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Hsinchu
2nd March 2009 - 02:32 PM
Hello everyone,
I have a question concerning to Ebeam writing technique. The dose is calculated based on some parameters, among them there is "current" (of electron beam). In some papers, I see that the current is determined as current at position of PCD blanker, in some others it is determined as the current at Faraday Cup - at the sample holder. I found that, in SEM, these two current are very different in value, thus, the doses calculated by these two currents will be very different.
Can anyone tell me which current is correct for calculation of dose?
Thank you very much
Hsinchu
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1st April 2009 - 12:37 PM
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guiding_light
1st May 2009 - 04:32 PM
QUOTE (Hsinchu+Mar 2 2009, 02:32 PM)
Hello everyone,
I have a question concerning to Ebeam writing technique. The dose is calculated based on some parameters, among them there is "current" (of electron beam). In some papers, I see that the current is determined as current at position of PCD blanker, in some others it is determined as the current at Faraday Cup - at the sample holder. I found that, in SEM, these two current are very different in value, thus, the doses calculated by these two currents will be very different.
Can anyone tell me which current is correct for calculation of dose?
Thank you very much
Hsinchu

We recently encountered a similar dose uncertainty problem, it is based on how many electrons fail to be collected but are emitted or scattered out instead. This would be from materials differences.
nanomvp
1st May 2009 - 05:00 PM
Yeah especially if it's for a SEM we are supposed to expect secondary electrons to come shooting up from a bombarded surface. So I wonder if we can't just measure power consumed at the electron gun.
guiding_light
1st May 2009 - 05:09 PM
QUOTE (nanomvp+May 1 2009, 05:00 PM)
Yeah especially if it's for a SEM we are supposed to expect secondary electrons to come shooting up from a bombarded surface. So I wonder if we can't just measure power consumed at the electron gun.

That is the total emission current, but usually the blanking aperture cuts off most of it to allow the beam to be focused to smaller spot.
guiding_light
1st May 2009 - 06:16 PM
Besides secondaries, the backscattering electrons are more dangerous since they can escape through the beam entry point.
nanomvp
3rd May 2009 - 05:45 PM
How about X-rays from the electron beam striking the target? The X-rays then go on to release electrons elsewhere, changing the charge balance.
guiding_light
4th May 2009 - 11:53 AM
QUOTE (nanomvp+May 3 2009, 05:45 PM)
How about X-rays from the electron beam striking the target? The X-rays then go on to release electrons elsewhere, changing the charge balance.

Once again, a beautiful opportunity for a thought experiment.

Let's consider that only one primary electron is incident on the Faraday cup. On the first strike, it produces many secondary electrons and is itself backscattered. It could be backscattered several more times before finally getting stuck in the wall. But all the secondary electrons are collected back as well. We should register just one count for the incident electron, but how many do we get in all the commotion and in how much time?
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