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 stylus profiler	Optical Profiler (Sensofar)	Optical Profiler (Filmetrics)	AFM Icon 1 and AFM Icon 2	Dektak 150 stylus profiler	Dektak 3ST stylus profiler
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.	3D Profiler for measuring micro structures and surface roughness. Can do wafer mapping. Positioned in the basement.	AFM for measuring nanostructures and surface roughness	Profiler for measuring micro structures.	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)	Only 10x objective: 2.0 mm x 1.7 mm	90 µm square	Line scan x: 50-50000 µm	Line scan x: 50-55000 µm
Max. scan range z	50 Å to 1 mm	50 Å to 1 mm	Depending on the objective and Z resolution: 94.4 µm ->9984 µm	10 mm (piezo range 500 µm)	1 µm (can go up to 5 µm under special settings)	100 Å to 130 nm	50 Å to 1 mm
Resolution xy	down to 0.067 µm	down to 0.003 µm	Depending on the objective: 0.5µm -> 5µm	Resolving power og the lense: 0.92 µm	Depending on scan size and number of samples per line and number of lines - accuracy better than 2%		down to 0.003 µm
Resolution z	1 Å, 10 Å, 40 Å or 160 Å depending on range	1 Å, 10 Å, 40 Å or 160 Å depending on range	Depending on measuring methode: PSI down to 0.01 nm VSI down to 1 nm Confocal (depending on objective): 1nm -> 50nm	Accuracy 0.7% Precision 0.1%	<1Å - accuracy better than 2%	1 Å, 10 Å or 20 Å depending on range	1 Å, 10 Å, 40 Å or 160 Å depending on range
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	Depending on material and trench width.	~1:1 with standard cantilever.	1.2*(W[µm]-2.5µm)	1.2*(W[µm]-5µm)
Standard tip radius	5 µm 45o cone	5 µm 45o cone	No tip - using light Blue monochromatic LED: 460nm White broadband LED: 550nm	No tip - using light Blue monochromatic LED: 460nm White broadband LED: 550nm	<12 nm on standard cantilever	2.5 µm 45o cone	5 µm 45o cone
Stress measurement	Can be done	Can be done	No stress calculation capability	Cannot be done	Cannot be done	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 line or an area	Can be done on a selected surface area	Recommended to use Dektak XTA or Dektak 8.	Can be done on a line scan
Substrate size	up to 8"	up to 6"	Up to more than 6"	100x100 mm	6" or less	4" or less	up to 6"
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, please check the responsible group for any non standard materials	Almost any material that does not leave residual on the stage.	Almost any material that does not leave residual on the stage.