JP2000249520A - Method for measuring thickness of multilayer thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure the thickness of each layer of the multiplayer thin film of a phase-change-type optical disk with a polycarbonate resin substrate by measuring a spectral reflection factor at the specific wavelength region of the multiplayer thin film that is made of a thin film with a different optical constant and substituting the maximum value, the minimum value, and the wavelength value of the maximum point into a specific expression. SOLUTION: In an optical information storage medium, a first dielectric layer, a recording layer where the phase change between a crystal and an amorphous occurs according to the intensity of illumination light, a second dielectric layer, and a heat transfer layer with metal as a main constituent are successively laminated on one surface of a transparent substrate. Then, when the thickness of the dielectric layer and the recording layer is to be measured, a spectral reflection factor is measured from a substrate side at a wavelength region of 380 nm or higher and 800 nm or lower while the recording layer is in amorphous state. A maximum value Rtop, a minimum value Rbot, a wavelength value of a maximum point of a measured spectral reflection factor are substituted into expressions I-III to calculate the thickness of each layer, where in the expression Td1 and Td3, Tr, a/c/d/e/g/h/l, and b/f/j indicate the thickness of the first and second electric layers, the thickness of the recording layer, coefficients, and constants, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for measuring the thickness of a multilayer thin film, which is suitable as a method for measuring the thickness of each layer constituting an optical information recording medium.

[0002]

2. Description of the Related Art Optical information recording media have attracted attention because they have a higher recording density than conventional recording media and can be increased in recording capacity in a small size, and have been used in various applications. For example, as a read-only optical disk, a compact disk or a CD dedicated to data reproduction is used.
ROM, etc., which are widely used in the music field, computer field, game field, and the like. In addition, write-once optical discs that can be recorded only once are used in document filing systems, data filing systems, and the like, particularly in fields where data security is important.

[0003] Furthermore, rewritable optical discs capable of erasing and re-recording recorded information are expected to contribute to expanding the use of optical discs, because they are capable of restoring and updating data and can be used repeatedly by rewriting. Is done. As such rewritable optical disks, magneto-optical disks and phase-change optical disks have been put to practical use, and are used for data files and the like.

As a recording layer material of a phase change type optical disk, there are GeSbTe-based, GeTe-based, TeSe-based, and TeO-based.
x-based, InSb-based, InSbTe-based, InSbTeAg
Chalcogenide-based materials, such as those based on phenols, are generally known.
Since these materials can reversibly change phase between crystal and amorphous, information is recorded and erased by changing the intensity of irradiation light using this property.

[0005] The layer structure of a general phase-change type optical disk includes a first dielectric layer, a recording layer, and a second layer on one surface of a substrate.
A four-layer structure in which a dielectric layer and a heat transfer layer are sequentially provided. As the substrate, there is a substrate made of a plastic material such as a polycarbonate resin, an acrylic resin, an epoxy resin, and polystyrene, or a substrate made of glass, but from the viewpoint of optical characteristics and strength, a substrate made of a polycarbonate resin is generally used. Have been.

The first and second dielectric layers are provided for the purpose of preventing moisture and the like from entering the recording layer and increasing the signal intensity during reproduction by the optical interference effect. The first and second dielectric layers are made of metal or metalloid oxides, fluorides, nitrides, sulfides, carbides and borides, inorganic or organic metals, or mixtures or composites thereof. The heat transfer layer contains a metal such as Al or Au as a main component.

[0007] In addition to the four-layer structure, a crystallization promoting layer (metal nitride or metal nitride) for promoting crystallization of the recording layer is provided between the recording layer and the first dielectric layer or the second dielectric layer. There is also a phase-change type optical disk having a five-layer structure provided with an oxide layer). This crystallization promoting layer is provided for the purpose of erasing and forming minute recording marks quickly with the increase in speed and capacity of the optical disk system.

[0008] Each layer of such a phase-change type optical disk has
In order to obtain desired optical and thermal characteristics, it is necessary to control the thickness to a predetermined value. In particular, since the thicknesses of the recording layer and the dielectric layer greatly affect the recording and erasing characteristics of the optical disk, it is necessary to accurately control the thickness. Conventionally, the thickness measurement of each layer of the phase change optical disc
The measurement is performed using a step meter or a fluorescent X-ray device.

However, in the method using the step gauge,
Since it is difficult to measure the film thickness of each layer constituting the multilayer film in a laminated state, the film thickness of each layer is measured while forming each layer. Therefore, since the production conditions are changed at the time of measuring the film thickness, there is a problem that the production efficiency is reduced when the continuous production is performed while measuring the film thickness. If the thickness of the layer to be formed is not a thickness suitable for the step gauge, this layer is formed with a thickness suitable for the step gauge for measuring the thickness, and the thickness of the layer is measured. There is a need. In this case, the film formation rate is determined based on the measured value of the film thickness different from the actual film thickness of each layer of the optical disc, and thus there is a problem that an error corresponding thereto is involved.

