JP3141498B2 - Ellipsometer parameter measurement method and ellipsometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ellipsometric parameter measuring method for measuring an ellipsometric parameter used for measuring a thin film thickness and an ellipsometer using the method, and more particularly to a phase difference .DELTA. Ratio tan
The present invention relates to an ellipsometric parameter measurement method and an ellipsometer for quickly obtaining ellipsometric parameters Δ and さ れ る determined by ψ and ψ.

[0002]

2. Description of the Related Art As a technique for measuring the thickness of a thin film, an ellipsometry technique has been proposed. In this approach,
The change in the polarization state when light is reflected on the sample surface such as a thin film, that is, the reflectance Rp of the component (P component) parallel to the plane of incidence of the electric field vector and the reflectance Rs of the component (S component) perpendicular to the plane of incidence. The ratio ρ is measured by the equation (8), and according to the already established relationship between the polarization reflectance ratio ρ and the film thickness d, this film thickness d
Ask for. ρ = Rp / Rs = tanψexp [jΔ] (8)

Here, since the polarization reflectance ratio ρ is generally a complex number as shown in equation (8), it is necessary to determine two ellipso parameters, that is, an amplitude ratio tanψ and a phase difference Δ.

Conventionally, there is a method called an extinction method as a method for obtaining the ellipsometric parameters ψ and Δ. In this method, for example, light polarized at a predetermined angle from a light source is incident on a measurement target, and elliptically polarized reflected light from the measurement target is transmitted through a quarter-wave plate and an analyzer and received. Guide to the vessel. Then, while monitoring the light intensity signal obtained by the light receiver, for example, with a measuring instrument, the quarter-wave plate and the analyzer are rotated to obtain a rotation angle at which the light intensity is minimized. Calculate the parameters. However, in this method, it is necessary to rotate the analyzer to search for the minimum angle position of the light intensity, so that much time is required for the measurement.

Therefore, as a method for measuring the above-mentioned ellipsometric parameters at a relatively high speed, a method using a rotary analyzer has been proposed. That is, in this measurement method,
As with the quenching method, for example, 4
When linearly polarized light is incident at a predetermined angle such as 5 °, and the rotating analyzer on the measurement side is rotated at the angular frequency ω, the output waveform of the light intensity obtained by the light receiver is, except for a constant multiple, It is expressed by equation (9) using Jones vector.

[0006]

(Equation 2) Indicates incident linearly polarized light in the 45 ° direction. The first component of equation (10) represents a P-polarized component, and the second component represents an S-polarized component. Also,

[0007]

(Equation 3)

Is a matrix showing the action at time t of the rotating analyzer rotating at the angular frequency ω. However, time t = 0
The rotary analyzer is positioned so as to detect P-polarized light (linearly polarized light at 0 ° with respect to the reference direction). in this case,
The ellipsometric parameters Δ and ψ are obtained from Eq. (9).

[0009]

However, the ellipsometric parameter measuring method using the above-mentioned rotary analyzer has the following problems.

1) Find ellipso parameters Δ and ψ
As can be understood from the expression (9), the information of the phase difference is [c
osΔ], it is indistinguishable whether the correct phase difference is Δ or (360 ° −Δ). The output waveform when circularly polarized light is used as the incident light is (13)
It is shown by the formula.

[0011]

(Equation 4)

Also in this case, since the information on the phase difference among the ellipso parameters is obtained in the form of [sinΔ], it can be distinguished whether the correct phase difference is Δ or (90 ° −Δ). Absent.

Therefore, the obtained phase difference Δ is the first
From the quadrant (0 ° to 90 °) to the fourth quadrant (270 ° to 360 °)
°), it is necessary to determine which quadrant (zone) it belongs to. This determination is generally called zone determination. As a general zone determination method, an output waveform when a quarter-wave plate is inserted into the optical path of the incident light with respect to the measurement target to make the incident light circularly polarized, and the incident light without the quarter-wave plate is inserted. An output waveform in the case of linearly polarized light is obtained, and a comparison is made between the two output waveforms to determine a belonging zone. However, in this method, it is necessary to perform two measurements for the same measurement point, and the measurement efficiency does not always increase significantly as compared with the quenching method described above.

2) The reflected light from the object to be measured is in an elliptically polarized state, but when the ellipse is close to a circle, there is a problem that the measurement accuracy is reduced. That is, cos2ψ and sin2ψco obtained by performing discrete Fourier transform on the waveform of equation (9) or (13)
The phase difference Δ is obtained from s Δ (or sin2ψ · sin Δ),
For example, when the phase difference Δ is near 90 ° when linearly polarized light is incident,
(Sin2ψ · cos Δ · cos2ωt) is almost always 0, the effective signal component including the information of the phase difference Δ is reduced, and the measurement accuracy of the phase difference Δ is greatly reduced. Therefore, in order to obtain high measurement accuracy, depending on the measurement target,
By inserting a quarter-wave plate in the optical path of incident light or reflected light,
It is necessary to change the elliptically polarized state of the reflected light incident on the measurement system. Therefore, the measurement work efficiency is further reduced.

3) When performing one measurement, it is necessary to rotate the analyzer by one rotation, and the rotation requires a certain time or more. Therefore, it is impossible to obtain the ellipsometric parameters ψ and Δ of the measuring object moving at high speed and to measure the film thickness d from these ellipsometric parameters. Further, since there are mechanically movable parts, the apparatus itself is not used. However, it has not been possible to measure the film thickness of a measurement object supplied continuously, for example, continuously on a production line of a factory, for example, online.

4) A mechanism for rotating the analyzer and a mechanism for inserting and removing the quarter-wave plate from the optical path are required. Since a large number of movable members are incorporated in these mechanisms, and the size of the apparatus itself is increased, the installation place of the ellipsometer is limited to a relatively large and environmentally friendly place such as a laboratory.

Further, since it is mechanically movable, much time is required for the movement. As a result, if the analyzer is rotated twice by inserting and removing the quarter-wave plate with respect to one measurement point, it takes several seconds to perform the measurement for one measurement point, and the high speed in the online state is required. Measurement was not possible.

