JPH04109147A - Method and device for measuring complex refractive index - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to the measurement of the complex refractive index of thin film materials, etc., and in particular to the measurement of the complex refractive index expressed by the refractive index and extinction coefficient in the infrared and ultraviolet regions. This invention relates to a measuring method and a measuring device.

[Conventional technology]

Conventional methods for measuring the complex refractive index include ellipsometry, which utilizes the fact that the polarization characteristics of reflected light depend on the complex refractive index of the material, to measure the refractive index and extinction coefficient. The most basic technology for structural design of optical disks or photoresists is analysis based on optical theory, which requires data on complex refractive index in the infrared region (emission wavelength of semiconductor laser). Note that the complex refractive index 7 is expressed by n=n-1k, where n is the refractive index and the extinction coefficient is n.

In measurements by ellipsometry, a He-Ne laser (wavelength: 632.8 nm), which is light in the visible light range, is generally used. A thin film of the measurement material is formed on the substrate, and linearly polarized He
-Ne laser light is incident obliquely, and the state of polarization of the reflected light (the reflectance ratio of the vibration component parallel to the incident plane and the vibration component perpendicular thereto, and the phase difference between the two components) is measured. Using these data, the complex refractive index of the material to be measured is determined using a complex refractive index calculation formula derived from optical theory. These methods are discussed in detail in the Optical Technology Handbook, Breakfast Shoten (published in 1961), pages 304 to 305.

[Problem to be solved by the invention]

In the conventional method for measuring the complex refractive index, a He-Ne laser light source is used, and since the light source is visible light, the optical axis can be aligned with high accuracy, and the measurement accuracy of the complex refractive index is also high. In the case of a light source in the infrared or ultraviolet region outside the visible light region, there is a problem in that it is difficult to align the optical axes, resulting in low measurement accuracy. Furthermore, in the case of a photoresist having relatively high intensity of measurement light and photoreactivity, there is a problem that the complex refractive index fluctuates during measurement, making accurate measurement impossible.

SUMMARY OF THE INVENTION An object of the present invention is to provide a complex refractive index measuring method and apparatus for measuring the complex refractive index of a material to be measured using a light source in the infrared and ultraviolet regions. Another object of the present invention is to provide an apparatus for measuring complex refractive index in the infrared and ultraviolet regions using a spectrophotometer. Still another object of the present invention is to provide a method for measuring the complex refractive index of photosensitive photoresists and optical recording materials.

[Means to solve the problem]

In order to achieve the above object, the method for measuring a complex refractive index according to the present invention is a method for measuring a complex refractive index expressed by a refractive index and an extinction coefficient. Measure the transmittance and reflectance, measure the film thickness of the material to be measured, and calculate the reflectance and transmittance of the material to be measured based on optical theory using the film thickness and initial assumed values of refractive index and extinction coefficient. 1. Set the tolerance for error between the calculated values of reflectance and transmittance and their measured values, correct the initial assumed values according to the error, repeat the calculation until the values are below the tolerance, and then calculate the final assumed values. is determined as the refractive index and extinction coefficient of the measurement material.

The configuration is such that the allowable error value is +1 to -1%.

Further, the measurement material may be a photoresist.

Furthermore, the measuring material may be an optical recording material.

In addition, the complex refractive index measuring device includes a means for forming a thin film of a measurement material on a substrate, a means for measuring the thickness of the thin film, a means for measuring transmittance and reflectance of the thin film, and a means for measuring the refraction of the thin film. The complex refractive index is calculated by setting the assumed values of the index and extinction coefficient, repeating the calculation of transmittance and reflectance using the film thickness and calculated data, and using the refractive index and extinction coefficient that match the measured values within the tolerance range. The configuration consists of a calculation means for determining the calculation result, and a means for outputting the calculation result.

Further, the means for measuring the transmittance and reflectance of the thin film may be a spectrophotometer.

Furthermore, the complex refractive index measuring device includes a means for measuring the thickness, transmittance, and reflectance of a thin film of the measurement material formed on the substrate, and a means for storing each measured value and calculation data and storing each measured value. The structure may include means for determining a complex refractive index using a substantially satisfied refractive index and extinction coefficient.

[Effect]

According to the method for measuring a complex refractive index of the present invention, first, a thin film of the material whose complex refractive index is to be measured is formed on a transparent substrate such as quartz glass by some means (for example, a vapor deposition device, a sputtering device, etc.). .

