JPH0791926A - Method and device for measuring characteristic value - Google Patents

Abstract

PURPOSE:To make it possible to measure the film thickness, refractive index and adsorption coefficient of an objective thin film to be measured, by the measurement of a reflected light intensity change of the thin film when the incident angle of a lighting beam is changed. CONSTITUTION:A lighting beam 15 from a light source 1 is converged on an objective thin film 12 to be measured by a lens 5 on a lighting side, the reflected beam 16 is converged by a lens 6 of a detecting side on a detector 7 set on a focal plane, and the detected signal is stored in a memory 8 as the incident- angle-dependent characteristics I(theta) of a reflected light intensity of the thin film 12. About a reference sample 13 also, the same measurement is carried out, detected signal thereof is stored in the memory 9 as the incident-angle- dependent characteristics Iref(theta) of a reflected light intensity of the reference sample 13. These I(theta) and Iref(theta) are divided by each other by an operation part 10, the incident-angle-dependent characteristics R(theta) of the reflectance of the thin film 12 is obtained, from these and the incident-angle-dependent characteristics Rref(theta) of the reflectance of the reference sample 13 theoretically found. The R(theta) is operated by an operation part 11, and the film thickness, refractive index and absorption coefficient of the thin film 12 are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the characteristic values of thin films and mirror surfaces,
That is, the present invention relates to a method and apparatus for measuring the film thickness, refractive index, absorption coefficient, etc. of a thin film, and particularly to a characteristic value measuring method and apparatus suitable for use in measuring the state of a resist film during an LSI manufacturing process.

[0002]

2. Description of the Related Art A method for measuring the characteristic value of a thin film is first described by Toshiharu Tayuki et al., "Optical Measurement Handbook," Asakura Shoten (1981), pp. 256-265 and the like are ellipsometry methods. In general, the thin film to be measured is obliquely irradiated with light, and mainly P-polarized light and S
This is a method that focuses on the difference in the phase change of the polarized light.

There is also a reflectance analysis method for measuring the film thickness, the refractive index, and the absorption coefficient of a thin film by using the reflectance.
No. 4-75902, Japanese Patent Laid-Open No. 63-128210, Japanese Patent Laid-Open No. 3-17505. JP-A-64-75902 and JP-A-63-12
The reflectance analysis method disclosed in Japanese Patent Publication No. 8210 measures the change in reflected light intensity associated with the change in incident angle of measurement light, that is, the incident angle dependent characteristic of the reflected light intensity, and determines the incident angles of the three extreme values. It is a method of obtaining the characteristic value of a thin film by using the method. The reflectance analysis method disclosed in Japanese Patent Application Laid-Open No. 3-17505 is a method for obtaining a characteristic value of a thin film from an incident angle dependence characteristic of reflected light intensity obtained by detecting light intensity on the rear side of a detection lens. Is.

[0004]

In order to measure the characteristic value of the thin film with high accuracy by the above-mentioned polarization analysis method, it is necessary to rotate the polarizer and the analyzer with high accuracy, and the apparatus becomes large in scale, and There was a problem of becoming expensive.

Further, JP-A-64-75902, JP-A-63-128210 and JP-A-3-17505.
In order to measure the characteristic value of the thin film with high accuracy by the reflectance analysis method disclosed in Japanese Patent Publication, it is necessary to measure the incident angle dependence property of the reflected light intensity with high accuracy.

However, in the method of mechanically scanning the incident angle of the measuring light, such as the reflectance analysis method disclosed in JP-A-64-75902 and JP-A-63-128210, the movable part is Therefore, high-speed and high-accuracy measurement is very difficult, and since only three points of information showing the extreme values in the incident angle dependence characteristics of reflected light intensity are used, the incident angle of reflected light intensity There is a problem that it is greatly affected by the measurement error of the dependence characteristic.

On the other hand, in the reflectance analysis method disclosed in Japanese Unexamined Patent Publication No. 3-17505, the moving part is not included in the optical system for measuring the incident angle dependence characteristic of the reflected light intensity, and the Japanese Laid-Open Patent Publication No. -75902 and JP-A-63-128210
In general, rather than the reflectance analysis method disclosed in the publication,
Since many measurement points of the incident angle dependence characteristic of the reflected light intensity are used, it is suitable for high-speed and high-precision measurement.

However, when a laser is used as a light source as described in Japanese Patent Laid-Open No. 3-17505, the following problems occur. That is, when measuring a resist film, the measured value at the exposure wavelength is important, but a laser having the same wavelength as the exposure wavelength, that is, the emission line spectrum of mercury such as i-line or g-line is used. Even if a gas laser that does not exist and has a wavelength close to that does not exist, there is a problem that the device becomes large in size. Further, there is a problem that the measurable wavelength is limited to the wavelength where the laser light source exists.

Therefore, when measuring the resist film, it is necessary to extract light of wavelengths such as i-line and g-line from a light source such as a mercury lamp with an interference filter or the like.
This causes the following problems. Further, even when the measurement target is not limited to the resist film, if the measurement value at an arbitrary wavelength is required, it is necessary to extract and use the light of the required wavelength from a white light source such as a xenon lamp.
After all, the following problems occur.

In the method of measuring the incident angle dependence characteristic of the reflectance with an optical system using convergent light illumination, which is found in the reflectance analysis method disclosed in Japanese Patent Laid-Open No. 3-17505, etc., first,
It is necessary to convert the reflected light intensity into a reflectance by forming a plane wave with a constant intensity distribution, measuring the incident angle dependence characteristic of the reflected light intensity, and multiplying this by a constant coefficient. In this case, if a mercury lamp or the like is used as the light source, there is uneven illuminance,
To avoid this effect, a pinhole must be placed at the position where the illumination light is collected. However, if a pinhole is used, the amount of light is limited, and it is not possible to measure the incident angle dependence characteristic of the reflected light intensity with a sufficient S / N ratio. Therefore, it is possible to avoid using pinholes. In this case, if the distribution shape of the illuminance unevenness of the light source is not known in advance, it is possible to accurately measure the incident angle dependence characteristic of the reflected light intensity. Therefore, the characteristic value of the thin film cannot be accurately obtained.

