Hello Everyone,
I am depositing CIS thin film using the thermal co-evaporation method. To study the composition, I use Hitachi S-4800 SEM/EDS instrument. Due to some limitations, I deposited only ~ 80 nm (instead of 1.6 micrometer) of CuInSe on a Si wafer.
I am wondering what is the suitable voltage/conditions for this kind of sample to get good EDS results.
BTW, the substrate is not rotating.
If someone tried that before, please let me know.
Thank you in advance.
You should not go below 5-6 kV for proper excitation of L-lines of your elements of interest. If you do not have access to special (optional) "thin film analysis" software no satisfactory quantification is possible. And, as was already said, increase time and beam intensity.
Dear Kuok Kuok Sum Cheong and Vladimir Vladimir Dusevich
Thank you for your replies, I agree with you about the time and yes, I increased the time for more counts but of course, there is also a limit for this factor.
For me, time is a critical factor, as I need to map a 4"x4" sample using 100 locations (a matrix of 10x10 measurements). The appropriate time, for 10 kv to get ~ 10000 counts, is around 120 seconds.
Setting the voltage to 5 kv is suitable for the excitation of L-lines, but this will need at least 240 seconds.
I also monitor the dead time and always keep it below 20%.
Unfortunately, I dont have access to any special software, I just use the software attached to the instrument.
Thank you,
You can try to increase the energy count by increasing the Condenser Lens current by changing value for Condenser Lens 1 and 2 setting on Hitachi machines. You will notice a smoother image or less grainy image is achieved when the lens current is increased. However, a balance need to be strike as increasing CL current would reduce the resolution (but the effect should be small in FE-SEM which is what you are using). However, higher lens current would also means it is easier to cause damage to your sample.
Unfortunately, I have to agree with you. It is precision VS time. For EDS this is always the case.
I have checked on the depth of penetration of your sample using the simulation software I have indicated in the previous post (using the CuInSe layer and Si substrate you have indicated in your post). I would still recommend to use 5keV due to the depth of penetration. The reason is that EDS is semiquantitative method, and the results for total element present is always equals to 100%. While using 5keV, the depth of penetration of the electron beam is about 250nm. There is higher percentage for ratio for Cu, In and Se element in ratio to Silicon. This will also contribute to a better precision and accuracy.
At 10keV, the depth of penetration of the electron beam is about 1 micrometer (1000nm). While your sample is only 80nm thick. Because of this, high % of the results would be Si element. Chances are, total value of Cu, In and Se elements detected is only below 10%. Because of the small value, changes in 0.1% would affect your results tremendously.
Hope this helps.
Dear Kuok Sum Cheong , EDS is a quantitative method when used properly. Results are summarized to 100% only if box "Normalize" is checked in EDS software interface.
That’s when one uses actual standards for calibration. Standards are usually expensive and to obtain one with B to U will cost about 5000 USD.
Otherwise when using standardless analusis, it will be normalized to 100%. Most people used the standardless analysis where calculation is made based on the peak ratios or ZAF corrections.
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