ABSTRACT
Basically, ellipsometry is an optical measurement technique that characterizes light refl ection (or transmission) from samples [1-6]. Specifi cally, ellipsometry measures the change in polarized light upon light refl ection on a sample (or light transmission by a sample). Table 27.1 summarizes the features of ellipsometry. In principle, ellipsometry measures the two values (y, D) that represent the amplitude ratio y and phase difference D between light waves known as p-and s-polarized light waves (see Figure 27.2). In spectroscopic ellipsometry, (y, D) spectra are measured by changing the wavelength of light in the ultraviolet (UV)/visible region or infrared region [1,4-6]. The ellipsometry technique has also been applied as a tool for real-time monitoring of fi lm processing because light is employed as the probe. Unlike refl ectance/transmittance measurement, ellipsometry allows the direct measurement of the refractive index n and extinction coeffi - cient k, which are also referred to as optical constants. From the two values (n, k), the complex refractive index defi ned by ( 1)N n ik i≡ − = − is determined. The complex dielectric constant e ≡ e1 − ie2 and absorption coeffi cient a can also be obtained from N using the simple relations expressed by
2 2 21 2 , 2 ( ) ,n k nk N= − = =e e e (27.1)
4 /k= π ,a l
(27.2)
where l is the wavelength of light. When samples have thin fi lm structures, the fi lm thicknesses of the samples can be estimated. Moreover, from optical constants and fi lm thicknesses obtained, the refl ectance R and transmittance T are calculated.
