US 6,485,872 B1Granted

Method and apparatus for measuring the composition and other properties of thin films utilizing infrared radiation

AssigneeMKS Instruments, Inc.

InventorsPeter A. Rosenthal, Sylvie Charpenay, Victor A. Yakovlev

Life of this patent

Estimating the term…

Loading patent…

Abstract

The composition, free carrier concentrations, and other properties of thin films and graded layers embedded in film stack structures are measured by the method of the invention, which is based upon the application of two novel algorithms to extract the composition of a measured layer independently of the confounding effects of additional layers, and which can be effected even when calibration samples are not available with the same layered structure as the samples to be measured. The method uses sample model-based analysis algorithms to extract the dielectric function of the layer to be measured, combined with model-based analysis to relate the composition of the layer to its dielectric function. Because the dielectric function of a layer is a bulk spectral property of the material, and is inherently independent of the thickness of the layer, the composition of the material can be determined more easily and unambiguously from its dielectric function than from raw spectral quantities such as reflectance, ellipsometry, and transmittance, which spectral data are influenced strongly by the optical properties of the overlayers, the underlayers, and the substrate material. The method enables the measurement of layer composition with significantly fewer calibration samples, it allows product wafer analysis with structures that are significantly more complicated than the calibration samples, and it is intrinsically more reliable for transferring calibrations between tools even when the measurement geometry varies from tool-to-tool.

Claims32

Dependent claims

A method for estimating at least one parameter of a sample, determined from the dielectric function of a material of which at least one layer of the sample consists, comprising the steps:

(a) providing a sample comprised of at least one layer and having a substantially specular surface;
(b) defining an optical model of said sample along a direction perpendicular to said surface and based upon reflectance values, said at least one layer being defined in said model by a thickness value and, for each of a multiplicity of wavelengths in the infrared spectral region, by a dielectric function value;
(c) providing a traing set consisting of measured values of said at least one parameter and an associated dielectric function, said measured values being obtained from a multiplicity of samples selected to represent a range of values of said at least one parameter;
(d) determining from said traing set a predictive mathematical relationship between said at least one parameter and said associated dielectric function, so as to enable prediction of said at least one parameter from input values of dielectric function;
(e) irradiating said specular surface of said sample with infrared radiation, including said multiplicity of wavelengths, and obtaining a measured reflectance spectrum composed of values obtained over said multiplicity of wavelengths;
(f) simulating a reflectance spectrum from said optical model at said multiplicity of wavelengths using values of said dielectric function calculated from assumed dielectric function descriptors and a value of said thickness of said at least one layer, and computing said various values of said dielectric function descriptors so as to minimize the difference between said simulated reflectance spectrum and said measured reflectance spectrum, thereby determining an optimized dielectric function value for said at least one layer at said multiplicity of wavelengths;
and
(g) calculating the value of said at least one parameter using said optimized dielectric function value and said predictive mathematical relationship.

5 more elements

Apparatus for estimating at least one parameter of a sample, determined from the dielectric function of a material of which at least one layer of the sample consists, comprising:

means for irradiating a surface of a sample with infrared radiation, including each of multiplicity of wavelengths in the infrared spectral region, and for obtaining a measured reflectance spectrum composed of values obtained over said multiplicity of wavelengths;
and electronic data processing means, said data processing means being programmed to:
(a) define an optical model of the sample along a direction perpendicular to a surface thereof and based upon reflectance values, the at least one layer of the sample being defined in said model by a thickness value and, for each of a multiplicity of wavelengths in said infrared spectral region, by a dielectric function value;
(b) provide a training set consisting of measured values of said at least one parameter and an associated dielectric function, said measured values being obtained from a multiplicity of samples selected to represent a range of values of said at least one parameter;
(c) determine from said training set a predictive mathematical relationship between said at least one parameter and said associated dielectric function, so as to enable prediction of said at least one parameter from input values of dielectric function;
(d) simulate a reflectance spectrum from said optical model at said multiplicity of wavelengths using values of said dielectric function calculated from assumed dielectric function descriptors and a value of said thickness of said at least one layer, and to compute the values of said dielectric function descriptors so as to minimize the difference between said simulated reflectance spectrum and said measured reflectance spectrum, thereby determining an optimized dielectric function value for said at least one layer at said multiplicity of wavelengths;
and
(e) calculate the value of said at least one parameter using said optimized dielectric function value and said predictive mathematical relationship.

5 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/718,602Filed 22 Nov 2000 · us provisional application
Priority: 3 Dec 1999
Granted: 26 Nov 2002
Term ends: Not estimatedThe source records don’t support an estimate.

Classification9 codes

G01N 21/8422
Systems specially adapted for particular applications: investigating thin films, e.g. matrix isolation method
G01B 11/0625
Of coating: with measurement of absorption or reflection
G01N 21/3563
Using infrared light: for analysing solids; Preparation of samples therefor
G01N 21/35
Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry:…