The present invention has been made in view of such circumstances, and separates elliptically polarized light reflected from an object to be measured into four or more mutually different polarization components to detect the light intensity of each polarization component. By calculating the ellipsometric parameters from the four or more light intensities using a calculation formula, there is no need to rotate the analyzer and no need to insert and remove the quarter-wave plate with respect to the optical path. , It can be composed only of fixed members, it can omit the time required for movement due to the use of movable members, can measure ellipsometric parameters almost instantaneously in one measurement, and even if it is a moving object, It is another object of the present invention to provide an ellipsometer parameter measurement method and an ellipsometer that can measure ellipsometer parameters online and can also measure film thickness.

[0019]

In order to solve the above-mentioned problems, in the ellipsometric parameter measuring method according to the present invention, polarized light is made incident on a measuring object at a predetermined angle, and reflected lights of the measuring objects are mutually reflected. The light is separated into four or more different polarized light components, and the phase difference Δ and the amplitude ratio t in the reflected light are obtained from the light intensities of the separated four or more polarized light components.
The ellipsometric parameters Δ and さ れ る determined by anψ are obtained including the belonging quadrant of Δ.

Further, in the ellipsometer of the present invention, the light source unit for causing the polarized light to enter the object to be measured at a predetermined angle and the light reflected by the object to be measured are different from each other.
An optical system that separates the light into two or more polarized light components, four or more light receivers that detect the light intensity of each polarized light component separated by the optical system, and each light that is detected by the four or more light receivers. A calculation unit for obtaining ellipsometric parameters Δ and さ れ る determined from a phase difference Δ and an amplitude ratio tan に お け る in the reflected light, including the quadrant to which the Δ belongs.

In the ellipsometer of another invention, the arithmetic unit is determined by the phase difference Δ and the amplitude ratio tan in the reflected light using the following equations (1), (2), (3), and (4). The ellipsometric parameters Δ and る are obtained including the belonging quadrant of Δ. tanψ = (| A | / | D |) ^1/2 .. (1) tan (Δ−φ ₀ ) = | B | / | C | (2) where | A |, | B |, | C |, and | D |
Matrix defined by equation (3) This is the determinant of B, C, and D.

[0022]

(Equation 5) Where a _i = α _1i ² b _i = 2 · χ · sin (β _2i −β _1i ) · α _1i · α _{2ic i} = 2 · χ · cos (β _2i −β _1i ) · α _1i · α _{2id i} = −χ ² ・ Α _2i ² (I = 1,2,3,4)… (4)

## EQU1 ## Also, α _1i , α _2i , β _1i , β _2i
Is a parameter determined by the optical system that separates the reflected light into four or more polarization components, χ, φ ₀ are parameters determined by the polarization state of the incident light, and I _i (i = 1, 2, 3, 4) Is the light intensity detected by each light receiver. Further, in the ellipsometer of another invention, each of the parameters α _1i , α
_2i , β _1i , β _2i (i = 1, 2, 3, 4) are set as shown in equation (5). α _1i = cosAi α _2i = σi · sinAi β _1i = 0 β _2i = φ _i (i = 1,2,3,4)… (5)

Here, Ai is the azimuthal angle of the polarized light with the direction parallel to the plane of incidence of the incident light on the object being measured as the reference direction.
σ _i and φ _i are constants determined by an optical system that separates the reflected light into four or more polarized light components. In the equations (1) and (2), the quadrant to which the calculated phase difference Δ belongs is determined according to the positive / negative relationship between (| B | / | C |) and (| C | / | D |). I just need.

Further, there is provided an optical system for separating the reflected light reflected by the object to be measured into four or more different polarization components.
A non-polarization beam splitter that splits the light reflected by the measurement target into light in different directions from each other, and a plurality of light sources that decompose each light split by the non-polarization beam splitter into polarization components in different directions. What is necessary is just to comprise with a polarization beam splitter.

In another ellipsometer measurement method according to another invention, polarized light is incident on a measurement object at a predetermined angle, and reflected light from the measurement object is separated into four different polarization components, respectively. From the respective light intensities I ₁ , I ₂ , I ₃ and I _{4 of the four} polarized components obtained, the following (6) and (7)
The ellipsometric parameters Δ and 決定, which are determined by the phase difference Δ and the amplitude ratio tan に お け る in the reflected light, are calculated by using the equation, including the belonging quadrant of Δ. tan (Δ−φ ₀ ) = σT (I ₁ −I ₂ ) / σR (I ₃ −I ₄ ) (6) tanψ = [｛χ ² (ΣT ² (I ₁ + I ₂ ) −σR ² _{(I 3 + I 4))} } ÷ {(I 1 + I 2) - (I 3 + I 4)}] 1/2 … (7)

Here, 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 object to be measured, and σR and σT are constants determined by an optical system that separates the reflected light into four polarization components.

Further, as a material for determining the belonging quadrant of the calculated phase difference Δ, [σT (I ₁ −I ₂ )] in the equation (6) is used.
And σR (I ₃ −I ₄ )].

Further, in the ellipsometer according to another invention, a light source section for causing polarized light to enter a measuring object at a predetermined angle, and an optical system for separating reflected light reflected by the measuring object into four different polarized components. And a wave plate interposed in an optical path in the optical system and relatively changing a phase difference between mutually orthogonal polarization components of the reflected light, and detecting the light intensity of each polarization component separated by the optical system And the light intensities I ₁ , I ₁ detected by the four light receivers
_The ellipsometric parameters Δ and さ れ る determined by the phase difference Δ and the amplitude ratio tan に お け る in the reflected light are obtained from ₂ , ₂ , ₃ and I _{4 using the} above-described equations (6) and (7), including the quadrant to which the Δ belongs. And an operation unit.

The optical system includes a non-polarization beam splitter that splits the reflected light reflected from the object to be measured into light beams in two different directions, and separates the light beams split by the non-polarization beam splitter from each other. It is composed of two polarization beam splitters that decompose into polarization components in two directions.

