CeNSE/IISc Rigaku 2017 GaN-AlxGa(1-x)N-AlN-Si (0002)s CeNSE/IISc Rigaku 2017 XRDAnalyze: GaN on Si 25 mm diameter half wafer. The image below shows AXIS-TAS25 mounted and positioned around 0o 2θ. The diffractometer axis to detector surface distance at its center was about 206 mm, the diffractometer radius.
Image below is the incident beam with sample surface positioned at z=0 mm, 2ϴ=ω=ϴ=χ=φ=0o. There is some slit edge scattering signal clearly observable at the edges of the beam.
Beam geometry and optics used for the (0002)s reflection rocking curve analysis are Specimen surface to incidence beam orientation is illustrated below for the “reflection” geometry utilized. The beam illumination or irradiated sampling area on the specimen is visualized in the next image.
The diffractometer axis and rocking axis were aligned parallel to . In this case the GaN. Note that the inordinate axis is also 2ϴ on the 2D detector surface. At the diffractometer radius of roughly 206mm the 25mm diameter detector window covers nearly 7o 2ϴ. Each 27.5µm pixel subtends an angle of 0.00765o (133µRad) at the diffractometer axis.
shown above. Dimensions b & d in the image, both equatorial beam widths, are equal in this case of symmetric reflection, θ=ω. The 2D detector is placed at position #1, orthogonal to the diffracted (exit) beam direction. At an average θ of roughly 17.75o the average magnification factor on the sample surface, b/Sinϴ, is 3.28X. Therefore, the effective equatorial Pixel size on the sample surface would be around 90µm while the axial Pixel size would remain 27.5µm. These values may be additionally corrected for the “system divergence
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CeNSE/IISc Rigaku 2017 GaN-AlxGa(1-x)N-AlN-Si (0002)s factor” through experimental observations at this diffractometer radius of 206 mm.
Image shows CeNSE, IISc, Rigaku Main Beam 2015 at the SDD of 206mm. For a 2D X-ray incident beam, intensity is a function of the Cartesian co-ordinates on the detector screen (x-Pixel, y-Pixel), an invariant for each pixel. The diffracted intensity or the observed relative intensity, Id, is a convolution of Io, incident beam, with a modulation function Iµ corresponding to the Nano structure (or micro structure) in the VOXEL being examined on the sample surface.
define Io as a function of x-Pixel and y-Pixel then we will be able to compute and observe the diffracted intensity for each Pixel as a function of the variable used in reciprocal space measurement. Meaning the “scan type”. E.g. in this case of ω-2θ (same as θ-2θ), the variable would be ω or
θ. The green ROI shown in the image below is roughly 19 mm long by 1 degree wide equatorially. These ROI (region of interest) dimensions are typical for slit sizes used in traditional X-ray diffractometery to integrate data with a scintillation counter or 0D detector.
Id = Io * Iµ IOBSERVED = IDIFFRACTED = f(x,y,2θ,ω,φ,χ)
Io= f(x,y), Invariant for each spatial pixel. Image following depicts a Rigaku SmartLab with a rotating anode X-ray generator exploiting high dynamic range imaging techniques through multiple frame integration. The faint duplicate image towards the bottom is clearly visible and may be attributed to another remnant frequency after the “beam conditioner”. This image shows the importance of recording the Io, incident beam, individually for each experiment. Note that once we
Literature survey via Google produced several XRD profiles for similar materials. Manufactured structure typical for GaN film on Si substrate with multiple (AlGaN/AlN) buffer layers is shown in the following image. There were at least two data sets
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CeNSE/IISc Rigaku 2017 GaN-AlxGa(1-x)N-AlN-Si (0002)s that were the best fit with our XRD observations. The extreme left peak was indexed as GaN (0002)s while the extreme right peak was indexed as that from AlN.
This literature data compares exceptionally well with our observations. Our data was normalized with respect to the AlN relative intensity and then superimposed. The diminishing intensity of the GaN (0002)s reflection relative intensity is indicative of reduced film thickness. XRD system calibration is required for quantitative direct layer thickness measurements.
A second literature data set shows as good a match with our observed XRD data. Further confirmation of correct indexing of our pattern as (0002)s. The peak at the far left is that from GaN. The Bragg peak at the far right is from AlN. The analyses displayed clearly indicate a significant spatial variations in the GaN film’s (0002)s relative intensity for this specimen.
Illustrated below is the automatically computed ROI (green) from the subject data set. This includes every Pixel on the 816x816 image frame with above “threshold” or “dark image” (detector image with shutter closed) information in each pixel. It is roughly at least 19mm long by 1o wide equatorially.
