JP2003050108A - Film thickness measuring method and film thickness measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure a film thickness, even when the refractive index of a measuring thin film has wave number dependence. SOLUTION: On a substrate where a thin film is formed, a plurality of lights having an optical path difference from a light source and capability of passing a thin film are irradiated, and the reflection light intensities of a plurality of lights reflected on the substrate are detected by varying the optical path difference so that the film interference spectrum of a distance function is obtained; while a simulation film interference spectrum, corresponding to the film interference spectrum of the distance correlation, is calculated with a parameter of a wave number function of light for the thin film of a postulated thickness of the same material as the thin film. The thickness of the thin film is determined by the film interference spectrum of a distance function, based on the correlation between the pattern of the simulation film interference spectrum and the postulated film thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film thickness measuring method and a film thickness measuring apparatus, and particularly, even when the refractive index of a thin film to be measured has wave number dependence, the film thickness can be accurately measured. The present invention relates to a film thickness measuring method and a film thickness measuring device that can be performed.

[0002]

2. Description of the Related Art FIG. 7 is a diagram for explaining the configuration of an optical system of a Fourier transform infrared spectrophotometer used for film thickness measurement according to the related art and the present invention. Fourier transform infrared spectrophotometer (hereinafter F
The Michelson interferometer shown in FIG. 7 is generally used for the optical system (referred to as T-IR). In FIG. 7, 1 is a light source, 2 is a half mirror, 3 is a fixed mirror, and 4
Is a movable mirror, 5 is a reflection mirror, 6 is a sample, and a thin film 6b is formed on a substrate 6a. 7 is a detector.

The principle of film thickness measurement using FT-IR will be described with reference to FIG. In FIG. 7, continuous light emitted from the light source 1 is separated by the half mirror 2, one of which is incident on the fixed mirror 3 and the other of which is incident on the movable mirror 4. The light reflected by each mirror returns to the half mirror 2 again,
After the light is reflected by the reflection mirror 5, it goes to the sample 6. The light reflected by the sample 6 is captured by the detector 7.

The movable mirror 4 is moved to measure the dependency of the light intensity detected by the detector 7 on the moving distance of the movable mirror 4. The film interference spectrum obtained in this way is called an interferogram. The moving distance of the movable mirror 4 corresponds to the optical distance, and the interferogram can be said to be the film interference spectrum of the optical distance function. Figure 8
FIG. 4 is a diagram illustrating an interferogram.
As shown in FIG. 8, in the interferogram, the horizontal axis is the moving distance of the movable mirror, the vertical axis is the light intensity, 8 is the main burst, 9 is the peak called side burst, and side burst 9 is It is seen at a symmetrical position with respect to the main burst 8.

Next, the main burst 8 and the side burst 9 will be described. FIG. 9 is a diagram for explaining light reflection on the sample. In FIG. 7, light incident on the sample 6 has a path from the light source 1 through the movable mirror 4 and the reflection mirror 5 to the sample 6 (hereinafter referred to as path A), and from the light source 1 to the fixed mirror 3 and reflection. There is a path for entering the sample 6 through the mirror 5 (hereinafter referred to as path B). As shown in FIG. 9, there are light 10 which is incident on the path A and reflected by the sample 6 and light 11 which is incident on the path B and is reflected by the sample 6, and is reflected on the surface of the thin film 6b. 10a and 11a, and reflected light 10b and 11b at the interface between the thin film 6b and the substrate 6a. When the optical distance of the light of the path A reaching the detector 7 after reflection at the sample 6 and the optical distance of the light of the path B reaching the detector 7 after reflection at the sample 6 match, the light of all wave numbers Against
Since the phases match and the lights intensify each other, the signal strength increases.
The peak in which the light intensity is increased is the main burst 8. Further, if the two optical distances differ by shifting the position of the movable mirror, some of them strengthen each other or cancel each other out depending on the wave number. Get smaller.

However, the optical distance of the light of the path A reaching the detector 7 after being reflected on the surface of the thin film 6b, and the light of the path B being reflected at the interface between the thin film 6a and the substrate 6b, the detector 7 When the optical distances to reach the same are matched, the phases are matched with the light of all wave numbers and the lights are strengthened, so that the signal strength is increased. Similarly, the light of the path A reaches the detector 7 through the reflection at the interface between the thin film 6a and the substrate 6b, and the light of the path B reaches the detector 7 through the reflection on the surface of the thin film 6b. Even when the optical distances are the same, the phases are the same and the lights are strengthened with respect to the light of all wave numbers, so that the signal strength is increased. These peaks are side burst 9.

