JPS63168541A - Ellipsometer - Google Patents

Abstract

PURPOSE:To measure refractive index on an object at a high accuracy in a short time with a high S/N ratio free from background light, by inserting a phase modulation element into an optical path to a sample to control an angle of incidence into the sample with the regulation of the bearing of a linearly polarizing element or an analyzer. CONSTITUTION:A mechanism 18 is provided to control an angle phi0 of incidence into the surface of the sample 1 and a linearly polarizing element 12 is placed in an incidence optical path so that the polarization bearing of incident linearly polarized light is + or -45 deg. in the initial state. A bearing control mechanism 21 is provided to turn the bearing of the element 12 by theta deg. from + or -45 deg. and a phase modulation element 13 with the amplitude delta0 and the modulation angle frequency omega is arranged in a reflection optical path so that the delay axis bearing thereof is + or -45 deg.. An analyzer 14 is provided on the incident side of the element 13 so that the transmission axis thereof is 0 deg. (90 deg.) and moreover, a photo detector 15 is provided while a separation circuit 16 is provided to extract omega and 2omega and DC components of a detection signal independently. The polarization bearing of the element 12 is turned to zero the 2omega component and fixed at an angle theta of rotation from + or -45 deg.. Under a condition, the angle phi0 of incidence is controlled to max the component and then, refractive index of the sample surface and the thickness of a thin film are determined from angles theta and phi0.

Description

Detailed Description of the Invention Field of Industrial Application This invention is an ellipsometer that uses the polarization property of light to measure the thickness of a thin film on an object (sample surface) and the refractive index related to the physical properties of the film on the specimen surface. It's about.

Conventional technology As shown in Fig. 1, if linearly polarized light is incident obliquely from above on the surface of a sample 1 having a thin film 2 on the surface at an incident angle ψ0, the reflected light will vary depending on the thickness and refractive index of the thin film on the sample surface. The polarization state of the light changes, and it is usually reflected as elliptically polarized light.

By measuring the amount of change in polarization of this reflected light and performing analytical calculations, it is possible to determine 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, the important parameter of the amount of polarization change of reflected light necessary to determine the thickness and refractive index of a thin film is that the p component wave on the horizontal p coordinate plane and the perpendicular S coordinate plane due to reflection are Changes in the principal axis direction of polarization due to the phase shift T generated between the S component wave and the difference in amplitude of the image component wave caused by the difference in reflectance between the P component wave and the S component wave. There is.

By the way, conventional ellipsometers can be roughly divided into two types: photometric type and extinction type. In the photometric type, a polarizing prism is continuously rotated, and the phase shift γ and the amount of change ψ in the principal axis direction are calculated from the relationship between the angle and the detected light intensity. On the other hand, in the extinction type, polarized light that has changed in the sample is returned to its original state by rotating an optical element, and the phase shift T and change in principal axis direction are determined from the compensation angle. Both of these two methods obtain the necessary information by measuring the amount of change in light intensity, that is, the DC output of the photodetector.

Problems to be Solved by the Invention Among conventional ellipsometers, photometric type ellipsometers calculate the phase shift γ and the change amount ψ in the principal axis direction, which are parameters for the amount of change in polarization. There is a problem that measurement accuracy deteriorates in areas close to .

On the other hand, the extinction type directly measures the polarization angle as an angle, so it has the advantage of achieving high measurement accuracy to the extreme of a polarizing prism. There are long drawbacks.

A common drawback of both the photometric type and the extinction type is that because the light intensity is detected as a DC component, they are directly affected by background light and the like, resulting in a poor signal-to-noise ratio (S/N).

Therefore, an object of the present invention is to provide an ellipsometer that can measure thin films and refractive indexes on objects with high precision and in a short time with high S/N without being affected by background light. .