That is, when the wavelength of the illumination light is used as the exposure wavelength when measuring the resist film, when a light source other than a laser is used, the incident angle dependence characteristic of the reflectance is changed from the incident angle dependence characteristic of the reflected light intensity. Conversion to is a big issue.

An object of the present invention is to eliminate such a problem and remove the illuminance unevenness of the light source to determine the characteristic value of the thin film when the characteristic value of the thin film is determined by using the illumination system other than the optical system having no movable part and the illumination light. It is an object of the present invention to provide a method and an apparatus capable of accurately obtaining the incident angle dependence characteristic of reflectance necessary for the above.

[0013]

In order to achieve the above object, the present invention provides a measurement of an incident angle dependent characteristic Iref (θ) of reflected light intensity of a reference sample whose refractive index and absorption coefficient are known, and The incident angle dependence characteristic Rref (θ) of the reflectance of the reference sample is calculated in advance. The incident angle dependent characteristic I (θ) of the reflected light intensity of the thin film to be measured is measured and
After dividing by ref (θ), the Rref (θ) is multiplied.

The incident angle-dependent characteristic theoretical value of the reflectance obtained by the above procedure is calculated by variously changing the film thickness value, the refractive index value, and the absorption coefficient value of the thin film, and the calculated value. By searching for a theoretical value that overlaps with, the film thickness, refractive index, and absorption coefficient of the thin film to be measured are determined.

[0015]

The incident angle dependence characteristic I (θ) of the reflected light intensity of the thin film to be measured is represented by the product of the incident angle dependence characteristic R (θ) of its reflectance and the illuminance unevenness S (θ) of the illumination light. . Similarly, the incident angle dependence characteristic Iref (θ) of the reflected light intensity of the reference sample also has the incident angle dependence characteristic Rref (θ) of its reflectance and the illuminance unevenness S of the illumination light.
It is expressed as the product of (θ). Therefore, when the incident angle dependence characteristic I (θ) of the reflected light intensity of the thin film to be measured is divided by the incident angle dependence characteristic Iref (θ) of the reflected light intensity of the reference sample, the term of S (θ) common to these is obtained. The ratio of the incident angle dependence characteristic R (θ) of the reflectance of the thin film to be measured and the reflectance of the reference sample Rref (θ) is obtained. The incident angle dependence characteristic Rref (θ) of the reflectance of the reference sample can be obtained by theoretical calculation because the refractive index and the absorption coefficient of the reference sample are known, and can be measured by multiplying the ratio by the above. The incident angle dependence characteristic R (θ) of the reflectance of the target thin film can be obtained.

That is, according to the present invention, even if a light source having uneven illuminance such as a mercury lamp is used, the absolute reflectance corresponding to each incident angle of the thin film to be measured can be easily measured without measuring the uneven illuminance. It can be calculated.

The incident angle-dependent characteristic theoretical value of the reflectance is calculated by variously changing the film thickness value, the refractive index value, and the absorption coefficient value of the thin film, and the measured value of the incident angle-dependent characteristic of the reflectance obtained by the above procedure is used. By searching for overlapping theoretical values, the film thickness value, refractive index value, and absorption coefficient value used in the calculation of the theoretical values can be used as the characteristic values of the thin film to be measured.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a characteristic value measuring method and apparatus according to the present invention, in which 1 is a light source, 2 is a collimating lens, 3 is a polarizing plate, 4 is a wavelength limiting optical element, and 5 is an illumination side. A lens, 6 is a detection side lens, 7 is a detector, 8 and 9 are storage devices, 10 and 11 are arithmetic units, 12 is a thin film to be measured, 1
2a is a bare silicon wafer, 13 is a reference sample, 14 is an illuminance distribution, 15 is an illumination light beam, 16 is a parallel reflected light beam, 17 is the back focal plane of the detection side lens 6, and 18 is the reflection intensity detection axis (X
Axis).

In this embodiment, the characteristic value of the thin film is measured by measuring the incident angle dependence characteristic of the reflection intensity of the thin film. Here, since the film thickness, the refractive index, and the absorption coefficient of the thin film are measured without using the movable part, it is possible to perform high speed and highly accurate measurement. Hereinafter, this embodiment will be described.

In FIG. 1, an illumination light beam 15 from the light source 1
Is collimated by the collimating lens 2, passes through the polarizing plate 3 and the wavelength limiting optical element 4, and is placed at a predetermined position by the illumination side lens 5 for condensing.
It is focused on the thin film 12 to be measured or the reference sample 13 on 2a. The incident angle of the illumination light beam 15 on the measurement target thin film 12 or the reference sample 13 is θ. The reflected light beam 16 from the thin film 12 to be measured or the reference sample 13 is detected by the detection lens 6
Thus, it is converged on the rear focal plane 17 of the detection side lens 6. After this, a detector 7 for the intensity of reflected light is provided on the focal plane 17. The detection result of the detector 7 when the thin film 12 to be measured is irradiated with the illumination light beam 15 is stored in the storage device 8.
Is stored in the reference sample 1 and is irradiated with the illumination light beam 15.
The detection result of the detector 7 when the value is 3 is stored in the storage device 9. The data of the storage devices 8 and 9 are calculated by the calculation unit 10 to obtain the reflectance of the measurement target thin film 12, and the reflectance is calculated by the calculation unit 11 to calculate the film thickness, the refractive index, and the absorption coefficient of the measurement target thin film 12. Characteristic values such as

By using the convergent rays in this way,
The reflected light intensity corresponding to a wide range of incident angles can be measured at the same time, and the incident angle dependence characteristic of the reflectance of the measurement target thin film 12 can be measured at high speed.

