JP3495797B2 - Optical constant measuring method and device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring an optical constant and an apparatus therefor, and more specifically, it illuminates a substrate having a light-transmitting property and detects a light intensity distribution of the reflected light to transmit the light. TECHNICAL FIELD The present invention relates to a method and an apparatus for measuring an optical constant of a transparent substrate or an optical constant of a thin film formed on a surface of a transparent substrate. The optical constant is
It is a concept including film thickness, refractive index, and extinction coefficient, and all constants or some constants are measured as necessary.

[0002]

2. Description of the Related Art Conventionally, as a method for measuring the optical constants of a non-translucent substrate or a single-layer or multi-layer thin film layer formed on the substrate, a method disclosed in Japanese Patent Laid-Open No. 17505/1993. Is proposed. This method is a method of irradiating a thin film on the surface of a non-translucent substrate with a light beam and measuring the optical constants by measuring the light intensity distribution of the reflected light, for example, when measuring the film thickness. Is the light intensity distribution of the reflected light obtained by irradiating a thin film with a known film thickness in advance, and then irradiating the thin film to be measured with the light beam to obtain the light intensity of the reflected light. The distribution is obtained, and the film thickness of the thin film is obtained based on the obtained light intensity distribution. However, when measuring the optical constants of a translucent substrate or a thin film formed on the substrate by this method, the light intensity distribution of the reflected light shows that not only the reflected light on the surface of the thin film but also the translucent light. Since the reflected light from the back surface of the substrate having the property is also included, there is a disadvantage that the optical constant cannot be accurately measured.

In view of this inconvenience, (1) a method of applying black paint or the like to the back surface of the transparent substrate to reduce the amount of reflection on the back surface of the substrate, and (2) A method has been proposed in which the back surface of a certain substrate is roughened to scatter the reflected light beam from the back surface of the substrate.

Further, (3) the theoretical value of the light quantity of the reflected light beam on the back surface of the transparent substrate is obtained, the theoretical value is removed in advance from the actual measured value, and the theoretical value is removed based on the value. A method of measuring the optical constant has also been proposed.

[0005]

When the methods (1) and (2) are adopted, it is essential to stain or scratch the back surface of the transparent substrate. Even if there is an effect that the amount of reflection on the back surface of a certain substrate can be reduced to improve the measurement accuracy of the optical constant,
It is hard to say that it is practical. That is, destructive measurement is unavoidable in the measurement of optical constants that should be performed nondestructively.

Further, when the method (3) is adopted, there is no guarantee that the theoretical value of the light quantity of the reflected light beam on the back surface of the light-transmitting substrate coincides with the actual measurement value. There is no guarantee that the constant can be measured accurately.
Further, when the optical constant of the translucent substrate is unknown, it is difficult to estimate the light quantity of the reflected light beam on the back surface of the substrate, and in practical application, its application range is significantly limited. There is an inconvenience of causing. That is, the optical constants of the transparent substrate must be known, and the light quantity of the reflected light beam on the back surface of the substrate must be easily estimated.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and does not require destructive treatment, and eliminates the influence of reflected light on the back surface of a transparent substrate to reduce the optical constant. It is an object of the present invention to provide an optical constant measuring method and an apparatus therefor capable of enhancing the measurement accuracy.

[0008]

According to a first aspect of the present invention, there is provided a method for measuring optical constants, wherein a light-transmissive substrate surface is irradiated with convergent light or divergent light, and the convergent light or divergent light is transmitted through the light-transmissive substrate. The light intensity distribution in the light beam of the reflected light in is detected by using an array detector, and in the light intensity distribution, in the range where the reflected light of the convergent light or the divergent light is guided and the reflected light on the back surface does not enter. It is a method of measuring an optical constant of the transparent substrate or an optical constant of a thin film formed on the surface of the transparent substrate based on a light intensity distribution.

