JPH05264229A - Ellipsoparameter measuring method and ellipsoparameter - Google Patents

Abstract

PURPOSE:To increase accuracy in the measuring of film thickness while keeping high measuring speed by separating light reflected at a subject for measurement into more than a predetermined number of polarized components, and calculating an ellipsoparameter according to the intensity of each polarized component using a statistical method. CONSTITUTION:Incident light 17 is reflected at a sample surface 13 and is converted into elliptically polarized reflected light 18 and is separated by a nonpolarizing beam splitter 19 into rays of light 20a, 20b being elliptically polarized. The reflected rays of light 20a, 20b are incident on respective polarizing beam splitters 21, 22 and transmitted rays of light 21a, 21b. output from the splitter 21 are incident on respective light receivers 23a, 23b. The transmitted rays of light 22a, 22b output from the splitter 22 are incident on respective light receivers 23c, 23d. The light receivers 23a-23d obtain the intensity I1-I4 of the rays of light projected on the longitudinal and transverse axes of the elliptically polarized light and on a line tilted by + or -45 deg. to the transverse axis; i.e., the reflected light 18 is separated into polarized components in four directions, and an ellipsoparameter PSI, DELTA for specifying the elliptical polarization of the reflected light 18 is calculated according to the intensity I1-I4 using the method of least squares. Therefore, high measuring speed is maintained and high accuracy is obtained in measuring film thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ellipsometer measuring method for measuring an ellipsometer used for accurately measuring a thin film thickness and an ellipsometer using this method, and more particularly, to an ellipsometer using a plurality of detected light intensities. The present invention relates to an ellipsometer parameter measuring method and ellipsometer for calculating highly accurate ellipsometer parameters using a statistical method.

[0002]

2. Description of the Related Art The ellipsometry method is used as a method for measuring the thickness of a thin film. This method changes the polarization state when light is reflected by the sample surface such as a thin film, that is, the reflectance Rp of the component (P component) parallel to the incident surface of the electric field vector.
And the ratio ρ between the reflectance Rs of the vertical component (S component) is (5)
This film thickness d is obtained according to the established relationship between the polarization reflectance ratio ρ and the film thickness d, which is already measured. ρ = Rp / Rs = tan ψ exp [jΔ] (5)

Here, the polarization reflectance ratio ρ is generally a complex number as shown in the equation (5), and therefore, two ellipso parameters, that is, an amplitude ratio tan ψ and a phase difference Δ, ψ are determined. Need to ask.

Conventionally, there is a method called a rotational analyzer method as a method for obtaining the ellipso parameters ψ and Δ. In this method, for example, light polarized at a predetermined angle is incident on a measurement target from a light source, and elliptically polarized reflected light from the measurement target is transmitted through a rotating analyzer and guided to a light receiver. Then, the ellipso parameter is calculated from the light intensity signal waveform obtained by the light receiver at that time.

However, when performing one measurement, it is always necessary to rotate the analyzer once to observe the light intensity signal, and therefore it is always necessary to rotate the analyzer for a certain time or longer. Therefore, it is impossible to measure the film thickness of the measurement target moving at high speed. In addition, since the mechanical moving parts are present, the device itself becomes large in size, and it is impossible to install the device on a manufacturing line of a factory or the like and measure a measurement target continuously supplied online.

In order to eliminate such inconvenience, FIG.
As shown in FIG. 6, a three-channel ellipsometer without moving parts has been developed (Japanese Patent Laid-Open No. 63-3610).
5 and JP-A-1-28509).

For example, the light having a single wavelength output from the laser light source 1 is converted into linearly polarized light by the polarizer 2 and is incident on the sample surface 3 to be measured at a predetermined angle φ. In addition,
On the sample surface 3, the incident surface is parallel to the paper surface, and as shown in the figure, the direction parallel to the incident surface is the P direction and the direction orthogonal to the incident surface is the S direction. The reflected light from the sample surface 3 is split into three lights by the three non-polarized beam splitters 4a, 4b and 4c.

Then, the two beam splitters 4a, 4
The light transmitted through b is incident on the light receiver 7a via the analyzer 5a and the condenser lens 6a. The light receiver 7a detects the light intensity I1. Similarly, the light transmitted through the beam splitter 4a and reflected by the next beam splitter 4b is incident on the light receiver 7b via the analyzer 5b and the condenser lens 6b. The light receiver 7b detects the light intensity I2. Further, the light reflected by the beam splitter 4a and transmitted through the next beam splitter 4c is analyzed by the analyzer 5c and the condenser lens 6.
It is incident on the light receiver 7c via c. The light receiver 7c detects the light intensity I3.

Here, the polarization direction of the analyzer 5a is set to the reference direction (azimuth 0 °), and the polarization direction of the analyzer 5b is set to be tilted + 45 ° with respect to the reference direction.
The polarization direction of c is set to be inclined -45 ° with respect to the reference direction. The reference direction is a direction in which the direction parallel to the light incident surface on the sample surface 3 (P direction) is 0 °, as shown by the arrow a direction in the figure when viewed from the light receiver 7a side. .. The angle is counterclockwise from the reference direction when viewed from the light receiver 7a side.

Therefore, when the light reflected by the sample surface 3 is elliptically polarized as shown in FIG. 14, the light intensity I1 obtained by the light receiver 7a is the abscissa of the elliptically polarized light shown in FIG. The amplitude of the orthographic projection in the (0 ° direction) is shown. Further, the light intensity I2 obtained by the light receiver 7b indicates the amplitude of the orthographic projection on the line inclined + 45 ° in the elliptically polarized light. Further, the light intensity I3 obtained by the light receiver 7c indicates the amplitude of the orthographic projection on the line inclined at -45 ° in the elliptically polarized light.

Now, the output waveform of the light intensity obtained by the photodetector for detecting the light of the polarization direction of the angle Ai (i = 1,2,3) is obtained by using the Jones vector (excluding the constant multiple). 6) It is shown by a formula.

[0012]

[Equation 2]

[0013] indicates incident polarized light having an amplitude ratio χ of P polarized light and S polarized light and a phase difference φ ₀ . j is an imaginary unit.
The first component of the equation (7) indicates the P-polarized component, and the second component indicates the S-polarized component. Also,

[0014]

[Equation 3] Is a matrix showing the analyzers placed at the angle Ai. Then, in the equation (6), A1 = 0 °, σ1 = σT ² _{, Φ 1 = 0 A2 = +} 45 °, σ2 = σTσR, φ 2 = 0 A3 = -45 °, σ3 = σTσR, φ 3 = 0 ... When (11), from (6), obtained in the respective channels The light intensity Ii (i = 1,2,3) is as shown in equation (12) if the gain of the light receiver is properly selected. I 1 = I ₀ tan ² _{ψ I2 = [I 0/2} ] × [tan 2 ψ + (σT · σR · χ) ² + 2σT · σR · χ · tanψ · cos (Δ-φ 0)] I3 = [I 0/2] × [tan 2 ψ + (σT · σR · χ) ² −2σT · σR · χ · tan ψ · cos (Δ−φ ₀ )] (12) where I ₀ is a constant that depends on the intensity of incident light and the reflectance of the measurement target.

Therefore, the phase difference Δ of the ellipso parameters and the amplitude ratio tan ψ are calculated for each light intensity I 1,
It can be obtained from I2 and I3 by the following equations (13a) and (13b). cos (Δ−φ ₀ ) = [(I 2 −I 3) / 2I 1] × [I 1 / (I 2 + I 3 −I 1)] ^1/2 (13a) tan ψ = | σT · σR · χ | [I1 / (I2 + I3-I1)] ^1/2 … (13b)

[0016]

However, as shown in FIG.
The conventional ellipsometer shown in (1) also had the following problems to be improved.