Since nondestructive measurement cannot be performed by a method using a fluorescent X-ray apparatus, it is necessary to form a film on a sample substrate for film thickness measurement together with a product. Therefore, it takes time to set the sample substrate. Further, in the method using the fluorescent X-ray device, when the two dielectric layers are formed of the same material, whether the thickness of the first dielectric layer has changed or the thickness of the second dielectric layer has changed. There is also a problem that it is difficult to distinguish whether it has changed.

As a film thickness measuring method which can solve such a problem, Japanese Patent Application Laid-Open No. Hei 10-9829 discloses a method of measuring the spectral reflectance of a multilayer thin film, and determining the wavelength value at the point where the reflectance is minimum, and a plurality of wavelength values. A method for measuring the film thickness of each layer based on a certain maximum value of the reflectance is disclosed. Specifically, based on the difference between the wavelength value at the point where the reflectance is minimal and the standard value, the film thickness of the first layer on the substrate is obtained, and the maximum values of the two reflectances and their maximum values are calculated. The thicknesses of the second and third layers are obtained based on the difference from the standard value.

[0012]

However, in the case of a general phase-change type optical disk (one in which the above four or five layers of thin films are formed on a substrate made of polycarbonate resin), Japanese Patent Laid-Open No. It was difficult to accurately measure the thickness of each layer by the method described in JP-A-9829. The reason is described below.

The transmittance of a substrate made of a polycarbonate resin sharply decreases when the wavelength is shorter than 380 nm, so that it is difficult to measure the reflectance accurately at a wavelength lower than 380 nm. Further, this is a general phase-change type optical disk, in which the film thickness of the first dielectric layer is relatively small (90 to 110n).
m) As shown in FIG. 1, the spectral reflectance of the optical disk has only one maximum reflectance point in a wavelength range from 380 nm to 800 nm where accurate reflectance can be measured. In the method described in the above-mentioned publication, two maximum values of the reflectance are required when obtaining the thicknesses of the second and third layers.

Therefore, in the case of a phase change type optical disk having a spectral reflectance as shown in FIG. 1, the thicknesses of the second and third layers are accurately measured by the method described in the above publication. It is not possible. In addition, as can be seen from FIG. 1, a general phase-change type optical disk in which the first dielectric layer has a relatively small thickness has a minimum point of reflectance on the high wavelength side. Since the amount of change in the reflectance with respect to the amount of change in the wavelength is small, the error included in the wavelength value at the point where the reflectance is minimal is large. Therefore, for the phase-change optical disk having a spectral reflectance as shown in FIG. 1, the film of the first layer obtained by using the wavelength value at the point where the reflectance is minimum by the method described in the above publication. Thickness may have low measurement accuracy.

The present invention has been made in view of such problems of the prior art. Even in the case of a general phase-change type optical disk having a substrate made of a polycarbonate resin, the spectral reflectivity of the multilayer thin film is reduced. It is an object to provide a method capable of accurately measuring the film thickness of each layer based on the method.

[0016]

In order to solve the above-mentioned problems, the present invention measures the spectral reflectance of a multilayer thin film composed of a plurality of thin films having different optical constants laminated on a substrate, and measures the measured spectral reflectance. The maximum value and the minimum value of the reflectance and the wavelength value of the maximum point are calculated by using these values (the maximum value of the reflectance, the minimum value of the reflectance,
Provided is a method for measuring the thickness of a multilayer thin film, characterized in that the thickness of each layer is calculated by substituting it into a previously calculated formula for calculating the thickness of each layer, using the wavelength value of the maximum point as a variable.

According to this method, it is possible to measure the thickness of each layer of the multilayer thin film having only one maximum point of the spectral reflectance and also having the minimum point. When there are two or more minimum points, the minimum value of the minimum point having the longest wavelength is used. The film thickness calculation formula used in this method is, for example, the maximum value of the reflectance, the minimum value of the reflectance, and the wavelength value of the maximum point are each represented by a linear expression in which the film thickness of each layer is approximately a variable. Using the fact, it is derived as follows.

First, the spectral reflectances of a number of multilayer thin films having the same layer structure but different thicknesses are measured. Next, the maximum value and the minimum value of each of the obtained spectral reflectances and the wavelength value of the maximum point are shown, and the relationship between these values and the film thickness of each layer is approximately shown.
Then, the coefficients and constants of each linear expression are determined so that the residual is reduced (for example, by the least squares method) by substituting the film thickness value of each layer into these linear expressions. As a result, three linear equations are determined, and a film thickness calculation equation for each layer is derived from these three linear equations.

