JP3695017B2 - Groove shape measurement method using diffracted light - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a groove shape measuring method for measuring the groove shape of a periodic groove using diffracted light, and more particularly to measuring the groove shape of a periodic groove carved on the surface of an optical disc, using the diffracted light. About.
[0002]
[Prior art]
Grooves are periodically carved on the surface of the optical disk. In order to manufacture an optical disc, it is necessary to accurately manage the groove shape of the periodic groove, that is, the groove width and depth. As a conventional groove shape measuring method for measuring the groove shape of the periodic groove, a method using diffracted light is known. This measurement method can measure the groove shape very efficiently without contact compared to contact types such as Taly Step and AFM (Atomic Force Microscope).
[0003]
This conventional measurement method will be described with reference to FIG.
First, a laser beam is irradiated on a periodic groove carved on the surface of the optical disc 1.
The zero-order, first-order, and second-order diffracted light generated by this irradiation is received by the light receiver 2, and the intensity of each diffracted light is measured.
Two types of diffracted light intensity, a first diffracted light intensity ratio (first-order light intensity / 0th-order light intensity) and a second diffracted light intensity ratio (second-order light intensity / first-order light intensity) obtained by this measurement, respectively. The groove shape (groove width and groove depth) of the periodic groove is determined based on the ratio.
In this conventional measuring method, the first diffracted light intensity ratio and the second diffracted light intensity ratio with respect to various groove widths and groove depths are calculated in advance. A curve group in FIG. 14 shows the calculation results in contour lines. The curve group of the diffracted light intensity ratio is calculated with high accuracy by the vector diffraction theory. In FIG. 14, the horizontal axis indicates the groove depth, and the vertical axis indicates the groove width.
When the first diffracted light intensity ratio obtained by measurement is 0.2 and the second diffracted light intensity ratio is 1.0, a curve having the first diffracted light intensity ratio of 0.2 and the second The groove depth and groove width are obtained from the intersection A with the curve having a diffracted light intensity ratio of 1.0.
As described above, according to the conventional groove shape measuring method, when the groove shape is rectangular, the two diffracted light intensity ratios obtained by the measurement (the first groove width and the groove depth) are two types (the first number). 1 and the second diffracted light intensity ratio), the groove shape of the rectangular periodic groove can be determined.
[0004]
[Problems to be solved by the invention]
However, in the conventional groove shape measuring method, when the groove shape is trapezoidal, the groove shape parameters are the groove depth, the upper bottom width, and the lower bottom width, and these three unknowns are obtained by measurement. Since there are two types of diffracted light intensity ratios, there is a problem that the trapezoidal groove shape cannot be determined.
The present invention has been made paying attention to such conventional problems, and the problem is to provide a groove shape measuring method using diffracted light that can determine the groove shape of a trapezoidal periodic groove. It is.
[0005]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a groove shape measuring method for measuring the groove shape of a periodic groove carved on the surface of a substrate using diffracted light, wherein one of two types of linearly polarized light having different polarization planes is used. A step of irradiating the periodic groove, measuring the intensities of the 0th, 1st and 2nd order diffracted light, and obtaining two kinds of diffracted light intensity ratios from the intensity of these three diffracted lights, and two kinds of straight lines Irradiating the other of the polarized light on the periodic groove, measuring the intensity of the 0th, 1st and 2nd order diffracted light generated at this time, and determining two kinds of diffracted light intensity ratios from the intensity of these three diffracted lights; Determining the groove shape of the periodic groove based on four kinds of diffracted light intensity ratios of two kinds of diffracted light intensity ratios of one linearly polarized light and two kinds of diffracted light intensity ratios of the other linearly polarized light A groove shape measuring method using diffracted light, comprising: A.
[0006]
In order to solve the above problems, the present invention provides a groove shape measuring method for measuring the groove shape of a periodic groove carved on the surface of a substrate using diffracted light, and one of two types of polarized light having different incident angles. , The intensity of the 0th, 1st and 2nd order diffracted light generated at this time is measured, and two kinds of diffracted light intensity ratios are obtained from the intensity of these three diffracted lights, Irradiating the other of the polarized light to the periodic groove, measuring each intensity of the 0th order, 1st order and 2nd order diffracted light, and obtaining two kinds of diffracted light intensity ratios from the intensity of these three diffracted lights; And determining a groove shape of the periodic groove based on four kinds of diffracted light intensity ratios of two kinds of diffracted light intensity ratios by one polarized light and two kinds of diffracted light intensity ratios by the other polarized light. Is a groove shape measuring method using diffracted light.
