JPH0321805A - Method for measuring depth of recessed part of optical disk replica - Google Patents

Abstract

PURPOSE:To speedily and easily measure the depth of the recessed part of a replica by projecting laser light on the optical disk replica from both sides, and measuring the intensity values of the interference waves, and calculating the respective degrees of modulation and their ration from measurement data on the measured intensity. CONSTITUTION:Laser spots are projected on the replica to be inspected, which is obtained by transferring the recessed part of the original disk of an optical disk to the surface of a transparent plastic base, from its plastic base side and the opposite air side. Intensity value I1(0) and I2(0) of reflected at a position where no recessed part is present and intensity values I1(d) and I2(d) of the interference wave generated by an optical path difference due to the depth (d) of the recessed part at the periphery including the recessed part are measured, the degrees M1 and M2 of modulation for the interference waves and their ratio Rm are found from equations I - III based upon the measured intensity data are found, and the depth (d) of the recessed part of the replica to be measured is found by referring to the logic curve of the ratio Rm including the depth (d) of the recessed part as a variable.

Description

[Detailed Description of the Invention] [Industrial field in Icheon] The present invention relates to a method for measuring the depth of a recess in an optical disc replica, and more specifically, it is directed to a replica transferred from an optical disc master. A groove or pit set or drilled in a
The depth of the concave portion is determined based on interference wave data measured by an optical disk inspection device.

[Conventional technology] Optical discs, which have recently been developed, come in the form of treads, but all of them have extremely small pins. Information data is recorded at high density by recording. To describe the manufacturing process, first, a master disc with grooves for control information and pin holes for recorded data is produced, and then, through a process called a stamper, it is transferred to a plastic base and a replica is made.

The concept of grooves and pits of an optical disc and the method of detecting them will be explained with reference to FIGS. 4(a), (b) and (C). In Figure (a), concentric grooves g are carved at a fine pitch on an optical disk 1 to control the positioning of the read head, and pits p indicating data are formed along these grooves.
is perforated. IXI (b) shows the cross section of groove g and pit p; in case (a), pit p is drilled at the 7th position of groove g, and in case (b), pit p is drilled between groove g. . In both cases, pinot p is twice as deep as groove g. Depending on the type, only pits may be drilled without grooves. As will be described later, the readout of the pit p is performed using the 1-wavelength phenomenon of the reflected laser, and the depth of the pit p is suitably 1/4n of the wavelength λ of the laser. Here n is disk l
k1{refraction index. If there is a defect in the pits of the master, stamper, or replica, an error will occur in the read data, so it is inspected by an optical disk inspection device. Since the original disc and stamper are made of metal, the inspection is performed by projecting a laser spot onto the front side or, in the case of a replica, from the transparent plastic base side.

FIG. 4(c) explains the method of detecting pits on a replica in an optical disc inspection device. The objective lens 2 focuses the laser beam L onto a spot with a diameter commensurate with the size of the pit, and Irradiate the vicinity including Pinoto p through the base 1'. When the depth of the pit is d and the refractive index of the base 1' is n, there is an optical path difference of 2 n between the reflected light from the focal point p and the reflected light from a surface other than the pit.
d, and both reflected lights interfere. When the depth d is 1/4n of the wavelength λ as described above, the phase difference between both reflected lights becomes π, and the 'F interfering wave disappears. -1 beam is received by the objective lens 2, and a pit p is detected by a change in the received light beam. Also, the depth of groove g is half of d.
However, the necessary control information can be read out nJ.

[Problem to be Solved 1] As is clear from the above, the depth of grooves and pits plays an important role in their detection, so inspection is performed at the master stage. This method involves observation using a microscope, and although it is highly accurate, it takes a long time to inspect, and it is impossible to apply it to replicas. However, it is useful because it is possible to measure the depth of the recess on the replica and, if it is incorrect, feed back this data to the previous level to improve the work. On the other hand, when inspecting an original disc, stamper, or replica using an optical disc inspection device, as shown in FIG. A method has been used to inspect groove defects on a macro level using diffracted light by the isoorptive r formed by a group of grooves, but the depth of individual grooves and pits has not been inspected. do not have. On the other hand, since the inspection device has the above-mentioned detection function for grooves and pits, if this can be used to measure the depth, it will be possible to measure more efficiently than the method using a microscope, which is an f+' effect. However, conventionally, no original PLL or method for measuring depth using such a detection function is known.

This invention has been made in view of the following, and has a 1-1 objective of providing a method for measuring the depth of an optical disc replica based on the detection signal of a groove or focus detected by an optical disc inspection device. That is.

[Step P for Solving the Problems] This invention projects a laser spot onto an optical disc, retrieves grooves set on the optical disc and pits corresponding to test data drilled along the grooves. The recess (groove or focus) of an optical disc replica in an optical disc inspection device that inspects recording performance
This is a depth measurement method.