An optical constant measuring device according to a second aspect of the present invention is an irradiation optical system for irradiating a surface of a transparent substrate with convergent light or divergent light, and reflection of the convergent light or divergent light on the transparent substrate. A light receiving optical system that guides light, an array detector that detects the light intensity distribution in the light beam of the reflected light guided by the light receiving optical system, and the light transmission based on the detected light intensity distribution in the light beam A constant substrate optical constant or an optical constant calculating means for calculating the optical constant of the thin film formed on the transparent substrate surface, and the light receiving optical system, the convergent light or the divergent light Of at least a part of the reflected light on the surface of the transparent substrate of the array detector to the light receiving portion where the reflected light of the convergent light or the divergent light on the rear surface of the transparent substrate is not guided. Leading and before The optical constant calculating means is based on an intensity distribution in the light beam detected by a light receiving part of the array detector where the reflected light of the convergent light or the divergent light on the back surface of the transparent substrate is not guided. The optical constant of the transparent substrate or the optical constant of the thin film formed on the surface of the transparent substrate is calculated.

According to a third aspect of the present invention, in the optical constant measuring device, the light receiving optical system has an area of a light receiving portion of an array detector to which the reflected light of the convergent light or the divergent light on the transparent substrate surface is guided. , The reflected light on the transparent substrate is made to be twice or more the area of the light receiving portion of the array detector to which the reflected light on the back surface of the transparent substrate of the convergent light or the divergent light is guided. It uses the one that guides.

An optical constant measuring device according to a fourth aspect of the invention employs a one-dimensional or two-dimensional array sensor as the array detector, and has the translucency of the convergent light or the divergent light as the light receiving optical system. The reflected light on the front surface of the substrate is guided, and the reflected light on the back surface of the transparent substrate of the convergent light or the divergent light is guided so that the number of light receiving pixels in the light receiving portion of the array sensor is 10 or more. The one that guides the reflected light from the transparent substrate is adopted.

However, the reflected light from the substrate is used as a concept including the reflected light from the front and back surfaces of the substrate and the scattered light inside the substrate.

[0013]

According to the optical constant measuring device of claim 1, the surface of the transparent substrate is irradiated with convergent light or divergent light, and the converged light or divergent light is reflected by the transparent substrate. The light intensity distribution in the light beam is detected by using an array detector, and the reflected light of the convergent light or the divergent light is guided in the light intensity distribution, and the light intensity distribution in the range where the reflected light on the back surface does not enter is obtained. Since the optical constant of the transparent substrate or the optical constant of the thin film formed on the transparent substrate surface is measured based on the influence of reflected light on the back surface of the transparent substrate. As a result, the optical constant can be measured with high accuracy.

According to another aspect of the optical constant measuring device of the present invention, the irradiation optical system irradiates the transparent substrate surface with convergent light or divergent light, and the light receiving optical system illuminates the convergent light or divergent light. Since the reflected light from the substrate having properties is guided to the array detector, the array detector can detect the light intensity distribution in the light beam of the reflected light. In this case, the light receiving optical system may be configured such that the optical constant of the transparent substrate or the optical constant of a thin film formed on the transparent substrate surface is based on the detected light intensity distribution in the light beam. And an optical constant calculation means for calculating, and, the light receiving optical system, at least a part of the reflected light on the transparent substrate surface of the convergent light or the divergent light, the array detector, Since the reflected light of the convergent light or the divergent light on the transparent substrate back surface is guided to the light receiving part where it is not guided, at least a part of the reflected light on the substrate surface affects the influence of the knitting light on the substrate back surface. I will not receive it. Then, the optical constant calculation means calculates the intensity distribution within the light beam detected by the light receiving portion of the array detector, to which the reflected light on the back surface of the transparent substrate of the convergent light or the divergent light is not guided. Based on the calculation of the optical constants of the transparent substrate or the optical constants of the thin film formed on the transparent substrate surface based on only the light intensity distribution in the light beam of the reflected light on the substrate surface The optical constant can be measured with high accuracy based on

According to another aspect of the optical constant measuring device of the present invention, the light receiving optical system includes a light receiving portion of an array detector to which the reflected light of the convergent light or the divergent light on the transparent substrate surface is guided. Reflection on the translucent substrate so that the area is at least twice the area of the light receiving portion of the array detector through which the reflected light of the convergent light or the divergent light on the rear surface of the translucent substrate is guided. Since the one that guides the light is adopted, it is possible to sufficiently increase the area of the light receiving portion that is not affected by the reflected light on the back surface of the substrate.
As a result, the optical constant can be measured with high accuracy.