[0007]
Furthermore, in order to solve the above problems, the present invention provides a groove shape measuring method for measuring the groove shape of a periodic groove carved on the surface of a substrate by using diffracted light. A step of measuring each intensity of the 0th order, 1st order, 2nd order diffracted light and 3rd order diffracted light, and obtaining three kinds of diffracted light intensity ratios from the intensity of these four diffracted lights, and based on the three kinds of intensity ratios And a step of determining the groove shape of the periodic groove. A groove shape measuring method using diffracted light.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2 show a groove shape measuring method using diffracted light according to the first embodiment of the present invention. In this groove shape measuring method, the groove shape of the trapezoidal periodic groove 10a carved on the surface of the optical disk 10 is measured using 0th order, 1st order and 2nd order diffracted light. The linearly polarized light is used. That is, linearly polarized light whose polarization plane is parallel to the periodic groove 10a (referred to as E-polarized light) and linearly polarized light whose polarization plane is perpendicular to the periodic groove 10a (referred to as H-polarized light) are used. In E-polarized light, the plane of polarization is perpendicular to the plane of incidence, that is, S-polarized light. In H-polarized light, the polarization plane is included in the incident plane, that is, P-polarized light.
In general, the intensity of diffracted light differs depending on whether the direction of the polarization plane (vibration plane of the electric field vector) is parallel or perpendicular to the groove. The groove shape of the trapezoidal periodic groove 10a can be determined using this polarization difference. This polarization difference cannot be explained by scalar diffraction theory, but must be based on vector diffraction theory.
[0009]
Now, the measuring machine for carrying out the groove shape measuring method using the diffracted light according to the first embodiment includes a half-wave plate 11, 0th order, 1 for rotating the polarization plane of the incident laser light. A light receiver 12 and the like that receive the second-order and second-order diffracted light and output an electrical signal corresponding to the intensity thereof are provided. The light receiver 12 is configured by, for example, a two-divided light receiving element. One light receiver 12 may be provided so as to be movable to the light receiving position of each diffracted light, or the light receiver 12 may be disposed at each light receiving position of each diffracted light.
[0010]
The groove shape measuring method using diffracted light according to the first embodiment includes the following steps (1) to (4).
(1) A group of diffracted light intensity curves for various trapezoidal periodic grooves 10a is prepared in advance for each of E-polarized light and H-polarized light.
For example, for each of the case where the E-polarized light is irradiated on the periodic groove 10a and the case where the H-polarized light is irradiated on the periodic groove 10a,
w₁: Upper base width of trapezoidal periodic groove 10a
w₂: Bottom width of periodic groove 10a
Δ: Sagging of periodic groove 10a (Δ = w₁-W₂)
Then, a diffracted light intensity ratio curve group as shown in FIGS. 3 and 4 is calculated for three patterns of Δ = 0 nm, 200 nm, and 400 nm. In both figures, the horizontal axis represents the groove depth h, and the vertical axis represents the average groove width w._m(W_m= (W₁+ W₂) / 2) are shown respectively.
[0011]
That is, when Δ = 0 nm for E-polarized light, the ratio of two kinds of diffracted light intensity a_E, B_EA curve group (see FIG. 3) is prepared. Similarly, for each of the cases where Δ = 200 nm for E-polarized light and Δ = 400 nm for E-polarized light, two kinds of diffracted light intensity ratios a_E, B_ECurve groups (both not shown in the same curve group as in FIG. 3) are prepared. Similarly to E-polarized light, the two diffracted light intensity ratios a when H = 0-polarized and Δ = 0 nm are used._E, B_EA curve group (see FIG. 4) is prepared. Similarly, for each of the cases where Δ = 200 nm for H-polarized light and Δ = 400 nm for H-polarized light, the two diffracted light intensity ratios a_H, B_HThe curve group (both not shown in the curve group similar to FIG. 4) is prepared.
Thus, three types of curve groups for E-polarized light, three types of curve groups for H-polarized light, and six types of curve groups are prepared. The calculation of each curve group uses vector diffraction theory.
[0012]
(2) Next, by rotating the half-wave plate 11 and rotating the polarization plane of the laser light, one of two types of linearly polarized light having different polarization planes, for example, E-polarized light is irradiated to the periodic groove 10a. . The respective intensities of the 0th, 1st and 2nd order diffracted light generated at this time are measured by the light receiver 12, and two kinds of diffracted light intensity ratios, that is, the first diffracted light intensity ratio a are determined from the intensity of these three diffracted lights._E(First-order light intensity / zero-order light intensity) and second diffracted light intensity ratio b_E(Secondary light intensity / primary light intensity) is obtained.
