Atomic Force Microscopes are capable to provide non-destructive high resolution, CD-metrology and precise defect analysis. However, a conventional AFM has not enough throughput for today’s large scale semiconductor manufacturing. The primary point remains the increase of the scanning area in case of large wafers, masks, displays or dies. Cantilever array-based AFMs are intended to increase the imaging throughput by parallelizing the work of many AFM probes that may be practiced by parallel AFM systems that are capable to operate autonomously. An active cantilever scheme makes it possible to sense electronically the deflection and individually to control the actuation of every cantilever in the array. Each cantilever in the array represents a self-sustaining AFM-hardware system for metrology and imaging. In that, the multiple parallel probes are forming many AFMs capable to work independently.
KEYWORDS: Scanning electron microscopy, Atomic force microscope, Electron microscopes, Metrology, Electron beams, Nanofabrication, Diamond, Scanning probe lithography, Microscopy, Overlay metrology
An integration of atomic force microscopy (AFM) and scanning electron microscopy (SEM) within a single system is opening new capabilities for correlative microscopy and tip-induced nanoscale interactions. Here, the performance of an AFM-integration into a high resolution scanning electron microscope and focused ion beam (FIB) system for nanoscale characterization and nanofabrication is presented. Combining the six-axis degree of freedom (DOF) of the AFM system with the DOF of the SEM stage system, the total number of independent degree of freedom of the configuration becomes eleven. The AFM system is using piezoresistive thermomechanically transduced cantilevers (active cantilevers). The AFM integrated into SEM is using active cantilevers that can characterize and generate nanostructures all in situ without the need to break vacuum or contaminate the sample. The developed AFM-integration is described and its performance is demonstrated. The benefit of the active cantilever prevents the use of heavy and complex optical cantilever detection technique and makes the AFM integration into a SEM very simple and convenient. Results from combined examinations applying fast AFM-methods and SEM-image fusion, AFM-SEM combined metrology verification, and tip-based nanofabrication are shown. Simultaneous operation of SEM and AFM provides a fast navigation combined with sub-nm topographic image acquisition. The combination of two or more different types of techniques like SEM, energy dispersive x-ray spectroscopy, and AFM is called correlative microscopy because analytical information from the same place of the sample can be obtained and correlated [1]. We introduced to the SEM/FIB tool correlative nanofabrication methods like field-emission scanning probe lithography, tip-based electron beam induced deposition, and nanomachining/nanoidentation.
KEYWORDS: Metrology, Atomic force microscopy, Inspection, Semiconducting wafers, Actuators, Photomasks, Silicon, Digital signal processing, Field programmable gate arrays, Imaging systems
Atomic Force Microscopy (AFM) is a capable to provide high resolution CD-metrology and precise defects analysis on large wafers, masks or displays. However, AFM is not enough productive for high-throughput industrial uses. Standard single probe AFMs are showing low throughput as a serial imaging tools. The use of an array of four cantilevers as a Quattro-Array results in effective speed of 6 to 10 mm/s. An image size of 0.5mm x 0.2mm is achieved employing a piezoelectric positioner with a scan range of 200μm x 200μm and a resolution of 0.25nm (x,y) and 0.2nm (z), respectively. These capabilities are qualifying the Quattro-cantilever array system as fastest tool for. In this paper we present new results obtained with our Quattro-AFM high-throughput parallel SPM system that exhibits two key advances that are required for a successful deployment of SPM in time-efficient metrology, defect analysis and mask inspection.
Cost-effective generation of single-digit nano-lithographic features could be the way by which novel nanoelectronic devices, as single electron transistors combined with sophisticated CMOS integrated circuits, can be obtained. The capabilities of Field-Emission Scanning Probe Lithography (FE-SPL) and reactive ion etching (RIE) at cryogenic temperature open up a route to overcome the fundamental size limitations in nanofabrication. FE-SPL employs Fowler-Nordheim electron emission from the tip of a scanning probe in ambient conditions. The energy of the emitted electrons (<100 eV) is close to the lithographically relevant chemical excitations of the resist, thus strongly reducing proximity effects. The use of active, i.e. self-sensing and self-actuated, cantilevers as probes for FE-SPL leads to several promising performance benefits. These include: (1) Closed-loop lithography including pre-imaging, overlay alignment, exposure, and post-imaging for feature inspection; (2) Sub-5-nm lithographic resolution with sub-nm line edge roughness; (3) High overlay alignment accuracy; (4) Relatively low costs of ownership, since no vacuum is needed, and ease-of-use. Thus, FE-SPL is a promising tool for rapid nanoscale prototyping and fabrication of high resolution nanoimprint lithography templates. To demonstrate its capabilities we applied FE-SPL and RIE to fabricate single electron transistors (SET) targeted to operate at room temperature. Electrical characterization of these SET confirmed that the smallest functional structures had a diameter of only 1.8 nanometers. Devices at single digit nano-dimensions contain only a few dopant atoms and thus, these might be used to store and process quantum information by employing the states of individual atoms.
