XRD Procedure 2016
- Byron Aguilar
XRD Procedure 2016
Written by NTS from training and notes, March 2016. H/T to VDD, RS, ESW, KMM, SDS.
For Philips XRD, no longer in use.
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 and shutter is closed
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
GaSb [0 0 4]
2theta = 60.7142; omega = 30.3571
Si [ 1 1 1]
2theta = 28.4410; omega = 14.2205
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 vice versa. 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].
Crystal Planes
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 prep 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
To setup alignment for RSM:
Run Omega and 2Theta coarse alignment and fine alignment
Run Psi coarse alignment (is usually a broad peak)
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.
It’s really more inputting to a GUI and saving and stacking steps (like PECVD)
Measure > Run Program
Start scan and make sure it starts with no errors
Remember LabAccess time limit
Switching from XRR
The XRD switchover from XRR oftentimes results in problems. Open software if closed (user/user). Connect 3rd thing – Rocking Curve [what?]. Click Yes to Offsets question [wrong?]. User Options > Options > Change to Rocking Curve (offsets 2t =11, O =1.75) [should be about 2.5 and 1.8 when aligned]. Double check black cable is in XRD detector, not analyzer crystal.
Incident Beam Optics
Check Slits (1/4 degree, 1 mm) and that software has correct slits.
Beam attenuator Ni 0.125 mm auto (important to avoid detector damage). Select 147.54.
Usage at pre-set intensity, Activate 500k (or 600k?). Deactivate 400k (or 200k?).
[What are radius and take off angle?]
Proceed as normal from Load and Prep, and if there are issues you may have to do 2theta and Z scans, omega and 2theta scans iteration, then restart from 2theta and Z scans.