[0031]

First, the operation principle of the ellipsometer parameter measuring method and the ellipsometer configured as described above will be described.
As described above, when light polarized from the light source unit enters the measurement object at a predetermined angle φ, for example, as shown in FIG. 3, the reflected light reflected by the measurement object is a constant light determined by the film thickness of the measurement object. The shape becomes elliptically polarized light. The ellipsometric parameters ψ and Δ are the amplitude ratio tan of the P component and the S component of the reflected light.
位相 and the phase difference Δ. Therefore, originally,
There are two parameters. For example, when the incident light is linearly polarized light, the sign of the phase difference Δ is determined depending on whether the elliptically polarized light is clockwise or counterclockwise. However, since the light intensity measured by the light receiver does not include information on the rotation direction of the elliptically polarized light, another independent light intensity is required. As long as three light intensities can be obtained in this manner, four light intensities are required to perform a dimensionless calculation that does not depend on the absolute light amount. The procedure for obtaining equations (1) and (2) will be described below. For example, the incident light Ein

[0032]

(Equation 6)

The light reflected by the surface of the object to be measured and passed through an optical system that separates the reflected light into four or more polarization directions, that is, the polarization direction is the azimuth Ai (i = 1, 2, 3, The electric field of the light after passing through the analyzer or the polarizing beam splitter that detects the light in the polarization direction of (4) is KiR (Ai) PR (-Ai) BSEin (i = 1,2,3,4) (1)
5) can be expressed as Here, Ki is a transmission coefficient of each optical path.

R (Ai) is a rotation matrix, P is a matrix representing an analyzer or a polarizing beam splitter, and B is a beam splitter or an optical element for providing a phase difference between P-polarized light and S-polarized light or a combination thereof. The matrix to be expressed, S, is a matrix indicating the effect on the polarization of the measurement target. Each of these matrices is defined as shown below.

[0035]

(Equation 7) Therefore, the light intensity I _i detected by the light receiver is

[0036]

(Equation 8) Becomes Here, Gi is the gain of the electric system, and Kia is Kia = Ki Kp KbiRs

Is as follows. In the process of deriving the equation,
The fact that the magnitude of the vector is invariable by the rotation matrix of equation (16) is used. However, the above I _i can be basically referred to as “light receiver output proportional to the light intensity detected by the light receiver”. However, in this specification, the term "light intensity detected by the light receiver" is used for convenience. Here, when determining the gain Gi by a suitable technique, the light intensity I _i shown in equation (20) becomes the following equation (21). I _i = 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] = I ₀ [tan ² ψ ・ COS ² Ai + (σi χ) ² sin ² Ai

[0038] + 2σi · χ · tanψ · sin (Δ-φ 0) · sinφ i · COSAi · sinAi + 2σi · χ · tanψ · cos (Δ-φ 0) · cosφ i · COSAi · sinAi (i = 1,2, 3,4)… (21)

Here, I ₀ is a constant that depends on the method of adjusting the gain, the incident light intensity, the reflectance of the object to be measured, and the like. In addition,
Depending on the gain adjustment method, I _{0 on} each side of the equation (21)
(i = 1,2,3,4). In such a case, if each I _i (i = 1, 2, 3, 4) multiplied by a correction coefficient is redefined as I _i , then formally i (i = 1, 2, 3, 3) 4) It can be expressed as in equation (21) using a constant I ₀ that does not depend on:

Accordingly, the light intensities detected by each of the four photodetectors are defined as I ₁ , I ₂ , I ₃ , and I ₄ .
Substituting 2,3,4 in order gives four equations. Then, in order to simplify each equation, a _i , b _i , c _i , d _i
Is defined as in equation (22). a _i = cos ² _{Ai b i = 2σi · χ ·} sinφ i · cosAi · sinAi c i = 2σi · χ · cosφ i · cosAi · sinAi d i = - (σi · χ) 2 sin ² Ai (i = 1,2,3,4) (22) Accordingly, these four equations can be arranged as shown in equation (23).

[0041]

(Equation 9)

Therefore, in order to obtain the ellipsometric parameters ψ and Δ, the simultaneous equations of the equation (23) are calculated as tanψ, sin
It is sufficient to solve for (Δ−φ ₀ ) and cos (Δ−φ ₀ ). Solving equation (23), tan ² ψ, tanψ · sin (Δ−φ
₀ ) and tanψ · cos (Δ−φ ₀ ), the following (24)
It becomes an expression. tan ² ψ = | A | / | D | tanψ · sin (Δ−φ ₀ ) = | B | / | D | tanψ · cos (Δ−φ ₀ ) = | C | / | D | (24) Equation (24) can be transformed as follows. tanψ = (| A | / | D |) ^1/2 ... (1) sin (Δ−φ ₀ ) = [| B | / | D |] · [| D | / | A |] ^1/2 … (25) cos (Δ−φ ₀ ) = [| C | / | D |] · [| D | / | A |] ^1/2 (26) or tan (Δ−φ ₀ ) = | B | / | D | (2) Where | A |, | B
│, │C│, │D│ are the matrices A. This is the determinant of B, C, and D.

[0043]

(Equation 10)

Since is linearly dependent, no solution can be found. Therefore, in this case, an optical element such as a wavelength plate having a function of changing the phase difference between the P-polarized light and the S-polarized light is required. Next, a description will be given of a procedure for determining the belonging quadrant of the phase difference Δ among the ellipso parameters ψ and Δ calculated by the above-described calculation procedure.

As shown in the above equations (25) and (26), sin (Δ−φ
₀ ) and cos (Δ−φ ₀ ). Therefore, it can be automatically determined to which quadrant from the first quadrant to the fourth quadrant the phase difference Δ calculated by the equation (2) belongs. That is, (| B | / | D |) and (| C | / | D
Can be determined as follows according to the positive / negative relationship between | (1) | B | / | D |> 0, | C | / | D |> 0, the first quadrant _{(0 ° <Δ-φ 0} <90 °) (2) | B | / | D | > 0, | C | / | D | < 0, the second quadrant _{(90 ° <Δ-φ 0} <180 °) (3) | B | / | D | <0, | C | / | D | If <0, the third quadrant (180 ° <Δ−φ ₀ <270 °) (4) If | B | / | D | <0, | C | / | D |> 0, the fourth quadrant (270 ° <Δ−φ ₀ <360 °)

Therefore, it is possible to simultaneously determine which quadrant from the first quadrant to the fourth quadrant the calculated phase difference Δ belongs to. As a result, the true value of the obtained phase difference Δ is Δ
Or (360 ° −Δ), (90 ° −
Δ),... Can be accurately determined.

