JP2003075127A - Measuring method of ultrathin film and thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring method using a spectral ellipsometer by a minimal value calculation method (BLMC), for determining precisely and accurately wavelength dependency of an ultrathin film, a thin film structure and a permittivity. SOLUTION: This measuring method using the spectral ellipsometer by the minimal value calculation method (BLMC) includes following steps. Concerning the thin film on the substrate surface which is a measuring object, measuring spectrums ΨE (λi ) and ΔE (λi ) which are the change of polarization of incident light and reflected light relative to each wavelength λi are acquired by changing the wavelength of incident light. (N0 , (n0 , k0 )) of the substrate and (d, N(n, k)) of the thin film on the substrate are assumed by using a dispersion formula, and plural film thicknesses (d±mΔd) in the anticipated range and plural incident angles (ϕ±mΔϕ) in the anticipated range are set, and each ΨM, ΔM are acquired therefrom. The ΨE, ΔE spectrums are compared with each ΨM, ΔM modeling spectrum, and fitting is performed by using the minimal value calculation method (BLMC), and a structure reaching a standard is determined as a measuring result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses data obtained by using a spectroscopic ellipsometer to calculate a minimum value (Best Local Mi
nimum Caluculation (BLMC)
The present invention relates to an ultrathin film, an ultrathin film on a substrate surface for accurately measuring the film thickness and optical constants of the thin film, and a thin film measuring method.

[0002]

2. Description of the Related Art A polarization change amount of incident light and reflected light is measured by using a spectroscopic ellipsometer, and from the result, the film thickness (d),
The complex refractive index N (N = n-ik) can be calculated. The polarization change amount (ρ) is represented by ρ = tan ψ exp (iΔ) and depends on parameters such as wavelength (λ), incident angle (φ), film thickness, and complex refractive index. Therefore, the relationship is as follows. . (D, n, k) = f (Ψ, Δ, λ, φ)

When the incident angle is fixed, in the single wavelength ellipsometer, for three unknowns of (d, n, k),
Since only two independent variables can be measured, it is necessary to fix any one of d, n, and k as known. The measurement variable increases when the incident angle is changed even at a single wavelength. However, due to the difference in the incident angle (φ) (Ψφ ₁ , Δφ
₁ ) and (Ψφ ₂ , Δφ ₂ ) have a strong correlation,
It is difficult to accurately obtain d, n, k.

[0004]

The information (Ψ _E , Δ _E ) spectrum of the polarization change amount of the multilayer thin film formed on the substrate, which is measured by using a spectroscopic ellipsometer, is the n, k information of each substrate and each layer. It includes all the information of n, k, and d. However, thin film analysis is impossible for the following reasons.

The polarization change amount can be expressed by the volume through which light passes (phase angle (β) × area of beam diameter). The phase angle (β) is expressed by the following equation. When the beam diameter is constant, the polarization change amount is as follows. Polarization change amount ∝ Thickness (d) × complex refractive index N × φ Here, φ is the incident angle. Therefore, the value of the polarization change amount also changes depending on the correctness of the incident angle. By correctly obtaining the incident angle, the value of the polarization change amount can also be correctly obtained.

As described above, the information (Ψ _E , Δ _E ) spectrum of the measured polarization change amount of the multilayer thin film includes all the n, k information of the substrate and the n, k, d information of each layer. However, from now on, n, k information of the substrate, n, k of each layer,
It is not possible to calculate the only combination of k and d information. Therefore, the optimum model is determined by fitting parameters using a dispersion formula. The dispersion formula is a formula showing the wavelength dependence of the dielectric constant of a substance, and in the near infrared to ultraviolet region, this dielectric constant ε (λ) is determined from the bonding mode of the constituent atoms of the material. As a dispersion formula, a calculation formula based on a harmonic oscillator, a calculation formula based on quantum mechanics, an empirical formula, and the like are known, and usually include two or more parameters. By calculating (fitting) this parameter, the dielectric constant ε (λ) of the material can be obtained. An object of the present invention is to set a combination model such as a film thickness and a complex refractive index, calculate a simulation spectrum of the combination model, and perform fitting of the simulation spectrum and the measurement spectrum with a minimum value calculation method (BLMC).
An object of the present invention is to provide an ultrathin film and a thin film measuring method using a spectroscopic ellipsometer by a minimum value calculation method (BLMC) for determining the structure of the ultrathin film and the thin film by using the method.

