Using Non-Contact Profilometry for Measuring 500 nm Glass Step Height

Currently, surface characterization topics are undergoing intense study. The surfaces of materials are important as they are the regions where chemical and physical interactions between the environment and material occur.

Therefore, the ability to image the surface with high resolution has been desirable because it allows scientists to observe the smallest surface details. Common surface imaging data includes roughness, vertical dimensions, lateral dimensions and topography. Identifying the spacing and step height and the load bearing surface of microstructures as well as defects on the surface are applications that can be obtained by surface imaging. However, not all surface imaging techniques are created equal.

Nanovea’s Non-Contact Profilometry Compared to AFM Technology

Mapping and characterizing surface details can be done at nearly an atomic level with the angstrom-level vertical resolution of Atomic Force Microscopy. Nanovea’s Profilometers have many significant benefits over AFM and are designed to reach nanometer level resolution. The ease of use of the Nanovea system minimizes sample preparation and setup time, its non-contact optical technology does not disturb the surface during measurements, its ability to measure all types of samples and much shorter scanning times are all factors that make the Nanovea system superior to AFMs.

Nanovea’s profilometers provide a system for almost any surface measurement application with the addition of the large XY scan areas and the z-heights possible. This study has investigated the measurement of low feature heights in order to showcase Nanovea’s resolution.

Measurement Objective

The step height of 500 nm was measured using a PS1 point sensor with a NIST traceable quartz step height standard. The HS2000 model was used for its air-bearing stage movement and zero-noise properties.

Picture of the test setup on the HS2000

Figure 1. Picture of the test setup on the HS2000

Measurement setup
Instrument Nanovea HS2000 - Standard Speed
Optical Sensor PS1 Lens (110 µm Z-Range)
Scan Size (mm) 3 mm x 1.5 mm
Step Size (µm) 0.9 µm x 4 µm
2D Profile Scan Time (h:m:s) 00:00:04
3D Area Scan Time (h:m:s) 01:03:10

Results

Step Height

The height map and 3D view of the scanned area can be seen below. After being scanned by Nanovea’s 3D Non-Contact Profilometer, the step height of 500 nm (which is not discernible to the eye), can be demonstrated distinctly. The step height measurement of 502.4 nm is almost exactly matched to the etched step height of 500 m. In total, 107 profiles were extracted from the area scan conducted and the step height was averaged to 502.5 ± 12.0 nm over the full 3D scan.

Height Map (left) and 3D step height analysis (right)

Figure 2. Height Map (left) and 3D step height analysis (right)

3D view of step height standard

Figure 2. 3D view of step height standard

Step height analysis of 107 profiles

Information
T-axis Y-Axis Profile = 107.0
Parameter display mode Statistical results across the series

Parameters Stat. Step 1 Unit
Mean height Mean 502.5 nm
Std dev 10.95 nm
Range 55.48 nm

Figure 3. Step height analysis of 107 profiles

Noise Level

The raw extracted profile from the area scans above can be seen below. This is the amount of noise generated when measuring the quartz step height standard. When not hidden in the noise, differences in height are easily discernible. Nanovea’s profilometer is not limited to 500 nm of height, it can measure features down to and below 10 nm and this is shown by the low noise observed.

Conclusion

By scanning a step height standard of 500 nm, the Nanovea 3D Non-Contact Profilometer demonstrates its high vertical resolution abilities. The step height can be clearly seen and the obtained value of 502.5 ± 12.0 nm demonstrates high accuracy. To display the amount of noise generated by the instrument, profile scans were taken. It is easy to discern differences in heights above the noise profile. This demonstrates that whilst a 500 nm step height was measured, higher vertical resolutions can also be achieved.

Nanovea’s chromatic confocal technology combined with the HS2000’s zero noise stages provide a system with nearly angstrom-level resolution. Compared to other high-resolution surface metrology instruments (e.g. AFMs) it is superior in all other practical aspects.

Therefore, unless angstrom level vertical resolution is a requirement, Nanovea’s Profilometers are the ideal instruments for all surface imaging due to their fast scan times, ease of use, ability to measure all types of materials and surfaces and non-contact technique.

Nanovea.

This information has been sourced, reviewed and adapted from materials provided by Nanovea.

For more information on this source, please visit Nanovea.

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