That is, the shape of the elliptically polarized light is calculated using the three light intensities I1 to I3 detected by the respective light receivers 7a to 7c. Therefore, if one of the three light intensities has a large error intensity, the calculated error rate of the ellipso parameters Δ and ψ becomes approximately equal to the error rate of the light intensity having the largest error. Therefore, the measurement accuracy of the ellipso parameter measured by this ellipsometer is lowered.

For example, when the elliptical shape shown in FIG. 17 becomes flatter, only the third light intensity I3 of the three light intensities I1, I2, I3 is extremely higher than the other light intensities I1, I2. Will be a small value.

On the other hand, each of the ellipso parameters ψ,
In order to calculate Δ by, for example, a computer, it is necessary to convert each analog light intensity I1 to I3 into a digital value by an A / D converter. Therefore, when the value of only one light intensity is small, the number of significant digits of the A / D converted value is small,
Each light intensity will contain a large error. As a result, the accuracy of the calculated ellipso parameters ψ and Δ decreases, which causes a problem that the measurement accuracy of the finally obtained film thickness d decreases.

As described above, the three-channel ellipsometer shown in FIG. 16 does not have any moving parts, and is thus a very useful device capable of measuring the film thickness of the object to be measured at high speed. Depending on the object, the measurement accuracy may be inferior to that of the ellipsometer using the rotating analyzer described above.

If the number of times of measurement at the same measurement point is increased and the average value of the measurement results is taken, the error is compressed to some extent, but if the same measurement point is repeatedly measured, not only the total measurement time becomes longer, but also For example, it cannot be applied to a measurement target that is moving at high speed such as a film thickness inspection in a factory production line.

The present invention has been made in view of such circumstances, and separates the reflected light having the elliptically polarized light reflected by the object to be measured into four or more polarization components having different polarization directions from each other. By detecting the light intensity of the component and statistically processing all the light intensities, the error rate of the calculated ellipso parameter can be significantly reduced, and the film thickness measurement accuracy can be improved while maintaining a high measurement speed. An object of the present invention is to provide an ellipsometer parameter measuring method and an ellipsometer which can be significantly improved.

[0023]

In order to solve the above-mentioned problems, in the ellipsoparameter measuring method of the present invention, polarized light is made incident on a measuring object at a predetermined angle, and reflected light of this measuring object is mutually reflected. It is separated into four or more different polarization components, and from the light intensities of the separated polarization components, the phase difference Δ and the amplitude ratio tan ψ in the reflected light are calculated using a statistical method such as the least square method. Obtain the determined ellipso parameters Δ and ψ.

Further, the ellipsometer of the present invention is an optical device for separating polarized light into a measuring object at a predetermined angle and separating the reflected light reflected by the measuring object into polarization components of four or more polarization directions different from each other. A system and a plurality of photodetectors for detecting the light intensity of each polarization component separated by this optical system,
Using a statistical method from a plurality of light intensities detected by the plurality of light receivers, an arithmetic unit for obtaining an ellipso parameter Δ, ψ determined from the phase difference Δ and the amplitude ratio tan ψ in the reflected light is provided. There is. Further, in the ellipsometer of another invention, the calculation unit calculates the ellipso parameters Δ and ψ using the statistical method shown in the following equations (1) (2) (3) (4). tan ψ = (A / C) ^1/2 (1) cos (Δ−φ ₀ −φ _B ) = (B / C) (C / A) ^1/2 (2) where A, B and C are

[0025]

[Equation 4] However, x _i = cos ² Ai y _i = 2σi · χ · cosAi · sinAi z _i = Ii u _i = − (σi · χ) ² sin ² Ai… (4)

[0026] Further, Ai is the azimuth angle of the polarization of the reference direction and a direction parallel to the plane of incidence of the incident light to the measurement target, σi (i = 1,2,3, ...... ), φ B is the reflected light a plurality of Is a constant that is determined by the optical system that separates it into polarized light components.
φ ₀ is a constant determined by the polarization state of the incident light, and Ii (i =
1, 2, 3, ...) Is the light intensity detected by the light receiver, and w _i (i = 1, 2, 3, ...) Is a weighting function. Each weighting function w _i (i = 1,2,3, ...) Is preferably a function of the light intensity Ii of the corresponding channel i.

Further, in the ellipsometer of another invention, the optical system for separating the reflected light into polarization components of four or more polarization directions different from each other splits the reflected light reflected by the object to be measured into light of a plurality of different directions. It is composed of a non-polarization beam splitter and a plurality of polarization beam splitters for decomposing each light split by the non-polarization beam splitter into polarization components in mutually different directions.

Further, in the ellipsometer of another invention, the optical system comprises a plurality of non-polarizing beam splitters for splitting the reflected light reflected by the object to be measured into light in four or more different directions, and the respective non-polarizing beams. It is composed of a plurality of analyzers that transmit polarization components of different directions in each light split by the splitter.

[0029]

First, the operation principle of the ellipso parameter measuring method thus constructed will be described.

As described above, when the polarized light from the light source enters the object to be measured at a predetermined angle φ, the reflected light reflected by the object to be measured is elliptically polarized light of a fixed shape determined by the film thickness of the object to be measured. Become. Then, the ellipso parameters ψ, Δ
Is the amplitude ratio t between the P and S components of the reflected wave from the measurement target
Since the value is determined from an ψ and the phase difference Δ, it can be obtained from the elliptical shape and the degree of inclination of the ellipse from the reference line. Therefore, as shown in FIG. 17, if at least three light intensities obtained by projecting an ellipse in each direction are obtained, the ellipse is uniquely determined.

Therefore, as shown in FIG. 2, it is possible to obtain projections from four or more directions with respect to the reference direction and obtain the elliptical shape using a statistical method. The statistical method in this case is, for example, a method of obtaining a value that is considered to have a statistically small error from a large number of data such as the least square method, the minimum absolute deviation estimation method, the orthogonal regression method, and the simple average method. is there. Therefore, in this case, it is possible to obtain the shape of the ellipse with which the error can be regarded as the minimum for all the light receivers. Therefore, the accuracy of the calculated ellipso parameters ψ and Δ is improved. The procedure for obtaining the above equations will be described below. For example, the incident light Ein

[0032]

[Equation 5] , The electric field after passing through the analyzer or the polarization beam splitter that detects the light with the polarization direction of azimuth angle Ai (i = 1,2,3,4, ..., n) is Ki R (Ai) PR It can be represented by (-Ai) BSEin (i = 1,2, ..., n). However, Ki is a transmission coefficient of each optical path.

Further, R (Ai) is a rotation matrix, P is a matrix representing an analyzer or a polarization beam splitter, B is a matrix showing the influence of an element that divides the reflected light into a plurality, and S is a matrix showing the influence of the measurement target. Is. Then, each of these matrices is defined as the following equation.

