In House Developments

Transcription

1 In House Developments 1. Nano Profiler with Instantaneous phase shifting 2. Dual Frequency interferometer for dynamic analysis 3. Speckle shearing interferometer for subsurface defect detection 4. Stroboscopic Interferometer for Dynamic Characterization 5. Stroboscopic Phase Shifting concept Department of Mechanical and Industrial Engineering 15-Feb-11 1

2 Stroboscopic Interferometer Objective: Static, Dynamic and surface characterization of high frequency microstructures on a single tool Reliable methodology for precision measurement Application: In MEMS, Microfluidics related industries Background: Stroboscopy give the motion details in whole field compared to LDV for dynamic analysis Department of Mechanical and Industrial Engineering 15-Feb-11 2

3 Stroboscopic Interferometer MEMS Device driven in sinusoidal Signal Snap Shot of Phase motion Department of Mechanical and Industrial Engineering 15-Feb-11 3

4 Stroboscopic Interferometer Design of Micro-Mirror and Microcantilever Simulated static and dynamic behavior using Rayleigh-Ritz Method DUT Micro-mirror Department of Mechanical and Industrial Engineering 15-Feb-11 4

5 Stroboscopic Interferometer Surface Metrology Results Interferogram of the Micro Mirror Surface Roughness in Nanometers Surface metrology - surface roughness information Feedback about the specific Microfabrication process Department of Mechanical and Industrial Engineering 15-Feb-11 5

6 Stroboscopic Interferometer Static Characterization Results Comparison with the theoretical model Electro-static testing to get the details of Interferogram of tested Cantilever deflection on various voltages Department of Mechanical and Industrial Engineering 15-Feb-11 6

7 Laser Doppler Vibrometer Dynamic Testing Disadvantage : Single/ Scanning system Courtesy : Polytec Inc Not Real Time Department of Mechanical and Industrial Engineering 15-Feb-11 7

8 Stroboscopic Interferometer Department of Mechanical and Industrial Engineering 15-Feb-11 8

9 Stroboscopic Interferometer Dynamic Characterization SEM image of AFM cantilever Interferogram of AFM cantilever First Mode at 17.2 KHz Second Mode at 119 KHz detect fundamental frequency s of the structure & mode shape when its resonating. Department of Mechanical and Industrial Engineering 15-Feb-11 9

10 Stroboscopic Interferometer Stable light source Capability to strobe at higher frequency (~ 4 MHz) Quick Processing using Fourier Transform Method. Single tool to test all the static and dynamic behavior Proven Result match with other commercial devices for MEMS Testing Department of Mechanical and Industrial Engineering 15-Feb-11 10

11 MECH 691T Engineering Metrology and Measurement Systems Lecture 10 Instructor: N R Sivakumar 11

12 Outline Applications To precision Measurement Length, Dynamic Characteristics Film Thickness - Ellipsometry Introduction to NanoMetrology X-Ray Interferometry Combined Optical X-Ray Interferometry Bio Metrology Optical Coherence Tomography 12

13 Length Measurement Applications To precision Measurement Length, Angle and Dynamic Characteristics Film Thickness - Ellipsometry 13

14 Length Measurement 14

15 Vibration Measurement Laser Doppler Vibrometry laser Doppler Vibrometer detects the Doppler shift of laser light, that is scattered from a small area of the vibrating object. f The Doppler frequency shift is used to measure the d 2 / component of velocity which lies along the axis of the laser beam. As the laser light has a very high frequency W (approx x10 14 Hz), a direct demodulation of the light is not possible. Hence, interferometer is used to mix the scattered light coherently with a reference beam. The photo detector measures the intensity of the mixed light whose (beat) frequency is equal to the difference frequency between the reference and the measurement beam. Such an arrangement can be a Michelson interferometer 15

16 Vibration Measurement Michelson Interferometer 16

17 Vibration Measurement Laser Doppler Vibrometry A laser beam is divided at a beam splitter into a measurement beam and a reference beam which propagates in the arms of the interferometer. The photo detector measures the time dependant intensity I(t) at the point where the measurement and reference beams interfere. light intensity I(t) varies in a periodic manner corresponding to the vibration. f d 2 / This rate of change of phase is proportional to the velocity of vibration Photodetector Measurement 17