Next, the thickness of the formed thin film is measured with a micro film thickness meter, the measurement wavelength is determined, and the transmittance and reflectance of the thin film are measured with a spectrophotometer, etc. The zero-order measured transmittance and reflection The refractive index and extinction coefficient that satisfy the index are calculated by the process shown below.

i) Assume initial values of refractive index and extinction coefficient.

it) Using the measured value of the film thickness and the initial assumed values of the refractive index and extinction coefficient, the reflectance and transmittance of the measurement material are calculated as follows based on optical theory.

This calculation method is described in IE Transactions on Electron Devices E-Day 22 (1975), pages 456 to 464 (I
E E , Trana, E 1ectronDev
ices, ED-22 (1975) PP, 456-46
4) is stated in part.

j of the multilayer film consisting of air, thin film, and substrate shown in Figure 7
-i-th amplitude reflectance rJ-1 and amplitude transmittance t1-1
is expressed by the following formula. Here, the thin film, where φ, = 2g;
(4) λ nJ=nJ ikJ, and Δd1 is the thickness of the j-th layer of the thin film divided into a plurality of pieces. The calculation starts from j=m (that is, the substrate side), proceeds sequentially to m-1, m-2, and finally reaches the thin film surface. The complex reflectance r1 and complex transmittance tlI at the interface between the substrate and the thin film are expressed by the following equations.

Here, no is the refractive index of air. Transmittance T of the entire layer
and reflectance R are calculated as shown in the following equation using to and ro finally obtained through repeated calculations using equations (1) and (2).

"Tltol" ・・・・・・・・・
・・・・・・・・・(7)Rlrol”
・・・・・・・・・・・・・・・・・・(8) In this way, the transmittance T is determined by the refractive index n, extinction coefficient k, and film thickness d.
However, it is difficult to calculate the refractive index n and extinction coefficient k from the transmittance T, reflectance R, and film thickness d. Therefore, we use the following calculation method.

in) Correct the assumed values of the refractive index and extinction coefficient little by little according to the error between the calculated value of transmittance T and reflectance R based on the initial assumed value and the measured value, and correct the error between the measured value and the calculated value. Repeat calculation until the value is below the allowable value. The method is shown in FIG. 8, and FIG. 9 is a data table for calculating the refractive index and attenuation coefficient. When calculating the transmittance T and reflectance R by changing the extinction coefficient k with respect to the refractive index n□, curve 28 and curve 3 are obtained, respectively.
When the transmittance T and reflectance R are similarly calculated for the linear refractive index n2, which is 4, the curve 31 and the curve 3 are obtained, respectively.
It will look like 3. If the measured value of transmittance is To and the measured value of reflectance is Ro, then the refractive index n from which To and RO are obtained is
x is between n2 and n3, and the extinction coefficient kx is between 2 and 8. The estimation method for nx and 8 is shown below.

First, the initial values of the refractive index n1 and n2 and the initial value of the extinction coefficient are relatively broadly assumed to be 1 and 8. Next, the transmittance T1 and the reflectance R1 for the refractive index ni and the extinction coefficient and transmittance T2 and reflectance R1 for refractive index n1 and extinction coefficient 1.
, furthermore, the refractive index n1, the extinction coefficient is the transmittance T for 2,
and reflectance R1 are calculated respectively. The refractive index nx and the extinction coefficient are calculated using the following equations.

nx=(lLe(Ro-Rt)-B2(To-TJ)/
(mtL-11zl13)÷n, ・・・・・・
...(9) kx=(I'3 (RO-R1)-11
1(To-Tj)bemzm3-1hj4)+1+++
+・+++ (10) Here, To and Ro are measured values of transmittance and reflectance, and 1m, m2, m, m are respectively expressed by the following formulas.

ml” (R, R2) / (n1n=)
−(igmt” (R1-R,) / (lc, −
) ”'(12) m, = (T1-T
yo)/(nl-B2)...(13)m, =(T□-T
, )/(kl-2)...(14) Calculate the transmittance and reflectance using the refractive index nx and extinction coefficient kx obtained in the first calculation, and calculate the measured values T0 and R distortion. Compare with. If the difference is not less than a predetermined error part 1 (usually ±1%), ±5
%, the refractive index n is B2, and the extinction coefficient is R2.
Set again and calculate T, T2, R1, and R2. Furthermore, the estimated values nX and 8 of the refractive index and extinction coefficient are calculated again using equations (9) to (14). Calculations are repeated in this manner until the error between the measured transmittance value T0, the measured reflectance value R0, and the calculated value falls below a predetermined error range.