[0007]

[Means for Solving the Problems] To achieve the above object
The method according to claim 1 of the present invention is a method for calculating a minimum value.
Measurement pair using spectroscopic ellipsometer by (BLMC)
Ultra thin film on elephant substrate surface and thin film measuring method,
The thin film on the substrate surface to be measured is changed by changing the wavelength of the incident light.
Long λ_i Is the change in polarization of the incident and reflected light for each
Vector Ψ_E (λ_i ) And Δ_E (λ_i ) Ψ_E , Δ_E 
Spectrum measurement step, and (N of the substrate₀, (N₀, k
₀ )), The dispersion formula of (d, N (n, k)) of the thin film on the substrate
Multiples that are hypothesized by using
Film thickness (d ± mΔd) and multiple within expected range
Setting the incident angle (φ ± mΔφ) of
Based on the combination of elevation angle and film thickness, the dispersion formula (DS
P) parameter (ε_s,ω_t) Fitting
Step and each Ψ obtained by the fitting _M 
(λ_i ) And Δ_M (λ_i ) From the above Ψ_E (λ_i ) And Δ
_E (λ_i Film thickness (d_best) And enter
Angle of incidence (φ_best) Of the model for which a combination of
Results (DSP_best) The first step to select
And the incident angle (φ_best)
Is a definite value, and the film thickness (d_best) And dispersion formula (DS
P_best) Consists of the second step of fitting
Has been. The method according to claim 2, wherein the first and second
In step, select the one with the smallest difference
The step is the average of the fitted and measured values.
Calculate the squared error and determine the one with the smallest mean square error
It can be decided.

A method according to claim 3 is a minimum value calculation method (B
LMC) of the measurement target using the spectroscopic ellipsometer
In the ultra-thin film on the substrate surface and the thin film measurement method,
Change the wavelength of the incident light on the thin film on the elephant substrate surface
_i Measurement spectrum, which is the change in polarization of incident and reflected light for each
Tor Ψ_E (λ_i ) And Δ_E (λ_i ) Ψ_E , Δ_E Space
Microscopically non-uniform thin film on the substrate and the step of measuring
Or if some materials are mixed together,
Of board (N₀, (N₀, k₀ )), (D, N of the thin film on the substrate
(N, k)) is an effective medium approximation
ximation EMA) is used for some
Assumed model using scatter or reference data
Step and multiple membranes within expected range
Thickness (d ± mΔd) and dispersion formula used in the model
Multiple mixing ratios (V_f ± m
ΔV_f ), Multiple incident angles (φ
± mΔφ) and the incident angle and film thickness
Parameters of dispersion formula based on combination of mixing ratios
(Ε_s,ω_t ) Fitting step, and
Each Ψ obtained by fitting_M (λ_i ) And Δ_M (
λ_i ) From the above Ψ_E (λ_i ) And Δ_E (λ_i ) With
The film thickness (d_best) And angle of incidence
(Φ_best), Mixing ratio (V_fbest ) Combination
Model fitting results (DSP_best) Is selected
The first step and the incident selected in the first step
Angle (φ_best) As a definite value, the film thickness (d _best) Mixed with
Ratio (V_fbest ), Distributed type (DSP_best) Fitting
It consists of a second step of

In the ultra-thin film and the thin film measuring method on the surface of the substrate to be measured using the spectroscopic ellipsometer by the minimum value calculation method (BLMC), the thin film on the surface of the substrate to be measured is
Measurement spectra Ψ _E (λ _i ) and Δ _E, which are changes in the polarization of incident light and reflected light for each wavelength λ _i by changing the wavelength of the incident light
Ψ _E , Δ _E spectrum measurement step for obtaining (λ _i ),
The parameters of the dispersion formula are selected from the results obtained under each measurement condition by performing the steps up to the second step of claim 1 or claim 3 for each of the plurality of measurement conditions (Z _j ) within the expected range. And the mixing ratio V _f is comprised of the third step of selecting the best χ ² among the combinations having the set maximum and minimum values.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the method according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an ellipsometer used in the method of the present invention. The spectroscopic ellipsometer shown in this block diagram performs the spectroscopic measurement data acquisition step 10 of the method described below.