[0019] The present invention also provides a transparent substrate on one side,
At least a first dielectric layer, a recording layer in which a phase change between crystal and amorphous occurs according to the intensity of irradiation light, a second dielectric layer, and a heat transfer layer mainly composed of metal are sequentially laminated. In the method for measuring the thickness of the first dielectric layer, the recording layer, and the second dielectric layer of the optical information recording medium, the thickness of the multilayer thin film is characterized by the following characteristics. Provide a measurement method. When the recording layer is in an amorphous state,
The spectral reflectance in the wavelength region of nm or less is measured from the substrate side, and the maximum value and the minimum value of the measured spectral reflectance and the wavelength value of the maximum point are determined by these values (the maximum value of the reflectance and the reflectance value). The film thickness of each layer is calculated by substituting the minimum value and the wavelength value at the maximum point into variables, which are derived in advance, into the equation for calculating the film thickness of each layer. When the recording layer is in an amorphous state,
After measuring the spectral reflectance in the wavelength region of nm or less from the substrate side, the recording layer is crystallized, and the recording layer is in a crystalline state, and the spectral reflectance in the same wavelength region is measured from the substrate side. The maximum value and the minimum value of the spectral reflectance in the state and the wavelength value of the maximum point, and the maximum value of the spectral reflectance in the crystalline state of the recording layer are represented by these values (the spectral reflectance in the amorphous state of the recording layer). The maximum value of the ratio, the minimum value, the wavelength value of the maximum point, and the maximum value of the spectral reflectance when the recording layer is in a crystalline state) are used as variables, and are substituted into the previously derived film thickness calculation formula of each layer. Calculate the film thickness.

As described above, for example, an optical information recording medium in which the substrate is made of polycarbonate and the first dielectric layer has a relatively small thickness (for example, 90 to 110 nm) is 38
There is only one maximum point and minimum point of the spectral reflectance in the wavelength region of 0 nm or more and 800 nm or less, and the measurement accuracy of the wavelength value of the minimum point is low. Even in the case of such an optical information recording medium, according to these methods, the film thickness of each layer is calculated by using the maximum value and the minimum value of the spectral reflectance and the wavelength value of the maximum point. The thickness can be accurately measured.

In the case where the substrate is made of polycarbonate and the thickness of the first dielectric layer is about 130 nm, the maximum point of the spectral reflectance in the wavelength region of 380 nm or more and 800 nm or less is obtained. There is only one and two minimum points. In this case, the minimum value of the minimum point on the long wavelength side is used. Further, the method of (1) has more variables in the equation for calculating the film thickness of each layer than the method of (1), and thus it is considered that the method of (2) has a higher accuracy in calculating the film thickness than the method of (2).

The formula for calculating the film thickness used in the above method is derived, for example, as follows. In the case of the optical information recording medium having the film configuration, in a range where the film thickness is as small as several nm, the recording layer has a spectral reflectance measured in an amorphous state.
The maximum value of the reflectance (Rtop) and the minimum value of the reflectance (Rbot)
) And the wavelength value (λtop) of the local maximum point are approximately the thickness of the first dielectric layer (Td1), the thickness of the second dielectric layer (Td2), and the thickness of the recording layer (Tr), respectively. Are represented by the following formulas (1) to (3), where

Λtop = a × Td1 + b (1) Rtop = c × Td1 + d × Tr + e × Td2 + f (2) Rbot = g × Td1 + h × Tr + i × Td2 + j (3) Therefore, first, the same layer With respect to a large number of optical information recording media in which the thickness of each layer is changed in the configuration, the spectral reflectance is measured in the above wavelength region while the recording layer is in an amorphous state. Next, the maximum value (Rtop) and the minimum value (Rbo) of each obtained spectral reflectance
t), the wavelength value at the maximum point (λtop), and the film thickness value (T
d1, Td2, Tr) are substituted into the above equations (1) to (3), and the coefficients (a, c, d, e, g, h, i) and constants (b,
f, j). Thus, equations (1) to (3) are determined.

From these three equations, the film thickness (Td1) of the first dielectric layer, the film thickness (Td2) of the second dielectric layer, and the film thickness (Tr) of the recording layer are defined as the maximum value (Rtop) and the minimum value. A formula for calculating each film thickness is represented by the value (Rbot) and the wavelength value (λtop) at the maximum point. The film thickness calculation formula used in the above method is derived, for example, as follows. In the case of the optical information recording medium having the above film configuration, in the range where the film thickness is as small as several nm, the maximum value of the reflectance (Rtop) and the minimum value of the reflectance (Rtop) in the spectral reflectance measured when the recording layer is in an amorphous state. Rbot) and the wavelength value of the maximum point (λtop) are approximately
The thickness of the first dielectric layer (Td1) and the thickness of the second dielectric layer (Td1)
d2), the above equation (1) using the recording layer thickness (Tr) as a variable
To (3). Also, regarding the spectral reflectance measured in a crystalline state of the recording layer, the maximum value of the reflectance (Rtop-
c) is approximately expressed by the following equation (4) using the thickness of the first dielectric layer (Td1) and the thickness of the recording layer (Tr) as variables.

