Comparison of Spectral Reflectance and Stylus Profilometry

Profilometry for Measuring Film Thickness SPECTRAL REFLECTANCE

Stylus profilometry is an easy-to-understand mechanical technique for measuring film thickness. It works by monitoring the height of a stylus as it drags across a step in the film (see figure to right). The primary advantage of stylus profilometry is that it can be used on all solid films, including opaque materials such as thick metal films.

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There are, however, disadvantages to stylus profilometry. Most importantly, a sample with a step must be formed to measure film thickness, and film steps thus formed are often not perfect (see figure). This, combined with calibration error and mechanical drift, can often lead to significant errors in measured thickness.

In contrast, Spectral Reflectance (SR) is a non-contact technique that requires no sample preparation to measure film thickness. Light that is reflected from the film is analyzed in about one second to determine both a film’s thickness and refractive index. Multiple-layer films can also be measured with SR.

A summary of the main advantages of each technique is listed below.

Thickness Measurement Range:
1nm - 3mm (non-metals)
0.5nm - 50nm (metals)*
2nm - 0.5mm (hard materials)
Measure Multiple Layers: Yes No
Measure Refractive Index: Yes No
Repeatability (500nm SiO2): 0.1nm 0.5nm
Measurement Speed: <1 second ~5 - 30 seconds
Sample Prep Required: No Yes
Moving Parts: No Yes
Price of Basic System: ~$10K ~$40K
*Film stack dependent