The Xe lamp 1 contains a large number of wavelength components,
It is a so-called white light source. The light emitted from the Xe lamp 1 is guided to the polarizer 3 via the optical fiber 2. The light polarized by the polarizer 3 is incident on the surface of the sample 4 to be measured at a specific incident angle (for example, φ = 75.00 °). The reflection from the sample 4 is caused by the photoelastic modulator (PE
M) 5 to the analyzer 6. Photoelastic modulator (P
EM) 5 phase-modulates to a frequency of 50 kHz,
From linear to elliptically polarized light is created. Therefore, Ψ and Δ can be determined with a resolution of several milliseconds. The output of the analyzer 6 is connected to the spectroscope 8 via the optical fiber 7. The output data of the spectroscope 8 is fetched by the data fetching section 9, and the step 10 of obtaining the spectroscopic measurement data is completed. PE
The position of M5 can be either after the polarizer 3 or before the analyzer 6.

Next, the case of measuring the incident angle near the nominal incident angle φ ₀ as a parameter will be described. As described above, the polarization change amount (ρ) is ρ = tan ψ exp (i
Δ), which depends on parameters such as wavelength (λ), incident angle (φ), film thickness, and complex refractive index, and the relationship is as follows. (D, n, k) = f (Ψ, Δ, λ, φ)

Even if the model is set with the nominal incident angle φ ₀ shown in FIG. 1, due to the delicate shape of the surface of the sample, etc.
It is expected that it is better to increase or decrease the incident angle φ ₀ slightly,
It is better to consider that the above-mentioned Ψ _E and Δ _E are also measured data obtained by correcting φ ₀ .

That is, in the thin film measuring method using the spectroscopic ellipsometer, the nominal incident angle in the Ψ _E , Δ _E spectrum measuring step is φ _0, and in the Ψ _M, Δ _M model simulation spectrum calculating step, the φ ₀ Simulation spectrum Ψ _M0 (λ
_i ), Δ _M0 (λ _i ) and a simulation spectrum Ψ _{Mk in} which the nominal incident angle is a function of φ _k in the vicinity of φ _0.
Obtain (λ _i ) and Δ _Mk (λ _i ). This model simulation spectrum is calculated in step and 21, and Ψ _E (λ
_i ), Δ _E (λ _i ).

FIG. 2 shows a first thin film measuring method according to the present invention.
3 is a flowchart showing an example of the above. (Step 10) Measurement is performed with the apparatus shown in FIG. (Step 20) This step is a step of converting spectroscopic measurement data into comparative data. The spectroscopic measurement data obtained in step 10 of obtaining the spectroscopic measurement data described above is divided into Ψ _E
Data is compared in the form of (λ) and Δ _E (λ).

(Step 21) This step 21 is a step of modeling a spectroscopic measurement target. Step 20
This is a step of making a model in consideration of the manufacturing process of the measurement target which is made into the comparative data. A plurality of film thicknesses (d ± mΔd) within the expected range, a dispersion formula according to the material formed on the substrate, and a plurality of incident angles (φ ± mΔφ) within the expected range are set. In this embodiment, it is assumed that the substrate is Si and the first layer SiON is 20 Å, 25 Å and 30 Å on the substrate, and the incident angle for measurement is 7
Prepare a large number of models from 5.00 ° to 0.01 ° to 75.05 °. (Step 22) In this step 22, Ψ _M , Δ _M calculated from the model and measurement data Ψ _E , Δ _E are displayed together.

(Step 23) Fitting is performed for each model. (Step 24) The result of fitting the variance value for each model is shown. The columns indicated by 24a, 24b, and 24c are the parameters (ε) of the dispersion formula (DSP) corresponding to the incident angle for SiON of 20Å, 25Å, and 30Å.
_s , ω _t ) fitting results. Here, N measurement data pairs Exp (i = 1, 2 ...
N) and the corresponding N model calculation data pairs Mod (i = 1, 2, ..., N), the measurement error has a normal distribution, and the standard deviation is σ _i , the mean square The error (χ ² ) is given as follows. Here, P is the number of parameters.

