Comparison of Spectroscopic Ellipsometry and Spectral Reflectance: Thickness Measurement Guide

Both SpectroscopicEllipsometry(SE) and Spectral Reflectance (SR) analyze reflected light to determine the thickness andrefractive indexof dielectrics, semiconductors, and thinmetal films. The primary difference between the ellipsometry and reflectometery measurement techniques is that SE uses light reflected off the film at a low incident angle, while SR uses light that is reflected perpendicular (normal) to the film.

This difference in spectroscopic ellipsometery's incident-light angle leads to differences in the cost, complexity, and capabilities of the two measurement techniques. Since an ellipsometer’s light is incident at an angle, it must analyze the polarization of the reflected light, as well as its intensity, which gives it better capabilities for measuring very thin and complicated film stacks. Analyzing the polarization, however, also means that expensive, precision-moving optical components are required.

By using light that is perpendicular to the film, SR can ignore polarization effects (since most films are rotationally symmetric). Thus, SR can be realized without any moving components, which results in much simpler and lower-cost instruments. Spectral reflectance systems can also easily include transmittance analysis for even greater power.

指的是下面的表格,光谱反射率is usually the preferred thickness measurement technique for films greater than 10um, while spectroscopic ellipsometry is generally preferred for films thinner than 10nm thick. Between these two thicknesses, there are many applications where both techniques can be used. When this is the case, spectral reflectance is often chosen due to its speed, simplicity, and low cost.

Spectral Reflectance Spectroscopic Ellipsometry
Thickness Measurement Range: 1nm - 3mm (non-metals)
0.5nm - 50nm (metals)*
1nm - 1mm (non-metals)
0.5nm - 50nm (metals)
Thickness Required for Index Measurement: >20nm (non-metals)
5nm - 50nm (metals)
>5nm (non-metals)
>0.5nm (metals)
Measurement Speed: ~0.1 - 5 seconds per location ~1 - 300 seconds per location
Special Training: No Required for most applications
Moving Parts: No Moving precision optics
Price of Basic System: ~15K ~55k
*film stack dependent