JPS58162806A - Device for measuring rugged shape - Google Patents

Abstract

PURPOSE:To determine the depth of pits from the intensity ratios of diffracted beams of the 1st order in a device for measuring ruggedness provided on an optical disc or the like by irradiating two light beams of different wavelengths to the optical disc. CONSTITUTION:The beams of different wavelengths are irradiated from laser light sources 11, 12 through half-mirrors 111, 112 to a disc 14 to be measured. The beams reflected by the half mirrors are detected and amplified and are inputted to a divider 116 in order to determine the ratio between the light intensity signals. The respective diffracted beams IL1', IL2' of the 1st order of the incident beams of the disc are detected and amplified and are inputted to a divider 19 in order to determine the ratio of the intensities of the diffracted beams. If the product of the ratio of the intensities of the incident beams and the ratios of the intensities of the diffracted beams is determined, the values of the equations including the refractive indices for the respective beams, the wavelengths lambda1, lambda2 of the respective beams, and the depth (d) of the pits are obtained, and the unknown (d) is obtained by substituting the other known parameters into the equation.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] To E! A relates to an apparatus for measuring the uneven shape of an information recording carrier, such as an optical video disc, on which information is recorded in an uneven shape.

[Technical background of the invention and its problems]

In so-called optical video disk devices and digital audio disk devices that read signals from an information recording carrier (hereinafter referred to as an optical disk) using a light beam such as a semiconductor laser, the information to be reproduced is based on the shape of the unevenness of the optical disk kK. It is recorded in This unevenness is called a bit,
It has a width of 0.5 .mu.m and a length of 0.5 to 3 .mu.m, and is formed in a spiral or concentric shape with the optical disk.

To read this bit signal, a normal light beam is focused on a minute spot by an objective lens, and the optical disk is irradiated with this to trace the bit.

At this time, the reflected or transmitted light of the light beam by the disk is p-diffracted by the bit. Therefore, by detecting this reflected or transmitted diffracted light with a photodetector, it is possible to obtain a reproduced signal corresponding to the uneven shape of the pit, that is, according to the recorded information.

As mentioned above, information reproduction utilizes the diffraction phenomenon caused by pits, so it is necessary to optimize the shape of the bits, such as the width, length, and depth. In particular, the modulation degree of the reproduced signal depends on the bit depth, and the depth is λ/4n.
The degree of modulation is maximum when (λ: wavelength of irradiation beam light, n * refractive index of optical disk). Therefore, in order to perform good reproduction, the pit depth must be set to the above-mentioned λ/4 n
It is desirable to set the value to . Therefore, when manufacturing an optical disk, it is necessary to measure the depth of the bit and check whether it matches the above value.

Conventionally, as a method for measuring the uneven shape, there is a method of irradiating a laser beam onto an optical disc master or a copy of the master disc, and taking the ratio of the reflected or transmitted diffracted light to the 000th-order diffracted light and the 1st-order diffracted light.

111 Zusha, observation method [This is an original luck chart for explanation and shows the case of p1 transmission. m1tt of the irradiated light beam (goods), usually 0. The light beam A (2) is diffracted by a large number of pits (2) in the optical disk. As a result, the track row direction (X direction)
, first-order diffracted lights expressed by Ill and -Ill appear, and first-order diffracted lights expressed by 11 and -Iat appear in the signal train direction (y direction). Note that Io is the 0th order diffraction source and is 69. Represents transmitted diffracted light that is not refracted.

Here, the wavelength of the pit is 9s Fcook spacing 'fct
If the duality of one bit is β and the bit -tr, then the one-choice-new party ItK, Iss O and the angles θ and φ satisfy the O relationship. However, ml and mfi are the orders of diffraction, and in this case, ml = ml = 1.

