JPH11271027A - Film thickness measuring method and film thickness measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film thickness measuring method and a film thickness measuring apparatus which are capable of highly precise measurement in the case of multilayer film structure. SOLUTION: This film thickness measuring method is provided with a first measuring process in which a specimen W is irradiated with a light, the reflected light is detected, film thickness range of a lower layer of a multilayer film is determined by a spectral reflectance system or a white light interference system, and the film thickness range of the uppermost layer is determined, and a second measuring process in which, on the basis of the film thickness range of the uppermost layer which is obtained by the first measuring process, the specimen W is irradiated with a polarized light, the state of polarization of the reflected light is analyzed, and the film thickness D1 of the uppermost layer is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the presence or absence or the thickness of a multilayer thin film formed on a substrate by using a measurement system having both an ellipsometric method and a spectral reflectance method or a white interference method. About.

[0002]

2. Description of the Related Art As a method for measuring the thickness of a thin film formed on a sample surface, an ellipsometry, a spectral reflectance method, or a white interference method is known.

The polarization analysis measures the amplitude ratio (tan Ψ) and phase difference between a polarization component (P-polarized light) in a direction parallel to the plane of incidence and a component (S-polarized light) in a direction perpendicular thereto. (△), which are functions of the refractive index n and the film thickness D.

As an example, Si formed on a Si substrate
FIG. 7A shows a relationship between tan Ψ and △ measured for the O ₂ film (0 Å to 2500 Å) and the film thickness D1. Based on this relationship, tan
By measuring Ψ and △, the film thickness D1 can be calculated.

However, in the ellipsometry, the measurement range is narrow due to the characteristics of the algorithm for calculating the thickness, and a thick film cannot be measured. That is, FIG. 7A shows the relationship between tan Ψ, △, and D1 when there is no lower layer, that is, when there is a single layer (D2 = O angstroms).

However, when a lower layer exists, that is, in the case of a multilayer film (D2 ≠ 0 angstroms), a plurality of tanΨ, Ψ exist as shown in FIG. 7B. In FIG. 7B, D2 is 0,500,100.
Tan Ψ, と き at 0.1500 Å. In addition, tan is obtained when D2 = O angstroms and when D2 = 1500 angstroms.
Ψ and △ partially overlap, making it difficult to distinguish.

On the other hand, the spectral reflectance method or the white interference method is disclosed in Japanese Patent Publication No. 7-55435 and Japanese Patent Publication No. 2-251711.
As disclosed in Japanese Patent Application Laid-Open No. 7-6 / 1990, a method of fitting a reflection spectrum and a theoretical spectrum using a film thickness as a parameter using a global optimization method to calculate a film thickness is disclosed.
3524, Japanese Patent Publication No. 8-20223, there is a method of calculating the film thickness from the characteristics of the envelope of the reflection spectrum.

[0008] These spectral reflectance methods or white interference methods can measure the film thickness over a wider range than the above-mentioned ellipsometric method, but the change of the theoretical spectrum waveform with respect to the wavelength of a thin film having a thickness of 500 Å or less is smaller. And the film thickness cannot be calculated accurately. Also,
The film thickness cannot be calculated unless the refractive index of the target film is known in advance.

In order to solve the above problem, a measurement system having both advantages of the polarization analysis system and the spectral reflectance system or the white interference system can be considered. Such a device is disclosed, for example, in Japanese Patent Application Laid-Open No. 5-71923.

That is, based on a predetermined thin film thickness control value, if the film thickness is about several hundred angstroms, the film thickness is calculated by the ellipsometry, and the thickness cannot be measured by the ellipsometer. The film thickness is measured by a spectral reflectance method or a white interference method.
The refractive index required by the spectral reflectance method or the white interference method is measured by an ellipsometry.

[0011]

However, the above-mentioned conventional film thickness measuring method has the following problems. That is, the ellipsometry measures tan Ψ and △ to measure the film thickness D, but this is effective only when the film formed on the substrate is a single-layer film, and the film to be measured is as shown in FIG. In the case of a multi-layered film, if the thickness of the uppermost film is the same and the thickness of the lower layer is different, a plurality of tan Ψ and △ appear as shown in FIG.

In addition, since the management value information of the thickness of the thin film is performed in advance and the polarization analysis method, the spectral reflectance method, or the white interference method is selected, which measurement method is to be selected when the film thickness is indefinite. There was a problem that it could not be decided.

Accordingly, an object of the present invention is to provide a film thickness measuring method and a film thickness measuring device capable of performing highly accurate measurement even with a multilayer film structure.

[0014]

Means for Solving the Problems In order to solve the above problems and achieve the object, the invention according to claim 1 is a method for measuring the thickness of the uppermost layer of a multilayer film formed on a sample surface. In the measurement method, light is incident on the sample, the reflected light is detected, and the thickness range of the lower layer of the multilayer film is determined by a spectral reflectance method or a white interference method, and the thickness range of the uppermost layer is determined. A first measuring step, and based on the thickness range of the uppermost layer obtained in the first measuring step, the polarized light is made incident on the sample, and the polarization state of the reflected light is analyzed to determine the polarization state of the uppermost layer. A second measurement step of measuring the film thickness.

