JPH0812148B2 - Ellipsometer - Google Patents

Description

TECHNICAL FIELD The present invention utilizes the property of light polarization to measure the thickness of a thin film on an object (sample surface) and the refractive index relating to the physical properties of the film on the sample surface. It is about.

2. Description of the Related Art As shown in FIG. 1, when linearly polarized light is incident on a surface of a sample 1 having a thin film 2 at an incident angle ψ ₀ from an obliquely upper side, it is reflected by a thin film thickness and a refractive index on the surface of the sample. The polarization state of light changes and is usually reflected as elliptically polarized light. Therefore, by measuring the amount of change in the polarization of the reflected light and performing an analytical calculation, it is possible to obtain the thickness and refractive index of the thin film on the sample surface.This is called ellipsometry, and the device is generally called an ellipsometer. There is. In such an ellipsometer, an important parameter of the polarization change amount of the reflected light required to obtain the thickness and the refractive index of the thin film is that the p-component wave on the horizontal p-coordinate plane and the s-coordinate plane perpendicular to it on reflection are reflected. The phase shift γ generated between the s-component wave and the variation Ψ of the principal axis direction of the polarization due to the difference in the amplitudes of the two component waves caused by the difference in the reflectance between the p-component wave and the s-component wave. There is.

By the way, conventional ellipsometers are roughly classified into two types, a photometric type and a quenching type. In the photometric type, the polarization prism is continuously rotated, and the phase shift γ and the change amount Ψ of the principal axis direction are calculated by the relationship between the angle and the detected light intensity. On the other hand, in the extinction type, the polarized light changed in the sample is returned to the original state by the rotation of the optical element, and the phase shift γ and the change amount Ψ of the principal axis direction are obtained from the compensation angle. In each of these two methods, necessary information is obtained by measuring the amount of change in the light intensity, that is, the output of the DC component of the photodetector.

Problems to be Solved by the Invention Among the conventional ellipsometers, the photometric type is a linearly polarized light with a large intensity ratio because it calculates the phase shift γ and the main axis azimuth variation Ψ, which are parameters of the polarization variation. There is a problem that the measurement accuracy is deteriorated in a place close to. On the other hand, the extinction type has the advantage that high measurement accuracy can be obtained up to the physical limit of the polarization prism because the polarization angle is measured directly as an angle, but the measurement time is increased because the polarization prism is rotated and moved during measurement. Has a long drawback.

As a drawback common to both the photometric type and the extinction type, since the light intensity is detected as a DC component, there is a problem that the signal-to-noise ratio (S / N) is badly affected by the back light.

Therefore, an object of the present invention is to provide an ellipsometer capable of measuring a thin film and a refractive index on an object with high S / N with high accuracy and in a short time without being affected by back light. .

Means for Solving Problems In the ellipsometer of the present invention, basically, linearly polarized light is made incident on a sample, and a phase modulation element is inserted in an incident light path or a reflected light path to the sample to make it incident on the sample. Light or reflected light is modulated, and a modulation frequency component, a frequency component twice the modulation number fraction, and a DC component are extracted from the signal of the photodetector in synchronization with the modulation frequency, and the frequency twice the modulation frequency. The azimuth of the linear polarization element or the analyzer is controlled so that the component V (2ω) becomes zero, and the incident angle ψ ₀ to the sample is controlled so that the frequency component V (ω) of the modulation frequency becomes maximum in that state. Then, the rotation angle θ of the orthogonal polarization element or the analyzer at that time was determined from the incident angle ψ ₀ to obtain the value of the refractive index of the sample and / or the thickness of the thin film.

