Specific Process Knowledge/Characterization/Dektak XTA: Difference between revisions
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===Influence of Calibration Standard Uncertainty=== | ===Influence of Calibration Standard Uncertainty=== | ||
[[File:intrinsic step h error.png|upright=2|alt=Axes with Measured values versus expected values and three lines illustrating measured=expected, plus two not-quite straight lines illustrating the confidence intervals growing as the values grow constrained by the calibration standard measurements. Two diamonds illustrate the location of the calibration sample measurement points. The plot's title says "Error from intrinsic uncertainty step height used for calibration".|right|thumb|Figure 1: Measurement uncertainty from uncertainty in the calibration standard. Not to scale. The linearity of the sensor means that the measurement error increases approximately linearly with the size of the feature being measured. The percentage-wise error on the smallest standard step is larger than on the bigger standard step, so the lines are not totally straight.]] | [[File:intrinsic step h error.png|350px|upright=2|alt=Axes with Measured values versus expected values and three lines illustrating measured=expected, plus two not-quite straight lines illustrating the confidence intervals growing as the values grow constrained by the calibration standard measurements. Two diamonds illustrate the location of the calibration sample measurement points. The plot's title says "Error from intrinsic uncertainty step height used for calibration".|right|thumb|Figure 1: Measurement uncertainty from uncertainty in the calibration standard. Not to scale. The linearity of the sensor means that the measurement error increases approximately linearly with the size of the feature being measured. The percentage-wise error on the smallest standard step is larger than on the bigger standard step, so the lines are not totally straight.]] | ||
Nanolab staff check the instrument's measurement accuracy with a standard step height of 917 nm for the smaller ranges and 24.925 µm for the larger ranges, so that the middle ranges are checked with both standards. The 95 % confidence intervals for the standards are 17 nm for the 917 nm standard and 0.072 µm for the 24.925 µm standard. If the control measurement is beyond the limit set in our Quality Control procedure, the instrument is calibrated and the users informed (see LabManager for details, for instance the DektakXT [http://labmanager.dtu.dk/d4Show.php?id=2493&mach=304 control instruction] and [https://labmanager.dtu.dk/view_binary.php?type=data&mach=304 control measurement data]) | Nanolab staff check the instrument's measurement accuracy with a standard step height of 917 nm for the smaller ranges and 24.925 µm for the larger ranges, so that the middle ranges are checked with both standards. The 95 % confidence intervals for the standards are 17 nm for the 917 nm standard and 0.072 µm for the 24.925 µm standard. If the control measurement is beyond the limit set in our Quality Control procedure, the instrument is calibrated and the users informed (see LabManager for details, for instance the DektakXT [http://labmanager.dtu.dk/d4Show.php?id=2493&mach=304 control instruction] and [https://labmanager.dtu.dk/view_binary.php?type=data&mach=304 control measurement data]) | ||
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===Total Uncertainty=== | ===Total Uncertainty=== | ||
[[File:Error probability distributions rev.png|upright=2|alt=Four different probability distributions that contribute to the total error on measurements with the DektakXT 6.5 micron range. By far the widest distribution is the one from the error on the standard step, which is a Gaussian. The others are the non-Gaussian spread of the average measurement of the standard height, which cuts off at the QC limits, the resolution, which is a very narrow uniform distribution, and the spread of measurement values for a given step being measured, which is a Gaussian whose width depends on the step in question.|right|thumb|Figure 2: The probability distributions of the main sources of error that are convoluted to create the total error on a profiler measurement.]] | [[File:Error probability distributions rev.png|upright=2|alt=Four different probability distributions that contribute to the total error on measurements with the DektakXT 6.5 micron range. By far the widest distribution is the one from the error on the standard step, which is a Gaussian. The others are the non-Gaussian spread of the average measurement of the standard height, which cuts off at the QC limits, the resolution, which is a very narrow uniform distribution, and the spread of measurement values for a given step being measured, which is a Gaussian whose width depends on the step in question.|right|thumb|Figure 2: The probability distributions of the main sources of error that are convoluted to create the total error on a profiler measurement.]] | ||