Name: in depth analyses of leds by a combination of x-ray computed tomography (ct) and light microscopy (lm) correlated with scanning electron microscopy (sem)
Uploaded: 2016-06-16T13:00:00
Description: Watch this Scientific Journal Video about In Depth Analyses of LEDs by a Combination of X-ray Computed Tomography CT and Light Microscopy LM Correlated with Scanning Electron Microscopy SEM at JoVE.co

The authors kindly acknowledge financial support from the &#34;Akademische Gesellschaft Lippstadt&#34; as well as from the &#34;Ministerium f&#252;r Innovation, Wissenschaft und Forschung des Landes Nordrhein-Westfalen&#34;. Photographs in Figures 1, 2 and 5 courtesy to Markus Horstmann, Hamm-Lippstadt University of Applied Sciences.

1. Sample Preparation for X-ray Computed Tomography (CT)
<ol>
	<li>Glue sample (LED cf. materials section) to a 2 mm &#216; hollow carbon fiber bar of appropriate length using hot-melt adhesive.</li>
	<li>Adjust position of specimen by using a hot-air gun if needed. Fix the sample in the CT-sample chamber using the three-jaw chuck.</li>
</ol>
2. CT Measurement Setup
<ol>
	<li>Perform warmup and centering procedures according to the control software of the X-ray tube. 
	NOTE: Use ...

<ol>
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High Density Packag. , 1-4 (2011).</li><li>Chen, Z., Zhang, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Study+on+the+reliability+of+application-specific+led+package+by+thermal+shock+testing,+failure+analysis,+and+fluid-solid+coupling+thermo-mechanical+simulation.">Study on the reliability of application-specific led package by thermal shock testing, failure analysis, and fluid-solid coupling thermo-mechanical simulation.</a> IEEE Trans. Components, Packag. Manuf. Technol. 2 (7), 1135-1142 (2012).</li><li>Luniak, M., Holtge, H., Brodmann, R., Wolter, K. -. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+Characterization+of+Electronic+Packages+with+Confocal+Microscopy.">Optical Characterization of Electronic Packages with Confocal Microscopy.</a> 2006 1st Electron. Syst. Technol. Conf. 2 (16), 1813-1815 (2006).</li><li>Marks, M. R., Hassan, Z., Cheong, K. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+Methods+for+Ultrathin+Wafer+and+Die+Quality:+A+Review.">Characterization Methods for Ultrathin Wafer and Die Quality: A Review.</a> IEEE Trans. Components, Packag. Manuf. Technol. 4 (12), 2042-2057 (2014).</li><li>Rosc, J., Hammer, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reliability+assessment+of+contact+wires+in+LED-devices+using+in+situ+X-ray+computed+tomography+and+thermo-mechanical+simulations.">Reliability assessment of contact wires in LED-devices using in situ X-ray computed tomography and thermo-mechanical simulations.</a> Proc. 5th Electron. Syst. Technol. Conf. , 1-6 (2014).</li><li>Zhaohui, C., Qin, Z., Kai, W., Xiaobing, L., Sheng, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reliability+test+and+failure+analysis+of+high+power+LED+packages.">Reliability test and failure analysis of high power LED packages.</a> J. Semicond. 32 (1), 014007 (2011).</li><li>Hamon, B., Bataillou, B., Hamon, B., Mendizabal, L., Gasse, A., Feuillet, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=N-contacts+degradation+analysis+of+white+flip+chip+LEDs+during+reliability+tests.">N-contacts degradation analysis of white flip chip LEDs during reliability tests.</a> 2014 IEEE Int. Reliab. Phys. Symp. , FA.1.1-FA.1.6 (2014).</li><li>Tsai, M. -. Y., Tang, C. -. Y., Yen, C. -. Y., Chang, L. -. 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The advantages of this multimodal approach consist in the location-dependent correlation of the acquired data. The multimodal approach described here should be contrasted in subsequent analyses with each technique separately. For example, luminescence properties visible in LM can be linked to compositions as detected using SEM/EDS. The volume information obtained by CT can be extended with in depth analyses of cross-sections prepared in a targeted fashion. CT data also enable fast location of possible areas of interest i...