Specifically, the first invention controls the incident angle ψ ₀ of the incident light on the sample surface in an ellipsometer in which linearly polarized light is incident on the sample surface and the value related to the sample surface is measured from the polarization state of the reflected light. An incident angle control mechanism is provided and linearly polarized so that the polarization direction of the linearly polarized light incident on the sample surface is + 45 ° or −45 ° with respect to the incident surface in the initial state in the optical path of the incident light on the sample surface. A azimuth control mechanism for arranging the elements and rotating the azimuth of this linear polarization element from ± 45 ° to θ ° is provided, and phase modulation with amplitude δ ₀ and modulation angular frequency ω is provided in the optical path of the reflected light from the sample surface. The element is arranged so that its delay axis azimuth is + 45 ° or −45 ° with respect to the incident surface, and the transmission axis azimuth is 0 ° or 90 ° with respect to the incident surface on the exit side of the phase modulation element. Place the analyzer so that A photodetector for photoelectrically converting light is disposed on the exit side of the child, and a ω component of the output signal of the photodetector, a 20ω component, and a signal component separation circuit for independently extracting the DC component are provided, The polarization direction of linearly polarized light is rotated so that the 2ω component becomes zero, and the polarization direction is fixed at a rotation angle θ from ± 45 ° at that time,
Further, the incident angle ψ ₀ is controlled so that the ω component becomes maximum in that state, and the refractive index of the sample surface and / or the thickness of the thin film on the sample surface is obtained from the rotation angle θ and the incident angle ψ _{0 at} that time. It is characterized by doing so.

The ellipsometer of the second invention is different from the ellipsometer of the first invention in that the phase modulation element is basically arranged in the incident optical path to the sample and the orientation of the analyzer is controlled. That is, the ellipsometer of the second invention is an ellipsometer in which linearly polarized light is made incident on the sample surface and the value relating to the sample surface is measured from the polarization state of the reflected light thereof, and the incident angle ψ ₀ for controlling the incident angle ψ ₀ of the incident light on the sample surface is A control mechanism is provided and a linear polarization element is arranged so that the polarization direction of the linearly polarized light is 0 ° or 90 ° with respect to the incident surface in the optical path of the incident light on the sample surface. A phase modulator with an amplitude δ ₀ and a modulation angular frequency ω between it and the surface is placed so that its delay axis azimuth is ₊ 45 ° or −45 ° with respect to the incident surface, and in the optical path of the reflected light from the sample surface. In addition, the analyzer is placed so that the transmission axis azimuth is + 45 ° or −45 ° with respect to the incident surface in the initial state, and the analyzer is provided with the azimuth control mechanism that rotates by θ from the ± 45 ° azimuth. , And the exit side of the analyzer Is provided with a photodetector for photoelectrically converting light, and a signal component separation circuit for independently extracting the ω component, the 2ω component, and the DC component of the output signal of the photodetector is provided, and the 2ω component is further provided. Rotate the direction of the analyzer so that
The polarization azimuth is fixed at a rotation angle θ from 45 °, and the incident angle ψ ₀ is controlled so that the ω component is maximized in that state, and the refraction of the sample surface from the rotation angle and the incident angle ψ _{0 at} that time is controlled. It is characterized in that the rate and / or the thickness of the thin film on the sample surface is obtained.

Action Before describing the difference of the ellipsometer of the present invention, the measurement principle of the ellipsometer will first be explained, and then the theoretical analysis of the ellipsometer of the present invention will be explained together with its action.

[A: Ellipsometer measurement principle] The ellipsometer observes the change in the polarization state when light is reflected on the surface of an object and determines the optical constant (refractive index) of the object itself or the thickness of the thin film attached to the surface of the object. This is a method of knowing the optical constant (refractive index). So, first of all, the measurement principle of the optical constant of the object itself, that is, the case where there is no thin film,
Subsequently, the principle of measuring the thickness of the thin film and the optical constant when the thin film is present will be described separately.

A-1: Measurement of optical constant of substrate First, the optical constant of the sample is set to = n-ik. Here, a complex number refractive index, n is a refractive index, k is an absorption coefficient, and i is an imaginary unit.

The amplitude reflectance (Fresnel coefficient) of the vibration component (p component) parallel to the incident surface of the monochromatic parallel light flux incident from the vacuum at the incident angle ψ ₀ is _p , and the amplitude reflection of the vibration component (s component) perpendicular to the incident surface is _{p Let s} be the ratio (Fresnel coefficient), and let _p = r _p exp (-iφ _p ) (1) _s = r _s exp (-iφ _s ) (2). These are the optical constant of the sample = n-ik and the incident angle ψ
It has a relationship with ₀ .

In a transparent sample with an absorption coefficient k = 0, φ _p and φ _s are generally 0 or π, and therefore _p and _s are real numbers, so the linearly polarized light that has entered is not elliptically polarized but is reflected as linearly polarized light. .

