JPH0820223B2 - Method and apparatus for measuring film thickness / refractive index - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to a method and apparatus for measuring the film thickness and refractive index of a thin film.

(Prior Art) Conventionally, as a method for measuring the film thickness and refractive index of a thin film formed on a substrate such as a quartz plate, the thin film is irradiated with light and the spectral characteristics of light reflected by the thin film are measured. Then, based on the spectral reflectance R _λ obtained for each wavelength λ from the spectral characteristics and the calculated spectral reflectance R _o λ obtained for the wavelength λ from the theoretical formula, the measured spectral reflectance for the wavelength region of the spectral characteristics. Index and the calculated spectral reflectance, the least square sum of the differences shows the minimum value, and extracts the film thickness and the refractive index that set it from the calculated spectral reflectance, and the extracted film thickness and refractive index. Are the film thickness and the refractive index of the thin film, respectively.

(Problems to be Solved by the Invention) However, in the conventional measurement method, the film thickness and the refractive index of the thin film are calculated using the least square sum of the difference between the measured spectral reflectance and the calculated spectral reflectance in the wavelength region of the spectral characteristics. Since the film thickness and the refractive index of the thin film are values determined in the wavelength region of the spectral characteristic by obtaining the refractive index, when the thin film has the dispersion characteristic in the wavelength region of the spectral characteristic, the dispersion characteristic It is not possible to deal with the change in the refractive index due to. As a result, the accuracy of the required film thickness and refractive index of the thin film changes depending on the dispersion characteristics of the thin film, which may reduce the reliability of the required film thickness and refractive index.

An object of the present invention is to provide a film thickness and refractive index measuring method and a refractive index measuring method and apparatus that can be applied to a thin film having dispersion characteristics.

(Means for Solving the Problems) A film thickness / refractive index measuring method of the present invention is to irradiate a thin film formed on a substrate such as a quartz plate with light, and to spectroscopically analyze the thin film from the light reflected by the thin film. A spectral characteristic curve indicating the spectral reflectance is obtained by a reflectance measuring unit that measures reflectance, and a spectral reflectance corresponding to a predetermined wavelength and a differential coefficient of the spectral reflectance with respect to the wavelength are calculated from the spectral characteristic curve. , The film thickness and the refractive index of the thin film with respect to the wavelength are obtained based on the spectral reflectance and the differential coefficient.

The film thickness / refractive index measuring apparatus of the present invention irradiates a thin film formed on a substrate such as a quartz plate with light, measures the spectral reflectance of the thin film from the light reflected by the thin film, Reflectance measuring means for generating a spectral characteristic curve indicating the reflectance, the spectral characteristic curve is given from the reflectance measuring means, and the spectral reflectance corresponding to a predetermined wavelength from the spectral characteristic curve and the spectral reflectance Calculation means for calculating a differential coefficient with respect to wavelength, and calculation for giving the spectral reflectance and the differential coefficient from the calculating means, and calculating the film thickness and the refractive index of the thin film based on the spectral reflectance and the differential coefficient. Processing means.

The arithmetic processing means has a setting unit in which a plurality of reference curves indicating a spectral reflectance and a relationship of a differential coefficient with respect to a wavelength of the spectral reflectance are set using a plurality of film thicknesses and a refractive index of the thin film as parameters, and the calculation unit. A reference curve showing a value close to the spectral reflectance and the differential coefficient from the calculating means is extracted from the reference curves set in the setting unit based on the spectral reflectance and the differential coefficient from the means, and the extracted. And a processing unit for calculating the film thickness and the refractive index of the thin film from the film thickness and the refractive index which are the parameters of the reference curve.

(Operation) According to the method of the present invention, the light reflected by the thin film is
Since the spectral characteristic curve shows the relationship between the spectral reflectance and the wavelength that change with the change in the refractive index of the thin film by changing according to the change in the refractive index due to the dispersion characteristic of the thin film, the spectral characteristic curve The film thickness and the refractive index of the thin film obtained from the spectral reflectance obtained from the above and the differential coefficient between the spectral reflectance and the wavelength corresponding thereto are values corresponding to the dispersion characteristics of the thin film.

According to the device of the present invention, it is possible to obtain a film thickness and a refractive index corresponding to the dispersion characteristics of the thin film.

The arithmetic processing unit calculates the film thickness and the refractive index of the thin film using a plurality of reference curves set in the setting unit, thereby facilitating the calculation of the film thickness and the refractive index.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the film thickness / refractive index measuring apparatus of the present invention, and FIG. 2 is a diagram showing the film thickness / refractive index measuring apparatus of FIG. FIG. 3 is a diagram showing a positional relationship between a substrate, a thin film, and incident light when measuring a refractive index, FIG.
FIG. 4 is a diagram showing an example of a spectral characteristic curve obtained from the film thickness / refractive index measuring device, and FIG. 4 is a diagram showing an example of a reference curve set in the film thickness / refractive index measuring device of FIG. .

