JPH07318321A - Method and apparatus for evaluation of film thickness of thin film - Google Patents

Abstract

PURPOSE:To evaluate a film thickness simply and with high precision by measuring the transmittance and the reflection factor of a thin film when light at a prescribed wavelength is incident on the thin film-whose film thickness is unknown. CONSTITUTION:In a standard sample 1, a thin film 12 of chromium oxide or the like in a thickness of d1 is formed on a quartz substrate 11. In a standard sample 2, a thin film 13 of chromium oxide or the like in a thickness of d2 is formed on a quartz substrate 11. In a data input part 21, individual measured values of the film thickness, the transmittance and the reflection factor of the standard samples 1, 2 as well as of the transmittance and the reflection factor of a thin film, to be measured, whose film thickness is unknown are input from the outside. An arithmetic part 22 finds individual computed values of the refractive index and the attenuation coefficient of the standard samples 1, 2 as well as of the film thickness of the thin film to be measured, and it judges and evaluates a solution in which an optical constant coincides with values of the film thickness, the transmittance and the reflection factor by the standard samples 1, 2. The individual measured values and the individual computed values are stored in a data storage part 23 temporarily or permanently, and a data output part 24 outputs the individual measured values and the individual computed values to the outside as an RT chart or numerical values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film thickness evaluation method and a thin film thickness evaluation apparatus, and more particularly, as represented by an optical component of a semiconductor integrated circuit manufacturing apparatus such as IC or LSI.
The present invention relates to a thin film thickness evaluation method and a film thickness evaluation device suitable for use in manufacturing a thin film optical element having delicate and uniform optical characteristics.

[0002]

2. Description of the Related Art Conventionally, for example, as an optical mask used in a lithography process of a semiconductor integrated circuit, a color filter used as one component of a liquid crystal display, an optical lens used as one component of an exposure apparatus, and one component of a CCD image pickup tube. A thin film optical element is known as an important component when performing optical image processing or image transfer such as a CCD filter used. The characteristics required for these thin film optical elements vary depending on the application, but in many cases, the optical constants such as transmittance, reflectance, refractive index, and attenuation coefficient when a light of a predetermined wavelength is incident on the thin film, the film Optical characteristics such as thickness and phase difference are directly related to the performance of the optical element. Therefore,
It is indispensable to directly or indirectly measure and evaluate these optical characteristics, and strict evaluation standards are usually set for these optical characteristics.

In manufacturing the thin film optical element, it is necessary to establish a method and an apparatus for measuring and evaluating various optical characteristics. FIG. 6 is a diagram showing an example of a conventional method for measuring the optical characteristics of a thin film optical element. After a target sample is prepared, film thickness measurement, transmittance / reflectance measurement, refractive index, attenuation coefficient, etc. Each measurement of optical constants is done separately. In each of the above measurements,
A dedicated measuring device is used for each characteristic.
Of course, depending on the purpose, it is not necessary to carry out all the above-mentioned measurements, and in some cases, optical characteristics other than the above, such as polarization, birefringence, absorbance, etc., may be additionally measured.

Here, each of the above measuring methods will be described in detail. First, the method of measuring the film thickness will be described. There are various methods for measuring the film thickness, but generally they can be roughly divided into contact measurement and non-contact measurement. The former is a straight needle type step measurement method, the latter is multiple reflection interferometry and ellipsometry. Is a typical measurement method. In the straight needle type step measuring method, for example, a minute needle of high hardness having a constant needle pressure, such as a diamond needle, is dropped into a groove portion of a thin film to be measured and scanned, and vertical vibration of the needle at the time of this scanning. Is a method of calculating the film thickness by converting into an electric signal, and the film thickness is generally output directly to a chart paper or the like or is displayed on the display after calculation by a built-in computer, which is relatively simple. Therefore, this method is often used in the actual production process.

Further, the multiple reflection interferometry or ellipsometry is a method of measuring each reflected light on the surface of the thin film and the surface of the substrate and obtaining the film thickness or the optical constant by optical calculation in consideration of the multiple interference effect in the film. It is possible to measure with high precision,
There is a feature that the product is not damaged because it is non-contact.
Among them, the ellipsometer applying the ellipsometry method has some difficulty in setting the conditions, but it is possible to perform highly accurate measurements by increasing the sensitivity of the measurement system, and the measured values can be calculated quickly using a computer. Therefore, it is often used.