That is, in the interferogram, the main burst 8 due to interference of light reflected from the outermost surfaces of the sample 6 and from the interfaces between the thin film 6a and the substrate 6b,
Light reflected from the outermost surface of sample 6, thin film 6a, and substrate 6
Side burst 9 due to interference of light reflected from the interface of b
Is obtained. The side burst 9 appears in a symmetrical position with respect to the main burst 8. Further, since the distance between the main burst 8 and the side burst 9 corresponds to the optical distance that light passes back and forth through the thin film 6b, the film thickness can be obtained by multiplying this optical distance by the refractive index of the thin film 6b. . The above description is for the case where the refractive index of the thin film 6b is smaller than the substrate 6a. When the refractive index of the thin film 6b is larger than the substrate 6a, the phase when reflected at the interface between the thin film 6b and the substrate 6a. Since it inverts, it weakens each other with respect to light of all wave numbers, so that the signal strength becomes small and the peak is inverted.

FIG. 3 is a diagram for explaining a flow for obtaining a spatialgram used for film thickness measurement by measurement. Figure 3
A flow for obtaining the spatial gram shown in (1) by measurement will be described. In the interferogram mentioned above,
The side burst peak is distorted because it also includes information such as the wavenumber dependence of the sensitivity of the detector 7 and the wavenumber dependence of the light intensity from the light source 1. Therefore, the detector 7 and the light source 1
In order to remove the characteristic of, the measurement is performed on the reference at the same time as the sample. As a reference, only a substrate on which a thin film is not formed is used. Interferogram I ₁ (x ₁ ) by the method described above for the sample
To get The film interference spectrum R ₁ (ν) depending on the wave number can be obtained by subjecting this interferogram I ₁ (x ₁ ) to apodization and Fourier transform. This is called a film interference spectrum of a wave number function. The apodization process is a process for smoothly connecting to zero so that there is no step at the terminal end of the interferogram.

On the other hand, also for the reference, the interferogram I ₂ (x ₁ ) is similarly subjected to apodization and Fourier transform to obtain a film interference spectrum R ₂ (ν) of a wave number function. The characteristic of the detector 7 and the characteristic of the light source 1 are canceled by dividing or subtracting the film interference spectrum R ₁ (ν) of the wave number function in the sample by the film interference spectrum R ₂ (ν) of the wave number function in the reference. The film interference spectrum R (ν) of the wave number function can be obtained. The film interference spectrum of the optical distance function from which the wave number dependence of the light source 1 and the detector 7 is removed by apodizing and Fourier transforming the film interference spectrum of this wave number function.
You can get S (x ₁ ). This film interference spectrum S (x ₁ )
Is called a spatial gram.

FIG. 10 is a diagram showing an example of a spatialgram obtained by a conventional film thickness measuring method. Figure 11
FIG. 6 is a diagram illustrating a conventional film thickness measuring method. In FIG. 10, 12 is a main burst and 13 is a side burst. In the spatialgram of FIG. 10, the distance between the main burst 12 and the side burst 13 corresponds to the optical distance over which light travels back and forth through the thin film, as in the case of the interferogram described above. Therefore, the peak positions of the main burst 12 and the side burst 13 of the spatial gram are calculated, and the distance between these peaks is calculated,
The film thickness can be calculated by giving the refractive index of the thin film to this.

[0011]

The peak width of the side burst in the interferogram or the spatialgram is the reciprocal of the wave number region of the light used. That is, the wider the wave number region is, the narrower the peak width of the side burst becomes, so that the measurement of a thin film becomes possible.
On the other hand, the refractive index of almost all substances has wave number dependence. Therefore, the optical distance of the film changes depending on the wave number of light.
This means that the side burst described in the above conventional example does not completely match for all phases. Therefore, the peak shape of the side burst is distorted, and the peak position is displaced. Since the peak position does not correspond to the interface position between the thin film and the substrate, there is a problem that the film thickness measurement accuracy decreases when the film thickness is measured based on the peak position.

The present invention has been made in order to solve the above problems, and accurately measures the thickness of a thin film even when the refractive index of the thin film whose thickness is to be measured changes depending on the wave number. It is an object of the present invention to provide a method and a measuring device that can do the above.

