Specific Process Knowledge/Characterization/Profiler: Difference between revisions
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===Height accuracy=== | ===Height measurement accuracy for the DektakXT=== | ||
The accuracy of | The accuracy of a height measurement with the profiler depends on the measurement settings, the nature of the steps you are measuring, the instrument calibration and the resolution. | ||
Regarding the measurement settings, both the force setting and the scan speed are important: Too high force may compress a soft material like Al, Au or some polymers, while too low force may lead to the stylus "jumping" over features, especially if the scan speed is high. However, if the scan speed is too low and you are measuring a small step <500 nm, you may experience drift in the measurement. Of course you also must make sure the feature you are measuring is wide enough for the stylus tip to reach the bottom ( | Regarding the measurement settings, both the force setting and the scan speed are important: Too high force may compress a soft material like Al, Au or some polymers, while too low force may lead to the stylus "jumping" over features, especially if the scan speed is high. However, if the scan speed is too low and you are measuring a small step <500 nm, you may experience drift in the measurement. Of course you also must make sure the feature you are measuring is wide enough for the stylus tip to reach the bottom (see the [http://labmanager.dtu.dk/d4Show.php?id=2346&mach=304 DektakXT manual], Figure 3 for details). | ||
We | We check the instrument's measurement accuracy with a standard step height of 9160 Å for the 65 kÅ range and 24.865 µm for the larger ranges. The 95 % confidence intervals for the standards are 300 Å for the 9160 Å standard and 0.15 µm for the 24.865 µm standard. If the control measurement is beyond the limit set in our Quality Control procedure, the instrument is calibrated and the users informed through the Status Log (see LabManager for details on the [http://labmanager.dtu.dk/d4Show.php?id=2493&mach=304 control instruction] and the [https://labmanager.dtu.dk/view_binary.php?type=data&mach=304 quality control measurement data]). | ||
The size of the calibration standard confidence intervals mean that the measurement uncertainty is much more significant when you measure very shallow steps below 500-1000 nm than when you measure steps in the micron range and a. This is because the 95 % confidence interval in the 65 kÅ range is obviously at least ± 30 nm, so measuring a 100-200 nm step will have a huge error percentage-wise. However, this error is a systematic one and the random error associated with repeated measurements will usually be much, much smaller (perhaps ± 5 nm). Therefore it may still make sense to measure shallow steps to be able to make compare step heights for different samples. | |||
The error stemming from the uncertainty on the calibration standard | We can numerically estimate the accuracy of a measurement based on the error of the calibration of the instrument combined with the error from the limits of the resolution and of the scatter of repeated measurements. You can see I (Rebecca) made an uncertainty budget for the Dektak measurements here: [[:File:uncertainty budget dektaks.xlsx]] based on the procedure described [https://www.nde-ed.org/GeneralResources/Uncertainty/Combined.htm here]. | ||
The error stemming from the uncertainty on the calibration standard dominates for all ranges except the 1 mm range, where the resolution also plays a role. This leads to the 95 % confidence intervals listed above in the table: just over 30 nm for the smallest range, about 0.17 µm for the medium ranges, and about 0.6 µm for the 1 mm range. Be aware that if you have a step height that is difficult to measure the scatter of repeated measurements could easily lead to larger confidence intervals. | |||
==Dektak 8 stylus profiler== | ==Dektak 8 stylus profiler== | ||