An optical constant measuring device according to a fourth aspect of the invention employs a one-dimensional or two-dimensional array sensor as the array detector, and has the translucency of the convergent light or the divergent light as the light receiving optical system. The reflected light on the front surface of the substrate is guided, and the reflected light on the back surface of the transparent substrate of the convergent light or the divergent light is guided so that the number of light receiving pixels in the light receiving portion of the array sensor is 10 or more. Since the one that guides the reflected light from the transparent substrate is adopted, the optical constant can be measured with sufficient accuracy based on the light intensity distribution detected by 10 or more light receiving pixels.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings showing embodiments. FIG. 1 is a schematic view showing an embodiment of the optical constant measuring device of the present invention. In this optical constant measuring device, the direction of the light beam emitted from the laser light source 1 is changed by the half mirror 2, and the light is converged by the lens 3 and the surface of the transparent substrate 4 (the side on which light is incident). The thin film layer 4a formed in the above is irradiated. Here, the optical axis of the light beam is set to be substantially perpendicular to the transparent substrate 4. A light beam having a wide incident angle is formed on the transparent substrate 4.

This light beam is reflected by the surface of the transparent substrate 4 and the thin film layer 4a, and the half mirror 2
Incident on the array detector 5. Here, the light quantity of the reflected beam detected by the array detector 5 is a value determined by the optical constant of the transparent substrate 4, the optical constant of the thin film layer 4a, and the incident angle. Therefore, by supplying the value detected by the array detector 5 to the computer 6 to perform a predetermined calculation, the optical constant of the thin film layer 4a can be determined.

The array detector 5 includes an array sensor including a one-dimensional or two-dimensional CCD or an image sensor such as an image intensifier capable of measuring at least one-dimensional light intensity distribution. It also includes a small single light receiving site moving in the beam with time. It will be described in more detail.

A light ray 20A emitted from the vicinity of the center of the light beam is bent by the half mirror 2 to become a light ray 20B, passes through a lens 3 and becomes a light ray 20C, and the substrate 4 and the thin film 4a.
Is incident almost vertically on. This light ray 20C is reflected by the substrate 4 and the thin film 4a to become a light ray 20D, and the lens 3
Then, it becomes a light beam 20E through the half mirror 2 and is incident on the sensor element 50 on the array detector 5. Further, the light ray 2nA emitted from the upper part of the light beam is bent by the half mirror 2 to become a light ray 2nB, and passes through the lens 3 and the light ray 2nC.
And enters the substrate 4 and the thin film 4a at an angle θ. The ray 2nC is reflected by the substrate 4 and the thin film 4a at an angle θ to become a ray 2nD, passes through the lens 3 and the half mirror 2 and becomes a ray 2nE, and is incident on the sensor element 5n on the array detector 5. In this way, the reflected light amounts of different angles are incident on the respective sensor elements of the array detector 5.

The values measured by each of these sensor elements are, for example, a film thickness formed on a silicon substrate of 5,000 angstroms, 10,000 angstroms, and 20,0.
In the case of an oxide film of 00 angstroms, FIGS.
It becomes a curve as shown in. 2 and 3, the solid line indicates the case of 5,000 Å, and the broken line indicates 1
In the case of 10,000 angstroms, the chain line is 2
The case of 10,000 angstroms is shown. Here, the P-polarized component observed in a direction parallel to the vibration direction of the linearly polarized light of the incident light beam and the S-polarized component observed in the vertical direction can be measured separately.
FIG. 2 shows the case of S-polarized light, and FIG. 3 shows the case of P-polarized light. Here, the case where the film thickness is changed has been described, but these curves are different even when the refractive index is changed.

Further, as shown in FIG. 4, consider a mathematical model in which light is multiple-reflected in response to light being incident on a thin film layer 4a formed on a transparent substrate 4. And the reflectance R thereof is expressed by Equation 1.

[0023]

[Equation 1]

Here, r1 is the reflectance at the boundary between the air layer and the thin film layer 4a, r2 is the reflectance at the boundary between the thin film layer 4a and the substrate 4, and t is the film thickness of the thin film layer 4a. k is given by the equation 2.

