Specific Process Knowledge/Characterization/Topographic measurement

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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 DTU Nanolab we have five systems for topographic measurements:

• Dektak stylus profilers (Dektak XTA, Dektak 3ST and Dektak 8) - 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 µm wide trench is etched deeper than approximately 18 µm, the tip of the Dektak will not be able to reach the bottom. The optical profiler uses a light beam that is focused through an objective. Therefore it is able to measure higher aspect ratios. The aspect ratio is limited by the possibility 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. Otherwise the solution is to cleave the sample along a line that is perpendicular to the trench and then inspect the profile in a scanning electron microscope or a microscope (for large structures).

Comparison of the two stylus profilers, the optical profiler and the AFM

	Dektak 8 stylus profiler	Dektak XTA_new stylus profiler	Optical Profiler (Sensofar)	AFM Icon	Dektak 3ST
Generel description	Profiler for measuring micro structures. Can do wafer mapping and stress measurements.	Profiler for measuring micro structures. Can do wafer mapping and stress measurements.	3D Profiler for measuring micro structures and surface roughness. Can do wafer mapping.	AFM for measuring nanostructures and surface roughness	Profiler for measuring micro structures.
Max. scan range xy	Line scan x: 50µm to 200mm	Line scan x: 50µm to 55mm in one scan. Maximum scan lenght with stiching 200mm.	Depending on the objective: One view: 127µmX95µm to 1270µmX955µm Stitching: In principel a hole 6" wafer (time consuming)	90 µm square	Line scan x: 50-50000 µm
Max. scan range z	50Å to 1mm	50Å to 1mm	Depending on the objective and Z resolution: 94.4µm ->9984µm	1 µm (can go up to 5 µm under special settings)	130 nm
Resolution xy	down to 0.067 µm	down to 0.003 µm	Depending on the objective: 0.5µm -> 5µm	Depending on scan size and number of samples per line and number of lines - accuracy better than 2%
Resolution z	1Å, 10Å, 40Å or 160Å	1Å, 10Å, 80Å or 160Å	Depending on measuring methode: PSI down to 0.01 nm VSI down to 1 nm Confocal (depending on objective): 1nm -> 50nm	<1Å - accuracy better than 2%
Max. scan depth [µm] (as a function of trench width W)	1.2*(W[µm]-5µm)	1.2*(W[µm]-5µm)	Depending on material and trench width: Somewhere between 1:1 and 1:12	~1:1 with standard cantilever.
Tip radius	5 µm 45o cone	5 µm 45o cone	No tip - using light Blue monochromatic LED: 460nm White broadband LED: 550nm	<12 nm on standard cantilever
Stress measurement	Can be done	Can be done	No stress calculation capability	Cannot 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 line or an area	Can be done on a selected surface area	Recommended to use Dektak XTA or Dektak 8.
Substrate size	up to 8"	up to 6"	Up to more than 6"	6" or less	4" or less
Allowed materials	Almost any material that does not leave residual on the stage, please check the responsible group for any non standard materials	Almost any material that does not leave residual on the stage, please check the responsible group for any non standard materials	Almost any material that does not leave residual on the stage, please check the responsible group for any non standard materials	Almost any material that does not leave residual on the stage, please check the responsible group for any non standard materials	Almost any material that does not leave residual on the stage.