Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1989-03-17
1991-07-23
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356357, G01N 2186
Patent
active
050346172
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
The present invention relates to a method and an apparatus for measuring the refractive index and thickness of a dielectric thin film formed on a substrate.
2. Background Art
In connection with the semiconductor related techniques or the like, it has become very important to develop an art for non-destructively measuring the refractive index and thickness of a dielectric thin film formed on a substrate.
In the state of art, a method called "LASER VAMFO" (LASER USING VARIABLE ANGLE MONOCHROMATIC FRINGE OBSERVATION) is known as method for measuring the refractive index and thickness of a thin film aiming to heighten the accuracy of the measurement (see REFRACTIVE INDEX DISPERSION IN SEMICONDUCTOR RELATED THIN FILMS: IBM J. RES. DEVELOP. MAY 1973). However, this known method has problems in that a large scale apparatus is necessitated for carrying out the method since a monochrometer must be used for the measurement and that it takes a relatively long time for the measurement.
SUMMARY OF THE INVENTION
The present invention was made considering the above mentioned problems of the state of the art. Therefore, it is an object of the present invention to provide a novel method and apparatus for measuring the refractive index and thickness of a dielectric thin film formed on a substrate wherein it becomes possible to carry out the measurement easily and accurately.
In accordance with the present invention, there is provided a method for measuring the refractive index of a dielectric thin film formed on a substrate, the method comprising the following four steps from a first step to a fourth step.
The first step is to irradiate a thin film on a substrate with a monochromatic light having a wavelength .lambda., changing an incident angle thereof so as to measure change of energy reflection ratio in response to the change of the incident angle and detect two incident angles .theta.1 and .theta.2 which correspond to an arbitrary two of the extreme values of the energy reflection ratio change, respectively. The second step is to irradiate the thin film on the sutstrate with a monochromatic light having a wavelength .lambda.', changing an incident angle thereof so as to measure change of energy reflection ratio, i.e., reflectance in response to the change of the incident angle and detect one incident angle .theta.3 which corresponds to on arbitrary one of the extreme value of the energy change. The third step is to calculate the refractive indices and thicknesses of the thin film, on the basis of the incident angle values -.theta.1 and .theta.2, with respect to a series of the interference degree numbers being used as parameters of the calculation. The fourth step is to determine the thickness of the thin film and the refractive index thereof with respect to the light having a wavelength .lambda. and the light having a wavelength .lambda.', respectively, on the basis of the incident angle value .theta.3 and the values of the refractive indices and thicknesses calculated in the third step. The sequence of the steps may be in the order of the above mentioned steps from the first step to the fourth step. Or otherwise, the order of the second step and the third step may be exchanged for each other.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is an explanatory view for explaining an embodiment of the present invention;
FIG. 2 is an explanatory view for explaining another embodiment of the present invention; and
FIG. 3 is an explanatory view for explaining the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The principle of the present invention will now be explained hereinafter with respect to an actual example of the invention. FIG. 3 represents a dielectric thin film 0 coated on a substrate 1 having a refractive index n.sub.s in a state in which a light irradiates the thin film at an incident angle .theta. and the light is reflected by the thin film.
Objects which are to be measured are refractive index n.sub.f and thickness d of the thin film 0.
When the incident angle
REFERENCES:
patent: 3601492 (1971-08-01), Reichard
patent: 4498772 (1985-02-01), Jastrzebski et al.
patent: 4625114 (1986-11-01), Bosacchi et al.
patent: 4707611 (1987-11-01), Southwell
Raif et al., "Rapid Nondestructive Method for Measuring the Refractive Index and Thickness of Thin Dielectric Films" Aug. 1972, pp. 48-50.
Warnecke et al., IBM J. Res. Develop, pp. 256-262 "Refractive Index Dispersion in Semiconductor-Related Thin Films".
Nelms David C.
Ricoh & Company, Ltd.
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