18 Vibration Measurement Due to the sinusoidal nature of the detector signal, the direction of the vibration is ambiguous. There are two ways to introduce a directional sensitivity: Solution 1: Introduction of an optical frequency shift into one arm of the interferometer Solution 2: Adding polarization components and an additional photo receiver. The most common form is the first solution. An acousto optic modulator ( Bragg cell) is incorporated into one arm of the interferometer. This type of interferometer is called heterodyne interferometer. 18

19 Vibration Measurement Heterodyne Interferometer 19

20 Vibration Measurement Acousto optic deflection An AOD is an acousto-optic crystal where a frequency ramp is applied to create a varying deflection angle of the diffracted light. An AOD is used to create the scan of the exposure laser beams in the raster scan systems. The AOD allows a high degree of flexibility and calibration of the beam deflection, which generates a very accurate scan. Together with an telecentric lens focus system, vibration-free scanning is achieved 20

21 Vibration Measurement Acousto optic principle Input laser Frequency F Output laser frequency (F+ F a ) Input laser angle Output laser angle depends on laser wavelength and acoustic freq. F a Acoustic frequency F a 21

22 Vibration Measurement Heterodyning Basic Layout Scanning Interference Data Acquisition 22

23 Vibration Measurement Acousto optic deflection Incoming laser beam at 632.8nm Deflected beam Acoustic wave Telecentric Lens 23

24 Vibration Measurement Laser Beam 2-Axes AOD Target Non - Mechanical Scanning 2 - axes Scanning Scanning Of Micro-structures Patent No: 09/222,731 ;09/350,901 24

25 Vibration Measurement Ink Jet Printer head 20 m 1 Khz 20 m 10 Khz 100 Khz 2.3 mm 4.8 mm 4.8 mm 25

26 33nm Displacement in m Vibration Measurement Ink Jet Printer Head Samples over Time 26

27 Vibration Measurement AFM cantilevers 100 m 20 m 130 m 100x130x20 m cantilever vibrating at 100 khz 27

28 LDV( Laser Doppler Vibrometer) Dynamic Testing Disadvantage : Single/ Scanning system Courtesy : Polytec Inc Not Real Time

29 Stroboscopic Interferometer Static/Dynamic Testing Disadvantage : LED( Light Emitting Diode)

30 Acousto Optic Modulator (AOM) in Stroboscopy

31 Digital Laser Microinterferometer Surface Profile, Static/Dynamic Testing Speckle Pattern Interferometry limits its capability

32 Rationale & Objective Rationale: Stroboscopy give the motion details in whole field of view than point scanning like in LDV for dynamic analysis. Can be implemented for static and surface profile. But needs alternative method for strobing light and better optical processing method to measure in nano resolution. Objective: To develop a simple yet viable stroboscopic interferometer with a CW laser for comprehensive mechanical characterization of microstructures.

33 Design and fabrication of MEMS device Design of Micro-Mirror and Microcantilever Simulated static and dynamic behavior using Rayleigh-Ritz Method DUT Micro-mirror

34 Static Behavior Parameter Considered Values Length of the cantilevers (L) Thickness (h) Maximum width ( w(x)) Dielectric gap(d 0 ) Young s modulus E Density 810 m (measured) 10.5 m (measured) 90 m (measured) ~11 m (measured) GPa (values given by the manufacturer) 2320kgm -3 (values given by the manufacturer) Voltage Magnitude of Tip at 810μm deflection (nm) 55V V V 27

35 Dynamic Behavior Parameter Considered Length of the cantilevers (L) Thickness (h) Maximum width ( w(x)) Young s modulus E Density Values 350 m (measured) 1 m (measured) 35 m (measured) GPa (values given by the manufacturer) 2330kgm -3 (values given by the manufacturer) Mode Natural frequency(simulated) Natural frequency (by manufacturer) 1 st 11.2 khz 10.0 khz ~3 khz 2 nd 70.4 khz n/a

36 Schematic layout Of AOMSI M Mirror; AOM Acousto-Optic Modulator; S Spatial Filter ; L1 100mm Collimating Lens ; L2 150mm Focusing Lens; O 50mm Microscopic Objective; QW Quarter Wave Plate; L3 300mm Imaging Lens; C CCD camera; PBS Polarized Beam Splitter, P1 polarizer, S1 Stopper

37 Digital image of the layout of the AOMSI Twyman-Green interferometer assembly CCD camera Microstructure support /10 mirror Laser AOM