Means for Solving the Problems In the ellipsometer of the present invention, basically linearly polarized light is incident on the sample, and a phase modulating element is inserted in the optical path of incidence on the sample or in the optical path of reflection. The light or reflected light is modulated, and the components of the modulation frequency and the two of the modulation frequency are synchronized with the modulation frequency from the signal of the photodetector.
The frequency component twice the modulation frequency and the DC component are extracted, and the direction of the linear polarizer or analyzer is controlled so that the frequency component V (2ω) twice the modulation frequency becomes zero, and in that state, the frequency component of the modulation frequency is ■ Control the incident angle ψO to the sample so that (ω) is maximum, and then change the rotation angle θ of the right-angle polarizer or analyzer from the incident angle ψ0 to the birefringence value of the sample and/or the thin film. I tried to find the thickness.

Specifically, the first invention provides an ellipsometer that makes linearly polarized light incident on a sample surface and measures a value related to the sample surface from the polarization state of the reflected light. An angle control mechanism is provided, and the polarization direction of the linearly polarized light incident on the sample surface is adjusted to +45 degrees or -45 degrees with respect to the incident surface in the initial state in the optical path of the incident light on the sample surface.
A linear polarizing element is arranged so that the angle is 0°, and an azimuth control mechanism is provided to rotate the azimuth of this linear polarizing element by θ° from +45°. A phase modulation element with a frequency of ω is arranged so that its delay axis orientation is +45° or -45° with respect to the incident plane, and a transmission axis orientation of 0° with respect to the incidence plane is placed on the output side of the phase modulation element. Alternatively, an analyzer is arranged so that the angle is 90', and a photodetector for photoelectric conversion of light is arranged on the output side of the analyzer, and the ω component, 2ω component, and DC component of the output signal of the photodetector are arranged. A signal component separation circuit for extracting each component independently is provided, and
Rotate the polarization direction of the linear polarizing element so that the ω component becomes zero, fix the polarization direction at the rotation angle θ from +45°, and set the incident angle ψ0 so that the ω component becomes maximum in that state. to control the rotation angle θ and the incident angle ψ
This method is characterized in that the refractive index of the sample surface and/or the thickness of the thin film on the sample surface are determined from O.

The ellipsometer of the second invention differs from the ellipsometer of the first invention basically in that a phase modulation element is disposed in the optical path of incidence on the sample and the orientation of the analyzer is controlled. That is, the ellipsometer of the second invention is an ellipsometer that makes linearly polarized light incident on the sample surface and measures a value related to the sample surface from the polarization state of the reflected light, and the ellipsometer has an incident angle control that controls the incident angle ψ0 of the incident light on the sample surface. A mechanism is provided, and a linear polarizing element is arranged in the optical path of the incident light to the sample surface so that the polarization direction of the linearly polarized light is 0° or 90' with respect to the incident plane, and the linear polarizing element and the sample surface are A phase modulation element with an amplitude δO1 and a modulation angular frequency ω is placed between the The initial axis orientation is + with respect to the plane of incidence.
Place the analyzer so that it is 45° or -45°,
The analyzer is equipped with an azimuth control mechanism that rotates it by θ° from the azimuth of =45°, and a photodetector for photoelectric conversion of light is placed on the output side of the analyzer, and the output of the photodetector is A signal component separation circuit is provided to independently extract the ω component, 2ω component, and DC component of the signal, and the orientation of the analyzer is rotated so that the 2ω component becomes zero, and the azimuth of the analyzer is ±45° at that time. The polarization direction is fixed at the rotation angle θ from
is controlled, and the refractive index of the sample surface and/or the thickness of the thin film on the sample surface are determined from the rotation angle and the incident angle ψ0 at that time.

Function Before explaining the function of the ellipsometer of the present invention, the measurement principle of the ellipsometer will be explained first, and then the theoretical analysis of the ellipsometer of the present invention will be explained together with its function.

A: Ellipsometer measurement 7. A ring ellipsometer measures the optical constant (refractive index) of the object itself by observing changes in the polarization state when light is reflected on the surface of the object.
Another method is to find out the thickness and optical constant (refractive index) of a thin film attached to the surface of an object. First, we will explain the principle of measuring the optical constants of the object itself, that is, the underlying material when there is no thin film, and then the principle of measuring the thickness and optical constants of the thin film when there is a thin film.

A-1: Measurement of i First, let the optical constant of the sample be 'fi=n-ik.