However, in the case of an absorber sample (k ≠ 0) such as a metal, the phase difference (retardation) γ due to reflection, that is, γ = φ _p −φ _s (3), varies from 0 depending on the value of the incident angle ψ _0. Since it continuously changes up to π, _p / _s is generally a complex number (each of _p and _s is also a complex number).

, And tan Ψ≡ρ (= r _p / r _s ) is called the amplitude reflectance ratio or the amplitude reflectance coefficient ratio (real number).

In this way, since _p / _s is a complex number in the absorber sample, the incident linearly polarized light is reflected as elliptically polarized light.

If two parameters of the elliptically polarized light (for example, the azimuth α of the long axis of the ellipse and the ellipticity X) are measured, then the amplitude reflectance ratio ρ≡tan Ψ and the phase difference (retardation) are obtained.
γ can be obtained. The following relational expression is known between these two quantities tan Ψ, γ and the refractive index n and the absorption coefficient k.

Therefore, by knowing the values of Ψ and γ, the refractive index n and the absorption coefficient k of the sample can be obtained.

A-2: Determination of thickness and optical constant of thin film As shown in FIG. 2, refractive index ₂ = n ₂ −ik ₂ (known) on the lower ground, refractive index ₁ = n ₁ −ik ₁ , thickness It is assumed that there is an isotropic homogeneous thin film 2 having a thickness d, and linearly polarized light is incident on this at an incident angle ψ ₀ .

The reflected light R is a combination of the light R ₁ reflected on the surface of the thin film, the light R ₂ reflected on the boundary surface between the thin film and the base, and the light of R _{3 and the} subsequent light emitted while reciprocating in the thin film. That is, R = R ₁ + R ₂ + R ₃ + ... (7) The amplitude reflectance of the entire surface considering the repetitive reflection interference in the film is as follows for the p component and the s component, respectively. Given in.

here, _j-1 sin ψ _j-1 = _j sin ψ _j (12) δ = 4π ₁ dcos ψ ₁ / λ (13), and _jp and _js are the first surface (vacuum-membrane) and j when j = 1. = 2 is the amplitude reflectance (Fresnel coefficient) of the p and s components on the second surface (film-base). Further, δ is a phase difference caused by one round trip of the film width, and λ is a wavelength in vacuum.

Here, _p / _s is a complex number even if the Fresnel coefficient such as _jp or δ is a real number, so the reflected light becomes elliptically polarized light.

The complex reflection coefficient ratio _p / _s is the same as in equation (4). Is represented.

Here, the values tan Ψ and γ on the right side are quantities measured by an ellipsometer, while the coefficient ratios on the left side are (6) to (11).
As can be understood from the formula, ₁ (n ₁ , k ₁ ), ₂ (n ₂ ,
k ₂ ), d, λ, ψ ₀ . That is, γ, Ψ = F (n ₁ , n ₂ , k ₁ , k ₂ , d, λ, ψ ₀ ) (15) Among the parameters on the right side of the equation (15), n ₂ , k ₂ , λ, ψ ₀
If the measured values γ and Ψ are used as
n ₁ and d can be solved.

For example, if k ₁ = 0 (transparent film), the unknowns are n ₁ , d
However, the value can be easily obtained by the computer. Even when k ₁ > 0 (absorption film), n ₁ , k ₁ , and d can be known by measuring γ and Ψ. A method of calculating the required quantities n ₁ , k ₁ , and d from the measured quantities γ and Ψ is known.

As described above, the thickness d of the thin film on the sample surface and the refractive index n ₁ and the absorption coefficient k ₁ which are optical constants are obtained from the amplitude reflection coefficient ratio tan Ψ (= ρ) and the phase difference γ measured by the ellipsometer. It is possible.

[B: Logical analysis of the present invention] The output of the ellipsometer optical array of the present invention is analyzed by the following procedure using the Mueller matrix analysis method. Here, the optical arrangement of the first invention shown in FIG. 3 will be described as an example.

First, regarding the signal of the photodetector, the component V (ω) having the same frequency as the modulation frequency of the phase modulation element, the component V (2ω) having the double frequency, and the direct current component V (DC) are described. Lead. Next, the conditions for controlling the polarization direction of the linear polarization element so that V (2ω) becomes zero are derived. Further, the conditions for controlling the incident angle ψ ₀ on the sample so that V (ω) is maximized with the polarization azimuth fixed at the angle θ so that V (2ω) becomes zero in this way are derived. Then, the relationship between the angle θ, the incident angle ψ ₀ , the complex number refractive index (refractive index n and absorption coefficient k), and the thin film thickness d is derived.