[0034]

[Equation 6] Therefore, the light intensity Ii obtained by the light receiver is

[0035]

[Equation 7] Becomes However, Gi is the gain of the electric system, and Kai is Kai = Ki Kp KbiRs (i = 1,2, ..., N). Here, if the gain Gi is determined by an appropriate method, the light intensity Ii shown in the equation (14) becomes the following equation. Ii = I ₀ [tan ² ψ ・ COS ² Ai ＋ (σi χ) ² sin ² Ai + 2σi · χ · tanψ · cos (Δ-φ 0 -φ i) · cosAi · sinAi]

However, I ₀ is a constant that depends on the intensity of incident light, the reflectance of the object to be measured, and the like. Further, assuming that φ _i is a constant value φ _B that does not depend on i, the light intensity I ₀ is
It can be expressed as in equation (15). Ii = I ₀ [tan ² ψ ・ COS ² Ai ＋ (σi χ) ² sin ² Ai + 2σi · χ · tan ψ · cos (Δ − φ ₀ − φ _B ) · cosAi · sinAi] (i = 1,2,…, n)… (15) where a ＝ tan ² ψ b = tan ψψ cos (Δ−φ ₀ −φ _B ) c = −1 / I ₀ x _i = cos ² Ai y _i = 2σi · χ · cosAi · sinAi z _i = Ii u _i = − (σi · χ) ² sin ² If Ai (i = 1,2, ..., n) is set, ax _i + by _i + cz _i = u _i (i = 1,2, ..., n) (16)

[0037] Therefore, (x _i , y _i ,
When there are four or more pairs of z _i , u _i ), a, b, c can be estimated by using a statistical method. For example, 3
The error can be made smaller than that of the conventional ellipsometer that determines a, b, and c from a pair of (x _i , y _i , z _i , u _i ). Next, of the statistical methods, for example, the estimation by the least square method will be considered. For example, each observation data (x
_i , y _i , z _i , u _i ) and an unknown regression line u = ax + by + cz, the square error which is the sum of squares of the distance in the u direction is an error function U.
(A, b, c) is defined as, the error function U (a, b, c) = Σ (ax i + by i + cz i -u i) 2

The estimated values of a, b, and c are calculated so that Here, Σ is an operator for calculating the total sum from i = 1 to i = n. As shown in the equation (17), it is possible to use a squared error obtained by multiplying the weighting function w _i as the error function U (a, b, c). U (a, b, c) = Σw i (ax i + by i + cz i -u i) 2 … (1
7)

The w _i may be 0. Thus, when it is clear that the error of a certain light intensity Ii is large, w _i = 0 can be set, and the light intensity Ii having a large error can be excluded from the calculation in advance. Also, 2 shown in equation (17)
When the squared error is used, the squared error U (a, b, c) becomes a, b, c

[0040]

[Equation 8] Therefore, this equation should be solved. That is,

[0041]

[Equation 9] To obtain the following equation. a = tan ² ψ = A / C b = tan ψ · cos (Δ−φ ₀ −φ _B ) = B / C Therefore, the above equations (1) and (2) are obtained. tan ψ = (A / C) ^1/2 (1) cos (Δ−φ ₀ −φ _B ) = (B / C) (C / A) ^1/2 (2) Here, it is found that A, B, and C are represented by the above-mentioned determinant (3).

[0042]

[Equation 10] Naturally, the calculation results of A, B, and C differ depending on the selection method of the weighting function w _i (i = 1,2,3, ..., n). But,
This weighting function w _{i is represented} by, for example, w _i = I i (i = 1,2,3, ..., n)

It is conceivable to set the function of _{i i} such as w _i = F (I _i ). Thus, by making the weighting function w _{i a} function of the measured light intensity I _i , the contribution rate of the light intensity of the channel having the high light intensity I _i is increased, and conversely, the light of the channel having the low light intensity I _i is used. It is possible to set the contribution ratio of strength to be small. As a result, the light intensity Ii
When A is small, the influence of an error at the time of A / D conversion becomes a problem. B. The degree to which the calculation result of C is given can be reduced. Therefore, finally, the ellipso parameters Δ, ψ
The measurement accuracy of is improved. The error function U (a,
It is also possible to define b, c) using an error other than the squared error. Next, an example of a gain adjusting method will be described. First, the known polarization

[0044]

[Equation 11]

The light intensity output from the light receiver when the reflected light is directly incident on the optical system is calculated. In this case, this light intensity Ixi can be expressed in the same manner as the expression (14).

[0046]

[Equation 12] However, Li = ξ ² ・ COS ² Ai + (σi η) ² sin ² Ai + 2 (ξ ・ η ・ σi) cos (φ _i + Φ) ・ cos coi ・ sinAi (i = 1,2, ..., n) (19) In equation (19), σi, φ _i , Ai, ξ, η , Φ are all known. Therefore, Li is also known.

Next, all the light intensities Ix1, Ix2, ..., Ix
i, a certain value ... Ixn as I _0a, respectively, I _0a
The gains G1, G2, ..., Gi, ..., Gn are determined so as to be equal to L1, I _0a L2, ..., I _0a Li, ..., I _0a Ln. That is, Gi = I _0a / | Kia | ² (i = 1,2, ..., n) (20), the above equation (14) can be expressed as equation (21). Ii = I ₀ [tan ² ψ ・ COS ² Ai ＋ (σi χ) ² sin ² Ai −2σi · χ · tan ψ · cos (Δ −φ ₀ −φ _B ) · cosAi · sinAi] (i = 1,2, ..., n) (21) where I ₀ = I _0a | Ep | ² Was defined. Therefore,
Equation (15) described above is obtained.

Therefore, if the gain Gi (i = 1,2, ..., n) of the electric system is determined by the above-described method, the gain of the light receiver is determined without depending on the transmittance of the entire optical system, The characteristics of each light receiver can be made uniform.

The gain adjustment process is generally carried out by adjusting the actual gain of the amplifier that amplifies the output signal of each light receiver. However, for example, the gain adjustment processing may be performed by the program processing means in the data processing process of the data value of the light intensity fetched from each light receiver into the calculation unit. Also, the known polarized light used for gain adjustment is as long as the output of each light receiver is not zero.
In principle, any polarized light beam may be used.

Thus, using four or more light intensities I1, I2, ..., In measured at the same time, the ellipso parameters Δ and ψ estimated to have the smallest error by the statistical method are calculated. is doing. Therefore, the present invention has a feature that the measurement accuracy can be significantly improved in addition to the advantage of the conventional device of FIG. 13 that can perform the film thickness measurement in the moving body and the in-plane measurement of the film thickness.

[0051]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram showing the entire ellipsometer adopting the ellipsometer parameter measuring method of the embodiment. In the ellipsometer of this embodiment, the reflected light from the sample surface is separated into four polarization components (n =
4).

In the figure, reference numeral 10 denotes an ellipsometer body housed in a case formed of a light metal material. The light intensities I1, I2, I output from the ellipsometer body 10
3, I4 are converted into digital values by the A / D converter 11, and then input to the personal computer 12 as an arithmetic unit. The personal computer 12 calculates ellipso parameters ψ and Δ by the least squares method using the input four light intensities I1, I2, I3 and I4.
Further, using the calculated ellipso parameters ψ and Δ, the film thickness d of the sample surface 13 to be measured is calculated using a predetermined arithmetic expression.

Here, the A / D converter 11 time-divisionally divides the light intensities I1, I2, I3, and I4 into A / D. The conversion time of one light intensity is about 10 μse
c. Therefore, including the calculation time in the personal computer 12, the measurement time of the ellipso parameters ψ and Δ and the film thickness d at one measurement point sampled on the sample surface 13 is about 100 μsec. Since the light intensities I1, I2, I3, and I4 are measured at the same time and held by the voltage holding circuit, even if the sample surface 13 moves at a high speed, it can be sufficiently dealt with. FIG. 1 is an internal configuration diagram of the ellipsometer body 10.

For example, a laser beam having a single wavelength output from the semiconductor laser light source 14 is converted into linearly polarized light by the polarizer 15. Therefore, the semiconductor laser light source 14 and the polarizer 15 form the light source unit 16. Incident light 17 converted into linearly polarized light is emitted from the light source unit 16 to the sample surface 13 at an angle φ
Is incident at. The reflected light 18 reflected by the sample surface 13 changes from linearly polarized light to elliptically polarized light shown in FIG. 2 due to the presence of the film on the sample surface 13, and the non-polarized beam splitter 1
It is incident on 9.