Here, the stone has a complex refractive index, n is the refractive index, k is the absorption coefficient,
i is an imaginary unit.

The vibration component (p component) parallel to the plane of incidence of a monochromatic parallel light beam incident from vacuum at an angle of incidence ψ0 (film width reflectance (Fresnel coefficient)) is P, and the vibration component (S component) perpendicular to the plane of incidence is The amplitude reflectance (Fresnel coefficient) is s, and these are respectively '?'p = rp exp (-iφp)
(1)'? ”s = r s exp (-rφs)
(2). These are the optical constants fi of the sample
=n-ik and the incident angle ψ0.

In a transparent sample with an absorption coefficient of =o, φP and φS are generally O.
or π, so 7′″p, 'Fs is a real number, so
The incident linearly polarized light does not become elliptically polarized light but is reflected as linearly polarized light.

However, in absorber samples such as metals (k≠O), the phase difference (retardation) T due to reflection, that is, γ = φP - φ5 (3), is continuous from 0 to π depending on the value of the incident angle ψ0. Generally speaking, 7"p/?"S is a complex number (teP, 7
'''Each of S is also a complex number).

= tan veXI) l γ =ρexp iγ (4), and tan
v=ρ(=rp/rs> is called amplitude reflectance ratio or (film width reflection coefficient ratio (real number)).

In this way, in the absorber sample'? ``Since p/?s is a complex number, the incident linearly polarized light is reflected as elliptically polarized light.

If we measure two parameters of the elliptically polarized light (for example, the azimuth α of the long axis of the ellipse and the ellipticity
It is possible to find T. These two i tan forces, γ
The following relational expression is known between n, refractive index, and absorption coefficient.

n2 -2 Therefore, if the values of W and γ are known, the refractive index and absorption coefficient k of the sample can be determined.

A-2: Determining the thickness of the thin film and its width - As shown in Figure 2, the refractive index h1 = n1-ik1, the thickness difference d is Assume that there is an isotropic homogeneous thin film 2, into which linearly polarized light is incident at an incident angle ψ0.

The reflected light R is a combination of the light R1 reflected on the surface of the thin film, the light R2 reflected on the interface between the thin film and the base, and the light R3 onward that comes out while reciprocating within the thin film. That is, R=R1+R2+R3+... (7) The amplitude reflectance of the entire surface, taking into account repeated reflection interference within the film, is given separately for the p component and the S component.

Here, (j-1,2> n j-+ sln (J) j-+ = n j s
:nψj (12)δ=4πntd
cosψ1/λ (13) necessarily, teJP
Ntejs is, when j=1, the first element (vacuum - membrane), j
The value of =2 is the amplitude reflectance (Fresnel coefficient) of the p and S components on the second surface (film-substrate). Also, δ is model width 1
This is the phase difference caused by the round trip, and λ is the wavelength in vacuum.

Here, since Rp/Rs is a complex number even if the Fresnel coefficient δ such as TeJP is a real number, the reflected light becomes elliptically polarized light.

The complex reflection coefficient HikiP/YiS is the same as equation (4). Hail.

Here, the value tanri, γ on the right side is the quantity measured with an ellipsometer, while the coefficient ratio on the left side is (6) to (11
) As can be understood from the formula, ? 'it (nt, k
t>,? 'i2 (n2. to 2), d.

It is a function of λ and ψ0. That is, γ, V = F(nl, 1 for n2., 2.d, λ, ψ0) (
15) Of the parameters on the right side of the equation, n2, k2, λ, ψ
If 0 is known and the measured values γ and ri are used, nl and d can be solved as unknowns.

For example, if k1=O (transparent film), the unknown quantity is nl
, d, and their values can be easily determined by calculation. Even when kl>O (absorbent membrane), nl, kl, and d can be determined by measuring γ and instep.

Measured quantity 7-. 14/, find ln1, kl, d
A method of calculating is publicly known.

As described above, the thickness d of the thin film on the sample surface, the optical constants refractive index n1, and absorption coefficient kl can be obtained from the amplitude reflection coefficient ratio -V (=ρ) and the phase difference force measured by an ellipsometer. This is possible.

