In 1985, I presented my first paper—at an SPIE conference on lithography. It was the perfect venue for my work—a topical meeting full of people with the same interests as me, eager to communicate their latest results. That remains the paradigm for SPIE conferences to this day. But after publishing a few papers in conference proceedings, I decided that I had some work that deserved a peer-reviewed publication. But unlike the SPIE conferences that were the perfect fit for the work I did, there was no journal that matched the topic. Over the next 15 years I published papers in a number of journals: Optical Engineering, Applied Optics, Journal of the Electrochemical Society, Journal of Vacuum Science and Technology, IEEE Transactions on Semiconductor Manufacturing, Japanese Journal of Applied Physics, and others. Every time, I felt like an orphan. My lithography papers were surrounded by good papers that I had no interest in—and I’m sure that most readers of those journals felt the same way about my papers. Lithography had no peer-reviewed home.

Abstract unavailable.

Gratings and step height standards are useful transfer standards for lateral and vertical length scale calibration of atomic force microscopes (AFMs). In order to have traceability to the SI-meter, the standards must have been calibrated prior to use. Metrological AFMs (MAFMs) with online laser interferometric position measurements are versatile instruments for the calibrations. The developed task-specific measurement strategies for step height and pitch calibrations with the Centre for Metrology and Accreditation's (MIKES's) metrological AFM are described. The strategies were developed to give high accuracy and to reduce measurement time. Detailed uncertainty estimations for step height and grating pitch calibrations are also given. Standard uncertainties are 0.016 and 0.018 nm for 300 and 700 nm pitch standards, respectively, and 0.21 and 0.44 nm for 7 and 1000 nm step height standards.

We give an overview of the design of a metrological scanning probe microscope (mSPM) currently under development at the National Measurement Institute Australia (NMIA) and report on preliminary results on the implementation of key components. The mSPM is being developed as part of the nanometrology program at NMIA and will provide the link in the traceability chain between dimensional measurements made at the nanometer scale and the realization of the International System of Units (SI) meter at NMIA. The instrument is based on a quartz tuning fork (QTF) detector and will provide a measurement volume of 100  μm×100  μm×25  μm with a target uncertainty of 1 nm for the position measurement. Characterization results of the nanopositioning stage and the QTF detector are presented along with an outline of the method for tip mounting on the QTFs. Initial imaging results are also presented.

A new three-dimensional atomic force microscopy (3D-AFM) for true 3D measurements of nanostructures has been developed at Physikalisch Technische Bundesanstalt (PTB), the national metrology institute of Germany. In its configuration, two piezo actuators are applied to drive the AFM cantilever near its vertical and torsional resonant frequencies. In such a way, the AFM tip can probe the surface with a vertical and/or a lateral oscillation, offering high 3D probing sensitivity. For enhancing measurement flexibility as well as reducing tip wear, a vector approach probing (VAP) method is applied. The sample is measured point by point using this method. At each probing point, the tip is approached toward the surface in its normal direction until the desired tip-sample interaction is detected and is then immediately withdrawn from the surface. Preliminary experimental results show promising performance of the PTB system. The measurement of an IVPS 100 sample using a flared AFM tip showed a repeatability of its 3D profiles better than 1 nm (p-v). A single crystal critical dimension reference material having features with almost vertical sidewalls was also measured using a flared AFM tip. These results show that the feature has average left and right sidewall angles of 89.5 and 89.4, respectively. However, the nonuniformity of the feature width within the measurement window of 1 μm may be up to 10 nm. The standard deviation of the average middle CD values from 10 repeated measurements is 0.1 nm. In addition, an investigation of long-term measurement stability was performed on a PTB photomask. The results changed at a rate of about 0.00033 nm per line, which confirms the high measurement stability and the very low tip wear of the system.

A method is described for the calibration of vertical piezoelectric transducer (PZT) stages using a large range metrological atomic force microscope (LRM-AFM). A vertical PZT stage is mounted onto the system and an optical-flat sample is attached on the top of the PZT stage. The AFM probe is operated in contact mode and used as a null indicator to measure the movement of the optical-flat as it is driven by the PZT stage. As the PZT stage is scanned vertically, the AFM probe is in contact with the test surface without lateral scanning. The displacement of the vertical stage of the LRM-AFM is measured by the integrated laser interferometer, and the corresponding laser interferometer readings and the nominal position of the PZT stage are recorded. This body of data is then used to establish the relationship between the laser interferometer reading and the nominal displacement of the PZT stage. Our results show that this method can be used to calibrate PZT stages up to a range of 250 µm with an expanded uncertainty of less than 5 nm.

