the frequency deviations in more than 80% of fabricated sensors are less than 1%.

The use and enhancement of a semi-automated wafer characterization tool, a dual channel capacitive sensor module, is demonstrated by implementing a new measurement algorithm for metallization process control. This tool is capable of measuring the deposited metal film thickness induced bow and warpage in a full wafer surface scan. The nondestructive solution can measure Cu metal film thickness with a total measurement uncertainty of 0.18 μm (1∂). The stress conversion map can be obtained based on the modified Stoney's formula and the capacitance-displacement technique. A wafer thinning process was also performed to characterize the warpage/bow of 8-in. wafers, which continues to increase as wafer thicknesses are reduced from 725 to 300 μm. There was a linear relationship between the wafer warpage and bow and the square of the inverse of the thickness. Metrology results from actual 3-D interconnect processing wafers are presented.

We developed an optimized inductively coupled plasma etching process to produce gallium arsenide (GaAs) pyramidal corrugated quantum well infrared photodetector focal plane arrays (C-QWIP FPAs). A statistically designed experiment was performed to optimize the etching parameters. The resulting parameters are discussed in terms of the effect on the etching rate and profile. This process uses a small amount of mask corrosion and the control of the etching mask gap to give a 45 deg to 50 deg V-groove etching profile, which is independent of the crystal orientation of GaAs. In the etching development, scanning electron microscope was used to observe the surface morphology and the pattern profile. In addition, x-ray photoelectron spectroscopy was used to obtain the elemental composition and contamination of the etching surface. It is found that extremely small stoichiometric change and surface damage of the etching surface can be achieved while keeping a relatively high etching rate and ~ 45 degV-groove etching profile. This etching process is applied to the fabrication of pyramidal C-QWIP FPAs successfully, which are expected to have better performance than the regular prism-shaped C-QWIPs according to electromagnetic modeling.

Multi-beam interference (MBI) represents a method of producing one-, two-, and three-dimensional submicron periodic optical-intensity distributions for applications including micro- and nano-electronics, photonic crystals, metamaterial, biomedical structures, optical trapping, and numerous other subwavelength structures. Accordingly, numerous optical configurations have been developed to implement MBI. However, these configurations typically provide limited ability to condition the key parameters of each interfering beam. Constraints on individual beam amplitudes and polarizations are systematically considered to understand their effects on lithographically useful MBI periodic patterning possibilities. A method for analyzing parametric constraints is presented and used to compare the optimized optical-intensity distributions for representative constrained systems. Case studies are presented for both square and hexagonal-lattices produced via three-beam interference. Results demonstrate that constraints on individual-beam polarizations significantly impact patterning possibilities and must be included in the systematic design of an MBI system.

A new analytical approach is presented to predict mask deformation during electrostatic chucking in next-generation extreme-ultraviolet-lithography. Given an arbitrary profile measurement of the mask and chuck nonflatness, this method has been developed as an alternative to time-consuming finite element simulations for overlay error correction algorithms. We consider the feature transfer of each harmonic component in the profile shapes via linear elasticity theory and demonstrate analytically how high spatial frequencies are filtered. The method is compared to presumably more accurate finite element simulations and has been tested successfully in an overlay error compensation experiment, where the residual error y-component could be reduced by a factor of 2. As a side outcome, the formulation provides a tool to estimate the critical pin-size and -pitch such that the distortion on the mask front-side remains within given tolerances. We find for a numerical example that pin-pitches of less than 5 mm will result in a mask pattern distortion of less than 1 nm if the chucking pressure is below 30 kPa.

Micro-optoelectromechanical systems (MOEMS) deformable mirrors are being developed for focus control in miniature optical systems including endoscopic microscopes and small form-factor camera lenses. A new process is described to create membrane mirrors made from the photoset polymer SU-8. The SU-8 also serves as the adhesive layer for wafer bonding, resulting in a simple, low cost fabrication process. The process details and the optical properties of the resulting focus control mirrors, which have a diameter of 2 mm, a stroke in excess of 8 μm and very low residual aberration, are described. Multiple actuation electrodes allow active control of more than 1.4 μm peak-to-peak of wavefront spherical aberration. The MOEMS mirror is demonstrated in a confocal microscope in which it provides focus control during capture of in vivo images.

Characterization of a stochastic process in lithography, giving rise to photoresist line-edge roughness (LER), requires elucidation of the power spectral density (PSD) for that process. Thus, any analytical model for LER requires an analytical model for the PSD. Using a previously derived formulation for the reaction-diffusion autocorrelation function, the PSD can be derived from its Fourier transform. The resulting analytical expression for the reaction-diffusion PSD provides an interesting and useful form that will aid modeling work in LER prediction. Numerically calculating the PSD for the stochastic development rate shows that this same analytical expression approximately matches the simulation but with a correlation length that decreases as the amount of development noise increases.