Rtop-c = p × Td1 + q × Tr + s (4) Therefore, first, for a large number of optical information recording media having the same layer configuration and different thicknesses of the respective layers, the above-mentioned wavelength is obtained when the recording layer is in an amorphous state. Measure the spectral reflectance in the area. Next, the spectral reflectance is measured in the above wavelength range while the recording layer of each optical information recording medium is crystallized.

For each of the obtained spectral reflectances, the maximum value (Rtop), the minimum value (Rbot) when the recording layer is in an amorphous state,
The wavelength value at the maximum point (λtop), the maximum value (Rtop-c) when the recording layer is in a crystalline state, and the film thickness values (Td1, Td2, Tr) of each layer.
Is substituted into the above equations (1) to (4), and the coefficients (a, c,
d, e, g, h, i, p, q) and constants (b, f, j,
s). As a result, equations (1) to (4) are determined.

From these four equations, the film thickness (Td1) of the first dielectric layer, the film thickness (Td2) of the second dielectric layer, and the film thickness (Tr) of the recording layer are defined as the maximum value (Rtop) and the minimum value. A formula for calculating each film thickness is derived, which is represented by the value (Rbot), the wavelength value (λtop) of the maximum point, and the maximum value (Rtop-c). When manufacturing an optical information recording medium, one surface of the substrate (the surface on which the thin film is not formed, this surface is referred to as the “front surface” and the surface on which the thin film is formed is referred to as the “back surface” ) May be provided with a film made of a transparent synthetic resin to prevent the surface of the substrate from being damaged during the film formation. This film is called a hard coat, and is usually formed by applying an ultraviolet curable resin to the surface of the substrate and irradiating it with ultraviolet light to cure the resin. When the spectral reflectance is measured at the portion where the hard coat is present, the spectral reflectance of the optical information recording medium becomes as shown in FIG. 2 due to the interference of the hard coat, and the spectral reflectance is not accurately measured.

Therefore, in the case of an optical information recording medium having a hard coat, the hard coat formation range is not set to the entire surface of the substrate, and the portion where the hard coat is not formed is provided in the range where the thin film is formed on the back surface side. . Then, light is incident from the front surface side of the substrate into a flat portion of the substrate where a thin film is formed on the back surface and a hard coat is not formed on the front surface, and the spectral reflectance is measured. Thereby, the spectral reflectance of the optical information recording medium is accurately measured. The size of the region needs to be larger than the spot size of the spectroscope to be used, and for example, is preferably larger than a circle having a diameter of 2 mm or more.

Regarding the thickness of each layer, for example, as the first dielectric layer, the optical constants (N: refractive index,
K: In the case of the optical information recording medium in which a thin film made of ZnS-SiO ₂ of the extinction coefficient) is formed, the film thickness of the first dielectric layer is equal to or less than 160 nm, the maximum point of the spectral reflectance one When the film thickness is smaller than 70 nm, the maximum point appears on the lower wavelength side than 380 nm. Therefore, in the case of an optical information recording medium having such a first dielectric layer, if the thickness of the first dielectric layer is 70 nm or more and 160 nm or less, highly accurate film thickness measurement can be performed by the method of the present invention. Done.

A first dielectric layer made of ZnS-SiO ₂ having a thickness of 100 nm is formed on a polycarbonate substrate.
GeSbTe recording layer, 20 nm thick ZnS-
Second dielectric layer made of SiO ₂ , 100 nm thick Al
With respect to an optical disk on which a heat transfer layer made of an alloy was sequentially formed, a change in the maximum value (Rtop) of the spectral reflectance when the film thickness of the recording layer was changed was examined by optical simulation. The results are shown in a graph in FIG.

As shown in this graph, when the thickness of the recording layer is in the range of 15 nm or more and 40 nm or less, the maximum value (Rtop) of the reflectance greatly changes as the thickness of the recording layer changes. In the range of a few nm within the range, there is an approximate first-order correlation between the thickness of the recording layer and the maximum value (Rtop) of the reflectance. However, outside this range, the rate of change of the maximum value (Rtop) of the reflectance with respect to the thickness of the recording layer is small. Therefore, in the case of the optical information recording medium having the above film configuration, if the thickness of the recording layer is 15 nm or more and 40 nm or less, highly accurate film thickness measurement is performed by the method of the present invention.

[0032]

Embodiments of the present invention will be described below. First, an optical disk having the layer configuration shown in FIG. 5 was manufactured in the following procedure. As the substrate 1, a disk made of a polycarbonate resin and having an outer diameter of 120 mm and a thickness of 0.6 mm is prepared. This substrate 1 has a center hole 11 having a radius of 15 mm.
Having. FIG. 6 is a sectional view of the optical disk. As shown in this figure, a hard coat 2 is formed on the front surface of a substrate 1 of the optical disk, and a multilayer thin film 3 is formed on the back surface. After the formation of the hard coat 2, the multilayer thin film 3 was formed.