Next-generation electronic and optical devices demand high-resolution patterning techniques and high-throughput fabrication. Thereby Field-Emission Scanning Probe Lithography (FE-SPL) is a direct writing method that provides high resolution, excellent overlay alignment accuracy and high fidelity nanopatterns. As a demonstration of the patterning technology, single-electron transistors as well as split ring electromagnetic resonators are fabricated through a combination of FE-SPL and plasma etching at cryogenic temperatures.
The conventional optical lever detection technique involves optical components and their precise mechanical alignment. An additional technical limit is the weight of the optical system in cases where a top-scanner is used with high-speed and high-precision metrology. An alternative represents the application of self-actuated atomic force microscopy (AFM) cantilevers with integrated two-dimensional electron gas (2-DEG) piezoresistive deflection sensors. A significant improvement in the performance of such cantilevers with respect to deflection sensitivity and temperature stability has been achieved by using an integrated Wheatstone bridge configuration. Due to employing effective crosstalk isolation and temperature drift compensation, the performance of these cantilevers was significantly improved. In order to enhance the speed of AFM measurements, we present an adaptive scanning speed procedure. Examples of AFM measurements with a high scanning speed (up to 200 lines/s) committed to advanced lithography process development are shown.
Marcus Kaestner, Cemal Aydogan, Tzvetan Ivanov, Ahmad Ahmad, Tihomir Angelov, Alexander Reum, Valentyn Ishchuk, Yana Krivoshapkina, Manuel Hofer, Steve Lenk, Ivaylo Atanasov, Mathias Holz, Ivo Rangelow
The routine “on demand” fabrication of features smaller than 10 nm opens up new possibilities for the realization of many devices. Driven by the thermally actuated piezoresistive cantilever technology, we have developed a prototype of a scanning probe lithography (SPL) platform which is able to image, inspect, align, and pattern features down to the single digit nanoregime. Here, we present examples of practical applications of the previously published electric-field based current-controlled scanning probe lithography. In particular, individual patterning tests are carried out on calixarene by using our developed table–top SPL system. We have demonstrated the application of a step-and-repeat SPL method including optical as well as atomic force microscopy-based navigation and alignment. The closed-loop lithography scheme was applied to sequentially write positive and negative tone features. Due to the integrated unique combination of read–write cycling, each single feature is aligned separately with the highest precision and inspected after patterning. This routine was applied to create a pattern step by step. Finally, we have demonstrated the patterning over larger areas, over existing topography, and the practical applicability of the SPL processes for lithography down to 13-nm pitch patterns. To enhance the throughput capability variable beam diameter electric field, current-controlled SPL is briefly discussed.
Ahmad Ahmad, Tzvetan Ivanov, Alexander Reum, Elshad Guliyev, Tihomir Angelov, Andreas Schuh, Marcus Kaestner, Ivaylo Atanasov, Manuel Hofer, Mathias Holz, Ivo Rangelow
The conventional optical lever detection technique involves optical components and its precise mechanical alignment.
An additional technical limit is the weight of the optical system, in case a top-scanner is used in high speed and high
precision metrology. An alternative represents the application of self-actuated AFM cantilevers with integrated 2DEG
piezoresistive deflection sensors. A significant improvement in performance of such cantilevers with respect to
deflection sensitivity and temperature stability has been achieved by using an integrated Wheatstone bridge
configuration. Due to employing effective cross-talk isolation and temperature drift compensation the performance of
these cantilevers was significantly improved. In order to enhance the speed of AFM measurements we are presenting a
fast cantilever-approach technology, Q-factor-control and novel adaptive scanning speed procedure. Examples of AFM
measurements with high scanning speed (up to 200 lines/s) committed to advanced lithography process development are
shown.
