Characterisation, Measurement & Analysis
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Semiconductor & Electronics

  • SXRTO Oscilloscopes Explained

    Pico Technology have launched their latest 5 GHz SXRTO Sampler Extended Real Time Oscilloscope, but what is SXRTO. Learn more about the benefits and cost savings compared to Real Time Oscilloscopes, RTO below.

    The real-time oscilloscope
    Real-time oscilloscopes (RTOs) are designed with a high enough sampling rate to capture a transient, non-repetitive signal with the instrument’s specified analogue bandwidth. According to Nyquist’s sampling theorem, for accurate capture and display of the signal the scope’s sampling rate must be at least twice the signal bandwidth. Typical high-bandwidth RTOs exceed this sampling rate by perhaps a factor of two, achieving up to four samples per cycle, or three samples in a minimum-width impulse.

    Equivalent-time sampling
    For signals close to or above the RTO’s Nyquist limit, many RTOs can switch to a mode called equivalent-time sampling (ETS). In this mode the scope collects as many samples as it can for each of many trigger events, each trigger contributing more and more samples and detail in a reconstructed waveform. Critical to alignment of these samples is a separate and precise measurement of time between each trigger and the next occurring sample clock.
    After a large number of trigger events the scope has enough samples to display the waveform with the desired time resolution. This is called the effective sampling resolution (the inverse of the effective sampling rate), which is many times higher than is possible in real-time (non-ETS) mode.
    As this technique relies on a random relationship between trigger events and the sampling clock, it is more correctly called random equivalent-time sampling (or sometimes random interleaved sampling, RIS). It can only be used for repetitive signals – those that vary little from one trigger event to the next.

    The sampler-extended real-time oscilloscope (SXRTO)
    The PicoScope 9404 SXRTO has a maximum effective sampling rate in ETS of 1 TS/s. This corresponds to a timing resolution of 1ps, 2000 times higher than its actual maximum sampling rate.
    The PicoScope 9404-05 SXRTO has an analogue bandwidth of 5 GHz. This means that it requires a sampling rate of at least 10 GS/s, but for an accurate reconstruction of wave shape, we need far higher than this. The PicoScope 9404 gives us 200 sample points in a single cycle at 5 GHz and 140 points in a minimum-width impulse.

    So is the SXRTO a sampling scope?
    All this talk of sampling rates and sampling modes may suggest that the SXRTO is a type of sampling scope, but this is not the case. The name sampling scope, by convention, refers to a different kind of instrument. A sampling scope uses a programmable delay generator to take samples at regular intervals after each trigger event. The technique is called sequential equivalent-time sampling and is the principle behind the PicoScope 9300 Series sampling scopes. These scopes can achieve very high effective sampling rates but have two main drawbacks: they cannot capture data before the trigger event, and they require a separate trigger signal – either from an external source or from a built-in clock-recovery module.
    We’ve compiled a table to show the differences between the types of scopes mentioned on this page. The example products are all compact, 4-channel, USB PicoScopes.

    *Higher-bandwidth real-time oscilloscopes are available from other manufacturers.
    **These functions are possible at low sampling rates, up to 1 MS/s.

    Click HERE for further information, application support, demo or quotation requests  please contact us on 01582 764334 or click  to email.

    Lambda Photometrics is a leading UK Distributor of Characterisation, Measurement and Analysis solutions with particular expertise in Electronic/Scientific and Analytical Instrumentation, Laser and Light based products, Optics, Electro-optic Testing, Spectroscopy, Machine Vision, Optical Metrology, Fibre Optics and Microscopy.

  • What is an FFT Spectrum Analyser?

    FFT Spectrum Analysers, such as the SRS SR760, SR770, SR780 and SR785, take a time varying input signal, like you would see on an oscilloscope trace, and compute its frequency spectrum. Fourier's theorem states that any waveform in the time domain can be represented by the weighted sum of sines and cosines.The FFT spectrum analyser samples the input signal, computes the magnitude of its sine and cosine components, and displays the spectrum of these measured frequency components.

    Click here to download the full Application Note.

     

    If you would like more information, to arrange a demonstration or receive a quotation please contact us via email or call us on 01582 764334.