The non-polarizing beam splitter 19 is composed of, for example, a non-polarizing glass plate. Then, the incident reflected light 18 is not polarized at all and is split into two lights 20a and 20b while maintaining the elliptically polarized state. The reflected light 20 a that has been reflected enters one polarization beam splitter 21. The transmitted light 20b that has passed therethrough is incident on the other polarization beam splitter 22.

Each of the polarization beam splitters 21 and 22 has the same structure, and is composed of, for example, a Glan-Thompson prism, a Glan-Taylor prism, etc., and splits the incident elliptically polarized light into polarization components in two directions orthogonal to each other. And output as transmitted light and reflected light, respectively. It should be noted that a Wollaston prism or the like in which the transmitted light is divided into two components at a certain angle may be used.

Then, the polarization beam splitter 21 has a polarization direction of the transmitted light 21a of the polarization beam splitter 21 with respect to the above-mentioned reference direction in which the direction parallel to the light incident surface on the sample surface 13 is 0 °. It is positioned so as to be + 90 ° counterclockwise when viewed from the side of the light receiver 23a. Then, the transmitted light 21a having a polarization direction of + 90 ° output from the polarization beam splitter 21 is incident on the light receiver 23a. The reflected light 21b output from the polarization beam splitter 21 and having a polarization direction of 0 ° is received by the light receiver 23b.
Is incident on.

Further, the other polarization beam splitter 22
Are positioned so that the polarization direction of the transmitted light 22a of the polarization beam splitter 22 is + 45 ° with respect to the reference direction. Then, the polarization beam splitter 22
The transmitted light 22a having a polarization direction of + 45 °, which is output from, enters the light receiver 23c. Further, the reflected light 2 output from the polarization beam splitter 22 and having a polarization direction of −45 °
2b is incident on the light receiver 23d.

Therefore, the light intensity I1 (1 channel) projected on the vertical axis of the elliptically polarized light of the reflected light 18 shown in FIG. 2 is obtained by the transmitted light 21a incident on the light receiver 23a. Further, the reflected light 21b incident on the light receiver 23b provides the light intensity I2 (2 channels) projected on the horizontal axis of the elliptically polarized light. Further, the light intensity I3 (3 channels) projected by the transmitted light 22a incident on the light receiver 23c onto a line inclined by + 45 ° with respect to the horizontal axis of the elliptically polarized light.
Is obtained. Then, the reflected light 22b incident on the light receiver 23d provides a light intensity I4 (4 channels) projected on a line inclined at -45 ° with respect to the horizontal axis of the elliptically polarized light.

That is, the reflected light 18 from the sample surface 13 has respective light intensities I1, I2, I3 and I4 90.
It is separated into respective polarization components in four directions of °, 0 °, + 45 °, and -45 °.

Then, as described above, using these four light intensities I1 to I4, the reflected light 1 is obtained by the least square method.
Ellipso parameters ψ and Δ that specify the elliptically polarized light of 8 are calculated.

Further, in the ellipsometer of this embodiment,
Enters the circularly polarized test light into the non-polarized beam splitter 19.
And the gain of the electric system is adjusted. Sanawa
Then, in equation (19) above, | ξ | = | η | = 1, Φ
= 90 °, in this embodiment ellipsometer
Is φi = 0, σ1 = σ2 = σR, σ3 = σ4 = σT
Therefore, L1, L2, L3, and L4 are L1 = σR² _{L2 = 1 L3 = (1 + σT} 2 ) / 2 L4 = (1 + σT² ) / 2. Therefore, each of the light receivers 23a, 23b, 23
The light intensities I1, I2, I3, detected at c and 23d,
Each I4 is expressed by the following equation. I1 = I₀・ ΣR² χ²  I2 = I₀・ Tan² ψ I3 = I₀[Tan² ψ + (σT · χ)²  + 2σT · χ · tan ψ · cos (Δ-φ₀-Φ_T)] I4 = I₀[Tan² ψ + (σT · χ)²  -2σT · χ · tan ψ · cos (Δ−φ₀-Φ_T)] …(twenty two)

However, I ₀ is a constant that depends on the intensity of incident light and the reflectance of the object to be measured. The phase difference φ ₀ and the amplitude ratio χ are parameters determined by the polarization state of the incident light with respect to the measurement target. In general, in order to facilitate the calculation, the phase difference φ ₀ = 0 ° and the amplitude ratio χ = 1

It is set to. Further, σR is the amplitude reflectance ratio of the non-polarizing beam splitter 19, and σT is the amplitude transmittance ratio. Furthermore, φ _T = 0. Then, the amplitude reflectance ratio σR and the amplitude transmittance ratio σT are expressed by the equation (23). Amplitude reflectance ratio σR = r _s / r _P Amplitude transmittance ratio σT = (1-r _s ² ) / (1-r _P ² ) …(twenty three)

However, r _P and r _s are P polarized light and S, respectively.
Fresnel reflection coefficients for polarized light, which are determined by the refractive index and the incident angle of the non-polarizing beam splitter 19.

When the refractive index of air is N ₀ , the refractive index of the non-polarizing beam splitter 19 is n _1, and the incident angle and the refraction angle on the non-polarizing beam splitter 10 are θ ₀ and θ ₁ , respectively, r _P , r _s is given by the equations (24) and (25). _{r P = (n 1 cosθ 0} -N 0 cosθ 1) / (n 1 cosθ 0 + N 0 cosθ 1) ... (24) r s = (N 0 cosθ 0 -n 1 cosθ 1) / (N 0 cosθ 0 + n ₁ cos θ ₁ )… (25)

For each of these constants, the test light having a known linearly polarized light or elliptically polarized light is made incident on the non-polarized beam splitter 19, and the true ellipso parameters ψ and Δ are obtained.
It is calculated in advance from the amount of deviation from. If the refractive index n _{1 of} the non-polarization beam splitter 19 is a real number, φ
Note that _T = 0.

Personal computer 1 as arithmetic unit
2 is input from the ellipsometer main body 10 through the A / D converter 11 according to the flow chart of FIG.
The film thickness d on the sample surface 13 from the respective light intensities I1 to I4
To calculate.

That is, when the flow chart is started, each of the four light intensities I1 to I4 is read. Next, the four light intensities are substituted into the above equations (1) and (2) to calculate the ellipso parameters ψ and Δ. However, the determinant of equation (3) is expanded in advance.
When the ellipso parameters ψ and Δ are obtained, the film thickness d on the sample surface 13 is calculated using a separate calculation formula.

With the ellipsometer constructed in this way, even if the measured four light intensities I1 to I4 are mixed with light intensities that include a large error, there is a statistical error using all the light intensities. Ellipso parameters ψ and Δ that can be regarded as the smallest are calculated. Therefore, the accuracy of the calculated ellipso parameters ψ and Δ is improved.

As described above, since the ellipso parameters are calculated by using the statistical method, the ellipso parameters ψ, Δ
In comparison with the conventional three-channel ellipsometer that uses the three fixed light intensities I1 to I3 for the calculation of, the measurement accuracy can always be maintained at a high value above a certain level. That is, there is little variation in measurement accuracy due to the measurement target or measurement conditions, and stable and high measurement accuracy can always be maintained.

Further, each optical component shown in FIG. 1 is fixed to, for example, a substrate, and there is no movable part. Therefore, the measurement required time for one measurement point can be regarded as only the conversion time of the A / D converter 11 and the arithmetic processing time in the personal computer 12, and as described above, approximately 1
It becomes 00 μsec, and it can be measured almost in real time. Therefore, the film thickness d can be correctly measured even if the measurement target moves at high speed. FIG. 5 is a diagram showing a state in which the ellipsometer of the present invention is incorporated in a device for measuring the distribution of the oxide film thickness of a silicon wafer.