The hard coat 2 is formed by applying an ultraviolet curable resin to the surface of the substrate 1 so that an unformed portion 2A having a radius of 22 mm is formed around the center hole 11 of the substrate 1 and then irradiating ultraviolet rays. It was formed by curing. The multilayer thin film 3 was formed by setting the size of the inner peripheral mask holding the center hole 11 to a radius of 15 mm so that the unformed portion 3A was formed around the center hole 11 of the substrate 1.

As a result, in the central portion of the substrate 1, a region 15 in which the multilayer thin film 3 is formed on the back surface and the hard coat 2 is not formed on the front surface has an inner diameter of 15 mm and an outer diameter of 22 mm
Are formed in an annular shape. This region 15 is a flat portion without a laser tracking groove or a peripheral groove generated by transfer of a stamper holding portion of a mold. The multilayer thin film 3 is formed on the substrate 1 with Zn having an optical constant shown in FIG.
A first dielectric layer 31 made of S-SiO ₂ , a recording layer 32 made of GeSbTe having an optical constant shown in FIG. 7 in an amorphous state, and ZnS-SiO same as the first dielectric layer 31
_{A second} dielectric layer 33 made of No. 2 and a reflective layer made of a metal containing Al as a main component and having an optical constant shown in FIG. 8 were formed by successive sputtering.

In order to protect the film formation surface of the substrate 1,
An ultraviolet curable resin was applied to the surface of the multilayer thin film 3 using a spin coater, and then cured by irradiating ultraviolet rays. The multilayer thin film 3 was formed by changing the thickness of each layer as shown in Table 1, thereby producing a large number of optical disks (A to M) having the same layer configuration and different thicknesses of each layer.

Next, for each optical disk, the recording layer 32
Was measured in a wavelength range of 380 nm to 800 nm in an amorphous state. This measurement is performed on the substrate 1
Light is incident from the surface on the hard coat 2 side into the region 15 of FIG. Since the recording layer 32 is formed in an amorphous state, if the measurement is performed immediately after the film formation without performing initialization (crystallization), the spectral reflectance in the amorphous state of the recording layer 32 is measured. You.

Next, with respect to each optical disk, after the entire surface of the recording layer 32 was crystallized using an initialization device, the spectral reflectance was measured in the same manner as described above. From the wavelength-reflectance characteristic curve of each optical disk obtained by the measurement, the maximum value (Rtop) of the reflectance when the recording layer is measured in an amorphous state,
The minimum value (Rbot), the wavelength value of the maximum point (λtop), and the maximum value (Rto) of the reflectance when the recording layer is measured in a crystalline state.
pc). These values are shown in Table 1.

[0038]

[Table 1]

As shown in Table 1, each of the optical discs of Samples A to M has a first group (Samples A to E) in which only the thickness of the first dielectric layer is different from a first group (Samples A to E) in which only the thickness of the recording layer is different. It is classified into two groups (samples F to I) and a third group (samples J to M) in which only the thickness of the second dielectric layer is different. From the results in Table 1, the wavelength value (λtop) of the maximum point is larger in the first group than the difference (2.5 nm, 0.5 nm) in the second and third groups. It can be seen that a difference (56.4 nm) has occurred. Therefore, in the optical disk having this film configuration, the wavelength value (λtop) at the maximum point is approximately determined when the thickness of the first dielectric layer is in the range of 90 nm or more and 110 nm or less.
It is expressed by a linear equation (the above-described equation (1)) with the thickness (Td1) of the first dielectric layer film as a variable.

As for the maximum value (Rtop), the minimum value (Rbot) and the maximum value (Rtop-c) of the reflectance, there is no large difference between the groups, and the respective values correspond to the first dielectric constant. It can be seen that the thickness depends on the thickness of the body layer, the second dielectric layer, and the recording layer. Therefore, in the optical disc having this film configuration, the maximum value (Rtop) and the minimum value (Rbo) of the reflectivity are obtained.
t), the maximum value (Rtop-c) indicates that the film thickness of the recording layer is 23 nm.
The thickness of the first dielectric layer (Td1) and the thickness of the second dielectric layer (Td2) are approximately within the range where the thickness of the second dielectric layer is not less than 27 nm and not more than 18 nm and not more than 21 nm. , A linear equation with the film thickness (Tr) of the recording layer as a variable (formula (2)
(4)).

Therefore, as a first method, first, the maximum value (Rtop) and the minimum value (Rbo) of each of the obtained spectral reflectances are obtained.
t), the wavelength value of the maximum point (λtop) and the film thickness of each layer (Td1, Td2, Tr) are substituted into the above equations (1) to (3), and the coefficients of each equation are calculated by the least square method. (A, c, d, e,
g, h, i) and constants (b, f, j). Thereby, Expressions (11) to (13) corresponding to Expressions (1) to (3) in this case were obtained.