[0013]
(3) Next, the half-wave plate 11 is rotated to rotate the polarization plane of the laser light, thereby irradiating the periodic groove 10a with the other of the two types of linearly polarized light, for example, H-polarized light. The respective intensities of the 0th, 1st and 2nd order diffracted light generated at this time are measured by the light receiver 12, and two kinds of diffracted light intensity ratios, that is, the first diffracted light intensity ratio a are determined from the intensity of these three diffracted lights._HAnd the second diffracted light intensity ratio b_HAsk for.
[0014]
(4) Two kinds of diffracted light intensity ratio a by E-polarized light_E, B_EAnd two kinds of diffracted light intensity ratio a by H-polarized light_H, B_HThe shape of the trapezoidal periodic groove 10a is determined based on the four diffracted light intensity ratios.
A specific procedure for making this determination includes the following steps (4a) to (4d).
[0015]
(4a) First, diffracted light intensity ratio a when E polarization is set to Δ = 0 nm_E, B_ECurve group (see FIG. 3) and two kinds of diffracted light intensity ratios a by E-polarized light obtained in step (2) above._E, B_EThus, the groove depth h (E, 0) and the average groove width w (E, 0) when Δ = 0 nm for E-polarized light are determined. For example, the first diffracted light intensity ratio a_EAbout 0.23, the second diffracted light intensity ratio b_EIs about 1.3, the intensity ratio a_E, B_EThe groove depth h (E, 0) and the average groove width w (E, 0) are determined from the intersection B of the curve group obtained.
Similarly, the diffracted light intensity ratio a in the case of Δ-200 nm for E-polarized light_E, B_ECurve group (not shown) and two kinds of diffracted light intensity ratios a by E-polarized light obtained in step (2)_E, B_EFrom these, the groove depth h (E, 200) and the average groove width w (E, 200) when Δ = 200 nm for E-polarized light are determined.
Similarly, the diffracted light intensity ratio a when Δ = 400 nm for E-polarized light_E, B_ECurve group (not shown) and two kinds of diffracted light intensity ratios a by E-polarized light obtained in step (2)_E, B_EThus, the groove depth h (E, 400) and the average groove width w (E, 400) when Δ = 400 nm for E-polarized light are determined.
[0016]
(4b) Next, the diffracted light intensity ratio a when H = 0 and Δ = 0 nm_H, B_HCurve group (see FIG. 4) and two kinds of diffracted light intensity ratios a by H-polarized light obtained in the step (3)._H, B_HFrom these, the groove depth h (H, 0) and the average groove width w (H, 0) when Δ = 0 nm for H-polarized light are determined. For example, the first diffracted light intensity ratio a_HAbout 0.23, the second diffracted light intensity ratio b_HIs about 0.9, the intensity ratio a_H, B_HThe groove depth h (H, 0) and the average groove width w (H, 0) are determined from the intersection C of the curve group obtained.
Similarly, the diffracted light intensity ratio a when H = polarized light and Δ = 200 nm_H, B_HCurve group (not shown) and two kinds of diffracted light intensity ratios a by H-polarized light obtained in step (3)_H, B_HFrom these, the groove depth h (H, 200) and the average groove width w (H, 200) in the case of H polarized light and Δ = 200 nm are determined.
Similarly, a diffracted light intensity ratio curve group (not shown) when Δ = 400 nm is set for H-polarized light, and two types of diffracted light intensity ratio a for H-polarized light obtained in step (3)._E, B_EFrom these, the groove depth h (H, 400) and the average groove width w (H, 400) in the case of H polarized light and Δ = 400 nm are determined.
[0017]
(4c) Next, the three average groove widths w (E, 0), w (E, 200) and w (E, 400) for the E-polarized light determined in the step (4a), and the step (4b) From the three average groove widths w (H, 0), w (H, 200) and w (H, 400) for the H-polarized light determined in step 1, the upper base width w of the trapezoidal periodic groove 10a₁And bottom width w₂To decide.
That is, when the three average groove widths for E-polarized light are connected by a curve, a curve P shown in FIG. 5 is obtained. In FIG. 5, the horizontal axis indicates the slack Δ of the periodic groove 10a, and the vertical axis indicates the average groove width w._mAre shown respectively. Similarly, when three average groove widths for H-polarized light are connected by a curve, a curve Q shown in the figure is obtained. Since the true groove shape is on the curve P and on the curve Q, it is the groove shape of the trapezoidal periodic groove 10a obtained by the intersection D of the two curves PQ. Therefore, from the intersection D, the trapezoidal periodic groove 10a sag Δ and the average groove width w_mCan be requested.
The obtained Δ and w_mTo the upper width w of the periodic groove 10a₁And bottom width w₂The
w_m= (W₁+ W₂) / 2 and
Δ = w₁-W₂
It can be determined based on the relational expression.
