XRD Procedure

Written for NTS by NTS from training and notes, 2016. H/T to VDD, RS, ESW, KMM, SDS.

Load and Prep

• Log in on LabAccess

• Clean Workspace

• Put on gloves

• Check Slits (1/4 degree, 1 mm) and that software has correct slits

• Check attenuator is set properly

• Generator On, Apply (45 kV, 40 mA)

• Mount sample on carrier using low stick tape

  • Use plastic tweezers if able

  • Tape is on bench or in XRD or in PL lab

  • Make sample as long as possible (left to right, with wafer flat on right)

  • Put tape on as little as possible of sample

  • Put on two opposite sides to leave beam window

  • Cover as little as sample as possible

• Mount carrier on stage

  • Place backing wafer on stage so that a flat is to the right and perpendicular to the beam

  • It is a MEMS stage, be gentle

  • Tape backing wafer on two sides

• Set Psi to 0 (for first sample only, leave psi at ~0 til done)

• Check sample offsets are 0 except 2theta and omega

  • User offsets are 2t ~= 2.5293, O ~= 1.8473

  • Do NOT click Set = 0 button

• Run 2theta coarse scan to find direct beam peak

  • Measure > Manual Scan > 2theta (continuous)

  • 2theta coarse scan (2, 0.01, 0.1, 0:25)

  • Range is specified around your center point, not by endpoints (range = 2 is +/- 1)

  • Scan runs and opens a plot

• Right click > Peak Mode > Move To (or Move Mode > go to manually)

  • Should auto-find Peak, or can go to Move mode and manually move light line

• Set Z position to expected value to move sample into beam

  • ~9 mm - substrate thickness = Z for new substrates

  • 8.4 mm for 625 um SI GaAs

• Run Z coarse scan (2, 0.01, 0.1)

  • Scan displays, change Y axis to linear and you should see a linear falloff

  • To change Y axis scale, right click on Y Axis > Axes > check Linear or Log

  • Then right click cursor > Move mode

• Click and hold cursor, observe peak counts, then move to half-peak value and release

  • (Go to Move mode, observe peak, and move light line to where counts get cut in half)

  • Stage will move here, positioning the instrument

  • Record higher counts in logbook, should be 6.5-7.5 M

  • If Z scan isn’t good, do an Omega scan to improve position and run a Z scan again

• Z scan should be OK without redoing at all for other samples

• Now your scans are setup

• Instrument Settings (for GaAs):

  • Select GaAs 001 unit cell

  • Set h k l : 0 0 4

  • Hit tab, press OK, moves instrument

Align Each Sample

• Run Omega coarse scan (2, 0.01, 0.1)

  • Switch axis back to log

  • Go to Peak with Peak or Move mode

  • Right click > Peak Mode > Move To (or move manually)

• Run 2theta coarse scan, Move To Peak (MTP)

• Run Omega fine scan (0.2, 0.001, 0.1), MTP

  • If scan has two peaks, higher peak is substrate, align to that

• Run Psi coarse scan, MTP

  • A broad dual peak isn’t necessarily bad – go to peak, or ignore, or redo omega

• Can run a Phi scan if worried about flat alignment

  • Will get gentle slope, can move to higher intensity

  • If you do this, do omega and 2theta coarse scans again after

• Run Omega fine scan, MTP

  • If line is on peak, good to continue

  • If not, run psi scan (recommended for when omega is off)

• If you want to double check, run 2theta fine and omega fine again

  • Wants peaks to be aligned when switching between 2theta and omega scans

  • Iterate 2theta and omega (and psi) as needed

• When peaks are hit by cursor, we’re good to continue

  • Fine 2theta isn’t really needed because 2theta peak is pretty wide like Ո

  • Always finish alignment with an omega fine scan

• Important: Set user offsets to GaAs: User Settings > Sample Offsets

  • Enter correct 2theta and omega values, click OK

  • GaAs: 2theta = 66.0479, omega = 33.0239

  • Substrate Angles:

    • GaAs [0 0 4]

      • 2theta = 66.0479; omega = 33.0239

    • InP [0 0 4]

      • 2theta = 63.3382; omega = 31.6691

    • InP [2 2 4]

      • 2theta = 80.0328; omega = 4.752

Run and Save

• Run omega-2theta fine scan (R, 0.001, 0.1, M minutes)

  • Choose parameters: Range R, Step size, Time per step

  • Pick range as needed, 2 is standard for AlAs/GaAs, larger needed for smaller layers

  • Range can vary based on needs of sample

• File > Save as…

  • Save in your folder with proper file name

• Close shutter (click button)

• Swap Samples

• Repeat from Align Each Sample for additional samples

End Use

• Close shutter

• Set stage numbers to 0 (psi to 90)