Next, a method of measuring the transmittance and the reflectance will be described. A spectrophotometer is usually used to measure the transmittance and reflectance of a thin film. With this spectrophotometer, the absorption, reflection, etc. of light from an optical element can be measured.The transmittance is the energy intensity ratio of the transmitted light when air or a substrate is used as a reference, and the reflectance is the reflection. It is defined as the energy intensity ratio of light. Figure 7
FIG. 4 is a diagram showing an example of a spectral curve showing the relationship between the wavelength of light of the thin film optical element and the transmittance (T) and reflectance (R). Here, the transmittance and reflectance at any wavelength within the measurement range can be obtained. The transmittance and the reflectance depend on the material of the thin film, that is, the optical constant of the thin film, and the film thickness.

Next, a method for measuring optical constants such as a refractive index and an attenuation coefficient will be described. The refractive index and the extinction coefficient are physical properties that are determined by the composition and structure of the material that forms the thin film, and are defined as the complex refractive index in a material that absorbs light, and the complex refractive index (n _mul. = N-ik) The real part (n) is called the refractive index, and the imaginary part (k) is called the attenuation coefficient (or extinction coefficient). These optical constants are basic quantities that represent the magnitude of the interaction between light and matter, and are important physical properties that are always dominant in most optical phenomena. The refractive index is a physical quantity of light velocity (c) in vacuum and light velocity (v) in a medium.
It is defined as the ratio (c / v) to the refractive index of the thin film, but when obtaining the refractive index of the thin film, the refractive index is usually obtained from the polarization and phase components of light by optical measurement, that is, reflection polarization measurement. Similarly, the attenuation coefficient is also obtained by optical measurement. The optical constants can be measured by ellipsometry or Kramers-Kroch.
Nig) Reflected light measurement by an analysis method or the like is generally performed.

On the other hand, according to the optical theory, it is known that there is a peculiar relationship between the above-mentioned optical characteristics. Based on this optical theory, the wavelength (λ) and the refractive index ( n) and optical constants such as attenuation coefficient (k) and film thickness (d)
With, the transmittance (T) and the reflectance (R) can be obtained. The optical theory is a theory that handles diffraction and interference phenomena of light in a broad sense, and is known as an optical thin film theory in a narrow sense. This optical theory is, for example, written by Born and Wolf:
"Principles of optics" I-III "(Tokai University Press, 197)
5) etc. are described in detail. The calculation formula for a single-layer thin film is shown below. As shown in FIG. 9, the refractive indices are n0 and n2, respectively.
Consider a case where there is a thin film having a uniform thickness d1 with a refractive index n1 between the two media and the light is transmitted in the vertical direction from the boundary surface a to the boundary surface b. The reflectance R and the transmittance T are expressed by the following equations using Fresnel's law.

[Equation 1] δ1 = 4πn1d1 / λ (2) T = 1-R (3) Since the refractive index is treated as a complex number in the case of an absorbing metal thin film, the formula is more complicated than the above, but the same applies. Can be asked. Based on this optical theory, optical constants such as the refractive index (n) and the attenuation coefficient (k) of the thin film can be obtained from the measured values of the transmittance, reflectance and film thickness of the thin film. It is called “RT method”.

FIG. 10 is a so-called RT chart and shows the relationship between the refractive index (n) and the attenuation coefficient (k) at each transmittance (T) and reflectance (R).
In this RT chart, the wavelength of light and the film thickness of the thin film that is the object to be measured are fixed, and the refractive index (n) and attenuation coefficient (k) and reflectance (R), refractive index (n) and attenuation coefficient ( The relation between k) and the transmittance (T) is calculated and the result is shown as a contour map. Here, two types of contour maps are displayed in an overlapping manner for convenience. In this RT chart, the reflectance (R) and the transmittance (T) are obtained from the respective values of the refractive index (n) and the attenuation coefficient (k), and conversely the reflectance (R)
The refractive index (n) and the attenuation coefficient (k) are obtained from the respective values of the transmittance and the transmittance (T).