  • EMC Pre-Compliance Testing

    Electronic products can emit unwanted electromagnetic radiation, or electromagnetic interference (EMI). Regulatory agencies create standards that define the allowable limits of EMI over specific frequency ranges.
    Testing designs and products for compliance to these standards can be difficult and expensive, but there are tools and techniques that can help to minimise the cost of testing and help to enable designs to pass compliance testing quickly.
    One of the most often used techniques for EMI testing is near field probing. In this technique, a spectrum analyser is used to measure electromagnetic radiation from a device-under-test using magnetic (H) field and electric (E) field probes.
    The application note describes some common techniques used to identify problem areas using near field probes, download it here

  • About Lock-In Amplifiers

    Lock-in amplifiers are used to detect and measure very small AC signals, all the way down to a few nanovolts. Accurate measurements may be made even when the small signal is obscured by noise sources many thousands of times larger. Lock-in amplifiers use a technique known as phase-sensitive detection to single out the component of the signal at a specific reference frequency and phase. Noise signals, at frequencies other than the reference frequency, are rejected and do not affect the measurement.

    Why Use a Lock-In?

    Let's consider an example. Suppose the signal is a 10 nV sine wave at 10 kHz. Clearly some amplification is required to bring the signal above the noise. A good low-noise amplifier will have about 5 nV/√Hz of input noise. If the amplifier bandwidth is 100 kHz and the gain is 1000, we can expect our output to be 10 µV of signal (10 nV × 1000) and 1.6 mV of broadband noise (5 nV/√Hz × √100 kHz × 1000). We won't have much luck measuring the output signal unless we single out the frequency of interest.

    If we follow the amplifier with a band pass filter with a Q=100 (a VERY good filter) centred at 10 kHz, any signal in a 100 Hz bandwidth will be detected (10 kHz/Q). The noise in the filter pass band will be 50 µV (5 nV/√Hz × √100 Hz × 1000), and the signal will still be 10 µV. The output noise is much greater than the signal, and an accurate measurement cannot be made. Further gain will not help the signal-to-noise problem.

    Now try following the amplifier with a phase-sensitive detector (PSD). The PSD can detect the signal at 10 kHz with a bandwidth as narrow as 0.01 Hz! In this case, the noise in the detection bandwidth will be 0.5 µV (5 nV/√Hz × √.01 Hz × 1000), while the signal is still 10 µV. The signal-to-noise ratio is now 20, and an accurate measurement of the signal is possible.

    The rest of this article describes the detailed operation of a lock-in amplifier together with various design and performance considerations plus practical advice to achieve the best performance in a number of different measurement scenarios.  This information will help you get the best out of the Stanford Research Systems (SRS) family of lock-in amplifiers (SR850, SR844, SR830, SR810, SR530, SR510, SR124). Please download below:

    pdficon

    About Lock-in Amplifiers_Application Note

     

  • Up to 10% Discount on Flexible Resolution Oscilloscopes!

    5000-PR-image-elektra The revolutionary architecture of the PicoScope 5000 Series oscilloscopes allows them to operate at a range of resolutions from 8 bits, like most standard digital oscilloscopes, all the way up to a very high-resolution 16 bit mode. Unlike software-enhanced resolution modes, these are true hardware resolutions achieved by combining multiple high-resolution ADCs to create minimal distortion and noise while maximizing bandwidth. The performance figures speak for themselves:
    Resolution Bandwidth Max. sampling rate THD (100 kHz FS)
    8 bits 60 to 200 MHz 1 GS/s < –60 dB
    12 bits 60 to 200 MHz 500 MS/s < –70 dB
    14 bits 60 to 200 MHz 125 MS/s < –70 dB
    15 bits 60 to 200 MHz 125 MS/s < –70 dB
    16 bits 60 MHz 62.5 MS/s < –70 dB

     

    The PicoScope 5000 Series contains a variety of bandwidth, buffer size and signal generator options to suit your technical requirements and your budget. Every model has the same high-quality flexible resolution design that will give you outstanding performance from 8 bits to 16 bits. What's more, all this power fits in a unit small enough to carry around with your laptop!

    Model Bandwidth Max. sampling rate Buffer size FG/AWG*
    PicoScope 5242A 60 MHz 1 GS/s 16 MS Function Generator
    … all the way up to …
    PicoScope 5444B 200 MHz 1 GS/s 512 MS Arbitrary Waveform Generator

     

    There isn't enough room here to discuss all the advanced features of these scopes, including channel math, spectrum analysis, serial decoding, measurements with statistics, mask testing and persistence display modes. All models include a function generator with 14-bit resolution and 200 MS/s sample rate, and in some models this is extended to a powerful arbitrary waveform generator. Watch the video below or download the data sheet and find out why a PicoScope 5000 Series Flexible Resolution Oscilloscope could be the only scope you need!