[0047] In the case where the reflected light to be measured has been separated into five or more polarization components, the light intensity I _i detected by the photodetector is 5 or more in (23) (i = 1,2.3.4.
Five.…) . In this case, it is possible to estimate the solution of the equation (23) by using a statistical method such as the least square method. further,
If the above equation (23) can be expressed as equation (28),

[0048]

[Equation 11] Using the light intensities I _{1 to} I ₄ of the output signals of the respective light receivers, the respective ellipsometric parameters Δ and ψ are calculated using the following equations (6) and (7). tan (Δ−φ ₀ ) = σT (I ₁ −I ₂ ) / σR (I ₃ −I ₄ ) (6) tanψ = [｛χ ² (ΣT ² (I ₁ + I ₂ ) −σR ² _{(I 3 + I 4))} } ÷ {(I 1 + I 2) - (I 3 + I 4)}] 1/2 … (7)

According to the above-mentioned equations, the phase difference is given between the P-polarized light and the S-polarized light in the equation (18).
You may give by another method. For example, an optical element that gives a phase difference δ, such as a wave plate, may be rotated by a certain angle θi and inserted into the optical path. In this case, if the optical element is represented by a matrix shown in Expression (29),

[0050]

(Equation 12)

In the calculation formula, R (θi) ΛR (−
θi). Therefore, the electric field on the light receiver in the optical system in which such an optical element is inserted is expressed by the following equation (30) instead of the above-described equation (15). Ki R (Ai) PR (-Ai) XSEin (i = 1,2,3,4)… (30)

Here, X is a matrix expressing the function of the entire optical system in which optical elements for giving a beam split or a phase difference are arbitrarily arranged, and R (θi) ΛR (−θi described above).
) And B are sequentially arranged according to the optical system.
Therefore, the signal strength of the output signal obtained by the light receiver is (31)
It becomes an expression. I _i = Gi | Ki R (Ai) PR (-Ai) XSEin | ² = Gi | Ki | ² ｜ PR (-Ai) XSEin ｜ ² (i = 1,2,3,4) (31) Here, PR (−Ai) X can be generally expressed by equation (32).

[0053]

(Equation 13) For example, when giving a phase difference between the already calculated P-polarized light and S-polarized light,

[0054]

[Equation 14] That is, α _1i = cosAi α _2i = σi · sinAi β _1i = 0 β _2i = φ _i (i = 1, 2, 3, 4) (5). Therefore, when substituting equation (32) into equation (31),
Equation (34) is obtained.

[0055]

(Equation 15) ＝ Gi ｜ Kia ・ Ep ｜^Two [Tan^Two ψ ・ α_1i ^Two + Χ^Two α_2i ^Two  ＋2 ・ χ ・ tanψ ・ cos (Δ−φ₀+ Β_1i−β_2i) ・ Α_1i・ Α_2i] = Gi | Kia · Ep |^Two [Tan^Two ψ ・ α_1i ^Two + Χ^Two α_2i ^Two  ＋2 ・ χ ・ tanψ ・ sin (Δ−φ₀) ・ Sin (β_2i−β_1i) ・ Α_1i・ Α_2i ＋2 ・ χ ・ tanψ ・ cos (Δ−φ₀) ・ Cos (β_2i−β_1i) ・ Α_1i・ Α_2i(I = 1,2,3,4) (34) Here, the gain Gi (i = 1,2,3,
(4), the signal strength Ii shown in the equation (34) becomes the equation (35).
You. I_i= I₀[Tan^Two ψ ・ α_1i ^Two + Χ^Two α_2i ² _{+ 2 · χ · tan · sin (Δ−φ 0} ) ・ Sin (β_2i−β_1i) ・ Α_1i・ Α
_2i ＋2 ・ χ ・ tanψ ・ cos (Δ−φ₀) ・ Cos (β_2i−β_1i) ・ Α_1i・ Α_2i] (I = 1,2,3,4)… (35)

Here, when α ₁ , α ₂ , β ₁ , and β ₂ are replaced by using equation (4), the four equations respectively corresponding to i = ₁ , _2, and 3.4 in equation (35) are described above. It can be shown as in equation (23). a _i = α _1i ² b _i = 2 · χ · sin (β _2i −β _1i ) · α _1i · α _{2ic i} = 2 · χ · cos (β _2i −β _1i ) · α _1i · α _{2id i} = −χ ² ・ Α _2i ² (I = 1,2,3,4)… (4)

[0057]

(Equation 16) From the equation (23), as described above, the ellipsometric parameters φ and Δ are obtained by the equations (1) and (2). tanψ = (| A | / | D |) ^1/2 … (1) tan (Δ−φ ₀ ) = | B | / | C | (2)

As described above, the ellipsometric parameters Δ and Δ are calculated from the light intensities I 1, I 2, I 3 and I 4 measured at the same time.
Since ψ is calculated including the belonging quadrant, it is possible to measure even a moving object to be measured. Further, the measurement time can be greatly reduced even when measuring very many points such as the in-plane distribution of the film thickness.

[0059]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing the entire ellipsometer employing the ellipsometric parameter measuring method of the embodiment. In the figure, reference numeral 1 denotes an ellipsometer main body housed in a case formed of a light metal material. The light intensities I ₁ , I ₂ , I ₃ , and I ₄ output from the ellipsometer main unit 1 are A / D
After being converted into a digital value by the converter 2, the digital value is input to a personal computer 3 as an arithmetic unit. The personal computer 3 receives the input light intensities I ₁ , I _1
2 , I ₃ and I ₄ are used to calculate the ellipsometric parameters Δ and 決定 determined by the phase difference Δ and the amplitude ratio tan 含 め, including the belonging quadrant of Δ. Further, using the calculated ellipsometric parameters と し て and Δ, the film thickness d of the sample surface 4 to be measured is determined.
Is calculated using a predetermined arithmetic expression.

