WO2013037833A1 - Procédé et dispositif de mesure de la lumière dispersée - Google Patents

Procédé et dispositif de mesure de la lumière dispersée Download PDF

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Publication number
WO2013037833A1
WO2013037833A1 PCT/EP2012/067852 EP2012067852W WO2013037833A1 WO 2013037833 A1 WO2013037833 A1 WO 2013037833A1 EP 2012067852 W EP2012067852 W EP 2012067852W WO 2013037833 A1 WO2013037833 A1 WO 2013037833A1
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WIPO (PCT)
Prior art keywords
light
sample
light components
different
signal
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PCT/EP2012/067852
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German (de)
English (en)
Inventor
Gunther Notni
Alexander VON FINCK
Marcus Trost
Angela Duparré
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Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Friedrich-Schiller-Universität Jena
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Publication of WO2013037833A1 publication Critical patent/WO2013037833A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/4738—Diffuse reflection, e.g. also for testing fluids, fibrous materials
    • G01N21/474—Details of optical heads therefor, e.g. using optical fibres
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/30—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces
    • G01B11/303—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces using photoelectric detection means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N2021/4704—Angular selective
    • G01N2021/4711—Multiangle measurement
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N2021/4792—Polarisation of scatter light
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/06—Illumination; Optics
    • G01N2201/069—Supply of sources
    • G01N2201/0691—Modulated (not pulsed supply)

Definitions

  • the present invention relates to a method for scattered light measurement according to the preamble of the main claim and to a device for scattered light measurement according to the preamble of the independent claim.
  • Measurement methods which are based on an evaluation of light scattered on a sample, which is referred to as scattered light in the following, are generally used for the efficient analysis of surfaces, materials and coatings, wherein they are distinguished by high sensitivity.
  • sample-specific parameters such as roughness or root-mean-square (rms) roughness, a roughness spectrum (power spectral density function, PSD), scattering losses, Schich thickness error, roughness propagation in
  • the present invention is therefore based on the object of proposing a method and a device for scattered light measurement, which avoid the disadvantages mentioned, which thus allow a scattered light measurement with different measurement parameters in the shortest possible time and without time-consuming retrofitting, at the same time a high sensitivity and the largest possible dynamic ranges to be achieved.
  • the proposed method for carrying out a scattered light measurement in which a sample is illuminated with light from at least one light source and a portion of the light scattered on the sample is detected as a measurement signal from at least one detector, makes use of the fact that the light emerging on the sample is at least two Includes light components that differ in at least one parameter.
  • the light components are also modulated with different modulation signals.
  • an output signal of the detector is split into several signal channels by filtering out with time The different modulation signals correlated proportions of the output signal, so that each of said light components or each of the modulation signals is assigned to at least one of the signal channels unique.
  • the assignment between light components or modulation signals on the one hand and signal channels on the other hand consists in that the signal channel of the selective processing assigned to a light component or the modulation signal of a light component is a signal attributable to this light component and thus modulated or time-correlated even with the modulation signal of this light component Proportion of the output signal is used, the latter is thus guided by that signal channel.
  • Scattering of the light at the sample should be understood to mean any conceivable scattering and, in particular, both a diffraction and a reflection, in particular a specular reflection in which the light has a vanishing azimuthal angle of reflection.
  • the at least one parameter in which the light components differ may include an angle of incidence or a wavelength.
  • the at least one parameter may include a different wavelength spectrum, a polarization, an intensity and / or a position at which the respective light component impinges on the sample for the different light components. Since scattering cross sections are sometimes wavelength or polarization dependent, or also dependent on the position on the sample at which the light is scattered, multiple information from the scattered light can be obtained in parallel by using these parameters.
  • ARS angle-resolved-scattering
  • Light for angle-resolved scattered light measurement can be varied.
  • the light components can be irradiated onto the sample at different angles of incidence.