A moving table 32 is provided on the base 31, and a rotary support 33 is attached on the moving table 32. Then, the silicon wafer 35 to be measured is mounted on the rotary support 33 by, for example, a suction mechanism. Therefore, silicon wafer 3
5 moves linearly in the direction of the arrow while rotating. Base 31
An existing thickness measuring device 36 for measuring the thickness of the entire silicon wafer 35 is arranged on the upper side, and an ellipsometer body 37 is fixed to a position facing the thickness measuring device 36 by a supporting member 38.

The thickness measuring device 36 and the ellipsometer main body 37 are connected to the moving table 32 and the rotary support table 3.
At 3, the total thickness of the silicon wafer 35 moving spirally at each measurement position (R, θ) and the thickness d of the oxide film are measured.

FIG. 6 is a flow chart showing the measuring process performed by the personal computer 12 incorporated in this ellipsometer. When the flow chart starts, silicon wafer 3
The measurement position (R, θ) on 5 is initialized. Next, the light intensities I1 to I4 at the corresponding measurement position are read. The read four light intensities are substituted into the above equations (1) and (2) to calculate the ellipso parameters ψ and Δ.

When the ellipso parameters ψ and Δ are obtained,
The film thickness d and the refractive index at the measurement position (R, θ) on the silicon wafer 35 are calculated using a separate calculation formula.
When the measurement of the film thickness d and the refractive index at one measurement position is completed, the measurement position (R, θ) is moved and the measurement is performed again. Then, when the measurement processing at all measurement positions is completed, the measurement of one silicon wafer 35 is completed.

FIGS. 7A and 8 show the phase difference Δ obtained by the rotation analyzer and the calculated phase difference when the film thickness is measured on a large number of silicon wafers 35 having various film thicknesses d. It is a figure which shows the relationship with (DELTA). Figure 7 (a)
Is the experimental result using the Example ellipsometer, and FIG.
Are experimental results using a conventional ellipsometer.

As shown in the figure, in the conventional ellipsometer shown in FIG. 8, when the phase difference Δ at which one of the three light intensities I1 to I3 becomes extremely small becomes 0 ° and 180 °. An error of 10 ° to 12 ° occurs.

On the other hand, in the ellipsometer of the embodiment shown in FIG. 7 (a), since the ellipso parameters which can be regarded as statistically small in error are calculated using all the light intensities I1 to I4, the phase difference Δ Is 0 ° and 180 °
Even in the vicinity, the absolute error could be reduced to 5 ° or less.

As described above, the ellipsometer is downsized while maintaining high speed, and the measurement accuracy is improved.
It can be additionally installed on the existing thickness measuring device 36.
In the semiconductor process line, in addition to the above silicon wafer, nitride film, polysilicon film, transparent electrode material, etc. can be applied to online measurement.

FIG. 9 is a view showing the schematic arrangement of an ellipsometer according to another embodiment of the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals. Therefore, detailed description of the overlapping portions is omitted.

In this embodiment, the reflected light 20a from the non-polarization beam splitter 19 is converted into the polarization beam splitter 21.
Therefore, + 45 ° and -4 with respect to the reference direction described above.
The polarized light component of 5 ° direction is separated, and the transmitted light 20b of the non-polarized beam splitter 19 is separated by the polarized beam splitter 22 into polarized light components of 90 ° and 0 ° directions with respect to the reference direction. In this embodiment, the light intensities of the light receivers 23c and 23d are I1 and I2, and the light intensities of the light receivers 23a and 23b are I3 and I4. Further, the constants σ1 and σ2 in the equation (4) are the amplitude transmittance ratios of the P-polarized light and the S-polarized light of the non-polarizing beam splitter 19, respectively, and the constants σ3 and σ4 are the amplitude reflectance ratios. further,
φ ₁ , φ ₂ , φ ₃ , and φ ₄ are all 0.

Even with such a configuration, the light intensities of the four polarization components in the respective directions deviated by 45 ° with respect to the reference direction from the reflected light 18 from the sample surface 13 can be obtained as in FIG. Therefore, it is possible to obtain substantially the same effect as that of the above-described embodiment.

Further, in the embodiment shown in FIG. 10, the light source section 16 to the sample surface 13 in the ellipsometer shown in FIG.
A quarter-wave plate 40 is inserted in the optical path of the incident light 17 with respect to. By inserting the quarter-wave plate 40 in this way, it is possible to convert the incident light 17 incident on the sample surface 13 from linearly polarized light to circularly polarized light. Therefore, it is possible to shift the measuring range of the film thickness d as compared with the ellipsometer of FIG.

FIG. 11 is a schematic diagram showing a schematic configuration of an ellipsometer according to still another embodiment of the present invention. Figure 1
The same parts as those in the above embodiment are designated by the same reference numerals. Therefore, detailed description of the overlapping portions is omitted.

In this embodiment, the optical system for separating the reflected light 18 from the sample surface 13 into four different polarization components is three non-polarizing beam splitters 19, 41, 42.
And four analyzers 43a, 43b, 43c, 43d.

That is, the reflected light 18 from the sample surface 13 is split by the non-polarizing beam splitter 19 into reflected light 20a and transmitted light 20b. The reflected light 20a is split into reflected light and transmitted light by another non-polarizing beam splitter 41. The reflected light is incident on the analyzer 43a, and the transmitted light is incident on the analyzer 43b. Further, the transmitted light 20b of the non-polarization beam splitter 19 is transmitted to another non-polarization beam splitter 42.
Is split into reflected light and transmitted light. The reflected light is incident on the analyzer 43c, and the transmitted light is incident on the analyzer 43d.

The four analyzers 43a to 43d are + 90 ° with respect to the above-mentioned reference direction of the incident light,
It transmits the polarization components in the respective directions of 0 °, + 45 °, and −45 °. As a result, the light intensities I1 and I of the four polarization components having mutually different polarization directions from the light receivers 23a, 23b, 23c, and 23d arranged behind the respective analyzers 43a to 43d.
2, I3, I4 are output. Therefore, it is possible to obtain substantially the same effects as those of the above-described embodiments.

FIG. 12 is a schematic diagram showing a schematic structure of an ellipsometer according to still another embodiment of the present invention. Figure 9
The same parts as those in the above embodiment are designated by the same reference numerals. Therefore, detailed description of the overlapping portions is omitted.

In this embodiment, the reflected light 18 from the sample surface 13 is separated into five polarization components having different polarization directions. That is, the reflected light 18 on the sample surface 13 is split into three lights 20a, 20c, 20d by the two non-polarizing beam splitters 19, 19a. The reflected light 20a of the non-polarization beam splitter 19 is incident on the analyzer 43e. The analyzer 43e transmits the polarized component of the incident light 20a in the direction of 90 ° with respect to the reference direction, and the light receiver 23e
Incident on.

Reflected light 2 from the non-polarization beam splitter 19a
0c enters the polarization beam splitter 45. The polarization beam splitter 45 extracts the polarization components of the incident light 20c in the directions of 30 ° and 120 ° with respect to the reference direction and makes them incident on the photodetectors 23a and 23b, respectively. The transmitted light 20d of the non-polarization beam splitter 19a is incident on the polarization beam splitter 46. The polarization beam splitter 46 extracts the respective polarization components of the incident light 20d in the directions of 60 ° and 150 ° with respect to the reference direction and makes them incident on the photodetectors 23c and 23d, respectively.