This article demonstrates the potential and advantages of a combination of X-ray computed tomography (CT) with correlative light and electron microscopy (CLEM) for the exemplary in depth characterization of light emitting diodes (LED). With this technique it is possible to plan the micro preparation of the LED in such a fashion that while a cross section can be imaged microscopically the electrical functionality is preserved in the remainder of the specimen. The procedure has several unique features: firstly, the planned micro preparation by aid of the rendered volume of the entire sample obtained by CT; secondly, the observation of the LED by light microscopy (LM) with the complete variety of imaging techniques available (bright and dark field, polarization contrast, etc.); thirdly, observation of the LED in operation by LM; fourthly, observation of identical regions with the full variety of electron microscopy imaging techniques comprising secondary electron (SE) and back scatter electron (BSE) imaging, as well as energy dispersive X-ray fluorescence spectroscopy (EDX).
LEDs for illumination applications are designed to emit white light, although in certain applications color variability may be favorable. This broad emission cannot be achieved by emission from one compound semiconductor, since LEDs emit radiation in a narrow spectral band (circa 30 nm full width half maximum (FWHM)). Therefore white LED light is commonly generated by the combination a blue LED with phosphors which convert the short-wavelength radiation into broad emission over a large spectral range1. Color variable LED solutions usually make use of at least three primaries, which generally results in higher market prices.2
The use of either CT, LM or SEM is of course well established (e.g., in failure analysis for LEDs3-15), however the comprehensive and purposeful combination of all three techniques described here may offer new insights and will enable faster tracks towards meaningful characterization results.
From 3D microstructural analysis of the packaged device in CT the regions of interest (ROIs) can be identified and selected. With this non-destructive method, electrical connections can also be identified and considered for further preparation. The precise preparation of a 2D cross section allows investigations of the device in operation despite the destructive nature of this method. The cross section can now be characterized by CLEM16,17 which enables a very efficient and flexible characterization of identical ROIs with LM as well as SEM. By this approach, the advantages of both microscopy techniques can be combined. For example, a fast identification of ROIs in the LM is followed by high-resolution imaging in the SEM. But furthermore, the correlation of information from the LM (e.g., color, optical properties, particle distribution) with the visualization and analysis techniques of the SEM (e.g., particle size, surface morphology, element distribution) allows a deeper understanding of functional behavior and microstructure within a white LED.

<table border="0" cellpadding="0" cellspacing="0" width="758">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">X-Ray Computer Tomograph</td>
			<td style="width:119px;">General Electric</td>
			<td style="width:139px;">not applicable</td>
			<td style="width:239px;">type: nanotom s research edition</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:263px;">acquisition software</td>
			<td style="width:119px;">General Electric</td>
			<td style="width:139px;">not applicable</td>
			<td>phoenix Datos| x2 acquisition and corresponding manual</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:263px;">reconstruction software</td>
			<td style="width:119px;">General Electric</td>
			<td style="width:139px;">not applicable</td>
			<td>phoenix Datos| x2 acquisition and corresponding manual</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">rendering software</td>
			<td style="width:119px;">Volume Graphics</td>
			<td style="width:139px;">not applicable</td>
			<td>VGStudio Max 2.2 and corresponding manual</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">grinder (manual)</td>
			<td style="width:119px;">Struers</td>
			<td align="right" style="width:139px;">5296327</td>
			<td>Labopol 21</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">sample holder</td>
			<td style="width:119px;">Struers</td>
			<td align="right" style="width:139px;">4886102</td>
			<td>UniForce</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">grinder (automated)</td>
			<td style="width:119px;">Struers</td>
			<td align="right" style="width:139px;">6026127</td>
			<td>Tegramin 25</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:263px;">epoxy resin/hardener</td>
			<td style="width:119px;">Struers</td>
			<td style="width:139px;">40200030/40200031</td>
			<td>Epoxy fix resin / Epoxy fix hardener</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">Ethanol</td>
			<td style="width:119px;">Struers</td>
			<td align="right" style="width:139px;">950301</td>
			<td>Kleenol</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">Light Microscope</td>
			<td style="width:119px;">Zeiss</td>
			<td style="width:139px;">not applicable</td>
			<td>Axio Imager M2m&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">Electron Microscope</td>
			<td style="width:119px;">Zeiss</td>
			<td style="width:139px;">not applicable</td>
			<td>Sigma&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">CLEM software</td>
			<td style="width:119px;">Zeiss</td>
			<td style="width:139px;">not applicable</td>
			<td>Axio Vision SE64 Rel.4.9 and corresponding manual</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">CLEM sample holder</td>
			<td style="width:119px;">Zeiss</td>
			<td style="width:139px;">432335-9101-000</td>
			<td>Specimen holder CorrMic MAT Universal B</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">SEM Adapter for CLEM sample holder</td>
			<td style="width:119px;">Zeiss</td>
			<td style="width:139px;">432335-9151-000</td>
			<td>SEM Adapter for Specimen holder CorrMic MAT Universal B</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">sputter coater</td>
			<td style="width:119px;">Quorum</td>
			<td style="width:139px;">not applicable</td>
			<td>Q150TES</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">EDS detector</td>
			<td style="width:119px;">R&#246;ntec</td>
			<td style="width:139px;">not applicable</td>
			<td>X-Flash 1106</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">solder</td>
			<td style="width:119px;">Stannol</td>
			<td align="right" style="width:139px;">535251</td>
			<td>type: HS10</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">LED</td>
			<td style="width:119px;">Lumileds</td>
			<td style="width:139px;">not applicable</td>
			<td>LUXEON Rebel warm white, research sample</td>
		</tr>
	</tbody>
</table>

