JPH0436421Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a polarization analyzer that measures the polarization state of light.

<Prior art> Ellipsometers are used to measure the thickness of sub-micron thin films (for example, the thickness of gate insulating films in thin film devices, interlayer insulating films, multilayer films, and polycrystalline semiconductors), and to measure the physical properties of substrates and films. It measures the refractive index to determine its characteristics.

First, the principle of polarization analysis will be briefly explained using FIG.

In the figure, S is a vertical component with respect to the plane of incidence, and P is a horizontal component. 1 is a sample on which a thin film was formed, 2
is the incident polarized light, and 3 is the reflected polarized light. In the figure, sample 1
This shows a state in which the vertical component of the S-wave incident on the image changes into elliptically polarized light after reflection.

By the way, this change consists of two parameters, one is the phase difference Δ between the vertical component S wave and the horizontal component P wave, and the other is the reflection coefficient ratio angle ψ between each component wave. These Δ and ψ can be expressed as Δ=δ _P −δ _S ψ=tan ⁻¹ (R _P /R _S ). The polarization analyzer uses this Δ,
This is a device that measures ψ.

FIG. 3 is a block diagram of the main parts of a conventional device used in such a polarization analyzer. In Figure 3, L is a light source, and the light from light source L is polarized.
The light is directly polarized by H ₁ and converted into circularly polarized light 2 by the quarter-wave plate Q. This circularly polarized light 2 is reflected by the sample 1 and becomes elliptically polarized light 3 due to the thickness and characteristics of the film formed on its surface, and is further converted into directly polarized light by the analyzer _H2 . P is a photoelectric conversion element that converts the light intensity of the linearly polarized light 4 into an electrical signal.

In the above configuration, the light intensity is measured by the photoelectric conversion element P while rotating the analyzer _H2 . At this time, the position where the light intensity is maximum is in the long axis direction of the ellipse. A position perpendicular to this position is the short axis direction of the ellipse, and the ratio between the long axis and short axis of the ellipse can be determined from the ratio of the light intensity in the long axis direction and the light intensity in the short axis direction.

<Problems to be solved by the invention> By the way, in such a configuration, in order to accurately measure the ratio of the long axis to the short axis, it is necessary to rotate the analyzer H ₂ with high precision, which makes the entire device It becomes complicated and large. Further, when it is desired to measure the film thickness in a vacuum during the thin film forming process, special measures are required to prevent oil leakage from the rotating mechanism.

The present invention has been made in view of the above-mentioned prior art, and aims to realize a polarization analyzer that does not require a rotation mechanism, can be made smaller and lighter, and can also perform measurements in vacuum.

<Means for solving the problems> The configuration of the present invention for solving the above problems is as follows:
means for converting light from a light source into circularly polarized light; a branching section for branching the circularly polarized light into two directions; and a shifting means for shifting the frequency of one of the branched circularly polarized lights;
a reflecting means for reflecting the other branched circularly polarized light; a coupling section for coupling the circularly polarized light shifted by the shifting means with the reflected light reflected by the reflecting means; a separating means for polarizing the combined light; and a separating means for polarizing the combined light. The apparatus includes a light detection means for detecting the light intensity of each light separated by the means, and uses a sample as the reflection means.

<Example> FIG. 1 is a configuration diagram showing an example of a polarization analyzer according to the present invention. In the figure, the same elements as in FIG. 3 are denoted by the same reference numerals and explanations are omitted, but in this example, light from the light source L is incident on the polarizer _H1 via the optical fiber F. The light that has become linearly polarized by polarizer H ₁ is made into circularly polarized light 2 by quarter-wave plate Q, and this circularly polarized light is diffused with titanium (Ti) on a substrate of, for example, lithium niobate (LiNbO ₃ ). The light is introduced into the waveguide K formed by the above-mentioned method, and is branched into two directions at a branching portion _Y1 . The frequency of one of the branched lights is shifted by a shift means M that applies a sawtooth wave electric field to shift the frequency.

At this time, the polarization components of the frequency-shifted S and P waves can be expressed by the following equation.