A laser spot is projected from the plastic base side and the opposite air side onto a replica to be inspected in which the concave portions of the optical disk master are transferred onto the surface of a transparent plastic base. Intensity of each reflected light II (0), I2 (0) at the part of the recess where no H operation is performed
, and the intensity 1i ( d
). I2 (d) was measured, and from the measured intensity data, the following formula = Mt = [ II (0) - I1 (
d) ] / If (0)...(1) M2 =
[I2 (0)-I2 (d) /12
(0) ... (2) RIM=M2/Mt
(3), the modulation degree Ml + M2 for each wave and the ratio Rm of both modulation waves are determined. On the other hand, the depth of the recess of the replica to be measured is determined by referring to a theoretical curve of the ratio Rm of the modulation degree, which uses the depth d of the recess of the optical disk as a variable.

When projecting the laser spot from the air side in the above, a transparent plate with the same refractive index and thickness as the above plastic base is installed between the objective lens that projects and receives the laser spot and the replica to be projected. Push in.

[Operation] Using FIG. 1 and FIGS. 2(a) and 2(b) together, the principle of determining the depth of the groove or pit of the replica described in "2" will be explained.

In general, two coherent lasers with the same wavelength λ are expressed as follows: A=ao exp(jωt) ={4)B
=b(1 exp(j(IJt+φ) −(5
), A. Intensity of interference wave obtained by combining B■
I=a0 2+b0 2+2aobO cosφ −(
6)? Become. φ is the phase difference between the two lasers, and when this is O or 2mπ (m: integer), ■ is the maximum value I wax
becomes.

Imax = (ao +bo) 2-(7) Now,
Considering the case where the laser is projected from the plastic base side of the optical disk replica, the phase angle φl is expressed by the following equation, where d1 is the depth of the recess, and n is the refractive index of the plastic base.

φ1 = 2nd●2π/λ −(ill)
In addition, in this case, the interfering intensity I1 is II (d)
=ag 2 +b0 2+2a■ b■ cosφl
...(3), and its maximum value is equation (7).

According to equation (9), I1 varies cos in with respect to depth d. Now, when Il and lwax are measured, φl can be obtained from these equations, and therefore the depth d of the C recess can be found. However, in such a method, φ
As a solution for l, 2 or more than 2 plants will grow, and the planting of d will not be determined. This will be explained with reference to FIG.

The line in Figure 1 is based on equation (9), and now I! When the measured value of is II', the corresponding curve has two points r and S, so the phase angle is φr or φS, and the depth according to equation (8) is not determined as either dr or ds. .

In this invention, a laser is further projected from the side of the replica in contact with the air to increase the intensity of the interference wave I2.
and find its maximum value i2max.

However, in this case, the refractive index n is set to 1, and the phase angle φ2 is calculated using the following formula: φ2=2d●2π/λ...(II)
Calculate by. In the following, since I uses d as a variable, it is expressed as I (d), and Imax occurs when d is 0, so it is expressed as I (0).

Next, using I (d) and I (0), the modulation degree Mt + M2 of F interference and their ratio Rm are determined by the following equation.

Ml=[It(0)-It(d)]/I
t (0)...0)M2 = [I2 (0)-1
2 (d)] / I2 (0)...(2)R+s
: M2 / Ml・”(
3) Below. For H, Figure 2 (a) shows M calculated using the above formulas, with the horizontal axis set as the depth d in units of λ/4n.
1, the theoretical curve of M2 is shown, and Figure (b) shows the instantaneous curve of Rm. On the other hand, as described above, the intensities of the interference waves or reflected light in the vicinity including the concave portion and in areas other than the concave portion from both sides of the replica are I l(d), I t (0
) and I 2 (d). The value of I 2 (0) is measured, and the modulation ratio Rm is calculated using equations 0) to (3). As shown in Figure (b), in this case, the ratio R+a and the depth d correspond one to one, so the value of d is determined in a negative sense. In addition, Figure (a) shows the standardized interference wave intensity, I
t / II (0), 12 / I2 (0), and in Figure (b), the intensity ratio I1/12 is described as Rl for reference, but d with respect to Rl is around d = 1. Since it takes a binary value, it is not determined as above and cannot be used.

Since the depth d is generalized in the following L, it can be applied to both pits and grooves.