Λtop = 2.88 × Td1 + 174.8 (11) Rtop = −0.104 × Td1 + 1.02 × Tr + 0.2 × Td2 + 8.39 (12) Rbot = −0.04 × Td1 + 0. 35 × Tr + 0.25 × Td2−4.04 (13) Then, by performing a predetermined approximate calculation using these three equations, the film thickness (Td1) of the first dielectric layer and the second dielectric The film thickness (Td2) of the body layer and the film thickness (Tr) of the recording layer are set to a maximum value (Rtop), a minimum value (Rbot), and a wavelength value (λto
Equations (5) to (7) for calculating each film thickness, which are expressed by p), were derived.

Td1 = 0.347 × λtop−60.7 (5) Td2 = 0.008 × λtop−1.89 × Rtop + 5.51 × Rbot + 36.7 (6) Tr = 0.034 × λtop + 1.35 × Rtop−1.08 × Rbot−21.6 (7) By using these formulas, the film thickness of the first dielectric layer and the second dielectric layer of each of Samples A to M And the thickness of the recording layer were calculated. Table 2 shows the results.

[0044]

[Table 2]

From the results shown in Table 2, the thickness of the first dielectric layer and the thickness of the second dielectric layer of each of the samples A to M were calculated using the calculation formulas (5) to (7). It can be seen that the value and the calculated value of the film thickness of the recording layer substantially coincide with the film thickness of each layer. Therefore, in the case of an optical disc having this layer structure,
The spectral reflectance is measured, and the maximum value (Rtop), the minimum value (Rbot), and the wavelength value (λtop) of the maximum point are calculated by Equation (5).
To (7), the first dielectric layer 31, the recording layer 3
2 and the film thickness of the second dielectric layer 33 can be accurately measured.

As a second method, the maximum value (Rtop-c) of the reflectance in the crystalline state of the recording layer and the film thickness (T
d1, Td2, Tr) are substituted into the above equation (4), and a coefficient (p, q) and a constant (s) are obtained by the least squares method. Thereby, Expression (14) corresponding to Expression (4) in this case was obtained. Rtop-c = −0.052 × Td1 + 0.70 × Tr + 28.7 (14) Using this equation (14) and the above four equations (11) to (13), A solution (Td1, Tr, Td2) that reduces the residual of is obtained. Expressions (11) to (14)
Is a formula that represents a plane with Td1, Tr, and Td2 as coordinate axes, and a solution exists inside a figure surrounded by four planes represented by each formula, that is, a tetrahedron.

Therefore, for example, the following equations (8) to (10) for calculating the center of gravity of this tetrahedron as an approximate solution are derived as equations for calculating each film thickness. Td1 = 0.26 × λtop−14.7 × Rtop + 11.7 × Rbot + 15.5 × Rtop-c−320.3 (8) Tr = 0.21 × λtop−0.75 × Rtop + 0.60 × Rbot + 2.22 × Rtop-c−58.8 (9) Td2 = 0.19 × λtop−0.045 × Rtop + 4.04 × Rbot−1.95 × Rtop-c + 69.4 (9) 10) If these formulas are used, the spectral reflectance (particularly Rbot)
Even when the measurement error is large, the calculation error of the film thickness becomes small, so that the film thickness can be measured with high accuracy.

Next, an optical disk having a layer structure shown in FIG. 9 was manufactured. Since this optical disc has a different layer configuration from the above-described optical disc shown in FIG. 5, the method of forming the multilayer thin film 3 is performed as follows. Other points (the formation range of the hard coat 2 and the multilayer thin film 3 and the like) were manufactured by the same method as the optical disk of FIG.

The multilayer thin film 3 is formed on the substrate 1 by a first dielectric layer 31 made of ZnS--SiO ₂ having an optical constant shown in FIG. 3 and a crystallization made of a metal nitride having an optical constant shown in FIG. Promoting layer 35, G having the optical constants shown in FIG.
recording layer 32 made of ESbTe, second dielectric layer 33 made of the same ZnS-SiO ₂ as the first dielectric layer 31, a reflective layer 34 made of a metal to Al main component having optical constants shown in FIG. 8, sequentially It was formed by forming a film by a sputtering method.

The multilayer thin film 3 is formed by changing the thickness of each layer as shown in Table 3 to produce a large number of optical discs (N to Z) having the same layer configuration and different thicknesses of each layer. did. Next, with respect to each optical disk, the spectral reflectance was measured in a wavelength range of 380 nm to 800 nm while the recording layer 32 was in an amorphous state. This measurement is performed by irradiating light from the hard coat 2 side into the region 15 of the substrate 1 shown in FIG.