38 Surface Metrology Surface metrology give the surface information of the structure. Its gives the feedback of how the device is formed after the Microfabrication. Interferogram of the Micro Mirror Surface Roughness in Nanometers

39 Low-Frequency Static Characterization In Static Characterization we can conduct electro-static testing to get the details of deflection on various voltages. k E MEMS structure V DC Piezo-shaker ~

40 Methodology (a) (b) (c)

41 Interferogram D U T

42 Deflection (m) Results Comparison of static characterization 1.4E E E E E-08 55V Exp 55V Theo 15V Exp 15V Theo 29.5 V Theo 29.5V Exp 4.0E E E E E E E E-04 Lenghth (m) Results Comparison with the theoretical model Voltage Magnitude of Tip deflection (nm) at 410 μm (Theo) Magnitude of Tip deflection (nm) (Exp) Error 55V ~3% 29.5V ~3% 15V ~9%

43 Dynamic Characterization In Dynamic Characterization we detect the fundamental frequency s of the microstructure and mode shape the structure takes when its vibrating in its resonating frequency. SEM image of AFM cantilever Interferogram of AFM cantilever

44 Methodology

45 Sweep of frequency on the PZT stage Visualization of the Q-factor Detection of the natural frequency Detection of Natural Frequency Mode Strobing the light at that frequency to visualize high-speed motion Natural frequency(simulated) Natural frequency (provided by the manufacture) 1 st 11.2 khz 10.0 khz ~3 khz Natural frequency(ex perimental) 10.7 khz 2 nd 70.4 khz n/a 74.6 khz

46 Digital Image during Dynamic Characterization

47 Static Image of the Interferogram in dynamic conditions DUT 35 m 350 m Highly deflected portion Node Highly deflected portion

48 Mode Shape comparison at 1st Resonance frequency

49 Mode Shape comparison at 2nd Resonance frequency

50 Film Thickness - Ellipsometry Introduction Ellipsometry is an optical technique for determining properties of surfaces and thin films. The instrument analyses polarized light. (A change in the polarization upon reflection from a surface). It does not measure a film thickness, or a surface coverage, or a refractive index. Optical methods are, for this purposes, indirect methods: Information about the samples is not directly obtained, but requires calculations based on idealized models. 50

51 Film Thickness - Ellipsometry We are interested in... film thickness surface coverage refractive index of the film 51

52 Film Thickness - Ellipsometry The phenomenon of polarization Malus law I I cos 2 0 Malus law describes the angular dependence of the intensity of light emitted from two polarizers in series. The angle is between the two polarization planes. I 0 is the maximum intensity. 0 0 cos cos 0 Maximum intensity Nil intensity 52

53 Film Thickness - Ellipsometry Polarized light Linear polarized light No phase shift Superposition of two linear polarized waves 90 phase shift, equal amplitudes 53

54 Film Thickness - Ellipsometry Elliptically polarized light The polarization can be described by: ratio of amplitudes phase shift 90 phase shift, unequal amplitudes Phase shift other than 0 or 90 elliptically polarized light 54

55 Film Thickness - Ellipsometry Elliptically polarized light Upon reflection the polarization will change Upon reflection from the sample surface: The amplitude ratio and/or the phase shift change D (Del) and Y (Psi) quantify these changes Ellipsometers measure two angles, called D (Del) and Y (Psi) tany is connected to the amplitude ratio, and D is connected to the phase shift. 55

56 Film Thickness - Ellipsometry Interaction of light with material When the light beam reaches the surface, some of the light is reflected and some passes into the material The law of reflection says that the angle of the incidence is equal to the angle of reflection Snell s law N 1 sin 1 N 2 sin 2 for dielectric materials k 0 n 1 sin 1 n 2 sin 2 56

57 Film Thickness - Ellipsometry Total reflection coefficients The incident beam and the reflected beam define the plane of incidence. Reflectivity. E p R the ratio of the amplitude of the outgoing wave compared to that of the incoming wave Reflectivity is calculated for linear polarized light (p- polarized or s-polarized), yielding R p and R s. P = parallel to the plane of incidence S = perpendicular to the plane of incidence E s Calculations are done with Fresnel s formulas. 57

58 Film Thickness - Ellipsometry p - WAVE E - electric vector H - magnetic vector i - incident r - reflected t - transmitted Hr Er Ei Et Ht Hi medium2 medium1 58