First, when the thin film 12 to be measured is installed, when the illumination light beam 15 having an incident angle θ is incident on the thin film 12 to be measured, it is multiply reflected within the thin film 12 and a parallel light beam 16 having a reflection angle θ is reflected. To be done. Here, in order to simplify the drawing, only two parallel reflected light beams 16 are shown.
The parallel reflected light flux 16 is condensed on the rear focal plane 17 of the detection side lens 6 by the detection side lens 6.

Here, as shown in FIG. 2, the distance along the reflection intensity detection axis (X axis) from the center on the rear focal plane 17 of the detection side lens 6 to the condensing position is x, and the detection side lens 6 If the angle formed by the parallel reflected light beam 16 with respect to the optical axis is defined as a, the sine condition is satisfied when the detection-side lens 6 is well corrected for aberration. The relationship shown in 1 is established.

[0024]

[Equation 1]

F: focal length of the detection-side lens 6, that is, the X-axis 1 taken on the rear focal plane 17 of the detection-side lens 6.
By measuring the reflected light intensity on 8 and using the above equation 1, the incident angle dependence characteristic I of the reflected light intensity of the thin film 12 to be measured is measured.
(θ) can be obtained.

By the way, when the illuminance distribution of the illuminating light beam such as laser light is uniform, the incident angle dependence characteristic I (θ) of the reflected light intensity of the thin film 12 to be measured is changed from the reflected light intensity to the reflectance. The incident angle dependence characteristic R (θ) of the reflectance of the thin film 12 to be measured can be obtained only by multiplying it by a constant for converting Differently, the illuminance distribution 14 of the illuminating light beam 15 cannot be made uniform, so that the obtained measurement target thin film 12
From the incident angle dependence characteristic I (θ) of the reflected light intensity, the incident angle dependence characteristic R of the reflectance of the thin film 12 to be measured is simply as described above.
(θ) cannot be calculated.

Therefore, in this embodiment, the incident angle dependent characteristic I (θ) of the reflected light intensity of the thin film 12 to be measured measured by the detector 7 is stored and held in the storage device 8, and then the reference sample is stored. The same measurement is performed for 13. Then, the measurement result of the detector 7 is stored in the storage device 9 as the incident angle dependence characteristic Iref (θ) of the reflected light intensity of the reference sample 13. Reference sample 13
Any may be used as long as it is a specular sample having a known refractive index and absorption coefficient. For example, a bare silicon wafer or the like can be used.

Now, assuming that the incident angle dependence characteristic of the reflectance of the reference sample 13 is Rref (θ) and the illuminance distribution 14 of the illumination light beam 15 is a function S (θ) of the incident angle θ, the reflected light intensity of the reference sample 13 is shown. The incident angle dependent characteristic Iref (θ) of can be expressed by the following equation 2.

[0029]

[Equation 2]

Further, regarding the incident angle dependence characteristic I (θ) of the reflected light intensity of the thin film 12 to be measured, if the incident angle dependence characteristic of the reflectance is R (θ),

[0031]

[Equation 3]

[Mathematical formula-see original document] Therefore, by dividing this formula 3 by the above formula 2, the incident angle dependence characteristic I (θ) of the reflected light intensity, which is the measurement result, can be obtained as shown in the following formula 4. Iref
The unknown value S (θ) can be eliminated by obtaining the ratio of (θ).

[0033]

[Equation 4]

Here, the incident angle dependence characteristic Rref (θ) of the reflectance of the reference sample 13 is theoretically calculated by using the known refractive index and absorption coefficient of the reference sample 13 by the following equations 8 to 13. Since this is obtained, the following formula 5 is obtained by multiplying the known incident angle dependence characteristic Rref (θ) of the reflectance on both sides of the above formula 4, and the incident angle dependence characteristic Rref (Rref ( θ) is obtained.

[0035]

[Equation 5]

That is, the incident angle dependence characteristics I (θ) and Iref (θ) of the reflected light intensity, which are the measurement results, and the incident angle dependence characteristics Rref (θ) of the reflectance of the reference sample 13, which are the theoretical calculation results, are used. The incident angle dependence characteristic R (θ) of the reflectance of the measurement target thin film 12 necessary for determining the film thickness, the refractive index, and the absorption coefficient of the measurement target thin film 12 can be obtained by the calculation on the left side of the equation 5. Such calculation is performed by the calculation unit 10.

The reflectance incident angle dependence characteristic R (θ)
According to the above calculation method, not only the illuminance distribution 14 of the illumination light beam 15 but also the nonuniformity of the transmittance due to the difference in the transmission position of each optical element is corrected. That is, the inhomogeneities of all the optical elements in the optical system are combined into one, and this is treated as a function T of the incident angle θ.
Letting (θ), the above equations 2 and 3 are expressed as the following equations 6 and 7 including them.

[0038]

[Equation 6]

[0039]

[Equation 7]

Therefore, by dividing the expression 7 by the expression 6, and multiplying both sides of the result by the incident angle dependence characteristic Rref (θ) of the reflectance of the known reference sample 13, the above expression 5 is obtained. , S (θ)
Similarly, T (θ) is also erased. Therefore, the influence of non-uniformity of the transmittance due to the difference in the transmission position of each optical element can be eliminated.

The calculation unit 11 obtains the film thickness, the refractive index, and the absorption coefficient of the measurement target thin film 12 from the incident angle dependence characteristic R (θ) of the reflectance of the measurement target thin film 12 obtained as described above. Is. Next, this point will be described.