(Step 25) In this step, one incident angle and film thickness are first selected. When the film thickness is 20 Å shown in the column 24a, the result of fitting is that the incident angle is 75.
The smallest χ ² value of 0.0315 is shown at 02 ° (see the column of 24d). Film thickness 2 shown in column 24b
In case of 5Å, as a result of fitting, the incident angle is 75.0
The smallest χ ² value of 0.0242 is shown at 3 ° (see column 24e). Film thickness 30 shown in column 24c
In case of Å, as a result of fitting, the incident angle is 75.04.
The smallest χ ² value is 0.0297 at the time of ° (see the column 24f). The model of 24e showing the smallest χ ² value of 0.0242 among these (φ
_{best = 75.03 °, d best =} 25Å) is selected. (Step 26) With the incident angle (φ _best ) selected in the first step as a definite value, the fitting of the film thickness (d _best ) and the dispersion equation parameters (ε _s , ω _t ) is performed. In the example, the incident angle (φ _best ) = 75.03 ° is set as a definite value, and the fitting of the film thickness (d _best ) = 25Å and the dispersion equation parameter (ε _s , ω _t ) = (2.00, 12.58) is performed. To do. This is the second stage. (Step 27) The fitting result of the second stage is shown. In the example, film thickness d (final result) = 24.24
Å, the parameters of the dispersion formula (ε _s , ω _t ) = (2.09,
13.24) is the final result. (Step 28) Save the data calculated in the above step. (Step 29) It is confirmed whether the stored data is physically unnatural.

(Step when Data Obtained by Fitting is Not Valid) It is possible that the results obtained in the first and second steps are not physically or empirically valid. In that case, it is determined that the model settings are not good, and the constituent substances of the model are added or changed to set a different model and the fitting is performed again. Step 22 of FIG. 2 →
21, step 25 → 21, step 27 → 21 correspond to this.

Next, in the ultra-thin film and the thin film measuring method of the substrate surface of the measurement object using the spectroscopic ellipsometer by the minimum value calculation method (BLMC), the film on the substrate surface is uneven or discontinuous, and some materials are An example in the case where the two are mixed will be described. For a medium composed of a plurality of substances that are sufficiently smaller than the wavelength order and are physically mixed, the model is estimated using the effective medium approximation (EMA). The effective medium approximation (EMA) when the substance A and the substance B are mixed is a dispersion formula or reference data for the volume fraction of the substance A, the volume fraction of the substance B, the film thickness of the A + B mixed layer, and the dielectric constant. Estimate and fit
evaluate.

In this embodiment, a mixed layer of SiO ₂ and SiN is formed on a Si substrate to be measured. (Measurement step) The thin film (Si
O ₂ and SiN mixed layer), the measurement spectra Ψ _E (λ _i ) and Δ _E (λ _i ) which are changes in the polarization of the incident light and the reflected light for each wavelength λ _i are changed by changing the wavelength of the incident light. obtain. The measuring device is the same as that described above.

(Target Model Forming Step) In this step, a model in which the thin film on the substrate is a mixed layer of SiO ₂ and SiN is formed. (N of the substrate Si
₀ , (n ₀ , k ₀ )) is easily determined because the substrate is a bulk. In order to use the effective medium approximation (EMA), (d, N (n, k)) of the thin film on the substrate is modeled by using some dispersion formula or reference data. The initial value of the model of the thin film is the mixing ratio (V _f ): SiO ₂ (30%) + SiN (70
%) Thickness (d): 20Å. From here, a plurality of film thicknesses (d ± mΔd) within the expected range and
A plurality of mixing ratios (V _f ± mΔV _f ) within an expected range such as the dispersion formula used in the model and a plurality of incident angles (φ ± mΔφ) within the expected range are set.

