Specific Process Knowledge/Characterization/Stylus Profiler Measurement Uncertainty: Difference between revisions
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===How does the underlying scan noise affect the measurement accuracy?=== | ===How does the underlying scan noise affect the measurement accuracy?=== | ||
The step determination will usually be better than the noise of the underlying scan - we don't expect an error in the measured step sizes as big as 30-60 nm. This comes down to removing some of the noise due to averaging parts of the scan during leveling and measuring. | The step determination will usually be better than the noise of the underlying scan - we don't expect an error in the measured step sizes as big as 30-60 nm. This comes down to removing some of the noise due to averaging parts of the scan during leveling and measuring. Also, usually it is not necessary (or recommended) to measure such steps across more than 1 cm. The closer together the measurement points, the "flatter" the underlying scan will be. | ||
For example, in the DektakXT we regularly measure shadow masked metal films made by e-beam evaporation that are around 100 nm thick. We have found good agreement between the DektakXT measurements of a 500 µm wide step and XRR measurements of films of the same thickness, so we see no reason not to trust these measurements to within around +/- 5 nm. We level the scan with the leveling cursors close to the step before and after it, so only the scan noise in an ~700 µm range is important. Additionally, since we average the thickness across approx. 400 µm at the top of the step compared to the ~40 µm leveling intervals nearby (where the height is also averaged), the variation comes out much smaller than what is seen across a full 2000 µm scan. | For example, in the DektakXT we regularly measure shadow masked metal films made by e-beam evaporation that are around 100 nm thick. We have found good agreement between the DektakXT measurements of a 500 µm wide step and XRR measurements of films of the same thickness, so we see no reason not to trust these measurements to within around +/- 5 nm. We level the scan with the leveling cursors close to the step before and after it, so only the scan noise in an ~700 µm range is important. Additionally, since we average the thickness across approx. 400 µm at the top of the step compared to the ~40 µm leveling intervals nearby (where the height is also averaged), the variation comes out much smaller than what is seen across a full 2000 µm scan. | ||