According to a second aspect of the present invention, in the first aspect, the first measuring step calculates the film thickness of the uppermost layer from a difference between a maximum value and a minimum value of a reflection spectrum. I decided that.

According to a third aspect of the present invention, there is provided a film thickness measuring device for measuring a thickness of an uppermost layer of a multilayer film formed on a surface of a sample, wherein light is incident on the sample and reflected light thereof is detected. A first measuring unit for determining a film thickness range of the lower layer and a film thickness range of the uppermost layer by the spectral reflectance method or the white interference method, and a film thickness range of the uppermost layer obtained in the first measuring unit Based on the above, a polarized light is made incident on the sample, the polarization state of the reflected light is analyzed to measure the thickness of the uppermost layer, and a calculation method is selected according to the measured thickness. And a calculation method selection unit for performing the calculation.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the calculation method selecting section is configured to determine whether the film thickness calculated by the first measuring section is equal to or less than a predetermined thickness. The measurement was performed by the second measurement unit.

As a result of taking the above-described measures, the following operation occurs. That is, in the invention described in claim 1, light is incident on the sample, the reflected light is detected, and the thickness range of the lower layer of the multilayer film is determined by the spectral reflectance method or the white interference method. After determining the film thickness range, based on this film thickness range, polarized light is made incident on the sample, the polarization state of the reflected light is analyzed, and the film thickness of the uppermost layer is measured. In this case, signals can be separated, and highly accurate film thickness measurement can be performed.

According to the second aspect of the present invention, in the first measuring step, the film thickness of the uppermost layer is calculated from the difference between the maximum value and the minimum value of the reflection spectrum. It can be performed.

According to the third aspect of the present invention, the light is incident on the sample, the reflected light is detected, and the film thickness range of the lower layer and the film thickness range of the uppermost layer are determined by a spectral reflectance method or a white interference method. The thickness range of the uppermost layer is determined, and the polarized light is incident on the sample based on the thickness range, and the thickness of the uppermost layer is measured by analyzing the polarization state of the reflected light. Therefore, when performing ellipsometry, signals can be separated, and highly accurate film thickness measurement can be performed.

According to the fourth aspect of the present invention, the calculation method selection unit performs the measurement by the second measurement unit when the film thickness calculated by the first measurement unit is equal to or less than a predetermined thickness. An optimal measurement method can be selected according to the film thickness.

[0022]

FIG. 1 is a diagram showing a configuration of a film thickness measuring apparatus 10 according to an embodiment of the present invention. The film thickness measurement device 10 includes a measurement system 11 of a spectral reflectance system and a measurement system 12 of an ellipsometry arranged above the sample W, and an arithmetic unit 20 for calculating the film thickness of the sample W from these outputs. ing.

The calculation unit 20 includes a spectral reflectance type film thickness calculation unit 21, an extreme value detection unit 22, a calculation method selection unit 23, and an ellipsometry type film thickness calculation unit 24. The calculation method selection unit 23 has a function of selecting whether or not to perform the film thickness measurement by the polarization analysis method based on the film thickness value measured by the spectral reflectance method film thickness calculation unit 21.

In the film thickness measuring apparatus 10 configured as described above, the thickness of the uppermost film of the multilayer film formed on the sample W is measured as follows. FIG. 2 schematically shows a multilayer film. The thickness of the film K1 is D1, the thickness of the film K2 is D2,..., And the thickness of the film Kn is Dn.

First, the thickness of the multilayer film is measured by the measuring system 11 of the spectral reflectance type. The reflectance R of the multilayer film having the film configuration shown in FIG. 2 is derived as follows. However, it is assumed that the incident light is perpendicularly incident on the target film. The characteristic matrix Mn of the film Kn is represented by Expression (1).

[0026]

(Equation 1)

Since the characteristic matrix M of the multilayer film is a product of the characteristic matrices of the respective layers,

(Equation 2)

Therefore, assuming that the amplitude reflectance of the multilayer film shown in FIG. 2 is r, the reflectance R is expressed by equation (4).

[0029]

(Equation 3)

[0030] Here, for example, a substrate as shown in FIG. 3 (n _S = 3.85-0.02i) film on K2 (n ₂ =
2.0), on which the membrane K1 (n ₁ = 4.5-0.5i)
Consider a multilayer film structure as follows.

First, when the film thickness of the lower layer is roughly known, that is, when the film thickness D2 = 0 angstrom and the film thickness D2 = 1500 angstrom, the film thickness D1 = O
The spectrum at 1000 to 1000 angstroms is as shown in FIGS. Here, a difference appears in the number and size of the maximum value and the minimum value, and the corresponding wavelength.