 Next, these analysis procedures are described by dividing them into sections.

B-1: Relationship between each signal component, phase difference, and reflection coefficient ratio First, each optical element is represented by a Mueller matrix. The Mueller matrix A _{0 of the} analyzer is Is represented by

The Mueller matrix M ₄₅ , δ (ω) of the phase modulator is However, δ is represented by δ = δ ₀ sinωt (18) where ω is the angular frequency (angular velocity) of the modulation of the optical phase modulator and δ ₀ is the amplitude.

Also, the Mueller matrix Si of the reflection surface of the sample with respect to the polarization plane of 45 ° is given by the reflection coefficient ratio r _p / r _s , Is represented by However, γ is the difference in phase change (phase difference = retardation), and r _p and r _s are reflection coefficients of the p component and the s component, respectively.

Mueller matrix T for rotating the azimuth of the polarization state by θ °
_θ is Is represented by

Furthermore, the Mueller matrix I ₄₅ of 45 ° linearly polarized light is Is represented by

The output I (d) of the photodetector in this case is (16)
It is represented by the product of the Mueller matrices of equations (17) and (19) to (21).

I (d) = A ₀ · M ₄₅ , δ (ω) · Si · T ₀ · I ₄₅ (22) Then, from equations (16), (17), (19) to (21), I (d ) Is calculated as follows.

Here using Bessel functions sin [delta, if deployed _{cosδ, sinδ = sin (δ 0} sinωt) = 2J 1 (δ 0) sinωt + 2J 3 (δ 0) sin3ωt + ... (2
_{4) cosδ = cos (δ 0} sinωt) = J 0 (δ 0) + dJ 2 (δ 0) cos2ωt + 2J 4 (δ 0) cos4ωt + ... given by (25).

Letting V (d) be the electrical signal of the output of the photodetector proportional to the light intensity I (d), V (d) is the DC component V (DC), ω
Component V (ω), 2ω component V (2ω), and 3ω component V
It can be expressed as follows by a harmonic component of (3ω) or more.

V (d) = V (DC) + V (ω) + V (2ω) + (harmonic term) (26) In the equations (24) and (25), the term J ₀ (δ ₀ ) is the DC component, The term J ₁ (δ ₀ ) corresponds to the ω component, and the term J ₂ (δ ₀ ) corresponds to the 2ω component. Therefore, equation (23) and (24)
From equation (25), each component of equation (26) V (DC), V
If (ω) and V (2ω) are calculated, V (DC) = r _p ² + r _s ² − (r _p ² −r _s ² ) sin ² θ + (r _p ² −r _s ² ) · J ₀ (δ ₀ ) − (R _p ² + r _s ² ) sin θ · J ₀ (δ ₀ ) (27) V (ω) = − 4r _p r _s · J ₁ (δ ₀ ) · cos 2θ sinγ (28) V (2ω) = 2 ( r _p ² −r _s ² ) · J ₂ (δ ₀ ) −2 (r _p ² + r _s ² ) sin ² θ · J ₂ (δ ₀ ) (29).

B-2: Control of polarization azimuth and control of incident angle Here, when the azimuth of the polarizer is rotated from ± 45 ° so that the magnitude of the 2ω component becomes zero, V is given by the equation (29).
With (2ω) = 0, r _p ² −r _s ² = (r _p ² + r _s ² ) sin2θ (30) holds.

Under the condition that the 2ω component becomes zero in this way, the direct current component V (DC) is expressed by V (DC) = (r _p ² + r _s ² ) cos by substituting the formula (30) into the formula (27). It becomes ^{2 2} θ (31).

On the other hand, under the condition that the 2ω component becomes zero, the reflection coefficient ratio r _s / r _p
If (= tan Ψ) is obtained, from equation (30) In this way, the linear polarization element is rotated so that the magnitude of the 2ω component becomes zero and fixed at the azimuth angle θ (however, the azimuth angle from the initial ± 45 °), and in that state the ω component V (ω) is If the condition that maximizes is obtained, in order to maximize V (ω) in the formula of V (ω) in the above formula (28), sin γ = 1, that is, γ = π / 2 (33) I know it's good.