The incident angle dependence characteristic Rth (θ) of the reflectance of the thin film obtained by theoretical calculation is the Fresnel coefficient and the multiple interference showing the amplitude reflectance at the boundary surface, if the film thickness, the refractive index and the absorption coefficient of the thin film are determined. It can be obtained using a theoretical formula. Now, when considering the model as shown in FIG. 3, the reflected light intensity at the convergence point P on the rear focal plane 17 of the detection side lens 6 when the intensity of the incident light ray 15 is set to Represented by R. This represents the reflectance of intensity. It should be noted that Equations 8 to 13 are equations when the incident light ray 15 is P-polarized light.

[0043]

[Equation 8]

However, r _p is an amplitude reflectance and is a complex number, [r _p ].
Is a complex complex number of r _p ,

[0045]

[Equation 9]

However, it is assumed that the thin film 12 to be measured is formed on the bare silicon wafer 12a, δ: optical path difference generated in one round trip in the thin film 12 to be measured r _01p : boundary surface between air and the thin film 12 to be measured Amplitude reflectance of P-polarized light at 12 r _12p : thin film 12 to be measured and bare silicon wafer 12a
Is the amplitude reflectance of P-polarized light at the interface with

[0047]

[Equation 10]

Λ: wavelength of illumination light d: film thickness of thin film θ ₁ : angle of refraction within the thin film of a light ray having an incident angle θ from air to the thin film

[0049]

[Equation 11]

[0050]

[Equation 12]

Θ ₂ : It is expressed as a refraction angle of a light beam having an incident angle θ from the air to the thin film in the bare silicon wafer. However, n ₀ is the refractive index of air and can be regarded as 1. n _1c and n _2c are complex refractive indices of the thin film 12 to be measured and the bare silicon wafer as the reference sample 13, that is, complex numbers having the refractive index as the real part and the absorption coefficient as the imaginary part. Further, θ ₁ , θ ₂ and θ are given by Snell's law,
There is a relationship shown by the following Expression 13.

[0052]

[Equation 13]

When S-polarized light is used as the illuminating light ray 15 which is the incident light ray, by _replacing r _01p and r _{12p in equation} 9 with r _01s and r _12s shown in the following _equations 14 and 15, _respectively . , The amplitude reflectance r _s is obtained.

[0054]

[Equation 14]

[0055]

[Equation 15]

Where r _01s : S at the interface between air and thin film
Amplitude reflectance of polarized light r _12s : Amplitude reflectance of S-polarized light at the boundary surface between the thin film and the bare silicon wafer Therefore, if the polarization state of the incident light beam 15 is known, The theoretical value Rth (θ) of the incident angle dependence characteristic of reflectance can be obtained by theoretical calculation.

The theoretical value Rth (θ) of the incident angle dependence characteristic of the reflectance takes various shapes depending on how to take the three characteristic values of the thin film thickness, the refractive index and the absorption coefficient. Therefore, by assigning these three characteristic values, the theoretical value Rth that best overlaps the incident angle dependence characteristic R (θ) of the reflectance of the measurement target thin film 12 by actual measurement.
(θ) is searched, and a set of three characteristic values that generate it is output as the measurement result of the film thickness, refractive index, and absorption coefficient of the thin film 12 to be measured.

Three characteristic values are assigned to each coordinate axis of the three-dimensional space, and the theoretical value Rth (θ) of the incident angle dependent characteristic of reflectance is calculated using the three characteristic values corresponding to each point in the space. Then, the degree of overlap with the incident angle dependence characteristic R (θ) of the reflectance obtained from the measured value is calculated. As an evaluation function of the degree of overlap between R (θ) and Rth (θ), for example, the following equation 16
Alternatively, the one shown in Expression 17 is used.

[0059]

[Equation 16]

[0060]

[Equation 17]

Equation 16 is the absolute value of the difference between the theoretical value Rth (θ) of the incident angle dependence characteristic of the reflectance and the measured value R (θ) of the incident angle dependence characteristic of the reflectance at a plurality of incident angles with M. The total sum is represented by the equation (17). Theoretical value R of the incident angle dependence characteristic of the reflectance that minimizes M
The th (θ) is searched, and three characteristic values that generate the theoretical value Rth (θ) are output as a result.

In order to achieve both high resolution of measurement results and shortening of calculation time, a three-dimensional structure corresponding to a set of three characteristic values for calculating the theoretical value Rth (θ) of the incident angle dependence characteristic of reflectance The intervals between the points in the space may be gradually reduced. In the first stage, rough grid points are calculated for calculating the theoretical value Rth (θ) of the incident angle dependence characteristic of reflectance set in the three-dimensional space. Of these values, the measured value R (θ) of the incident angle dependence characteristic of reflectance and the theoretical value Rth of the incident angle dependence characteristic of reflectance are the best.
A grid point that is a set of characteristic values that matches (θ) is searched for. In the second step, the three-dimensional space around the lattice point is divided into smaller pieces than in the first step, and the measured value R (θ) of the incident angle dependence characteristic of the reflectance and the theoretical value of the incident angle dependence characteristic of the reflectance are the best. A lattice point that is a set of characteristic values that matches Rth (θ) is searched for. In the same manner, this operation is repeated until the interval between the grid points reaches the target measurement resolution.

In order to start the search from a larger grid point interval in the first stage, if the grid point is to reduce M, the points other than the grid point that minimizes M are left up to the second stage and thereafter. You may do it. After proceeding with the search by gradually narrowing the grid point intervals around the plurality of grid points as described above, M
Select the grid point that minimizes. By this operation,
Even if the grid points are roughened, it is possible to prevent erroneous detection of grid points that minimize M.