(Dispersion Equation Parameter Fitting Step) The dispersion equation parameters (ε _s, ω _t ) are fitted based on the combination of the incident angle, the film thickness, and the mixing ratio. (First Selection Step) From the respective Ψ _M (λ _i ) and Δ _M (λ _i ) obtained by the fitting, the Ψ _E (
The film thickness (d that minimizes the difference between λ _i ) and Δ _E (λ _i )
_best ), incident angle (φ _best ) and mixture ratio (V _fbest ), the fitting result of the model (DSP)
_best ).

(Second selection step) In the first step
Selected incident angle (φ_best) As a definite value
(D _best) And mixing ratio (V_fbest ), Distributed (DS
P_best) Fitting. As a result, in the example,
SiO₂ (57.1%) + SiN (42.9%) Thickness (d): 32.5Å results.

(Step when Data Obtained by Fitting is Not Valid) It is possible that the results obtained in the first and second steps are physically or empirically invalid. It is judged that the setting of the model is not good, further, addition or change of the constituent material of the model is performed, a different model is set and fitting is performed again, and the process is repeated until a correct result is obtained. Although this step is indispensable in reality, it is an artificial judgment and is not a part of the invention.

[0026]

As described above in detail, according to the present invention, the previously difficult ultra-thin film and thin film structure are fitted by using the model and the minimum value calculation method (BLMC). It can measure accurately and accurately.

Various modifications can be made to the embodiment described above in detail within the scope of the present invention. For ease of understanding, we have used Ψ, Δ consistently in connection with data acquisition and model setup. Similar measurements and fittings are possible using the following data pairs, which are well known to those skilled in the art, and are within the scope of the present invention. (N, k), (ε _i , ε _r ), (tan Ψ, cos Δ),
(I _s, I _c ) Also, an example of forming one SiON layer on the substrate has been shown.
It can also be used to measure different multilayer structures and a wide range of film thicknesses. Although the substrate is made of Si as an example, other materials (glass, quartz, compound semiconductor, etc.) can be used as well.

In the example, the fitting was described as fitting all all parameters simultaneously,
The fitting may be performed separately, and this is also included in the technical scope of the present invention.

In the example, the fitting is described by the combination of the incident angle and the film thickness, but depending on the software, the incident angle may be fitted simultaneously with the dispersion formula, which is also included in the technical scope of the present invention. .

Even when the incident angle is fixed without fitting, it is also included in the technical range.

Although the classical formula is used as the dispersion formula in the above-described embodiments, other formulas and parameters can be used in the same manner, and these are included in the technical scope of the present invention. To do.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a spectroscopic ellipsometer used in step 10 of acquiring spectroscopic measurement data according to the method of the present invention.

FIG. 2 is a flow chart for explaining a thin film measuring method according to the present invention.

[Explanation of symbols]

1 Xe Lamp 2 Optical Fiber 3 Polarizer 4 Sample 5 Photoelastic Modulator (PEM) 6 Analyzer 7 Optical Fiber 8 Spectrometer 9 Data Acquisition Unit 10 Spectroscopic Measurement Step 20 Spectroscopic Measurement Comparison Data Conversion Step 21 Model Comparison Data Conversion Step 22 Simulation step 23 Fitting step 24 Step 25 showing fitting process First selecting a combination of one incident angle and film thickness
Step 26 Fitting step (second step) 27 Result acquisition step 28 Data storage step 29 Confirmation step

Continued front page    (72) Inventor Yoko Kazui             Ai, 4-13-4 Kitakasai, Edogawa-ku, Tokyo             Atago Bussan Co., Ltd. F term (reference) 2F065 AA30 BB22 CC31 DD00 FF50                       GG03 GG24 HH09 HH12 HH17                       HH18 JJ01 JJ08 LL02 LL33                       LL34 LL57 NN08 QQ17 QQ42                       SS03 UU05 UU07                 2G059 AA02 AA10 BB16 BB20 EE02                       EE05 EE12 GG10 JJ17 JJ19                       MM20

Claims (4)

