[Spm] Recalibration of Calibration Standards

Fri May 15 07:57:53 EDT 2009

We at Danish Fundamental Metrology can offer the calibration of step height standards as well as of lateral periodic gratings (1D and 2D). The calibrations are done traceable to the metre with our metrologic AFM, and they are accredited by the Danish accreditation body DANAK.

We can calibrate the step heights of standards ranging from 20 nm to 3000 nm, with the corresponding expanded uncertainties between 1 nm and 9 nm.
Two dimensional gratings with a pitch ranging from 500 nm to 12 000 nm can be calibrated with an expanded uncertainty between 0.9 nm and 18.0 nm, depending on the grating period.

We have our own transfer standards calibrated regularly every two years. From a metrologic point of view alone, it's always advisable to keep a history of your standards which ultimately provide the traceability of all your measurements to the metre convention. In addition, one cannot, in principal, be sure about the homogeneity of a growing oxide layer or other changes of the sample topography when it comes down to the nanometer range. For instance, we had a step height sample which grew spikes irregularly.

Please fell free to check our homepage for further information, or to contact me directly.

Best regards,

Kai Dirscherl

KAI DIRSCHERL
Ph.D., Staff scientist
Danish Fundamental Metrology
Matematiktorvet  307
DK-2800  Lyngby
Denmark

Tel: +45 4525 5878
Fax: +45 4593 1137
e-mail: kdi at dfm.dtu.dk
home-page: http://www.dfm.dtu.dk

>>> "Don Chernoff at ASM" <donc at asmicro.com> 2009-05-07 21:57 >>>
My message today is motivated by questions asked by a quality systems auditor who recently visited my lab.

We calibrate the XYZ scan axes of our AFM using a traceable height and pitch standard made of thermally grown silicon dioxide on silicon.  The specimen contains these patterns:

10 um pitch, 2-dimensional array of pits, nominally 200 nm deep

2 um pitch, 1-dimensional array of ridges, same depth as the pits.

The manufacturer's certificate of traceability does not discuss recalibration or indicate any need for it. 

Based on the materials of construction, I believe that the pitch values and the pit depth are stable and that no recalibration is needed, provided that we are careful in handling and using the specimen.  For example, any nanodebris visible in the image is excluded from the measurement.

However, the quality consultant says that it is common to send such samples to an outside lab for recalibration.  He added that we should either do recalibration or write a justification for why recalibration is not necessary. 

I am curious what other people do about this.  One can consider this in several different environments:

-the AFM manufacturer, who wants to provide good calibration for the instruments

-the AFM user who is supporting a production or QC application

-the AFM user who is mainly supporting R&D, but needs to show traceability in order to meet the requirements of a quality management system.

Here are a few practical questions to start the discussion.

If you have such a standard recalibrated, what is the time interval?  

If you do not recalibrate the standard, what rationale do you give for why it is unnecessary?  

Can you articulate the reasons so that it is clear they are based on good science and engineering data and practices?

Do you have any other comments on this subject?

regards,
Don
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Don Chernoff, Ph.D., President
Advanced Surface Microscopy, Inc.    E-Mail:  donc at asmicro.com 
3250 N. Post Rd., Ste. 120           Voice:   317-895-5630
INDIANAPOLIS IN 46226  USA      Toll free: 800-374-8557 (in USA & Canada)
web:  http://www.asmicro.com         Fax:     317-895-5652
[business activities:  analytical services in AFM, AFM probes, consulting, training,
calibration and test specimens, calibration and measurement software,
 used NanoScope equipment.]
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