A spectroscopic ellipsometry system directs a near infra-red (NIR) probe
beam at a test sample to allow metrology to be performed on vertical
structures within the test sample. Because silicon is relatively
transparent to NIR light, structural information can be determined from
the polarization effects produced by the test sample, in a manner similar
to that used with IR spectroscopic ellipsometry systems. However, unlike
IR light, which requires delicate and costly optical and measurement
components (e.g., vibration-sensitive Fourier transform sensors), NIR
light can be directed and detected using more robust and inexpensive
components (e.g., array-based detectors), thereby making a NIR
spectroscopic ellipsometry system much more affordable and usable than
conventional IR spectroscopic ellipsometry systems.