Today, complex nanostructures and nanodevices are used in photonics, quantum technology and nanoelectronics, and increasingly in healthcare and in novel materials research. Fast, accurate and traceable High-Speed Scanning Probe Microscopy (HS‑SPM) has great potential for use in identifying faulty nano‑products across multistage production processes and offers the benefits of increased productivity and reduced wastage. Conventional scanning probe microscopy (SPM) is either too slow to cover large sample areas or if fast, it lacks positioning accuracy. This project will develop essential scanning probe microscope components and ultimately a validated and traceable prototype HS-SPM measurement system suitable for use in industrial measurements.
Nanotechnology is expected to grow as its use in new applications increases across many diverse sectors, from consumer goods and healthcare, to energy production. For example, the progressive miniaturisation of advanced nanomanufacturing techniques which currently deliver nanodevices with feature sizes below 22 nm and complex nano-objects in the size range below 100 nm requires the introduction of fast, accurate and traceable measurement methods for the quality control of nanostructures and nanodevice dimensions and properties during production processes.
Industry, universities, and research institutes perform many high-resolution measurements; however, high resolution or high precision does not necessarily mean high accuracy. Without proper calibration and a good understanding of probe sample interactions, dimensional/property measurement errors may be as large as 30 %. At present, in the nanomanufacturing, semiconductor, nanometrology and quantum technology fields, a lack of measurement traceability to the SI metre, the associated uncertainties, and the effects of speed on measurement accuracy do not meet user requirements for higher speed (>1 mm/s) combined with larger scanning area (>1 mm2) and better accuracy (~nm).
To turn high-speed SPMs from qualitative imaging instruments to high accuracy measurement instruments suitable for industrial quality control applications, requires the development of scanning microscope stages with far greater stability (Objective 2), improved probing systems (Objective 1) and advanced measurement strategies (Objective 3) that combine high-speed scanning with the possibility to collect local electrical or mechanical properties. The aim of this project is to enable the expansion of multi-functional probing microscopy, which is currently used for topography, to measurements of the localised functional electrical and mechanical properties of nanostructures and to produce guidance on the measurement methods needed to enable the demonstration of combined topography and electrical and/or mechanical properties as a starting point for future standardisation (Objective 4 and 5).
The overall objective of this project is to design and develop technologies for transforming HS‑SPM (~10 mm/s) metrology instruments for use in industrial high-speed quantitative multi-sensing metrology with a target traceable position measurement uncertainty of 1 nm. The developed instrument will be suitable for the industrial characterisation of functional nanostructure property combinations (electrical, chemical, mechanical, dimensional).
The specific objectives of the project are:
- To design, develop, manufacture and characterise the frequency response, and noise level of multi-functional high-frequency (resonance frequency ω0 = 1 MHz) self-sensing and/or self‑actuating probes and control electronics that will form a sub system suitable for a compact HS‑SPM prototype designed for use in industrial environments.
- To develop a new generation of scanning stages for HS‑SPMs, which will be capable of high‑speed motion (~10 mm/s) and large stroke (~10 mm) with inherent metrological traceability to the SI metre. The scanning stages should include high-speed 6-DoF interferometry sensors, which will enable real-time measurements in industry without dynamic position errors. The target position noise is 0.5 nm.
- To develop open source experimental control and data processing software tools, for adaptive scanning and compressive sampling suitable for high speed SPM (~10 mm/s) surface nanometrology measurements over large areas (1 cm2), using hybrid stage combinations (piezo‑electric and/or MagLev). This will enable real-time traceable quantitative multi-sensing measurements (topography combined with electrical or mechanical properties).
- To incorporate the probes, scanning stages and software tools developed in objectives 1–3 into at least one new fully assembled and characterised custom-designed prototype HS‑SPM which will be capable of multi-sensing measurements for the industrial characterisation of functional nanostructure property combinations (topography combined with electrical or mechanical properties). In addition, to demonstrate its performance against other HS-AFM and/or HS‑SPM by comparative measurements of reference samples and by measurements of industrially relevant samples (e.g. an optical industry ultra-smooth optical surface, rectangular gratings, silicon samples relevant for the semiconductor industry, etc.).
- To facilitate the take up of the technology and measurement infrastructure developed in the project by the measurement supply chain (accredited laboratories, instrumentation manufacturers), standards developing organisations (CEN, ISO) and end users (SPM manufacturers).
Progress beyond the state of the art and results
Objective 1: Multi-functional probes and control electronics
Currently, SPM probes with silicon-based cantilevers typically use bulky optical beam deflection detector read‑out sensors. Although of high sensitivity (<<1 nm) and low cost (~tens of euros) these require long set‑up times (~10 min) and measurements suffer from interference from sample reflected light, which significantly impacts measurement accuracy. This project will deliver a multi-functional high-frequency self-sensing and self‑actuating probe having an active cantilever operating at increased resonance frequency (~1 MHz) with moderate stiffness (<20 N/m). The probe will use a piezo resistive read-out sensor integrated in its cantilever, thus reducing set-up time as well as eliminating undesired optical interferences.