[0018]
(4d) Next, three groove depths h (E, 0), h (E, 200) and h (E, 400) for the E-polarized light determined in the step (4a), and the step (4b) The groove depth h of the trapezoidal periodic groove 10a is determined from the three groove depths h (H, 0), h (H, 200) and h (H, 400) for the H-polarized light determined in step (1).
That is, when three groove depths for E-polarized light are connected by a curve, a curve P shown in FIG. 6 is obtained. In FIG. 6, the horizontal axis represents the slack Δ of the periodic groove 10a, and the vertical axis represents the groove depth h. Similarly, when three groove depths for H-polarized light are connected by a curve, a curve Q shown in the figure is obtained. Since the true groove shape is on the curve P and on the curve Q, it is the groove shape of the trapezoidal periodic groove 10a obtained by the intersection F of the two curves PQ. Therefore, from the intersection point F, the slack Δ and the groove depth h of the trapezoidal periodic groove 10a can be obtained. The droop Δ obtained here and the drool Δ obtained in the above step (4c) are the same value.
In this way, the upper base width w of the periodic groove 10a in the step (4c).₁And bottom width w₂The groove depth h can be determined in the step (4d).
[0019]
According to the first embodiment, by utilizing the fact that the diffracted light intensity differs between E-polarized light and P-polarized light (polarization difference), two kinds of diffracted light intensity ratios a to E-polarized light a_E, B_EAnd diffracted light intensity ratio a for P-polarized light_H, B_HRespectively, and these four kinds of diffracted light intensity ratios a_E, B_E, A_H, B_HSince the groove shape of the trapezoidal periodic groove 10a is determined based on (four parameters), the groove shape, that is, the upper bottom width w₁, Bottom width w₂And three unknowns of the groove depth h can be determined.
[0020]
In the first embodiment, the three average groove widths for E-polarized light, the three average groove widths for H-polarized light, the three groove depths for E-polarized light, and the three groove depths obtained for three kinds of slant Δ, respectively. Curves P in FIG. 5, curve Q in FIG. 5, curve P in FIG. 6, and curve Q in FIG. 6 are drawn with three groove depths for H-polarized light. Of course, when the number of Δ is larger than three, the curves P and Q can be drawn with higher accuracy and the groove shape can be determined with higher accuracy. However, even if there are three Δ, the curves P and Q can be drawn with sufficient accuracy by using parabolic approximation.
[0021]
In the first embodiment, the two diffracted light intensity ratios obtained from the intensities of the three diffracted lights are set to the first diffracted light intensity ratio a._E, A_H(First-order light intensity / zero-order light intensity) and second diffracted light intensity ratio b_E, B_H(Secondary light intensity / first-order light intensity), the two kinds of diffracted light intensity ratios are the primary light intensity / zero-order light intensity ratio and the secondary light intensity / zero-order light intensity ratio, Alternatively, the intensity ratio of secondary light intensity / 0th-order light intensity and the intensity ratio of secondary light intensity / primary light intensity may be used.
[0022]
In the above description of the first embodiment, in order to facilitate understanding of the present invention, diffracted light intensity curve groups for various trapezoidal periodic grooves 10a are prepared in advance for each of E-polarized light and H-polarized light. I explained that I did. For example, three types of curve groups (see FIG. 3) for E-polarized light respectively corresponding to three kinds of drool Δ and three types of curve groups (see FIG. 4) for H-polarized light respectively corresponding to three kinds of droop Δ are prepared. I explained that I did. However, actually, instead of preparing a group of curves as shown in FIGS. 3 and 4, a group of diffracted light intensity data for various trapezoidal periodic grooves 10a is calculated by vector diffraction theory, Using this data group, the groove shape can be directly obtained from the measurement result by numerical calculation.
[0023]
Next, a groove shape measuring method using diffracted light according to the second embodiment of the present invention will be described with reference to FIGS.
This groove shape measuring method uses two types of polarized light having the same polarization state and different incident angles.
In general, the diffracted light intensity varies depending on the incident angle. The trapezoidal groove shape can be determined using this incident angle characteristic. This incident angle dependency cannot be explained by the scalar diffraction theory, but it must be based on the vector diffraction theory.
The polarization state of the laser light may be circular polarization, E polarization, or H polarization if the polarization state of the laser light does not change when the incident angle changes. However, E-polarized light is preferred because H-polarized light can cause anomalies and cannot be interpolated.
In the second embodiment, E-polarized light with a certain incident angle (for example, θ = 30 °) and E-polarized light with another incident angle (for example, θ = 60 °) are used as the two types of polarized light.