B: Today's Theoretical Analysis The output of the optical array of the ellipsometer of this invention will be analyzed using the Mueller matrix analysis method using the following procedure. Here, the optical arrangement of the first invention shown in FIG. 3 will be explained as an example.

First, regarding the output signal of the photodetector, what are the components V (ω) of the same frequency as the modulation frequency of the phase modulation element, the component V (2ω) of twice the frequency, and the direct current component V (DC)? guide.

Next, conditions for controlling the polarization direction of the linearly polarizing element so that V(2ω) becomes zero will be derived. Furthermore like this V
With the polarization direction fixed at angle θ so that
Deduce the conditions when controlling. Then, the angle θ, the incident angle ψ0, and the birefringence h (refractive index n and absorption coefficient k)
, and the thin film thickness d.

Next, these analysis procedures are divided into sections and described.

B-1: Relationship between each signal, phase difference, and reflection coefficient L. First, each optical element is expressed by a Mueller matrix.

The Mueller matrix AO of the analyzer is It is expressed as

Mueller matrix of phase modulator M45. δ(ω) is δ
is the angular frequency (angular velocity) of modulation of the optical phase modulator
, where the amplitude is δ0, δ = δ o s+nω t
It is expressed as (18).

Further, the Mueller matrix Si of the reflective surface of the sample for the 45° polarization plane is expressed as follows, given the reflection coefficient ratios rp, ,'r. However, γ is the difference in phase change (phase difference = retardation), rp and r'3 are the p component and S
is the reflection coefficient of the component.

Mueller matrix To that rotates the orientation of the polarization state by θ°
is expressed as .

The Mueller matrix 145 of roughly 45° linearly polarized light is expressed by .

The output I (d) of the photodetector in this case is (16
), (17), and (19) to (21).

1 (d) = Ao-M4s, δ(ω)・5i-TO・I45 Then, calculating 1 (d) from equations (16), (17), and (19) to (21), we get the following equation. Become.

1(d) Here, if we expand S1nδ and δ using the Bessel function, we get Sinδ=s+n (δ0SIn(IJt)=2J1
(bo)s+n(I)t+2J3(bo)s+n
3ωt+-(24)吋δ-COS(δosI11ωt) =Jo(δO)+2J2(δ0)COS2ωt+2J
4 (bo)cos4ωt+...

If the electrical signal of the output of the photodetector proportional to the light intensity 1 (d) is V (d), then V (d) is the direct current component V (DC
>, ω component ■(ω), 2ω component V(2ω), and 3ω
It can be expressed as follows using harmonic components of component V(3ω) or higher.

V(d) =VDc+V(ω) +V(2ω) 10(
Harmonic peak) In equations (24) and (25), J'o
The term (δ0) is the DC component, and the term Jl (δO) is ω
The term J2 (δ0) corresponds to the 2ω component.

Therefore, equations (23) and (24), ('25)
From the formula, (26bCf7) each component V (DC), V
(ω), V(2ω), we get V(DC)-rp"+ ms2- (rp2- r3"
) s+n2θ+ (rp2-ms”) ・Jo
(ro0)-(rP2+rs2)Slnθ ・Jo
(roo) (27)■(ω)=-
4rprs・mountain(5o)・cos2θ5In7'
(28) V(2ω) = 2 (rp2rs2) ・J
2(5o)-2(rp2+ ms2) SI+12θ・
J+ (bo> (29)).

B-2: Control of polarization direction il and incidence angle Here, if the direction of the polarizer is rotated from ±45° and controlled so that the magnitude of the 2ω component becomes zero, then in equation (29), V (
2ω)=O, rp2− rs2= (rp2+
ms2) 5rn2θ (30) holds true.

Under such conditions that the 2ω component is zero, the direct current component V (DC) can be obtained by substituting equation (30) into equation (27), V (DC) = (rp''+rs') co<20
(31).

On the other hand, under the condition that the 2ω component becomes zero, the reflection coefficient ratio rs/r
Once p (= tantl/) is determined, the linear polarizing element is rotated so that the size difference of the 2ω component becomes zero as shown in equation (30), and the azimuth angle θ (however, the azimuth angle from the initial ±45° ), and if we find a condition such that the ω component V(ω) is maximized in that state, then V(ω) in the above equation (28)
It can be seen that in order for V(ω) to be maximized in the equation, sin γ=1, that is, γ=π/2 (33).