The wavelength of each optical disk obtained by the measurement
From the reflectance characteristic curve, the maximum value (Rtop), the minimum value (Rbot), and the maximum value of the reflectance measured in the amorphous state of the recording layer.
The wavelength value (λtop) at the maximum point was examined. Table 3 shows these values.
Shown in

[0052]

[Table 3]

As shown in Table 3, each of the optical discs of samples NZ has a first group (samples N to R) in which only the thickness of the first dielectric layer is different from the first group (samples N to R) in which only the thickness of the recording layer is different. It is classified into two groups (samples S to V) and a third group (samples W to Z) in which only the thickness of the second dielectric layer is different. From the results in Table 1, the wavelength value (λtop) at the maximum point is larger in the first group than in the difference (2.2 nm, 0.2 nm) in the second and third groups. It can be seen that a difference (57.5 nm) has occurred. Therefore, in the optical disk having this film configuration, the wavelength value (λtop) at the maximum point is approximately determined when the thickness of the first dielectric layer is in the range of 90 nm or more and 110 nm or less.
It is expressed by a linear equation (the above-described equation (1)) with the thickness (Td1) of the first dielectric layer film as a variable.

Regarding the maximum value (Rtop) and the minimum value (Rbot) of the reflectance, there is no large difference between the groups, and the respective values correspond to the first dielectric layer and the second dielectric layer.
It can be seen that it depends on the thickness of each of the dielectric layer and the recording layer. Therefore, in the optical disk having this film configuration, the maximum value (Rtop) and the minimum value (Rbot) of the reflectance are as follows: the film thickness of the recording layer is 23 nm or more and 27 nm or less, and the film thickness of the second dielectric layer is 18 nm or more and 21 nm or less. Within the range shown below, a linear expression (approximately as described above) using the thickness of the first dielectric layer (Td1), the thickness of the second dielectric layer (Td2), and the thickness of the recording layer (Tr) as approximations is obtained. Expressions (2) and (3)).

Therefore, first, the maximum value (Rtop), the minimum value (Rbot), the wavelength value of the maximum point (λtop) of each obtained spectral reflectance, and the film thickness (Td1, Td2, Tr) of each layer.
Is substituted into the above equations (1) to (3), and the coefficients (a, c, d, e, g, h, i) and constants (b, f, j) of each equation are calculated by the least square method. Ask. Thereby, Expressions (21) to (23) corresponding to Expressions (1) to (3) in this case were obtained.

Λtop = 2.82 × Td1 + 193.2 (21) Rtop = −0.098 × Td1 + 1.00 × Tr + 0.20 × Td2 + 8.38 (22) Rbot = −0.03 × Td1 + 0. 27 × Tr + 0.15 × Td2−1.28 (23) Then, by performing a predetermined approximate calculation using these three equations, the film thickness (Td1) of the first dielectric layer and the second dielectric The film thickness (Td2) of the body layer and the film thickness (Tr) of the recording layer are set to a maximum value (Rtop), a minimum value (Rbot), and a wavelength value (λto
The formulas (14) to (16) for calculating each film thickness, which are expressed by p), were derived.

Td1 = 0.355 × λtop−68.5 (14) Td2 = 0.133 × λtop−2.81 × Rtop + 10.42 × Rbot + 34.3 (15) Tr = 0.032 × λtop + 1.56 × Rtop−2.08 × Rbot−22.0 (16) Using these formulas, the film thickness of the first dielectric layer and the second dielectric layer of each sample NZ And the thickness of the recording layer were calculated. Table 4 shows the results.

[0058]

[Table 4]

From the results in Table 4, the calculation formulas (14) to (1)
The calculated value of the thickness of the first dielectric layer, the calculated value of the thickness of the second dielectric layer, and the calculated value of the thickness of the recording layer of each sample NZ calculated using 6) are the formed film thickness of each layer. It can be seen that the values almost match. Therefore, in the case of an optical disk having this layer configuration, the spectral reflectance is measured, and the maximum value (Rtop), the minimum value (Rbot), and the wavelength value (λtop) of the maximum point are calculated by equations (14) to (16). Into the first dielectric layer 31,
The thickness measurement of the recording layer 32 and the second dielectric layer 33 can be accurately performed.

However, in the case of an optical disk having this layer configuration, the crystallization promoting layer 35 and the first dielectric layer 31 have similar optical characteristics, and thus the crystallization promoting layer 35 is formed by the method of this embodiment.
It is difficult to measure the film thickness. Note that the multilayer thin film to be measured in the method of the present invention is not limited to an optical information recording medium such as an optical disk, and any multilayer thin film having only one maximum point of spectral reflectance and also having a minimum point. It may be.

The method of forming the multilayer thin film to be measured in the method of the present invention is not limited to the above-mentioned sputtering method, but may be a known method other than the sputtering method, for example, a vacuum evaporation method, an ion beam sputtering method, an ion beam Methods such as a vapor deposition method, an ion plating method, an electron beam vapor deposition method, and a plasma polymerization method can be appropriately adopted according to the purpose, material, and the like.

The substrate of the multilayer thin film to be measured in the method of the present invention is not limited to a polycarbonate resin substrate, but may be an acrylic resin, an epoxy resin, a polystyrene resin, or the like.