Here, the A / D converter 2 determines each light intensity I
₁ , I ₂ , I ₃ , and I ₄ are time-divided and A / D converted sequentially. The conversion time for one light intensity is about 10 μsec.
It is. Therefore, including the calculation time in the personal computer 3, the measurement time of the ellipsometric parameters ψ and Δ and the film thickness d at one sampled measurement point on the sample surface 4 is about 100 μsec. Since the light intensities I ₁ , I ₂ , I ₃ , and I ₄ are measured at the same time and held by the voltage holding circuit, even if the sample surface 4 moves at a high speed, it is possible to cope with it.

FIG. 1 is an internal configuration diagram of the ellipsometer main body 1. For example, a laser beam having a single wavelength output from a laser light source 5 of a semiconductor laser is converted by a polarizer 6 into linearly polarized light of + 45 ° with respect to a reference direction. Therefore, the laser light source 5 and the polarizer 6 constitute a light source unit 7. The incident light 8 converted into linearly polarized light is incident on the sample surface 4 from the light source unit 7 at an angle φ. The reference direction is
As viewed from the sample surface 4 side, as shown by the arrow A direction in the figure, the direction parallel to the incident surface of the incident light 8 is a direction in which the azimuth is 0 °. Here, the incident surface is a plane perpendicular to the sample surface 4 including the incident light 8 and the reflected light 9.

Then, the reflected light 9 reflected on the sample surface 4 changes from linearly polarized light to elliptically polarized light shown in FIG. 3 due to the presence of the film on the sample surface 4, and enters the non-polarized beam splitter 10.

The non-polarizing beam splitter 10 is made of, for example, a non-polarizing glass plate. Then, the incident reflected light 9 is split into two lights 11a and 11b while maintaining the phase difference between the P-polarized light and the S-polarized light. The reflected light 11a is incident on the first polarization beam splitter 13 via the quarter-wave plate 12a. The transmitted light 11
b directly enters the second polarizing beam splitter 14.

The first and second polarization beam splitters 13,
Numeral 14 has the same configuration, and is composed of, for example, a Glan-Thompson prism, a Glan-Taylor prism, etc., which separates incident elliptically polarized light into two orthogonal polarization components and transmits and reflects the reflected light. Output as It should be noted that a Wollaston prism or the like that separates transmitted light into two components at an angle may be used.

Then, the first polarization beam splitter 13
Is the transmitted light 13 of the first polarizing beam splitter 13.
Positioning is such that the polarization direction of a is + 45 ° counterclockwise when viewed from the light receiver 15a side with respect to the above-described reference direction in which the direction parallel to the plane of incidence is 0 °. Then, the transmitted light 13a having the polarization direction of + 45 ° output from the first polarization beam splitter 13 is incident on the light receiver 15a. The light receiver 15a receives the light intensity I _{1 of the} received polarized light component.
And outputs a signal corresponding to. Also, the polarization direction output from the first polarization beam splitter 13 is necessarily -45.
° become reflected light 13b is incident on the light receiving device 15b, it is converted into the light intensity I _2.

Further, the second polarization beam splitter 14
Is transmitted light 14 of the second polarization beam splitter 14.
Positioning is performed such that the polarization direction of a is + 45 ° with respect to the reference direction. The second transmitted light 14a of the polarization direction output from the polarization beam splitter 14 + 45 ° is incident on the light receiver 15c, and is converted into the light intensity I _3. Further, the reflected light 14b the polarization direction output from the second polarization beam splitter 14 is -45 ° is incident on the light receiver 15d, is converted into the light intensity I _4.

Since the quarter-wave plate 12 a is interposed in the optical path of the reflected light 11 a incident on the first polarization beam splitter 13, the elliptically polarized reflection incident on the first polarization beam splitter 13 is obtained. The phase difference between the P-polarized light and the S-polarized light of the light 11a changes by 90 °. Therefore, each light receiver 15a
The values of the polarized light components incident on .about.15d are different. That is,
Each polarization component of the elliptically polarized light of the reflected light 9 obtained from each of the light receivers 15a to 15d contains, as it were, information on both cosΔ and sinΔ.

Then, as described above, using these four light intensities I _{1 to} I ₄ , the ellipsometric parameters ψ and Δ for specifying the elliptically polarized light in FIG. 3 are calculated using the above-described equations (1) and (2). You. In this embodiment, each light intensity I ₁ , I ₂ , I ₃ ,
The relationship between I ₄ and each of the ellipsometers Δ and ψ is described above (28)
Obtained from

[0070]

[Equation 17]

Here, when P-polarized light enters the optical system,
The gains Gi (i = 1, 2, 3, 4) of the electric system are adjusted so that the outputs from the light receivers become equal. The gain adjustment process is generally performed by adjusting the actual gain of an amplifier that amplifies the output signal of each light receiver.
However, for example, in a data processing step of the data value of the light intensity taken into the arithmetic unit from each light receiver, the gain adjustment processing may be performed by the program processing means. Therefore, from equation (28), each ellipsometric parameter Δ, ψ is
(6) It can be calculated using (7). tan (Δ−φ ₀ ) = σT (I ₁ −I ₂ ) / σR (I ₃ −I ₄ ) (6) tanψ = [｛χ ² (ΣT ² (I ₁ + I ₂ ) −σR ² _{(I 3 + I 4))} } ÷ {(I 1 + I 2) - (I 3 + I 4)}] 1/2 (7) where σR and σT are P-polarized light of the non-polarizing beam splitter 10. The amplitude reflectance ratio and the amplitude transmittance ratio of S-polarized light;
This is the eigenvalue given by equation (36). Amplitude reflectance ratio σR = r _s / r _P amplitude transmittance ratio σT = (1-r _s ² ) / (1-r _P ² …… (3
6)

Here, r _P and r _s are P-polarized light,
These are Fresnel reflection coefficients for S-polarized light, which are determined by the refractive index and the incident angle of the non-polarizing beam splitter 10. The refractive index of air is N ₀ , the refractive index of the non-polarizing beam splitter 10 is n ₁ , and the non-polarizing beam splitter 1
Assuming that the angle of incidence to 0 and the angle of refraction are θ ₀ and θ ₁ , r _P and r _s are given by equations (37) and (38). r _P = (n ₁ cos θ ₀ −N ₀ cos θ ₁ ) / (n ₁ cos θ ₀ + N ₀ cos θ ₁ ) (37) r _s = (N ₀ cos θ ₀ −n ₁ cos θ ₁ ) / (N ₀ cos θ ₀₎ + N ₁ cos θ ₁ ) (38) 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 object. In general, the phase difference φ ₀ = 0 ° and the amplitude ratio χ = 1 are set to facilitate the calculation.

