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I have been acquiring SCM 2D doping images using Veeco Multimode system. When the system was installed and setup the SCM was setup was in Open Loop mode. I fist noticed that my data was always 180 degrees out of phase. So N type regions were dark (neg) and P type regions were white/lite (pos) in cotrast. I first thought this was due to system setup Open loop. Now we are trying to acquire data in Closed loop with feedback. First try in this setup and I still have the data out of phase. I see many papers and the tradition is the Ptype regions are dark and Ntype regions are lite in contrast. What could be causing this? What in the setup need changing? Any help would be appreciated.
Rafael
Dear Rafel,
First, there has not been a convention to follow as whether to use negative phase to denote P type and positive phase for N type. I'm perfectly fine with, actually prefer to using Positive phase of P-type and Negative phase for N-type. It is improtant however to keep consistent among the data you collect whichever denotion you choose. Nevertheless, if you are to follow the tradition in literatures, you can simply change "SCM Lock-in Phase" such that you have a positive phase, for instnace +90 degree for n-type and -90 degree for p-type. For example, if indeed you have 180 degree out of phase, then you can simply change "SCM Lock-in phase" by 180 to reverse what you have.
You can also follow the procedure titled "Optimize the SCM Lock-In Phase" outlined in page 56 of manual "004-1020-000 APPLICATION MODULES, NANOSCOPE V7". If you do not have this manual, please let me know.
Chunzeng
Dear Chunzeng,
Thanks for the reply back. I understand and as I was going through the application notes I saw that our lockin phase was out of phase so this made perfect sense why we were oppisite. Now I have another question hopefully you can answer as well. We want to try to acquire dc/dv over voltage plots of the doped areas. What would be the easiest to do in open loop or closed? I have read literature stating Open loop but what are your thoughts.
Also in trying to obtain these dc/dv plots over voltage we were trying to determin the best lockin phase on our SCM module. We went through the application notes but our AC signal did not look like a perfect sine wave but more like a saw tooth waveform with lots of noise. Do you think there is a problem with our sensor?
Regards,
Dear Gafel,
dC/dV vs V is best done in open loop mode. You do not need to change the SCM Lock-in phase when taking dC/dV, the same SCM Lock-in phase as for imaging mode would be fine . Your AC signal is probably small so you do not see a sine waveform, you can use bigger AC bias, smaller SCM Lock-in bandwidth to attain a bigger, cleaner signal, and most likely cloaser to a sine wave.