Subject: Great Raith Quesion: Any Suggestions for SEM Imaging at High EHT?
From: James Conway <jwc@snf.stanford.edu>
Date: Wed, 17 Jan 2007 11:16:49 -0800
Wed, 17 Jan 2007 11:16:49 -0800
Bing Dai wrote:

Hi James,

I tried to do exposure under 25keV, Aperture 30 tonight but the noise was so
high that I couldn't even find the latex spheres, which were very easy to
locate under lower EHTs like 10keV. I also noticed that the aperture was very
dark under emission mode/scan speed 9, although it was centered in Gun
Alignment. I also tried 25keV, aperture 20 but the gun alignment was even
worse, the center aperture nearly totally dark.

So do you have any suggestions for adjusting brightness/contrast and doing 
focus/alignment under high EHT? Thanks a lot.

Bing Dai


Greetings Bing Dai,
This is an excellent question and will share my response with the
greater RAITH community too!

The RAITH's In-Lens Ultra High Efficiency detector does not have very
good performance above 20 keV acceleration voltage! More likely you will
need to use the normal Secondary Electron detector called SE in the
detector selection panel. This is simply a scintillation phosphor disk
and a photo-multiplier tube hooked to the back of it. It has much lower
point to point resolution than the other In-lens SE detector but will
perform better at higher acceleration voltages. (20 keV and Up...)

Another issue to keep in mind is that at higher acceleration voltages
you have a greater penetration depth of the Electron beam into, and in
this case through the latex spheres and into the substrate below. This
gives information on the material (Z contrast) but at a loss of some of
the surface or topographic contrast signal in the image.

Finally note that the latex spheres are simply hydrocarbons, made mostly
of polystyrene, and as such they have relatively little electron
scattering cross section resulting in very low secondary electron yield
to the detectors and reducing the signal to noise levels in the SE
detectors.


HINT for Users:
My normal practice is to burn a long contamination shot dot then
carefully focus and stigmate on this feature. I can then burn smaller
contamination dots easily; often by reducing the SEM magnification,
which increases the field of view, assisting in out-gassing a suitable
volume of hydrocarbons from the resist to aid in contamination dot
formation.

Hoping that this information is useful to you. Maybe other Users will
wish to expand and add on this thread?

Thank you,

James Conway





Bing Dai wrote:

Hi James,

I tried to do exposure under 25keV, Aperture 30 tonight but the noise was so
high that I couldn't even find the latex spheres, which were very easy to
locate under lower EHTs like 10keV. I also noticed that the aperture was very
dark under emission mode/scan speed 9, although it was centered in Gun
Alignment. I also tried 25keV, aperture 20 but the gun alignment was even
worse, the center aperture nearly totally dark.

So do you have any suggestions for adjusting brightness/contrast and doing 
focus/alignment under high EHT? Thanks a lot.

Bing Dai

Greetings Bing Dai,
This is an excellent question and will share my response with the greater RAITH community too!

The RAITH's In-Lens Ultra High Efficiency detector does not have very good performance above 20 keV acceleration voltage! More likely you will need to use the normal Secondary Electron detector called SE in the detector selection panel.  This is simply a scintillation phosphor disk and a photo-multiplier tube hooked to the back of it. It has much lower point to point resolution than the other In-lens SE detector but will perform better at higher acceleration voltages. (20 keV and Up...)

Another issue to keep in mind is that at higher acceleration voltages you have a greater penetration depth of the Electron beam into, and in this case through the latex spheres and into the substrate below.  This gives information on the material (Z contrast) but at a loss of some of the surface or topographic contrast signal in the image.

Finally note that the latex spheres are simply hydrocarbons, made mostly of polystyrene, and as such they have relatively little electron scattering cross section resulting in very low secondary electron yield to the detectors and reducing the signal to noise levels in the SE detectors.


HINT for Users:
My normal practice is to burn a long contamination
shot dot then carefully focus and stigmate on this feature.  I can then burn smaller contamination dots easily; often by reducing the SEM magnification, which increases the field of view, assisting in out-gassing a suitable volume of hydrocarbons from the resist to aid in contamination dot formation.

Hoping that this information is useful to you.
Maybe other Users will wish to expand and add on this thread?

Thank you,

James Conway