JPH05264227A - Ellipsoparameter measuring method and ellipsoparameter - Google Patents

Abstract

PURPOSE:To provide always high accuracy in measuring film thickness while keeping high measuring speed by separating the light reflected at a subject for measurement into more than a predetermined number of polarized components, and calculating an ellipsoparameter according to a specific number of intensity of the components selected therefrom. CONSTITUTION:Incident light 17 converted 15 into linearly poralized light is incident on a sample surface 13 at an angle PHI. The reflected light 18 is converted into elliptically polarized light by the presence of the sample surface 13 and a nonpolarization beam splitter 19 separates the light into rays of light 20a, 20b being elliptically polarized, which are then incident on respective polarizing beam splitters 21, 22. The transmitted rays of light 21a, 21b output from the splitter 22 are incident on respective light receivers 23c, 23d. The light receivers 23a-23d obtain the intensity I1-I4 of light projected on the longitudinal and transverse axes of the elliptically polarized light and on a line tilted by '45' relative to the trasverse axis; i.e., the reflected light 18 is separated into polarized components in four directions, and the three with larger intensity of the rays of light I1-I4 are used to calculate an ellipsoparameter PSI, DELTAfor specifying the elliptically polarized light.

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 that automatically calculate ellipsometer parameters for arbitrary combinations.

[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, the amplitude ratio tan ψ and the phase difference Δ need to be obtained.

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 object that is moving at high speed.Because there are mechanically movable parts, the device itself becomes large, and it is installed on the manufacturing line of the factory and online. For example, it was not possible to measure a measurement target that is continuously supplied.

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 on the sample surface 3 is elliptically polarized as shown in FIG. 17, 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 3]

[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 4] 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 light intensities I1 to I3 detected by the respective light receivers 7a to 7c are as shown in FIG.
It greatly changes depending on the shape of the elliptically polarized light included in the reflected light. 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 smaller than the other light intensities I1, I2. Becomes

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 thus is a very useful device capable of measuring the film thickness of the object to be measured at high speed, but the measurement is performed as described above. Depending on the object, the measurement accuracy may be inferior to that of the ellipsometer using the rotating analyzer described above.

It should be noted that if the number of measurements 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, 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 intensities of the components, for example, the optimum three light intensities with a small A / D conversion error can be selected, and using this, the calculation calculation of the ellipso parameter can be performed, and the high measurement speed is maintained. It is another object of the present invention to provide an ellipsometer parameter measuring method and an ellipsometer capable of significantly improving film thickness measurement accuracy.

[0022]

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, three light intensities are selected from the light intensities of the separated polarization components, and the phase difference and the amplitude ratio in the reflected light are determined from these three light intensities. Find the ellipso parameters.

In the ellipso parameter measuring method of another invention, the following equations (1), (2), (3) and (4) are used to determine the ellipso parameter Δ determined by the phase difference Δ and the amplitude ratio tan ψ in the reflected light. , Ψ is calculated. 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

[0024]

[Equation 5] However, a _i = cos ² Ai b _i = 2σi · χ · cosAi · sinAi c _i =-(σi · χ) ² sin ² Ai (i = k, l, m)… (4)

[0025] Ai is the azimuth angle of the polarized light with the direction parallel to the incident surface of the incident light as the reference direction, and σ i and φ _B are constants determined by the optical system that separates the reflected light into multiple polarization components. , Χ, φ ₀ are constants determined by the state of incident light, and Ii is the light intensity detected by the light receiver.

An ellipsometer according to another aspect of the invention separates a light source section that makes polarized light incident on a measurement target at a predetermined angle and a reflected light reflected by the measurement target into polarization components of four or more different polarization directions. An optical system, a plurality of light receivers for detecting the light intensity of each polarization component separated by this optical system, and three light intensities among a plurality of light intensities detected by the plurality of light receivers are selected. An arithmetic unit for obtaining an ellipso parameter determined by the phase difference and the amplitude ratio in the reflected light from the three light intensities of the lever.