  • ARS function a power of the scattered light in a solid angle element divided by a product of the intensity of the incident light and the solid angle element into which scattered may be defined.
  • a so-called bidirectional scattering distribution function- which is defined as the quotient of the ARS function and a cosine of the scattering angle
  • the light components are integrated over a specific angle range on the detector side angle-resolved scattered light measurement can be obtained.
  • the output signal in the respective signal channel can pass through a bandpass filter and / or a lock-in-Ve stronger.
  • the bandpass filter and the lock-in amplifier comprise a low-pass filter, a
  • An advantageous embodiment can provide that the components of the output signal remaining in the different signal channels are processed individually at the same time. Time-parallel processing minimizes the time required for the scattered light measurement and the analysis of this measurement. By splitting into several signal channels is the simultaneous, parallel processing of the in the individual signal channels guided signals easily possible.
  • intensities of the light components can be selected or adjusted in such a way that scattered portions of all the light components mentioned with the detector have powers of the same order of magnitude.
  • the same magnitude should be used to denote power or intensity values in the present specification if a difference between them is less than 50%, preferably less than 30%, particularly preferably less than 10%, of the larger of the stated values. Due to the approximately equal intensities of the individual light components none of these light components is detected as being too dominant and thus a result of the measurement distorting. This allows to obtain in all signal channels an optimal signal-to-noise ratio of the respective portion of the output signal.
  • To reduce the crosstalk between the signal channels and the individual light components can be passed through a polarization-dependent and / or wavelength-dependent division of the individual light components to different detectors.
  • the output signal can be prefiltered electronically in at least one of the signal channels. Independently of optical filtering, the electronic signal in the respective signal channel can thus also be processed for further processing.
  • a further development provides that a modulation frequency of at least one of the modulation signals corresponds to a minimum of a frequency-dependent transmission function of a filter, which is used for filtering out a temporally correlated with another of the modulation signals portion of the output signal.
  • a modulation frequency of at least one of the modulation signals corresponds to a minimum of a frequency-dependent transmission function of a filter, which is used for filtering out a temporally correlated with another of the modulation signals portion of the output signal.
  • the at least two light components can be combined to form a sample beam before impacting the sample.
  • the beam guidance is facilitated and - what may be desirable - achieved that meet the different light components with the same angle of incidence on the sample.
  • the proposed arrangement for scattered light measurement comprises at least one light source for illuminating a sample with light and at least one detector for detecting a portion scattered on the sample of the light. Between the at least one light source and the sample are at least two different ones
  • Beam paths are provided for at least two light components differing in at least one parameter.
  • the beam paths here run at least in sections differently.
  • the light components can be modulated independently of each other in intensity.
  • the arrangement also has a control unit which is set up to modulate the optical components with different modulation signals, and an evaluation unit which is set up to filter out in each of the signal channels in each case one portion of the output signal correlated in time with the different modulation signals, so that each of the said light components or each of the modulation signals is uniquely assigned to at least one of the signal channels.
  • the light components or each of the modulation signals there is thus at least one signal channel in each case in which a portion of the output signal attributable to this light component or modulated or modulated by this modulation signal is filtered out.
  • the light components can be modulated both independently of one another and also generated or manipulated in such a way that they differ from one another in the at least one parameter.
  • a beam path is to be understood here as meaning any possible path between the light source and the sample. Due to the multiple signal channels of the evaluation unit, it is possible to simultaneously process signals carried in the signal channels.
  • the arrangement may comprise a plurality of light sources.
  • the light sources may themselves already be arranged at different angles to the sample and / or designed to generate light of respectively different wavelengths or spectra and / or different polarizations. Due to several light sources with different properties, measurements with several measuring parameters can be carried out at the same time, so that the measuring time is reduced accordingly.
  • the angle of incidence between one of the light sources and the sample may be adjustable by a change in position of the respective light source and / or further components arranged in the beam path.