Each of these constants is such that test light having a known linearly polarized light or elliptically polarized light is incident on the non-polarizing beam splitter 10 and the true ellipsometric parameters ψ, Δ
Is calculated in advance from the amount of deviation from.

When calculating the phase difference Δ, as described above, σT (I ₁ −I ₂ ) = A, σR (I ₃ −I ₄ )
The belonging quadrant (zone) is determined according to the positive / negative condition of = B.

(1) When A> 0 and B> 0, the first quadrant (0 ° <
Δ−φ ₀ <90 °) (2) If A> 0, B <0, the second quadrant (90 ° <
Δ−φ ₀ <180 °) (3) If A <0, B <0, the third quadrant (180 ° <
Δ−φ ₀ <270 °) (4) In the case of A <0, B> 0, the fourth quadrant (270 ° <
(Δ−φ ₀ <360 °) Therefore, it is possible to simultaneously determine which quadrant from the first quadrant to the fourth quadrant the calculated phase difference Δ belongs to.
As a result, whether the true value of the obtained phase difference Δ is Δ,
Or (360 ° −Δ), (90 ° −Δ),...

When the ellipsometric parameters Δ and さ れ る determined by the amplitude ratio tan ψ and the phase difference 含 め are obtained including the belonging quadrant of Δ, the film thickness d on the sample surface 4 is calculated using a separate formula.

In the ellipsometer configured as described above, the four light intensities I ₁ , I ₂ , I ₃ , I ₃ detected at the same time by the respective photodetectors 15a, 15b, 15c, 15d.
_{From 4 on} , the personal computer 3 uses the equations (1) and (2) to almost instantaneously use the ellipsometric parameters 所属,
Since Δ is calculated, subsequently, the film thickness d on the sample surface 4 is calculated almost instantaneously.

Therefore, even if the object to be measured is moving at a high speed, the film thickness d at the designated measurement point can be measured. Accordingly, while the incident light 8 is output from the light source unit 7, the light intensity I _{1 to} I ₄ is read at a constant period while the measurement object is moved at a constant speed, and the ellipsometric parameters ψ and Δ are calculated and the film thickness is calculated. By calculating the thickness d, for example, the thickness d of the surface of the strip-shaped product continuously moving on the inspection line of the factory can be continuously measured online.

Further, as shown in FIG. 1, the elliptically polarized reflected light on the sample surface 4 is separated into four different polarization components, and the light intensities I _{1 to} I ₄ of the respective polarization components are read at the same timing. Therefore, unlike a conventional ellipsometer, there is no need to provide a rotating analyzer or a quarter-wave plate insertion / removal mechanism to obtain polarized components under different conditions. Therefore, all the optical components can be configured only with the fixed member, and the movable device is not used, so that the entire apparatus can be configured to be small and lightweight. Therefore, it can be installed in a narrow place such as a manufacturing site of a factory, and the applicable range can be expanded. FIG. 4 is a view showing a state in which the ellipsometer of the embodiment is incorporated in an apparatus for measuring the distribution of oxide film thickness of a silicon wafer.

A moving table 22 is provided on a base 21, and a rotating support 23 is mounted on the moving table 22. Then, a silicon wafer 25 to be measured is mounted on the rotary support 23 by, for example, a suction mechanism. Therefore, silicon wafer 2
5 moves linearly in the direction of the arrow while rotating. Base 21
An existing thickness measuring device 26 for measuring the thickness of the entire silicon wafer 25 is provided thereon, and an ellipsometer main body 27 is fixed by a support member 28 at a position facing the thickness measuring device 26.

The thickness measuring device 26 and the ellipsometer main body 27 are
At 3, the entire thickness and the thickness d of the oxide film at each measurement position of the silicon wafer 25 spirally moving are measured. Further, the position of the moving table 22 and the rotation angle of the silicon wafer 25 are controlled by a computer incorporated in the apparatus. Therefore, the measurement position and the measurement result are in one-to-one correspondence, and can be instantly grasped visually on a display screen of a CRT display device, for example.

In order to confirm the effect of the embodiment, FIG.
Was compared with the conventional apparatus using the rotary analyzer. An optical system was used in which linearly polarized light was incident on the measurement object at an incident angle of 62 ° as incident light. Further, a silicon wafer 25 having a nitride film having a refractive index of 1.65 and a film thickness d = 800 nm formed on the upper surface is used as a measurement target.

In this case, since the film thickness d is 800 nm,
The phase difference Δ of the ellipsometric parameter in the portion where the nitride film is formed is 94.1 ° in theory, and the phase difference Δ in the portion where the nitride film is not formed is 0 ° naturally.

Therefore, when the measurement is performed by a conventional apparatus using a rotary analyzer, the incident light is circularly polarized at the portion where the nitride film is formed, and is incident at the portion where the nitride film is not formed. The light needs to be linearly polarized. Therefore, when measuring the silicon wafer 25 under such conditions, for example, a 波長 wavelength plate is inserted into the portion where the nitride film is formed, and the portion where the nitride film is not formed is inserted into the portion where the nitride film is not formed. It is necessary to remove the quarter-wave plate for measurement. Therefore, when any point on the silicon wafer 25 is measured, the state in which the quarter-wave plate is inserted is the same as that in the case where the point is measured.
Two measurements must be performed with the quarter wave plate removed. It took about 5 hours to measure about 5,000 points on the entire surface of the silicon wafer 25 having a diameter of 6 inches used in the experiment at intervals of 2 mm. Therefore, as a practical matter, it is impossible to use this conventional apparatus in an actual silicon wafer production inspection line.

