Ellipsometer

Among the characterization processes of the materials and the device manufacturing process, the optic spectroscopy, specially, ellipsometric spectroscopy: is a techinque for information obtaining of the thin films used in the device manufacturing at the Microtechnologies management of CIDESI Queretaro.

Fig. 1. Ellipsometer of the CIDESI-Queretaro clean room, it is ideal for the study of semiconductors due its spectral range that goes from 250nm to 1100nm.

The ellipsometric spectroscopy is a non-destructive technique that consists of the measurement of the change in the light polarization it suffers when it is reflected on a surface, specially on thin films of one or more layers. The information that is obtained of the experiment is used to know the material properties and their quality (Figure 2). The optical parameters measured are Ψ and Δ.

Fig. 2. Adjust of the PSI spectra obtained by ellipsometry of the model air/silicon oxide/silicon.

Among the most widely used and characterized materials by ellipsometric spectroscopy crystalline and amorphous materials are found, whether dielectrics, semiconductors or conductors. In the ellipsometer located in the CIDESI Queretaro clean room, Figure 3, Measurements can be obtained changing the angle of the incident ace and the wavelenght, which may go from the visible electromagnetic spectra to close infrared.

Fig. 3. User performing a data analysis of the system air/silicon oxide/silicon by ellipsometer measurements. The thin film thickness of the materials is one of the parameters of frequent interest in the electronic device manufacturing, in this case, the film under study is silicon oxide.

For the obtaining of the parameters by ellipsometry such as thicknesses, optical constants, and volume fractions of the studied materials, and that depend on the material composition and the amorphous or crystalline structure. It is necessary to carry on a model of the sample that is being analyzed. The models used could be a single film or a set of thin films. It is important to mention that the representative model of the sample is fed with obtained data by different characterization techniques as AFM, XRD, Raman and some other complexities as stoichoimetric composition of the sample.

In order to establish the optical constants in a wide range of wavelenghts, it is necessary to use a spectral ellipsometer, which allows us to vary the wavelnght and the angles of the incident light beam, because of this, ellipsometry is known as one of the most important techinques for the study of optical properties of the materials.

Fig 4. Interaction of light with the study sample.

The most analyzed materials by this technique are mainly silicon oxides, nonetheless, for the study of dielectrical material films, semi-conductors and conductors there are very well studied models that allow to obtain the optical parameters through regresion analysis of many layer films.

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