[0025]

[Equation 2]

Here, λ is the wavelength of the light beam, and n1 is the refractive index of the thin film layer 4a. The reflectance r
The values of 1 and r2 are different for S-polarized light and P-polarized light, and are represented by Formulas 3 to 6, respectively. However, the subscripts S and P respectively indicate values for S-polarized light and values for P-polarized light.

[0027]

[Equation 3]

[0028]

[Equation 4]

[0029]

[Equation 5]

[0030]

[Equation 6]

Here, n0 is the refractive index of air, n2 is the refractive index of the substrate, θ1 is the refraction angle of the light beam incident on the thin film layer 4a from the air layer, and θ2 is the light beam incident on the substrate 4 from the thin film layer 4a. The respective refraction angles of are shown. In this way, the curve of the reflectance measured according to the continuous angle changes its shape when the optical constant such as the film thickness changes.By utilizing that, from the curve for the measured angle,
The optical constant of the thin film layer 4a can be obtained in reverse.

FIG. 5 illustrates a process in the computer 6 for obtaining the film thickness of the thin film layer 4a using the calculated value of the reflectance according to the angle, which is obtained from the output signal of each sensor element of the array detector 5. It is a flowchart to do. In step SP1, the reflectance is calculated based on the S-polarized component and the P-polarized component of the reflected light measured by each sensor element of the array detector 5 and the intensity of the emitted light from the laser light source 1, and in step SP2, the reflectance is calculated. The equation 1 is solved using the calculated reflectance values and the equations 2 to 6. By performing this processing, the solution of the film thickness is obtained for each calculated value of the reflectance obtained based on the output signal of each sensor element, and a group of solutions is obtained. Then
In step SP3, statistical analysis processing is performed to select the most probable solution from the group of solutions. Then, in step SP4, in order to improve the accuracy of the solution, the solution is obtained by the numerical solution method by the least square method using the equation 1 in which the contributions of the absorption of the material and the size of the array detector 5 are corrected. However, since this calculation is difficult,
In order to facilitate the numerical solution method, it is executed under the restriction by the solution in step SP3. In this way, it is possible to measure with an accuracy of 20 angstroms or less in the film thickness range of 50 angstroms to 50,000 angstroms. Then, in order to perform the calculation using these statistical analysis and the numerical solution method by the least square method, the number of measured values may be 10 or more. However, for example, when a thin film having a large film thickness is to be measured, the period of change in the curve of the reflectance is short (the number of extreme values above and below the change in the curve of FIG. 2 or FIG. 3 is large). It is preferable to increase the number of measured values. For example, if the film thickness is 50,000
When measuring the optical constants of a thin film of about 0 angstrom, it is preferable to use 15 or more measured values, and when measuring a thin film of about 100,000 angstrom, use 30 or more. Is preferred. In many cases, it is preferable to use the measured values obtained by the sensor elements evenly distributed over a wide range of the array detector 5 within a range where the reflected light from the back side of the substrate does not affect.

According to this optical constant measuring method, the refractive index of the thin film layer 4a or the substrate 4 can be calculated together with the film thickness of the thin film layer 4a. FIG. 6 illustrates a process in the computer 6 for obtaining the refractive index of the thin film layer 4a or the substrate 4 by using the calculated value of the reflectance according to the angle, which is obtained from the output signal of each sensor element of the array detector 5. It is a flowchart to do.

At step SP1, the array detector 5
The reflectance is calculated based on the S-polarized component and the P-polarized component of the reflected light measured by each sensor element, and the intensity of the light emitted from the laser light source 1, and in step SP2, the calculated value of the reflectance according to the angle, Equation 1 is solved using the estimated value of the film thickness of the thin film layer 4a and Equations 2 to 6. An approximate solution of the refractive index is obtained by performing this process. Then, in step SP3, Equation 1 is solved using the calculated value of the reflectance according to the angle, the approximate solution of the refractive index, and Equations 2 to 6. By performing this processing, the solution of the film thickness is obtained for each calculated value of the reflectance obtained based on the output signal of each sensor element, and a group of solutions is obtained. Next, in step SP4, statistical analysis processing is performed,
The most probable solution is selected from this group of solutions.
Then, in step SP5, in order to improve the accuracy of the solution, the solution is obtained by the numerical solution method by the least square method using the equation 1 in which the contributions of the absorption of the material, the size of the array detector 5 and the like are corrected. However, since this calculation is difficult, it is executed under the limitation of the solution in step SP4 in order to facilitate the numerical solution method.