in depth analyses of leds by a combination of x-ray computed tomography (ct) and light microscopy (lm) correlated with scanning electron microscopy (sem)

In failure analysis, device characterization and reverse engineering of light emitting diodes (LEDs), and similar electronic components of micro-characterization, plays an important role. Commonly, different techniques like X-ray computed tomography (CT), light microscopy (LM) and scanning electron microscopy (SEM) are used separately. Similarly, the results have to be treated for each technique independently. Here a comprehensive study is shown which demonstrates the potentials leveraged by linking CT, LM and SEM. In depth characterization is performed on a white emitting LED, which can be operated throughout all characterization steps. Major advantages are: planned preparation of defined cross sections, correlation of optical properties to structural and compositional information, as well as reliable identification of different functional regions. This results from the breadth of information available from identical regions of interest (ROIs): polarization contrast, bright and dark-field LM images, as well as optical images of the LED cross section in operation. This is supplemented by SEM imaging techniques and micro-analysis using energy dispersive X-ray spectroscopy.

The characterized LED is shown in Figure 1. It is a white emitting LED with a Chip size of 1 x 1 mm2 and a partially ceramic luminescent color converter. Gluing the LED in a slightly slanted position onto a carbon fiber bar avoids CT artifacts caused by sample symmetry (Figure 2). Results of the CT measurement allow for planning the position of the cross section of the sample, and ensure electrical operability after partial abrasion (Fi...

Watch this Scientific Journal Video about In Depth Analyses of LEDs by a Combination of X-ray Computed Tomography CT and Light Microscopy LM Correlated with Scanning Electron Microscopy SEM at JoVE.co

In Depth Analyses of LEDs by a Combination of X-ray Computed Tomography CT and Light Microscopy LM Correlated with Scanning Electron Microscopy SEM

A workflow for comprehensive micro-characterization of active optical devices is outlined. It contains structural as well as functional investigations by means of CT, LM and SEM. The method is demonstrated for a white LED which can be still be operated during characterization.

In Depth Analyses of LEDs by a Combination of X-ray Computed Tomography (CT) and Light Microscopy (LM) Correlated with Scanning Electron Microscopy (SEM)

In failure analysis, device characterization and reverse engineering of light emitting diodes (LEDs), and similar electronic components of ...