[0013]

According to a film thickness measuring method of the present invention, a substrate on which a thin film is formed is irradiated with light which can pass through a plurality of thin films having an optical path difference from a light source and is reflected by the substrate. A step of obtaining a film interference spectrum of a distance function by detecting the reflected light intensity of the light by changing the optical path difference,
A step of calculating a simulation film interference spectrum corresponding to the film interference spectrum of the distance function using the wave number function of the light as a parameter for a thin film of the same material as the thin film and a predetermined assumed film thickness, and a pattern of the simulation film interference spectrum Determining the film thickness of the thin film based on the film interference spectrum of the distance function based on the correlation with the predetermined assumed film thickness.

Further, the step of obtaining the film interference spectrum of the distance function comprises a step of converting the film interference spectrum obtained by changing and detecting the optical path difference from the distance function to the wave number function and then reconverting it into the distance function. It is a thing.

Further, in the step of obtaining the film interference spectrum of the distance function, the substrate on which the thin film is formed and the substrate on which the thin film is not formed are irradiated with light that can pass through a plurality of thin films having an optical path difference from the light source. , A step of obtaining a film interference spectrum of a distance function for each substrate by detecting reflected light intensities of a plurality of lights reflected by each substrate by changing the optical path difference,
One of the steps of converting the distance function film interference spectrum of each substrate into a wave number function to obtain the wave number function film interference spectrum of each substrate, and the other of the obtained wave number function film interference spectra of each substrate A step of reconverting to a distance function after division or subtraction.

Further, a step of irradiating a substrate having a thin film formed thereon with light that can pass through the thin film and detecting the intensity of light reflected by the substrate to obtain a film interference spectrum having a wave number function depending on the wave number of the light. And a step of obtaining a converted film interference spectrum by converting the film interference spectrum of the wave number function from the wave number function to a distance function, and the wave number function of the light as a parameter for a thin film of the same material as the thin film and having a predetermined assumed film thickness. As a step of calculating a simulation film interference spectrum corresponding to the conversion film interference spectrum, and based on the correlation between the pattern of the simulation film interference spectrum and the predetermined assumed film thickness, the film of the thin film is obtained by the conversion film interference spectrum. And a step of determining the thickness.

In the film thickness measuring device according to the present invention, the substrate on which the thin film is formed is irradiated with light that can pass through the plurality of thin films having an optical path difference from the light source, and a plurality of reflected lights of the light reflected by the substrate are reflected. A film interference spectrum measurement unit that obtains a film interference spectrum of a distance function by detecting the intensity by changing the optical path difference, and the above distance using the same wave number function of the light as a parameter for a thin film of the same material as the above thin film and having a predetermined assumed film thickness. The calculation unit for calculating the simulation film interference spectrum corresponding to the film film interference spectrum of the function, and the thin film based on the film interference spectrum of the distance function based on the correlation between the pattern of the simulation film interference spectrum and the predetermined assumed film thickness. And a calculation unit that determines the film thickness of the.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. FIG. 1 is a diagram illustrating a film thickness measuring method according to a first embodiment of the present invention. The first embodiment is different from the conventional method in that the conventional method measures a spatialgram which is a film interference spectrum of a distance function, obtains its peak position, and determines the peak position of the thin film at the distance between the main burst and the side burst. While the film thickness is obtained by giving the refractive index, in the first embodiment, the estimated film thickness is set in advance for a thin film of the same material as the thin film to be measured, and parameters including this estimated film thickness are set. The spatial gram is obtained by simulation using, and the correlation between the peak position and the interface position obtained from the assumed film thickness is derived, and the film thickness is calculated from the peak position of the spatial gram obtained by measurement based on this relationship. Is the point to seek. First, the spatial gram is obtained by measurement. The method of obtaining the spatial gram by measurement is the same as the conventional method described above, and is performed according to the flow shown in FIG. 3 using the optical system shown in FIG. That is, by irradiating a substrate formed on a thin film with two lights having an optical path difference from a light source and detecting the reflected light intensities of the two lights reflected by the substrate by changing the optical path difference, For the sample on which the thin film is formed and the reference on which the thin film is not formed on the substrate, the substrate formed on the thin film is irradiated with two lights having an optical path difference from the light source, and the two lights reflected by the substrate are irradiated. The film interference spectrum I ₁ (x _{1 of the} distance function) of the sample with the thin film formed on the substrate and the reference without the thin film formed on the substrate were detected by detecting the reflected light intensity of ), I ₂ (x ₁ ) (interferogram). This interferogram is the film interference spectrum of the optical distance function as in the conventional case.