However, when the substrate 4 is translucent like glass, a reflected beam from the back surface of the substrate 4 is generated. As shown in FIG. 7, the incident light beam focused on the point P of the thin film layer 4 a on the glass substrate 4 enters the glass substrate 4 and is reflected by the back surface of the glass substrate 4 as shown by the broken line. receive. At this time, the reflected light beam behaves as if it came out from the point Q, which is a mirror image point on the back surface of the point PK glass substrate 4. This reflected light beam is condensed by the lens 3 and then reaches the array detector 5 while expanding again. At this time, the reflected light beam from the back surface of the glass substrate 4 affects the sensor element located within the range of the optical path indicated by the broken line on the array detector 5. These are the thin film layers 4 on the surface of the glass substrate 4.
This will have a significant effect on the reflected light from a and will hinder accurate measurement as it is. However, if the irradiation range of the reflected light beam from the thin film layer 4a on the surface of the glass substrate 4 is larger than the range of the optical path indicated by the broken line, the output signal from the sensor element in the range of the optical path indicated by the broken line is not adopted. , Thin film layer 4 on the surface of glass substrate 4
By adopting the output signal from the sensor element in the range where only the reflected light beam from a is irradiated, the influence of the reflected light beam from the back surface of the substrate can be removed and accurate measurement of the optical constant can be achieved. Of course, on the array detector 5,
It is preferable to make the range of the optical path indicated by the broken line as small as possible.

In FIG. 7, with respect to the point Q'in which the position of the point Q which is the mirror image point of the point P is replaced with the position in the air, the formula 7
And Equation 8 holds.

[0037]

[Equation 7]

[0038]

[Equation 8]

Here, S1 is the distance from the lens 3 to the point Q ', S1' is the distance from the lens 3 to the point R where the point Q'is condensed by the lens 3, F1 is the focal length of the lens 3, and T is the focal length. Indicates the thickness of the glass substrate 4, and N indicates the refractive index of the glass substrate 4, respectively. When S1 ′ is obtained from the equations 7 and 8, the equation 9 is obtained.

[0040]

[Equation 9]

The lens 3 needs to be a lens having a large numerical aperture in order to widen the angle of the light beam, and a lens having a short focal length is advantageous in order to avoid distortion or the like. For example, when an objective lens for a microscope having a numerical aperture of 0.9 is adopted as the lens 3, it has a divergence angle of about 64 ° and is suitable for the above measurement, but the focal length is, for example, In the example of what is marketed, it is 2.25 mm. Therefore, assuming that the thickness of the glass substrate 4 is 1.1 mm and the refractive index is 1.54, the distance S1 ′ from the lens 3 at the position R from the formula 9 is 9.3 mm, and the array at the position R is The detector 5 may be arranged. However, it may be difficult to physically arrange.

FIG. 8 shows an embodiment for coping with the case where the physical arrangement is difficult. This embodiment differs from the embodiment of FIG. 7 in that a lens 7 is added between the lens 3 and the array detector 5. Here, the glass substrate 4
Of the array detector 5 with respect to the lens 7 so that the beam diameter D of the reflected light beam from the thin film layer 4a on the surface of the lens 7 irradiated on the array detector 5 by the lens 7 becomes the sensor surface size D of the array detector 5. Set the distance L2. However, if the beam diameter of the reflected light beam incident on the surface of the glass substrate 4 incident on the lens 7 is W and the focal length of the lens 7 is F2, the following formula 10 is obtained.

[0043]

[Equation 10]

The reflected light beam from the back surface of the glass substrate 4 is expressed by the following equations 11 to 14 with respect to the point Q'in which the position of the point Q which is the mirror image point of the point P is replaced with the position in the air. .