The National Institute of Standards and Technology (NIST) has a multifaceted program in atomic force microscope (AFM) dimensional metrology. One component of this program, and the focus of this paper, is the use of critical dimension atomic force microscopy (CD-AFM). CD-AFM is a commercially available AFM technology that uses flared tips and two-dimensional surface sensing to scan the sidewalls of near-vertical or even reentrant features. Features of this sort are commonly encountered in semiconductor manufacturing and other nanotechnology industries. NIST has experience in the calibration and characterization of CD-AFM instruments and in the development of uncertainty budgets for typical measurements in semiconductor manufacturing metrology. A third generation CD-AFM was recently installed at NIST. The current performance of this instrument for pitch and height measurements generally supports our relative expanded uncertainty (k = 2) goals in the range of 2.0×10−3 and lower. Additionally, a new generation of the NIST single crystal critical dimension reference material (SCCDRM) project is pushing toward feature widths below 10 nm, with the prospect of CD-AFM tip width calibration having expanded uncertainty (k = 2) below 1 nm.

Nanoparticle metrology with atomic force microscope (AFM) aims to determine an average particle size from measurements of individual nanoparticles derived by image analysis. This constrains the statistical relevance of the measurement due to the limited number of particles which can be practically imaged and analyzed. Consequently, the number density of particles on samples prepared for particle measurement is an important parameter of sample preparation. A number density that is too low makes it difficult to obtain sufficient measurement statistics, whereas a number density that is too high can result in particle agglomeration on the substrate and limit the area of uncovered substrate that is required to obtain a reliable reference for measuring the particle height. We present imaging and measurement results of a particle number density gradient of 16 nm gold nanoparticles deposited using a gradual immersion process. Results demonstrate how samples with particle number density gradients can facilitate identification of an area on a sample with optimal particle number density for AFM particle metrology and thereby improve measurement efficiency and reliability.

The data storage industry seeks data densities of several terabits per square inch, corresponding to dot pitch <15  nm. Cost constraints prohibit using commercial microscopes designed for accurate measurements. However, we show it is possible to routinely make accurate pitch measurements with commercial general purpose atomic force microscopes and scanning electron microscopes by using a calibrated grating as a transfer standard. This provides short-term traceable calibration. Our accuracy was validated in two collaborative projects with three national metrology institutes. In the first project, we measured the pitch of a 144-nm two-dimensional grating. Our mean value agreed within 0.033 nm with that obtained at the PTB (Germany) optical diffraction lab. In the second project, described in detail here, we measured the pitch of a 70-nm one-dimensional grating. Because we used two measurement runs, the statistical treatment is more elaborate. We use basic statistical methods, such as analysis of variance, correlation, and tests of statistical significance, to draw key conclusions and enable us to combine the results of both runs to get an improved mean pitch value with some reduction in uncertainty. Our mean value agreed within 0.025 nm of the values found using the calibrated AFMs at National Institutes of Standard and Technology (NIST, USA) and National Metrology Centre (NMC, Singapore); furthermore, our uncertainty matched that of the other labs. The relative standard deviation (SD/mean) of individual pitch measurements is a figure of merit for the measurement system consisting of grating plus microscope.If the relative SD can be held below 0.5%, we have a clear roadmap to provide useful traceability for pitch standards down to 5 nm.

To use atomic force microscope to measure narrow vertical features is challenging. Using carbon nanotube (CNT) probes is a possible remedy. However, even with its extremely high stiffness, van der Waals attractive force from steep sidewalls bends CNT probes. This probe deflection effect causes deformation (or "swelling") of the measured profile. When measuring 100-nm-high vertical sidewalls with a 27-nm-diameter and 265-nm-long CNT probe, the probe deflection at the bottom is estimated as large as 5.8 nm. This phenomenon is inevitable when using long and thin probes. We proposed a method to correct this probe deflection effect. Detecting torsional motion of the base cantilever of the CNT probe makes it possible to estimate the CNT probe deflection. Using this information, we have developed a technique for correcting the probe deformation effect from measured profiles. This technique, in combination with correction of the probe shape effect, enables vertical sidewall profile measurement with AFM.