In order to obtain the incident angle dependence characteristic R (θ) of the reflectance of the thin film 12 to be measured more accurately, the incident angle dependence characteristic I of the reflected light intensity, which is the measurement result of the thin film 12 to be measured, is measured.
(θ) and the incident angle dependence characteristic Ire of the reflected light intensity of Reference Material 13
It is necessary to perform dark level correction on f (θ). The light intensity is detected by the detector 7 with the thin film 12 to be measured removed from the front of the detection side lens 6, and this detected light intensity is used as a function Ib (θ) of the incident angle θ for the sake of convenience,
8 to the incident angle dependence characteristic R of the reflectance of the thin film 12 to be measured
Find (θ).

[0065]

[Equation 18]

Thus, the dark level correction (0 level correction) of the output of the detector 7 and the removal of the influence of stray light can be carried out at the same time, and the incident angle dependence characteristic R (θ) of the reflectance of the thin film 12 to be measured. Can be obtained with high precision.

The incident angle dependence characteristics Iref (θ) and I (θ) of the reflected light intensity of the reference sample 13 and the thin film 12 to be measured must be measured with the same light quantity. Therefore, when the light amount of the light source 1 varies, the incident angle dependence characteristic Iref (θ) of the reflected light intensity of the reference sample 13 is measured as the incident angle dependence characteristic I (θ) of the thin film 12 to be measured. By performing the measurement again each time, the error due to the fluctuation of the light amount can be reduced. In this case, the wafer of the measurement target thin film 12 and the wafer of the reference sample 13 may be exchanged manually, but as shown in FIG. The reference sample piece 20 is attached to the end portion, and the incident angle dependence characteristic of the reflected light intensity of the reference sample piece 20 and the wafer 21 of the thin film to be measured in the order of FIGS. 5A, 5B, and 5C. May be measured. With such a configuration, the operator can measure the thin film wafer 21
Therefore, it is not necessary to transfer the reference sample piece 20 and the reference sample piece 20, and efficient measurement becomes possible.

When the light source 1 whose light quantity is stable is used, the incident angle dependence characteristic Ire of the reflected light intensity of the reference sample 13
It suffices to measure f (θ) once, store the measurement result in the storage device 9, and read it every time the incident angle dependence characteristic I (θ) of the reflected light intensity of the measurement target thin film 12 is measured. By doing so, efficient measurement is possible.

FIG. 6 is a view showing another embodiment of the characteristic value measuring method and apparatus according to the present invention which is capable of correcting the light quantity variation of the light source more strictly.
Is a storage device, 26 is a calculation unit, 27 is a light amount sensor, 28 is a monitor lens, and 29 is a half mirror. The parts corresponding to those in FIG.

In the figure, first, the incident angle dependence characteristic Iref (θ) of the reflected light intensity and the dark level Ib (θ) of the reference sample are measured as described above and stored in the storage devices 22 and 23, respectively. Keep it. Also, a light source (not shown) at each measurement
The light amount value of the monitor lens 28 from the half mirror 29
The light amount sensor 27 detects the light from the light source passing through and measures it, and stores it in the storage devices 24 and 25, respectively.

Next, the incident angle dependence characteristic I (θ) of the reflected light intensity of the thin film 12 to be measured is measured, and the calculation unit 26 calculates the incident angle dependence characteristic of the reflected light intensity of the reference sample stored in the storage device 22. Iref (θ) and the incident angle dependent characteristic I (θ) of the reflected light intensity of the thin film 12 to be measured are corrected by the light amount value of the light source stored in the storage device 24, and the dark level stored in the storage device 23 is corrected. Ib (θ) is corrected by the light amount value of the light source stored in the storage device 24, and the incident angle dependent characteristic Iref (θ) of the reflected light intensity of the reference sample thus corrected, the reflected light of the measurement target thin film 12 Using the incident angle dependence characteristic I (θ) of the intensity and the dark level Ib (θ), the calculation is carried out in the above equation (18).

As a result, the influence of the fluctuation of the light amount of the light source can be removed with extremely high accuracy.

FIG. 7 is a diagram showing still another embodiment of the characteristic value measuring method and apparatus according to the present invention, in which 30 is an averaging unit and 31 and 32 are storage devices. Are denoted by the same reference numerals and redundant description will be omitted.

The detection signal of the detector 7 is usually the detector 7
Since white noise due to the S / N ratio of the device itself is mixed, the film thickness of the measurement target thin film obtained as described above from the incident angle dependence characteristic R (θ) of the reflectance of the measurement target thin film, The detection accuracy of the refractive index and absorption coefficient is reduced. This embodiment prevents such a decrease in detection accuracy.

In FIG. 7, the incident angle dependence characteristic Iref (θ) of the reflected light intensity of the reference sample (not shown), the thin film 1 to be measured.
2. Incidence angle dependence characteristic I (θ) of reflected light intensity and dark level I
The measurement of b (θ) is performed a plurality of times, and the average value of the plurality of detection signals of the detector 7 in each measurement is calculated by the averaging unit 30.
Required by. The incident angle dependence characteristic Iref (θ) of the reflected light intensity of the reference sample and the dark level Ib (θ) thus obtained are stored in the storage devices 31 and 32, respectively. Then, similarly, the thin film 12 to be measured, which is obtained as an average of a plurality of measurements
The incident angle dependent characteristic I (θ) of the reflected light intensity of the reference sample is supplied to the calculation unit 10, and the incident angle dependent characteristic Iref (θ) of the reflected light intensity of the reference sample stored in the storage devices 31 and 32 and the dark level Ib.
The calculation of the above equation 18 is performed using (θ).

By thus averaging the detection signals of the detector 7 a plurality of times by the averaging unit 30, the white noise generated in the detector 7 is averaged and reduced, and is not affected by the white noise. The incident angle dependent characteristic Iref (θ) of the reflected light intensity of the sample, the incident angle dependent characteristic I (θ) of the reflected light intensity of the measurement target thin film 12 and the dark level Ib (θ) are obtained. Therefore, the detection accuracy of the film thickness, the refractive index, and the absorption coefficient of the thin film 12 to be measured is improved.