[0045]

[Equation 11]

[0046]

[Equation 12]

[0047]

[Equation 13]

[0048]

[Equation 14]

Here, S2 indicates the distance from the point R to the lens 7, and S2 'indicates the distance from the lens 7 to the point R'where the point R is condensed by the lens 7. In addition,
S1, S1 ', F1, T, N are the same as in the case of FIG. If S2 'is obtained from the equations 11 to 14, the equation 15 is obtained.

[0050]

[Equation 15]

Therefore, by setting the condition that S2 'is equal to L2, the influence of the reflected light beam from the back surface of the glass substrate 4 on the array detector 5 can be minimized. 7 and 8, the sensor element near the center of the array detector 5 is affected by the reflected light beam from the back surface of the glass substrate 4. In FIG. 8, the range D2 affected by the reflected light beam from the back surface of the glass substrate 4 is given by Equation 16.

[0052]

[Equation 16]

Here, W ′ is the beam diameter of the reflected light beam incident on the lens 7 and reflected from the back surface of the glass substrate 4.
Therefore, it is preferable to make the range D2 as small as possible, but if the measurement accuracy is taken into consideration, this range D2
However, it may be set so that the reflected light beam from the thin film layer 4a on the surface of the glass substrate 4 becomes half or less of the area irradiated onto the array detector 5 by the lens 7. of course,
The processing based on the output signal from the sensor element in this range D2 is step SP1 in the flowcharts of FIGS.
The optical constant can be measured in a state of being excluded from the processing of No. 1 and being not affected by the reflected light beam from the back surface of the glass substrate 4.

Next, in the area of the range D2, the light beam reflected from the thin film layer 4a on the surface of the glass substrate 4 is reflected by the lens 7
1 of the area of the range D irradiated on the array detector 5 by
When L / m or less, the range that L2 can take is calculated as follows. However, the diameters of the respective ranges D and D2 are represented by d and d2, respectively. π (d / 2) ² / π
Since (d2 / 2) ² = m, d / d2 = m ^1/2 = M.

The minimum value L2min of L2 is determined by the following equation. S2 ′: W ′ = (S2′−L2min): D ′ Therefore, Equation 17 is obtained.

[0056]

[Equation 17]

From d / d2 = m ^1/2 = M and the equation 17, D / M = {(S2′−L2min) / S2 ′} W ′, and therefore the equation 18 is obtained.

[0058]

[Equation 18]

Similarly, when the maximum value L2max of L2 is obtained, S2 ': W' = (L2max-S2 '): D' Therefore, equation 19 is obtained.

[0060]

[Formula 19]

From d / d2 = m ^1/2 = M and the equation 19, D / M = {(L2max-S2 ′) / S2 ′} W ′, and therefore the equation 20 is obtained.

[0062]

[Equation 20]

Therefore, from Equation 18 and Equation 20, Equation 21
Is obtained.

[0064]

[Equation 21]

By setting M = 2 ^1/2 , the area of the range D2 can be reduced to 1/2 or less of the area of the range D. However, one that measures a one-dimensional light intensity distribution as the array detector 5 (one-dimensional light is detected by using the values of pixels arranged in a specific one-dimensional direction of the two-dimensional array detector). Including the case of measuring the intensity distribution.
The same applies hereinafter), d / d2 = m ^1/2 = M
Instead, d / d2 = m = M may be adopted (here, d and d2 are the lengths of the ranges D and D2, respectively).
Therefore, by setting M = 2 in the above equation, the area (length) of the range D2 can be made 1/2 or less of the area (length) of the range D.

The lens 3 in the embodiment shown in FIG.
If the distance between the array detector 5 and the array detector 5 is L, the range D2
When the area of is less than 1 / m of the area of the range D in which the reflected light beam from the thin film layer 4a on the surface of the glass substrate 4 is irradiated onto the array detector 5 by the lens 7, the range of L Is calculated as follows. π (d / 2) ²
Since / π (d2 / 2) ² = m, d / d2 = m ^1/2 =
It becomes M.

The minimum value Lmin of L is determined by the following equation. S1 ′: W ′ = (S1′−Lmin): D ′ Therefore, the equation 22 is obtained.

[0068]

[Equation 22]

Further, d / d2 = m ^1/2 = M and from the equation 22, D / M = {(S1'-Lmin) / S1 '} W', so Lmin = S1 '{1- (D / MW ')} is obtained. Therefore, Equation 23 is obtained from Equation 9.

