Null ellipsometer

Manual null ellipsometry is accurate but infrequently done, due to the length of time needed to acquire sufficient data for any meaningffil materials analysis. Automated null ellipsometers are used, for example, in the infrared, but are still slow. Numerous versions of last automated ellipsometers have been built. Examples... 

Ellipsometry. Layer thickness of GPS, PS, FPS and FSI on the flat silica wafers was evaluated at k = 633 nm and an angle of incidence of 70° with a SENTECH SE-402 microfocus null ellipsometer (lateral resolution is defined by the beam spot of about 20 pm). The measurements were performed for each sample after each step of modification to use the data of the previous step as a reference for the simulation of ellipsometric data. Initially, the thickness of the native SiC>2 layer (usually 1.4 0.2nm) is calculated at refractive indices n = 3.858 — iO.Ol8 and n = 1.4598... 

There are two basic kinds of ellipsometer nulling and intensity modulating. The nulling ellipsometer is historically the first to be invented and was the only kind available until the late sixties. The working principle is to... 

Ellipsometry, Table 1 Zone relations for a PCSA null ellipsometer. P is the polarizer angle, C is the compensator angle, and A is the analyzer angle... 

As the null ellipsometer is rather tedious to operate, dynamic ellipsometers have been developed. An example is that the analyzer is rotating continuously in the PCSA cMifiguration. A Foirrier analysis of the intensity signal gives the eflipsometer angles A and T if the position of the compensator C and polarizer P are known. 

The primary data obtained from a null ellipsometer are O and A, which are easily obtained from the position of the polarizer, compensator and analyser. These quantities are related to the R and R coefficients through the following ... 

Figure 18-1. Geometry of standard null ellipsometer (a) and rotating analyzer ellipsometer (b). L, P, C, A, D and S represent the laser, polarizer, compensator, analyzer, detector and sample, respectively (after Jenkins, 1999).

Historically, the most important type of instrument has been the classical null ellipsometer, although today this has been superseded by the automatic spectroscopic ellipsometer (SE), which can take measurements over a wide range of... 

Null ellipsometer with phase modulation. Opt Express, 12(2004) 6040-6045. 

Welin-Klinstroem et al used a null ellipsometer equipped with an automatic sample scanning device for studies of adsorption and desorption of fibrinogen and IgG at the liquid/solid interface on surface wettability gradients on silicon wafers. To follow the processes along the wettability gradient, off-null ellipsometry was used. The kinetics of adsorption and nonionic-surfactant-induced desorption varied considerably between fibrinogen and IgG. In the hydrophilic region, veiy little protein desorption was seen when a nonionic surfactant was used. 

To overcome this difficulty, several methods are proposed for obtaining the three unknowns without assumptions. First, one has to measure reflectance, R, in addition to F and A. " During the oxide film formation, the reflectance change, AR, is measured with the changes of F and A. Since lo in Eq. (18) corresponds to the reflection intensity from the sample surface, the photometric ellipsometer can easily be modified to the simultaneous measurement of reflectance. For the nulling ellipsometer, however, it is difficult to simultaneously measure the reflectance with F and A. From the three parameters of F, A, and R, one can calculate the three unknowns, h, and d with help of computer program. 

The angles yj and A are the traditional ellipsometry angles, and are the naturally measured parameters for nulling ellipsometers (see below). The matrix M simplifies considerably when the sample is isotropic M is block-diagonal, with eight elements equal to 0, and... 

The oldest and most common type of ellipsometer is the nulling ellipsometer, shown schematically in Figure 4A. The light source for a modern nulling ellipsometer is usually a small laser, but other monochromatic sources can also be used. The PSG is a polarizer-retarder pair, and the PSD is a linear... 

The nulling ellipsometer is one of the simplest ellipsometers and it is capable of very accurate measurements with proper calibration. However, it normally uses a single-wavelength source and it is not easily made spectroscopic. Moreover, measurement times are slow, so this type of instrument is not useful for spectroscopic ellipsometry or for fast time-resolved measurements. 

Figure 4 Schematic diagrams of three ellipsometers in common use. (A) The nulling ellipsometer, which normally uses monochromatic light. (B) The rotating analyser ellipsometer. (C) The polarization modulation ellipsometer.

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