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.
|Spectral Reflectance||Stylus Profilometry|
|Thickness Measurement Range:||1nm - 3mm (non-metals)
0.5nm - 50nm (metals)*
|0.5mmm (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|
|Price of Basic System:||~10K||~40k|
|*film stack dependent|