However, in the latter case, the solutions of the refractive index (n) and the attenuation coefficient (k) are not limited to one, and there may be a plurality of solutions. In this case, in order to determine the actual refractive index (n) and attenuation coefficient (k), in a thin film manufactured under the same conditions, the refractive index (n) and the attenuation coefficient (k) usually change depending on the film thickness. Since it can be assumed that this is not the case, the reflectance (R) and the transmittance (T) of each of several different thin film thicknesses may be measured to determine a suitable solution. According to this RT chart, the reflectance (R) and the transmittance (T) can be read from the refractive index (n) and the attenuation coefficient (k), and conversely from the reflectance (R) and the transmittance (T) to the refractive index ( Since n) and the damping coefficient (k) can be read, the characteristic value can be easily obtained.

[0011]

By the way, in the above-mentioned straight needle type step measuring method, since noise is generated due to the roughness of the surface of the thin film to be measured, the measurement error is large and the measured value tends to be unstable. There was a point. If the scanning speed is slowed down, noise can be reduced and the accuracy can be improved to some extent, but it takes a lot of time and the convenience is lost. In addition, in order to form a measurable groove in a thin film, it is necessary to form a pattern on the substrate after forming the thin film, which means that a kind of destructive test is performed. There was a problem that it could not be used as.

In addition, the film thickness measurement by the ellipsometry method has a problem that the influence of the reflection on the substrate surface cannot be completely removed in the optical calculation and an accurate measured value may not be obtained. Theoretically, the value of the film thickness in ellipsometry can be obtained as a plurality of solutions as a periodic solution in calculation, and therefore different information for determining the optimum value, for example, when the film thickness range can be limited from the manufacturing conditions, is necessary. Especially when the film thickness is small, the interval of the periodic solution of the film thickness becomes narrow, so that it becomes difficult to select the optimum value. Further, when the measurement wavelength is in the ultraviolet region, the change in the optical characteristics becomes large depending on the substrate material, so that the influence of the reflection of the substrate becomes relatively large, which may affect the film thickness measurement.

Further, in this ellipsometry, there is a problem that the average characteristic analysis of the thin film becomes complicated because the optical constants change very sharply at the boundary surface such as the film surface and the substrate surface. there were. Specifically, for example, when there is an extremely thin oxide layer on the surface of the thin film, or when the boundary layer between the substrate and the thin film has a mixed composition, the optical properties of the inside of the thin film and the oxide layer or boundary layer are Since the constants are different, they are sensitive to the influence of these layers, and there are problems that the measured value changes and the error increases. Therefore, in order to eliminate these error factors during measurement and obtain a more accurate film thickness measurement value, it is necessary to have a high degree of optical knowledge and grasp the optical characteristics under various conditions through many preliminary experiments. there were. From the above, when non-contact and simple measurement is required in the film thickness measurement of a thin film, it is difficult to satisfy this requirement by using any of the above methods.

On the other hand, in the RT method, since each characteristic value is read from the RT chart, the accuracy of each characteristic value is limited by the accuracy of the scale of the RT chart and cannot be improved.
There is also a problem that reading errors are unavoidable. Of course, the accuracy can be improved by subdividing the scale of the RT chart, but the number of charts increases, which requires time and effort for preparation, and the accuracy is actually limited due to measurement errors and calculation errors. Also, RT
Since the chart uses wavelength and film thickness as parameters and depends on these values, it is necessary to prepare a large number of charts according to the required wavelength and film thickness, and also when the measurement wavelength, film thickness, etc. are changed. However, it was inconvenient because of the labor required for preparation before the measurement, such as the need to newly create an RT chart.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thin film thickness evaluation method and a thin film thickness evaluation apparatus that enable simple and highly accurate film thickness evaluation. .

[0016]

In order to solve the above problems, the present invention employs the following thin film thickness evaluation method and film thickness evaluation apparatus. That is, in the thin film thickness evaluation method according to claim 1, light having a predetermined wavelength is incident on a thin film of unknown film thickness, and the transmittance and reflectance of the thin film are measured. The film thickness of the thin film is obtained from the refractive index and the attenuation coefficient of the thin film.

According to a second aspect of the present invention, there is provided a thin film thickness evaluation method, wherein light having a predetermined wavelength is incident on one or more standard thin films, and the thickness, transmittance and reflectance of each standard thin film are measured. Obtaining the refractive index and the attenuation coefficient of the standard thin film from these measured values, then, incident light of a predetermined wavelength on the thin film to be measured unknown film thickness, to measure the transmittance and reflectance of the thin film to be measured,
The film thickness of the thin film to be measured is determined from the measured values of the transmittance and the reflectance and the refractive index and the attenuation coefficient of the standard thin film.