From the k formula, the renewal angle φ of the first new party I11 in the signal train direction is:
It depends on the wavelength λ of the light beam and the wavelength p of the bit, and generally the pit wavelength p varies depending on the recording signal, so it is distributed in a slightly shimmy manner. Therefore, the measurement of the pit shape is performed by detecting its (its) coming from the first-order diffracted light in the track row direction. The strong II Ill of Ivx is expressed by the diffraction theory. Here, A3 is a constant that corresponds to the intensity of the light beam 12p. Moreover, as shown in FIG. 1(b)K,
With the pit (2) as the boundary, the Off refractive index tns on the incident side of the light beam (21) and that on the transmission side are defined as f of the pit.
If ly@td, the value of ψ in the equation (:) is Itt
It is expressed as n goose 1ci 9 g= 2π□...(1) λ. Sara KO next rebirth new party. The strength of I-
(1+2 (1-coat)'-!-('-!-
1)) ...@p tpt.

Conventionally, the unevenness shape is measured by detecting the strength of 6 1 - 1 in the first direction of the track row direction and I, which is the O-th direction.
The ground line between the strength It1 of the 01st new party tt and the strength of the 0th new party I, whose ratio was calculated, is (-) and (calculated from one set. One set, -X- !-!- is the bit depth d ((see formula 17), pit depth d) as a variable.
I have had several meetings. Therefore, in order to obtain the value of the uneven shape, for example, the depth d of the bit, from the value of T, two other variables are required, and r o g is determined using another measurement method p.
There is no company without making a decision based on t. However, above, −
! It is difficult to determine each value with accuracy, and with this conventional method, it is impossible to precisely determine the bit depth dO value. [One way to know this is to directly measure it using an interference microscope, but the resolution is low and it is impossible to determine the value of d even with this method.[Objective of the invention] SUMMARY OF THE INVENTION An object of the present invention is to provide an unevenness shape measuring device that can determine the pit depth dO value, which cannot be determined by the conventional unevenness shape measuring f& position.

[Summary of the invention]

The present invention aims to apply two light beams of different wavelengths to the same location on a master disc of an optical disc or an optical disc ho reproduced from the master disc, and to receive and detect the first-order diffracted light of each light beam, and to obtain a ratio of the intensities of the first-order diffracted lights. Provided is an unevenness shape measuring device that determines the pit depth dt1ml based on this value.

〔Effect of the invention〕

According to the present invention, the value of the pit depth d, which must be known because it affects the playback performance of an optical disc, is determined by the ratio of the track interval t to the pit @r and the pit desty ratio l. Knowing the value allows you to determine it uniquely without fear.

[Example of the present invention]

First, 1 about the measurement principle of the uneven shape measuring device of the present invention.
! I will clarify.

Now, there are two light beams 1iILs with different wavelengths.

I, and each wavelength is λ! ,λyi(λ1←λri).In addition, each light intensity ft of the beam light heavy, I■
Let IhI be the intensity of the first-order diffracted light in the direction of one track row when both beams are irradiated onto the same location on the optical disk.

In the present invention, the light beam IL1. 1 of each of l11m
becomes. Here, AX'', A- are respectively equal to the intensity of the two irradiated light beams 1jl, I)8, and the person, ''=
Iz, Mu=IJ2. Also, fs t fs is pl according to the equation (-). When the set is t-transformed, the following can be found. The right side of equation (Vl) is the refractive index n1 as a variable.
゜−1 Wavelength λ1 of the light beam. λ1, further (s1 of pit
can be handled. Therefore, it is expressed in the formula (糟).
+×) Since P is a function of only the depth of the pit d and O,
The depth d of the pit can be uniquely measured by the ratio of l*-new intensity of the nine light beams.

FIG. 92 is a block diagram showing an embodiment of the unevenness shape measuring device of the present invention based on the novel measurement principle described above.

