Specific Process Knowledge/Characterization/Profiler

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Overview of the Nanolab profilers

All the profilers are compared on the topographic measurement page.

The sections below describe each profiler (stylus profilers and optical profilers) in more detail.

Dektak XTA stylus profiler

The Dektak XTA stylus profiler from Brüker is used for profiling surfaces of samples with structures in the micro- and nanometer range. The size of the structures that can be measured is limited by the tip dimensions.

A profile measurement can be done across a specific structure by using a high magnification camera to locate the structure. It is also possible to program the stylus to measure in several positions, defined with respect to some deskew points. Stress measurements of thin films can be done by measuring the wafer bow.

The user manual, quality control procedure and results, technical information and contact information can be found in LabManager:

Dektak XTA in LabManager

Equipment performance and process related parameters

Purpose	Profiler for measuring micro structures	Single line profiles Wafer mapping Stress measurements by measuring wafer bow Surface roughness on a line scan
Performance	Scan range x y	Line scan x: 50 µm to 55 mm in a single scan, up to 200 mm with stiching
	Scan range z	50 Å to 1 mm
	Resolution x y	Down to 0.003 µm theoretically, in practice limited by the tip radius
	Resolution z	1 Å, 10 Å, 80 Å or 160 Å (for ranges 65 kÅ, 655 kÅ, 5240 kÅ and 1 mm respectively)
	Height accuracy z (95 % confidence)	For very well defined steps ~ 2 % for a 1 µm step and ~ 1 % for a 25 µm step (see below)
	Max scan depth as a function of trench width W	1.2*(W[µm]-5µm)
Hardware settings	Tip radius	5 µm 45^o cone
Substrates	Substrate size	Up to 6"
	Substrate materials allowed	In principle all materials

Height measurement accuracy

The accuracy of a height measurement with the profiler depends on the measurement settings, the sample, the instrument calibration and the resolution.

Use the right measurement settings for your sample

Both the force setting and the scan speed are important: Too high force may compress a soft material like Al, Au or some polymers, while too low force may lead to the stylus "jumping" over features, especially if the scan speed is high. Too low scan speed may result in drift of the measurement and lots of noise while too high scan speed may mean that the stylus tip does not have time to reach the bottom of the features you are measuring (see the DektakXT manual, Figure 3 for details).

A sharp vertical step is easiest to measure. If the step is gradual or the surface is very rough, it can be difficult to determine where to measure and how the scan should be leveled.

Influence of calibration standard uncertainty

Nanolab staff check the instrument's measurement accuracy with a standard step height of 917 nm for the three smaller ranges and 24.925 µm for the three larger ranges, so that the two middle ranges are checked with both standards. The 95 % confidence intervals for the standards are 17 nm for the 917 nm standard and 0.072 µm for the 24.925 µm standard. If the control measurement is beyond the limit set in our Quality Control procedure, the instrument is calibrated and the users informed (see LabManager for details on the control instruction and the control measurement data).

All this means that the 95 % confidence interval of a 1 µm step measured with the 6.5 kÅ range is at least the 1.8 % error of the standard step while the 95 % confidence interval of a 25 µm step measured with the largest range is at least the 0.3 % error of the standard step. Steps between 1 and 25 µm measured with the intermediate ranges will presumably have an intermediate error just due to the calibration uncertainty while the calibration-related uncertainty increase slightly percentagewise for smaller or larger steps. This because an actuator has to translate the vertical stylus movement to an electronic signal and if there is a slight offset or error in the calibration factor this is amplified the further you get from the calibration value.

Total uncertainty

Apart from the error due to the calibration standard's uncertainty, there will be random noise in any measurement, which we have found for many repeated measurements of the standard step height (a rigid, well defined vertical step) is on the order of ± 5 nm for the 917 nm standard and 0.05 µm for the 24.925 µm sample. There is also a tiny contribution to the error from the instrument's resolution and a contribution from the spread of values that the Dektak actually measures compared to the theoretical height of the standard step height.

To estimate the overall accuracy of the Dektak's measurements you can convolute the various sources of error. The error sources to be convoluted are shown graphically on the right. You can see an uncertainty budget for the Dektak measurements here (made by Rebecca Ettlinger): Media:uncertainty budget Dektak rev.xlsx. It is based on the assumption that all the error sources are independent and can therefore be added by the sum of squares method.

The resulting error calculation for a 1 µm very well defined standard step is about 2 % (as the uncertainty on the calibration standard dominates), while for a very well defined step of 25 µm the cumulative error is about 0.7-1 %. These are the uncertainties listed in the table. However, in real devices the random error will often be much larger than for our standard samples and so the real confidence interval will be larger.