[0024]
The groove shape measuring method using diffracted light according to the second embodiment includes the following steps (1) to (4).
(1) A group of diffracted light intensity curves for various trapezoidal periodic grooves 10a is prepared in advance for each of E-polarized light with an incident angle of 30 ° and E-polarized light with an incident angle of 60 °.
For example, for each of the case where the periodic groove 10a is irradiated with E-polarized light having an incident angle of 30 ° and the case where the E-polarized light having an incident angle of 60 ° is irradiated onto the periodic groove 10a, three patterns of Δ = 0 nm, 200 nm, and 400 nm are illustrated. 7 and a diffracted light intensity ratio curve group as shown in FIG. 8 are calculated.
That is, the two kinds of diffracted light intensity ratio a when E = 0 polarized light with an incident angle of 30 ° is set to Δ = 0 nm.₃₀, B₃₀A curve group (see FIG. 7) is prepared. Similarly, for each of the cases where Δ = 200 nm and Δ = 400 nm for E-polarized light with an incident angle of 30 °, two kinds of diffracted light intensity ratios a₃₀, B₃₀The curve group (both not shown in the curve group similar to FIG. 7) is prepared. Similarly to the E-polarized light with an incident angle of 30 °, the two diffracted light intensity ratios a when E = 0 polarized light with an incident angle of 60 ° are set to Δ = 0 nm.₆₀, B₆₀A curve group (see FIG. 8) is prepared. Similarly, for each of the cases where Δ = 200 nm and Δ = 400 nm for E-polarized light with an incident angle of 60 °, two kinds of diffracted light intensity ratios a₆₀, B₆₀Curve groups (both not shown in the same curve group as in FIG. 8) are prepared.
In this way, three types of curve groups for E-polarized light with an incident angle of 30 °, three types of curve groups for E-polarized light with an incident angle of 60 °, and six types of curve groups are prepared.
[0025]
(2) Next, one of two types of polarized light having the same polarization state and different incident angles, for example, E-polarized light having an incident angle of 30 ° is irradiated onto the periodic groove 10a. The respective intensities of the 0th, 1st and 2nd order diffracted light generated at this time are measured by the light receiver 12, and two kinds of diffracted light intensity ratios, that is, the first diffracted light intensity ratio a are determined from the intensity of these three diffracted lights.₃₀(First-order light intensity / zero-order light intensity) and second diffracted light intensity ratio b₃₀(Secondary light intensity / primary light intensity) is obtained.
[0026]
(3) Next, the periodic groove 10a is irradiated with the other of the two types of linearly polarized light, for example, E-polarized light with an incident angle of 60 °. The respective intensities of the 0th, 1st and 2nd order diffracted light generated at this time are measured by the light receiver 12, and two kinds of diffracted light intensity ratios, that is, the first diffracted light intensity ratio a are determined from the intensity of these three diffracted lights.₆₀And the second diffracted light intensity ratio b₆₀Ask for.
(4) Next, two kinds of diffracted light intensity ratio a by E-polarized light with an incident angle of 30 ° a₃₀, B₃₀And two kinds of diffracted light intensity ratios a by E-polarized light with an incident angle of 60 °₆₀, B₆₀The shape of the trapezoidal periodic groove 10a is determined based on the four diffracted light intensity ratios.
[0027]
A specific procedure for making this determination includes the following steps (4a) to (4d).
(4a) First, the diffracted light intensity ratio a when E = 0 polarized light with an incident angle of 30 ° is set to Δ = 0 nm.₃₀, B₃₀And two kinds of diffracted light intensity ratios a by E-polarized light having an incident angle of 30 ° determined in the above step (2).₃₀, B₃₀Therefore, the groove depth h (30 °, 0) and the average groove width w (30 °, 0) when Δ = 0 nm is set for E-polarized light with an incident angle of 30 ° are determined. For example, the first diffracted light intensity ratio a₃₀About 0.21, the second diffracted light intensity ratio b₃₀Is about 0.8, the intensity ratio a₃₀, B₃₀The groove depth h (30 °, 0) and the average groove width w (30 °, 0) are determined from the intersection point G of the curve group obtained.
Similarly, the diffracted light intensity ratio a when E = polarized light with an incident angle of 30 ° is set to Δ = 200 nm.₃₀, B₃₀Curve group (not shown) and two kinds of diffracted light intensity ratio a obtained in step (2)₃₀, B₃₀Thus, the groove depth h (30 °, 200) and the average groove width w (30 °, 200) when Δ = 200 nm for E-polarized light with an incident angle of 30 ° are determined.