  • the sample itself and / or the at least one detector can be adjustable in position, so that the angle of incidence and / or the scattering angle can be variably adjusted.
  • a wavelength-selective element and / or a polarizer can be arranged in at least one of the beam paths in order to give the light component guided by this beam path a different wavelength or spectral composition and / or polarization from at least one other of the light components. This also makes it possible to ensure that the light components are in the desired parameter (s) - ie z. B. wavelength or polarization - different.
  • an attenuation device preferably a filter, for adjusting an intensity of the light or one of the light components is arranged in one of the beam paths located between the light source and the sample and / or in a beam path located between the sample and the detector ,
  • the scattered components of all light components detected by the detector can be normalized to powers of the same order of magnitude, thereby improving the signal-to-noise ratio and, in particular, minimizing tiber Grafen between the signal channels.
  • the evaluation device may comprise at least one band-pass filter and / or at least one lock-in amplifier for filtering out the portions of the output signal correlated in time with the various modulation signals in each of the signal channels.
  • filtering of the output signal can be performed efficiently.
  • a lock-in amplifier is used as a reference signal to a reference input of this lock-in amplifier, preferably each exactly the modulation signal used to modulate the light component, the proportion of the output signal in this signal path is filtered out.
  • the modulation signals can be z. B. generated in a control unit and time correlated to be passed both to the modulators or light sources and to the lock-in amplifier.
  • At least one optical component for beam shaping, beam folding, minimization of scattered light in the beam path or polarization adjustment can be arranged in at least one of the beam paths.
  • scattered light in the beam path is intended here located in the beam paths, externally generated by ambient light or internally generated by unwanted scattering of optical elements of the beam path, unwanted light, which can adversely affect the measurement.
  • this optical component is a mirror, semipermeable or dichroic mirror, lens, spatial filter, aperture, polarizer, ⁇ / plate, or ⁇ / 2 plate, or comprises one or more of these elements.
  • mirrors have the advantage over lenses of having a smaller number of optical surfaces, which reduces scattered radiation.
  • mirrors in polychromatic illumination are also color-defective.
  • a modulator controllable via the control unit can be arranged.
  • the arrangement for at least one of the light components may have its own modulatable light source.
  • the modulator preferably comprises a mechanical chopper or a
  • the modulatable light source preferably comprises a laser diode or a solid-state laser.
  • the light component can already be provided with a modulation directly in their generation, so no additional components must be provided in the beam path and the arrangement can be carried out space-saving.
  • this is a modulation with a sinusoidal shaped modulation signal, which is more favorable in terms of crosstalk, easier possible.
  • the proposed arrangement may preferably be used.
  • Fig. 1 is a schematic view of an arrangement for carrying out an angle-resolved scattered light measurement
  • Fig. 2 is a Fig. 1 corresponding representation ⁇
  • Fig. 3 shows a modification of that shown in Fig. 1
  • FIG. 4 a the Fign. 1 and 2 corresponding view of another arrangement for angle-resolved scattered light measurement, in the
  • Fig. 5 a frequency-dependent transfer function of two filters
  • FIG. 6 is an exemplary diagram of the crosstalk Behavior for different ratios of interfering signal to signal to be measured.
  • Fig. 1 an arrangement for angle-resolved scattered light measurement is shown in a schematic view.
  • Three lasers 1, 2, 3 or laser diodes each generate a light component which is guided in a beam path to a sample 17.
  • Beams such as light sources on.
  • the light components guided in the different beam paths differ in at least one parameter from each other, in their wavelength in the illustrated embodiment, since the lasers 1, 2, 3 each emit different wavelengths.
  • the individual light components are combined by a mirror 13 and two dichroic mirrors 14 and 15 and passed to the sample 17 as a sample beam. In front of the dichroic mirror 15, however, the beam paths are guided differently.
  • the three lasers 1, 2, 3 are shown as light sources, but it can of course also be provided more than three light sources and a correspondingly higher number of beam paths.