To improve the accuracy of your particular measurement, you should repeat the measurement several times and estimate the standard deviation. If the scatter is quite small you can try to include the calibration error as a percentage of the step height in your estimate of the total error using the sum of squares method as done in the uncertainty budget above. If the scatter of your measurements is large that will probably be the dominant source of error in your measurement.

Stylus Profiler (Tencor P17)

The P17 Stylus Profiler from KLA Tencor is used in a similar manner to the Dektak XTA for profiling surfaces with structures in the micro- and submicrometer range as well as for measuring stress. Compared to the DektakXT, the P17 has more advanced options for stress measurements and allows the user to measure a stress map with up to 5° radial resolution. Programming a sequence of predefined scans in fixed locations on a wafer is also somewhat easier and the manual for doing it much better for the P17 than for the Dektak XTA. A disadvantage of the P17 is that is can be hard to locate structures as the maximum field of view of the camera is 1x1.5 mm. We recommend having a map of the sample design available so you can easily locate the features of interest. Otherwise the P17 is easy to use, fast, and accurate, just like the DektakXT.

The user manual, quality control procedure and results, technical information and contact information can be found in LabManager:

P17 page in LabManager

Info about using the analysis software from outside the cleanroom: Apex software access

Acceptance test

Acceptance measurements on the P17: Media:Appendix 3 Acceptance test p17 final_v2_Completed.pdf
Vendor's own conformity test results after installation: File:Acceptance P17 ctd results.pdf

Equipment performance and process related parameters

Purpose	Profiler for measuring microstructures	Single line profiles Wafer mapping Stress measurements by measuring the wafer bow Surface roughness on a line scan
Performance	Scan range X Y	Line scan X: 20 µm to 200 mm in a single scan. No stitching. Map scan XY: In principle any rectangle that can be inscribed in a 200 mm circle, but resolution is limited to max. 4 million points and scanning is slow. In practice to get good resolution scan a very small area (e.g., 100 x 500 µm)
	Scan range Z	50 nm to 900 µm. It is possible to measure smaller steps but not recommended as the results may not be accurate.
	Resolution X Y	Down to 0.025 µm in theory, but the tip radius is 2 µm, so the meaningful resolution is at the same order of magnitude
	Resolution Z	0.01 Å, 0.08 Å, or 0.6 Å according to the manufacturer for ranges 13 µm, 131 µm, and 1 mm.†
	Height accuracy z (95 % confidence)	~ 2 % for the smallest range for a 1 micron step and ~ 1 % for a 25 micron step for well-defined steps that are easy to measure, see section above.
	Max scan depth as a function of trench width W	0.87(W[µm]-2µm) = tan(60^o)/2(W[µm]-2µm) (empirically validated by Nanolab staff)
Hardware settings	Tip radius	2 µm 60^o cone
Substrates	Substrate size	Up to 8"
	Substrate materials allowed	In principle all materials that do not leave residues on the chuck.

†The resolution for the smallest range is theoretical, as this is below the noise threshold at least in our lab.

Height measurement accuracy for the Tencor P17 Stylus Profiler

This is similar to what applies to the DektakXT as described above. The P17 has slightly better reproducibility but as the uncertainty for small steps is dominated by the uncertainty on the standard step height's actual size, this does not make much difference. Just as for the Dektak, the reproducibility of your own measurements of your particular step can make a relatively large contribution to the total uncertainty, Steps in real devices are not always as easy to measure or as well defined as our standard step height measurements.

Optical Profiler (Sensofar S Neox)

The Sensofar S Neox 3D Optical Profiler has a sensor head that combines confocal, interferometry and focus variation techniques as well as thick and thin film measurement capabilities.

The Neox sensor head provides standard microscope imaging, confocal imaging, confocal profiling, PSI (Phase Shift Interferometry), CSI (Coherence Scanning Interferometry), Active illumination (Ai) Focus Variation and high resolution thin film thickness measurements on a single instrument.

The main purpose is 3D topographic imaging of surfaces, step height measurements in smaller trenches/holes than can be obtained with standard stylus methods (i.e. with aspect ratios higher that 1:1), roughness measurements with larger FOV (Field Of View) than the AFM, but less horisontal resolution.

For most samples the optical profiler provides fast and easy information without any sample preparation. However, it can be necessary to cover thin transparent layers (< 2 µm) with a thin layer of metal.

The resolution is limited by the objectives and the pixel resolution.