Next image shows the RCP (rocking curve profile) using a signal integrating area of 816x816 (22mm x 22mm) yielding a 0D conventional diffractogram representing the entire detector plane as one data point without spatial resolution. This would be the integrated conventional approach to XRD profile data acquisition using a “line” or “point” source and a conventional 0D point or scintillation detector. Note, this method takes 10 times longer and is completely insensitive to the local specimen Nano structure due to the large sampling area
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CeNSE/IISc Rigaku 2017 GaN-AlxGa(1-x)N-AlN-Si (0002)s Now let’s consider the Bragg profiles for a much smaller ROI like 3x3 Pixels showing high signal sensitivity for local Nano structure in the smaller voxel on the sample surface.
integration involved. The following image is the 0D equivalent Bragg profile for the automatically computed “green” ROI of 671x167 Pixels. These two OD profiles are the “gross” rocking curves for the entire sample surface without any “receiving slit”. Both these profiles are clearly insensitive to local Nano structural changes.
The 3x3 ROI is equivalent to 82.5x82.5 µm2 on the detector surface and 270.6x82.5 µm2 on sample surface for this geometry. Using an average magnification factor of 3.28X (equatorial) for the (0002)s reflection geometry. Next, we illustrate a ROI 360x18 Pixels, 10x0.5 mm2 for XRD data integration. The 0.5 mm equatorial width translates to about 0.14o.
Significant changes in the RCPs were observed as the ROI was moved equatorially from the center of the reflection towards either of the extremities (up/down). There are many other differences in the RCPs that are worth noting. These are on the left, lower angle (larger
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CeNSE/IISc Rigaku 2017 GaN-AlxGa(1-x)N-AlN-Si (0002)s reciprocal space dimension), side of the RCP. There are distinct changes in the base line (left “shoulder/tail” area compared with the right) at various locations on the 2D topographic image. These Bragg profile perturbations are worth investigating further in terms of their correlation with local sample surface voxel’s Nano structure. Deconvoluting layer influence alone may be accomplished by translating the sample surface into the pixel or ROI chosen. The incident beam is known to have a spatial dependence for relative intensity. Io, may be measured as a function of detector pixel (x,y). By using the exact same pixel or ROI (to integrate), the effect of spatial variation in relative intensity of the incident beam may be experimentally deconvoluted from the RCP.
FWHM Map:
Integrated Intensity Map:
Based on these reciprocal space image dimensions for the (0002)s reflection the effective sampling area on the specimen surface was estimated at least 19mmX15mm (ROI) which covers nearly the entire half wafers.
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CeNSE/IISc Rigaku 2017 GaN-AlxGa(1-x)N-AlN-Si (0002)s steps of 100 pixels (2.75 mm equivalent displacement axially on the sample surface).
Appendix: Individual Layer Thickness Characterization RCPs along horizontal and vertical cursor lines are illustrated below on the Bragg micrograph:
It is possible to measure relative thickness of individual layers by RECORDING the rocking curve for the same pixel or group of pixels (ROI) while translating various sample surface locations through the fixed pixel or group of pixels (ROI). This will be slow but will not require normalizing the spatial relative intensity data since the incident beam is INVARIANT FOR ANY PIXEL OR ROI. The “incident beam” and the detector are both fixed (invariant) spatially.
A 10x3 ROI (0.275x0.27mm2 on the sample surface) was selected and placed at (200:190). This ROI was incrementally moved along the inordinate axis, along the equatorial plane, 5 pixels (0.1375mm) at a time on the detector plane image, equivalent to a displacement of 0.451 mm on specimen surface. This ROI was then moved axially from 200 through 800 in
The only assumptions needed are that the sample surface is flat and the translation is occurring parallel to the sample surface. These are fairly reasonable general assumptions with electronic materials such as wafers and the special specimen manipulators on most modern diffractometers. The following are analyses of RCPs 10x3 ROI for statistics. The objective was to develop numerical criteria to detect the onset of thin film signal, “wafer/film edge”. SD= Standard Deviation for the last 50 data points on the RCP, MAX = Maximum data value on RCP, and SNR = MAX/SD. The ordinate axes in all the following charts are in mm displacement on the sample surface.
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This picture depicts the sample surface image corrected with a 3.28X equatorial magnification.
The yellow is sample wafer outline. The "blue" is incident beam image at sample surface, 19mm x 15mm. "Green" is Relative intensity ratio of GaN to AlN peak for the ROI (10x3) marched down the center radius of the "half wafer" sample with 5-pixel steps. Purple is effective sample surface coverage by incident beam. The ROI was stepped 10 pixels axially across the topograph, along ordinate asis.
Most likely full contour of the incident beam for this observation is shown above. 775x173 pixel2 21.53mm X 4.80mm is the estimated full dimension. The sample surface incident beam equatorial magnification is depicted as a function of incidence angle in the image below.
