Foreword

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This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings, in collaboration with ISO/TC 35, Paints and varnishes, SC 9, General test methods for paints and varnishes.

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Introduction

The ellipsometry measuring method is a phase-sensitive reflection technique using polarized light in the optical far-field. Ellipsometry has been established as a non-invasive measuring method in the field of semiconductor technology, in particular the field of integrated production. The method was originally conceived as a single-wavelength measuring method, then as a multiple-wavelength and later as a spectroscopic measuring method.

Ellipsometry can be used to determine optical or dielectric constants of any material as well as the layer thicknesses of at least semi-transparent layers or layer systems. Ellipsometry is an indirect measuring method, the analysis of which is based on model optimization. The measurands, which differ according to the procedural principle, are converted into the ellipsometric transfer quantities Ψ (psi, amplitude information) and Δ (delta, phase information). The physical target quantities of interest (optical or dielectric constants, layer thicknesses) are determined based on these measurands by means of a parameterized fit.

Ellipsometry shows a high precision regarding the ellipsometric transfer quantities Ψ and Δ, which can be equivalent to a layer thickness sensitivity of 0,1 nm for ideal layer substrate systems. As a result, the measuring method can detect even the slightest discrepancies in surface characteristics. This is closely linked to the homogeneity and the isotropy of the material surface. In order to achieve high precision, carrying out measurements at the exact same measuring point is a prerequisite for inhomogeneous materials. The same applies to the orientation of the incident plane relative to the material surface for anisotropic materials.

For the bulk material model, a fitting procedure is optional since exactly two independent parameters can be determined per measurement (per wavelength and at one angle of incidence) using the formula system consisting of formulae for p- and s-polarization. This, moreover, is the only case where a determination of target figures (optical or dielectric constants) can be carried out analytically.

1 Scope

This document specifies the process for determining the optical or dielectric constants by means of ellipsometric measurements and their analysis based on the bulk material model.

If the assumptions of the bulk material model are strictly met, it is possible to determine the optical constants (refractive index n and extinction coefficient k) or the dielectric constants (real part ε₁ and imaginary part ε₂) of the material directly. Alternatively, optical (<n> and <k>) or dielectric (<ε₁> and <ε₂>) pseudo constants are determined, which depend on the measurement angle of incidence φ. The degree of consistency of the pseudo constants in the relevant spectral range, determined from measurements at different angles of incidence, represents a necessary prerequisite for the validity or quality of the bulk material model.

2 Normative references

3 Terms, definitions and symbols

3.1 Terms and definitions

3.2 Symbols and abbreviated terms

4 Bulk material model

4.1 Optical path

4.2 Assumptions

4.3 Special characteristics of the bulk material model

4.4 Validation

4.5 Measurement uncertainty

5 Test report

Bibliography