Analysis software:

Free analysis software for visualizing and analyzing AFM and Optical profiler files (Sensofar) Gwyddion
SensoView software from Sensfar want also be downloaded for all users: U:\Nlab\CleanroomDrive\_Equipment\Optical profiler Sensofar\SensoVIEW 1.6.0

The user manual, technical information (SensoSCAN and SensoVIEW manuals) and contact information can be found in LabManager:

Optical profiler (Sensofar S Neox) info page in LabManager

Process Information

Sensofar presentation on how the sensofar works (for the previous system but the techniques are the same)
S Neox leaflet including specifications
Results from the Optical Profiler (Sensofar) acceptance test - for the previous system - expired!!
Acceptance measurements on the S Neox Sensofar: Media:Acceptance measurements on Nanolab samples.pdf

Equipment performance and process related parameters

Equipment		Optical profiler
Purpose	3D topographic imaging of surfaces.	3D imaging of surfaces Roughness measurements Step height measurements 3D topographic measurements Thick and thin film thickness measurements in small spots
Posibilities	Confocal, interferometric and AI focus variation tophography and reflectometry Standard microscope imaging Confocal imaging Confocal profiling PSI (Phase Shift Interferometry) CSI (Coherence Scanning Interferometry) Active illumination (Ai) Focus Variation High resolution thin film thickness measurement using reflectrometry Stitched scans Wafer mapping
Performance	Depending on the objective chosen	See the performance of the different objectives here:
Substrates	Substrate size	Substrates no bigger than 150 mm x 150mm
	Substrate materials allowed	In principle all materials as long as they are allowed in the cleanroom outside fumehoods - no liquids!

Optical Profiler (Filmetrics)

The Profilm3D optical profiler from Filmetrics uses white-light-interferometry (WLI) and phase-shifting-interferometry (PSI) to produce surface profiles and depth-of-field color images.

The main purpose is 3D topographic imaging of surfaces, step height measurements and roughness measurements with larger FOV (Field Of View) than the AFM, but less horisontal resolution.

For most samples the optical profiler provides fast and easy information without any sample preparation. However, it can be necessary to cover thin transparent layers (< 2 µm) with a thin layer of metal.

The resolution is limited by the objective and the sampling resolution.

The user manual, technical information and contact information can be found in LabManager:

Optical profiler (Filmetrics) info page in LabManager

Equipment performance and process related parameters

Equipment		Optical profiler
Purpose	3D topographic imaging of surfaces.	3D imaging of surfaces Roughness measurements Step height measurements 3D topographic measurements
Posibilities	Interferometric profiling	Standard microscope imaging PSI (Phase Shift Interferometry) WLI (White light Interferometry) Stitched scans Wafer mapping
Performance	With the current 10x objective	See here the data sheet for this instrument
Substrates	Substrate size	Substrates no bigger than 100 mm x 100mm
	Substrate materials allowed	In principle all materials

Dektak 3ST

The Dektak 3ST is intended for profile measurements on samples outside the cleanroom.

The user manual, technical information and contact information can be found in LabManager:

Dektak 3ST (Dektak) in LabManager

The computer connected to the Dektak 3ST is pretty old and runs Windows 98 SE. It is not connected to the network but traces can be saved on either USB memory stick or floppy disk. The USB driver is an old universal driver and has been shown to work with small size USB sticks. However it did not work with an 8GB Kingston stick.

Equipment performance and process related parameters

Performance	Vertical Range	65 kÅ, 655 kÅ, 1310 kÅ
	Scan length range	50-50000 µm
	Stylus track force	Recommended: 3-10 mg, depending on the softness of the surface
	Scan speed ranges	High speed: 3s for 50µm to 50000µm Medium speed: 12s for 50µm to 10000µm Low speed: 50s
Materials	Allowed substrate materials	III-V Silicon polymer

Stylus Profiler: Dektak150

The stylus profiler Dektak150 is intended for profile measurements on samples outside the cleanroom.

The user manual, technical information and contact information can be found in LabManager:

Stylus profiler:Dektak150 in LabManager

The computer is not connected to the network but data can be saved on a dedicated USB and transfered to a computer on the network.

Equipment performance and process related parameters

Purpose	Profiler for measuring micro structures	Single line profiles Surface roughness on a line scan
Performance	Scan range x y	Line scan x: 50 µm to 55 mm in a single scan
	Scan range z	50 Å to 1 mm
	Resolution x y	Theoretically down to 0.003 µm (in practice the resolution is limited by the tip size)
	Resolution z	1Å (@65kÅ), 10Å (@655 kÅ), 80 Å (@5240 kÅ), 160 Å (@1mm)
	Maximum sample thickness	100 mm
Hardware settings	Tip radius	5 µm 45^o cone 0.2 µm 45^o cone on request
Substrates	Substrate size	Up to 6"
	Substrate materials allowed	In principle all materials