[0063]

As described above, according to the method of the present invention, even in the case of a general phase change optical disk having a substrate made of a polycarbonate resin, the thickness of each layer is determined based on the spectral reflectance of the multilayer thin film. Can be accurately measured. Therefore, the thickness of a general phase-change optical disk having a polycarbonate resin substrate can be measured with high accuracy without destruction and without changing the manufacturing conditions.

In particular, according to the method of claims 2 and 3, the optical information has at least a multilayer thin film composed of a first dielectric layer, a phase-change recording layer, a second dielectric layer, and a heat transfer layer on a substrate. With respect to the recording medium, the thicknesses of the first dielectric layer, the recording layer, and the second dielectric layer can be accurately measured. Further, according to the method of the third aspect, the measurement accuracy of the film thickness of the first dielectric layer, the recording layer, and the second dielectric layer can be further improved.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of the spectral reflectance of a general phase change optical disc.

FIG. 2 is a graph showing an example of the spectral reflectance measured at a portion where a hard coat is provided on the same optical disk as in FIG. 1;

FIG. 3 is a graph showing optical constants of a first dielectric layer of the optical disc manufactured in the embodiment.

FIG. 4 is a graph showing a result obtained by examining a relationship between a film thickness of a recording layer and a maximum value (Rtop) of a spectral reflectance with respect to a general phase change optical disk by optical simulation.

FIG. 5 is a cross-sectional view showing a layer configuration of one optical disk manufactured in the embodiment.

FIG. 6 is a cross-sectional view illustrating a positional relationship among a substrate, a hard coat, and a multilayer thin film of the optical disk manufactured in the embodiment.

FIG. 7 is a graph showing optical constants of a recording layer of the optical disc manufactured in the embodiment.

FIG. 8 is a graph showing optical constants of a heat transfer layer of the optical disc manufactured in the embodiment.

FIG. 9 is a cross-sectional view illustrating a layer configuration of the other optical disc manufactured in the embodiment.

FIG. 10 is a graph showing optical constants of a crystallization promoting layer of the optical disc manufactured in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 11 Center hole 15 Spectral reflectance measurement area 2 Hard coat 2A Unformed portion of hard coat 3 Multilayer thin film 3A Unformed portion 31 First dielectric layer 32 Recording layer 33 Second dielectric layer 34 Heat transfer layer 35 Crystallization Promotion layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yuji Ushiwaka 2nd, Samejima, Fuji-shi, Shizuoka Prefecture HH04 HH11 HH14 HH18

Claims (3)

[Claims] 1. The spectral reflectance of a multilayer thin film composed of a plurality of thin films having different optical constants laminated on a substrate is measured, and the measured maximum value, the minimum value, and the wavelength value of the maximum point of the spectral reflectance are determined. A method for measuring the film thickness of a multilayer thin film, wherein the film thickness of each layer is calculated by substituting these values into a previously-calculated formula for calculating the film thickness of each layer. 2. The method according to claim 1, wherein at least one surface of the transparent substrate has at least
An optical element in which a first dielectric layer, a recording layer in which a phase change between crystal and amorphous occurs according to the intensity of irradiation light, a second dielectric layer, and a heat transfer layer mainly containing metal are sequentially laminated. A first dielectric layer, a recording layer, and a second dielectric layer of the information recording medium;
The method for measuring the thickness of a multilayer thin film for measuring the thickness of a dielectric layer, wherein the recording layer is in an amorphous state and has a thickness of 380 nm or more and 800 n
m from the substrate side in the wavelength range below m
The maximum value and the minimum value of the measured spectral reflectance and the wavelength value of the maximum point are substituted into the previously calculated film thickness calculation formula of each layer using these values as variables to calculate the film thickness of each layer. A method for measuring the thickness of a multilayer thin film, comprising: . 3. At least one surface of a transparent substrate has at least
An optical element in which a first dielectric layer, a recording layer in which a phase change between crystal and amorphous occurs according to the intensity of irradiation light, a second dielectric layer, and a heat transfer layer mainly containing metal are sequentially laminated. A first dielectric layer, a recording layer, and a second dielectric layer of the information recording medium;
The method for measuring the thickness of a multilayer thin film for measuring the thickness of a dielectric layer, wherein the recording layer is in an amorphous state and has a thickness of 380 nm or more and 800 n or more.
After measuring the spectral reflectance in the wavelength region of m or less from the substrate side, the recording layer is crystallized. When the recording layer is in a crystalline state, the spectral reflectance in the same wavelength region is measured from the substrate side. The maximum value and the minimum value of the spectral reflectance in the state and the wavelength value of the maximum point, and the maximum value of the spectral reflectance in the crystalline state of the recording layer, with these values as variables, each layer derived in advance. A method for measuring the thickness of a multilayer thin film, wherein the thickness of each layer is calculated by substituting it into a thickness calculation formula.