That is, when the incident angle ψ ₀ on the sample is changed and the ω component V (ω), which is the same as the modulation frequency, is the maximum incident angle, the phase difference (retardation) γ is 90 ° (π / 2). Become.

Generally, the incident angle at which γ = π / 2 is called the main incident angle, and therefore V (ω) is fixed under the condition that the azimuth θ of the linear polarization element is fixed so that V (2ω) = 0. If the incident angle ψ ₀ is controlled to be the maximum, the incident angle at that time is the main incident angle, and the phase difference γ is π / 2.

Although the above relationship has been described with respect to the example of the first invention of FIG. 3, in the case of the second invention of FIG. 4 as well, the difference is that θ is the azimuth angle of the analyzer, and the same relationship as above. Is established.

B-3: Relation of Calculation of Refractive Index Generally, light is incident from the medium A (its optical constant ₁ = n ₁ + ik ₁ ) to the medium B (its optical constant ₂ = n ₂ −ik ₂ ) at an incident angle ψ ₁
Assuming that the refraction angle is ψ ₂ , and the phase change is γ, the S-polarized Fresnel coefficient r _s and the P-polarized Fresnel coefficient r _p that represent the amplitude reflectance are given by the following equations.

S polarization P polarization However, jcos ψj = (j ² −sin ² ψj) ^1/2 (36) Therefore, when light is projected onto a medium that absorbs in air at an incident angle ψ ₀ , Using this formula, the following formula can be derived.

Where P and Q are Is.

By dividing Eq. (40) into real and imaginary parts and arranging as ρ≡r _s / r _p = tan Ψ (41), the following equation is obtained.

If n ² −k ² >> sin ² ψ ₀ holds when the absorption is small and the incident angle is smaller than a certain range, the equation (38) is simplified, and n and k are given by the following equations. To be

When the measurement is performed at the main incident angle ψ ₀ = such that γ = π / 2, the _equations (42), (43), (44), and (45) can be written as follows.

n ² −k ² = sin ² (1 + cos4Ψ tan ² ) (46) 2nk = sin4 Ψsin ² tan ² (47) n ≈ cos ² Ψsintan ² (48) k ≈ sos2 Ψsintan ² (49) From the equation (33) already mentioned, r _s / r _p ≡tan Ψ ＝ tan (45 ° -θ) Therefore Ψ = 45 ° -θ (50) holds. Therefore, equations (48) and (49) are (5
It can be rewritten as follows using equation (0).

n ≈ sin2θsintan (51) k ≈ cos2θsintan (52) Here, the positive incident angle is such that V (ω) becomes maximum with the azimuth θ fixed so that V (2ω) = 0. It is known because it is the incident angle when the incident angle is controlled. Also, Ψ is known from θ according to equation (50). Therefore, from θ and,
The refractive index n and the absorption coefficient k can be obtained from the equation (2).

B-3: Calculation of the thickness d of the thin film The amount to be obtained for the thin film on the sample surface, that is, the refractive index
The relationship between n ₁ , the absorption coefficient k ₁ , the thickness d of the thin film, the phase difference γ measured by the ellipsometer, and the amplitude reflectance ratio tan Ψ (= ρ) is as described above. And γ and Ψ are functions determined by the following equation.

Ψ = f (n ₁ , k ₁ , d, n ₂ , k ₂ , ψ ₀ , λ) (54) γ = f (n ₁ , k ₁ , d, n ₂ , k ₂ , ψ ₀ , λ) ( 55) Therefore, if n ₁ , k ₁ , d, n ₂ , k ₂ , ψ ₀ , λ are given, Ψ and γ can be calculated, and conversely, if Ψ and γ are obtained,
d can be obtained. It is already known that the formulas (54) and (55) are calculated and tabulated. If a detailed chart of this kind is made, the thin film thickness d can be immediately known from the measured value by interpolation. You can It is also possible to obtain d from the measured values of γ and Ψ using a computer.

Embodiment FIG. 3 shows an embodiment of the ellipsometer of the present invention (first embodiment).
Example of invention).

