IEC TR 63258-2021 pdf free download – Nanotechnologies – A guideline for ellipsometry application to evaluate the thickness of nanoscale films.
4.2.3Sample handling
Ellipsometry is very sensitive to physical and chemical properties of the sample’s surface, so itis advisable to keep the sample in a clean and dry place after the preparation.Touching andscratching the surface should be avoided,because non-professional cleaning might affect thesurface state and therefore change the result.
4.2.4Experimental procedures
The general protocol of ellipsometry measurement is as follows.
– Step 1: Positioning of the sample on the stage.
– Step 2: Adjustment of the angle of incidence, height and tilt.
– Step 3: Measurement of the sample.
– Step 4: Data analysis.
– Step 5: Validation of analysis result.
NOTE This protocol is valid for non scattering and isotropic sample planes.
ln order to minimize the data variation, the following practical recommendations apply.
1) The ellipsometry measurement should be done at an angle of incidence close to the
Brewster’s angle of the substrate.
2) The ellipsometry measurement should be done over a measurement wavelength range as
wide as possible.For example, if there is absorption in the visible range, it needs to bemeasured including the near-infrared range.
3) The fitting analysis should be performed by changing the initial value of the film thickness
and the type of dispersion formula at the time of analysis. The comparison should be doneto confirm that equivalent results can be obtained. See Annex A.
5 Reporting data
– Documentation of the environment (temperature, humidity, cleanroom or normal ambient).
– Instrument used, including specification of the measurement programs and settings.
– Visual appearance of samples (to document any dust, cracks, moisture or other noticeable
visual items).
– Individual measurement values.
– Calculated averages if applicable.
6 Data analysis / interpretation of results
6.1 General
Ellipsometry measures changes in light polarization to evaluate the material properties,suchas film thickness and dielectric constants. In spectroscopic ellipsometry, the measured spectraare analysed by using the model fitting. Generally，in the case of nanomaterials，there istypically a surface oxide, roughness, and intermixing at the heterointerface of the sample.Thecommon procedure to deduce material properties from ellipsometry measurements is shown inFigure 2. Evaluations of nanomaterial characteristics by using the ellipsometry measurementsare shown in Annex B.
In the case of ellipsometry measurements, the intensities or polarization state ratios (complexrelative amplitude attenuation) are measured and the ellipsometric angles, that is ellipsometrictransfer quantities P and 4, are calculated.No direct access exists to the parameters in whichwe are usually interested, such as the dielectric functions (e), refractive indices (N).compositions and film thicknesses (d).
In general, for any planar structure on the substrate, P and 4 could be calculated if thicknessesand refractive indices are known.On the other hand, for the inverse case, even if and a areknown, d and N could not be directly calculated. ln order to obtain d and N for each layer,modelling is required.The modelling approach is based on the assumption that the measuredP(z.) and a(l.) change at each wavelength according to dispersion law.
Determination of material properties could be done by describing the fundamental response ofa material to an applied electromagnetic field.Each material has unique energy dependence ofdielectric function :. ln the visible-near UV range,dielectric response is determined almostentirely by the electronic properties of a material.
A mathematical description of the dielectric properties of a material,as well as its opticalproperties, as a function of energy (wavelength) is provided by dispersion law (formulae) andcan be divided into four categories:
1) empirical formulas;
2) classical dispersion models (harmonic oscillator treatment);
3) models based on quantum mechanical calculations;
4) point-by-point calculations.
The flow of spectroscopic ellipsometric data analysis procedure is shown in Figure 2.IEC TR 63258 pdf download