Metrology and control of critical dimensions (CDs) are key to the success of nanotechnology. Modern nanotechnology and nanometrology are largely based on knowledge developed during the last 10 to 20 years of semiconductor manufacturing. Semiconductor CD metrology entered the nanotechnology age in the late 1990s. Work on 130-nm- and 90-nm-node technologies led to the conclusion that precision alone is an insufficient metric for the quality assessment of metrology. Other components of measurement uncertainty (MU) must also be considered: 1. sample-to-sample measurement bias variation, 2. sampling uncertainty, and 3. sample variation induced by the probe-sample interaction. The first one (sample-dependent systematic error) is common for indirect and model-based CD metrologies such as top-down and cross-sectional scanning electron microscopy (SEM) and scatterometry (OCD). Unless special measures are taken, bias variation of CDSEM and OCD could exceed several nanometers. Variation of bias and therefore MU can be assessed only if reference metrology (RM) is employed. The choice of RM tools is very limited. The CD atomic force microscope (AFM) is one of a few available RM tools. The CDAFM provides subnanometer MU for a number of nanometrology applications. Significant challenges of CDAFM remain, such as the following: 1. the finite dimensions of the probe are limiting characterization of narrow high-aspect spaces, 2. the flexibility of the probe complicates positioning control, 3. the probe apex sharpness limits 3D AFM resolution, 4. the lifetime of atomically sharp probes is too short, and 5. adsorbates change properties and dimensions of nanometer-sized objects considerably. We believe that solutions for the problems exist; therefore, we will discuss the role of RM in nanometrology, current RM choices, and the challenges of CDAFM as well as suggest some potential solutions.

Critical dimension atomic force microscopy is employed in semiconductor manufacturing as a reference system, used to provide accurate information to calibrate other tools. However, faced with increasingly challenging features, operators of these systems have needed to use multiple specialized tip types and scan modes on a sample in order to acquire a complete data set. To overcome this need, we measure the potential biases introduced within such a hybrid data set with respect to sidewall slope angle. Measurement results are presented for features with varying sidewall slope across a range of angles just above and below 90 deg. This sample was scanned with a variety tips and two different scan modes: critical dimension (CD) mode, an adaptive sidewall scanning mode able to detect limited undercut; and deep trench (DT) mode, a dynamic top-down-only mode commonly employed on small, challenging measurement features. In DT mode, we detected a cutoff point at 89 deg, below which all tips track the surface with a size-dependent bias. In contrast, CD mode produced results that were much more invariant to tip size except for the smallest tips. The smallest tips in CD mode exhibited divergent behavior, compared to both the mid-range CD tips and one another.

The deposition of films with nonuniform residual stress can induce local changes in wafer shape and contribute to overlay errors with magnitudes that may be significant in advanced lithographic patterning processes. Understanding the fundamental relationship between residual stress, localized wafer shape changes, and overlay error is crucial for realizing new schemes to manage overlay errors, particularly at advanced nodes where feature sizes are smaller. In the present work, finite element modeling is used to quantitatively relate nonuniform residual stress in a deposited thin film to localized wafer shape changes and overlay errors. The results demonstrate that there is a strong correlation between localized shape variations induced by nonuniform residual stresses and noncorrectable overlay errors.

In extreme ultraviolet lithography, particle-free mask handling is a critical issue because the use of pellicles is impractical. We measured the long-term change in the number of particle adders on a mask blank during transfer processes using a reticle SMIF pod (RSP) and a dual pod, which consists of an outer pod and an inner pod that holds the mask. In the RSP, the number of particle adders during the transfer test of a load port in air to an electrostatic chuck chamber in vacuum decreased from 0.053/cycle to 0.032/cycle because of a clean-up during the pumping down and purging operations. However, the number of particle adders during vacuum transfer did not change with long-term use. Moreover, we found that particles were added by mask blank sliding on a robot hand during vacuum transfer. In contrast, for the dual pod, no accident was observed during the 2000-cycle transfer test, and the number of particle adders was 0.004/cycle. We confirmed that the filter effect and gap effect for protecting the mask from particles were effective. We concluded that the dual pod was a reliable mask carrier for vacuum transfer.

In addition to the well-known wavelength challenges in optical lithography, sustaining increases in total layout information density-a doubling every two years or so, per Moore's Law-further strains pattern transfer capabilities and costs for advanced designs. Emerging lithography methods address these barriers by leveraging optical, materials, and process techniques that deliver more useful information to the wafer image on top of modest improvements to the spatial bandwidth of the lithography channel. Lithography is a communication channel specialized in delivering high-definition, high-density physical images to silicon wafers. Parallels can be drawn to communication theory, where key innovations have steadily improved the efficiency of digital communication within increasingly precious bandwidth. Several recent lithography process innovations will be outlined in terms of communication theory concepts, and their impact on economic trade-offs and implications to layout design styles will be discussed.