As a result, each of the light receivers 23a, 23b, 23
The light intensities I1, I2, I3, I4, and I5 of the five polarization components whose polarization directions are different from each other are output from c, 23d, and 23e. In this case, the respective light intensities I1, I2, I3, I4,
I5 is given by the following equation (26) similarly to the equation (14). I1 = G1 | Kb1 · Ep | ² [(Σ1R · χ) ² sin ² 90] I2 = G2 | Kb2 · Ep | ² × [tan ² ψ ・ cos ² 30+ (σ1T ・ σ2R ・ χ) ² sin ² 30 ＋ 2σ1T ・ σ2R ・ χ ・ tanψ ・ cosΔ ・ cos30 ・ cos30] I3 = G3 ｜ Kb3 ・ Ep ｜ ² × [tan ² ψ ・ cos ² 120 + (σ1T ・ σ2R ・ χ) ² sin ² 120 ＋ 2σ1T ・ σ2R ・ χ ・ tanψ ・ cosΔ ・ cos120 ・ cos120] I4 = G4 ｜ Kb4 ・ Ep ｜ ² × [tan ² ψ ・ cos ² 60+ (σ1T ・ σ2T ・ χ) ² sin ² 60 + 2σ1T ・ σ2T ・ χ ・ tanψ ・ cosdelta ・ cos60 ・ cos60] I5 = G5 ｜ Kb5 ・ Ep ｜ ² × [tan ² ψ ・ cos ² 150 + (σ1T ・ σ2T ・ χ) ² sin ² 150 ＋ 2σ1T ・ σ2T ・ χ ・ tanψ ・ cosΔ ・ cos150 ・ cos150]… (26)

Here, σ1R and σ1R are the amplitude reflectance ratio and the amplitude transmittance ratio of the beam splitter 19, respectively. Further, σ2R and σ2T are the amplitude reflectance ratio and the amplitude transmittance ratio of the beam splitter 19a, respectively. For example, outputs I1x, I2x, I3x, and I4 when circularly polarized light is directly incident
x and I5x are given by equation (27). I1x = G1 | Kb1 | ² [(Σ1R) ² sin ² 90] I2x = G2 | Kb2 | ² [Cos ² 30+ (σ1T ・ σ2R) ² sin ² 30] I3x = G3 | Kb3 | ² [Cos ² 120 + (σ1T ・ σ2R) ² sin ² 120] I4x = G4 | Kb4 | ² [Cos ² 60+ (σ1T ・ σ2T) ² sin ² 60] I5x = G5 | Kb5 | ² [Cos ² 150 + (σ1T ・ σ2T) ² sin ² 150] (27) Therefore, for each constant value I _{0b of} each of the light intensities I 1x, I 2x, I 3x, I 4x and I 5x, I 1x = I _0b · L 1 I 2x = I _0b · L 2 I 3x = I _0b · L 3 I 4x _{= I 0b · L4 I5x = I} 0b · L5 ... (28) become as G1, G2, G3, determine the G4, G5.
However, L1 = (σ1R) ² sin ² 90 L2 = cos ² 30+ (σ1T ・ σ2R) ² sin ² 30 L3 = cos ² 120 + (σ1T ・ σ2R) ² sin ² 120 L4 = cos ² 60+ (σ1T ・ σ2T) ² sin ² 60 L5 = cos ² 150 + (σ1T ・ σ2T) ² sin ² It is 150 (29). Thus, if G1, G2, G3, G4, and G5 are determined, the light intensities I1, I2, I3, I4, and I5 are respectively given by equation (30). I 1 = I ₀ [(σ1R · χ) ² sin ² _{90] I2 = I 0 [tan} 2 ψ ・ cos ² 30+ (σ1T ・ σ2R ・ χ) ² sin ² 30 ＋ 2σ1T ・ σ2R ・ χ ・ tanψ ・ cosΔ ・ cos30 ・ cos30] I3 = I ₀ [tan ² ψ ・ cos ² 120 + (σ1T ・ σ2R ・ χ) ² sin ² 120 ＋ 2σ1T ・ σ2R ・ χ ・ tanψ ・ cosΔ ・ cos120 ・ cos120] I4 = I ₀ [tan ² ψ ・ cos ² 60+ (σ1T ・ σ2T ・ χ) ² sin ² 60 ＋ 2σ1T ・ σ2T ・ χ ・ tanψ ・ cosΔ ・ cos60 ・ cos60] I5 = I ₀ [tan ² ψ ・ cos ² 150 + (σ1T ・ σ2T ・ χ) ² sin ² 1
50 ＋ 2σ1T ・ σ2T ・ χ ・ tanψ ・ cosΔ ・ cos150 ・ cos150]… (30)

Here, it should be noted that the light that directly enters does not have to be circularly polarized light. For example, it may be a known polarization such as S polarization. However, if P-polarized light is used, the output of I1 will be 0, and the gain of I1 cannot be determined.
The polarized light such that the above cannot be used for gain adjustment.

Further, the determination of the gain may be realized by an electronic circuit or may be processed by a computer after the data is taken in by any method. Here, the circularly polarized light is directly incident to change the variable resistance of the amplifier attached to the light receiver, thereby making the output of each light receiver constant. Then, when actually measuring, when each light intensity is taken into the computer and then calculated, L1 is input to I1, I2, I3, I4, and I5, respectively.
The light intensities I1, I2, I3, I4, and I5 are set again by multiplying L2, L3, L4, and L5. Therefore, from these five light intensities I1 to I5, the ellipso parameters Δ and ψ, which are statistically estimated to have the smallest error, can be calculated using the equations (1) and (2). In this case, the weighting function w _i =
Ii (i = 1, 2, ..., 5).

FIG. 7 (b) shows the phase difference obtained by the rotation analyzer when the film thickness is measured on a large number of silicon wafers having various film thicknesses d using the 5-channel embodiment ellipsometer. It is a figure which shows the relationship between (DELTA) and the phase difference (DELTA) calculated with the Example ellipsometer. It can be seen that very good results are obtained as in the case of the 4-channel embodiment ellipsometer shown in FIG. 7 (a).

FIG. 13 is a schematic diagram showing a schematic configuration of an ellipsometer according to still another embodiment of the present invention. Figure 1
The same parts as those in the second embodiment are designated by the same reference numerals. Therefore, detailed description of the overlapping portions is omitted.

In this embodiment, the reflected light 18 from the sample surface 13 is separated into six polarization components having different polarization directions. That is, the reflected light 18 on the sample surface 13 is split into three lights 20a, 20c, 20d by the two non-polarizing beam splitters 19, 19a. And each light 2
0a, 20c and 20d are incident on polarization beam splitters 44, 47 and 48, respectively, and are separated into polarization components in different directions.

The polarization beam splitter 44 receives the incident light 2
The polarized components of 0 ° and 90 ° with respect to the reference direction of 0a are extracted and made incident on the photodetectors 23e and 23f, respectively. Further, the polarization beam splitter 47 is arranged at 30 ° and 12 ° with respect to the reference direction of the incident light 20c.
Each of the polarization components in the 0 ° direction is extracted and the light receiver 23
It is incident on a and 23b. Further, the polarization beam splitter 48 is 6 degrees relative to the reference direction of the incident light 20d.
The respective polarization components in the 0 ° and 150 ° directions are extracted and made incident on the photodetectors 23c and 23d, respectively.

As a result, each of the light receivers 23a, 23b, 23
Light intensities I1, I2, I3, I4 and I of six polarization components having different polarization directions from c, 23d, 23e and 23f.
5 and I6 are output. Therefore, the ellipso parameters Δ and ψ, which are statistically estimated to have the smallest error, can be calculated from the six light intensities I1 to I6 using the equations (1) and (2). In this case, gain adjustment can also be performed using circularly polarized light. Therefore, it is possible to obtain substantially the same effects as those of the respective embodiments described above.

Further, among the light intensities I1 to I6, the ellipso parameters Δ and ψ that can be estimated to be statistically small by not using the light intensities below a certain value which can be regarded as including an error. Can be calculated. In this case, the weighting function w _i corresponding to the light intensity I _i not used in the calculation
Should be set to 0. By doing this,
The accuracy is slightly improved as compared with the case where the ellipso parameters Δ and ψ are calculated using all the light intensities of I1 to I6 described above.