K) In this way, the final assumed values of the refractive index and extinction coefficient finally obtained are used as the refractive index and extinction coefficient of the material, and the measurement of the complex refractive index is completed.

Furthermore, the complex refractive index measuring device operates as follows.

That is, after a thin film of the material to be measured is formed on the substrate using a thin film forming means, the thickness of the thin film is measured using a film thickness measuring means. Next, measure the transmittance and reflectance of the thin film using the transmittance and reflectance measuring means.Next, input the measured values of the film thickness, transmittance and reflectance, and the calculation program into the storage means and store them. . Using these stored data and programs, the calculation means calculates the refractive index and extinction coefficient of the measurement material, and outputs the calculation results to the output means.

The spectrophotometer described above operates as follows.

Measure the transmittance and reflectance of a thin film material formed by another device using a means for measuring transmittance and reflectance, and store the calculation data and calculation program together with the film thickness of the material measured by the other measuring device. The refractive index and extinction coefficient are calculated using a calculation program by the means for calculating the refractive index and extinction coefficient. These calculated values are output to an output means.

In addition, in the process of calculating the refractive index and extinction coefficient of a photoresist, first, a photoresist is applied to a substrate using a spinner, and then the film thickness of the photoresist is measured.

Furthermore, the transmittance and reflectance of the photoresist are measured using a spectrophotometer, and the refractive index and extinction coefficient of the photoresist are calculated using the method described above using these measured values of film thickness, transmittance, and reflectance. do.

Furthermore, in the process of calculating the refractive index and extinction coefficient of an optical recording material, first a thin film of the optical recording material is formed on a substrate, and then the film thickness, transmittance, and reflectance are measured using a spectrophotometer. Using these measured values of film thickness, transmittance, and reflectance, the refractive index and extinction coefficient of the optical recording material are calculated by the method described above.

〔Example〕

An embodiment of the present invention will be described with reference to FIG.

FIG. 1 shows a block diagram of a method for measuring a complex refractive index according to the present invention. First, a thin film 8a of the material whose complex refractive index is to be measured is formed on a transparent substrate, and then the thickness of the thin film is measured 8b, and then the transmittance and reflectance are measured 9. Calculate the refractive index and extinction coefficient using the following method. This embodiment has the advantage of providing a method for measuring complex refractive index.

Next, another embodiment of the present invention will be described with reference to FIG.

Figure 2 shows a thin film forming section (forming means) 1, transmittance and reflectance measuring section (measuring means) 2, film thickness measuring section (measuring means) 7, data input section 3, optical constant calculating section (calculating 4 shows the configuration of an optical constant measuring device consisting of a data memory section 5, and a data output section 6. Thin film forming section 1
may be provided separately, and may include devices for forming thin films of various materials, such as spinners for applying photoresist, sputtering devices suitable for forming thin films of high melting point materials, and devices for forming thin films of low melting point materials. The device comprises at least one of a suitable vapor deposition device and a chemical vapor deposition (CVD) device that utilizes chemical reactions to form thin films to form a thin film of the material whose optical constants are to be measured on a transparent substrate.

The transmittance and reflectance measurement section 2 measures the transmittance and reflectance of a material whose complex refractive index is unknown. An example of its mechanism is shown in FIG. 6 diffraction gratings 1 that are focused, corrected into parallel light by a collimator lens 13, and incident on a diffraction grating 14 for spectroscopy
Since the light reflected from the diffraction grating 14 is reflected in different directions depending on the wavelength, the wavelength of the light incident on the thin film material 17 is selected by adjusting the angle θ.
transparent substrate 18 on which a thin film 17 of the material is formed.
After passing through, the light enters the optical sensor 19. The reflected light from the thin film 17 is reflected by the half mirror 16 and enters the optical sensor 15. The transmittance and reflectance can be determined by comparing the measured values of the light intensity by the optical sensors 19 and 15, respectively, with the light source intensity. As the optical sensor 19 that receives transmitted light and the optical sensor 15 that receives reflected light, a semiconductor optical sensor using a Si pn junction or a photomultiplier tube can be used. In addition to the apparatus shown in FIG. 3, spectrophotometers with transmittance and reflectance measurement mechanisms are also available.

The complex refractive index calculation unit (calculation means) 4 sets assumed values of the refractive index and extinction coefficient of the thin film, repeats calculations of transmittance and reflectance using the film thickness and calculated data, and compares the calculated values with the measured values. The present embodiment has the effect of providing a complex refractive index measuring device, in which the complex refractive index can be determined using the transmittance and reflectance within the allowable range.