  • the light generated by this light source can be split, for example, by a beam splitter into several light components, which would then be guided again in each case a separate beam path.
  • the light components by color filters in each case be given a different wavelength or spectral composition of the other light components.
  • each of the beam paths is a modulator 7, 8, 9th contain, which modulates the respective light component independently of other light components in their intensity.
  • the modulators 7, 8, 9 modulate the different light components with different modulation signals, with which the modulators 7, 8, and 9 are driven to and which can differ from each other in frequency, waveform and phase.
  • the modulator 7 is an acousto-optic modulator in the illustrated embodiment, while the modulators 8 and 9 are mechanical choppers.
  • the lasers 1, 2, 3 may themselves be modulated, for example by using modulatable laser diodes.
  • the modulators 7, 8, 9 are each controlled independently of one another in FIG. 1 for reasons of clarity not shown control units. Alternatively, only a single control unit with several outputs for driving the modulators 7, 8, 9 may be provided. If the lasers 1, 2 and 3 themselves are externally or internally modulated, instead of the then eliminated modulators 7, 8 and 9, the laser 1, 2 and 3 are driven accordingly.
  • an optical filter 4, 5, 6 is arranged, which ensures that the individual light components have an adjusted intensity such that the later detected scattered proportions of all light components have powers of the same order of magnitude. This serves to limit a crosstalk behavior to between three and ten orders of magnitude, in order to allow a reliable measurement.
  • the optical filters 4, 5, 6 as mechanical filters, crosstalk limitation is achievable to one to ten orders of magnitude, while Using only a lock-in amplifier to improve the crosstalk behavior typically the crosstalk behavior can be limited to three orders of magnitude.
  • the crosstalk behavior can be further improved so that the individual signal channels can have a signal difference of more than ten orders of magnitude.
  • a required number of filter stages for achieving the dynamic range necessary for the scattered light measurement can also be reduced by improving the crosstalk behavior of the lock-in amplifier. Due to the extremely high dynamics of scattered light measurements, such a low crosstalk behavior between the individual signal channels is crucial for the success of the measurement.
  • an optical component 10, 11, 12 included for beam shaping which may also consist of several individual components, that can be realized by a group of components.
  • the optical components 10, 11, 12 each comprise a spatial filter for homogenizing the respective light component and a lens for adjusting a focus on the sample 17.
  • the mirror 13 and the dichroic mirrors 14 and 15 are the same.
  • the sample beam passes through a further optical filter 16, which adjusts the intensity of the sample beam to a level not damaging the sample 17 and / or adjusts the intensity of the light scattered on the sample 17 in such a way that a signal-to-noise ratio of one for detection detector 18 is optimized and / or the intensities stician in the linear region of the detector 18 is located.
  • the optical filters 4, 5, 6 and 16 can be arranged at different positions in the respective beam paths and each have an adjustable attenuation ratio.
  • a beam splitter, a grating, a prism, a waveguide and / or a light-conducting fiber can also be used to guide the beam paths.
  • the sample beam can also be conducted to the sample 17 via a fiber, which makes possible a compact beam guidance and a compact design of the arrangement with precise superimposition of the light components and low sensitivity to mechanical instabilities in the case of long beam paths.
  • the optical components 10, 11, 12 do not comprise a spatial filter, preferably all of the mirrors and lenses used have super polishes, otherwise advantageously such elements with superpolicies are used only for mirrors and lenses arranged in the beam paths between the spatial filter and the sample 17 , Mirrors are generally preferable to lenses due to the lower number of optical surfaces and associated less unwanted scattered radiation.
  • the optical components 10, 11, 12 are also used to set the largest possible beam diameter and a divergence or homogenization of the individual light components as equal as possible.
  • spatial filters or diaphragms or components for adjusting a polarization such as polarizers or ⁇ / 4 plates or ⁇ / 2 plates.
  • a wavelength-selective element such as a color filter may be provided to give the guided by the respective beam path light component of the light components of the other beam paths different wavelength or spectral composition.