No. 31'4(a). (b), (c), and (d) explain the action of the transparent plate inserted between the objective lens and the projection surface when projecting the laser spot from the constricted side in the above measurement. . Figure (a) shows the case where the laser is projected onto the replica from the plastic base side.The laser focused by the objective lens 2 is refracted by the plastic base 1', so the focal point moves compared to the case without this. This may cause aberrations and cause the lens to be out of focus. Taking this into consideration, the objective lens 2 is designed to produce a highly accurate spot. On the other hand, when projecting from the air side using the same objective lens 2, since there is no plastic base 1', a transparent plate 3 having the same refractive index n and thickness D as shown in FIG. , objective lens 2
and a plastic base l' to focus on the same spot. However, since the transparent plate 3 does not come into contact with the replica, the optical path difference due to the depth d is 2d with respect to the air side, assuming n=1. Figure (C) is a supplementary explanation of the action of the transparent plate 3. Light incident on the transparent plate 3 at an incident angle of 0 is refracted, but travels parallel to the original direction, and moves outward at the focal point F. The larger the incident angle θ is for the mobile acid δS,
Also, the larger the plate thickness D is, the thicker the plate is. On the other hand, in Figure (d), a normal convex lens has spherical aberration, and the larger the angle of incidence θ' is, the larger the movement at the focal point F is, δS'. However, since the direction of movement is opposite to δS of the transparent plate, the insertion of the transparent plate eliminates the convergence X5 to some extent, although not completely. Equivalent spots are formed on the transparent plate 3 by means of the following.

[Embodiment] In an embodiment of the method for measuring the depth of a recess in an optical disk replica according to the present invention, the replica is stopped at an appropriate position in an optical disk inspection device (not shown), and a laser is projected onto both surfaces. The intensities h and I2 of the interference waves in the vicinity including the recess, and II(0) and 12(0) at locations where the recess does not exist are measured, respectively.

Using a microprocessor or the like, the above equations (1), (
2) and (3), the modulation degree M for each
Calculate l + M2 and its ratio R + s, and with reference to the theoretical curve Rm in Figure 2 (b) described above, determine the depth d for the calculated value.
seek.

- In addition, a transparent plate 3 is removably attached between the objective lens 2 of the optical disk inspection device and the projection target using a suitable support, and the transparent plate 3 is inserted into the optical path when measuring the air side. be.

[Effects of the Invention] As is clear from the following explanation, according to the method for measuring the depth of the recess of an optical disk replica according to the present invention, the depth of the recess of the groove or pit of the replica can be determined by measuring the depth of the recess of the replica in the optical disk device. Lasers are projected from both sides and the interference wave intensity of each is measured, and from the measurement data, the respective modulation degrees Ml, M2 and the ratio RII1 of both modulation degrees are determined.
is calculated, and the theory {see line 11I F. (The depth d of the I'l part relative to the ratio Rm calculated by L can be uniquely obtained, and compared to the conventional microscopic method, the tail velocity can be easily measured and the depth data can be replicated. The effect of providing feedback to Ume and others to improve their work is great.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the 10,000 method for measuring the depth of a recess in an optical disk replica and its drawbacks, and Figures 2 (a) and (b)
) is the modulation degree Ml+M2 E of the interference wave in the method for measuring the depth of a recess in an optical disk replica according to the present invention.
II! , a theoretical curve diagram of the theoretical IIh line and the ratio Rm of the modulation depth, FIG. 3(a). (b). (c) and (d) are 1! of this optical disc replica by Tamaki! Explanatory diagram of the effect of the transparent plate in the depth measurement method of part q, Fig. 4 (a), (
b) and (c) are grooves and pits of an optical disc;
FIG. 5 is an explanatory diagram of a groove defect inspection method using an optical disk inspection apparatus. DESCRIPTION OF SYMBOLS 1... Optical disc or replica, 1'... Plastic base, 2... Objective lens, 3... Transparent plate, g...
Groove, p...Binoto, L...Laser, S...Laser Spot, To, I, Il, I
2...1 - Intensity of interfering wave, d... Depth of recess,
φ...M7 phase angle, M...Modulation degree, Rn
+... Ratio of modulation degree, D... RTL of plastic base and transparent plate, F... Focus.

Claims (2)

[Claims] (1) In an optical disc inspection device that projects a laser spot onto an optical disc and reads out a groove set on the optical disc and a pit for test data punched along the groove to inspect the recording performance of the optical disc, The laser spot is projected from the plastic base side and the opposite air side onto the replica to be inspected, in which the concave portions of the original have been transferred to the surface of a transparent plastic base, and the respective reflections at locations where the concave portions do not exist are measured. Light intensity I_1(0), I_
2(0), and the intensities I_1(d) and I_2(d) of the respective interference waves caused by the optical path difference due to the depth d of the recess in the vicinity including the recess, and from the measured intensity data, The following formula: M_1=[I_1(0)-I_1(d)]/I_1(0
)...(1)M_2=[I_2(0)-I_2(d)
]/I_2(0)...(2)R_m=M_2/M_1
...(3) According to the following, the modulation degrees M_1, M_2,
and the ratio R_m of both modulation degrees, and the depth d of the recess
A method for measuring the depth of a recess in an optical disk replica, the method comprising determining the depth d of a recess in a replica to be measured with reference to the theoretical curve of the ratio R_m with R_m as a variable. (2) In the projection of the laser spot from the air side in the above, a transparent material having the same refractive index and thickness as the plastic base is provided between the objective lens that projects and receives the laser spot and the projection surface of the replica. 2. The method for measuring the depth of a recess in an optical disk replica according to claim 1, wherein a plate is inserted.