Therefore, the film thickness to be measured is, for example, (D1, D2) = (0 to 1000 angstroms, O
Angstrom) or (D1, D2) = (O
１０００1000 Å, around 1500 Å).

Next, the film thickness D1 can be measured by the measurement system 12, which is an ellipsometry, based on any of α to δ in FIG.

If the thickness range of the lower layer is not known, the thickness range can be further limited by the following method using the spectral reflectance method. That is, D1 = 0 angstroms, D
The spectrum at 2 = 1500 angstroms is as shown by ε in FIG. 5, and the maximum value R0m
The difference C0 between ax and the minimum value R0min is R0max−R0m.
can be expressed as in.

Similarly, D1 is 0 angstrom to 100.
Difference C between local maximum and local minimum at 0 Å
When i is Ci = Rimax−Rimin and the film thickness D2 is 1500 Å ± 100 Å, the difference C measured by the spectral reflectance method is obtained from FIG.
When i is 0.25, for example, the existing range of the film thickness D1 is 16
0 angstrom or about 450 angstrom to 550 angstrom.
The range of 1 and D2 can be further limited. As a result, the thickness measurement range by the ellipsometry can be limited, and the accuracy of the thickness measurement can be improved.

That is, according to the film thickness measuring apparatus according to the present embodiment, even if a sample whose thickness is unknown is given, the range of the film thickness is limited by the spectral reflectance method and the film thickness is 1000 Å or less. If it is found, the thickness is calculated based on the approximate value by the ellipsometry, and if it is found that the thickness is several thousand angstroms to several tens of μm, the measured value by the spectral reflectance method is used. The film thickness can be accurately measured without performing the film thickness information. Further, since the approximate value of the film thickness can be obtained by the spectral reflectance method even in the thin film region, the measurement accuracy when the polarization analysis method is used can be improved.

Therefore, it is possible to accurately measure the thickness of a multilayer film having an arbitrary thickness from several tens of μm to a thin film of 1000 Å or less.

The present invention is not limited to the embodiment. That is, in the above-described embodiment, the measurement is performed by the spectral reflectance method, but the measurement may be performed by the white interference method. In addition, it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0039]

According to the present invention, light is incident on a sample, the reflected light is detected, and the thickness range of the lower layer of the multilayer film is determined by a spectral reflectance method or a white interference method.
The thickness range of the uppermost layer is determined, and based on this thickness range,
Since the polarized light is made incident on the sample and the polarization state of the reflected light is analyzed to measure the thickness of the uppermost layer, signals can be separated when performing polarization analysis,
Highly accurate film thickness measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a film thickness measuring apparatus according to one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the principle of film thickness measurement by a spectral reflectance method.

FIG. 3 is an explanatory diagram showing the principle of applying a spectral reflectance method to a two-layer film.

FIG. 4 is a diagram showing a spectrum when D2 = 0 angstrom;

FIG. 5 is a diagram showing a spectrum when D2 is around 1500 angstroms.

FIG. 6 is a diagram showing a relationship between Ci and D1 when D2 is around 1500 angstroms.

FIG. 7 shows tan Ψ, Δ,
The figure which shows the relationship of D1 and D2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Film thickness measuring device 11, 12 ... Measurement system 20 ... Calculation part 21 ... Spectral reflectance type film thickness calculation part 22 ... Extreme value detection part 23 ... Calculation method selection part 24 ... Polarization analysis type film thickness calculation part

Claims (4)

[Claims] 1. A film thickness measuring method for measuring a film thickness of an uppermost layer of a multilayer film formed on a surface of a sample, wherein light is incident on the sample, reflected light is detected, and a spectral reflectance method or a white interference method is used. Determining the thickness range of the lower layer of the multilayer film, and determining the thickness range of the uppermost layer, based on the thickness range of the uppermost layer obtained in the first measurement step. A second measuring step of causing polarized light to be incident on the sample, analyzing the polarization state of the reflected light, and measuring the thickness of the uppermost layer. 2. The film thickness calculation method according to claim 1, wherein said first measurement step calculates a film thickness of said uppermost layer from a difference between a maximum value and a minimum value of a reflection spectrum. 3. A film thickness measuring device for measuring a film thickness of an uppermost layer of a multilayer film formed on a surface of a sample, wherein light is incident on the sample, reflected light is detected, and a spectral reflectance method or a white interference method is used. A first measuring unit for determining the thickness range of the lower layer and the thickness range of the uppermost layer of the multilayer film, and converting polarized light based on the thickness range of the uppermost layer obtained in the first measuring unit. A second measurement unit configured to measure the thickness of the uppermost layer by analyzing the polarization state of the reflected light that is incident on the sample and a calculation method selection unit that selects a calculation method according to the measured film thickness; A film thickness measuring device, characterized in that: 4. The apparatus according to claim 1, wherein said calculation method selection section performs measurement by said second measurement section when the film thickness calculated by said first measurement section is equal to or less than a predetermined thickness. 4. The film thickness measuring device according to 3.