Similarly, diffracted light intensity ratio a when E-polarized light with an incident angle of 30 ° is set to Δ = 400 nm.₃₀, B₃₀Curve group (not shown) and two kinds of diffracted light intensity ratio a obtained in step (2)₃₀, B₃₀Thus, the groove depth h (30 °, 400) and the average groove width w (30 °, 400) when Δ = 400 nm with E-polarized light at an incident angle of 30 ° are determined.
[0028]
(4b) Next, the diffracted light intensity ratio a when E = 0 polarized light with an incident angle of 60 ° is set to Δ = 0 nm.₆₀, B₆₀Curve group (see FIG. 8) and two kinds of diffracted light intensity ratios a obtained in the above step (3).₆₀, B₆₀From these, the groove depth h (60 °, 0) and the average groove width w (60 °, 0) when Δ = 0 nm for E-polarized light with an incident angle of 60 ° are determined. For example, the first diffracted light intensity ratio a₆₀About 0.17, the second diffracted light intensity ratio b₆₀Is about 1.3, the intensity ratio a₆₀, B₆₀The groove depth h (60 °, 0) and the average groove width w (60 °, 0) are determined from the intersection J of the curve group obtained.
Similarly, the diffracted light intensity ratio a when E = polarized light with an incident angle of 60 ° is set to Δ = 200 nm.₆₀, B₆₀Curve group (not shown) and two kinds of diffracted light intensity ratio a obtained in step (3)₆₀, B₆₀From these, the groove depth h (60 °, 200) and the average groove width w (60 °, 200) in the case of E-polarized light with an incident angle of 60 ° and Δ = 200 nm are determined.
Similarly, the diffracted light intensity ratio a when E = polarized light with an incident angle of 60 ° is set to Δ = 400 nm.₆₀, B₆₀Curve group (not shown) and two kinds of diffracted light intensity ratio a obtained in step (3)₆₀, B₆₀Thus, the groove depth h (60 °, 400) and the average groove width w (60 °, 400) in the case of Δ-400 nm with E-polarized light at an incident angle of 60 ° are determined.
[0029]
(4c) Next, three average groove widths w (30 °, 0), w (30 °, 200) and w (30 °, 400) for E-polarized light having an incident angle of 30 ° determined in the above step (4a). ) And three average groove widths w (60 °, 0), w (60 °, 200) and w (60 °, 400) for E-polarized light having an incident angle of 60 ° determined in the above step (4b). The upper base width w of the trapezoidal periodic groove 10a₁And bottom width w₂To decide.
That is, when the three average groove widths for E-polarized light with an incident angle of 30 ° are connected by a curve, a curve P shown in FIG. 9 is obtained. Similarly, when three average groove widths for E-polarized light with an incident angle of 60 ° are connected by a curve, a curve Q shown in the figure is obtained. Since the true groove shape is on the curve P and on the curve Q, it is the groove shape of the trapezoidal periodic groove 10a obtained by the intersection K of the two curves PQ. Therefore, from the intersection K, the trapezoidal periodic groove 10a sag Δ and the average groove width w_mCan be requested.
The obtained Δ and w_mTo the upper width w of the periodic groove 10a₁And bottom width w₂The
w_m= (W₁+ W₂) / 2 and
Δ = w₁-W₂
It can be determined based on the relational expression.
[0030]
(4d) Next, three groove depths h (30 °, 0), h (30 °, 200) and h (30 °, 400) for E-polarized light having an incident angle of 30 ° determined in the step (4a). ) And three groove depths h (60 °, 0), h (60 °, 200) and h (60 °, 400) for E-polarized light with an incident angle of 60 ° determined in the above step (4b). The groove depth h of the trapezoidal periodic groove 10a is determined.
That is, when the three groove depths for E-polarized light with an incident angle of 30 ° are connected by a curve, a curve P shown in FIG. 10 is obtained. Similarly, when three groove depths for E-polarized light with an incident angle of 60 ° are connected by a curve, a curve Q shown in the figure is obtained. Since the true groove shape is on the curve P and on the curve Q, it is the groove shape of the trapezoidal periodic groove 10a obtained by the intersection L of the two curves PQ. Therefore, from the intersection L, it is possible to obtain the slack Δ and the groove depth h of the trapezoidal periodic groove 10a. The droop Δ obtained here and the drool Δ obtained in the step (4c) are the same value.
[0031]
In this way, the upper base width w of the periodic groove 10a in the step (4c).₁And bottom width w₂The groove depth h can be determined in the step (4d).
