Specific Process Knowledge/Characterization/Topographic measurement
Topographic measurements are measurements were you can measure hight differences on your substrate. If you measure in many spots of the substrate you can get a topographic image of the substrate.
AT DANCHIP we have three systems for topographic measurement:
- Dektak - Profiler for measuring micro structures
- Optical Profiler (Sensofar) - 3D Profiler for measuring micro structures
- Nanoman - AFM for measuring nano structures
High Aspect ratio structures
The fact that the tips of the Dektak profilers and the AFM are shaped like a cone with some tip angle causes a problem when characterizing high aspect ratio structures. For instance, if a 20 Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \mu}
m wide trench is etched deeper than approximately 18 Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \mu}
m, the tip of the Dektak will not be able to reach the bottom. The optical profiler uses a light beam that are focused through an objective therefore it is able to measure higher aspect ratios. The aspect ratio is limited by the posibility for the light to reach the bottom and get back to the detector. On some samples we have been able to measure aspect ratios above 1:10. Other wise the solution is to cleave the sample along a line that is perpendicular to the trench and then put it in a scanning electron microscope.
Comparison of the two profilers and the AFM
| Dektak | Optical Profiler (Sensofar) | Nanoman | |
|---|---|---|---|
| General description | Profiler for measuring micro structures. Can do wafer mapping and stress measurements. | 3D Profiler for measuring micro structures. Can do wafer mapping. | AFM for measuring nanostructures and surface roughness |
| Substrate size | up to 8" | Up to more than 6" | 6" or less |
| Max. scan range xy | Line scan x: 50µm to 200mm | bbb | 90 µm square |
| Max. scan range z | <100Å to~0.3mm | 50Å to 262µm | 1 µm (can go up to 5 µm under special settings) |
| Resolution xy | up to 5900 data points per profile | down to 0.067 µm | Depending on scan size and number of samples per line and number of lines - accuracy better than 2% |
| Resolution z | 1Å or 25Å | 1Å, 10Å or 20Å | <1Å - accuracy better than 2% |
| Max. scan depth [µm] (as a function of trench width W) | 0.87(W[µm]-5µm) | 1.2(W[µm]-5µm) | ~1 with standard cantilever. |
| Tip radius | 5 µm 60o cone | 5 µm 45o cone | <12 nm on standard cantilever |
| Stress measurement | Can be done | Can be done | Cannot be done |
| Surface roughness | Can be done on a line scan | Can be done on a line scan | Can be done on a selected surface area |