Further, a thin film thickness evaluation method according to claim 3 is the thin film thickness evaluation method according to claim 2, wherein the film thickness and the measured thin film are calculated based on the film thickness of the measured thin film. It is characterized in that a ratio to a desired film thickness and a predicted transmittance and a predicted reflectance when the film thickness of the thin film to be measured is set to the desired film thickness are obtained.

Further, in the thin film thickness evaluation apparatus according to the present invention, the measured values of the standard thin film thickness, the transmittance and the reflectance, and the measured thin film of the unknown thickness and the reflectance are input. A data input part, a refractive index and an attenuation coefficient of the standard thin film based on each measured value, a calculation part for determining and evaluating each calculated value of the film thickness of the measured thin film, each measured value and each calculation A data storage unit for storing values and a data output unit for outputting the measured values and the calculated values are provided.

According to a fifth aspect of the present invention, there is provided a thin film thickness evaluation apparatus according to the fourth aspect, wherein the arithmetic unit is configured to determine the thickness of the thin film based on the thickness of the thin film to be measured. A calculation means was provided for obtaining and evaluating the ratio of the measured thin film to the desired film thickness, and the calculated values of the predicted transmittance and predicted reflectance when the film thickness of the measured thin film is the desired film thickness. It is characterized by that.

[0021]

In the thin film thickness evaluation method according to the first aspect of the present invention, the transmittance and the reflectance of the thin film when a light of a predetermined wavelength is incident on the thin film having an unknown thickness are measured. Quickly and accurately determine the thickness of thin films.

Further, in the thin film thickness evaluation method according to the second aspect, the refractive index and the attenuation coefficient when the light having the predetermined wavelength is incident on the standard thin film serving as a reference are obtained in advance, and then the light having the predetermined wavelength is obtained. By measuring the transmittance and reflectance of the measured thin film when incident on the measured thin film of unknown film thickness,
The film thickness of the thin film to be measured is quickly and accurately determined.

Further, in the thin film thickness evaluation method according to the third aspect, a desired value is obtained by obtaining a ratio of the desired film thickness of the measured thin film based on the film thickness of the measured thin film. The film thickness to be corrected with respect to the film thickness of is easily and accurately obtained. Further, the transmittance and the reflectance of the obtained thin film are measured by obtaining the predicted transmittance and the predicted reflectance when the film thickness of the thin film to be measured is the desired film thickness, and these measured values are By comparing the predicted transmittance and the predicted reflectance, a suitable film thickness can be quickly obtained.

Further, in the thin film thickness evaluation apparatus according to the present invention, the data input unit measures the thickness, transmittance and reflectance of the standard thin film, and the transmittance and reflectance of the measured thin film of unknown thickness. By inputting a value, the calculation unit determines the refractive index and the attenuation coefficient of the standard thin film based on each measured value, obtains each calculated value of the film thickness of the measured thin film, determines and evaluates it, and each measured value is stored by the data storage unit. And save each calculated value. The measured values and the calculated values are output by the data output unit. This makes it possible to measure the film thickness of the thin film to be measured stably, quickly and with high accuracy.

Further, in the thin film thickness evaluation apparatus according to the fifth aspect, the calculating unit is configured to
Computation means for calculating the ratio between the film thickness and the desired film thickness of the thin film to be measured, and the calculated values of the predicted transmittance and the predicted reflectance when the film thickness of the thin film to be measured is the desired film thickness. With the provision, the film thickness to be corrected of the thin film can be easily and quickly obtained, and the film thickness can be easily and quickly managed.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 FIG. 1 is a flow chart showing a method for evaluating the film thickness of a thin film of Example 1 of the present invention, and FIG. 2 is two thin film optical elements having different standard film thicknesses (standard thin film; hereinafter referred to as standard sample). )
It is a schematic diagram which shows the transmission and reflection of each light. In the standard sample 1 shown in FIG. 2, for example, a thin film 12 of chromium oxide or the like having a thickness d1 is formed on a transparent quartz substrate 11, and in the standard sample 2, for example, a thin film 12 having a thickness d2 is formed on the transparent quartz substrate 11. A thin film 13 of chromium oxide or the like is formed.