Next, the sample and reference interferograms I ₁ (x ₁ ) and I ₂ (x ₁ ) are converted from a distance function to a wave number function, and the film interference spectrum R ₁ (ν ), R ₂ (ν). Fourier transform is used for the conversion from the distance function to the wave number function. Also, the apodization is performed so as to smoothly connect to zero so that there is no step at the terminal end of the interferogram. Film interference spectrum R ₁ wavenumber function of sample ([nu), by dividing or subtracting a film interference spectrum R ₂ wavenumber function of the reference ([nu), canceled the characteristics and properties of the light source 1 of the detector 7, The film interference spectrum R (ν) of the wave number function is obtained, and the film interference spectrum of this wave number function is re-converted into a distance function by apodization and Fourier transform to remove the wave number dependence of the light source 1 and the detector 7. Shallgram S (x ₁ ) (converted film interference spectrum) can be obtained.

Next, a method for obtaining a spatialgram by simulation will be described. FIG. 2 is a diagram illustrating a flow for obtaining a spatial gram used in the film thickness measurement according to the first embodiment of the present invention by simulation. First, a sample in which a thin film is formed on the substrate,
For a reference in which a thin film is not formed on the substrate, film interference spectra I _S1 (x ₁ ) and I _S2 (x ₁ ) (interferogram) of the distance function are obtained by simulation. The interferogram I ₁ obtained by measurement is the method of obtaining the spatial gram S _S (x ₁ ) from the interferogram I _S1 (x ₁ ) and I _S2 (x ₁ ) obtained by simulation.
This is the same as the method of obtaining the spatial gram S (x ₁ ) from (x ₁ ) and I ₂ (x ₁ ). The details of the simulation will be described below.

In FIG. 7, when the movable mirror 4 is at a position, the light intensities output by the detector 7 for the sample in which the single-layer film is formed on the substrate and the reference of only the substrate are respectively I _S1 , I _S2 , the light intensity
I _S1 and I _S2 can be simulated using equations (1) and (2). I _S1 = ∫dν [(ρ _f・ r _layer + ρ _m・ r _layer ) ・ (ρ _f・ r _layer + ρ _m・ r _layer ) ^*・ ρ _d ] (1) I _S2 = ∫dν [(ρ _f・ R _sub + ρ _m・ r _sub ) ・ (ρ _f・ r _sub + ρ _m・ r _sub ) ^*・ ρ _d ] (2) In equations (1) and (2), ν is the wave number of light, and ρ _f Is the amplitude of the light incident on the sample and the reference via the fixed mirror (path B above), and ρ _m is the amplitude of the light incident on the sample and the reference via the movable mirror (path A above), r
_sub is the amplitude reflectance when only the substrate is used, r _layer is the amplitude reflectance when a monolayer film is formed on the substrate, ρ _d is the sensitivity of the detector, and ^* is the complex conjugate.

Where ρ _f , ρ _m , r _sub , r _layer , ρ _d
Usually has wave number dependence, and these wave number dependences are obtained in advance, and the light intensity output by the detector is simulated by integrating in all wave number regions according to equations (1) and (2). The values I _{S 1} and I _{S 2} can be obtained. By changing the position of the movable mirror, the simulation values I _{S 1} and I _S2 of the light intensity are obtained for each position, and by plotting this as a function of the optical distance x _1, a simulated interferogram I _S1 (x ₁ ), I _S2 (x ₁ ) can be obtained.

The amplitude ρ _f of light incident on the path B depends on the wave number, and the amplitude ρ _m of light incident on the path A depends on the wave number and the position x of the movable mirror. The amplitude ρ _in of the light incident on the sample and the reference is the sum of ρ _f and ρ _m as in equation (3), and ρ _f and ρ _m are represented by equations (4) and (5), respectively. . _{ρ in (ν, x) =} ρ f (ν) + ρ m (ν, x) (3) ρ f (ν) = f s (ν) · g f (ν) · exp (iτ) (4) ρ m _{(ν, x) = f s} (ν) · g m (ν) · exp (i (τ + δ)) (5) δ = 2πνx (6)

In the equations (4) and (5), f _s is the amplitude of the light emitted from the light source, g _f is the ratio of the light emitted from the light source to the sample and the reference via the fixed mirror, g _m Is the ratio of the light emitted from the light source to the sample and the reference via the movable mirror, which usually depends on the wave number. τ is the phase shift of the light incident on the sample and the reference via the fixed mirror, and i is the imaginary unit. Formula (3),
In (5) and (6), x represents the difference in optical distance between the light incident on the sample and the reference via the fixed mirror and the light incident on the sample and the reference via the movable mirror.

