Covalent’s director of optical characterization, Dr. Matt Wong, breaks down four of the most tactical profilometry tools: Chromatic Dispersion Profilometry (CDP / FRT), Laser Scanning Confocal Microscopy (LSCM), White Light Interferometry (WLI), and Wide Area Patterned / Structured Light. He’ll explain how images are generated on each system, and flag their unique benefits and limitations.
A lot of factors come into play when deciding what technique and instrument are best suited for topographical analysis. Resolution, magnification, stage area, and mode of imaging will each affect the ease, speed, and value of your data. This webinar dives into one of the most versatile families of imaging techniques: optical profilometry.
Watch this webinar to expand your toolkit for topographic imaging and find out how smooth operators tackle surface roughness characterization using optical profilometers.
This Webinar Will Answer:
- Why are optical profilometry techniques useful? What makes them advantageous over stylus profilometry options?
- What kinds of problems can optical profilometry methods help you solve?
- Beyond measuring surface roughness, how else are these techniques used?
- What are the key measurement principles and applications for each of the following:
- Laser Confocal Scanning Microscopy
- White Light Interferometry
- Wide Area Patterned / Structured Light
- Chromatic Dispersion Profilometry
Frequently Asked Questions
You noted the (x,y) and z resolutions for each of the techniques. what is the difference in the maximum z-range for each?
In the current configuration, the Zygo ZeGage Plus is ~10mm, the Keyence VK-X1100, is ~7mm, the Keyence VR-5200 is ~65mm, and the FRT MicroProf is ~3mm. This depended on the magnification and the working distance of the objective. Each can also be configured to achieve greater z range, but it depends on the application. These are the objective travel ranges, but in general practice we would not use the scopes to these limits as the measuring times would be very long.
Has any one used chromatic dispersion for 300mm wafer bow measurement?
Yes, our instrument in-house is limited by a 200mm stage. However, we have access to one that can measure a 300mm wafer.
Is there a handheld machine that can scan the datum with hard to access area?
It depends on the parameter of interest on the datum. If it is surface roughness, there are handheld stylus profilometers. If it is a reference datum for flatness, that would be near impossible.
Can you comment on the difficulties to measure transparent surfaces when sub micron z height information is desired?
If ALD or thin deposited coating can be applied to the surface, it is possible to create a uniform coating that is reflective enough for the optical instruments. Also, depending on the optical properties, the Keyence VK-X1100, Zygo ZeGage, or FRT Chromatic Dispersion can sometimes register a signal from transparent substrates.
Please re-iterate differences between laser confocal and traditional confocal. What is the advantage of using a laser?
For the VK-X1100, the light source is a 404nm laser. The shorter wavelength of light in comparison to white light for example will have a smaller spot size.
Can these methods be used to measure thin film thicknesses?
Yes, it is possible but you will likely need to know the refractive indices of the material. The Keyence VK-X1100 and FRT Chromatic Dispersion can be used to measure thin film thicknesses. The basic principle used is that there is a measurable signal off both the front and back surfaces of the thin film. Our experience with using these techniques for thin film thickness is mixed, however. The film must be transparent, first of all. Beyond that, it generally only works well for homogenous thin films with very planar interfaces. The accuracy and resolution is not as good as ellipsometry, which is a much better instrument/technique to use.
What is the max lateral resolution for WLI? I saw 160nm for Zygo, which i believe is below light diffraction limit, is it true?
160nm is the pixel resolution of the CCD for the highest magnification objective we have on the Zygo ZeGage Plus. Resolution is determined by the optical system with respect to the wavelength of the light used and the NA of the final lens. 160 nm (1600 Angstroms) is the field of view divided by the pixel size and is not the actual optical lateral resolution. This type of calculation assumes an isolated feature in a wide plane using phase contrast. For a more detailed explanation:
Speakers:
Matt Wong
PhD, Director of Optical Characterization at Covalent Metrology