Further, in the ellipsometer of another invention, the ellipsometer determined by the phase difference Δ and the amplitude ratio tan ψ in the reflected light by using the above-mentioned equations (1), (2), (3) and (4) in the ellipsometer of the invention. The parameters Δ and ψ are obtained.

Further, in the ellipsometer of another invention, the optical system for separating the reflected light into polarized light components of four or more polarization directions different from each other splits the reflected light reflected by the object to be measured into light in 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 polarization beam splitters that decompose each light split by the splitter into polarization components in different directions.

[0030]

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
It is determined by an ψ and the phase difference Δ. It is obtained from the elliptical shape and the degree of inclination of the ellipse from the reference line. Therefore, FIG.
As shown in, if at least three light intensities obtained by projecting an ellipse in each direction are obtained, the ellipse is uniquely determined.

Therefore, for example, as shown in FIG. 2, projections from four or more directions with respect to the reference direction are obtained, three directions are selected from the projections, and projections from these three directions are obtained. However, the ellipse is uniquely determined. In this case, the ellipso parameter is calculated using three optimal light intensities, for example, the conversion error in the A / D converter that converts the obtained analog light intensity into digital light intensity is small. 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

[0033]

[Equation 6] , 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.

[0035]

[Equation 7] Therefore, the light intensity Ii obtained by the light receiver is

[0036]

[Equation 8] = Gi ｜ Kia ・ Ep ｜ ² [Tan ² ψ ・ COS ² Ai ＋ (σi χ) ² sin ²
Ai + 2σi · χ · tanψ · cos (Δ-φ 0 -φ i) · cosAi · sinAi] (i = 1,2, ..., n) ... a (14). However, Gi is the gain of the electric system, and Kia is Kia = Ki Kp KbiRs. 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 depending 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)

Therefore, the n light intensities I1, I2,
..., Ii, ..., In to three light intensities Ik of i = k, l, m,
Assuming that Il and Im are selected, three equations can be obtained by substituting i = k, l, m into equation (15). Then, in order to simplify each equation, if a _i , b _i , and c _i are defined as in equation (4), then a _i = cos ² Ai b _i = 2σi · χ · cosAi · sinAi c _i =-(σi · χ) ² sin ² Ai (i = k, l, m) (4) These three equations can be arranged as shown in equation (16).

[0039]

[Equation 9] Therefore, in order to obtain the ellipso parameters ψ and Δ, the simultaneous equations in Eq. (16) are calculated using tan ψ and cos (Δ−φ ₀
Solve for −φ _B ). In this case, tan ² ψ = (A / C) tan ψ · cos (Δ−φ ₀ −φ _B ) = B / C That is, tan ψ = (A / C) ^1/2 (1) cos (Δ−φ ₀ −φ _B ) = (B / C) (C / A) ^1/2 It can be calculated as (2). However, A, B, C are (1
By calculating equation (6), each is expressed by the determinant shown in equation (3).

[0040]

[Equation 10] For example, when the above determinant is calculated, A becomes the following equation. A = [c _k b _l I _m + c _l b _m I _k + c _m b _k I _l ]-[c _k b _m I _l + c _l b _k I _m + c _m b _l I _k ] Next, a gain adjustment method An example will be described. First, the known polarization

[0041]

[Equation 11]

The light intensity output from the photodetector 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).

[0043]

[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, ..., Ixn are given constant values as I _0a , and I ₀
Gains G1, G2, ..., Gi, ..., Gn are determined so as to be equal to _0a 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. Further, the known polarized light beam used for gain adjustment may be any polarized light beam in principle as long as the output of each light receiver does not become zero.

As described above, by using the four or more light intensities I1, I2, ..., In measured at the same time, the optimum three light intensities Ik, Il, Im are selected from among them. Ellipso parameters Δ and ψ are calculated using the three light intensities. 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.

[0048]

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 material surface is separated into four polarization components (n =
4).