E _RS・exp j(ω+ω′)t ……(1) E _RP・exp j{(ω+ω′)t+θ} ……(2) Here, E _RS ：Electric field strength of S component of circularly polarized light E _RP ：Circle Electric field strength of the P component of polarized light ω; Frequency of light ω′; Difference between the shifted frequency of light and the original frequency t: Time θ: Phase (π/4) The other branched circularly polarized light passes through the waveguide. The light is emitted from K, enters the sample 1, and is reflected as elliptically polarized light depending on the surface condition of the sample.

At this time, the polarization components of the S and P waves of elliptically polarized light can be expressed by the following equation.

E _SS・exp j(ωt+B _s ) ……(3) E _SP・exp j(ωt+B _P +θ) ……(4) Here, E _SS ; electric field strength of S component of elliptically polarized light E _SP ; P of elliptically polarized light electric field strength of the component B _S ; phase difference of the S component caused by reflection B _P ; phase difference of the P component caused by reflection t; time θ; phase (π/4) This elliptically polarized light is guided again. The light enters the wave path K and is combined with the circularly polarized light shifted by the frequency shifting means at the coupling portion _Y2 .

At this time, the shifted combined light of the circularly polarized light and the elliptically polarized light (A _S . . . S wave, A _P . . . P wave) can be expressed by the following equation from equations (1) to (4).

A _S =E _RS・exp j(ω+ω′)t+E _SS・exp j(ωt+B _S ) ……(5) A _P =E _RP・exp j{(ω+ω′)t+θ} +E _SP・exp j(ωt+B _P +θ )...(6) This combined light is incident on the analyzer H ₂ to undergo polarization separation, and the light intensity is detected by means for detecting light intensity (for example, photodiodes) PD ₁ and PD ₂ . The output of the photodetecting means at this time can be expressed as in the following equation.

PD ₁ = |A _S | ² =E _SS ² +E _RS ² +2E _SS・E _RS cos(ω′t−B _S ) ……(7) PD ₂ = |A _P | ² =E _SP ² +E _RP ² +2E _SP ·E _RP cos(ω′t−B _P ) (8) The output from this photodetecting means is removed by a direct current cut means (not shown), and an alternating current component expressed by the following equation is extracted.

PD _1AC = 2E _SS・E _RS cos (ω′t−B _S ) ……(9) PD _2AC = 2E _SP・E _RS cos (ω′t−B _P ) ……(10) Above (9), ( The intensity ratio of the S and P components of the reflected light can be determined from the ratio of the AC signal output shown in equation 10), and the
The phase difference between the S and P polarization components of the reflected light can be determined from the phase difference between the AC signals. Then, the thickness and characteristics of the thin film on the sample surface can be analyzed from the above two parameters.

<Effects of the invention> As specifically explained above with the embodiments, according to the invention, there is no rotation mechanism, so it is possible to construct a compact and lightweight polarization analyzer, and it is easy to perform measurements in vacuum. can do.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the main part configuration showing one embodiment of the present invention, Fig. 2 is an explanatory diagram showing the principle of polarization analysis, and Fig. 3 is an explanatory diagram showing the principle of polarization analysis.
The figure is a configuration diagram of main parts of a conventional polarization analyzer. 1... Sample, 2... Incident polarized light (linear polarized light), 3
...Elliptically polarized light, 4...Circularly polarized light, L...Light source, F...
...Optical fiber, H ₁ ... Polarizer, H ₂ ... Separation means (analyzer), K ... Waveguide, M ... Frequency shift means, PD ₁ , PD ₂ ... Light detection means, Y ₁ ... branch,
Y ₂ ...Connection part.

Claims (1)

[Scope of utility model registration request] means for converting light from a light source into circularly polarized light, a branching section for splitting the circularly polarized light into two directions, a shifting means for shifting the frequency of one of the branched circularly polarized lights, and a reflector for reflecting the other branched circularly polarized light. a reflecting means, a coupling part for coupling the circularly polarized light shifted by the shifting means and the reflected light reflected by the reflecting means, a separating means for separating the polarized light from the combined light, and a separating means for separating the polarized light by the separating means. A polarization analyzer comprising a light detection means for detecting light intensity, and using a sample as the reflection means.