More Results on Wax layers, and how easily they are removed!
To recap, I previously applied layers of Collinite using a damp microfibre cloth to clean silicon wafers and allowed to haze dry before buffing with a clean microfibre cloth.
The wax thickness was estimated from accurate measurements of the refectance over a broad wavelength range (400 to 1100 nm)..
(The refractive index of the dried wax layer was previously estimated by fitting ellipsometry results.)
The rig used ensures that the silicon wafers are replaced in the same position so that subsequent measurements are from the same place on the wafer.
A previous post shows how the thickness varies over the 6 inch wafer surface.
For information, If I repeat the measurement without moving the wafer, then the stability of the equipment is such that I will get the same thickness (+- 0.1 nm) over and over again.
If I remove the wafer from the rig and then replace it, I can get the same thickness again with a variation of no more than +-0.2 nm.
The results shown in these posts are therefore due to real changes in the wax thicknesses.
Well, the idea today was to add a third layer of wax (Collinite no 915) to four silicon wafers that had previously been coated with 2 wax layers (see previous posts).
Before doing this I thought it would be a good idea to remeasure the wafers to see if 24 hours ageing had made any difference to the existing layers.
Here are the results along with yesterday`s results:-
Wafer 1:
Thickness after first application: 22.7 nm
Thickness after 2nd application: 18.8 nm
Remeasured 24 hours later: thickness = 15.3 nm
Wafer 2:
Thickness after first application: 20.6 nm
Thickness after 2nd application: 23.8 nm
Remeasured 24 hours later: thickness = 22.5 nm
Wafer 3:
Thickness after first application: 15.9 nm
Thickness after 2nd application: 25.0 nm
Remeasured 24 hours later: thickness = 24.9 nm
Wafer 4:
Thickness after first application: 16.9 nm
Thickness after 2nd application: 27.8 nm
Remeasured 24 hours later: thickness = 26.7 nm
So - a slightly larger variation from wafer 1, but overall around 4% loss.
Now I applied a third layer with the damp microfibre, waited 10 minutes and buffed with a clean, dry microfibre cloth.
To make it easier to compare, I show the results above once more, along with the new thicknesses.
Wafer 1:
Thickness after first application: 22.7 nm
Thickness after 2nd application: 18.8 nm
Remeasured 24 hours later: thickness = 15.3 nm
Thickness after 3rd application: 22.1 nm
Wafer 2:
Thickness after first application: 20.6 nm
Thickness after 2nd application: 23.8 nm
Remeasured 24 hours later: thickness = 22.5 nm
Thickness after 3rd application: 17.0 nm
Wafer 3:
Thickness after first application: 15.9 nm
Thickness after 2nd application: 25.0 nm
Remeasured 24 hours later: thickness = 24.9 nm
Thickness after 3rd application: 20.1 nm
Wafer 4:
Thickness after first application: 16.9 nm
Thickness after 2nd application: 27.8 nm
Remeasured 24 hours later: thickness = 26.7 nm
Thickness after 3rd application: 21.5 nm
The results were a bit surprising; wafer1 gained, but the other three lost thickness!
I think you detailers will like the next bit!
Today I`m sure that I wasn`t quite as constant with the buffing effort that I applied to the wafers as I had been on the previous two days
and it does seem (for this product anyway) that the final thickness depends crucially on how much pressure is applied in buffing.
To test this I tried re-buffing around the measurement area with clean parts of a dry microfibre cloth.
This time I tried to be consistent with the number of rubs and the pressure applied each time (as far as is possible manually)
The realy interesting thing is that each time I rubbed the area, I removed product - down to a fairly stable minimum of around 6 nm!
A typical result (I did this on several diffeent areas) was :-
Initial wax thickness = 20.1 nm
Light re-buff, remaining wax thickness = 14.9 nm
Light re-buff, remaining wax thickness = 7.3 nm
Light re-buff, remaining wax thickness = 5.8 nm
Light re-buff, remaining wax thickness = 5.8 nm
Light re-buff, remaining wax thickness = 5.6 nm. Looking at the clock, it`s getting near to 6:30 pm so -
Heavy re-buff, remaining wax thickness = 5.6 nm!
OK, having seen this interesting result, I thought I may as well look at the effect of wiping over with a solvent laden cloth.Again this might be of interest to people here.
Note that I am using pure, reagent grade, solvents, uncontaminated by impurities, oils etc.
1)Initial wax thickness:- 18.0 nm
Wipe with ethanol, remaining thickness = 4.5 nm
Re-wipe with ethanol, remaining thickness = 4.0 nm
2)Initial thickness:- 24.2 nm
Wipe with iso-propanol, remaining thickness = 7.2 nm
This solvent left a distinct haze over the wiped area, so I stopped here.
3) Initial thickness:- 22.2 nm
Wipe with acetone, remaining thickness = 0.0 nm !
Note, acetone is a constituent of nail varnich remover, but that product also contains oils etc
That`s all for today - some controversial (I`m sure) statements based on this series of measurements tomorrow!
Great stuff.
TBH, I`m not thrilled with how it looks on those platics either, but eh...OK, good enough since they`re >20YO Dailies.