Next, a block diagram of a method for measuring refractive index and extinction coefficient using a spectrophotometer according to another embodiment of the present invention is shown in FIG.
What differs from FIG. 1 is the measurement 36 of transmittance and reflectance using a spectrophotometer. Since this embodiment uses a spectrophotometer, it has the advantage that conventional equipment can be used.

Next, a method for measuring the refractive index and extinction coefficient of a photoresist according to another embodiment of the present invention is shown in FIG.

First, photoresist coating 2o is performed on a transparent substrate using a spinner. Next, the photoresist film thickness is measured 21.
Next, the transmittance and reflectance l are measured 22, and the refractive index and extinction coefficient are calculated 23 using the method described above.In this example, the method for measuring the complex refractive index of the photoresist is There is an effect that can be provided.

Next, a method for measuring the refractive index and extinction coefficient of an optical recording material used in an optical disk, which is another embodiment of the present invention, is shown in FIG. This embodiment performs the film thickness measurement 25 of the zero-order optical recording material in which the formation 24 is performed on a transparent substrate, and the measurement 26 of the transmittance and reflectance, and then the calculation 27 of the refractive index and extinction coefficient. This has the effect of providing a method for measuring the complex refractive index of optical recording materials.

〔Effect of the invention〕

According to the present invention, it is possible to provide a method and apparatus for measuring a complex refractive index expressed by a refractive index and an extinction coefficient of a measurement material using measured values of transmittance and reflectance. Furthermore, it is possible to provide a method for measuring the complex refractive index of photoresists and optical recording materials.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is a block diagram showing another embodiment of the present invention, Fig. 3 is an enlarged view of the main part of Fig. 2, and Figs. FIG. 6 is a block diagram showing another embodiment of the present invention, FIG. 7 is a diagram explaining a method of calculating transmittance and reflectance, and FIG. 8 is a diagram explaining a method of calculating refractive index and extinction coefficient. , FIG. 9 is a diagram showing data for calculating the refractive index and extinction coefficient. 1... Thin film forming section (forming means) 2... Transmittance and reflectance measuring section (measuring means) 4.
... Complex refractive index calculation section (means for calculating) 7 ... Film thickness measurement section (means for measuring) 8a ... Thin film formation of measurement material 8b ... Thin film thickness measurement 9 ... Transmittance and Measurement of reflectance 10... Calculation agent for refractive index and extinction coefficient Tatsuno Unouma 1 Figure 2 Figure 3 Figure 5

Claims (1)

[Claims] 1. In a method for measuring a complex refractive index represented by a refractive index and an extinction coefficient, a measurement wavelength is set, and the transmittance and reflectance of the measurement material are measured using the measurement wavelength, The film thickness of the material is measured, and the reflectance and transmittance of the measurement material are calculated based on optical theory using the film thickness and the initial assumed values of the refractive index and extinction coefficient. Set a tolerance value for the error between the calculated value of the ratio and its measured value, correct the initial assumed value according to the error, repeat the calculation until the value falls below the tolerance value, and set the final assumed value as the measured value. A method for measuring multiple refractive indices, characterized in that the refractive index and extinction coefficient of a material are determined. 2. The method for measuring a complex refractive index according to claim 1, wherein the tolerance for error is +1 to -1%. 3. The method for measuring a complex refractive index according to claim 1 or 2, wherein the measuring material is a photoresistor. 4. The method for measuring a complex refractive index according to claim 1 or 2, wherein the measuring material is an optical recording material. 5. Means for forming a thin film of a measurement material on a substrate, means for measuring the film thickness of the thin film, means for measuring transmittance and reflectance of the thin film, and assumptions for the refractive index and extinction coefficient of the thin film. calculation means that calculates a complex refractive index by setting values and repeating calculations of the transmittance and reflectance using the film thickness and calculation data, and using the refractive index and extinction coefficient that match the measured values within a tolerance range; A device for measuring a complex refractive index, comprising: and means for outputting a calculation result. 6. A complex refractive index measuring device, characterized in that the means for measuring the transmittance and reflectance of a thin film is a spectrophotometer. 7. A means for measuring the thickness, transmittance, and reflectance of a thin film of the measurement material formed on the substrate, and a refractive index and extinction that store the respective measured values and calculated data and substantially satisfy the respective measured values. A device for measuring a complex refractive index, comprising means for determining a complex refractive index using coefficients.