The film thickness / refractive index measuring device includes a reflectance measuring means 10 as shown in FIGS. Reflectance measuring means 10
Is a light source unit 12 and a spectroscopic unit 14 that disperses the light from the light source unit 12.
And the substrate 18 on which the thin film 16 is vapor-deposited, and the spectroscopic unit 14
Sample chamber that guides the light dispersed by the thin film 16 at a specified incident angle
With 20 and. According to the illustrated example, the light having the wavelength λ from the spectroscopic unit 14 is incident on the thin film 16 at the angle θ ₀ through the gas having the refractive index n ₀ in the sample chamber 20, and the light from the spectroscopic unit 14 The parts are reflected on the surface of the thin film 16. A part of the light from the spectroscopic unit 14 enters the substrate 18 through the thin film 16 at an incident angle θ. The substrate 18 has a refractive index n _g , the light reflected by the substrate 18 travels through the thin film 16 to the outside, and the refraction angle of the light traveling into the substrate 18 is θ _g .

The light reflected by the thin film 16 is received by the photometric unit 22 and
Reference numeral 22 measures the spectral reflectance from the light reflected by the thin film 16 and the light from the spectroscopic unit 14 received as the reference light, and outputs a signal corresponding to the spectral reflectance. The signal output from the measurement unit 22 is given to the curve generation unit 24. The curve generator 24 uses the third
As shown in the figure, a spectral characteristic curve 102 indicating the spectral reflectance is generated based on the signal.

The spectral characteristic curve 10 from the curve generation unit 24 of the reflectance measuring means 10
2 is given to the calculation means 26. Calculating means 26, the differential coefficient for the wavelength lambda _n of the spectral reflectance R _{lambda] n} and spectroscopic reflectance R _{lambda] n} spectral characteristic curve 102 corresponding predetermined wavelength lambda _n from to (d
R / dλ) _λn is calculated.

The spectral reflectance R _λn and the differential coefficient (dR / dλ) _λn calculated by the calculating means 26 are given to the arithmetic processing means 28. The arithmetic processing means 28 uses a plurality of film thicknesses d and a refractive index n with respect to the thin film 16 as parameters to indicate the relationship between the spectral reflectance R _S and the differential coefficient dR _S / dλ _S of the spectral reflectance R _S with respect to the wavelength λ _S. It has a setting unit 30 in which a reference curve is preset. As shown in FIG. 4, six reference curves 104, 106, 108, 110, 112, 114 are set in the setting unit 30. The reference curve 104 is a curve drawn when the value of the refractive index n which is a parameter is 1.4 and the value of the film thickness d is sequentially increased from 0. The reference curve 106 is a curve when the value of the refractive index n is 1.2 and the value of the film thickness d is sequentially increased from 0. Each reference curve
The curves 104 and 406 change in the counterclockwise direction as the film thickness d increases. The reference curve 108 has a refractive index n of 2.0, the reference curve 110 has a refractive index n of 2.5, the reference curve 112 has a refractive index n of 3.0, and the reference curve 114 has a refractive index n of 3.0. The value is 3.5. Each of the reference curves 108, 110, 112, 114 changes in the reaction clockwise direction as the film thickness d increases.

The relationship between the film thickness d and the refractive index n of the thin film 16 formed on the substrate 18 having the refractive index n _g and the spectral reflectance R _S of the thin film 16 satisfies the following expression (1).

Where K ₁ = N (N _O −N _g ) cos (δ / 2) K ₂ = (N _O N _g −N ² ) sin (δ / 2) K ₃ = N (N _O + N _g ) cos (δ / 2) K ₄ = (N _O N _g + N ² ) sin (δ / 2) For the S component of the light N _O ＝ n _o cos θ _o N = n cos θ N _g ＝ n _g cos _{g For} the P component of the light hand n _o sin θ _o = n sin θ = n _g sin θ _g Is. The film thickness d and the refractive index n of the thin film 16 satisfy the following conditional expressions (2), (3) and (4),
Alternatively, the expressions (3), (4), and (5) are satisfied.

0 <n <n _l (2) _ng <n (3) 0 <d <λ / (2πdcosθ) (4) n _l <n <n _g (5) From the above equations, the spectral reflectance is obtained. Wavelength of R _S and spectral reflectance R _S λ _S
A reference curve showing the relationship with the differential coefficient dR _S / dλ _S can be created by using the refractive index n and the film thickness d as parameters, and from the reference curve, a set of (R _S , dR _S / dλ _S ) is obtained. On the other hand, one set (n, d) can be determined.

Reference curves 104, 106, 108, 11 set in the setting unit 30
0, 112, 114 are given to the processing unit 32 together with the spectral reflectance R _λn and the differential coefficient (dR / dλ) _λn from the calculating means 26. The processing unit 32 uses the spectral reflectance R _λn and the differential coefficient (dR
/ dλ) Each reference curve 104,106,108,110,112,11 based on _λn
Spectral reflectance R _λn and differential coefficient (dR / dλ) out of 4
A reference curve having a value closest to _λn is extracted, and the film thickness d and the curve rate n, which are the parameters of the extracted reference curve, are sequentially calculated as initial values, and the spectral reflectance R _λn and the differential coefficient (dR / dR / dλ) A film thickness d and a refractive index n, which are parameters of a reference curve showing a value equal to _λn , are calculated, and the calculated film thickness d and refractive index n are calculated as the film thickness and the refractive index of the thin film 16.

