Specific Process Knowledge/Characterization/Topographic measurement

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Topographic measurements

Topographic measurements are measurements of height differences on your sample. If you measure many spots on the sample you can get a topographic image of the surface.

At DTU Nanolab we have eight systems for topographic measurements:

• Stylus profilers (P17, Dektak XTA, Dektak 150 and Dektak 3ST) - Profilers for mechanically measuring topography
• Optical profilers (Optical profiler Sensofar and Optical profiler Filmetrics) - 3D Profilers for optically measuring topography
• AFMs (AFM Icon-PT1 and AFM Icon-PT2) - AFMs for "mechanically" measuring topography (nano-regime)

High Aspect Ratio Structures

The fact that the stylus tip of a stylus profiler or an AFM is shaped like a cone with some finite 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).

Thin Film Thickness

The profilers can be used to measure the thickness of optically transparent thin films or etched non-transparent thin films. There are also other options for measuring film thickness. All the methods are compared on the "Measurement of Thin Film Thickness and Optical Constants" page.

Comparison of Stylus Profilers, Optical Profilers and AFMs at Nanolab

	Tencor P17 (Stylus Profiler)	Dektak XTA (Stylus Profiler)	Dektak 150 (Stylus Profiler)	Dektak_3ST (Stylus Profiler)	Sensofar S Neox (Optical Profiler)	Filmetrics (Optical Profiler)	AFM Icon 1 and AFM Icon 2 (Atomic Force Microscopy)
Generel description	Profiler for measuring microstructures in cleanroom. Excellent stress measurements. Excellent sequence programs. Plus wafer mapping and roughness measurements.	Profiler for measuring microstructures in cleanroom. Quick and easy vertical profiling. Plus wafer mapping, roughness and stress measurements.	Profiler for measuring microstructures in building 347.	Profiler for measuring microstructures in building 346 basement.	3D Profiler for measuring microstructures and surface roughness. Can do wafer mapping. In cleanroom	3D Profiler for measuring microstructures and surface roughness. Can do wafer mapping. In basement below cleanroom.	AFM for measuring nanostructures and surface roughness
Max. Scan Range xy	Line scan x: 1 µm to 200mm. Map scan xy: up to the largest square that can be inscribed in an 8" wafer	Line scan x: 50 µm to 55 mm in one scan. Maximum scan length with stitching 200mm.	Line scan x: 50 µm to 55 mm	Line scan x: 50 µm to 55 mm	Depending on the objective: One view: 127µmX95µm to 1270µmX955µm Stitching: In principle a whole 6" wafer (time consuming)	Only 10x objective: 2.0 mm x 1.7 mm	90 µm square
Max. Scan Range z	up to 900 µm	50 Å to 1 mm	50 Å to 1 mm	100 Å to 130 nm	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)
Resolution xy	down to 0.025 µm	down to 0.003 µm	down to 0.003 µm	down to 0.5 µm	Depending on the objective: 0.5µm -> 5µm	Resolving power of the lens: 0.92 µm	Depending on scan size and number of samples per line and number of lines - accuracy better than 2%
Resolution z	0.01, 0.08 or 0.6 Å depending on range (note resolution below 1 Å is below the noise level)	1 Å, 10 Å, 40 Å or 160 Å depending on range	1 Å, 10 Å or 20 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%
Max. Scan Depth [µm] (as a function of trench width W)	0.866*(W[µm]-2µm)	1.2*(W[µm]-5µm)	1.2*(W[µm]-5µm)	1.2*(W[µm]-2.5µm)	Depending on material and trench width: Somewhere between 1:1 and 1:12	Depending on material and trench width.	~1:1 with standard cantilever.
Standard Tip Radius	2 µm 60o cone	5 µm 45o cone	5 µm 45o cone	2.5 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
Stress Measurement	Excellent capability	Can be done			No stress calculation capability	Cannot be done	Cannot be done
Surface Roughness	Can be done on a line or map (parallel line scans)	Can be done on a line scan	Can be done on a line scan	Recommend P17 or Dektak XTA	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
Substrate Size	up to 8"	up to 6"	up to 6"	up to 4"	Up to more than 6"	100x100 mm	6" or less
Allowed Materials	Almost any material that leaves no residuals; please ask responsible group about non-standard materials.	Almost any material that leaves no residuals; please ask responsible group about non-standard materials.	Almost any material that leaves no residuals; please ask responsible group about non-standard materials.	Almost any material that leaves no residuals; please ask responsible group about non-standard materials.	Almost any material that leaves no residuals; please ask responsible group about non-standard materials.	Almost any material that leaves no residuals; please ask responsible group about non-standard materials.	Almost any material that leaves no residuals; please ask responsible group about non-standard materials.
Location	Cleanroom F-2	Cleanroom B-1	Building 347, SupportLab	Basement, building 346, room 904	Cleanroom C-1	Basement, building 346, room 904	AFM Icon1: Cleanroom C-1 AFM Icon2: Basement, building 346, room 904