• Uncheck X-ray generator

• Do NOT close software

• Open all data

• Convert all data to x00 and csv, and Save all as converted files

• Copy converted files to flash drive

• Remove sample

• Cleanup work space

• Log out of LabAccess

Setup Notes

• Source: ¼ degree slit

• Detector: 1 mm slit

• Use XRD detector; There are two, one is normal, one is analyzer crystal for RSM

• Settings Window > Diffracted beam optics

  • Rocking Curves for XRD

  • Diffracted beam path 2

• Settings Window > Incident beam optics

  • Monochromator selected (Fixed hybrid monochrom, Optics 1 or 2)

  • Beam attenuator factor ~147.5

  • Activate level = 600k

  • Deactivate level = 200k

  • Divergence slit set to correct value, either ¼ or ½

• Sample size and shape not critical as long as XRD hits it

  • Sample must be big enough

  • Sample must be centered

  • XRD beam is 1 cm line

Misc Notes

• XRD Theory

  • XRD measures periodicity, directly related to lattice constant

Lattice matched will have substrate and layer peak overlap Fringes measure periodicity and thickness Thicker layers have more closely spaced fringes and v.v. Substrate is so thick we can’t resolve fringes Fringes we see are layer/s

• Scans

Omega-2Theta is normal scan with fringes Rocking curve is 2Theta scan for one Omega manually controlled. Can do for multiple Omega to make a 3D mapping Sometimes a Z scan will be needed to adjust Z a little

• Slits

There are apertures e.g. ½ degree and ¼ degree that block beam to give a known output spatial range ½ degree gives higher signal, lower resolution ¼ degree gives lower signal, higher resolution

• Samples

Stage can handle ¼ 3” pieces but not ¼ 2” pieces [This seems wrong] Put ¼ 2” pieces on a backing wafer [or OK]

• Why is h k l : 0 0 4 ?

  • In zincblende crystal for (001) growth, the next atomic plane is a/4 away (above)

  • So a scan in {001} direction is a (004) scan; (00 ¼) in real space

  • We care about the distance between planes

  • When doing rare-earth measurements (rock salt on zincblende crystal), use h k l : 0 0 2; this should give 2theta = 31.6255, omega = 15.8128

Reciprocal Space Map

To run a Reciprocal Space Map (RSM) Click Tools > Reciprocal Space Map Check that 004 point has correct Omega and 2Theta values Click on 224 Point and write down Omega and 2Theta values

Run Omega and 2Theta coarse alignment and fine alignment Then run Psi coarse alignment (is usually a broad peak) Then run Psi coarse Run another Omega to check location Go to sample offsets and put in supposed numbers

To run RSM: You need to have a program written Rodolfo wrote his own Measure > Run Program It’s really more inputting to a GUI and saving and stacking steps (like PECVD) Start scan and make sure it starts with no errors Remember LabAccess time limit

Switching from XRR

XRD was just switched over from XRR which oftentimes results in problems Software was closed (user/user) Check Slits (1/4 degree, 1 mm) and that software has correct slits Connect 3rd thing – Rocking Curve Click Yes to Offsets question User Options > Options > Change to Rocking Curve (offsets 2t =11, O =1.75) Double check black cable is in XRD detector, not analyzer crystal Incident Beam Optics Set divergence slit to ¼ degree Beam attenuator Ni 0.125 mm auto (important to avoid detector damage) Click Select, Select 147.54 Usage at pre-set intensity Activate 500k (or 600k?), deactivate 400k (or 200k?) [What are radius and take off angle?] Turn on Generator and try to proceed Set offsets to 0 2theta coarse scan, Move to Peak (offsets 2t =-2.4385, O =1.2193) Z coarse and wide scan Z position was off (Z = 6.563 mm) Set crystal lattice to GaAs (001), hkl = 0 0 4 Omega coarse scan is messed up for range =2 and range =5 Seek help Iterate some coarse 2theta and omega scans Improves counts to low 100k’s Do more and it is weird [Remove crystal lattice?] Z scan coarse and wide, very low counts and midway position is at 8.249 mm User offsets keep changing (2t =2.942, O =1.8516) 2theta coarse scan, Peak Mode > Move To Z scan coarse and wide again, get proper counts Set crystal lattice to GaAs Omega coarse and wide, crappy, peak ~100, Move To Peak (MTP) 2theta coarse and wide, similar, MTP Psi coarse and wide, similar Z coarse and wide, similar Omega coarse and wide, similar I’m lost, seek more help Set all offsets and positions to 0 2theta coarse again, crap again 2theta coarse again, MTP Z coarse, get proper counts, go to halfway Set crystal lattice to GaAs 2theta coarse and wide, MTP Omega coarse and wide, MTP Iterate between 2theta and omega, decrease range each time (3 more pairs, for 4 total pairs) Run Psi coarse, MTP Run omega fine, MTP Set user offsets to GaAs Run omega-2theta fine scan (2, 0.001, 0.1, 3:25) Goes fine File > Save as… [save in your folder with proper file name] Close shutter Swap Samples