Optics: measuring and testing – By polarized light examination – Of surface reflection
Patent
1992-09-22
1995-08-01
Pham, Hoa Q.
Optics: measuring and testing
By polarized light examination
Of surface reflection
356367, G01B 1106
Patent
active
054384150
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an ellipsometer for measuring the thickness of thin films accurately, and more particularly to a compact, highly accurate ellipsometer with a reduced number of optical parts of the light sensing section, the parts being fixed, and a method of controlling a coating thickness therewith.
BACKGROUND ART
Ellipsometry is used to measure the thickness of thin films of, for example, several 100 nm or less. In this method, what is measure is a change in the polarized state when light is reflected by the surface of a specimen such as a thin film, or the ratio .rho. of the reflectivity Rp of a parallel component (P component) to the plane of incidence of electric-field vector to the reflectivity Rs of a perpendicular component (S component), expressed as equation (1). According to an already known specific relationship between polarization reflectivity ratio .rho. and film thickness d, the thickness d of the thin film is calculated as:
The polarization reflectivity ratio .rho. is expressed by two ellipsoparameters, amplitude ratio .psi. and phase difference .DELTA., as shown in equation (1). These two ellipsoparameters are physical quantities obtained by measurement.
To compute these ellipsoparameters .psi. and .DELTA., an 3-channel ellipsometer with no moving parts as shown in FIG. 18 has been developed, as disclosed in Published Unexamined Japanese Patent Application No. 1-28509.
The light of a single wavelength emitted from a light source 1 made up of a laser light source is converted into linearly polarized light by a polarizer 2 and is directed to the surface of a specimen 3, the object to be measured, at an incident angle of .phi.. At the specimen surface 3, the plane of incidence is parallel to the paper on which the figure is drawn. It is assumed that the direction parallel to the paper is direction P and the direction perpendicular to the paper is direction S. The reflected light from the specimen surface 3 is split into three light beams by three nonpolarization beam splitters 4a, 4b, and 4c.
A first light passing through two beam splitters 4a and 4b is directed to a first photodetector 7a via a first analyzer 5a and a first condenser lens 6a. The first photodetector 7a converts the intensity I1 of the first light into an electric signal. Similarly, a second light reflected by beam splitter 4b after passing through beam splitter 4a is directed to a second photodetector 7b via a second analyzer 5b and a second condenser lens 6b. The second photodetector 7b converts the intensity I2 of the second light into an electric signal. A third light passing through beam splitter 4c after being reflected by beam splitter 4a is directed to a third photodetector 7c via a third analyzer 5c and a third condenser lens 6c. The third photodetector 7c converts the intensity I3 of the third light into an electric signal.
The analyzers 5a to 5c pass only optical components oscillating in a preset direction. The polarizing direction of the first analyzer 5a is set to the reference direction (with an angle of 0.degree.); that of the second analyzer 5b is set to a direction inclined +45.degree. with respect to the reference direction; and that of the third analyzer 5c is set to a direction inclined -45.degree. with respect to the reference direction. The reference direction is determined in such a way that a direction (direction P) parallel to the plane of incidence on the specimen surface 3 has an angle of 0.degree., as shown by arrow "a" when viewed from the photodetector 7a.
Therefore, when the light reflected by the specimen surface 3 is polarized elliptically as shown in FIG. 19, the first light intensity I1 at the first photodetector 7a indicates an amplitude of the orthogonal projection of the elliptically polarized light on the abscissa (in the direction with an angle of 0.degree.); the second light intensity I2 at the second photodetector 7b represents an amplitude of the orthogonal projection of the elliptically polarized light on a line inclined +45.degree.; and the third lig
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Kazama Akira
Nomura Shuichiro
Oshige Takahiko
Takayama Takamitsu
Yamada Takeo
NKK Corporation
Pham Hoa Q.
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