When measuring the film thickness and the refractive index of the thin film 16 deposited on the substrate 18 of the fused silica plate having the refractive index n _g of 1.5, the third
As shown in the figure, the curve generator 24 of the reflectance measuring means 10 generates a spectral characteristic curve 102.

Then, the calculating means 26 calculates the spectral reflectance R _λn and the differential coefficient (dR / dR) corresponding to the predetermined wavelength λ _n from the spectral characteristic curve 102.
dλ) _λn is calculated. For example, when the wavelength λ _n is 6300Å, the value of the spectral reflectance R _λn is 27% and the value of the differential coefficient (dR / dλ) _λn is 0.005.

The arithmetic processing means 28 uses the value of the spectral reflectance R _{λn and} the value of the differential coefficient (dR / dλ) _{λn to} generate the reference curves 104, 106, 108 ,.
The reference curves 108 and 110 are extracted from 110, 112 and 114. From the refractive index n value of 2.0 of the reference curve 108 and the refractive index n value of 2.5 of the reference curve 110, the refractive index of the thin film 16 was calculated to be 2.3,
From the film thickness d of the reference curve 108 and the film thickness d of the reference curve 110, the film thickness of the thin film 16 is calculated to be 6000Å.

(Effect of the Invention) According to the method of the present invention, the film thickness and the refractive index of the thin film can be obtained from the spectral reflectance obtained from the spectral characteristic curve and the derivative of the spectral reflectance and the wavelength corresponding thereto. As a result, the obtained film thickness and refractive index of the thin film have values corresponding to the dispersion property of the thin film, and thus the thin film having the dispersion property can be applied.

According to the device of the present invention, it is possible to obtain the film thickness and the refractive index of a thin film having dispersion characteristics.

The arithmetic processing means facilitates the calculation of the film thickness and the refractive index by calculating the film thickness and the refractive index of the thin film using a plurality of reference curves set in the setting section.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a film thickness / refractive index measuring device of the present invention, and FIG. 2 is a film thickness / refractive index measuring device using the film thickness / refractive index measuring device of FIG. FIG. 3 is a diagram showing a positional relationship among a substrate, a thin film, and incident light when the above is performed, FIG. 3 is a diagram showing an example of a spectral characteristic curve obtained from the film thickness / refractive index measuring apparatus of FIG. 1, and FIG. It is a figure which shows an example of the reference curve set to the film thickness and refractive index measuring device of the figure. 10 ... Reflectance measuring means, 16 ... Thin film, 18 ... Substrate, 26 ...
… Calculation means, 28 …… Calculation processing means, 30 …… Setting section, 32…
... Processing unit, 102 ... Spectral characteristic curve, 104,106,108,110,11
2,114 …… Reference curve.

Claims (3)

[Claims] 1. A spectral reflectivity measuring means for irradiating a thin film formed on a substrate such as a quartz plate with light and measuring the spectral reflectivity of the thin film from the light reflected by the thin film. Obtaining a spectral characteristic curve, calculating a spectral reflectance corresponding to a predetermined wavelength from the spectral characteristic curve and a differential coefficient of the spectral reflectance with respect to the wavelength, the thin film for the wavelength based on the spectral reflectance and the differential coefficient Method for measuring the film thickness and refractive index of the film. 2. A thin film formed on a substrate such as a quartz plate is irradiated with light, the spectral reflectance of the thin film is measured from the light reflected by the thin film, and a spectral characteristic curve showing the spectral reflectance is obtained. The reflectance measuring means to be generated and the spectral characteristic curve are given from the reflectance measuring means, and the spectral reflectance corresponding to a predetermined wavelength and the differential coefficient of the spectral reflectance with respect to the wavelength are calculated from the spectral characteristic curve. From the calculating means and the calculating means,
A film thickness / refractive index measuring apparatus comprising: arithmetic processing means that is provided with the spectral reflectance and the differential coefficient and calculates the film thickness and the refractive index of the thin film based on the spectral reflectance and the differential coefficient. 3. A setting in which the arithmetic processing means is set with a plurality of reference curves indicating a spectral reflectance and a relationship of a differential coefficient of the spectral reflectance with respect to a wavelength using a plurality of film thicknesses and refractive indexes of the thin film as parameters. Section and a reference curve showing a value close to the spectral reflectance and the differential coefficient from the calculating means is extracted from the reference curves set in the setting section based on the spectral reflectance and the differential coefficient from the calculating means. The film thickness / refractive index measuring apparatus according to claim 2, further comprising a processing unit that calculates the film thickness and refractive index of the thin film from the film thickness and refractive index that are parameters of the extracted reference curve.