On the other hand, in the embodiment apparatus for measuring four light intensities at a time, it takes about 2 msec to add the time for moving the measuring point to measure one point. It takes about 10 hours to measure
sec. Therefore, the processing speed can be sufficiently incorporated in an actual production inspection line.

As described above, the speed and size of the ellipsometer are reduced, and the ellipsometer can be additionally installed on the existing thickness measuring device 26. In a semiconductor process line, in addition to the above-mentioned silicon wafer, application to online measurement of a nitride film, a polysilicon film, a transparent electrode material and the like is possible.

FIG. 5 is a diagram showing a schematic configuration of an ellipsometer according to another embodiment of the present invention. 1 are given the same reference numerals. Therefore, the detailed description of the overlapping part is omitted. In this embodiment, 1
The 波長 wavelength plate 12 b is used as the second polarization beam splitter 14
Is inserted in the optical path of the transmitted light 11b from the non-polarized beam splitter 10 incident on the light. The quarter-wave plate 12a in FIG. 1 has been removed.

In the ellipsometer configured as described above, the phase difference between the elliptically polarized P-polarized light and the S-polarized light in the transmitted light 11b incident on the second polarizing beam splitter 14 changes by 90 °. Light receiver 15a ~
Four different polarization components are incident on 15d. And
In this case, the light intensities of the light receivers 15c and 15d are I1, I2
2 and the light intensities of the photodetectors 15a and 15b are I3 and I3, respectively.
It becomes 4. Further, the constants σR and σT in the equations (6) and (7) are the amplitude transmittance ratio and amplitude reflectance ratio of the P-polarized light and the S-polarized light of the non-polarizing beam splitter 10. Therefore, the same operation as the embodiment of FIG. 1 can be obtained.

FIG. 6 is a schematic diagram showing a schematic configuration of an ellipsometer according to still another embodiment of the present invention. The same parts as those in the embodiment of FIG. 1 are denoted by the same reference numerals, and the description of the overlapping parts will be omitted.

In this embodiment, the transmitted light 36a output from the first polarizing beam splitter 36 is oriented at 90 ° with respect to the aforementioned reference direction.
The attitude of the first polarization beam splitter 36 is fixed. The orientation of the second polarization beam splitter 37 is fixed such that the polarization direction of the transmitted light 37a output from the second polarization beam splitter 37 is oriented in the + 45 ° direction with respect to the reference direction. Therefore,
Inevitably, the reflected light 3 of the first polarization beam splitter 36
The polarization direction of 6b is oriented in the + 0 ° direction, and the polarization direction of the reflected light 37b of the second polarization beam splitter 37 is oriented in the −45 ° direction. The quarter-wave plate 12a is installed at an angle of 45 °. In this case, the aforementioned equation (32) becomes

[0091]

(Equation 18) Therefore, extracting the condition of i = 1 in equation (4) gives (41)
It becomes an expression. a ₁ = 1 b ₁ = 2 · χ · σR c ₁ = 0 d ₁ = −χ ² ・ ΣR ² (41) When A2 = 0, equation (32) becomes equation (42).

[0092]

[Equation 19] Therefore, as in the case of 90 °, i =
If the condition of 2 is extracted, it becomes the formula (43). a ₂ = 1 b ₂ = −2 · χ · σR c ₂ = 0 d ₂ = −χ ² ・ ΣR ² (43) Accordingly, the result is the same as the expressions I ₁ and I _{2 in} the expression (28). Thus, the ellipsometric parameters Δ,
ψ is calculated in (6) and (7) described above. tan (Δ−φ ₀ ) = σT (I ₁ −I ₂ ) / σR (I ₃ −I ₄ ) (6) tanψ = [｛χ ² (ΣT ² (I ₁ + I ₂ ) −σR ² _{(I 3 + I 4))} } ÷ {(I 1 + I 2) - (I 3 + I 4)}] 1/2 (7) As a result, substantially the same effects as in the embodiment of FIG. 1 can be obtained.

[0093]

As described above, in the ellipsometric parameter measuring method and the ellipsometer according to the present invention, the reflected light in the elliptically polarized state reflected by the measurement object is separated into four or more different polarization components different from each other. The light intensity of the polarized light component is detected, and for example, (4)
The ellipsometric parameters Δ and ψ, which are determined by the phase difference Δ and the amplitude ratio tan て, are calculated using the equation, including the quadrant to which the Δ belongs. Therefore, unlike the conventional method, there is no need to rotate the analyzer, and there is no need to insert / remove the quarter-wave plate from / to the optical path for inputting / outputting the object to be measured.

Therefore, the optical measurement system can be composed of only the fixed member, the time required for movement due to the use of the movable member can be omitted, and the ellipso parameter can be measured almost instantaneously in one measurement. Ellipso parameters can be measured online for measurement targets
And the film thickness can also be measured. Further, it can be simultaneously grasped to which quadrant the calculated phase difference belongs. In addition, high measurement accuracy can be maintained over a wide film thickness range. Also,
Since there are no movable parts, the entire apparatus can be formed small and lightweight, and can be installed in a narrow place in a product inspection line or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing an internal structure of a main body of an ellipsometer according to an embodiment;

FIG. 2 is a diagram showing an overall configuration of an ellipsometer according to an embodiment;

FIG. 3 is a diagram showing an elliptically polarized light state of reflected light in the example ellipsometer;

FIG. 4 is a schematic configuration diagram of an apparatus for measuring an oxide film thickness of a silicon wafer using an example ellipsometer,

FIG. 5 is a diagram showing an embodiment structure using a wave plate on the other side of the embodiment of FIG. 1,

FIG. 6 is a diagram showing an embodiment structure using polarization beam splitters set in polarization directions different from each other.