As described above, in the present invention, the sample surface 1
It is possible to realize an optical system for separating the reflected light 18 from 3 into four or more polarization components by combining various components.

The present invention is not limited to the above embodiments. In the embodiment, the least squares method is used as the statistical method for calculating the most accurate ellipso parameters Δ and ψ from the detected four or more light intensities, but it is particularly limited to the least squares method. Not something
Other statistical methods that reduce the error can be used.

The gain adjusting method used in the present invention is
Generally, it is applicable to a multi-channel ellipsometer. In the embodiments, the case of 4 channels and 5 channels was specifically described, and the case of 6 channels was also described, but it is naturally applicable to the conventional 3 channel ellipsometer. For example, in the ellipsometer already shown in FIG. 16, the light intensities I1, I2, I3 of each channel can be expressed by the equation (31). I1 = G1 | Kc1 · Ep | ² [Tan ² ψ] I2 = G2 | Kc2 · Ep | ² × [tan ² ψ ・ cos ² 45 + (σT · σR · χ) ² sin ² 45 ＋ 2σT ・ σR ・ χ ・ tanψ ・ cos (Δ−φ ₀ ) ・ cos45 ・ cos45] I3 = G3 ｜ Kc3 ・ Ep ｜ ² × [tan ² ψ ・ cos ² (-45) + (σT · σR · χ) ² sin ² (-45) + 2σT · σR · χ · tanψ · cos (Δ-φ 0) · cos (-45) · cos (-45)] ... (31)

However, σR and σT are the amplitude reflectance ratio and the amplitude transmittance ratio of the non-polarizing beam splitter. Here, for example, the receiver outputs I1x, I2x, when P-polarized light is directly incident,
I3x is I1x = G1 | Kc1 | ² I2x = G2 | Kc2 | ² / 2 I3x = G3 | Kc3 | ² / 2 ... (32), each output I1x, I2x, I3x has a certain constant value I
Against _{0c, I1x = I 0c I2x =} I 0c / 2 I3x = I 0c / 2 ... and so as to gain G1 (33). If G2 and G3 are determined, I1 = I ₀ tan ² ψ I2 = I ₀ [tan ² ψ ・ cos ² 45 + (σT · σR · χ) ² sin ² 45 + 2σT · σR · χ · tan ψ · cos (Δ-φ ₀ ) · cos45 · cos45] I3 = I ₀ [tan ² ψ ・ cos ² (-45) + (σT · σR · χ) ² sin ² (-45) + 2σT · σR · χ · tan ψ · cos (Δ − φ ₀ ) · cos (-45) · cos (-45)] ... (34). Therefore, the equations (13a) and (13b) described above are obtained by solving the equation (34).

Further, the 3-channel ellipsometer has
In addition to the one using only the non-polarization beam splitter shown in FIG. 16, an ellipsometer using a polarization beam splitter as shown in FIG. 14 can be considered. That is, the laser light output from the light source unit 16 enters the material surface 13 via the quarter-wave plate 49. Light reflected from the document surface 1
A non-polarizing beam splitter 19 splits the light into two light beams. One of the branched lights is incident on the photodetector 23a via the analyzer 50 that allows only the polarization component in the 0 ° direction to pass. The other split light is further split by the polarization beam splitter 22 into polarized light components in the + 45 ° and −45 ° directions and incident on the photodetectors 23b and 23c, respectively.
The light intensities I1, I2, I3 obtained by the respective light receivers 23a, 23b, 23c can be expressed by the equation (35). I1 = G1 | Kd1 · Ep | ² [Tan ² ψ] I2 = G2 | Kd2 · Ep | ² × [tan ² ψ ・ cos ² 45 + (σT · χ) ² sin ² 45 + 2σT ・ χ ・ tanψ ・ cos (Δ−φ ₀ ) ・ cos45 ・ cos45] I3 = G3 ｜ Kd3 ・ Ep ｜ ² × [tan ² ψ ・ cos ² (-45) + (σT · χ) ² sin ² (-45) + 2σT · χ · tan ψ · cos (Δ − φ ₀ ) · cos (-45) · cos (-45)] (35) Here, for example, the receiver output I1x when P-polarized light is directly incident , I2x, I3x are: I1x = G1 | Kd1 | ² I2x = G2 | Kd2 | ² / 2 I3x = G3 | Kd3 | ² / 2 (36), each output I1x, I2x, I3x has a constant value I
Against _{0d, I1x = I 0d I2x =} I 0d / 2 I3x = I 0d / 2 ... (37) and so as to gain G1. If G2 and G3 are determined, I1 = I ₀ tan ² as in the case described above. ψ I2 = I ₀ [tan ² ψ ・ cos ² 45 + (σT · χ) ² sin ² 45 + 2σT · χ · tan ψ · cos (Δ-φ ₀ ) · cos45 · cos45] I3 = I ₀ [tan ² ψ ・ cos ² (-45) + (σT · χ) ² sin ² (-45) + 2σT · χ · tan ψ · cos (Δ − φ ₀ ) · cos (-45) · cos (-45)] ... (38). Therefore, by solving this equation (38), (3
Equation (9) is obtained. cos (Δ−φ ₀ ) = [(I 2 −I 3) / 2I 1] × [I 1 / (I 2 + I 3 −I 1)] ^1/2 tan ψ = | σT · χ | [I1 / (I2 + I3-I1)] ^1/2 (39) Further, when circularly polarized light is used as a light beam used for gain adjustment, the receiver outputs I1x, I2x, and I3x are I1x = G1 | Kd1 | ² I2x = G2 | Kd2 | ² (1 + σT ² ) / 2 I3x = G3 | Kd3 | ² (1 + σT ² ) / 2 (40), each output I1x, I2x, I3x has a constant value I
Against _{0d, I1x = I 0d I2x =} I 0d (1 + σT 2 _{) / 2 I3x = I 0d (} 1 + σT 2 ) / 2 ... (41) so that the gain G1. If G2 and G3 are determined, the above equation (39) can be obtained.

Further, as the three-channel ellipsometer, in addition to the structure shown in FIGS. 16 and 14, an ellipsometer using a composite polarization beam splitter 51 as shown in FIG. 15 can be considered. Compound Polarization Beast Splitter 51
As shown in the figure, the non-polarizing glass 51a and the polarizing beam splitter 51b are integrally configured.

That is, the laser light output from the light source section 16 enters the material surface 13. The reflected light 18 from the material surface 13 is incident on the non-polarizing glass 51a forming the composite polarizing beam splitter 50 at the Breester angle θ.
Light incident at the Breester angle θ is separated into reflected light reflected on the incident surface and transmitted light entering the inside. The reflected light has only a polarization component that is polarized in a direction parallel to the incident surface (reflection surface). Therefore, the reflected light becomes only the polarized component in the reference direction (0 ° direction) and is incident on the light receiver 23a.