In other words, when the incident angle ψ0 to the sample is changed and the incident angle is the one where the ω component V(ω), which is the same as the modulation frequency, is maximum,
The phase difference (retardation) T is 90° (π/2).

Generally, the angle of incidence such that T = π/2 is called the main angle of incidence T. Therefore, under the condition that the azimuth θ of the linear polarizer is fixed so that V(2ω) - 〇, V(ω) If the angle of incidence ψ0 is controlled so that the angle of incidence is maximized, the angle of incidence at that time is the main angle of incidence T, and the phase difference γ is π/2.

Although the above relationship has been described for the example of the first invention shown in FIG. 3, the same relationship as above applies to the second invention shown in FIG. 4, with the only difference being that θ is the azimuth angle of the analyzer. holds true.

B-3 = Calculation relationship of refractive index Generally, light is medium 1 (its optical constant nt = n1 - ik1
) to the medium 2 (its optical window number 2 = n2 - ik2) at an incident angle ψ1, the refraction angle is ψ2, and the phase change is T.
Then, the Fresnel coefficient rs of S-polarized light representing the amplitude reflectance is
, Pli light Fresnel coefficient rp is given by the following equation.

S-polarized light rs=rse'φ5 P-polarized light p=rpe'φp where n-cosψ・=(Pi・2-siriψ・)ear (
36) JJ J J Therefore, when light is projected onto an absorbing medium in the air at an incident angle ψ0, using this equation, the following equation can be derived.

5irfψ0 [mlψ0 Here, P and Q are respectively It is.

Divide equation (40) into a real part and an imaginary part, and ρ=rs/rp=tcn14/(
41), we obtain the following equation.

n2− to 2 = 5irfψO(1+ P2cos2 Qtariψ
0)2 n k=-P2 s+n2Qs*rfψ
OknψOHere, if the absorption is small and the incident angle is smaller than a certain range and n2-k2>51riψO holds, then equation (38) is simplified, and n and k are given by the following equations.

When measuring at the main angle of incidence ψo=T where γ=π/2, (
Equations 42), (43), (44), and (45) can be written as follows, respectively.

2=s;nT (1+cOS4vtariT) in nl
(46) 2 n k=5in4'J'5iff
TtariT (47)n #COS
2 vsln T tan T
(48) k :Sin 2 vsin T tari
T (49) By the way, from the equation (33) already mentioned, rs / rp = tanv = tan (45° - θ)
Therefore, army = 45° - θ (50) holds true. Therefore, equations (48) and (49) are (50
) can be rewritten as follows.

n#5in2 θ Sin T tan T
(51)k#
cos2 θ S10 TtanT
(52) Here, the normal incidence angle T is the incidence when the angle of incidence on the sample is controlled so that V(ω) is maximized with the azimuth angle θ fixed so that V(2ω) = ○. It is known because it is a corner. Furthermore, the village is also known from θ using equation (50). Therefore, from θ and T, the refractive index n and the absorption coefficient k can be found by equations (51) and (52).

B-3: Calculation of the "d" of the thin film The calculation for the thin film on the sample surface is, that is, the refractive index n
1. Absorption coefficient kl, thin film thickness d, phase difference γ measured by an ellipsometer, and amplitude reflectance ratio ta11v (=ρ
), as mentioned above, = tan”V eXD (i T ＞=p ex
pi 7 (53), and γ and ri are functions determined by the following equation.

! /=f (nl, kl, d, nl, 2.ψ0.
λ)7=f (nl, 4, d, nl, 2.ψ0
．． λ) Therefore, nl, kl, d, nl, k2, ψ0, λ
If A and γ are given, then γ can be calculated, and conversely, if A and γ are found, d can be found. Equation (54), (
55) A graphical representation of the calculated formula is already known, and if such a detailed diagram is created, the thin film thickness d can be immediately determined from the measured value by interpolation.