  • the sample beam strikes the sample 17 at an angle of incidence Q ⁇ and is scattered on the sample 17.
  • the angle of incidence can be adjusted by tilting the sample 17.
  • the lasers 1, 2, 3 together with the optical filters 4, 5, 6, 16 can also be used for modu ⁇ lators 7, 8, 9 optical elements 10, 11, 12, the mirror 13 and the Dxchroitician mirrors 14 and 15 are tilted.
  • the detector 18 can be held stationary or also correspondingly
  • the detector 18 includes a photomultiplier but may also include a photodiode or a matrix sensor.
  • the detector 18 may be set at different angles to the sample 17 to detect portions of the light scattered at different scattering angles Q s .
  • the scattering angles Q s can also be azimuthal scattering angles. It is also possible to provide a plurality of detectors for detecting the scattered light at different scattering angles, which results in a multiplication of a spatial frequency scan. made possible.
  • the spatial frequency f as an in-plane component is over
  • ⁇ denotes the wavelength
  • polarization optics such as correspondingly oriented ⁇ / 4 plates or ⁇ / 2 plates, or polarizers
  • polarization properties of the sample 17 can be characterized in a more comprehensive manner in order to be able to draw conclusions about different scattering causes.
  • optical fibers, waveguides or fibers in order to guide the scattered portion of the light to the detector 18, which in turn allows a compact construction of the arrangement.
  • the detector 18 converts the scattered portion of the light into an electrical signal, which is divided into a plurality of signal channels in an evaluation unit comprising three lock-in amplifiers 19, 20, 21. In each of the signal channels, one of the lock-in amplifiers 19, 20, 21 is arranged. Output signals of the lock-in amplifiers can be fed simultaneously for further processing.
  • the evaluation unit thus has several parallel signal channels.
  • the modulation signal corresponds to one of the light components, wherein all the modulation signals in the present case in each case at exactly one of the lock-in amplifier 19, 20, 21 abut.
  • each of the mentioned light components is uniquely assigned to one of the signal channels - in the case of modifications more than one signal channel could also be provided for each of the light components, for example when using a plurality of detectors whose analog signals are evaluated at the same time.
  • band-pass filters can also be used for filtering out the components of the output signal of the detector 18 attributable to the various light components.
  • ARS background level a noise level of less than 10 -7 sr -1 due to the separate treatment of the individual components of the output signal in different signal channels.
  • Fig. 2 shows an embodiment of an arrangement for scattered light measurement with a single laser 1 is shown as a light source.
  • the in this figure illustrated arrangement corresponds to the arrangement shown in Fig. 1, however, only the laser 1 is used instead of several lasers and the light emitted by the laser 1 light is split by two dichroic mirrors 14 and 15 in the individual light components and by the dichroic mirrors 14 and 15 and the mirror 13 and directed to the modulators 7, 8 and 9 in the beam paths.
  • the filters 4, 5 and 6 are also wavelength-selective in this case, so that after passing through said filters each light component has a different wavelength.
  • Fig. 3 a modification of the arrangement shown in Fig. 1 is shown, which has been extended by an additional structure for multiple modulation.
  • the sample beam after passing through the further optical filter 16, but even before hitting the sample 17, again divided and modulated.
  • the individual light components are circularly polarized in the embodiment shown in FIG. Behind the further optical filter 16, the sample beam is divided by a polarizing beam splitter 25 into two sub-beams, wherein a first sub-beam has an s-polarization and is guided by a first additional modulator 27, while a second sub-beam has a p-polarization and by a second additional modulator 28 is performed.
  • the said further modulators 27, 28 in turn modulate the two partial beams independently of each other in different ways.
  • a further polarizing beam splitter 26 the two partial beams finally combined with each other and passed to the sample 17.
  • the individual light components can also be linearly polarized and split by a respective ⁇ / 4 plate in each of the partial beams into a right-circularly polarized component and a left-circularly polarized component.
