Browse Prior Art Database

Angle of Incidence Calibration With a Tapered Film for Ellipsometers

IP.com Disclosure Number: IPCOM000037062D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 4 page(s) / 49K

Publishing Venue

IBM

Related People

Ray, M: AUTHOR

Abstract

Angles of incidence on an ellipsometer are more accurately measured utilizing a varying thickness or tapered film sample to calibrate the instrument. Error margins for the calibrated angle of incidence are also provided.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 51% of the total text.

Page 1 of 4

Angle of Incidence Calibration With a Tapered Film for Ellipsometers

Angles of incidence on an ellipsometer are more accurately measured utilizing a varying thickness or tapered film sample to calibrate the instrument. Error margins for the calibrated angle of incidence are also provided.

A new method of calibrating angles of incidence on ellipsometers is superior to other means, e.g., prisms and mechanical techniques. The new technique also facilitates accurate angle of incidence measurements for multifilm structures. A multiple measurement technique is utilized to determine angle of incidence as a parameter. This technique is explained in many publications and textbooks [*].

A varying thickness or tapered film on a substrate can be purchased from optic suppliers, produced in a wet etch bath process, or fabricated on polishing equipment. The optical properties for the film and substrate are selected in order to determine the angle of incidence with the least uncertainty of determination. Uniform properties are required to achieve an accurate determination of angles of incidence. The thickness range should be from: 0 to g/(2Re{ N2 - sin 2 d}),

where g is the wavelength, N is the complex index for the film, and d is the angle of incidence.

The equation of ellipsometry for the film model is written as follows: tan eiW = f (n, k, ns ks d, d, G), where and W are the ellipsometric parameters, n and k are the refractive index and absorption coefficient for the film, ns and ks are the index and coefficient for the substrate, and d is the film thickness. Since the equation cannot be analytically inverted to solve for optical parameters, it is required to solve it by iterative methods. It can determine two optical or geometrical parameters with a measurement which yields and W. An ellipsometer has some control-varying parameters, such as angle of incidence, wavelength, thickness, and ambient index. An independent equation can be obtained when another measurement is taken with a new value of a control parameter. When one of the control parameters varies, measurements become independent of each other. This means that additional optical or geometrical parameters can be solved when additional independent measurements are taken, and this is called multiple measurement.

Some measurements are not totally independent because they are correlated with each other; therefore, all of the correlating parameters cannot be determined simultaneously. Correlating factors include optical properties, layered structures in the sample, and angle of incidence. A test on the independence of multiple measurements can be made by observing a correlation matrix to describe the correlation between parameters. The uncertainties of observed parameters can be tested with a sensitivity matrix with respect to the uncertainty of ellipsometric parameters.

Let a number of measurements be taken at each of N points along a sample with tapered film. See Table 1. There are 2N ind...