According to the second embodiment, by using the incident angle characteristic that the diffracted light intensity changes depending on the incident angle, two kinds of diffracted light intensity ratios a with respect to E-polarized light having an incident angle of 30 ° are used.₃₀, B₃₀And two kinds of diffracted light intensity ratio a for E-polarized light with an incident angle of 60 °₆₀, B₆₀Respectively, and these four kinds of diffracted light intensity ratios a₃₀, B₃₀, A₆₀, B₆₀Since the groove shape of the periodic groove 10a is determined based on (four parameters), the groove shape of the trapezoidal periodic groove 10a, that is, the upper bottom width w₁, Bottom width w₂And three unknowns of the groove depth h can be determined.
[0032]
In the second embodiment, the two diffracted light intensity ratios obtained from the intensities of the three diffracted lights are set to the first diffracted light intensity ratio a.₃₀, A₆₀(First-order light intensity / zero-order light intensity) and second diffracted light intensity ratio b₃₀, B₆₀(Secondary light intensity / first-order light intensity), the two kinds of diffracted light intensity ratios are the primary light intensity / zero-order light intensity ratio and the secondary light intensity / zero-order light intensity ratio, Alternatively, the intensity ratio of secondary light intensity / 0th-order light intensity and the intensity ratio of secondary light intensity / primary light intensity may be used.
[0033]
Next, a groove shape measuring method using diffracted light according to the third embodiment of the present invention will be described.
This groove shape measuring method uses four diffracted lights from the 0th order to the 3rd order. That is, three types of diffraction intensity ratios determined from four diffracted light intensities from the 0th order to the 3rd order are used.
For example, by using three kinds of diffracted light intensity ratios of primary light intensity / zero-order light intensity, secondary light intensity / primary light intensity, and tertiary light intensity / secondary light intensity, the trapezoidal period Three unknowns regarding the groove shape of the groove 10a (upper bottom width w₁, Bottom width w₂And the groove depth h) can be determined.
[0034]
In each of the above-described embodiments, the case where transmitted diffracted light is used has been described. However, even when reflected diffracted light is used, the same operations and effects as when transmitted diffracted light is used can be obtained. The case where the reflected diffracted light is used is more suitable for measurement because the groove depth is four times as sensitive as the case of the transmitted diffracted light.
[0035]
Next, the actual optical disk is examined by examining the polarization characteristics and incident angle characteristics of the diffracted light intensity ratio.
The wavelength of the laser beam is 0.488 μm,
The refractive index of the optical disk (substrate) 10 is 1.5,
The groove period of the periodic groove (trapezoidal groove) 10a is 0.8 μm,
Groove depth h is 80 nm,
The upper base width of the trapezoidal groove is w₁,
The bottom width of the trapezoidal groove is w₂,
Trapezoidal groove sag Δ = w₁-W₂,
Average groove width w of trapezoidal groove_mW_m= (W₁+ W₂) /2=0.4 μm,
The 0th-order transmitted diffraction light intensity is T0,
The first-order transmitted diffraction light intensity is T1,
11 and 12 show changes in the transmitted diffraction light intensity ratio (first-order light intensity / zero-order light intensity) due to trapezoidal groove slack Δ. Calculations for both figures were based on vector diffraction theory.
[0036]
FIG. 11 shows the difference in transmitted diffracted light intensity ratio depending on the polarization state. In this figure, T0 is the 0th-order transmitted diffracted light intensity, and T1 is the 1st-order transmitted diffracted light intensity. From this figure, it can be seen that when the incident angle is 45 °, the diffracted light intensity ratio T1 / T0 is completely different between E-polarized light and H-polarized light. According to the first embodiment, the groove shape of the trapezoidal groove can be accurately determined by using such a polarization difference (polarization characteristic).
[0037]
FIG. 12 shows the difference in transmitted diffracted light intensity ratio depending on the incident angle. From this figure, it can be seen that when the incident angle is 45 °, the transmitted diffracted light intensity ratio T1 / T0 is completely different between the E-polarized light with the incident angle of 30 ° and the E-polarized light with the incident angle of 60 °. According to the second embodiment, the groove shape of the trapezoidal groove can be accurately determined by using such incident angle characteristics.
[0038]
【The invention's effect】
As described above, according to the present invention, since the shape of the periodic groove is determined based on four types of diffracted light intensities, the groove shape of the trapezoidal periodic groove, that is, the upper base width, the lower base width, and the groove depth. The three unknowns can be determined.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a groove shape measuring method according to a first embodiment of the invention.
FIG. 2 is an explanatory diagram for explaining two types of polarized light irradiated to a periodic groove
FIG. 3 shows two kinds of diffracted light intensity ratios a when E polarization and trapezoidal groove slack Δ is 0 nm._E, B_EGraph showing a group of curves
FIG. 4 shows two kinds of diffracted light intensity ratios a when H = 0 and Δ = 0 nm._H, B_HGraph showing a group of curves
FIG. 5 is a graph used for explanation to determine the average groove width and the slant Δ of trapezoidal grooves.
