CD AFM for LER and SWR

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Robert Melzer Posted: Tue, Jun 22 2010 11:41 AM

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What experience have you made while measuring LER, LWR and SWR with a CD AFM in terms of choosing appropiate scan size and number of lines for

a good resolution. Obviously we have to take the shape of the CD tip and the wavelength/frequency of the linewidthvariation into account.

But how would you generally start? Resolution of 10nm per line? Is less than that even suitable, when we don't know CD tip radius in slow scan direction (here X)?

I am refering to 'PreliminaryInvestigations for Ultimate GatePatterning, Metrology Challenges»-J. Foucher et al AVS 2000'

and 'Sidewall Roughness Analysis with 3D AFM, Veeco Technical Seminar 12th July 2005 '

Thank you for your replies. I hope to get a better understanding in preparation for upcoming application opportunities.

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SeanHand replied on Tue, Jun 22 2010 9:28 PM

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Hi Robert -

    You make very good points and determining the balance point between high resolution CD imaging,  throughput and tip wear is vital to minimizing the uncertainty of these measurements.  In the media section there is a document titled:  Normal 0 false false false MicrosoftInternetExplorer4 CDAFM Sampling Guidelines (rev_06182008)  Authored by Vladimir Ukrainstev,  now of Nanometrology Intl.   In this document, Vladimir provides several algorithmic approaches to determining a sampling BKM for a given feature based on general assumptions of MOSFET production processes.  These include isolated and dense features as well as 2D features such as end-to-end lines or spaces, noses and pinch points.  These assumptions directly address some of your concerns such as knowledge of tip shape and it's effect on the resultant LER/LWR measurements.  

   Sidewall Roughness can be a little trickier.  In this case,  you are going to face the same challenges that you would for a surface roughness application.  Namely,  that to get a good, high resolution image,  you will need a lot of data and a very sharp tip.    Here,  your choice of probes will be vital and I would suggest Trident or BiPod probes.   Frequent tip qual on the I2FSR for VEH monitoring will likely be required for both tip wear (rough materials such as Poly Si) and contamination (soft materials such as Resist).   If the SWR for which you are looking is mainly standing waves ADI I would suggest using a CDR probe rather than a sharp Trident or BiPod.   Just make sure that the VEH is less than the expected wavelegth of the standing waves.

Best Regards,

Sean

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SeanHand replied on Tue, Jun 22 2010 9:29 PM

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Hi Robert -

   Just to folow up,  the Sampling Guidelines document is in the Veeco Media/Software, Documents and Tools section.

Best Regards,

Sean

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Robert Melzer replied on Wed, Jun 23 2010 3:08 AM

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Thank you. I can not find the document (could it be that I don't have access to Veeco Media - SW, Documents section?) I just have application notes, brochures. What I have is 'Impact of Sampling on Uncertainty: Semiconductor Dimensional Metrology Applications'.