FIG. 3 is a block diagram showing a thin film thickness evaluation apparatus of Example 1 of the present invention.
Is a data input section for inputting the measured values of the film thickness, the transmittance and the reflectance of the standard samples 1 and 2 and the measured transmittance and the reflectance of the thin film to be measured whose film thickness is unknown, and 22 is based on the measured values. The calculated values of the refractive index and the attenuation coefficient of the standard thin films 1 and 2 and the film thickness of the thin film to be measured are calculated,
An arithmetic unit for determining and evaluating a solution in which the optical constants match the film thickness, the transmittance, and the reflectance value, and 23 is a data storage unit that temporarily or permanently stores the measured values and the calculated values. 24 indicates the measured value and the calculated value by RT.
It is a data output unit that outputs it as a chart or numerical values to the outside. The calculation unit 22 has a secondary function of calculating an unknown value based on the optical theory when one of the optical characteristic values is unknown and the other values are known. FIG. 4 is a flow chart showing the operation of the film thickness evaluation device.

Next, a method for obtaining the optical constant of the standard sample by using the film thickness evaluation device will be described. First, using a spectrophotometer, light of wavelength λ is incident on the standard samples 1 and 2, and the transmittance T1 of the standard sample 1 at the transmitted light t1 and the reflectance R1 of the reflected light r1 at the standard sample 2 are measured.
T2 in the case of reflection light and reflectance R2 in the reflected light r2
And the respective film thicknesses d1 and d2 of the standard samples 1 and 2 (where d1 ≠ d
2) is measured directly. Then, the wavelength λ, the film thickness d1 of the standard sample 1, the transmittance T1 and the reflectance R1, the film thickness d2 of the standard sample 2, the transmittance T2, and the reflectance R2 are respectively input to the data input unit 21 of the film thickness evaluation apparatus. input.

In the calculation unit 22, the measured values, that is, the wavelength λ, the film thickness d1 of the standard sample 1, the transmittance T1 and the reflectance R1, the film thickness d2 of the standard sample 2, the transmittance T2 and the reflectance R are obtained.
By substituting each value of 2 into the following equations (1) and (2), the solution of only one compatible optical constant of the standard sample, that is, the only refractive index n and the extinction coefficient k are obtained. The calculation procedure is as follows. First, in order to obtain the values of n and k from a set of measured values of d, R and T (denoted as Y), the successive approximation method (Newton-Raphson method) is used.
Calculate using d). FIG. 5A shows an algorithm of the successive approximation method.

In this calculation, the values of Y and the initial values of n and k (set as X) set in an appropriate range are input, and the values of R and T calculated from the initial values (Y '). ) And the measured value. This calculation is repeated to bring it closer to the actually measured value, and finally the value of the solution at which the difference becomes almost 0 is obtained. However, the value of the solution may be different depending on how the initial value is taken, that is, the starting point of the calculation is different. In the actual calculation procedure, the appropriate range of n and k values and the step size are set in consideration of the characteristics of the target substance, and the same calculation is performed for all the points Xi (ni, ki) to obtain different solutions. look for.

Next, as shown in FIG. 5 (b), two or more sets of measured values Yi (di, Ri, Ti) are calculated by the successive approximation method, and a match is found among the obtained solution sets Xi. Value, that is, a common solution for different measured values Y is obtained. At this time, the Fresnel equations (1) to (3) described above may be used as the equations for calculating R and T, but the following matrix method is more convenient for computation using a computer. The following formula is a formula for calculating R and T in the case of a single layer film by the matrix method.

[Equation 2] N1 = n1-ik1 (5a) δ1 = 2πN1d1 / λ (5b)

[Equation 3]

[Equation 4]

For example, when obtaining the value of the optical constant from the measured value of only one standard sample 1, there is a possibility that a negative value or a plurality of values may be theoretically obtained. By limiting in advance, an appropriate value can be obtained more reliably. For example, n> 1.0 and k> 0. If multiple solutions are still obtained, the optical constant does not change due to the difference in film thickness, so only the solution that matches between multiple standard samples 1 and 2 can be regarded as a compatible solution. Thus, the optical constants of the standard samples 1 and 2 can be determined. That is, a plurality of standard samples 1, 2
The measured value of can be used to determine the unique optical constant in any case.