Further, the amplitude reflectances r _sub and r _layer of the reference and sample are expressed by equations (7) and (8), respectively. r _sub = (Y ₀ −Y ₂ ) / (Y ₀ + Y ₂ ) (7) r _layer = (r ₂₁ + r ₁₀ · exp [iγ]) / (1 + r ₂₁ · r ₁₀ · exp [iγ]) (8)

In equations (7) and (8), Y ₀ , Y ₁ ,
Y ₂ is k = 0, 1, in the equations (9) and (10).
It is obtained by 2. Y _k = n _k · cos θ _k (9) Y _k = n _k / cos θ _k (10)

In equations (9) and (10),
n ₀ , n ₁ and n ₂ are the refractive indices of the substrate, the thin film and air, θ ₀ , θ ₁ and θ ₂ are the refraction angle of the light incident on the substrate, the refraction angle of the light incident on the thin film and the light, respectively. Shows the incident angle of.
Between n ₀ , n ₁ and n ₂ and θ ₀ , θ ₁ and θ ₂ , equation (11),
There is a relationship of Expression (12). n ₀ · sin θ ₀ = n ₂ · sin θ ₂ (11) n ₀ · sin θ ₀ = n ₁ · sin θ ₁ (12)

The expression (9) is for S-deflection oscillating in the direction perpendicular to the incident surface, and the expression (10) is for P-deflection oscillating in the incident surface. As Y ₀ , Y ₁ , and Y ₂ used in the equations (7) and (8), those corresponding to the ratio of the S deflection component and the P deflection component of the light incident on the sample are used. As an example, S when the deflection component and a P polarized component of each half, and 1 and Y _k which is obtained by the formula (9) Y _k and equation obtained in (10) of each half was added both The thing is used as Y _k .

In the equation (8), r ₂₁ is the amplitude reflectance when reflected from the surface of the thin film to the air side, and r ₁₀ is the amplitude reflectance when reflected from the interface between the thin film and the substrate to the thin film side. , And (14), respectively. _{r 21 = - (Y 1 -Y} 2) / (Y 1 + Y 2) (13) r 10 = - (Y 0 -Y 1) / (Y 0 + Y 1) (14)

In equation (8), γ is given by equation (1)
5), and Δ in equation (15) is obtained by equation (16). In Expression (16), d ₁ is the film thickness of the thin film. γ = 2πνΔ (15) Δ = 2n ₁ · d ₁ · cos θ ₁ (16) Amplitude reflectances r _sub and r input to the equations (1) and (2)
_{The layer} is defined by the equations (7) to (16), where the incident angle of light is θ ₂ , the refractive index of the substrate is n ₀ , the refractive index of the thin film is n ₁ , the refractive index of air is n ₂ ,
It can be obtained by inputting the estimated thin film thickness as the thin film thickness d ₁ . Since the refractive index has wave number dependence, wave number dependence data of the refractive index n _{0 of} the substrate and the refractive index n ₁ of the thin film are prepared in advance. The wave number dependence of the refractive index n ₂ of air can usually be ignored, and a fixed value can be used.

The film interference spectra I _S1 (x ₁ ) and I _S2 (x ₁ ) of the distance function are obtained for the sample in which the thin film is formed on the substrate and the reference in which the thin film is not formed on the substrate by the method described above, respectively. ) (Interferogram), and then subjecting it to apodization and Fourier transform, respectively, to obtain the film interference spectrum R _S1 (ν), R of the wavenumber function.
_{Find S2} (ν). Samples of wavenumber function of film interference spectrum R _S1 ([nu), by dividing or subtracting a film interference spectrum R _S2 wavenumber function of the reference ([nu), canceled the characteristics and properties of the light source 1 of the detector 7, By obtaining the film interference spectrum R _S (ν) of the wave number function and reconverting this film interference spectrum of the wave number function into a distance function by apotization and Fourier transform, the wave number dependence of the light source 1 and the detector 7 is removed. Membrane Interference Spectra of Different Distance Functions
Calculate S _S (x ₁ ) (spatial gram).