Note that it is also possible to obtain d using a computer from the measured values of γ and the military.

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

In FIG. 3, light from a white light source 10 is incident on a monochromator 11 to select monochromatic light with a wavelength λ, and the monochromatic light with a wavelength λ is passed through a linear polarizing element (polarizer= The light is incident on the sample 1 as linearly polarized light with a polarization direction of 145° or 145° relative to the plane of incidence in the initial state. Note that this linearly polarizing element 12 is attached with an azimuth controller 121 for rotating the polarization direction by θ from ±45°. As described above, the reflected light from the sample 1 usually becomes elliptical sunlight and enters a phase modulation element (optical polarization modulation element) 13, for example a photoelastic modulator 13 such as a Faraday cell. This phase modulation element 13 has an amplitude δ
0, the incident elliptically polarized light is alternately changed into counterclockwise polarized light and clockwise polarized light at angular frequency ω, and is arranged so that the delay axis direction is +45° or -45° with respect to the plane of incidence. has been done. Roughly speaking, on the output side of the phase modulation element 13, the transmission axis direction is Oo or 90' with respect to the incident plane.
An analyzer 14 is arranged so that the analyzer 14 has the following properties, and a photodetector 15 such as a photomultiplier for photoelectrically converting light is arranged on the output side of the analyzer 14. 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 output from the photodetector 15.

The output signal of the photodetector 15 is sent to a signal component separation circuit 16.
The direct current component V (DC) and the ω component V (ω), 2
The ω component V (2ω) is separated and extracted. This signal component separation circuit 16 is constructed using a filter, a synchronous rectifier circuit, and the like. Among the signals of each component (DC), V(ω), and V(2ω) (signals after synchronous rectification) obtained from the signal component separation circuit 16, the 2ω component V(2ω) is determined by the incident angle with respect to the sample 1. It is applied to the incident angle control mechanism 18 for controlling ψ0, and is used to control the incident angle ψ0 so that ■(ω) is maximized. Note that it is desirable that the incident angle control mechanism 18 not only simply control the incident angle but also control the specularly reflected light from the sample 1 so that it is incident on the optical system of the reflected optical path. Therefore, for example, as shown in FIG. As shown in FIG.
0 with respect to the sample 1, or the angle of a sample base (not shown) that holds the sample 1 and the angle of the optical system of the incident optical path or the angle of the output optical path may be controlled simultaneously. 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 is adjusted so that the V (DC) becomes constant. The amplification factor is controlled. Furthermore, the azimuth angle θ when the azimuth angle of the linear polarizing element 12 is controlled so that V(2ω) becomes zero as described above, and the incident angle so that ■(ω) is maximized in that state. The angle of incidence (that is, normal incidence angle T) when controlled is input to a calculation device 17 such as a computer or a dedicated calculation device. In this calculation device 17, the above azimuth angle θ
From the values of the incident angle T, the wavelength λ, etc., the refractive index n, the absorption coefficient k, and roughly the thickness d of the thin film are determined by the method described above.

FIG. 4 shows another embodiment (an example of the second invention) of the ellipsometer of this invention. - In the ellipsometer of FIG. 4, the phase modulation element 13 is arranged in the incident optical path to the sample 1. That is, a phase modulating element 13 having an amplitude δ0 and a modulation angular frequency ω is arranged between the linear polarizing element 12 and the sample 1 so that its delay axis direction is +45° or -45° with respect to the plane of incidence. The polarization direction of the linear polarizing element 12 is fixed at 0° or 90°, and the -5 analyzer 14 is set so that its transmission axis direction is +45° or -45° in the initial state. The orientation control mechanism 21 allows rotation by θ from +45°. Further, the 2ω component V(2ω) after synchronous rectification obtained from the signal component separation circuit 16 is:
It is used to control the azimuth of the analyzer 14. The other configurations are similar to the example shown in FIG.

In addition, in each of the above, the monochromator 1 of the light source part
1. By using an element such as a diffraction grating with a variable selection wavelength and performing measurements while scanning the wavelength, it is also possible to know the wavelength dispersion of the polarization state.

