JPS612028A - Method for detecting phase difference between rotary analyser and rotary phase detecting element in elliptic polarizer - Google Patents

Abstract

PURPOSE:To detect simply and accurately a phase difference by using a substance having prescribed relation between its refractive index and a light incident angle. CONSTITUTION:The reflected light 12 of light projected to the surface of a sample 9 with a previously fixed incident angle theta is made incident upon the rotary analyser 2 formed coaxially with the rotary phase detecting element 3 and light projected from the analyser 2 is received by a photodetector 4. A substance having the relation of n=tan theta between its refractive index (n) and a light incident angle theta is used as a sample 9. The polarizing state of the reflected light due to the sample 9 is determined in accordance with the angle incident upon the sample 9, the thickness of the sample 9 and an optical constant. Consequently, the phase difference between the analyser 2 and the element 3 can be easily detected on the basis of the time axial changing state of an output signal from the photodetector 4 which is obtained on the basis of an output signal from the element 3 formed coaxially with the analyser 2.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an ellipsometer using a rotating analyzer.

An ellipsometer that measures the rate without destroying the sample.
By observing changes in the state of polarization of reflected light from the sample, it is possible to measure the optical constants of the sample and the thickness of extremely thin single-layer films with high precision. It is well known that the ellipsometer is used for purposes such as measuring the film thickness of a sample, and the ellipsometer using a rotating analyzer is also used for automatically measuring the film thickness of a sample. is often used.

Now, the reflected light of the light projected onto the sample surface at a predetermined incident angle is made to enter a rotating analyzer such as that provided coaxially with the rotating phase detection element.

In an elliptical polarimeter that is configured to receive light emitted from the rotating analyzer with a photodetector, the angle of incidence of the light on the sample surface must be made to accurately match the predetermined angle described above. For optical systems where the angle of incidence is fixed, the phase difference between the rotating analyzer and the rotating phase detection element must be known accurately.

Until now, there was no known method for measuring the phase difference between the rotating analyzer and the rotating phase detection element installed in the optical system, so a conventional elliptical polarimeter was used to detect the rotating analyzer and rotating phase detection element. To detect the phase difference with the element, light from a light source, that is, linearly polarized light whose polarization state is known, is used.
The phase difference between the rotating analyzer and the rotating phase detection element is detected by making light directly enter the rotating analyzer without passing through a reflective surface.

(Problem to be solved by the invention) However, by making light from a laser that emits linearly polarized light whose polarization state is known directly enter the rotating analyzer without going through a reflective surface, it is possible to When using an elliptical polarimeter that detects the phase difference with a phase detection element for actual measurements, the light from the light source is accurately positioned at a predetermined incident angle with respect to the sample surface. In order to ensure that the incident angles match, and that the reflected light from the sample surface is correctly incident on the rotating analyzer through the pinhole, the part that contains the light source and the rotating The part that includes the analyzer means that the light from the light source is directly incident on the rotating analyzer with the optical axes aligned without passing through a reflective surface, and the rotating analyzer and rotational phase are detected. When detecting the phase difference with the element and when making the light from the light source enter the sample surface at a predetermined angle of incidence, the mounting angle of each part is different for each case. Each needs to be set very accurately to the desired angle.

However, in order to allow the mounting angle of each component to be variably adjusted extremely precisely as described above, the configuration of the mechanism is precise and complicated, resulting in less freedom in design and making the product expensive. In addition to this, there is a possibility that the measurement accuracy will be reduced due to the angle deviation, and there is also a possibility that the measurement accuracy may be reduced due to the angle deviation. l! There was a problem in that difficult optical axis alignment work was required when replacing worn parts.

(Means for Solving the Problems) The present invention provides a means for coaxially directing reflected light of light projected onto a sample surface at a predetermined angle of incidence to a rotating phase detection element.
The light is made incident on a rotating analyzer such as a 2-digit rotary analyzer, and the light emitted from the rotary analyzer is detected by a photodetector (W).

4:, f > l (in the ellipsometry performed)
By the method of detecting the phase difference between the rotary collar and the rotary phase-transfer element, when the beam is projected onto the sample surface at a predetermined angle of incidence of 0, As a sample onto which light is to be projected at θ, its refractive index 11 is n = t;o11? The output from the co-rotating phase detection element (based on No. A rotating analyzer and a rotating phase detecting element of an elliptical polarimeter are characterized in that the phase difference between the rotating analyzer and the rotating phase detecting element is detected based on the mode of change of the output signal on the time axis. This provides a phase difference detection method.