[0070]

[Equation 23]

Similarly, when the maximum value Lmax of L is obtained, S1 ': W' = (Lmax-S1 '): D' Therefore, the following equation 24 is obtained.

[0072]

[Equation 24]

Since d / d2 = m ^1/2 = M and D / M = {(Lmax−S1 ′) / S1 ′} W ′ from the equation 24, Lmax = S1 ′ {1+ (D / MW ′)} Is obtained. Therefore, Equation 25 is obtained from Equation 9.

[0074]

[Equation 25]

Therefore, from Expressions 22 and 24, Expression 26 is obtained.
Is obtained.

[0076]

[Equation 26]

By setting M = 2 ^1/2 , the area of the range D2 can be reduced to 1/2 or less of the area of the range D. However, when a one-dimensional array detector 5 is adopted, d / d2 = m = M may be adopted instead of d / d2 = m ^1/2 = M (here, d,
d2 is the length of the ranges D and D2, respectively). Therefore, by setting M = 2 in the above equation, the range D
The area (length) of 2 can be half or less of the area (length) of the range D.

FIG. 9 and FIG. 10 are views in which the measurement error changes with respect to the ratio of the influence of the reflected light beam from the back surface of the substrate 4 on the light receiving width of the array detector 5, and FIG. FIG. 10 shows a case where a one-dimensional array detector 5 is adopted, and FIG. 10 shows a case where a two-dimensional array detector 5 is adopted. In addition, FIG.
Shows the variation of the measurement error (angstrom) when the ITO film having a film thickness of 3710 angstrom is measured, with respect to the change of (length affected by reflected light on back surface of substrate / light receiving width of array detector). There is. FIG. 10 shows an IT having a film thickness of 3710 angstroms.
The figure shows the variation of the measurement error (angstrom) when the measurement is performed on the O film with respect to the change of (area affected by reflected light on substrate back surface / light-receiving area of array detector). If the measurement error is within a range of about 1 angstrom, it can be said that the measurement error is sufficiently satisfactory for use. When the array detector 5 is one-dimensional, this range is such that (length affected by reflected light on the back surface of the substrate / light receiving width of the array detector) is about 70% or less, When the array detector 5 is two-dimensional, (area affected by the reflected light on the back surface of the substrate / light-receiving area of the array detector) is in the range of about 50% or less. However, when it is necessary to reduce the measurement error, (length affected by reflected light on the back surface of the substrate / light receiving width of the array detector) is set within a range of about 30% or less, and the array detector 5 Is a two-dimensional one,
(Area affected by reflected light on the back surface of the substrate / light receiving area of the array detector) may be set within a range of about 10% or less.

Although the case where the converging position of the incident light beam by the lens 3 is on the surface of the thin film layer has been described above, the converging position is before the thin film layer and the incident light beam is once Even when the thin film layer is irradiated with light that has been condensed and then diverged, the optical constants can be similarly measured. Further, although the array detector 5 is directly irradiated with the reflected light beam from the back surface of the substrate 4 as described above, a mask member is provided on the front surface of the array detector 5 to provide the substrate 4
It is also possible to prevent irradiation of the reflected light beam from the back surface of the.

[0080]

According to the first aspect of the present invention, it is possible to eliminate the influence of the reflected light on the back surface of the transparent substrate, and as a result, it is possible to measure the optical constant with high accuracy. Play. The invention of claim 2 has a unique effect that the optical constant can be measured with high accuracy based only on the light intensity distribution in the light beam of the reflected light on the substrate surface.

According to the third aspect of the present invention, the area of the light receiving portion on the back surface of the substrate that is not affected by the reflected light can be made sufficiently large, and as a result, the optical constant can be measured with high accuracy. Produce an effect. The invention of claim 4 has a unique effect that the optical constant can be measured with sufficient accuracy based on the light intensity distribution detected by 10 or more light receiving pixels.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of optical constant measurement according to the present invention.

FIG. 2 is a diagram showing an example of a change characteristic of reflectance of an S-polarized component with respect to an incident angle.