On the other hand, the transmitted light entering the non-polarizing glass 51a is separated by the next polarizing beam splitter 51b into two polarized components of + 45 ° and -45 ° directions with respect to the reference direction, and each of them is a light receiver. It is incident on 23b and 23c. The light intensities I1, I2, and I3 obtained by the light receivers 23a, 23b, and 23c can be expressed by the equation (42). I1 = G1 | Ke1 · Ep | ² (ΣR · χ) ² I2 = G2 | Ke2.Ep | ² × [tan ² ψ ・ cos ² 45 + (σT · χ) ² sin ² 45 + 2σT · χ · tan ψ · cos (Δ−φ ₀ ) · cos45 · cos45] I3 = G3 | Ke3 · Ep | ² × [tan ² ψ ・ cos ² (-45) + (σT · χ) ² sin ² (-45) + 2σT · χ · tan ψ · cos (Δ − φ ₀ ) · cos (-45) · cos (-45)] (42) Here, when circularly polarized light is used as the light beam used for gain adjustment. The receiver outputs I1x, I2x, I3x are I1x = G1 | Ke1 | ² ・ ΣR ² I2x = G2 | Ke2 | ² (1 + σT ² ) / 2 I3x = G3 | Ke3 | ² (1 + σT ² ) / 2 (43), each output I1x, I2x, I3x has a constant value I
Against _{0e, I1x = I 0e · σR} 2 _{I2x = I 0e (1 + σT} 2 _{) / 2 I3x = I 0e (} 1 + σT 2 ) / 2 ... (44) Gain G1. If G2 and G3 are determined, the equation (42) can be expressed as the equation (45) as described above. I 1 = I ₀ (σR · χ) ² I 2 = I ₀ [tan ² ψ ・ cos ² 45 + (σT · χ) ² sin ² 45 + 2σT · χ · tan ψ · cos (Δ-φ ₀ ) · cos45 · cos45] I3 = I ₀ [tan ² ψ ・ cos ² (-45) + (σT · χ) ² sin ² (-45) + 2σT · χ · tan ψ · cos (Δ − φ ₀ ) · cos (-45) · cos (-45)]… (45) Therefore, by solving this equation (45), the equation (46) becomes can get. cos (Δ−φ ₀ ) = [σR ² (I2-I3) / (2σT · I1)]

× [I 1 / {σR² (I2 + I3)-[sigma] T² ・ I1}]^1/2 _{tan ψ ＝ ｜ χ ｜ [{σR} 2 (I2 + I3)-[sigma] T² .I1} / I1]^1/2  (46) As described above, the present invention is suitable for ellipsometers having various structures.
Can be used.

[0112]

As described above, according to the ellipso parameter measuring method and ellipsometer of the present invention, the reflected light having the elliptically polarized light reflected by the object to be measured is separated into four or more polarization components having different polarization directions. Then, the light intensity of each polarization component is detected, and using all the detected light intensities,
The ellipso parameters Δ and ψ, which can be considered statistically the most accurate, are calculated. Therefore, it is possible to always obtain a high film thickness measurement accuracy above a certain level while maintaining a high measurement speed.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an internal structure of an ellipsometer body according to an embodiment of the present invention,

FIG. 2 is a diagram showing elliptically polarized light of reflected light in an example ellipsometer,

FIG. 3 is a schematic configuration diagram of an entire ellipsometer according to an embodiment,

FIG. 4 is a flow chart showing the operation of the embodiment ellipsometer,

FIG. 5 is a schematic configuration diagram of an oxide film thickness measuring device for a silicon wafer using an example ellipsometer,

FIG. 6 is a flow chart showing the operation of the oxide film thickness measuring apparatus,

FIG. 7 is a diagram showing a relationship between a phase difference Δ obtained by an example ellipsometer and a phase difference Δ obtained by a rotation analyzer method,

FIG. 8 is a diagram showing a relationship between a phase difference Δ obtained by a conventional ellipsometer and a phase difference Δ obtained by a rotation analyzer method,

FIG. 9 is a view showing the internal structure of the body of an ellipsometer according to another embodiment of the present invention,

FIG. 10 is a view showing the structure of another embodiment ellipsometer,

FIG. 11 is a view showing the structure of an ellipsometer according to still another embodiment,

FIG. 12 is a view showing the structure of yet another embodiment of an ellipsometer,

FIG. 13 is a diagram showing the structure of yet another embodiment of an ellipsometer,

FIG. 14 is a diagram showing the structure of yet another embodiment of an ellipsometer,

FIG. 15 is a diagram showing the structure of yet another embodiment of an ellipsometer,

FIG. 16 is a schematic diagram showing a schematic configuration of a conventional ellipsometer,

FIG. 17 is a diagram showing elliptically polarized light of general reflected light.

[Explanation of symbols]

10 ... Ellipsometer body, 11 ... A / D converter,
12 ... Personal computer, 13 ... Sample surface, 14 ...
Semiconductor laser light source, 15 ... Polarizer, 16 ... Light source section, 17
... incident light, 18 ... reflected light, 19, 19a ... non-polarizing beam splitter 21, 22, 44, 45, 46, 47, 4
8 ... Polarizing beam splitter, 23a-23f ... Photo receiver,
35 ... Silicon wafer, 40, 49 ... Quarter wave plate, 43a-43d, 50 ... Analyzer, 51 ... Composite polarization beam splitter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomoyuki Kaneko 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (7)

[Claims] 1. Polarized light is incident on a measurement target at a predetermined angle, and reflected light of the measurement target is separated into four or more polarization components different from each other, and the separated polarization components are separated. An ellipso parameter measuring method, characterized in that the ellipso parameters Δ and ψ determined from the phase difference Δ and the amplitude ratio tan ψ in the reflected light are obtained from the light intensity of the above using a statistical method. 2. The ellipso parameter measuring method according to claim 1, wherein the statistical method is a least squares method. 3. A light source section for making polarized light incident on a measurement target at a predetermined angle, an optical system for separating reflected light reflected by the measurement target into polarization components of four or more polarization directions different from each other, and this optical system. A plurality of photodetectors for detecting the light intensity of each polarization component separated by the system, and a statistical method from the plurality of light intensities detected by the plurality of photoreceivers are used to calculate the phase difference Δ in the reflected light. And an arithmetic unit for obtaining ellipso parameters Δ and ψ determined from the amplitude ratio tan ψ. 4. A light source section for making polarized light incident on a measurement target at a predetermined angle, an optical system for separating reflected light reflected by the measurement target into polarization components of four or more polarization directions different from each other, and this optical system. The following (1) (2) (3) (4) formula from the multiple light receivers that detect the light intensity of each polarization component separated by the system and the multiple light intensity detected by this multiple light receivers And an arithmetic unit for obtaining the ellipso parameters Δ and ψ determined from the phase difference Δ and the amplitude ratio tan ψ in the reflected light. tan ψ = (A / C) ^1/2 (1) cos (Δ−φ ₀ −φ _B ) = (B / C) (C / A) ^1/2 (2) where A, B and C are as follows: However, x _i = cos ² Ai y _i = 2σi · χ · cosAi · sinAi z _i = Ii u _i = − (σi · χ) ² sin ² Ai ... (4). Ai is the azimuth angle of polarized light with the direction parallel to the incident surface of the incident light on the measurement target as the reference direction, and σi (i =
1,2,3, ...), φ _B is a constant determined by the optical system that separates the reflected light into a plurality of polarization components, and χ, φ ₀ is a constant determined by the polarization state of the incident light, and Ii (i = 1,2,3, ……)
Is the light intensity detected by the light receiver, and w _i (i = 1,2,3,
......) is a weighting function. 5. The ellipsometer according to claim 4, wherein each of the weighting functions w _i (i = 1,2,3, ...) Is a function of the light intensity I i of the corresponding channel i. 6. The non-polarization beam splitter that splits the reflected light reflected by the measurement target into light beams in different directions, and each of the light beams split by the non-polarization beam splitter. The ellipsometer according to claim 4, wherein the ellipsometer comprises a plurality of polarization beam splitters that decompose into polarization components in different directions. 7. The optical system comprises a plurality of non-polarizing beam splitters for splitting the reflected light reflected by the measuring object into light beams in four or more different directions, and each of the non-polarizing beam splitters. The ellipsometer according to claim 4, wherein the ellipsometer comprises a plurality of analyzers that transmit polarization components of respective lights in different directions.