In the above embodiments, the illumination direction of the illumination light beam 15 and the detection direction of the detector 7 are oblique. However, the illumination side lens 5 and the detection side lens 6 are shared by one lens, and vertical illumination Vertical detection may be used. However, in such a vertical detection method, adjustment of the optical system is easy, but as shown in FIG. 8, due to surface reflection between the shared lens 6 ′ and the sample, the incident angle dependence characteristic I (θ) of the reflected light intensity is obtained. Error occurs in). When an objective lens for a microscope is used as the shared lens 6 ', since the objective lens is composed of a plurality of lenses, as shown in FIG. Due to the reflection at 1, an error occurs in the incident angle dependent characteristic I (θ) of the reflected light intensity.

FIG. 10 is a view showing the essential parts of still another embodiment of the characteristic value measuring method and apparatus according to the present invention, which is capable of solving such a problem, in which 33 is a light shielding plate and 34 is a mirror. , 35 are half mirrors, and the same reference numerals are given to the parts corresponding to the above-mentioned drawings, and duplicate description will be omitted.

In the same figure, the illumination light beam 15 from a light source (not shown) is shielded by the light shielding plate 33 in the vicinity of its optical axis, passes through the mirror 34 and the half mirror 35, and passes through the shared lens 6'and the thin film to be measured. 12 and so on. As a result, the light reflected by the common lens 6'in the optical axis portion of the illumination light beam 15 and the common lens 6'and the thin film 1 to be measured.
No light is repeatedly reflected between the two.

When a thin film to be measured is a resist film and measurement is performed using illumination light having an exposure wavelength, the resist film is exposed to the illumination light and is altered. In order to suppress the exposure of the resist film and improve the measured S / N ratio of the incident angle dependent characteristic I (θ) of the reflected light intensity of the resist film, as shown in FIG. The illumination light 15 passes through a part of the shared lens 6 ', and the parallel reflected light beam 16 passes through another part of the shared lens 6'. In this case, even if the amount of illumination light is the same as that of the embodiment shown in FIG. 10, unlike the embodiment of FIG. 10, since half mirror is not used, a large amount of reflected light is obtained, and the reflected light is not exposed to the resist film so much. The incident angle dependence of intensity is S /
It is possible to measure with good N ratio.

The detector 7 used in the above embodiments may be a one-dimensional sensor or a two-dimensional sensor. 1
If a dimension sensor is used, the time required to read the detection signal is shortened. Therefore, when the detection signal is read multiple times and averaged, the number of times of reading can be increased, and therefore the white color generated in the sensor can be increased. The influence of noise can be sufficiently suppressed. If a two-dimensional sensor is used, the time required to read out the detection signal, that is, the time required to obtain the average by reading out multiple times increases, but instead, the two-dimensional image of the back focal plane 17 can be viewed, There is an advantage that the adjustment of the optical system becomes easy.

As the illumination method, critical illumination for forming a light source image on the surface of the thin film to be measured or the surface of the reference sample,
Any of the Koehler illuminations that forms an image on the back focal plane of the illumination side lens may be used. In the above examples, since the effect of uneven illuminance is removed by comparison with the reference sample, even if Koehler illumination in which a light source image is formed on the back focal plane is used, there is no problem depending on the incident angle dependence of the reflectance of the thin film to be measured. The characteristic R (θ) can be detected.

Further, the illumination light beam may be P-polarized light or S-polarized light, and may include P-polarized light and S-polarized light if the amplitude ratio is known. The incident angle dependence characteristic of the reflectance considering the multiple interference in the thin film of the P-polarized light beam can be obtained by using the above-mentioned equations 8 to 13, and the S-polarized light ray can be calculated by the same theoretical formula. Even in the case of including polarized light, the incident angle dependence characteristic of the reflectance can be calculated from the reflectance and the amplitude ratio for each polarized light calculated using these expressions.

FIG. 12 is a view showing still another embodiment of the characteristic value measuring method and apparatus according to the present invention.
Is a storage device, and the portions corresponding to those in FIG.

In this embodiment, even if the thin film to be measured has a large absorption coefficient, its characteristic value can be accurately obtained. When the absorption coefficient of the thin film to be measured is large, there are almost no light rays that enter the thin film to be measured and are reflected by the underlying layer and emitted from the thin film to be measured. As a result, the amplitude of the vibration of the incident angle dependent characteristic I (θ) of the reflected light intensity caused by the reduction becomes small. Therefore, the difference in the incident angle-dependent characteristics of the reflectance due to the difference in the parameters during the waveform matching becomes small, and if the three characteristic values of the film thickness, refractive index, and absorption coefficient of the measurement target thin film are to be determined at the same time, the accuracy of the determination will be small. Is reduced.

In order to prevent this, the measurement light of long wavelength is set to 1
You can use more than one type. Since the absorption coefficient has a spectral characteristic and becomes smaller as the wavelength becomes longer, the film thickness, the refractive index, and the absorption coefficient of the thin film to be measured are first measured using the measurement light having the long wavelength. Since there is no spectral characteristic in the film thickness, from the film thickness value obtained here and the incident angle dependence characteristic I (θ) of the reflected light intensity by the measuring light of the exposure wavelength, the refractive index and the absorption coefficient of 2 at the exposure wavelength are calculated. It is only necessary to obtain two characteristic values.