The impact of edge profile roughness of the absorber lines on an optical photomask has been studied by means of rigorous electro-magnetic field (EMF) simulation for the mask diffraction spectrum and subsequent imaging. Roughness has been modeled using two different approaches, a sinusoidal description and an algorithm known from literature-based on Fourier transformation. The latter can arbitrarily create rough profiles and surfaces based on the three morphological parameters standard deviation σ, roughness exponent α, and correlation length ξ. In this study, the standard deviation has been kept fixed while varying the remaining two morphological parameters, still showing impact on the lithographic process. A software interface for use of the generated profiles with the Waveguide EMF solver of the Dr.LiTHO lithography simulation suite has been implemented. It was shown by means of image analysis and study of the resulting process windows that mask roughness is partially transferred to the aerial image. Isolated and dense features behave differently, leading inter alia to an iso-dense bias different to that of ideal lines. Due to the roughness, process windows now depend on the position along the line. Determing process windows at multiple positions for statistical analysis implies a reduction of the effective process window. Correlation length ξ has shown to be an important parameter and, thus, morphology should not be ignored in the modeling of rough lines. Tapered sidewalls can add to the shift of the process windows in the same order of magnitude.

Development of an array of ultrasensitive capacitive pressure sensors which is both optically transparent in the visible range and flexible would represent a significant advance over current sensor capabilities. To construct these micromachined pressure sensors, the efficacy of oxygen plasma to bond the microfluidic network constructed out of polydimethlysiloxane and various plastic substrates has been examined. These pressure sensing elements can find potential applications in lab-on-a-chip environments, biosensors and photonic switching. The design, modeling, fabrication and measurement results are presented.

This work focuses on the design of torsional microelectromechanical systems (MEMS) varactors to achieve highdynamic range of capacitances. MEMS varactors fabricated through the polyMUMPS process are characterized at low and high frequencies for their capacitance-voltage characteristics and electrical parasitics. The effect of parasitic capacitances on tuning ratio is studied and an equivalent circuit is developed. Two variants of torsional varactors that help to improve the dynamic range of torsional varactors despite the parasitics are proposed and characterized. A tuning ratio of 1:8, which is the highest reported in literature, has been obtained. We also demonstrate through simulations that much higher tuning ratios can be obtained with the designs proposed. The designs and experimental results presented are relevant to CMOS fabrication processes that use low resistivity substrate.

We investigate an affordable, accurate and large-scale production method to fabricate subwavelength grating structures by hot embossing replication in polycarbonate substrates. We use inorganic hydrogen silsesquioxane (HSQ), a high resolution, binary, negative electron beam resist, on silicon substrate to make a stamp for replication. The stamp is fabricated without any etching processes and with simple process steps. The process starts by spin coating an HSQ-resist layer on a silicon substrate. The desired film thickness is achieved by adjusting the spinning speed and time. The resist material is then subjected to e-beam writing and development followed by a heat treatment to enhance the hardness and to obtain hot embossing stamp material properties comparable with solid SiO2. A comparison with and without the silicon etching is also performed. We demonstrate that a high quality stamp for thermal nano-imprint lithography for optical gratings can be fabricated using an inexpensive process without an etching step. The process results in a uniform imprinting density over the entire grating surface and high imprint fidelity. The reflectance spectra of replicated grating structures are also shown to be in agreement with theoretical calculations.

Reduction in power consumption while maintaining trajectory alignment and ensuring precise attitude control in microsatellites has been a global bottleneck in the coupled fields of inertial navigation and micropropulsion systems research. This paper presents the development of a novel microelectromechanical Pyrex/Si binary valve with piezoelectric stack-actuation for applications in microsatellite propulsion systems. The Pyrex 7740 and silicon wafers have been processed in parallel with two different structures being microfabricated and bonded eutectically to realize the microvalve. Electrochemical spark erosion method has been used to realize the inlet/outlet holes in Pyrex 7740 and KOH bulk micromachining to fabricate the top membrane structure in silicon. The device has been subjected to extensive analyses and characterization and has been shown to comply with the requirements of generic ion thrusters used for microsatellite propulsion.