[Explanation of symbols]

1. Ellipsometer body, 2. A / D converter, 3.
Personal computer, 4 sample surface, 5 laser light source, 6 polarizer, 7 light source unit, 8 incident light, 9 reflected light, 10 non-polarizing beam splitter, 12a, 12d
1/4 wavelength plate, 13, 36... First polarization beam splitter, 14, 37... Second polarization beam splitter, 15a
-15d: photodetector, 25: silicon wafer.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tomoyuki Kaneko 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (56) References JP-A-3-160331 (JP, A) JP-A-2 -62930 (JP, A) JP-A-62-251629 (JP, A) JP-A-51-131655 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 11/06 G01J 4/04

Claims (10)

(57) [Claims] 1. A 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 four or more polarization components are separated from each other. Ellipsometric parameters Δ and ψ determined by the phase difference Δ and the amplitude ratio tan に お け る in the reflected light, including the quadrant to which the Δ belongs. 2. A light source unit for causing polarized light to enter a measurement target at a predetermined angle; and an optical system for separating reflected light reflected by the measurement target into four or more different polarization components.
Four or more light receivers for detecting the light intensity of each polarized light component separated by the optical system, and a phase difference Δ in the reflected light from each light intensity detected by the four or more light receivers. An ellipsometer including an arithmetic unit for obtaining ellipso parameters Δ and 決定 determined by the amplitude ratio tanψ, including the belonging quadrant of Δ. 3. A light source unit for causing polarized light to enter a measurement object at a predetermined angle, an optical system for separating reflected light reflected by the measurement object into four or more different polarization components,
Four or more light receivers for detecting the light intensity of each polarized light component separated by this optical system, and the respective light intensities detected by the four or more light receivers, the following (1) (2) (3 And (4) an ellipsometer provided with a calculation unit for obtaining ellipso parameters Δ and さ れ る determined by the phase difference Δ and the amplitude ratio tan に お け る in the reflected light, including the belonging quadrant of Δ, by using equation (4). tanψ = (| A | / | D |) ^1/2 .. (1) tan (Δ−φ ₀ ) = | B | / | C | (2) where | A |, | B |, | C |, and | D |
Matrix defined by equation (3) This is the determinant of B, C, and D. (Equation 1) Where a _i = α _1i ² b _i = 2 · χ · sin (β _2i −β _1i ) · α _1i · α _{2ic i} = 2 · χ · cos (β _2i −β _1i ) · α _1i · α _{2id i} = −χ ² ・ Α _2i ² (I = 1,2,3,4) ... (4). Α _1i , α _2i , β _1i , and β _2i are parameters determined by an optical system that separates reflected light into four or more polarization components, χ and φ ₀ are parameters determined by the polarization state of incident light, I _i (i = 1, 2, 3, 4) is the light intensity detected by each light receiver. 4. The parameters α _1i , α _2i , β _1i , β
_2i (i = 1,2,3,4) is obtained by the following equation (5).
The ellipsometer as described. _{α 1i = cosAi α 2i = σi} · sinAi β 1i = 0 β 2i = φ i (i = 1,2,3,4) ... (5) where, Ai is parallel to the plane of incidence of the incident light to be measured such direction is the azimuth angle of the polarization of the reference direction, .sigma.i, the phi _i is a constant determined by the optical system for separating the reflected light into four or more polarization components. 5. In the formulas (1) and (2), (| B | / |
5. The ellipsometer according to claim 3, wherein a belonging quadrant of the calculated phase difference Δ is determined according to a positive / negative relationship between (C |) and (| C | / | D |). 6. The non-polarizing beam splitter, which splits the light reflected by the measurement target into light in a plurality of directions different from each other, and separates each of the lights split by the non-polarizing beam splitter. 4. The ellipsometer according to claim 3, comprising a plurality of polarization beam splitters for decomposing into polarization components in different directions. 7. A polarized light is incident on a measurement object at a predetermined angle, and reflected light of the measurement object is separated into four different polarization components, respectively, and each light intensity of the separated four polarization components is separated. From I ₁ , I ₂ , I ₃ , I ₄ , the following (6)
Using equation (7), the phase difference Δ and the amplitude ratio in the reflected light
An ellipsometric parameter measuring method characterized in that elliptic parameters Δ and さ れ る determined by tan 含 め are obtained including a belonging quadrant of Δ. tan (Δ−φ ₀ ) = σT (I ₁ −I ₂ ) / σR (I ₃ −I ₄ ) (6) tanψ = [｛χ ² (ΣT ² (I ₁ + I ₂ ) −σR ² _{(I 3 + I 4))} } ÷ {(I 1 + I 2) - (I 3 + I 4)}] 1/2 (7) where 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 object, and σR and σT are constants determined by an optical system that separates the reflected light into four polarization components. It is. 8. A quadrant to which the calculated phase difference Δ belongs according to the positive / negative relationship between [σT (I ₁ −I ₂ )] and [σR (I ₃ −I ₄ )] in the equation (6). The ellipsometric parameter measurement method according to claim 7, wherein the determination is made as follows. 9. A light source unit for causing polarized light to enter a measurement object at a predetermined angle, an optical system for separating reflected light reflected by the measurement object into four different polarization components, and an optical system in the optical system. A wave plate interposed in an optical path and relatively changing a phase difference between mutually orthogonal polarization components of the reflected light, and four light receivers for detecting light intensity of each polarization component separated by the optical system From the light intensities I ₁ , I ₂ , I ₃ , and I ₄ detected by the four light receivers, the phase difference Δ and the amplitude ratio tanψ in the reflected light are obtained using the following equations (6) and (7).
And an operation unit for determining the ellipsometric parameters Δ and さ れ る determined by the above, including the belonging quadrant of Δ. tan (Δ−φ ₀ ) = σT (I ₁ −I ₂ ) / σR (I ₃ −I ₄ ) (6) tanψ = [｛χ ² (ΣT ² (I ₁ + I ₂ ) −σR ² _{(I 3 + I 4))} } ÷ {(I 1 + I 2) - (I 3 + I 4)}] 1/2 (7) where 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 object, and σR and σT are constants determined by an optical system that separates the reflected light into four polarization components. It is. 10. The non-polarizing beam splitter, which splits the reflected light reflected by the measurement target into light in two different directions, and separates each of the lights split by the non-polarizing beam splitter. 10. The ellipsometer according to claim 9, comprising two polarization beam splitters for separating polarization components in two different directions.