In FIG. 3, the light from the white light source 10 is incident on the monochromator 11 to select the monochromatic light having the wavelength λ, and the monochromatic light having the wavelength λ is a linear polarization element (polarizer = polarizer = The light is incident on the polarizer (12), and in the initial state, becomes linearly polarized light having a polarization direction of + 45 ° or −45 ° with respect to the incident surface and is incident on the sample 1. The linear polarization element 12 is additionally provided with an azimuth control mechanism 12 for rotating its polarization azimuth by ± θ from ± 45 °. The reflected light of the sample 1 is normally elliptically polarized light as described above, and is incident on the phase modulation element (optical polarization modulation element) 13, for example, a photoelastic modulator 13 such as a Faraday cell. The phase modulation element 13 alternately changes the incident elliptically polarized light into a left-handed polarized light and a right-handed polarized light with an amplitude δ ₀ and an angular frequency ω, and its delay axis azimuth is + 45 ° with respect to the incident surface. Alternatively, it is arranged at −45 °. Further, on the emission side of the phase modulation element 13, an analyzer (analyzer) 14 is arranged so that the transmission axis azimuth is 0 ° or 90 ° with respect to the incident surface, and the emission side of the analyzer 14 is on the emission side. ,
A photodetector 15 such as a photomultiplier for photoelectrically converting light is arranged. Therefore, the sample reflected light polarization-modulated by the phase modulation element 13 is incident on the photodetector 15 via the analyzer 14, and a signal corresponding to the incident light is detected by the photodetector 15.
Output from

The output signal of the photodetector 15 is subjected to a DC component V (DC), a ω component V (ω), and a 2ω component V by a signal component separation circuit 16.
(2ω) are separated and taken out. The signal component separation circuit 16 is configured by using a filter, a synchronous rectification circuit, or the like. Each component V (D obtained from the signal component separation circuit 16
C), V (ω), and V (2ω) signals (however, signals after synchronous rectification), the 2ω component V (2ω) is an incident angle control mechanism 18 for controlling the incident angle ψ ₀ with respect to the sample 1. And is used to control the incident angle ψ ₀ so that V (ω) is maximized. Here, the incident angle control mechanism 18
It is desirable to control not only the incident angle but also the specularly reflected light from the sample 1 to be incident on the optical system of the reflected light path. Therefore, for example, as shown in FIG. The angle of the system 19 and the reflected light path of the optical system 20 with respect to the sample 1 is controlled at the same time, or the angle of the sample base (not shown) holding the sample 1 and the angle of the optical system of the incident light path or the angle of the output light path are simultaneously controlled. It may be configured as follows. On the other hand, the direct current component V (DC) separated by the signal component separation circuit 16 is given to the photodetector 15 or an amplifier (not shown), and the sensitivity of the photodetector 15 and V (DC) are kept constant. The amplification factor is controlled. Furthermore, as described above, V
The azimuth angle θ when the azimuth angle of the linear polarization element 1 is controlled so that (2ω) becomes zero, and the incident angle (when the incidence angle is controlled so that V (ω) becomes maximum in that state ( That is, the positive incident angle) is input to a computing device 17 such as a computer or a dedicated computing device. In this arithmetic unit 17, the refractive index n, the absorption coefficient k, and the thickness d of the thin film are obtained from the above-described values of the azimuth angle θ, the incident angle, the wavelength λ, etc. by the method as described above.

FIG. 4 shows another embodiment (example of the second invention) of the ellipsometer of the present invention.

In the ellipsometer shown in FIG. 4, the phase modulator 13
Are arranged in the incident optical path with respect to the sample 1. That is, the phase modulator 13 having an amplitude δ ₀ and a modulation angular frequency ω is arranged between the linear polarization element 12 and the sample 1 such that the delay axis azimuth thereof is ₊ 45 ° or −45 ° with respect to the incident surface.
The linear polarization element 12 has a polarization direction of 0 ° or
It is fixed at 90 °, while the analyzer 14 has its transmission axis azimuth set to + 45 ° or −45 ° in the initial state, and the azimuth control mechanism 21 rotates it from ± 45 ° to θ. It has become. In addition, the signal component separation circuit
The synchronously rectified 2ω component V (2ω) obtained from 16 is used to control the azimuth angle of the analyzer 14. Other configurations are the same as those in the example of FIG.

In each of the above examples, the monochromator for the light source
If an element such as a diffraction grating having a variable selection wavelength is used as 11 and measurement is performed while performing wavelength scanning, the wavelength dispersion of the polarization state can also be known.