The overall goal of this multimodal micro-characterization procedure is to provide a method for the location-dependent correlation of the data acquired by X-ray Computed Tomography, Light Microscopy and Scanning Electron Microscopy. This method can help answer key questions in the micro-characterization field such as failure analysis or reverse engineering of microelectronic devices. The main advantage of this technique is that optical properties of a sample may be linked to the microstructure and even to submicrometer structural details.The implications of this technique extends toward prevention of device failure because optical defects or in homogeneities can definitively and traceably be linked to structural or electrical defects of the devices. So this method can provide insight into microelectronic devices. It can also be applied to other structural analysis such as characterization of composite materials.Begin this procedure with simple preparation and CT measurement setup as described in text protocol. Select the region of interest or ROI by identifying the area not obscured by the measured object during one full rotation. In the measurement window with the live image press and hold the left mouse button and draw a red frame window.Right-click on this window's frame to open a context menu. Then select Set as Observation Window. The frame's color will change to yellow and the observation window will be fixed in the measurement window.Activate the software module Auto-scan Optimizer, through which nine images are taken before the actual scan of the sample. These are images are taken in 40-degree steps while rotating the sample. Simultaneously, activate the module Detector Shift routine.The simultaneous activation of these two modules before starting the actual CT scan ensures correction for movements of the sample and for ring artifacts. Next, scan the sample by starting the Data Acquisition routine in the acquisition software. Transfer the reconstruction data to the CT Data Analysis software and align the sample in X-Y, X-Z and Y-Z planes using the simple registration function in the software.Apply median filtering using a filter size of 3. For micro preparation embed LED in epoxy resin using transparent supports. Drill two small holes on opposite sides of the support and feed the silver wire through it.At this point it's crucial the carefully position of the sample. If the deviation from the ideal position is defined by the CT scan as too big, electrical failures may result and the protocol will have to be started from the beginning. Position the LED by means of tightening or loosening the silver wire to align the front edge of the LED and the support.Fill the ring with epoxy inside a silicon beaker pre-treated to ensure that it will not stick to the epoxy. Then, allow the epoxy to harden. Mechanically remove any excessive resin by grinding with coarse-abrasive paper.Using a stereo microscope, visually ensure that the support and LED are aligned, then fix the LED embedded in the epoxy resin in a planer fashion to a simple holder for precision grinding. Use a grinder with abrasion measurement and remove the sample surface up to 100 microns from the targeted plane's position. After polishing, observe the smooth and scratch-free surface using a stereo microscope.Clean the specimen with de-ionized water and cotton pads, then remove the water by rinsing with ethanol, and drying using a hair dryer. Melt the specimen in an appropriate sample holder for Correlative Light and Electron Microscopy, or CLEM for short. Ensure that the sample holder fixes the sample for use in LM, sputter coater and SEM.Adjust the calibration marks to the same height as sample's surface. Ensure that the polished surface is parallel to the focal plane of the LM.Next, fix the sample holder on to the motorized X-Y stage of the LM.Connect the LED to the power supply. The power supply should operate in constant current mode.Using the microscope software, calibrate the sample holder position on the X-Y stage by saving the position of calibration marks as reference points. Move the X-Y stage of the LM such that the ROI of the sample is in the field of view of the LM.Switch on the power supply and tune the LED emission. Switch off LM illumination and adjust the exposure time of the LM camera.Obtain the LM image of the light distribution within the sample. If applicable, image luminescence together with other contrasts by activating LM Illumination and LED simultaneously. Save all LM images together with the corresponding stage position as described in the user manual.Prepare for SEM analysis by sputter coating the sample and performing setup as described in the text protocol. Move the stage to show the ROI on the sample and perform SEM analysis in the same location as done for LM.Select Backscattered Electron Detector for material contrast. For this sample, choose an Electron Energy of 20 keV.Set the aperture to 30 microns and position the sample at a working distance of 8.7 mm. Select Secondary Electron Detector for microstructure surface imaging. Then change to EDS Detector for element mapping.For this sample, select an aperture of 60 microns to increase the beam current, and position the sample at a working distance of 9 mm. Representative results for the Micro-characterization of an electrically operable LED are shown here. Here is the specimen prepared for a CT scan, with chip surface of 1 squared mm.Reconstructive CT volume information enables planning of cutting planes for micro-preparation. By carefully positioning the cross section of the sample, electrical operability after partial operation is ensured. Information of the luminescence behavior is gained by optical microscopy of the electrically-driven LED.Blue emission of the semiconductor is well distinguished from red and yellow emission of the phosphors using this device. Overlay of the light microscopy images with SE Microgras through Correlated Microscopy enhances information depth. In this example, the microstructure of the two phosphors is revealed.Further information may be gained by energy Dispersive X-ray Fluorescence Spectroscopy overlays. Once mastered the fluid device characterization including all models shown can be done in 48 hours if it's performed properly. While attempting this procedure it's important to remember to check repeatedly for device operability during cross section preparation.Following this procedure, other methods like Fluorescence Microscopy can be performed in order to answer additional questions like excitation and emission behavior of the phosphors. This technique enables researchers in the field of micro-characterization to explore electro-optical devices in full function.

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