In the data storage unit 23, the wavelength λ, the film thickness d1 of the standard sample 1, the transmittance T1 and the reflectance R1, the film thickness d2 of the standard sample 2, the transmittance T2 and the reflectance R2, and the refractive index n.
And the damping coefficient k. Here, the data output unit 2
4, the measured values and the calculated values can be taken out.

Next, the film thickness of a thin film optical element of unknown film thickness (hereinafter referred to as a target sample) is evaluated. The target sample is a thin film material having the same composition as the standard samples 1 and 2, and thin film materials having the same composition are formed on the same type of substrate under the same conditions.
Next, the transmittance and reflectance of the target sample are measured, and these measured values are input to the data input unit 21. The computing unit 22 can obtain a suitable film thickness by using these measured values and the optical constant values of the standard sample stored in the data storage unit 23.

Here, it is assumed that the thin films produced under the same conditions have the same optical constants, and it has been confirmed that sufficient reproducibility can be obtained within the measurement error. Further, when the target film thickness is set, the deviation amount between the film thickness value obtained by the film thickness evaluation device and the target film thickness value is obtained, and the transmittance when the film thickness is corrected to the target film thickness Also, the reflectance can be obtained as a predicted value. As described above, by performing film formation under the same conditions as the standard sample and using the film thickness evaluation device, the film thickness can be obtained and evaluated only from the measured values of the transmittance and the reflectance.

As described above, according to the method for evaluating the film thickness of a thin film of this embodiment, the film thickness of the target sample can be quickly and highly accurately obtained only by measuring the transmittance and reflectance of the target sample. You can Further, by measuring the transmittance and reflectance of the target sample of unknown film thickness and comparing these measured values with the predicted transmittance and predicted reflectance, the suitable film thickness can be quickly obtained.

Further, according to the thin film thickness evaluation apparatus of this embodiment, the film thickness of the target sample of unknown film thickness can be obtained stably, quickly and with high accuracy. Further, the film thickness of the target sample to be corrected can be measured easily and quickly, and the film thickness can be controlled easily and quickly.

[Embodiment 2] FIG. 5 is a schematic diagram showing light transmission and reflection of each of a plurality of thin film optical elements having different film thicknesses, to which the thin film thickness evaluation method of Embodiment 2 of the present invention is applied. is there. The thin film optical element is a projection exposure transfer master plate (so-called optical mask) in a lithography process of a semiconductor circuit.
Among the optical mask blanks which are the materials of (1), it is used for manufacturing the halftone mask blank used in the "halftone phase shift method" which is one means of the phase shift exposure technique.

First, as shown in FIG. 6A, a chromium oxide film 32 is formed on a transparent synthetic quartz substrate 31 having a refractive index of 1.47, and optical mask blanks ( Three types of standard thin films; hereinafter referred to as standard samples) 33 were prepared. In-line type (tray movement type)
Sputtering was performed under the predetermined film forming conditions by using the DC sputtering apparatus described in 1. The film forming condition was that the tray moving speed was changed in order to change the film thickness, that is, the film forming time, and all other film forming conditions were the same.

Next, as shown in FIG. 6B, three types of standard samples 33a to 33 are used by using a spectrophotometer for a large substrate.
The respective transmittances T1 to T3 and reflectances R1 to R3 were measured. Here, air (refractive index 1.0) is used as a reference medium (reference), and standard samples 33a to
The transmittance and reflectance (unit:%) of each of the 33c were used as measured values. Further, the film thickness d1 to d3 of each of the standard samples 33a to 33c was measured using a straight needle type film thickness measuring device (device name: Dektak). The minimum scanning speed is 0.001mm so that measurement can be performed with high accuracy.
/ S and the measurement was repeated 10 times, and the average value was taken.

Table 1 shows the standard samples 33a to 33c.
The measured values of transmittance, reflectance and film thickness (indicated as a to c in the table) are shown.

[Table 1] The measured values of the transmittance, the reflectance, and the film thickness were input to the film thickness evaluation device, and the refractive index of 2.45 and the attenuation coefficient of 0.73 were obtained as the optical constants of the standard sample 33.