In order to realize this, in the embodiment shown in FIG. 12, the wavelength limiting optical element 4 of the illumination light beam 15 which is the measurement light is used for a plurality of wavelengths so that they can be easily replaced. deep. Further, the incident angle dependence characteristics of the reflectance between the reference sample and the dark level when the long-wavelength measurement light is used are detected in advance, and the characteristics are stored in the storage devices 38 and 40, respectively. The incident angle-dependent characteristics of the reflectance of the sample and the dark level are detected and stored in the storage device 39,
It is stored in 41. When the long wavelength measurement light is used, the data stored in the storage devices 38 and 40 is used, and when the measurement light of the original wavelength is used, the data stored in the storage devices 39 and 41 is used.

As described above, in this embodiment, the characteristic value of the thin film to be measured can be measured at any wavelength, especially at a short wavelength.

FIG. 13 is a view showing still another embodiment of the characteristic value measuring method and apparatus according to the present invention, which are 42 to 44.
Is a storage device, and the portions corresponding to those in FIG.

When the resist film is used as the thin film to be measured, if the absorption coefficient of the resist film is large and the three characteristic values cannot be simultaneously and accurately determined at the exposure wavelength, as in the embodiment shown in FIG. This embodiment is suitable.

When the absorption coefficient of the resist film is large,
Since there is almost no light that enters the resist film, is reflected by the underlying layer, and exits from the resist film, the amplitude of vibration of the incident angle dependent characteristic I (θ) of the reflected light intensity of the resist film becomes small. For this reason, the difference in the incident angle dependence characteristic of the reflectance due to the difference in the parameters at the time of wavelength matching becomes small, and when the three characteristic values of the resist film thickness, the refractive index, and the absorption coefficient are determined at the same time, the determination accuracy is reduced. To do.

Therefore, in the embodiment shown in FIG. 13, when the absorption coefficient of the resist film is large, the resist film is first exposed to reduce the absorption coefficient, and the incident angle of the reflected light intensity at that time is decreased. The film thickness is obtained from the dependence characteristic, and the film thickness value is measured, that is, the refractive index and the absorption coefficient of the resist film at the start of exposure are obtained from the incident angle dependence characteristic of the reflected light intensity at the start of exposure.

Hereinafter, this embodiment will be described more specifically with reference to FIG.

In the figure, the detection signals of the detector 7 after exposure of the resist film and at the start of exposure, that is, at the start of measurement,
Incident angle dependence characteristics Ie (θ) and Is of reflected light intensity
(Θ) is stored in the storage device 42. Further, the reference sample and the incident angle dependence characteristics of the dark level reflectance at the time of detection are also stored in the storage devices 43 and 44, respectively. And
First, the film thickness of the resist film is obtained using the incident angle dependence characteristic Ie (θ) of the reflected light intensity when the absorption coefficient is decreased by the exposure, and this film thickness value and the reflected light intensity at the start of exposure The refractive index and the absorption coefficient at the start of exposure are obtained using the angle-dependent characteristic Is (θ).

As the incident angle dependence characteristic Ie (θ) of the reflected light intensity, the reflected light intensity is incident after the measurement light is irradiated for a sufficiently long time or after the absorption coefficient is sufficiently reduced and the reflected light is sufficiently increased. The angle-dependent characteristic may be used.

In this embodiment, as shown in FIG. 14, in addition to a light source for measurement (not shown), a light source 46 for exposing the resist film and an exposure lens 47 are used for exposure. The light illumination system 45 may be used to irradiate the measuring portion of the resist film 12 with the light beam 48 for exposure. By thus separating the exposure light source and the measurement light source, the exposure wavelength and the measurement wavelength can be set arbitrarily and independently.

[0097]

As described above, according to the present invention,
Since it is possible to measure the thickness, refractive index, and absorption coefficient of a thin film, particularly the resist film during the LSI manufacturing process with high accuracy,
It is possible to easily detect variations in the film thickness, refractive index, and absorption coefficient of the resist film that deteriorate the accuracy of the resist pattern line width dimension after exposure and development, which can greatly contribute to the improvement in the yield of LSI.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a characteristic value measuring method and apparatus according to the present invention.

FIG. 2 is a diagram showing a condensing action of a detection side lens in FIG.

FIG. 3 is a diagram for explaining multiple interference in a thin film in FIG.

FIG. 4 is a perspective view showing a specific example of a means for exchanging a thin film to be measured and a reference sample in the embodiment shown in FIG.

FIG. 5 is a diagram illustrating an example of a replacement procedure by the replacement means shown in FIG.

FIG. 6 is a diagram showing another embodiment of the characteristic value measuring method and apparatus according to the present invention.

FIG. 7 is a diagram showing still another embodiment of the characteristic value measuring method and apparatus according to the present invention.

FIG. 8 is a diagram illustrating multiple reflection on a lens surface.

FIG. 9 is a diagram illustrating multiple reflection on a lens surface.

FIG. 10 is a diagram showing a main part of still another embodiment of the characteristic value measuring method and apparatus according to the present invention.

FIG. 11 is a diagram showing a main part of still another embodiment of the characteristic value measuring method and apparatus according to the present invention.

FIG. 12 is a diagram showing still another embodiment of the characteristic value measuring method and apparatus according to the present invention.

FIG. 13 is a diagram showing still another embodiment of the characteristic value measuring method and apparatus according to the present invention.