The ellipsometer of the present invention performs phase modulation on the sample reflected light or the sample incident light at the angular frequency ω to separate the DC component, ω component, and 2ω component of the detected light intensity signal,
2 The azimuth angle θ of the linear polarization element or analyzer is controlled so that the ω component becomes _zero , and the incident angle ψ ₀ on the sample is controlled so that the ω component becomes maximum in that state (thus, the positive incident angle is set. Control) to determine the refractive index and thickness of the sample from these rotation angle θ and incident angle. Since such modulation to separate the signal components means AC detection, Compared with the case of DC detection, the influence of back light etc. is significantly reduced to improve the S / N and the refractive index and thickness can be obtained with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the general concept of ellipsometry,
2 is a schematic diagram showing the concept of ellipsometry for a thin film on the sample surface, FIG. 3 is a block diagram showing an example of the ellipsometer of the first invention, and FIG. 4 is a block showing an example of the ellipsometer of the second invention. It is a figure. 1 …… Sample, 2 …… Thin film, 12 …… Linear polarizing element, 13 ……
Phase modulator, 14 ... Analyzer, 15 ... Photodetector, 16 ...
Signal component separation circuit, 18 ... Incident angle control mechanism, 21 ... Direction control mechanism.

Claims (2)

[Claims] 1. An ellipsometer for injecting linearly polarized light into a sample surface and measuring a value related to the sample surface from the polarization state of the reflected light, an incident angle control mechanism for controlling an incident angle ψ ₀ of the incident light on the sample surface. A linear polarization element is provided so that the polarization direction of the linearly polarized light incident on the sample surface is + 45 ° or −45 ° with respect to the incident surface in the initial state in the optical path of the incident light on the sample surface. Further, an azimuth control mechanism for rotating the azimuth of this linear polarization element from ± 45 ° to θ ° is provided, and a phase modulation element having an amplitude δ ₀ and a modulation angular frequency ω is provided in the optical axis of the reflected light from the sample surface with its delay axis Direction is + 45 ° or − with respect to the incident surface
At the same time, the analyzer is arranged so that the transmission axis is 0 ° or 90 ° with respect to the incident surface on the emission side of the phase modulation element, and the light is emitted on the emission side of the analyzer. And a signal component separation circuit for independently extracting the ω component, the 2ω component, and the DC component of the output signal of the photodetector.
The polarization azimuth of the linear polarization element is rotated so that the 2ω component becomes zero, the polarization azimuth is fixed at a rotation angle θ from ± 45 ° at that time, and the ω component is incident in such a state that the ω component becomes maximum. An ellipsometer, wherein the angle ψ ₀ is controlled and the refractive index of the sample surface and / or the thickness of the thin film on the sample surface is obtained from the rotation angle θ and the incident angle ψ _{0 at} that time. 2. An ellipsometer for injecting linearly polarized light into a sample surface and measuring a value related to the sample surface from the polarization state of the reflected light thereof, an incident angle control mechanism for controlling an incident angle ψ ₀ of the incident light on the sample surface. A linear polarizing element is provided so that the polarization direction of the linearly polarized light is 0 ° or 90 ° with respect to the incident surface in the optical path of the incident light to the sample surface, and the linear polarizing element and the sample surface are A phase modulator with an amplitude of δ ₀ and a modulation angular frequency of ω is placed in such a way that its delay axis azimuth is ₊ 45 ° or −45 ° with respect to the incident surface, and passes through the optical path of the reflected light from the sample surface. The analyzer is arranged so that the axial azimuth is + 45 ° or −45 ° with respect to the incident surface in the initial state, and the analyzer is provided with an azimuth control mechanism that rotates by θ ° from the ± 45 ° azimuth. The light is photoelectrically converted to the output side of the analyzer. And a signal component separation circuit for independently extracting the ω component, the 2ω component, and the DC component of the output signal of the photodetector, and further, so that the 2ω component becomes zero. The analyzer azimuth is rotated to fix the polarization azimuth at a rotation angle θ from ± 45 ° at that time, and the incident angle ψ ₀ is controlled so that the ω component becomes maximum in that state, and the An ellipsometer characterized in that the refractive index of the sample surface and / or the thickness of the thin film on the sample surface is obtained from the rotation angle θ and the incident angle ψ ₀ .