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Application Notes |
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Home » Application Notes |
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| Surface Micro Roughness |
Surface micro-roughness testing is performed on an area of a wafer that could be anywhere from 1μm x 1μm to 10μm x 10μm. It is a product of atomic force microscopy (AFM), which measures this tiny section of the wafer on the near-atomic level. In this discipline, a probe is energized and scans the section in a raster pattern. The probe detects minute variations in the electromagnetic forces between itself and the wafer, which translate into tiny differences in the height of the surface.
Below is a set of data for some wafers that were polished and cleaned in SQI’s Santa Clara facility. These measurements were performed for surface micro-roughness at an outside analytical lab: |
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| Wafer size |
RMS in nm |
Mean Roughness in nm |
| 3" |
0.11 |
0.09 |
| 8" |
0.15 |
0.11 |
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| Definitions: |
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Wafer size – The diameter of the wafer. |
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RMS – Root mean square. This is a statistical tool sometimes referred to as the quadratic mean. It is used primarily to approximate variation from the center line where the values are both positive and negative, as in a wave. As an example, if the values of dataset A were (-2, -1, 0, 1, 2) and the values of B were (-50, -25, 0, 25, 50), the average (mean) value of both sets would be zero, even though the sets are vastly different. However, the RMS of set A is 1.414 and the RMS of set B is 35.355, thus generating a better approximation of the sets. |
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Edge chips |
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Mean roughness – The average, which is computed by adding the values together and then dividing by the total number of values. |
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R max – The highest peak in the measured area. |
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| Anything below 0.2 nm is a high quality wafer. In fact, 0.2 nm is smaller than a single silicon atom! On the next pages, you’ll find the graphical representations of these tests. |
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| 3” Wafer |
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| 8” Wafer |
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