  • the evaluation unit now comprises three further lock-in amplifiers 22, 23, 24, ie a total of six lock-in amplifiers.
  • the lock-in amplifiers 19, 20, 21, 22, 23 and 24 two demodulators are connected in series, so that a demodulation of the modulation signal of the modulators 7, 8, 9 arranged in the beam paths is present in all illustrated lock-in modes.
  • Amplifiers 19, 20, 21, 22, 23, 24 and a demodulation of the modulation signal of the first further modulator 27 in the lock-in amplifiers 19, 20, 21 and a demodulation of the modulation signal of the second further modulator 28 in the lock-in Amplifiers 22, 23 and 24 takes place.
  • two lock-in amplifiers can each be connected in series, so that based on the embodiment shown in FIG. 3, a total of twelve paired lock-in amplifiers are used.
  • scattered signals of different wavelengths or spectra can each be reconstructed for s- or p-polarized light components.
  • two parallel lock-in amplifiers can also be used initially to separate the modulation signals of differently polarized light components, whereby the signals separated in this way are fed separately from each other to three further lock-in amplifiers, through which each of the signals after the modulation signals the first, second or third wavelength of the light component is split.
  • a total of eight lock-in amplifiers are required in this embodiment.
  • This arrangement of lock-in amplifiers is based on the fact that in the first stage n different parameters and in the second stage m different parameters are to be separated so that a total of n + n * m lock-in amplifiers are required for the demodulation.
  • n 2 for two different polarizations
  • U7 3 for three different wavelengths.
  • a development of the exemplary embodiment illustrated in FIG. 3 provides for using a polarization-sensitive detector in order to separate the s and p polarized components directly at the detector.
  • a detector may, for. B. provide an optical separation after the detector aperture in beams of different polarization via a polarizing beam splitter and detection via various sensors of the detector.
  • a wavelength-sensitive detector for example for characterizing inelastic scattering or Raman scattering.
  • the scattered proportion of the light are wavelength-dependent split on several sensors of the detector.
  • Fig. 4 shows in a FIGS. 1, 2 and 3 corresponding view another embodiment of an arrangement for angle-resolved scattered light measurement.
  • the individual light components are no longer combined with one another and passed to the sample 17 as a sample beam.
  • the lasers 1, 2, 3 are arranged at different angles to the sample 17, so that the light components generated by them impinge on the sample 17 at a respectively different polar and / or azimuthal angle of incidence.
  • the further optical filter 16 is now fixed directly in front of the detector 18 to protect it from damage by scattered radiation to high intensity, and is moved with this.
  • the attenuation ratio of the filter 16 is also chosen so that the detector 18 can be operated in the linear range and the signal-to-noise ratio is optimized.
  • the lasers 1, 2, 3 in this embodiment all have a same wavelength or polarization, so that the light components may differ from each other here only in the parameter angle of incidence , In the exemplary embodiment shown in FIG. 4, all the light components strike the sample 17 at the same location, but it may of course also be provided that the individual light components impinge on the sample 17 at different positions.
  • the intensities of the light components can be equalized by the optical filters 4, 5, 6.
  • an electronic prefiltering be made to attenuate noise and / or by another of the signal channels to leading portion of the output signal. This can be achieved by electronic low-pass or band-pass filters with a corresponding passband.
  • An optical prefiltering has already been explained above by a complete or partial division of the individual light components onto different detectors or sensors of a detector.
  • demodulation or filtering can be performed in one of the lock-in amplifiers 19, 20, 21, 22, 23, 24 by multiplying the Fourier series by an internally generated signal be achieved with the same modulation frequency.
  • phase ⁇ 0.
  • An analog deep filter of first order and an integration time ⁇ can be described in the frequency domain by the amount of the transfer function ⁇ ⁇ 1 ( ⁇ ):
  • Digital lock-in amplifiers offer the possibility of both digital low-pass filtering and moving-average filters, the latter being offer decisive advantages for the elimination of non-statistical interference signals with a known modulation frequency.