Objective 2: Scanning stages
Conventional SPM scanners typically use polycrystalline piezo materials for fast small-area scanning. Although of low-cost and with high dynamic capabilities, these scanners have very poor positioning accuracy due to piezo material behaviour and strokes of less than 100 µm. To achieve long-stroke measurements, micro positioning stages using mechanical guiding are applied, but these suffer from poor dynamic properties and considerable motion errors (mainly straightness and angular errors).
This project will deliver a novel SPM scanner based on a hybrid combination of three stages: a 3-axes monocrystalline piezo stage, a 6-axes polycrystalline piezo stage and a 6-axes large-stroke magnetic levitation (MagLev) stage. The advantages of a MagLev stage are its smooth and controllable accuracy and perfect cleanness during scan movements compared to conventional mechanically guided or air bearing systems.
Objective 3: Scanning strategies
Typical high-speed AFM collect data sets as a set of individual high-speed frames. If a large scanning area e.g. 1 mm2 to 1 cm2 needs to be covered, a coarse motion stage scans slowly over the sample slightly overlapping individual frames, and the collected data is merged to form a larger area image.
A general XYZ data handling approach developed in EMRP JRP IND58 6DOF will be implemented on the high-speed SPM systems developed in this project, to show both the benefits of the XYZ data processing and also those of having metrological traceability for the X, Y and Z coordinates. The XYZ data handling will also be extended towards multi-functional measurements, such as combining high-speed scanning with spectroscopic methods or with the collection of local current or mechanical properties.
Objective 4: High-speed SPM for industrial measurements
Practical use of SPMs in industrial quality control is limited by their slow scanning speed and small measurement range whilst available high-speed variants are only qualitative instruments. AFM, traditionally a slow technique with few μm/s scan speeds, has been developed to have high speed capabilities, but these instruments lack metrological positioning traceability. Currently over 10 metrological low speed AFM (<<100 µm/s) operating over a limited measurement range (~100 µm) exist at NMIs.
This project will turn high-speed scanning probe microscopy from a qualitative imaging process into traceable instrumentation that can be used for routine measurements to examine large area (cm2) samples at probe‑sample speeds of ~10 mm/s, with dimensional traceability to the SI metre through the use of a 6-DOF interferometry system.
Impact on industrial and other user communities
Future innovations in nanotechnologies and nanoscience are reliant on developments in nanometrology such as the improvements to measurement capabilities resulting from the implementation of HS‑SPM developed in this project. The HS‑SPM subsystems and methods will be directly implementable in industrial applications; SPM manufacturers will be able to use the developed techniques in their instruments which will improve their end-user measurements; and improved measurement capabilities generated at NMIs will be available as measurement services to end-users. This project aims to make commercially available new multi-functional probes and stage subsystems which can be easily installed on most commercial AFMs. The newly developed scanning stages, once commercially available, will be suitable for other applications such as coordinate measuring machines, optical measurement and inspection devices, or lithography tools. Improved traceability, and accuracy for evaluating the performance of new products or manufacturing procedures is a major goal of this project.
As a result of this project new NMI based nanometrology services will be commissioned and promoted to end‑users based on upgrades to existing SPM instrumentation to assist with product development and the characterisation of innovative components and materials – helping to keep European industry competitive.
Impact on the metrology and scientific communities
This project’s main goal is traceability to the metre for high-speed SPM leading to more reliable, cost efficient nanomanufacturing. Project outcomes will be shared with the rest of the NMI community through dissemination activities within EURAMET TC-L and CIPM CCL, co-operation with non-European NMIs and directly to European Industry. This research will lead to new and improved CMC entries. The results of the project will be disseminated via conferences featuring dimensional nanometrology.
Impact on relevant standards
This project will generate measurement good practice guidance on characterisation for HS‑SPM that has the potential for future incorporation into new documentary standards for ‘high-speed SPM metrology’. The consortium has membership of ISO 201/TC201/SC9 “scanning probe microscopy” and will actively promote project results to this committee throughout the project’s lifetime with a view to getting a new working group formed. The project will also have direct impact on several other standard development technical committees (e.g. ISO/TC 213/WG 16 surface texture, VDI/VDE GMA 3.41 surface measurement techniques in the micro‑ and nanometre range, and ISO/TC229/JWG2 nanotechnologies: measurement and characterisation). An example is surface roughness metrology, where the high-speed SPMs from this project will create highly accurate, traceable nano-positioning for high-speed, high resolution areal surface metrology for the first time. The project already has members on these standardisation working groups who will keep them informed of the results aiming for future incorporation into updated standards.
Longer-term economic, social and environmental impacts
Nanotechnology is a rapidly growing area with potential applications in many sectors of the global economy, namely healthcare, cosmetics, energy, and agriculture among others. The technology is revolutionising every industry, while attracting tremendous worldwide attention. It is making significant improvements in technologies for protecting the environment. Nanoscale devices are being used for enhanced sensing, and for treating and remediating environmental contaminants. From the energy point of view, the improved nanomanufacturing industry will result in products with less energy consumption or they will bring better energy harvesting capability. On the other hand, nanotechnology's unique characteristics may also lead to unforeseen environmental problems. One known issue is the eco-toxicity of some nanomaterials. The project directly underpins the metrological needs, for instance, for the EU legislation of nanomaterials.