(Example) Hereinafter, a method for detecting a phase difference between a rotating analyzer and a rotating phase detection element of an elliptical polarimeter according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an example configuration of an elliptical polarimeter to which a phase difference detection method between a rotating analyzer and a rotating phase detection element of the ellipsoidal polarimeter of the present invention is applied.
2 is a light source and an optical system on the output side, and from this light source and the optical system 1 on the output side, light 11 in a predetermined polarization state is projected onto the surface of the sample 9 at a predetermined incident angle O. For example, a HeNe laser is used as the light source and the optical system 1 on the output side, and the optical system on the output side includes a 174 wavelength plate, a shutter, and a polarizer (for example,
A Glan-Thompson prism) and a 174-wave plate can be used.

The light 12 reflected on the surface of the sample 9 is incident on a rotating analyzer 2 (for example, a Glan-Thompson prism), and the light 13 emitted from the rotating analyzer 2 is provided to a photodetector 4. Reference numeral 3 denotes a rotary phase detecting element which is configured to rotate coaxially and integrally with the rotary analyzer 2 described above. As this rotary phase detecting element 3, for example, a rotary encoder can be used, and the following description is given. , it is sometimes explained that a rotary encoder is used as the rotary phase detection probe 3.

The rotation analyzer 2 and the rotation encoder 3 are supported by bearings (not shown), and are rotated at a predetermined speed (for example, by power supplied from a drive source (not shown).
It is designed to rotate at a speed of several hundred revolutions per minute.

The light with a specific polarization state projected onto the sample 9 from the light source and the optical system I on the output side is reflected by the sample 9 and given to the rotating analyzer 2 as described above, but the light reflected by the sample 9 The state of polarization is determined depending on the angle of incidence of the incident light on the sample 9, the thickness of the sample 9, the optical constants of the sample, etc.

Therefore, by knowing the state of change on the time axis of the output signal 31 from the photodetector 4, which changes in accordance with the change in the rotation angle of the single-turn analyzer 2, it is possible to obtain the unknown parameter. For example, rotary encoder 3
The output signal 21 from the photodetector 4 is given to the electronic computer 7 as a timing signal, and the output signal 31 from the photodetector 4 is converted to a digital signal 32 by the analog-to-digital converter 6.
This can be easily realized by converting the data into the form, feeding it to the electronic computer 7, and performing predetermined calculations. In the figure, 8 is a display.

However, when the above-mentioned calculation is performed by the electronic computer 7, if the azimuth in the rotary analyzer 2 and the reference phase in the one-rotation encoder 3 do not precisely match, a correct answer cannot be obtained from the result of the calculation. By the way,
In an elliptical polarimeter, it is not uncommon to be required to keep the difference between the azimuth in the rotational analyzer 2 and the reference phase in the one-rotation encoder 3 to no more than 8.

The present invention makes reflected light of light projected onto a sample surface at a predetermined angle of incidence enter a rotating analyzer such as that provided coaxially with respect to a rotating phase detection element. In order to detect the phase difference between a rotating analyzer and a rotating phase detection element in an elliptical polarimeter, which is designed to receive light emitted from As a sample, the refractive index n of the sample is such that n=
The time of the output signal of the photodetector obtained using a substance that has a relationship of tanθ and based on the output signal from the rotating phase detection element installed coaxially with the rotating analyzer in the above state. The phase difference between the rotating analyzer and the rotating phase detection element can be easily detected based on the mode of change on the axis.

That is, in the phase difference detection method between the rotating analyzer and the rotating phase detecting element of the elliptical polarimeter of the present invention, the sample 9 used for detecting the phase difference between the rotating analyzer and the rotating phase detecting element of the elliptical polarimeter is By using a material in which the incident angle θ is equal to the deflection angle, the reflected light from the sample 9 becomes plane polarized light that is polarized perpendicular to the incident plane (Brevster'
s law...Brewster's law), therefore, by using a material having a refractive index n that satisfies the relationship n=tanθ as described above, the sample 9
In the case of FIG. 1, the reflected light is polarized light consisting only of components in the direction perpendicular to the plane of the paper (polarized light consisting only of the S-polarized component). Taking an example of the sample 9 as described above, if the incident angle θ is 58°, a material (glass) with a refractive index n of 1.6003 may be used.