[Claims] 1. A spectroscopic image by a minimum value calculation method (BLMC).
An ultra-thin film on the surface of the substrate to be measured using a lipometer and
And thin film measurement method, The thin film on the surface of the substrate to be measured is changed by changing the wavelength of the incident light.
Wavelength λ_i Is the change in polarization of incident light and reflected light for each
Spectrum Ψ_E (λ_i ) And Δ_E (λ_i ) Ψ_E , Δ
_E Spectrum measurement step, (N of the substrate₀, (N₀, k₀ )), Of the thin film on the substrate
(D, N (n, k)) is assumed using the dispersion formula, and
Multiple film thicknesses within the expected range (d ± mΔd) and
And multiple incident angles within the expected range (φ ± mΔφ)
And the step of setting Based on the combination of the incident angle and the film thickness, the dispersion formula
(DSP) parameter (ε_s,ω_t ) Fitting
The steps to do Each Ψ obtained by the fitting_M (λ_i ) And Δ
_M (λ_i ) From the above Ψ_E (λ_i ) And Δ_E (λ_i ) When
The film thickness (d_best) And angle of incidence
(Φ_best) Model fitty
Results (DSP_best) The first step of selecting The incident angle selected in the first step (φ_best)
As a constant value, the film thickness (d _best) And dispersion formula (DSP_best)of
Consisting of the second step of fitting, A spectroscopic ellipsometer using the minimum value calculation method (BLMC)
Ultra thin film and thin film measuring method on the substrate surface used for measurement
Law. 2. In the first and second steps,
The step of selecting the one having the smallest difference is to obtain the mean square error between the fitted value and the measured value, and determine the one having the smallest mean square error by using the spectroscopic ellipsometer by the minimum value calculation method (BLMC). Ultra thin film and thin film measuring method. 3. A spectroscopic image by a minimum value calculation method (BLMC)
An ultra-thin film on the surface of the substrate to be measured using a lipometer and
And thin film measurement method, The thin film on the surface of the substrate to be measured is changed by changing the wavelength of the incident light.
Wavelength λ_i Is the change in polarization of incident light and reflected light for each
Spectrum Ψ_E (λ_i ) And Δ_E (λ_i ) Ψ_E , Δ
_E Spectrum measurement step, The thin film on the substrate is microscopically non-uniform or some material
If they are mixed, the (N₀, (N₀, k
₀ )), (D, N (n, k)) of the thin film on the substrate
In order to use quality approximation (EMA)
Or make a model by using the reference data.
Step, Multiple film thicknesses within the expected range (d ± mΔd) and
And expected range such as the dispersion formula used in the above model
A plurality of mixing ratios (V_f ± mΔV_f ),is expected
Set multiple incident angles (φ ± mΔφ) within the range
Steps, Based on the combination of the incident angle, film thickness and mixing ratio
Dispersion parameter (ε_s,ω_t ) Fitting
Steps, Each Ψ obtained by the fitting_M (λ_i ) And Δ
_M (λ_i ) From the above Ψ_E (λ_i ) And Δ_E (λ_i )
The film thickness (d_best) And incident angle (φ
_best), Mixing ratio (V_fbest ) Combination
Dell Fitting Results (DSP_best) Choose
1 step, The incident angle selected in the first step (φ_best)
As a constant value, the film thickness (d _best) And mixing ratio (V_fbest ), Minutes
Dispersal (DSP_best) The second step for fitting
Spectroscopy based on minimum value calculation method (BLMC)
Ultra thin film on the surface of the substrate to be measured using an ellipsometer
And thin film measurement method. 4. An ultrathin film and a thin film measuring method of a substrate surface of a measurement target using a spectroscopic ellipsometer according to a minimum value calculation method (BLMC), wherein the thin film of the substrate surface of the measurement target is changed by changing the wavelength of incident light to each wavelength. Ψ _E , Δ for obtaining measured spectra Ψ _E (λ _i ) and Δ _E (λ _i ) which are changes in polarization of incident light and reflected light for each λ _i
Among the results obtained under each measurement condition, perform the _E spectrum measurement step and the second step of claim 1 or claim 3 for each of the plurality of measurement conditions (Z _j ) within the expected range. From the above, the minimum value calculation including the third step of selecting the best χ ² among the combinations in which the parameters of the dispersion formula and the mixing ratio V _{f fall} between the set maximum and minimum values Method for measuring ultra-thin film on substrate surface using spectroscopic ellipsometer by method (BLMC) and thin film measuring method.