  • a moving average filter over the time period 2 ⁇ of the signal X (t) can be described as a convolution of X (t) with a rect function m, i (t). For T mr i (t), the following applies:
  • a multiple application N of the mean value filter thus corresponds to higher order mean value filters N with
  • FIG. 5 shows in a diagram the course of the transfer function for the first-order analog lowpass filter (dashed line) and for the first order digital mean value filter (solid line).
  • the ordinate represents the transfer function H and the abscissa the frequency f of the demodulated signal X (t), which is a function of the modulation frequency.
  • t the transfer function
  • the modulation frequency is at least one of the modulation signals in front of in a manner suitable for filtering out a portion of the output signal correlated in time with another of the modulation signals so that it corresponds precisely to a zero position of the transfer function of the filter.
  • FIG. 6 shows by way of example the crosstalk behavior for different ratios of interference signal to signal to be measured in a double-logarithmic diagram.
  • a quotient of the amplitude of the interference signal A 3 and the amplitude of the signal A m to be measured is plotted on the abscissa the ordinate is a quotient of the output signal
  • Xour (t) one of the lock-in amplifier and an output signal without portions of the interference signal X 0 ur, o (t) plotted as a measure of the crosstalk behavior.
  • a dotted curve plotted in the diagram denotes one of the modulation frequencies, which corresponds to a local maximum of the transfer function of the digital mean value filter shown in FIG.
  • a curve shown by a solid line in FIG. 6 designates one of the modulation frequencies which corresponds to a local minimum of the transfer function of the digital signal shown in FIG
  • Average filter corresponds, so one of the frequencies at which interference signals are ideally mitigated as possible.
  • the noise signal may be much stronger than in the aforementioned case before the output signal is negatively affected by the strong noise signal.
  • interference signals ie, for example, intensities of other signal channels, and signal to be measured by up to three powers of ten, without to negatively influence the crosstalk behavior.

Abstract

La présente invention concerne un procédé et un dispositif pour mesurer la lumière dispersée. À cet effet, un échantillon (17) est éclairé avec de la lumière d'au moins une source de lumière (1, 2, 3), et une fraction de la lumière dispersée sur l'échantillon (17) est détectée en tant que signal de mesure par au moins un détecteur (18) sous un angle de dispersion. La lumière qui tombe sur l'échantillon (17) comprend deux composantes de lumière qui se distinguent en au moins un paramètre et qui sont modulées avec des signaux de modulation différents. Un signal de sortie du détecteur (18) est réparti en plusieurs canaux de signaux par filtrage de fractions du signal de sortie corrélées dans le temps avec les différents signaux de modulation, de sorte qu'à chacune desdites composantes de lumière est associé univoquement au moins l'un des canaux de signaux. Ceci permet d'effectuer des mesures de la lumière dispersée avec une dynamique élevée et un comportement diaphonique réduit entre les différents canaux de signaux.
PCT/EP2012/067852 2011-09-14 2012-09-12 Procédé et dispositif de mesure de la lumière dispersée WO2013037833A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE102011113134 2011-09-14
DE102011113134.9 2011-09-14
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DE102012005417B4 (de) 2012-03-14 2013-10-24 Friedrich-Schiller-Universität Jena Vorrichtung und Verfahren zur winkelaufgelösten Streulichtmessung
EP2846129A1 (fr) * 2013-09-10 2015-03-11 BAE Systems PLC Mesure optique de rugosité de surface
US9976850B2 (en) 2013-09-10 2018-05-22 Bae Systems Plc Optical surface roughness measurement
DE102021105946A1 (de) 2021-03-11 2022-09-15 Asml Netherlands B.V. Messvorrichtung und Verfahren zur Rauheits- und/oder Defektmessung an einer Oberfläche

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