FIG. 3 is a diagram showing an example of a change characteristic of reflectance of a P-polarized component with respect to an incident angle.

FIG. 4 is a diagram schematically showing a mathematical model for multiple reflection of incident light.

FIG. 5 is a flowchart illustrating a process for obtaining a film thickness of a thin film layer by using a calculated value of reflectance according to an angle, which is obtained from an output signal of each sensor element of an array detector in a computer.

FIG. 6 is a flowchart illustrating a process for obtaining a refractive index of a thin film layer or a substrate by using a calculated value of reflectance according to an angle, which is obtained from an output signal of each sensor element of an array detector in a computer. is there.

FIG. 7 is a schematic view showing an embodiment for reducing the influence of a reflected light beam from the back surface of the substrate.

FIG. 8 is a schematic view showing another embodiment for reducing the influence of the reflected light beam from the back surface of the substrate.

FIG. 9 is a diagram in which a state in which the measurement error changes with respect to the ratio of the influence of the reflected light beam from the back surface of the substrate to the light receiving width of the one-dimensional array detector is actually measured.

FIG. 10 is a diagram that actually measures how the measurement error changes with respect to the ratio of the influence of the reflected light beam from the back surface of the substrate with respect to the light receiving area of the two-dimensional array detector.

[Explanation of symbols]

3,7 lens 4 translucent substrate 4a thin film layer 5 array detector 6 computer

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Claims (4)

(57) [Claims] 1. A light in a light beam of a convergent light or a divergent light irradiated onto a surface of a transparent substrate (4) and a reflected light of the convergent light or the divergent light on the transparent substrate (4). The intensity distribution is detected using an array detector (5), and in the light intensity distribution, the reflected light of the convergent light or the divergent light on the front surface of the transparent substrate (4) is guided, and at the back surface. The optical constant of the translucent substrate (4) or the optical constant of the thin film (4a) formed on the surface of the translucent substrate (4) is determined based on the light intensity distribution in the range where reflected light does not enter. A method for measuring optical constants, which comprises measuring. 2. An irradiation system optical system (3) for irradiating the surface of a transparent substrate (4) with convergent light or divergent light, and the transparent substrate (4) of the convergent light or divergent light. A light receiving optical system (3) (7) that guides the reflected light in the light source, and an array detector (5) that detects the light intensity distribution in the light beam of the reflected light guided by the light receiving optical system (3) (7). , An optical constant of the transparent substrate (4) or an optical constant of a thin film (4a) formed on the surface of the transparent substrate (4) based on the detected light intensity distribution in the light beam And an optical constant calculating means (6) for calculating, and the light receiving optical systems (3) and (7) of the reflected light of the convergent light or the divergent light on the surface of the transparent substrate (4). At least a portion of the array detector (5) is transparent to the convergent or divergent light. The reflected light on the back surface of the substrate (4) is guided to the light receiving part of the array detector (5) where it is not guided, and the optical constant calculation means (6) is the converged light of the array detector (5). Alternatively, the translucent substrate (4) having the translucent light based on the intensity distribution in the light beam detected by the light receiving part of the array detector (5) in which the reflected light on the back surface of the translucent substrate (4) is not guided Board (4)
2. The optical constant measuring device for calculating the optical constant of or the optical constant of the thin film (4a) formed on the surface of the transparent substrate (4). 3. The light receiving optical system (3) (7) receives light of an array detector (5) to which reflected light of the convergent light or the divergent light on the surface of the transparent substrate (4) is guided. The area of the part is at least twice as large as the area of the light receiving part of the array detector (5) to which the reflected light of the convergent light or the divergent light on the back surface of the transparent substrate (4) is guided. The optical constant measuring device according to claim 2, which guides light reflected by the transparent substrate (4). 4. The array detector (5) is one-dimensional or two-dimensional.
-Dimensional array sensor, the light receiving optical system (3)
In (7), the reflected light of the convergent light or the divergent light on the surface of the transparent substrate (4) is guided, and the reflected light of the convergent light or the divergent light on the rear surface of the transparent substrate (4). The reflected light from the transparent substrate (4) is guided so that the number of light receiving pixels in the light receiving portion of the array sensor (5) to which reflected light is not guided is 10 or more. Optical constant measuring device.