    If you have further questions regarding the Picoscope range please contact Peter Davenport on 01582 764334  or click to email.

  • Semiconductor wafer surface measurement

    The surface measurement results shown below are from sample GaAs compound semiconductor wafers manufactured by Wafertech Ltd

     

    The requirement from Wafertech was to measure surface distortion, surface finish and other parameters such as TTV (total thickness variation) across both polished and unpolished wafers. For polished wafers the Zygo GPI Fizeau Interferometer provides accurate surface measurement of wafers in a matter of seconds. Measuring unpolished “as cut” GaAs compound semiconductor wafer samples makes use of the Zygo NewView 7300 an optical profiler with a much higher resolution able to not only measure the profile but also the roughness of surfaces. This is achieved by multiple measurement scans of the surface using a high magnification objective lens and stitching the scanned data to create a much larger data set covering the whole of the wafer surface.

    Figure 1 
    Figure 1 

    Figure 1 is a screenshot from the Zygo GPI showing the distortion across a 4” GaAs compound semiconductor wafer. This surface measurement delivers over 300,000 data points in seconds. A snap line has been placed across the 3D data (top left) and this is displayed underneath as a 2D plot similar to what you would achieve with a much slower stylus surface profiler. This measurement is fast and non-contact and will display a host of parameters (including peak to valley, rms etc) to suite the measurement requirements. The system is able to measure deviations from flatness to better than 16nm across the full 4” aperture of the system.




    Figure 2 
    Figure 2 

    Figure 2 shows the measurement results and screenshot from the Zygo NewView 7300 non-contact optical surface profiler. With this system an objective lens with a higher magnification is used to measure a smaller area of the surface and multiple measurements are stitched together with the inbuilt software to provide a complete and accurate data set for the whole surface. Each scan takes a few seconds and large surfaces such as this 2” wafer can be covered in 10’s of minutes with a lateral resolution of 11 microns. This approach works well when the surface is unpolished and where surface roughness is required in addition to just a profile. In this example of a GaAs compound semiconductor wafer the peak to valley value across the wafer is 27 microns with a Ra of 1.9 microns

  • Capacitive MEMs Switch Characterisation App Note

    Capacitive MEMS Switch Characterisation

    Description: One of the participants in the Zygo Dynamic MEMS Workshop, the Tyndall Institute  in Cork, Ireland provided some novel devices that were measured during the workshop.

    Recommended Product: Zygo NewView 7000

    Capacitive MEMS switches are micron-scale devices that employ the movement of a mechanical component to place a variable capacitance in the path of a radio-frequency transmission line, thereby either blocking or enabling transmission of an RF signal along that line.

    Research at Tyndall has developed a low-voltage capacitive shunt microswitch for use at radio frequencies, using a low-temperature, CMOS compatible fabrication process. The switch requires an operating voltage of 10-15 V, which represents a substantial improvement on many current devices that require a voltage of up to 70 V. RF performance is also promising: the switches have shown an insertion loss of -0.2 dB at 30 GHz and an isolation of -19.3 dB at 30 GHz.

    How it works: Two versions are shown below, with 200x200 microns and 100x100 microns plates, the CPW (coplanar waveguide) Radio-frequency capacitive shunt switches consists of a grounded metallic membrane supported a few microns over a passivated CPW (coplanar waveguide) transmission line. In the up-state of the membrane, the switch capacitance is low and does not affect transmission of a radio-frequency signal along the line. Superimposition of a DC actuation voltage onto the RF signal causes the membrane to become attracted downwards due to the electrostatic force between the membrane and transmission line, at some value of the voltage called pull-in voltage the membrane snaps down and the switch is closed.


    workshop1
    Measurements of the SIMSWITCH (100x100 microns) using a Zygo NewView 6300 scanning white light interferometer



    Zygo NewView 6000 measurement of SIMSWITCH
    These images show an alternative SIMSWITCH (200x200 microns) design measured on a Zygo NewView 6300 showing movement from open to closed after a voltage has been applied to activate it.



    Micromachined Beams

    Micromachined Beams: these devices have been developed as a part of materials characterisation and process development project. Micromachined beams are commonly used as a test structures for material and process characterisation. Based on the pull-in voltage and resonance frequency measurements the material/mechanical properties can be extracted. Fixed-fixed beams and their modifications can be used as micromachined mechanical resonators.