Marcus Kaestner, Cemal Aydogan, Hubert-Seweryn Lipowicz, Tzvetan Ivanov, Steve Lenk, Ahmad Ahmad, Tihomir Angelov, Alexander Reum, Valentyn Ishchuk, Ivaylo Atanasov, Yana Krivoshapkina, Manuel Hofer, Mathias Holz, Ivo Rangelow
The routine “on demand” fabrication of features smaller than 10 nm opens up new possibilities for the realization of
many novel nanoelectronic, NEMS, optical and bio-nanotechnology-based devices. Based on the thermally actuated,
piezoresistive cantilever technology we have developed a first prototype of a scanning probe lithography (SPL) platform
able to image, inspect, align and pattern features down to single digit nano regime. The direct, mask-less patterning of
molecular resists using active scanning probes represents a promising path circumventing the problems in today’s
radiation-based lithography. Here, we present examples of practical applications of the previously published electric field
based, current-controlled scanning probe lithography on molecular glass resist calixarene by using the developed tabletop
SPL system. We demonstrate the application of a step-and-repeat scanning probe lithography scheme including
optical as well as AFM based alignment and navigation. In addition, sequential read-write cycle patterning combining
positive and negative tone lithography is shown. We are presenting patterning over larger areas (80 x 80 μm) and feature
the practical applicability of the lithographic processes.
Marcus Kaestner, Konrad Nieradka, Tzvetan Ivanov, Steve Lenk, Yana Krivoshapkina, Ahmad Ahmad, Tihomir Angelov, Elshad Guliyev, Alexander Reum, Matthias Budden, Tomas Hrasok, Manuel Hofer, Christian Neuber, Ivo Rangelow
Within last two years, we have shown the positive-tone, development-less patterning of calixarene molecular glass resists using highly confined electric field, current-controlled scanning probe lithography scheme. Herein, we give a more detailed view insight describing the applied Scanning Probe Lithography (SPL) technology platform applying selfactuating, self-sensing cantilever. The experimental results are supported by first preliminary simulation results estimating the local electric field strength, the electron trajectories, and the current density distribution at the sample surface. In addition, the diameter of Fowler-Nordheim electron beam, emitted from SPL-tip, was calculated as function of the bias voltage for different current set-points and tip radii. In experimental part we show the reproducible writing of meander line patterns as well as the patterning of individual features using specially developed pattern generator software tool.
High Performance Single Nanometer Lithography (SNL) is an enabling technology for beyond CMOS and future
nanoelectronics. To keep on with scaling down nanoelectronic components, novel instrumentation for nanometer precise
placement, overlay alignment and measurement are an essential pre-requirement to realize Next Generation Lithography
(NGL) systems. In particular, scanning probe based methods for surface modification and lithography are an emerging
method for producing sub-10 nm features. In this study, we demonstrate nano-scale lithography using a scanning probe
based method in combination with a Nanopositioning and Nanomeasuring Machine. The latter one has a measuring
range of 25 mm x 25 mm x 5 mm, 0.1 nanometer resolution and outstanding nanometer accuracy. The basic concept
consists of a special arrangement allowing Abbe error free measurements in all axes over the total scan range.
Furthermore, the Nanopositioning and Nanomeasuring Machine is able to store the exact location that can be found again
with an accuracy of less than 2.5 nanometers. This system is also predestinated for critical dimension, quality and
overlay control. The integrated scanning probe lithography is based on electric-field-induced patterning of calixarene. As
a result, repeated step response tests are presented in this paper.
As present CMOS devices approach technological and physical limits at the sub-10 nm scale, a ‘beyond CMOS’
information-processing technology is necessary for timescales beyond the semiconductor technology roadmap. This
requires new approaches to logic and memory devices, and to associated lithographic processes. At the sub-5 nm scale, a
technology platform based on a combination of high-resolution scanning probe lithography (SPL) and nano-imprint
lithography (NIL) is regarded as a promising candidate for both resolution and high throughput production. The practical
application of quantum-effect devices, such as room temperature single-electron and quantum-dot devices, then becomes
feasible. This paper considers lithographic and device approaches to such a ‘single nanometer manufacturing’
technology. We consider the application of scanning probes, capable of imaging, probing of material properties and
lithography at the single nanometer scale. Modified scanning probes are used to pattern molecular glass based resist
materials, where the small particle size (<1 nm) and mono-disperse nature leads to more uniform and smaller
lithographic pixel size. We also review the current status of single-electron and quantum dot devices capable of room-temperature operation, and discuss the requirements for these devices with regards to practical application.
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