59 Film Thickness - Ellipsometry s - WAVE E - electric vector H - magnetic vector i - incident r - reflected t - transmitted Er Hr Hi Ht Ei Et medium2 medium1 59

60 Film Thickness - Ellipsometry The fundamental equation of ellipsometry These total reflection coefficients (R p and R s ) contain complete information on the change in polarization. tanye (id) = R p / R s (precisely measured) (calculated for a given model) 60

61 Film Thickness - Ellipsometry The fundamental equation of ellipsometry tany e (id) = R p / R s R R s p N N N 1 1 N N cos 1 N cos N cos 1 N cos N n ik 1 1 cos 2 cos 2 cos 2 cos 2 N 1 2 N 1 N 2 n=index of refraction k=extinction coefficient The complex index of refraction The incident angle The refracted angle The complex index of refraction of material 1 The complex index of refraction of material 2 n c v Speed of light in a vacuum Speed of light in a material k measures how much light is absorbed in the material and is dependent on Optical constants n and k describe how light interacts with the material 61

62 Film Thickness - Ellipsometry Apparatus Basics nulling ellipsometer Light detector Light source Polarizer Quarter wave plate (compensator) Analyzer Sample 62

63 Film Thickness - Ellipsometry Ellipsometer 63

64 Film Thickness - Ellipsometry Reflections with films Multiple interfaces If more than one interface is present, the resultant reflected beam is made up of the initially reflected beam and the infinite series of beams which are transmitted from medium 2 back into medium 1 Rp and Rs in this case are function of b, where: 2 d b N cos 2 2 the wavelength of the operation. From Rp/Rs we find the thickness of the film. 64

65 Film Thickness - Ellipsometry Examples The delta/psi domain D The lower left quadrant is where the D /Y points for a free-film material (a substrate) will be located. The film-free values for several dielectrics, metals and semiconductors are shown 65

66 Film Thickness - Ellipsometry Examples Transparent film The delta/psi trajectory for a transparent film of SiO 2 (n=1.46, k=0) on a silicon substrate. The thickness where the trajectory closes on itself is a function of the angle of incidence, a wavelength and n air and n film. For measured D and Y there is a specific thickness of the film. 66

67 Film Thickness - Ellipsometry Examples Transparent film The D /Y trajectories for transparent films with different indices of refraction on silicon. Note that there are regions where the curves are not well separated. In these regions it is hard to determine the exact index of refraction. 67

68 Film Thickness - Ellipsometry Examples lips_e.html (ellips 2.xls) Absorbing film The D /Y trajectory for a growing film of Ta on a silicon substrate. For a very thick film of an absorbing material, the delta/psi point will be characteristic of a substrate of the film material. The film-growth trajectory, therefore, is the movement from the silicon point to the tantalum point. 68

69 X-Ray Interferometry x-ray interferometry developed by Bonse and Hart Most x-ray interferometers are monolithic - single silicon Si There are 3 lamellae 800 µm thick and cut so that the faces are perpendicular to the crystal planes from which x-rays are diffracted The first is a beamsplitter, the second is a mirror and the third is an analyzer A flexure stage is machined around the analyzer lamella and a piezoelectric actuator (pzt) fitted to the side of the monolith applies a force parallel to the [220] axis, resulting in the motion of the analyzer lamella in this direction

70 X-Ray Interferometry The x-ray interferometer is aligned so that x-rays are incident on the beamsplitter at Bragg angle. Two diffracted coherent beams are produced, which are incident on the mirror lamella. Each give rise to 2 beams, and inner ones go to the analyzer fringe spacing independent of the wavelength of x-rays; but is equal to the lattice spacing of the 220 planes (0.192 nm) This interference pattern interferes with the crystal planes in the analyzer lamella to produce a Moire fringe pattern

71 X-Ray Interferometry As the analyzer lamella is moved through a distance equal to the lattice spacing, the intensity of the beam transmitted by the x-ray interferometer goes from a maximum to a minimum and back to a maximum. By measuring the x-ray intensity as the pzt moves the third lamella, one has a measure of the motion of the analyzer lamella and the instrument can be thought of as a ruler where the graduations are spaced at the distance between successive crystal planes from which x-rays are diffracted The lattice parameter is now regarded as a traceable standard of length; Consequently, measurements of displacement made using an x-ray interferometer are traceable