Next, as shown in FIG. 6C, an optical mask blank of unknown film thickness (thin film of unknown film thickness; target sample) 4
1 was produced. The target sample 41 is a synthetic quartz substrate 31.
A chromium oxide film 42 was formed thereon under the same film forming conditions as the standard sample. Here, the tray moving speed of the film forming apparatus was arbitrarily changed to intentionally change the film thickness. Note that the relationship between the tray moving speed and the film thickness of the formed film deviates slightly from the linear proportional relationship and is not necessarily expressed as a linear function. Further, since the film thickness varies depending on the position of the substrate placed in the tray, the placement position in the tray was also fixed.

Next, the transmittance T0 and the reflectance R0 of the target sample 41 were measured by using the spectrophotometer for a large substrate, and the transmittance 4.3 (%) and the reflectance 22.5 (%) were obtained.
Met. Next, the transmittance T0 and the reflectance R0 were input to the film thickness evaluation device to obtain a film thickness of 115 nm. Furthermore, the target film thickness (desired film thickness) is set to 50 nm,
As a result of inputting these numerical values into the film thickness evaluation device, the film thickness deviation amount (film thickness to be corrected:%) is + 130%, the predicted transmittance at the target film thickness is 21.7%, and the predicted reflectance is 24.6%. Each predicted value of was obtained. In addition, for the target samples formed in the same manner and having different film thicknesses, the film thickness could be obtained in the same manner from the measurement results of the transmittance and the reflectance. Further, for confirmation, a target sample having a film thickness of 50 nm was prepared, and the transmittance and the reflectance were measured in the same manner as above, and the transmittance was 1.4.
%, The reflectance was 25.0%, and the results were almost the same as the predicted values.

As described above, the transmittance, reflectance and film thickness of the standard sample are directly measured, and the optical constants are obtained from these measured values, whereby the transmittance and reflectance of the target sample can be easily measured. By performing only this, the film thickness of the target sample can be quickly and highly accurately obtained. Further, by using the film thickness evaluation device, the film thickness of the target sample can be evaluated easily.

Although the film is formed by the DC sputtering method in the present embodiment, the present invention is not limited to the DC sputtering method, and for example, the vapor phase such as the RF sputtering method, the vapor deposition method, the CVD method, the ion plating method, etc. Of course, a growth method, a liquid phase growth method or the like may be used. Also, D
Although the film was formed using the C sputtering apparatus, the same operation can be performed when various film forming apparatuses other than the DC sputtering apparatus are used.

[0046]

As described above, according to the first aspect of the present invention.
According to the thin film thickness evaluation method described, light of a predetermined wavelength is incident on a thin film of unknown film thickness, the transmittance and reflectance of the thin film are measured, and the transmittance and reflectance and the refraction of the thin film are measured. Since the film thickness of the thin film is obtained from the coefficient and the attenuation coefficient, the film thickness of the thin film can be obtained quickly and accurately.

Further, according to the thin film thickness evaluation method of the second aspect, the refractive index and the attenuation coefficient of the standard thin film are obtained from the respective measured values of the standard thin film, the transmittance and the reflectance, and the measured film is measured. Since the film thickness of the thin film to be measured is determined from the measured values of the transmittance and reflectance of the thin film and the refractive index and the attenuation coefficient of the standard thin film, the film thickness of the thin film to be measured is quickly and highly accurately obtained. be able to.

Further, according to the thin film thickness evaluation method of the third aspect, the ratio of the film thickness to the desired film thickness of the measured thin film, the measured film thickness of the measured thin film based on the film thickness of the measured thin film. Since it was decided to obtain the predicted transmittance and the predicted reflectance when the film thickness of the thin film was the desired film thickness, the transmittance and reflectance of the obtained thin film were measured, and these measured values were used as the predicted transmittance. A suitable film thickness can be quickly determined by comparing the index and the predicted reflectance.