Reference numeral 10 in the drawing denotes an ellipsometer body housed in a case made 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 the ellipso parameters .psi. And .DELTA. Using the remaining three light intensities in which the lowest light intensity among the input light intensities I1, I2, I3, and I4 is discarded. 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 transmitted light 21a incident on the light receiver 23a provides the light intensity I1 (1 channel) of the reflected light 18 projected on the vertical axis of the elliptically polarized light shown in FIG. 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, the ellipso parameters ψ and Δ that specify this elliptically polarized light are calculated using the three light intensities of these four light intensities I1 to I4.

In the ellipsometer of this embodiment, four light intensities I1 to I4 to three light intensities Ik and Ik are used.
The magnitude of light intensity is used as a reference for selecting l and Im. As described above, by adopting the three light intensities having large values, the ellipso parameters can be used without using the light intensities that can be regarded as having a large error at the time of A / D conversion in the A / D converter 11 shown in FIG. ψ and Δ are calculated. Therefore, the calculation accuracy of the ellipso parameters ψ and Δ is improved.

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 + σT² ) / 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/ 2) [tan² ψ + (σTχ)²  + 2σT · χ · tan ψ · cos (Δ-φ₀-Φ_T)] I4 = (I₀/ 2) [tan² ψ + (σTχ)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. That is, 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 to the non-polarizing beam splitter 10 are θ ₀ and θ, respectively.
If it is set to ₁ , r _P and r _s are 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 )… (2
5)

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-polarizing beam splitter 19 is a real number,
Note that φ _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 minimum light intensity of the four light intensities is discarded. Then, the remaining three light intensities are substituted into the 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.

In the ellipsometer thus constructed, the light intensity having the smallest value among the four measured light intensities I1 to I4 which is considered to have the largest error is discarded. Then, the ellipso parameters ψ and Δ are calculated using the remaining three light intensities whose values are considered to be small in error. Therefore, the accuracy of the calculated ellipso parameters ψ and Δ is improved.

As described above, since the light intensity under the best condition is always selected and used for the calculation, the ellipso parameters ψ and 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 measurement accuracy can always be maintained.

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 view 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 mounted 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 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 minimum light intensity of the read four light intensities is discarded. And
The remaining three 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.

FIG. 8 shows the ellipso parameter of the phase difference Δ calculated when the film thickness is measured for a large number of silicon wafers 35 having various film thicknesses d, and the error rate (%) with respect to a certain phase difference Δ. It is a figure which shows the relationship of.
And, FIG. 7 is a diagram showing an experimental result using a conventional ellipsometer.

As shown in the figure, in the conventional ellipsometer in FIG. 7, when the phase difference Δ at which the value of one of the three light intensities I1 to I3 becomes extremely small is 0 ° and 180 °, There is an error of up to ~ 12%.

On the other hand, in the ellipsometer of the embodiment shown in FIG. 8, one of the four light intensities I1 to I4 whose value is extremely small is removed, so that the phase difference Δ is 0 °. Also, the error rate could be reduced to 3 to 5% even in the vicinity of 180 °.

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. 11 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 ° from the reference direction by the reflected light 18 from the sample surface 13 can be obtained as in the case of 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. 12, 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. 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 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-polarization beam splitters 19, 41, 42.
And four analyzers 43a, 43b, 43c, 43d.

That is, the reflected light 18 from the sample surface 13 is branched 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. 14 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 first 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 unpolarized 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 expressed by the equation (26) similarly to the equation (22). 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 ² 150 ＋ 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.

Therefore, these five light intensities I1 to I5
By selecting three light intensities Ik, Il, Im having a large value from and solving the corresponding three equations, highly accurate ellipso parameters Δ, ψ can be calculated. FIG. 9 is a diagram showing a relative error of Δ when a certain phase difference Δ is used as a reference. It can be understood from this figure that good characteristics can be obtained. Therefore, it is possible to obtain substantially the same effects as those of the respective embodiments described above.

Further, FIG. 10 shows the ellipso parameters Δ and ψ obtained from the five light intensities I1 to I5 using any three light intensities exceeding a certain reference value in the five-channel embodiment shown in FIG. It is a figure which shows the relative error in the case. As can be understood from this figure, it can be understood whether the performance comparable to the relative error shown in FIG. 9 can be secured.