    Zygo NewView 6000 measurement of RF MEMS Switch
    Shown is a beam fixed from both sides (other beams used were fixed only from one side), the detail of this structure can be clearly seen i.e. thickness and anchor region.


    Measurement of the mechanical resonance frequency for the beam fixed on both sides gave a value of 263kHz very close to the theoretical prediction of 251.9KHz.


    Click here to see the beam being dynamically measured using the NewView 6300 (WMV file 1.2Mb)

  • MEMS Application Note

    This article introduces some of the concepts behind Scanning White Light Interferometry (SWLI) for the measurement of Micro-Electro Mechanical Structures (MEMS) under static and dynamic operating conditions. SWLI has created a revolution in surface measurement and has been facilitated by advances in precision mechanics, camera and computer technology, which now makes it possible to rapidly acquire, process and analyze interference patterns across thousands of image pixels. This has enabled the non-contact surface profiling of complex 3D structures such as MEMS devices and allows the rapid measurement of smooth and rough surfaces, large step heights, multiple surfaces and thick films to sub-nanometer vertical resolution all within a single metrology platform, see Figure 1.

    Zygo Scanning White Light Interferometer
    Figure 1, a commercial SWLI from Zygo Corporation



    Fig 2 shows a simplified diagram of a typical SWLI arrangement. An extended white light illuminator often an LED (Light Emitting Diode) provides the source of incoherent light for the instrument. The light is collimated and reflected down into the microscope objective which is mounted on a PZT (Piezoelectric Translator) and allows the objective lens to be translated vertically by typically 150 microns. The objective in this case is a Mirau that incorporates a beam splitter and reference mirror. The light from the LED is split in the objective so that part of the light is passed to the reference mirror and reflected back up the microscope towards the camera and the remaining light is focussed onto the surface of the sample to be imaged and the reflected light from the sample surface is also passed back up the microscope to be detected by the camera, which is typically a CCD electronic imaging device.

    A typical SWLI arrangement
    Figure 2, a typical SWLI arrangement



    If the sample surface is brought into focus by vertically translating the objective such that the distance the light has travelled from the beam splitter to the surface and back matches the distance from the beam splitter to the reference mirror and back an intensity interference pattern will be imaged by the camera. The incoherent LED light source has a coherence length of only several microns so that interference fringes only occur at a particular focal distance from the sample when the path length difference is zero or close to zero. If only a single point on the surface of the sample is considered and imaged onto a pixel of the camera then as the objective is translated vertically and linearly over a fixed range through the point of zero path difference an interference intensity signal is detected by the camera as shown in Figure 3. Clearly the maximum intensity signal variation occurs when the optical path difference from the sample and reference mirror is zero and it is this position that defines the vertical position of the surface point on the sample. By measuring every point on the surface with the imaging camera as the objective is translated vertically it is then possible to process the data and accurately determine the relative vertical position of every point on the sample imaged by the objective and thus obtain a very accurate surface profile.

    Amplitude with optical path difference
    Figure 3, shows the interference signal amplitude with optical path difference, the peak occurs when the optical path difference is zero.



    Using this basic technique the instrument is capable of measuring the form, roughness, and step height of surfaces as well as measuring multiple surfaces and films and can scan larger areas than the field of view of the objective lens by stitching many imaged fields together. It is also possible to then adapt the basic instrument to cope with dynamic measurements where the structure under observation is periodically excited.

    Using a masking technique to define areas manually or a histogram analysis to measure the relative heights of surfaces automatically it is possible to isolate surfaces scanned by the instrument. Figure 4 shows an example of the histogram analysis applied to a small scale structure comprising surfaces at three different heights, which have been separated and can be analysed independently.

    Histogram analysis
    Figure 4, histogram analysis to separate surfaces at three different heights



    When a film is present on the sample substrate, as is often the case with many fabricated microstructures, then it is necessary to monitor the light reflected from the top surface and the film/substrate interface. The signal detected as the objective is scanned vertically by the PZT leads to two interference peaks as shown in Figure 5. As long as the interference signals can be sufficiently separated (and the refractive index is known or can be approximated) then the film thickness can be measured. Examples of results obtained from such measurements are shown in Figure 6, anticlockwise from

    Interference signals
    Figure 5, shows the two interference signals as the SWLI scans through the top surface of the film and film/substrate interface



    top left to bottom right, showing the profile of the surface of the film, film thickness and substrate surface.

