Ellipsometer (Woollam) - Measuring thin metals with oxide pre-measurement

How to measure thin ≤50nm metal dep. rates using ellipsometry, with "reflectivity enhancement" on a Silicon wafer with SiO2 coating. Also useful for Witness samples (ie. inserted for deposition along with production wafers)

Deposition rate test w/ TOX Witness samples	For thin metals - eg. ≤50nm (exact limit is different for various metals, based on optical absorption)
Wafers for rate cal:	Silicon with ~500nm-1000nm Thermal Oxide (TOX).  Cleave into quarters (2" wafers or thin ~300µm wafers preferred for easy cleaving).
Ellipsometer: pre-measure before dep	Normal "Cauchy on Silicon" recipe Fit only 300nm+
	Once fit is very good, [Save Snapshot] and save file into your directory (top-right of window)
Metal Deposition: Any technique
(optional) Include above TOX Witness piece with sample
Target ~5-30nm of dep	If very short (eg. 30sec), make sure uniformity will be ok (eg. AJA substrate rotation is at Max)
Ellipsometer: measure after dep
Measure with "Standard" setting [√] SAVE DATA	You can also save data *after* the scan with Data (top-left of screen) > [Save] Later, we will load this NEW (post-dep) data into the pre-dep Snapshot
Open Snapshot from pre-measurement
Turn off ALL fitting params in Cauchy (thickness, A/B/C) Turn off Angle fit and set Angle = 0
Turn off "Fit Options" > "Thickness pre-fit" (I think it's in Model params)
Load *new* data with Data (top-left of screen) > [Open]	Will still show model + fit from pre-meas.
Select wavelengths 300nm+
Add Layer Basic > B-SPLINE on top of layer stack	Best fit wih BSPLINE model on top of Cauchy,
B-Spline params: - Starting mat = Au - Thickness = 15nm Only fitting Thickness on this layer	Pre meausred undep'd TOX and then added bspline (with Au starting mat) on top.
Click Model > [FIT]	Can do [Generate] first to see how close it is.
[Save Snapshot] when have good fit
Record Thickness of B-SPLINE, nm

Demis D. John, 2022-10-27 - based on J.A.Woollam instructions.