The wave number dependence data of the refractive index of the substrate and the thin film can generally be measured using a spectroscopic ellipsometer or the like. Further, known data described in a handbook or the like, data obtained by a theoretical formula from the composition of the thin film, and the like can also be used.

As an example, a sample having a GaAs substrate and an AlGaAs film formed on the surface thereof will be described below.
A method for obtaining the wave number dependence of the refractive index will be described. G
In the case of a thin film made of a material such as aAs or a compound thereof, a calculation formula based on the theory of the wavenumber dependence of the refractive index is required, and these can also be used. For example, those described in Kenichi Iga, "Applied Physics Series Semiconductor Laser", Ohmsha, H6, 1st edition, pages 35-37 can be used. For the AlGaAs film, Al
And Ga composition ratio is y: (1-y), direct transition band gap E _g (eV), single vibration energy E
₀ (eV) and the dispersion energy E _d (eV) are obtained from Equations (17) to (19), respectively, and Planck's constant is h,
When the speed of light is c and the wave number of light is ν, the refractive index n can be obtained from equation (20) for each wave number. Formula (2
In 0), η is obtained by the equation (21). E _g = 1.420 + 1.087y + 0.438y ² (17) E ₀ = 3.65 + 0.871y + 0.179y ² (18) E _d = 36.1−2.45y (19) n ² −1 = E _d / E ₀ + (hcν) ^{_{2 E d / E 0 3 +}} (hcν) 4 η / π · ln [{2E 0 2 -E g 2 - (hcν) 2} / {E g 2 - (hcν) 2}] (20) η = πE _d / {2E ₀ ³ (E ₀ ² −E _g ² )} (21)

When a GaAs substrate is used as the substrate, E _g , E ₀ and E _d are obtained by setting y = 0 in the above equations (17) to (19), and equations (20) and ( 21) makes it possible to obtain the wavenumber dependence of the refractive index.

FIGS. 4 and 5 are views showing examples of spatialgrams obtained by simulation used for film thickness measurement according to Embodiment 1 of the present invention, and Al _0.4 Ga _0.6 As formed on a GaAs substrate, respectively. This is a case where the assumed film thickness of the film is 0.7 μm and 1.5 μm. Figure 4
In 5 and 5, 14 is the main burst and 15 is Al _0.
An interface position between the ₄ Ga _0.6 As film and the GaAs substrate, 16 is a side burst, and 16 a is a peak at the interface position 15 on the main burst 14 side (hereinafter referred to as peak A), 16
b is a peak on the opposite side of the main burst 14 at the interface position 15 (hereinafter referred to as peak B). In the case of FIGS. 4 and 5, peak A16a is one of the side burst peaks.
The maximum convex peak B16b is the maximum convex peak of the side burst peaks. Interface position 1
5 is the assumed film thickness of the Al _0.4 Ga _0.6 As film and the Al _0.4 Ga film.
_{It is} calculated from the average refractive index of the _0.6 As film by the formula (22). An average refractive index of 3.25 is used for the Al _0.4 Ga _0.6 As film. (Interface position) = (Assumed film thickness)-(Average refractive index) -2 (22)

For each of FIGS. 4 and 5, the equation (2
2) the interface position 15 and the peak A position 16a obtained by
When the relative positional relationship with the peak B position 16b was obtained, the relationship of Expression (23) was obtained in both FIGS. 4 and 5. (Interface position) = 1/2 {(peak A position) + (peak B position)} (23)

FIG. 6 is a diagram showing a spatialgram obtained by the measurement used for the film thickness measurement according to the first embodiment of the present invention. In FIG. 6, 24 is the main burst and 25
Is the interface position between the Al _0.4 Ga _0.6 As film and the GaAs substrate,
26 is a side burst, 26a is a peak A corresponding to the peak A, and 26b is a peak B corresponding to the peak B. Position of peak A26a and peak B26
b position (ie optical distance from main burst 24)
The interface position 25 can be obtained by the equation (23) by obtaining The relationship between the interface position 25 and the film thickness is expressed by the equation (24) similarly to the equation (22), and the interface position 25 and the average refractive index 3.25 obtained by this equation are substituted into Al.
The film thickness of the _0.4 Ga _0.6 As film is 1.0 μm.
Met. (Interface position) = (film thickness)-(average refractive index) -2 (24)

As described above, the relative positional relation between the peak position of the side burst of the spatial gram and the interface position, which is obtained by simulation using the estimated film thickness of the thin film and the parameters of the wave number function, is obtained in advance, and this relationship is obtained. Based on this, by obtaining the film thickness of the thin film from the peak position of the side burst of the actually measured spatial gram, the film thickness of the thin film can be obtained accurately even when the refractive index of the thin film changes depending on the wave number. .