    Thin film results
    Figure 6 shows surface of the film, film thickness and substrate surface



    By scanning the instrument laterally in a raster pattern and taking multiple images it is possible to “stitch” together a surface profile of a sample far larger than the field of view of the objective as shown in the example of a coin in Figure 7

    Image Stitching
    Figure 7 stitching several fields of view to image a much larger object



    As MEMS development has matured and more sophisticated devices have been created it has become important to characterise and understand the functionality of devices while in motion. By strobing the light source from the SWLI in synchronism with the periodic motion of the device it is possible to freeze the sample motion and allow measurements to be undertaken as if the part were fixed in space. Dynamic measurement of a MEMS device is useful for both research and development and production quality control. Sweeping of device drive frequencies and illumination phase delays can be used by the researcher to validate design parameters and examine device resonances. As a quality check, dynamic measurement mimics the MEMS actual usage for a true functional test. Rapid characterization over the full range of motion and frequencies experienced is possible by a combination of strobe phase delay and frequency sweep. Figure 8 shows an example of a micro-fabricated cantilever that has been excited at a range of resonant frequencies.

    Deformation of a cantilever
    Figure 8 shows the deformation of a cantilever at multiple resonant frequencies (75kHz, 450kHz, and 1.2MHz).



    Recent results by the University of Newcastle have been successful in characterising a new type of biosensor the MEMSens, figure 9, 10 and 11 show some examples of the membrane structure as it is passed through a sequence of tests following manufacture and the method employed for printing antibodies to functionalise the device.

    Device quality
    Figure 9, Surface profile to give a quick indication of device quality. Underlying electrodes leave their impression on the membrane and curvature indicates stress



    Electrostatic deflection
    Figure 10, Electrostatic deflection of the membrane following application of 200V



    PDMS stamp
    Figure 11, 7 micron deep silicon template used to make PDMS stamp for printing antibodies


    This article has demonstrated how a SWLI can form a platform for a comprehensive range of measurements to characterise MEMS devices in both static and dynamic mode for both R&D and production. A number of sample MEMS structures have been shown to illustrate the breadth of potential for SWLI metrology. For further details please contact info@lambdaphoto.co.uk

  • Measuring Dynamic MEMS Devices

    Introduction

    Optical profilers are valuable tools for characterizing the surfaces of MEMS devices. Traditionally, an optical profiler such as the NewView 7300™ was used for measuring a wide range of surface features and device parameters. However, one fundamental requirement was that the surface and device be kept in a static condition during measurement. As industries such as MEMS manufacturing matured and began creating more dynamic devices, it also became more important to characterize and understand the functionality of the device while it is in motion. Advancements in optical profiling instruments now make this possible. Using the NewView 7300™ and the new Dynamic Metrology Module (DMM), it is now possible to synchronize the illumination source to the motion of the device, in essence freezing the sample motion and allowing the user to effectively measure as if the part were fixed in space.

    Stroboscopic Illumination

    When measuring a sample with a white light profiler (such as the NewView 7300™), the sample is typically held in a stationary position. Motion of the part will cause a blurred image, poor data integrity, or even loss of data. For samples such as MEMS devices, however, it can be extremely useful to characterize how the shape of the sample changes when the device is activated and therefore in motion.

    Figure 1.

    Figure 1 - Schematic of Dynamic Metrology Module (DMM) components

    In a dynamic configuration, a strobed LED illuminator is synchronized with the drive signal of the device. By adjusting the strobe frequency of the light source, the motion can be effectively frozen, allowing precision scanning white light interferometer (SWLI) measurements to be made on the dynamic device. Adjustment of the illumination phase delay—the lag between the drive signal and the illuminator strobe—allows the device’s full range of motion to be examined. The DMM option includes MetroPro™ software which allows these parameters to be adjusted automatically to ‘sweep’ through ranges of frequencies and phase delays to fully characterize the device under test. The modularity of the Dynamic Metrology Module also makes it possible to upgrade existing NewView 7300™ systems with these enhanced capabilities.

    Why Dynamic Measurements?

    Dynamic measurement of a MEMS device is useful for both research and development and production quality control. Sweeping of device drive frequencies and illumination phase delays can be used by the researcher to validate design parameters and examine device resonances. As a quality check, dynamic measurement mimics the MEMS actual usage for a true functional test. Rapid characterization over the full range of motion and frequencies experienced is possible.