In this way, in the phase difference detection method between the rotating analyzer and the rotating phase detection element of the elliptical polarimeter of the present invention, the state of polarization of the light reflected by the sample 9 and given to the rotating analyzer 2 can be determined. Therefore, the intensity IO of the light after passing through the rotating analyzer 2 is Io = gin2 ωt (with respect to the direction perpendicular to the sample 9, where ω is the angular velocity of the rotating analyzer 2)
However, the amplitude is assumed to be 1).

By the way, when there is a phase difference of φP between the rotating analyzer and the rotating phase detection element of the elliptical polarimeter, the output signal 31 from the photodetector 4 is synchronized with the output signal 21 from the rotary encoder 3. If the output Ip obtained at that time is 1, the amplitude is 1, and Ip=sin2(ωt+φP
).

FIG. 2 illustrates the outputs Io and Io described above,
A phase difference of φp exists between the two outputs io and Ip.

1. In the phase difference detection method between the rotating analyzer and the rotating phase detection element of the elliptical polarimeter of the present invention, the state of polarization of the light reflected by the sample 9 and given to the rotating analyzer 2 is specified. Therefore, if the output signal of the photodetector obtained in correspondence with the output signal of the reference phase in the rotary phase detection element 3, which is provided coaxially with the rotary analyzer 2, is not zero, it becomes zero. The period until the state becomes
represents the phase difference φp between the azimuth and the base phase of the rotary phase detection element 3.

Therefore, the phase difference φp between the azimuth of the rotating analyzer 2 and the reference phase of the rotating phase detection element 3 can be easily detected by comparing the waveform of Io with the waveform Ip. When comparing waveforms, for example, if you use a method such as least squares approximation,
The phase difference φp between the orientation of the rotating analyzer 2 and the reference phase of the rotating phase detection element 3 can be detected with high accuracy.

(Effects of the Invention) As is clear from the detailed explanation above, the phase difference detection method between the elliptical polarimeter-cut-rotating analyzer and the rotating phase detection element of the present invention is effective at a predetermined incident angle. The reflected light of the light projected onto the sample surface is made incident on a rotating analyzer such as that provided coaxially with the rotating phase detection element, and the light emitted from the rotating analyzer is received by a photodetector. In order to detect the phase difference between a rotating analyzer and a rotating phase detection element in an elliptical polarimeter, light is projected onto the sample surface at a predetermined angle of incidence θ, and its refraction is The rate n is n=tan with respect to the incident angle θ of the light mentioned above.
The time of the output signal of the photodetector obtained using a substance that has a relationship of Since the phase difference between the rotating analyzer and the rotating phase detecting element is detected based on the mode of change on the axis, the rotating analyzer and the rotating phase detecting element of the elliptical polarimeter of the present invention According to the phase difference detection method with By using a material with a deflection angle of 0 equal to a predetermined incident angle of 0 as a sample, it is extremely easy to detect the rotating analyzer and rotating phase in an ellipsometer. According to the phase difference detection method between the rotating analyzer and the rotating phase detection element of the elliptical polarimeter of the present invention, all of the conventional problems mentioned above can be detected precisely. It can be solved well.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an example configuration of an elliptical polarimeter to which a phase difference detection method between a rotating analyzer and a rotating phase detection element of the present invention is applied, and FIG. 2 is a waveform diagram for explanation. 1... Optical system on the light source and emission side, 2... Rotating analyzer,
3... Rotational phase detection element, 4... Photodetector, 6...
・Analog-digital converter, 7...Electronic computer, 8.
...Display, 9...Sample,

Claims (1)

[Claims] The reflected light of the light projected onto the sample surface at a predetermined angle of incidence is made incident on a rotating analyzer such as that provided coaxially with the rotating phase detection element, and the light emitted from the rotating analyzer is A method of detecting the phase difference between a rotating analyzer and a rotating phase detection element in an elliptical polarimeter that is configured to receive light with a photodetector, in which light is projected onto a sample surface at a predetermined incident angle θ. When the sample is to be irradiated with light at the above-mentioned incident angle θ, a material whose refractive index n is in the relationship n=tanθ with respect to the above-mentioned incident angle θ is used. , based on the mode of change on the time axis of the output signal of the photodetector obtained with reference to the output signal from the rotating phase detection element provided coaxially with the rotating analyzer in the above state, A method for detecting a phase difference between a rotating analyzer and a rotating phase detecting element of an elliptical polarimeter, which is characterized by detecting a phase difference between the rotating analyzer and the rotating phase detecting element.