72 X-Ray Interferometry X-ray interferometer combined with SPM

73 X-Ray Interferometry

74 Need for Nanometrology A study conducted by the EU committee on 13 AFMs from 7 countries shows that the measurements are not consistent i.e. different machine give different result * X-ray Interferometry We need nano-scale traceability and calibration We must overcome the limit of laser wavelength 0.3nm x-ray Fringe 400nm Laser Fringe * Intercomparison of scanning probe microscopes - Journal of international societies for precision engineering and nanotechnology 74

75 Why COXI Combined Optical & X-ray Interferometer Lack of interchangeability of current nano- measuring instruments for length & dimension due to Lack of calibration ( traceability to the SI unit for length - the metre) lack of measurement standards Limit of current technology 75

76 COXI Optical Interferometry long range with limited resolution X-ray Interferometry high resolution with limited by range COXI - Compliment each other sub-nanometer accuracy over long range establish traceability to SI units for nanomeasurements 76

77 X-ray Interferometry Monolithic Silicon Crystal X-ray Source Splitter Mirror Analyser 77

78 COXI Principle and Operation X-ray Fringes nm Laser Fringes nm X-ray interferometer - accurate ruler/linear interpolator for sub fringe displacement 78

79 COXI 79

80 Optical Coherence Tomography Z=7.17 mm 500 um 80

81 Optical Coherence Tomography When using a broad band light source, acceptable visibility is obtained only for the zero th -order fringe. Lasers are used in standard interferometry However, this effect is taken to advantage in low-coherence interferometry Michelson interferometer with a low-coherence light source S If the optical path lengths from the beamsplitter to the mirrors M1 and M2 are equal, we get a bright zero-order fringe at the detector If we move M2, the fringe visibility (intensity) at the detector drops If intensities are equal (I), the intensity at the detector drops from 4I (full coherence) to 2I (no coherence) 81

82 Optical Coherence Tomography By moving M1, until the intensity again reaches maximum, the optical paths are again equal and the unknown movement of M2 is equal to the known movement of M1 This is the operating principle of LCR. Michelson interferometer with a low-coherence light source S Here the mirror M2 is replaced by the object under investigation. This technique is especially suited for measurement on semitransparent materials such as biological tissues When light beam is directed to such material, it is reflected from boundaries between different tissues of differing optical properties 82

83 Optical Coherence Tomography By a scanned motion of M1, intensity maxima at the detector are found and thereby the depth of such boundaries can be measured. This principle is analogous to ultrasound imaging which relies on measuring echoes Example of axial range measurements performed in the eye Measurement of the anterior chamber depth using low-coherence interferometry. The graph displays the magnitude of the reflected intensity as a function of distance. From Puliafito, C.A., et al. (1996) 83

84 Optical Coherence Tomography The graph shows the intensity at the detector as a function of the position of the reference mirror The intensity is a measure of the discontinuity of the optical properties of the tissue To determine the actual depth of the various boundaries, the distance between the echoes has to be multiplied by the index of refraction of the tissue Measurement of the anterior chamber depth using low-coherence interferometry. The graph displays the magnitude of the reflected intensity as a function of distance. From Puliafito, C.A., et al. (1996) 84

85 Optical Coherence Tomography This method is developed further by scanning the light in the transverse direction This technique is called optical coherence tomography (OCT) Grey scale Optical Coherence Tomography image of the anterior chamber of a human eye obtained in vivo. The image is displayed using a logarithmic mapping of the measured optical signal to brightness. From Puliafito, C.A., et al. (1996) Example of a tomographic image of the anterior chamber of the eye displayed in grey scale. The optical beam was scanned in the transverse direction and 200 axial measurements were taken 85

86 Optical Coherence Tomography Fibre optic technology has made it possible to engineer compact, robust and low-cost OCT systems Schematic representation of a fibre optic version of the interferometer A F Fercher, W Drexler, C K Hitzenberger, T Lasser, Optical coherence tomography - principles and applications, Reports on progress in physics, 66 (2003) Fibre-optic interferometer OCT system. From Puliafito, C.A., et al. (1996) 86

87 OCT Images Tearney GJ, Brezinski ME, Bouma BE, et al. In vivo endoscopic optical biopsy with optical coherence tomography SCIENCE 276 (5321): JUN

88 OCT Images Drexler W, Fernandez EJ, Hermann B, et al. Adaptive optics ultrahigh resolution optical coherence tomography INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE 45: U929-U Suppl. 1 APR