FIG. 6 is a graph used for explanation to determine the groove depth h and the slant Δ of the trapezoidal groove.
FIG. 7 is a diagram showing a groove shape measuring method according to a second embodiment of the present invention, in which two kinds of diffracted light intensity ratio a when E is polarized with an incident angle of 30 ° and the slack Δ is 0 nm;₃₀, B₃₀Graph showing a group of curves
FIG. 8 shows two kinds of diffracted light intensity ratios a when the slant Δ is 0 nm for E-polarized light with an incident angle of 60 °.₆₀, B₆₀Graph showing a group of curves
FIG. 9 is a graph used for explanation to determine the average groove width and the slant Δ.
FIG. 10 is a graph used for explanation to determine the groove depth h and the drooping Δ.
FIG. 11 is a graph showing the difference in the diffracted light intensity ratio depending on the polarization state.
FIG. 12 is a graph showing the difference in the diffracted light intensity ratio depending on the incident angle.
FIG. 13 is an explanatory view showing a conventional groove shape measuring method.
FIG. 14 is a graph showing a group of two diffracted light intensity ratio curves;
[Explanation of symbols]
10 ... Optical disk 10a ... Trapezoidal periodic groove
11 ... 1/2 wavelength plate 12 ... receiver

Claims (7)

In the groove shape measuring method for measuring the groove shape of the periodic groove carved on the surface of the substrate using diffracted light,
One of two types of linearly polarized light having different polarization planes is irradiated on the periodic groove, and the intensities of 0th-order, first-order and second-order diffracted light generated at this time are measured. Obtaining a diffracted light intensity ratio of
The other of the two types of linearly polarized light is irradiated to the periodic groove, and the intensities of the 0th, 1st and 2nd order diffracted light generated at this time are measured. Determining the ratio;
Based on the four kinds of diffracted light intensity ratios of the two kinds of diffracted light intensity ratios of the one linearly polarized light and the two kinds of diffracted light intensity ratios of the other linearly polarized light, the groove shape of the periodic groove is determined. A groove shape measuring method using diffracted light. 2. The groove using diffracted light according to claim 1, wherein the polarization plane of the one linearly polarized light is parallel to the periodic groove, and the polarization plane of the other linearly polarized light is perpendicular to the periodic groove. Shape measurement method. The two kinds of diffracted light intensity ratios of the one linearly polarized light and the two kinds of diffracted light intensity ratios of the other linearly polarized light are both the intensity ratio of the first order diffracted light to the zeroth order diffracted light and the second order diffracted light to the first order diffracted light. The groove shape measuring method using diffracted light according to claim 1 or 2, wherein the intensity ratio is as follows. In the groove shape measuring method for measuring the groove shape of the periodic groove carved on the surface of the substrate using diffracted light,
One of two types of polarized light having different incident angles is irradiated on the periodic groove, and the intensities of the 0th, 1st and 2nd order diffracted light generated at this time are measured. Obtaining a diffracted light intensity ratio;
The other of the two types of polarized light is irradiated onto the periodic groove, and the intensities of the 0th, 1st and 2nd order diffracted light generated at this time are measured. The process of seeking
The groove shape of the periodic groove is determined based on four kinds of diffracted light intensity ratios of the two kinds of diffracted light intensity ratios by the one polarized light and the two kinds of diffracted light intensity ratios by the other polarized light. And a groove shape measuring method using diffracted light. 5. The groove shape measuring method using diffracted light according to claim 4, wherein the two kinds of polarized light are linearly polarized light having a polarization plane parallel to the periodic groove. The two kinds of diffracted light intensity ratios of the one polarized light and the two kinds of diffracted light intensity ratios of the other polarized light are both the intensity ratio of the first order diffracted light to the zeroth order diffracted light and the intensity of the second order diffracted light to the first order diffracted light. The groove shape measuring method using diffracted light according to claim 4 or 5, wherein the ratio is a ratio. In the groove shape measuring method for measuring the groove shape of the periodic groove carved on the surface of the substrate using diffracted light,
The periodic grooves are irradiated with laser light, and the respective intensities of the 0th, 1st, 2nd and 3rd order diffracted light generated at this time are measured, and the three diffracted light intensity ratios are determined from the intensity of these 4 diffracted lights. The desired process;
A step of determining a groove shape of the periodic groove based on the three kinds of intensity ratios, and a groove shape measuring method using diffracted light.

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