Effects of the Invention The ellipsometer of the present invention performs phase modulation on sample reflected light or sample incident light at an angular frequency ω to separate the DC component, ω component, and 2ω component of the detected light intensity signal.
The azimuth angle θ of the linear polarizer or analyzer is controlled so that the ω component becomes zero, and in this state the incident angle ψ0 to the sample is controlled so that the ω component becomes maximum (therefore, the angle of incidence is normal, T). ), and these rotation angles θ and incidence angles T
This method determines the refractive index and thickness of the sample from the 100-degree angle, and separating signal components by modulating in this way means alternating current detection. The refractive index and thickness can be determined with high accuracy by significantly reducing the influence of .

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the concept of general ellipsometry.
FIG. 2 is a schematic diagram showing the concept of ellipsometry for an N film on a sample surface, FIG. 3 is a block diagram showing an example of the ellipsometer of the first invention, and FIG. 4 is an example of the ellipsometer of the second invention. It is a block diagram. DESCRIPTION OF SYMBOLS 1... Sample, 2... Thin film, 12... Linear polarization element, 13... Phase modulation element, 14... Analyzer,
15... Photodetector, 16... Signal component separation circuit, 18... Incident angle control mechanism, 21... Azimuth control I mechanism.

Claims (2)

[Claims] (1) In an ellipsometer that makes linearly polarized light incident on the sample surface and measures values related to the sample surface from the polarization state of the reflected light, an incident angle control mechanism is provided to control the incident angle ψ_0 of the incident light on the sample surface, and A linear polarizing element is placed in the optical path of the incident light on the sample surface so that the polarization direction of the linearly polarized light incident on the sample surface is +45° or -45° with respect to the incident plane in the initial state, and An azimuth control mechanism that rotates the azimuth of the polarizing element by θ° from ±45° is provided, and a phase modulation element with an amplitude δ_0 and a modulation angular frequency ω is placed in the optical path of the reflected light from the sample surface so that its delay axis orientation is the incident plane. +45 against
or -45°, and the transmission axis is 0° with respect to the incident plane on the output side of the phase modulation element.
Alternatively, an analyzer is arranged so that the angle is 90°, and a photodetector for photoelectric conversion of the light is arranged on the output side of the analyzer, and the ω component, 2ω component, and DC component of the output signal of the photodetector are arranged. A signal component separation circuit is provided to extract each component independently, and the polarization direction of the linear polarization element is rotated so that the 2ω component becomes zero, and the polarization direction is adjusted at a rotation angle θ from ±45° at that time. The angle of incidence ψ_0 is fixed and controlled so that the ω component is maximized in that state, and the refractive index of the sample surface and/or the thickness of the thin film on the sample surface are calculated from the rotation angle θ and the incident angle ψ_0 at that time. An ellipsometer characterized by the following features. (2) In an ellipsometer that makes linearly polarized light incident on the sample surface and measures values related to the sample surface from the polarization state of the reflected light, an incident angle control mechanism is provided to control the incident angle ψ_0 of the incident light on the sample surface, and A linear polarizing element is arranged in the optical path of the incident light to the sample surface so that the polarization direction of the linearly polarized light is 0° or 90° with respect to the incident plane, and the amplitude is set between the linear polarizing element and the sample surface. A phase modulation element with δ_0 and modulation angular frequency ω whose delay axis direction is +45 with respect to the incident plane.
In the optical path of the reflected light from the sample surface, place the analyzer so that the transmission axis direction is initially +45° or -45° with respect to the incident plane. The analyzer is equipped with an orientation control mechanism that rotates it by θ° from the ±45° orientation, and a photodetector for photoelectric conversion of light is placed on the output side of the analyzer. A signal component separation circuit is provided to independently extract the ω component, 2ω component, and DC component of the output signal,
Furthermore, rotate the orientation of the analyzer so that the 2ω component becomes zero, fix the polarization orientation at the rotation angle θ from ±45°, and then adjust the incident angle so that the ω component becomes maximum. An ellipsometer characterized in that the refractive index of the sample surface and/or the thickness of a thin film on the sample surface are determined by controlling ψ_0 and the rotation angle θ and the incident angle ψ_0 at that time.