Continuous shrinkage of critical dimension in an integrated circuit impels the development of resolution enhancement techniques for low k₁ lithography. Recently, several pixelated optical proximity correction (OPC) and phase-shifting mask (PSM) approaches were developed under scalar imaging models to account for the process variations. However, the lithography systems with larger-NA (NA > 0.6) are predominant for current technology nodes, rendering the scalar models inadequate to describe the vector nature of the electromagnetic field that propagates through the optical lithography system. In addition, OPC and PSM algorithms based on scalar models can compensate for wavefront aberrations, but are incapable of mitigating polarization aberrations in practical lithography systems, which can only be dealt with under the vector model. To this end, we focus on developing robust pixelated gradient-based OPC and PSM optimization algorithms aimed at canceling defocus, dose variation, wavefront and polarization aberrations under a vector model. First, an integrative and analytic vector imaging model is applied to formulate the optimization problem, where the effects of process variations are explicitly incorporated in the optimization framework. A steepest descent algorithm is then used to iteratively optimize the mask patterns. Simulations show that the proposed algorithms can effectively improve the process windows of the optical lithography systems.

Roughness on the surface of phase-only micro-optical elements limits their performance. An optical vortex phase element was fabricated, using additive lithography, with an optimized process to achieve minimal surface roughness. Shipley S1827 photoresist was used in order to obtain the appropriate additive lithography dynamic range for the desired phase profile. We investigated the effects of both postapplied and postexposure baking processes, bias exposure dose, as well as the effects of surfactant in the developer. We found the resist surface roughness to be a function of both the temperature and the time of the postapplication baking cycles, as well as the developer surfactant content. Based on our findings, an empirical correlation model was constructed to relate the process parameters with surface roughness measured quantities. The maximum roughness of the optical surface, for the optimized process, was reduced to 40 percent of the value for the unoptimized process and the additive lithography useful exposure range was increased by 10 percent.

The control of line-edge or line-width roughness (LER/LWR) is a challenge, especially for future devices that are fabricated using extreme-ultraviolet (EUV) lithography. Accurate analysis of the LER/LWR plays an essential role in this challenge and requires the noise involved in scanning-electron-microscope (SEM) images to be reduced by appropriate noise filtering prior to analysis. To achieve this, we simulated the SEM images using a Monte Carlo method, and detected line edges in both experimental and theoretical images after noise filtering using new image-analysis software. The validity of this software and these simulations was confirmed by a good agreement between the experimental and theoretical results. In the case when the image pixels aligned perpendicular (crosswise) to line edges were averaged, the variance var(φ) that was additionally induced by the image noise decreased with a number N PIX,X of averaged pixels, with exceptions when N PIX,X was relatively large, whereupon the variance increased. The optimal N PIX,X to minimize var(φ ) was formulated based on a statistical mechanism of this change. LER/LWR statistics estimated using the crosswise filtering remained unaffected when N PIX,X was smaller than the aforementioned optimal value, but monotonically changed when N PIX,X was larger contrary to expectations. This change was possibly caused by an asymmetric scan-signal profile at edges. On the other hand, averaging image pixels aligned parallel (longitudinal) to line edges not only reduced var(φ ) but smoothed real LER/LWR. As a result, the nominal variance of real LWR, obtained using simple arithmetic, monotonically decreased with a number N PIX,L of averaged pixels. Artifactual oscillations were additionally observed in power spectral densities. Var(φ ) in this case decreased in inverse proportion to the square root of N PIX,L according to the statistical mechanism clarified here.

A dose-focus monitoring technique using a critical-dimension scanning electron microscope (CD-SEM) is studied for applications on product wafers. Our technique uses two target structures: one is a dense grating structure for dose determination, and the other is a relatively isolated line grating for focus determination. These targets are less than 6 μm, and they can be inserted across a product chip to monitor dose and focus variation in a chip. Monitoring precision is estimated to be on the order of 1% for dose and 10 nm for focus, and the technique can be applied to dose and focus monitoring on product wafers. The developed technique is used to analyze spatial correlation in dose and focus over a wide range of distances, using a mask with a multitude of these targets. The variation (3σ ) of dose and focus difference between two monitor targets is examined for various separation distances, and the variation of focus difference increases from 10 to 25 nm as the separation distance increases from ∼20  μm to ∼10  mm . The variation of 10 nm observed at the shortest distance reflects focus monitoring precision, and focus variation sources such as wafer thickness variation come into play at longer distances.

This article [J. Micro/Nanolith. MEMS MOEMS. 10, , 043013 (2011)] was published online on 1 December 2011 without three additional coauthors: Isabel Alvarez, Maria Teresa Fernandez, and Agustin Costa, all from the Physical Chemistry Department, University of Oviedo, Oviedo, Spain. The authors regret the omissions.