Specific Process Knowledge/Characterization/Profiler: Difference between revisions

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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 (Dektak 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 Dektak XTA

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
	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)	~ 300 Å for the 65 kÅ range, ~ 0.17 µm for the intermediate ranges, and ~0.6 µm for the 1 mm range for well-defined steps that are easy to measure reproducibly (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 for the DektakXT

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.

If the scan speed is too low and you are measuring a small step <500 nm, you may experience drift in the measurement. Of course you also must make sure the feature you are measuring is wide enough for the stylus tip to reach the bottom (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 9160 Å for the 65 kÅ range and 24.865 µm for the larger ranges. The 95 % confidence intervals for the standards are 300 Å for the 9160 Å standard and 0.15 µm for the 24.865 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).

The size of the calibration standard confidence intervals mean that the measurement uncertainty is much more significant for very shallow steps below 500-1000 nm than for steps in the micron range: The 95 % confidence interval in the 65 kÅ range is obviously at least ± 30nm, so measuring a 100-200 nm step will have a large error percentage-wise. Note that this error (from the calibration standard) is systematic. The random error associated with repeated measurements is usually smaller (perhaps ± 5 nm). One can therefore measure shallow steps to compare samples even if the absolute numbers are not very reliable.

Total uncertainty

To estimate the accuracy of the Dektak's measurements we have to combine the error of the calibration with the error from the limit on the resolution and the scatter of repeated measurements. This is shown graphically on the right. You can see an uncertainty budget for the Dektak measurements here (made by Rebecca Ettlinger in 2020): Media:uncertainty budget dektaks.xlsx. It is based on the procedure described here.

The error stemming from the uncertainty on the calibration standard dominates for all ranges except the 1 mm range, where the resolution also plays a role. This leads to the 95 % confidence intervals listed above in the table: just over 30 nm for the smallest range, about 0.17 µm for the medium ranges, and about 0.6 µm for the 1 mm range. As noted above, be aware that if you have a step height that is difficult to measure, the scatter of repeated measurements could easily lead to larger confidence intervals.

Dektak 8 stylus profiler

The Dektak 8 stylus profiler is a product of Veeco Instruments. It 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.

It can measure specific structures found with the help of a high magnification video camera or it can be programmed to measure several points defined with respect to some deskew points. It can also be used for stress measurements of thin films by measuring the wafer bow.

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

Dektak 8 in LabManager

The original user manual can be obtained from the staff.

Equipment performance and process related parameters Dektak 8 stylus profiler

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 100 mm
	Scan range z	50 Å to 1 mm
	Resolution x y	Down to 0.067 µm
	Resolution z	1 Å, 10 Å, 40 Å or 160 Å (for ranges 65 kÅ, 655 kÅ, 2620 kÅ and 1 mm respectively)
	Height accuracy z (95 % confidence)	~ 300 Å for the 65 kÅ range, ~ 0.16 µm for the intermediate ranges, and ~0.6 µm for the 1 mm range for well-defined steps that are easy to measure (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
Performance	Substrate size	Up to 8"
Performance	Substrate material allowed	In principle all materials

Height measurement accuracy

See above for the DektakXTA as the considerations for the Dektak 8 are the same, though the resolution and measurement repeatability is a tiny bit better for the Dektak 8 than for the DektakXTA.

Optical Profiler (Sensofar)

The PLu Neox 3D Optical Profiler (from Sensofar) has a dual-technology sensor head that combines confocal and interferometry 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), VSI (Vertical Scanning Interferometry) 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. Also the depth of focus is limited, especially for higher magnifications.

Analysis software: Free analysis software for visualizing and analyzing AFM and Optical profiler files (Sensofar) Gwyddion

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

Optical profiler (Sensofar) info page in LabManager

Process Information

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 (down to 4 µm)
Posibilities	Confocal and interferometric profiling and reflectometry	Standard microscope imaging Confocal imaging Confocal profiling PSI (Phase Shift Interferometry) VSI (Vertical Scanning Interferometry) 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

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	Down to 0.003µm
	Resolution z	1Å (@65kÅ), 10Å (@655 kÅ), 80 Å (@5240 kÅ), 160 Å (@1mm)
	Maximum sample thickness	100mm
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

@@ Line 93: / Line 93: @@
 ====Total uncertainty====
-[[File:Error probability distributions.png|Upright=1.5|alt=Four different probability distributions that contribute to the total error on the Dektak measurement for the 6.5 micron range. By far the widest distribution is the one from the error on the calibration standard, which is a Gaussian. The others are the non-Gaussian spread of the average measurement of the calibration standard height, which cuts off at the QC limits, the resolution, which is a very narrow uniform distribution, and the spread of measurement values for a given step being measured, which is a Gaussian whose width depends on the step in question.|right|thumb|The probability distributions of the main sources of error that are convoluted to create the total error on a Dektak measurement.]]
+[[File:Error probability distributions.png|upright=2|alt=Four different probability distributions that contribute to the total error on the Dektak measurement for the 6.5 micron range. By far the widest distribution is the one from the error on the calibration standard, which is a Gaussian. The others are the non-Gaussian spread of the average measurement of the calibration standard height, which cuts off at the QC limits, the resolution, which is a very narrow uniform distribution, and the spread of measurement values for a given step being measured, which is a Gaussian whose width depends on the step in question.|right|thumb|The probability distributions of the main sources of error that are convoluted to create the total error on a Dektak measurement.]]
 To estimate the accuracy of the Dektak's measurements we have to combine the error of the calibration with the error from the limit on the resolution and the scatter of repeated measurements. This is shown graphically on the right. You can see an uncertainty budget for the Dektak measurements here (made by Rebecca Ettlinger in 2020): [[Media:uncertainty budget dektaks.xlsx]]. It is based on the procedure described [https://www.nde-ed.org/GeneralResources/Uncertainty/Combined.htm here].