In the above description, the case where the single-layer film is formed on the substrate has been described. However, when the multi-layer film is formed on the substrate, the amplitude reflectance can be calculated, for example, by Shiro Fujiwara et al. “Optical technology series, optical thin film” can be obtained by the method described in Chapter 3 of Kyoritsu Publishing Co., Ltd., 1st edition of 1985, and simulated in the same manner.

When deriving the relative positional relationship between the interface position and the side burst peak position, the relative positional relationship between the peak positions on both sides of the interface position and the interface position was used, but the invention is not limited to this. The relative positional relationship between any of the peak positions forming the burst and the interface position may be derived.

In the above description, the assumed film thickness is 0.7.
The simulation was performed for two different film thicknesses of μm and 1.5 μm, but the present invention is not limited to this, and the simulation may be performed for at least one assumed film thickness.

The film thickness measuring device for measuring the film thickness by the above-mentioned film thickness measuring method includes a film interference spectrum measuring unit for measuring the film interference spectrum of a distance function, and an arithmetic unit for obtaining the film interference spectrum by simulation. A calculation unit that determines the film thickness from the film interference spectrum of the distance function obtained by measurement and the film interference spectrum obtained by simulation.

Embodiment 2. In the first embodiment,
Samples and References Interferogram
I _S1 (x ₁ ) and I _S2 (x ₁ ) are calculated, and the film interference spectrum R _S (ν) of the wave number function and the film interference spectrum S _S (x ₁ ) of the optical distance function are simulated based on this. However, in the second embodiment, R _S (ν) is directly obtained by simulation.

[0044] It is inter by a Fourier transform of the interferogram, the sample and film interference spectrum R ₁ wavenumber function of reference, R ₂ is accurately obtained, a sample of the film interference spectrum R ₁ reference film interference spectrum R ₂ If the effect of the light source and detector can be removed by dividing by, then the amplitude reflectance r _laye from the sample
_r can be regarded as the signal amount when the incident intensity is 1 over each wave number, and the film interference spectrum R _S (ν) of the wave number function
Has a relationship as shown in Expression (25). R _S (ν) = r _layer (ν) ・ r _layer (ν) ^* (25)

A method for obtaining the film thickness by comparing the spatial gram obtained by the simulation obtained by converting the film interference spectrum R _S (ν) of the wave number function into the distance function with the spatial gram obtained by the actual measurement is as follows. This is similar to the above-described first embodiment. As in the second embodiment,
The calculation can be simplified by directly obtaining R _S (ν) by simulation.

In the case of the second embodiment, FT-IR
In addition to the case of using a conventional infrared spectrophotometer, the light source is dispersed, the light of different wave number is directly applied to the sample, and the film interference spectrum of the wave number function is obtained by sequentially scanning the wave number. The same applies when used. When the conventional infrared spectrophotometer is used, the film interference spectrum of the wave number function can be directly obtained by the measurement, and therefore the film interference spectra of the distance function I _S1 (x ₁ ) and I _S2 ( It is not necessary to obtain x ₁ ), apotize it, and perform Fourier transform.

Embodiment 3. In the first and second embodiments
The spatial gram obtained by actual measurement and the simulation
For comparison with the spatial gram obtained by
The method for obtaining the film thickness has been described, but the embodiment
In 3, the measured interferogram and the stain
The ratio with the interferogram obtained by simulation
Calculate the film thickness by comparison. About the substrate with the thin film
Then, in the same way as in the first embodiment,
Terferogram I₁(x₁) And the simulation
Interferogram I_S1(x₁). Simulation
Interferogram I_S1(x ₁) Side
Obtain the relative position relationship between the burst peak position and the interface position.
Therefore, the interface obtained by measurement based on this relative positional relationship
ー Ferrogram I₁(x₁) To obtain the film thickness of the thin film. This
To determine the film thickness using an interferogram
By reference of the interferogram
Measurement and simulation are not required and wave number
No need to convert to function and re-convert to distance
Thus, the film thickness measurement of the thin film can be further simplified.