The following image is what a potential relative thickness profile plot for our GaN sample would look like mapped on the wafer surface. To avoid the challenge of “beam foot print” image and its use to normalize spatial RCP data, we could just position each sample surface voxel at the same beam position and detector pixel by translating the sample surface. Since the incidence beam is INVARIENT we ought to be able to detect relative layer thickness precisely by this method. Using integrated intensity values would be recommended to quantify diffracting volumes and hence layer thicknesses.
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CeNSE/IISc Rigaku 2017 GaN-AlxGa(1-x)N-AlN-Si (0002)s
Incident beam image for a Bruker D8 in full dynamic range as well as in real-time both in grey scale and pseudo color are displayed above. The detector surface was positioned orthogonal to the incident beam direction. To understand the image of the incident beam on the sample surface a series of images need to be recorded at various incidence angles around the Bragg angle used. In this case, that would be between 17o to 18o angles of incedence. Example following is for a Bruker D8 HRXRD system.
Incident beam at 17o to the detector plane simulating incident beam foot print on the sample surface at the Bragg angle (17o-18o). This image consists of both the saturated version and the HDRI (high dynamic range image) using multiple images to integrate. The equatorial magnification at these angles ranges between 3.23X to 3.42X (323% to 342%). Shown below is visualization of the half wafer specimen, incident beam contour on specimen surface and wafer diameter edge tipped w.r.t. incident beam edge.
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CeNSE/IISc Rigaku 2017 GaN-AlxGa(1-x)N-AlN-Si (0002)s
Most likely relation between, incident beam, half wafer specimen, irradiated area, FWHM, PS, II images are visualized in the following images. Note that the detector images were magnified 3.28X equatorially. No adjustments were made in the axial direction. The better method to accomplish this is by making the detector plane parallel to the specimen surface for the rocking curve measurements. This will create a 1-to1 spatial relation between sample surface voxel and detector surface pixel. Ideally, the detector surface should be rocked synchronously with the specimen surface always maintaining them parallel to each other. Shown are relative Bragg FWHM, Peak Position and Integrated Intensity spatial maps. Only the most intense peak for each pixel RCP was considered for these maps. Individual layer information is available in each RCP. Ideally, one would have to simulate the RCP numerically and then compare with observed RCPs to extract thickness information for individual layer.
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CeNSE/IISc Rigaku 2017 GaN-AlxGa(1-x)N-AlN-Si (0002)s Using Onsight’s XRDAnalyze Software: Start the XRDAnalyze program by double clicking the short-cut icon. Once the window opens, and the logo display terminates, then the program is ready to go. Open the window out to a convenient size to be able to see all the data. You will need to select the video data file to Open. Do so by clicking the “File” icon on the top left of the AXIS window. Select the desired Folder and File to open then double click. If it is the first time the video data is being opened, then wait a while for the auto analysis to conclude. If the file has been opened earlier, then the first window to display would be the ZERO-D summary of the video data file. The operator may then double click any data point on the 0D rocking curve to display the topograph for that relative Bragg condition. The choice of pseudo color or grey scale is also available for the 2D image display along the rocking curve near the Bragg condition.
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transistor structures on 200-mm silicon (111) substrates employing different buffer layer configurations. Sci. Rep. 6, 37588; doi: 10.1038/srep37588 (2016). Gay, Hirsch, and Kelly [P. Gay, P.B. Hirsch, and A. Kelly, Acta Met. 1 (1953) 315] Hordon and Averbach [M.J. Hordon and B.L. Averbach, Acta Met. 9 (1961) John E. Ayers, Tedi Kujofsa, Paul Rago, and Johanna Raphael, Heteroepitaxy of Semiconductors: Theory, Growth, and Characterization, Second Edition, CRC Press, Boca Raton, FL, 2016. Characterization of SiGe thin films using a laboratory X-ray instrument, Tatjana Ulyanenkova,a,* Maksym Myronov,b Andrei Benediktovitch,c Alexander Mikhalychev,c John Halpin,b and Alex Ulyanenkova - J Appl Crystallogr. 2013 Aug 1; 46(Pt 4): 898–902. https://www.ncbi.nlm.nih.gov/pmc/arti cles/PMC3769059/
References: 1. Watch YouTube Video: https://www.youtube.com/watch?v=4l5qiOcjj8&list=FL7u3nABX4YMdHDugoPsYcA&index=2 2. https://www.nature.com/articles/srep3 7588?WT.feed_name=subjects_materia ls-science Investigation of AlGaN/GaN high electron mobility transistor structures on 200-mm silicon (111) substrates employing different buffer layer configurations - H.-P. Lee, J. Perozek, L. D. Rosario & C. Bayram Lee, H.-P. et al. Investigation of AlGaN/GaN high electron mobility
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