    Making Measurements

    ZYGO’s Dynamic measurement option makes the characterization of dynamic MEMS devices just as simple as measuring a static device. All standard MetroPro™ numerical and graphical results can be used to quantify the motion of a dynamic device. These results can also create resonance amplitude and nyquist plots, and all plots are available for creating a movie of the device motion. For power users, custom results can be generated with ZYGO’s MetroScript™, an easy-to-use scripting language.

    For any dynamic measurement, the user needs to set up the drive parameters for the device including voltage, signal shape, and frequency. Depending on what metrology is required, one of four types of dynamic metrology can then be pursued.

     

    Single measurement
    A single measurement can be used to look at a device’s behavior at a particular drive signal and phase delay. One application where this would be particularly useful is a DC drive where a static offset would be expected based on the voltage applied. By examining the sample with the voltage turned on and off, the change in the device may be observed.

    Frequency Sweep
    A frequency sweep measures a device at a particular phase delay and steps through the desired frequency range. This can be a quick method for identifying which frequency ranges a device is most sensitive to. For devices whose responses are independent of phase delay, this can be an ideal approach to use for determining the resonant frequency of the device.

    Phase Sweep
    In a phase sweep, a device is driven at a single frequency while the phase delay of the light source is varied. The delay range and step size are user configurable from 0 to 360°, allowing the user to map a complete, single period of motion. If desired, the user can select a single measurement from the sweep to subtract from the subsequent measurements, showing shape change during motion. After the data is collected, the user can export the data as an .AVI movie that can be viewed through most standard media players.

    Figure 2.

    Figure 2 - Deformation of a cantilever at multiple resonance frequencies (75kHz, 450kHz, and 1.2MHz)

    Phase & Frequency Sweep
    The final measurement mode combines the previous two— sweeping and stepping both the drive frequency and the phase delay. The user can define the start, end, and step size for both frequency and phase. At each drive frequency in the sweep, a phase sweep as described above is performed. This is particularly useful for detection of system resonance.

    Dynamic Measurement Specs

    Parameter Specification
    Measurement Range Out of Plane: Heights / deflections up to 5mm depending on slope
    In Plane: microns to millimeters (FOV and Objective dependent)
    Measurement Resolution Vertical resolution: <1 nm (velocity dependant)
    Lateral resolution ≈.1 pixel (field-ofview/objective dependant)
    Frequency Range DC / Static (White LED)
    Dynamic: 400Hz to 10MHz (Green LED)
    Frequency Resolution 0.01Hz
    Frequency Resolution 0.01 Hz
    Device Voltage Range 0 to 10 volts peak-to-peak
    0 to ±200 volts peak-to-peak with supplied
    High Voltage Amplifier
    Phase Range 0-360 °
    Phase Resolution
    Waveforms DC, sine, triangular, square, or user-defined arbitrary waveform
    Light Source and Controller High-output LED with integrated controller
    Software Version Required MetroPro™ 8.1.5.3 and greater

    Conclusion

    Whether for quality control in production manufacturing, or for laboratory research, ZYGO’s NewView 7300™ with the DMM option provides all the tools necessary for inspection of both static and Dynamic MEMS. With best-in-class measurement range and speed, the NewView 7300™ and DMM Option are the ideal turnkey solution for dynamic MEMS measurement.

  • 3D information or surface topography

    These three images are screenshots taken from the measurement of different parts of a semiconductor die taken on the Zygo NewView 6300. A magnification of 20X (10x objective coupled to a 2x zoom) provided detailed surface topography of the semiconductor device with a lateral resolution close to 1 micron. In this application the aim was to identify defects in the 3D structure of the device against a reference structure which was defect free. As many defects in such devices are not confined to just variations in reflected light the use of 3D information or surface topography is a far more accurate method of determining and isolating defects.

    Figure 1 
    Figure 1 

    This measurement shows an isolated D shaped structure with a raised surface defect shown as a line on the intensity image map. By taking a 2D profile the height of this defect approximately 1 micron can be clearly seen.


    Figure 2 
    Figure 2 

    Measurement of the die in this particular area is seen to be free of defects and can be used as a reference 3D map.


    Figure 3 
    Figure 3 

    This measurement shows two sets of finger like or rib structures where the set on the left show that material has coalesced to create a defect. This is particularly evident when examining the 2D surface profile created by placing a snap line across the 3D topographic data.

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