[0048]

The film thickness measuring method and the film thickness measuring device according to the present invention can accurately measure the thickness of a thin film even if the refractive index of the thin film whose thickness is to be measured changes depending on the wave number. You can

[Brief description of drawings]

FIG. 1 is a diagram illustrating a film thickness measuring method according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a flow for obtaining a spatial gram used in film thickness measurement according to the first embodiment of the present invention by simulation.

FIG. 3 is a diagram illustrating a flow for obtaining a spatial gram used for film thickness measurement in the related art and the present invention by measurement.

FIG. 4 is a diagram showing an example of a spatialgram obtained by a simulation used for film thickness measurement according to the first embodiment of the present invention.

FIG. 5 is a diagram showing an example of a spatial gram obtained by simulation used for film thickness measurement according to the first embodiment of the present invention.

FIG. 6 is a diagram showing an example of a spatial gram obtained by measurement used for film thickness measurement according to the first embodiment of the present invention.

FIG. 7 is a diagram illustrating a configuration of an optical system of a Fourier transform infrared spectrophotometer used for film thickness measurement of the related art and the present invention.

FIG. 8 is a diagram illustrating an interferogram.

FIG. 9 is a diagram illustrating light reflection on a sample.

FIG. 10 is a diagram showing an example of a spatial gram obtained by a conventional film thickness measuring method.

FIG. 11 is a diagram illustrating a conventional film thickness measuring method.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2F065 AA30 BB17 CC31 DD03 FF41                       FF51 QQ16 RR08                 4M106 AA01 BA08 CA48 DH03 DJ15                       DJ17 DJ19

Claims (5)

[Claims] 1. A substrate on which a thin film is formed is irradiated with light that can pass through a plurality of thin films having an optical path difference from a light source, and the reflected light intensities of the plurality of lights reflected by the substrate are calculated as the optical path difference. A step of obtaining a film interference spectrum of a distance function by changing the detection, and a simulation corresponding to the film interference spectrum of the distance function using the wave number function of the light as a parameter for a thin film of the same material as the thin film and having a predetermined assumed film thickness. A step of calculating a film interference spectrum, and a step of determining the film thickness of the thin film by the film interference spectrum of the distance function based on the correlation between the pattern of the simulation film interference spectrum and the predetermined assumed film thickness. A film thickness measuring method provided. 2. The step of obtaining the film interference spectrum of the distance function comprises the step of converting the film interference spectrum obtained by detecting by changing the optical path difference from the distance function to the wave number function and then re-converting it into the distance function. The film thickness measuring method according to claim 1, wherein 3. The step of obtaining a film interference spectrum of a distance function includes a step of transmitting light that can pass through a plurality of thin films having an optical path difference from a light source for each of a substrate on which a thin film is formed and a substrate on which the thin film is not formed. A step of obtaining a film interference spectrum of a distance function for each substrate by irradiating and detecting the reflected light intensity of the plurality of lights reflected by each substrate by changing the optical path difference, and the distance for each substrate Converting the film interference spectrum of each function into a wave number function to obtain the film interference spectrum of the wave function for each substrate, and dividing or subtracting one of the film interference spectra of the wave function obtained for each substrate by the other. And then reconverting into a distance function. 4. A substrate on which a thin film is formed is irradiated with light that can pass through the thin film, and the intensity of light reflected by the substrate is detected to obtain a film interference spectrum of a wave number function that depends on the wave number of the light. A step of obtaining a converted film interference spectrum by converting the film interference spectrum of the wave number function from the wave number function to a distance function, and the wave number function of the light for a thin film of the same material as the thin film and having a predetermined assumed film thickness The step of calculating a simulation film interference spectrum corresponding to the conversion film interference spectrum using as a parameter, and the thin film by the conversion film interference spectrum based on the correlation between the pattern of the simulation film interference spectrum and the predetermined assumed film thickness. And a step of determining the thickness of the film. 5. A substrate on which a thin film is formed is irradiated with light that can pass through the plurality of thin films having an optical path difference from a light source, and the reflected light intensities of the plurality of lights reflected by the substrate are changed to the optical path difference. A film interference spectrum measurement unit that obtains a film interference spectrum of a distance function by changing the detection, and a film interference spectrum of the above distance function with a wave number function of the light as a parameter for a thin film of the same material as the above thin film and having a predetermined assumed film thickness The calculation unit for calculating the simulation film interference spectrum corresponding to the above, and the film thickness of the thin film is determined by the film interference spectrum of the distance function based on the correlation between the pattern of the simulation film interference spectrum and the predetermined assumed film thickness. A film thickness measuring device comprising: