METROLOGY AND STANDARDIZATION FOR NANOTECHNOLOGIES

Transcription

1 MEROLOGY AND SANDARDIZAION FOR NANOECHNOLOGIES P.A.odua Center for Surface and Vacuum Research (CSVR), Moscow, Moscow Institute of Physics and echnology (MIP) Key words: nanotechnology, nanometrology, standardization, uniformity of measurements. Abstract: A concept of measurement uniformity assurance for nanotechnology is considered. he peculiarities of linear measurement in nano range of linear sizes are discussed. Detailed recommendations are given on accurate calibration and verification of scanning electron, scanning probe and atomic force microscopes. Introduction he science and technology development history is inseparably linked with the development of measuring methods and means. he nanotechnologies have set the new specific problems due to the small sizes of elements and structures one has to deal with in this field. Here as nowhere the thesis «If you can not correctly measure, you can not create» is a topical problem. All countries involved in nanotechnology race very well know the need of advance development of metrology in this thriving area of expertise, since the accuracy level and the measurement reliability either stimulate the development of relevant industries, or become a constraint. he instrumental and technological components of nanotechnologies are working at their limits, and that means the rise of error probability, especially due to human factor. One of standardization in nanotechnologies primary tasks is the standardization of operation factors and features of materials, objects, elements and structures of nanotechnologies to be measured. Due to interdisciplinary and intersectoral character of nanotechnologies, different terminology, research and measuring ways and methods, this task becomes critically important. he need of terminology standardization also speaks on itself, because it ensures the solving of communication problem between different research groups within a separate country, and in the frames of interdisciplinary information exchange between different countries. All the above means the necessity of attested and standardized measuring methods, calibration and verification methods, used in nanotechnologies, and many more, which is determined by needs of nanoindustry infrastructure development. his standardization special aspect is the health and security for technology processes operators, including all persons dealing with nanotechnology products at all manufacturing, testing, research and usage stages, as well as ensuring the environment ecological safety

2 It is logically clear that the metrology carries «the biggest statistical weight», because it is the quantitative basis of standardization and certification. he specific character of nanotechnologies became the reason of development of the new metrology direction the nanometrology, with which all theoretical and practical aspects of metrological uniformity measurements assurance in nanotechnologies are connected. From the very meaning of nanotechnology, operating with nanometer lenght objects, the primary task of object s geometrical parameters measuring follows. Why in nanometrology so much is attended to problem of linear scale realization in nanometer and adjacent ranges? Firstly, because the solution of metrology in nanotechnologies primary task the securing of nanoobject geometry measurements uniformity is guided by the metrology of linear measurements. Secondly, as mentioned above, the measurements of optical, mechanical, electric, magnetic and many other nanotechnology objects, parameters and properties are connected with the need of measuring device probe positioning in predefined place with highest possible accuracy [1,2]. he securing of the uniformity of physicochemical parameters and properties measurement of the object means, that measuring device is to be linked with measurement standard, reproducing the given physical magnitude unit (e.g., the conductivity with standard resistance). In most of cases in nanotechnologies it means the obligatory linkage with the basic reference standard of lenght unit (fig.1) for accurate hit of the target. Metrology and standards for nanotechnologies Major branch Basic standard of the length unit in the 1 nm 100 µm range based on SEM, EM, probe microscopy, X-ray diffractometry and laser interferometry Measures of small length transfer standards Reference materials - standard samples of properties and composition calibration Measuring instruments Measuring instruments Objects at the nano-scale CSVR Fig.1 he spectrum of nanotechnology objects and the nanoindustry itself is vast; it lies from ultradisperse media to nanostructured multilayer material and crystals, including quantum size structures with the following dimension of localization: one so called quantum wells (ultra thin layers), two quantum wires, three quantum dots. he peculiarities of physical effects and relevant processes, including optical, luminescence,

3 electrical, magnetic, mechanical and many others, are determined by characteristic size. In the same material the different size linked effects become apparent in different ways. For example, the peculiarities of ultra dispersive size material s optical properties may become apparent at certain nanoparticles sizes, while the thermo physical properties peculiarities show themselves at another nano sizes. he most of research and measuring of nanoobjects methods: transmission and scanning electron microscopy, scanning probe microscopy, ion field microscopy, photoemission and X-ray diffractometry, etc. widely used in nanoindustry materials and objects properties measurement technique need the calibration of measuring means by reference samples of composition, structure, properties with known dimensional (geometric) characteristics. For example, one of familiar size determination methods for superdispersed particles is the study of the light dispersion from them. his dispersion depends from the particle sizes ratio, incident radiation wave lenght and polarization. For particle size determination, usually, the laser radiation is used, but for such measuring device calibration the special set of superdisperse particles with discrete range of precisely fixed sizes is required. When bringing the large forbidden band semiconductor compounds of A 2 B 6 group to superdisperse state, the blue shift of luminescence band appears, per which is possible to judge about the luminophore superdisperse particles sizes. But for each concreate semiconductor material the set of reference samples of the same material with whole range of sizes is required. When controlling the technology of multilayer thin film manufacturing creation processes, including multilayer heterostructures, the X-ray diagnostic control methods for hidden layers is required, and, accordingly, the standard samples of composition and structure for measuring means calibration are required. he metrology and standardization problems of physicochemical parameters measurements, the size of physical unit transfer to nanometer range [3], characterized by specific peculiarities, become critically important. he priority task of leading development of nanometrology is the need of nanoscale realization in nanometer and adjacent ranges. Many of conferences and numerous publications are devoted to this task. he significant contribution to this basic measurement problem solution is made by Russia. he utmost results achievement in measuring the lenght in nanometer range is due to use of high resolution scanning electron and scanning probe microscopy methods, combined with laser interferometry and X-ray difractometry at absolute binding with the primary meter standard. As a result of long term research in Russia the task of creating the metrological provision bases for lenght measurement in the range 1 nm 1000 nm, is conceptually solved. he following is worked out: the uniformity of measurement assurance methodology, for range of lengths 1 nm nm, based on probe microscopy and laser interferometry and X-ray difractometry principles ; the standard complex of measuring means, providing the reproducibility and the transfer of length unit size in 1 nm 1000 nm range to real length measures with 0.5 nm accuracy; the generation of small length measures for measuring means calibration in 1 nm 1000 nm range, including measures of surface nanorelief;

4 the methodology and measurement algorithms for micro- and nanostructures elements profile parameters and computer programs package for these measurements automatization. he important stage of metrological provision for length measurements in nanometer range was the creation of real lenght carriers the measures with programmable nanoralief of the surface, ensuring the measuring means calibration with maximum accuracy (fig.2,3,4) ransfer standard image in an atomic force microscope CSVR Fig.2 ransfer standard Pitch size: 2.0 µm, made of silicon Certification method: - Interferometry SEM image of the transfer standard, obtained at different magnifications Rated sizes Certification inaccuracy 2000 nm ±1 nm Pitch 2000 Line width nm ±1 nm Height (depth) nm ±1 % CSVR Fig.3

5 {111} {111} ransfer standard AFM images {100} SEM images of cleavages 80 nm 30 nm Width of the upper base of the protrusion CSVR Fig.4 he very same three dimensional small length measures, or reference standards the real size carriers, allowing to realize the complex calibration and principal parameters control of scanning electron and scanning probe microscopes, - are intended for the transfer of these complicated devices from the group of examined object visualization devices to the rank of measurement means, i.e. to linear size of investigated objects measuring instruments, ensuring the binding of measured units in nanometer range to primary length standard the meter. he calibration of transfer standards is carried out using the standard three dimensional interferometric nanodisplacement measuring system. he step of the measure and the upper and lower bases of protrusions and trenches (line width), well as the relief height (depth), are certified. It is possible at the same step of the structure to manufacture the reference standards with the lines width in the nm range and the relief height nm [4]. he measure allows by its scanning electron microscope (SEM) image only (even by one signal) to calibrate the microscope (fig.5) i.e. to determine the microscope magnification, scales linearity and electron probe diameter [5].

6 ransfer standard SEM calibration with the help of one image t s u p u t S L p L t ϕ h b p t b t B p B t D d << s= htanϕ s 1. 5d Determination of magnification M = t= S s Determination of the electron beam diameter d= D M= D t Calibration time: less than 5 minutes CSVR Fig.5 Besides, if the validity of measurements confirmation is required, it is possible to control the parameters of SEM directly during the investigated objects sizes measurement process, which is the additional warranty of measurements high quality. he measure allows the easy automation of linear measurements and the creation on SEM basis of the automated measuring complexes (AMC). In particular, in the CSVR the AMC for linear measurements within the range from 1 nm to 100 mm of the base of SEM JSM- 6460LV is already created. Similarly, by the given measure parameters, the calibration and control of such atomic force microscope (AFM) characteristics, as the scale factor and scales linearity along all three coordinates, the scanning system orthogonality, the probe (cantilever) tip radius, the microscope tuning and working regime stage teaching,- are carried out (fig.6) [6]. he AFM calibration and certification systems are successfully implemented at enterprises, specialized on the equipment for nanotechnology creation.

7 t s u p u t ransfer standard AFM calibration U p U t ϕ h ψ L H ψ R S L S R S L b p t b t B p B t AFM multiplying scale factor m x = t m S S ( ) 2 1 cos sin ϕ ϕ x L R Q ϕ = = 6 2 = x = m z 2H m U u m B b u m U b m B r = x p p = x p p = t x t = t x t CSVR Q( ϕ) Q( ϕ) Q( ϕ) Q( ϕ) Z m z =h H Z-scanner non-orthogonality S S L R + S > s m L R x inclination of the cantilever tip S 2 + S = s m L R x Z-scanner non-orthogonality S 2 Fig.6 Cantilever tip radius he nanotechnology development tightens the screws for requirements to measuring systems, the measuring error of which could be compared with inter-atomic distances. All the above means the necessity of very serious approach to the problem of the uniformity of linear measurements in nanometer range assurance. Scanning electron and scanning probe microscopes (SPM) could be considered as means only if their parameters are attested, calibrated and controlled; the latter done directly during the measurement process. he 3D measures of transfer standards the real size carriers are linking the measurement object and the meter standard and serve as ideal means to perform such operations. he measurement culture requires every SEM or SPM, irrespective of location in research or industry lab, teaching facility or being a part of technology process, - is to be equipped with measures, providing the calibration and control of this complex device parameters. Only then the measurements could be considered as authentic and reliable. o provide the normality base of nanometrology the following national standards are worked out in CSVR and put into action: -GOS R State system for ensuring the uniformity of measurements. Single-crystal silicon nanometer range relief measures. Requirements for geometrical shapes, linear sizes and manufacturing material selection - GOS R State system for ensuring the uniformity of measurements. Nanometer range relief measures with trapezoidal profile of elements. Methods for verification - GOS R State system for ensuring the uniformity of measurements. Atomic - force scanning probe measuring microscopes. Methods for verification - GOS R State system for ensuring the uniformity of measurements. Scanning electron measuring microscopes. Methods for verification - GOS R State system for ensuring the uniformity of measurements. Atomic - force scanning probe microscopes. Methods for calibration - GOS R State system for ensuring the uniformity of measurements. Scanning electron microscopes. Methods for calibration

8 - GOS R State system for ensuring the uniformity of measurements. Nanometer range relief measures with trapezoidal profile of elements. Methods for calibration Conclusion For the uniformity of measurements in nanotechnologies assurance problem solution it is necessary to realize several scientific methodological, technical and organizational measures. First of all it is the creation of a new structural scheme of physical units dimension transfer from primary standards to working measuring means, excluding the multistep character of this transfer (fig.1). hese activities include: the basic research of measuring system probe with measured object interaction, the investigation of new measuring algorithms and relevant software, considering the influence of working measuring mean, interaction with measured object, the creation of new measures real size carriers with properties analogueous to properties of secondary standard and measured objects, development and creation of composition, structure and surface relief standard samples and standardized measurement methods in nanometrology, securing the possibility to trace the transfer of physical unit magnitude from the standard to working measuring means into nanometer range without significant loss of the accuracy for attestation, calibration and verification of the measuring means. he achievement of this goal is quite realistic, since the base of this problem solution depends on basic standard concept (fig.1), in which the nanoscale is realized. his standard is the base for physical units magnitudes transfer to nanometer range. References 1. Michail.Postek. Proceedings of SPIE, v 4608, p.84, odua P.A. et al. Russian Nanotechnology, 2007, v.2, #1-2, p 61 (in Russian). 3.. odua P.A. Microsystem echnique, 2004, #1, p 38; #2, p.24; #3, p Novikov Yu.A. et. al. Proceedings of SPIE, v.6648, p.66480k1, Gavrilenko V.P. et. al. Ibid, p odua P.A. et. al. Ibid, p.66480s1.