DUV Broadband Spectroscopic Ellipsometer Based on All-Reflective Focusing Optical System

Ellipsometer is a powerful tool to determine the thickness and optical properties of thin films. Usually, traditional spectroscopic ellipsometer employing Tran missive lenses for beam collimation and focusing are only accurate over a limited spectral range due to high chromatic aberration and low transmittance. In this paper, we describe a ellipsometer that uses all-reflective focusing optical components to extend the wavelength range from Deep-UV 200 nm to near-infrared 1000 nm and focuses the collimated beam into a small spot size (36×49 μm). This focused beam spectroscopic ellipsometer includes four off-axis parabolic mirrors and two flat mirrors, in which flat mirrors are used to change the propagation direction and compensate the polarization changes caused by off-axis parabolic mirrors to obliquely focus on the sample surface. By careful construction, alignment, and calibration of the rotating-compensator ellipsometer, we measured the thickness of SiO2 thin film on Si substrate with a maximum absolute error of 2.15 Å, in the thickness range of 30 to 130 Å.