Electron-beam-direct-write lithography has been considered a candidate next-generation technique for achieving high resolution. An accurate point spread function (PSF) is essential for reliable patterning prediction and proximity-effects correction. It can be derived via an effective parametric PSF calibration methodology, typically involving the fitting of the absorbed energy distribution (AED) from an electron-scattering simulation. However, the existing parametric PSF calibration methodology does not employ a systematic approach to obtain a new PSF form that is both compact and accurate when conventional PSF forms are not satisfactory. Only the AED fitting quality (rather than its patterning-prediction quality) is considered during the conventional calibration methodology. It also lacks a process to consider whether the predicted deviation (as simulated using the chosen PSF form) is satisfactory. This paper proposes a new parametric PSF calibration methodology to systematically obtain a PSF form consisting of the smallest number of terms, with a better combination of basis functions and that optimizes pattern accuracy. The effectiveness of using the new methodology is demonstrated in terms of fitting accuracy, patterning-prediction accuracy, and patterning sensitivity.

As 193-nm immersion lithography is extended indefinitely to sustain technology roadmaps, there is increasing pressure to contain escalating lithography costs by identifying patterning solutions that can minimize the use of multiple-pass processes. Contact patterning for the 32/28-nm technology nodes has been greatly facilitated by the just-in-time introduction of new process enablers that allow the support of flexible foundry-oriented ground rules alongside high-performance technology, without inhibiting migration to a single-pass patterning process. The incorporation of device-based performance metrics, along with rigorous patterning and structural variability studies, was critical in the evaluation of material innovation for improved resolution and CD shrink. Additionally, novel design changes for single patterning incorporating mask optimization efforts, along with new capability in data preparation, were assessed to allow for minimal impact of implementation of a single patterning contact process late in the 32-nm and 28-nm development cycles. In summary, this paper provides a comprehensive study of what it takes to turn a contact-level double-patterning process into a single-patterning process consisting of design and data manipulation, as well as wafer manufacturing aspects, together with many results.

We combined photonic crystal (PC) and nanoporous structures in silicon (Si) to decrease the reflectance of the Si surface. Due to gradual increase of effective refractive index in this structure, reflection is reduced drastically over a broad spectral range. A two-dimensional Si PC was fabricated by interference lithography, then a nanoporous structure was made on the PC by using metal-assisted chemical etching. The obtained reflectance is about 3% across a spectral range of 400 to 2000 nm. This indicates an improvement of reflectance up to 90% compared to bare Si.

Macroscopic porous membranes with pore diameter uniformity approaching the nanometer scale have great potential to significantly increase the speed, selectivity, and efficiency of molecular separations. We present fabrication, characterization, and molecular transport evaluation of nanoporous thin silicon-based sieves created by laser interferometric lithography (LIL). This fabrication approach is ideally suited for the integration of nanostructured pore arrays into larger microfluidic processing systems, using a simple all-silicon lithographic process. Submilli-meter-scale planar arrays of uniform cylindrical and pyramidal nanopores are created in silicon nitride and silicon, respectively, with average pore diameters below 250 nm and significantly smaller standard error than commercial polycarbonate track etched (PCTE) membranes. Molecular transport properties of short cylindrical pores fabricated by LIL are compared to those of thicker commercial PCTE membranes for the first time. A 10-fold increase in pyridine pore flux is achieved with thin membranes relative to commercial sieves, without any modification of the membrane surface.

Cancer cells create a unique microenvironment in vivo that enables migration to distant organs. To better understand the tumor microenvironment, special tools and devices are required to monitor the interactions between different cell types and the effects of particular chemical gradients. Our study presents the design and optimization of a versatile chemotaxis device, the nano-intravital device (NANIVID), which consists of etched and bonded glass substrates that create a soluble factor reservoir. The device contains a customized hydrogel blend that is loaded with epidermal growth factor (EGF), which diffuses from the outlet to create a chemotactic gradient that can be sustained for many hours in order to attract specific cells to the device. A microelectrode array is under development for quantification of cell collection and will be incorporated into future device generations. Additionally, the NANIVID can be modified to generate gradients of other soluble factors in order to initiate controlled changes to the microenvironment including the induction of hypoxia, manipulation of extracellular matrix stiffness, etc. The focus of the article is to present the design and optimization of the device towards wide ranging applications of cancer cell dynamics in vitro and, ultimately, implantation for in vivo investigations.

Abstract unavailable.