FIG. 14 is a diagram showing a main part of still another embodiment of the characteristic value measuring method and apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 2 collimating lens 3 polarizing plate 4 wavelength limiting optical element 5 illumination side lens 6 detection side lens 7 detector 8, 9 storage device 10, 11 arithmetic unit 12 thin film to be measured 12a bare silicon wafer 13 reference sample 15 illumination light beam 16 Reflected parallel light flux 17 Rear focal plane of detection side lens 19 Wafer chuck 20 Reference sample piece 21 Wafer with measurement target thin film 22-25 Storage device 26 Calculation unit 27 Light intensity sensor 28 Monitor lens 29 Half mirror 30 Average calculation device 31, 32 storage device 33 light-shielding plate 34 mirror 35 half mirrors 36, 37 mirrors 38-44 storage device 45 exposure light illumination system 46 exposure light source 47 exposure lens 48 exposure light beam

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Kubota, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture

Claims (16)

[Claims] 1. A method for measuring a characteristic value of a thin film from a back focal plane intensity distribution of a lens, which illuminates a thin film sample with convergent light and detects divergent light reflected from the sample, and a reference having a known refractive index and absorption coefficient. After converting the back focal plane intensity distribution of the thin film sample into the incident angle dependent characteristic of the reflectance by using the theoretical calculation value of the back focal plane intensity distribution of the sample and the reflectance of the reference sample, A method for measuring a characteristic value, which comprises calculating at least one of a film thickness, a refractive index, and an absorption coefficient. 2. The characteristic value measuring method according to claim 1, wherein the incident angle dependence characteristic of the reflectance of the thin film sample is calculated by using the focal plane intensity distribution after the sample is retracted and detected. 3. The characteristic value measuring method according to claim 1, wherein the incident angle dependence characteristic of the reflectance of the thin film sample is calculated using the detected value of the illumination light intensity. 4. The characteristic value measuring method according to claim 1, wherein the back focal plane intensity is an average value of a plurality of measurement results. 5. The theory according to claim 1, wherein the incident angle dependence characteristic of reflectance obtained by converting the back focal plane intensity distribution of the thin film sample and a set of arbitrary film thickness, refractive index and absorption coefficient are substituted. A method for measuring a characteristic value, characterized in that the calculated incident angle dependence characteristics of the reflectance are compared with each other, and a pair of the film thickness, the refractive index, and the absorption coefficient is calculated when the two best match. 6. The method according to claim 1, wherein the film thickness is obtained at a wavelength at which the absorption coefficient of the thin film is small, and one or more of a refractive index and an absorption coefficient at a wavelength at which the absorption coefficient of the thin film is large is obtained using the film thickness value. A method for measuring a characteristic value, which comprises: 7. The film thickness value according to claim 1, wherein the back focal plane intensity distribution before and after exposing the photosensitive thin film is detected and stored, and the film thickness is obtained from the stored back focal plane intensity distribution after exposure. Is used to calculate at least one of the refractive index and the absorption coefficient of the thin film before exposure from the back focal plane intensity distribution before exposure. 8. A method for obtaining a film thickness at a wavelength having a small absorption coefficient of a thin film, and using the film thickness value to calculate at least one of a refractive index and an absorption coefficient at a wavelength having a large absorption coefficient of the thin film. Characteristic characteristic value measuring method. 9. A photosensitive thin film is exposed to light to reduce its absorption coefficient, and then the film thickness is obtained. The film thickness value is used to determine the refractive index and absorption coefficient when the absorption coefficient of the thin film at the start of exposure is large. A method for measuring a characteristic value, which comprises calculating one or more of them. 10. A device for measuring a characteristic value of a thin film, comprising: a light source, a lens for illuminating a sample with convergent light, a lens for detecting divergent light reflected from the sample, and a back focal plane intensity distribution of the lens. A thin film sample, a reference sample with a known refractive index and absorption coefficient, a thin film sample and a reference sample, the back focal plane intensity distribution, and the theoretical calculation value of the incident angle dependence characteristics of the reflectance of the reference sample. Thin film characteristic value measuring device comprising an arithmetic unit for calculating the incident angle dependent characteristic of the thin film sample and further calculating one or more of the film thickness, the refractive index and the absorption coefficient of the thin film from the incident angle dependent characteristic of the reflectance of the thin film sample. . 11. The thin film characteristic value measuring device according to claim 10, wherein the thin film sample and the reference sample are simultaneously mounted on a mounting table. 12. The lens for illuminating a sample with convergent light according to claim 10, wherein the optical axis is perpendicular to the sample and also serves as a lens for detecting reflected light, and the illumination light does not pass near the optical axis. A thin film characteristic value measuring device characterized by: 13. The lens for illuminating a sample with convergent light according to claim 10, wherein the optical axis is perpendicular to the sample and also serves as a lens for detecting reflected light, and the illumination light does not pass near the optical axis. Further, a thin film characteristic value measuring device characterized in that the lens transmission positions of the illumination light and the reflected light are different. 14. The device for extracting light of different wavelengths from a light source, the device for storing the detected value of the intensity distribution of the back focal plane at each wavelength, and the back focal plane at the wavelength where the absorption coefficient of the sample is small according to claim 10. A thin film having a calculation device for obtaining a film thickness from the intensity distribution and calculating at least one of a refractive index and an absorption coefficient from the film thickness value and the back focal plane intensity distribution at other wavelengths. Characteristic value measuring device. 15. The apparatus according to claim 10, wherein the measurement target is a photosensitive thin film, and a device for storing the detected values of the back focal plane intensity distribution detected before and after the exposure, and the film thickness from the back focal plane intensity distribution after the exposure. And a calculation device for calculating at least one of the refractive index and the absorption coefficient of the thin film before exposure from the film thickness value and the back focal plane intensity distribution before exposure. apparatus. 16. A method of measuring a characteristic value of a specular surface from a back focal plane intensity distribution of a lens for illuminating a specular sample with convergent light and detecting divergent light reflected from the specular sample, the method comprising: Is used to calculate the back focal plane intensity distribution of the reference sample and the theoretical calculation value of the incident angle dependent characteristic of the reflectance of the reference sample, and the back focal plane intensity distribution of the specular sample is set to the incident angle dependent characteristic of the reflectance. After conversion, at least one of the refractive index and the absorption coefficient of the mirror surface is calculated, and the characteristic value measuring method is characterized.