FIG. 15 is a schematic diagram showing a schematic structure of an ellipsometer according to still another embodiment of the present invention. Figure 1
The same parts as those in the fourth 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, from these six light intensities I1 to I6, three light intensities Ik, Il, I having large values are obtained.
By selecting m, highly accurate ellipso parameters Δ and ψ can be calculated. Therefore, it is possible to obtain substantially the same effects as those of the respective embodiments 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 examples, three light intensities having large values were selected as a method of selecting three light intensities to be used for calculation from a plurality of detected light intensities of four or more. However, it goes without saying that three light intensities may be randomly selected from the plurality of light intensities when the detected light intensities have sufficiently high measurement accuracy.

[0099]

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 the ellipso parameters Δ and ψ are calculated from the optimum light intensity, for example, three light intensities having large values among the detected light intensities, using a calculation formula. is doing. Therefore, it is possible to always obtain a high film thickness measurement accuracy higher than 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 an error rate of a conventional ellipsometer used for an oxide film thickness measuring device,

FIG. 8 is a diagram showing an error rate of an example ellipsometer used in an oxide film thickness measuring device,

FIG. 9 is a diagram showing an error rate in an ellipsometer of another example,

FIG. 10 is a diagram showing an error rate in the ellipsometer of the same example,

FIG. 11 is a view showing the internal structure of the body of an ellipsometer according to another embodiment of the present invention,

FIG. 12 is a view showing the structure of another embodiment 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 ... Quarter wave plate, 43
a-43d ... Analyzer.

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

Claims (6)

[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. The ellipso parameter measuring method is characterized in that three light intensities are selected from among the three light intensities and the ellipso parameter determined by the phase difference and the amplitude ratio in the reflected light is obtained from the three light intensities. 2. The polarized light is incident on the measurement target at a predetermined angle, and the 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. Of the three light intensities are selected, and from these three light intensities, using the following equations (1) (2) (3) (4),
An ellipso parameter measuring method, characterized in that the ellipso parameters Δ, ψ determined by the phase difference Δ and the amplitude ratio tan ψ in the reflected light are obtained. 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, a _i = cos ² Ai b _i = 2σi · χ · cosAi · sinAi c _i =-(σi · χ) ² sin ² Ai (i = k, l, m) (4). Ai is the azimuth angle of the polarized light with the direction parallel to the incident surface of the incident light on the measurement target as the reference direction, and σi, φ
_B is a constant determined by an optical system that separates the reflected light into a plurality of polarization components, χ and φ ₀ are constants determined by the polarization state of the incident light, and Ii is the light intensity detected by the light receiver. 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 light receivers for detecting the light intensity of each polarization component separated by the system, and three light intensities of the plurality of light intensities detected by the plurality of light receivers are selected to
An ellipsometer, which calculates an ellipsometer parameter determined from the phase difference and amplitude ratio of the reflected light from two light intensities. 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. A plurality of light receivers for detecting the light intensity of each polarization component separated by the system, and three light intensities of the plurality of light intensities detected by the plurality of light receivers are selected to
An ellipsometer including an arithmetic unit that obtains the ellipso parameters Δ and ψ determined from the phase difference Δ and the amplitude ratio tan ψ in the reflected light from the two light intensities using the following equations (1), (2), (3), and (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 as follows: However, a _i = cos ² Ai b _i = 2σi · χ · cosAi · sinAi c _i = − (σi · χ) ² sin ² Ai (i = k, l, m) (4). Ai is the azimuth angle of the polarized light with the direction parallel to the incident surface of the incident light on the measurement target as the reference direction, and σi, φ
_B is a constant determined by an optical system that separates the reflected light into a plurality of polarization components, χ and φ ₀ are constants determined by the polarization state of the incident light, and Ii is the light intensity detected by the light receiver. 5. The non-polarization beam splitter that splits the reflected light reflected by the measurement target into light beams in a plurality of 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. 6. 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.