Further, according to the thin film thickness evaluation apparatus of the fourth aspect, the measured values of the standard thin film thickness, the transmittance and the reflectance, and the measured thin film of the unknown thickness have the transmittance and the reflectance, respectively. A data input unit for inputting, a refractive index and an attenuation coefficient of the standard thin film based on the measured values, a calculation unit for determining and evaluating calculated values of the film thickness of the measured thin film, and the measured values and the Since the data storage unit for storing each calculated value and the data output unit for outputting each measured value and each calculated value are provided, it is possible to measure the film thickness of the thin film to be measured stably, quickly and highly accurately. You can

Further, according to the thin film thickness evaluation apparatus of the fifth aspect, the calculating unit calculates the film thickness and the desired film thickness of the measured thin film based on the film thickness of the measured thin film. Ratio, the calculation means for obtaining and evaluating each calculated value of the predicted transmittance and the predicted reflectance when the film thickness of the thin film to be measured is set to the desired film thickness is provided. It can be easily and quickly obtained, and the film thickness can be easily and quickly controlled.

[Brief description of drawings]

FIG. 1 is a flowchart showing a thin film thickness evaluation method of Example 1 of the present invention.

FIG. 2 is a schematic diagram showing light transmission and reflection of each of two standard samples having different film thicknesses.

FIG. 3 is a block diagram showing a thin film thickness evaluation apparatus of Example 1 of the present invention.

FIG. 4 is a flowchart showing the operation of the thin film thickness evaluation apparatus of Example 1 of the present invention.

FIG. 5 is a flowchart showing a calculation procedure of a calculation unit in the thin film thickness evaluation apparatus of Example 1 of the present invention.

FIG. 6 is a schematic diagram showing light transmission and reflection of each thin film optical element of Example 2 of the present invention.

FIG. 7 is a diagram showing an example of a conventional method for measuring optical characteristics of a thin film optical element.

FIG. 8 is a diagram showing an example of a spectral curve showing the relationship between the wavelength of light of a thin film optical element and the transmittance and reflectance.

FIG. 9 is a diagram showing a relationship between transmittance / reflectance observed in incident light on a thin film and reflection in the film.

FIG. 10 is a diagram showing a relationship between a refractive index and an attenuation coefficient at each transmittance and reflectance of the thin film optical element.

[Explanation of symbols]

1 and 2 standard sample (standard thin film) 11 quartz substrate 12 thin film 13 thin film 21 data input unit 22 arithmetic unit 23 data storage unit 24 data output unit 31 synthetic quartz substrate 32 chromium oxide film 33 optical mask blank (standard thin film) 41 film thickness Unknown optical mask blank (thin film of unknown thickness) 42 Chromium oxide film

Claims (5)

[Claims] 1. A light having a predetermined wavelength is incident on a thin film of unknown film thickness, the transmittance and reflectance of the thin film are measured, and the transmittance and reflectance and the refractive index and attenuation coefficient of the thin film are used to calculate the A method for evaluating the thickness of a thin film, which comprises determining the thickness of the thin film. 2. The light having a predetermined wavelength is incident on one or more standard thin films, the film thickness, the transmittance and the reflectance of each standard thin film are measured, and the refractive index and the attenuation of the standard thin film are measured from these measured values. Obtain the coefficient, then, the light of a predetermined wavelength is incident on the thin film to be measured of unknown film thickness, the transmittance and reflectance of the thin film to be measured are measured, and the measured values of this transmittance and reflectance, and the standard A method for evaluating the thickness of a thin film, which comprises obtaining the film thickness of the thin film to be measured from the refractive index and the attenuation coefficient of the thin film. 3. A ratio of the film thickness to a desired film thickness of the film to be measured based on the film thickness of the film to be measured, and a prediction when the film thickness of the film to be measured is set to the desired film thickness. The film thickness evaluation method according to claim 2, wherein the transmittance and the predicted reflectance are obtained. 4. A film thickness, a transmittance and a reflectance of a standard thin film,
A data input unit for inputting each measured value of the transmittance and reflectance of the measured thin film of unknown film thickness, a refractive index and an attenuation coefficient of the standard thin film based on each measured value, each of the film thickness of the measured thin film A calculation unit for calculating and determining / evaluating calculated values; a data storage unit for storing the measured values and the calculated values; and a data output unit for outputting the measured values and the calculated values. Characteristic thin film thickness evaluation device. 5. The calculation unit causes the ratio of the film thickness to the desired film thickness of the film to be measured, the film thickness of the film to be measured to be the desired film thickness based on the film thickness of the film to be measured. 5. The thin film thickness evaluation apparatus according to claim 4, further comprising arithmetic means for obtaining and evaluating the respective calculated values of the predicted transmittance and the predicted reflectance in the above case.