The first laser light source αυ emits a light beam ■L1 with a wavelength λ, and #! The second laser light source a has a light beam L with wavelength λ2.
! emits. Both light beams ILI and IL2 pass through half mirrors (110) and (112) having the same transmittance, respectively, and then are superimposed on a guichroic mirror a4,
The same location on the optical disc a4L is irradiated. The light beams IL1 and I111 irradiated onto the optical disc α are diffracted, and transmitted diffracted lights ILI and II are generated. light beam 'L
t and TLz have different wavelengths and different diffraction angles, and the transmitted diffracted lights JL'l and IL'2 travel straight in different directions.

Each i-adic direction II? : is provided with photodetectors aω and αe, the photodetector (15) receives the diffracted light ILI, and the next photodetector (LQ receives the diffracted light 11; '2 t-, respectively. A device haze and aS are Izt and ILm that receive light.
It emits an electrical signal according to the light intensity IhI. After being amplified to a predetermined value (by passing through amplifiers αη, as, respectively), they are led together to a divider alK. The divider a performs division between the supplied signals to obtain the transmitted diffracted light intensity I.

■ Calculate the northward direction of 11.

Now, when the light beams ILI and 111 pass through the bar and the 7-bar (110) and (112) t, respectively, a portion is reflected. The reflected light from the light beam is detected by a photodetector (11
1), the reflected light of the light beam Ihs is detected by a photodetector (
113) respectively. The photodetector (111) generates an electrical signal according to the intensity It of the light beam ILI, and the photodetector (113) generates an electric signal depending on the intensity It of the light beam ILI.
It generates electrical signals according to the
114), (115) After t-, it is led to the divider (o6).

The divider (116) has the same function as the previously described divider (II), and performs division between the supplied signals, and both light intensity values are guided to the multiplier (117). Multiplication amount IJ
I (117) is the supplied dimension, and the value can be found by multiplying by 97.

[Other embodiments of the invention]

In the embodiment described above, transmitted diffracted light was used as an example of the diffracted light received by the photodetectors Q5 and αQ, but similar measurements can also be made by detecting reflected diffracted light. In this case, the value of ψ shown in equation (-) can be treated as ψ24π.

In addition, although we have explained the case where two laser light sources are prepared to obtain light beams of different wavelengths, the laser light source 7 can be a single laser device that emits light of different wavelengths, such as an Ar laser device. You may use 1. In this case, it is sufficient to provide one photodetector that receives the light beam itself emitted from a single laser light source, and it is sufficient to provide only one half mirror in front of the photodetector. however,
Similarly, it is necessary to find the ratio of light intensity 111 and Ijm, so the light intensity 1 detected by a single photodetector is
A means for holding one of the values of light intensity xi1. rt1t-parallel divide 1) (11
6).

[Brief explanation of drawings]

Figure a11 is a 4-round field diagram illustrating the principle of the method for measuring the uneven shape, and FIG. 2 is a block diagram showing an embodiment of the uneven shape defining device of the present invention. Ql), a, 1... Laser light source, a◆... Optical guide, aS, α* t (111), (113)
...photodetector, αI s (tts) −,. Divider, (117)... Multiplier, Izt, Izt...
Light beam, Iit, IN, s...1st 1gl new party. Agent: Kensuke Noriyoshi Chika (and 1 other person) No. 1
Figure 2

Claims (1)

[Claims] An uneven shape measurement value for measuring the size of the uneven shape of an information recording carrier on which information is recorded in an uneven shape [(wherein the information recording carrier is irradiated with a light beam of #!1). 1 obtained by
a first photodetector for detecting the second-order diffracted light; and a second photodetector for detecting the first-order diffracted light obtained by irradiating the predistribution information recording carrier with a second light beam having a different wavelength from the light beam of J[l. and the first and second photodetectors obtained from the first and second photodetectors.
a first divider that is proportional to the intensity of the next-order diffracted light and takes a ratio of the nine-dimensional light beam; a Ji3 photodetector that receives the first light Im; and a fourth light beam that receives the ls2 light beam. a detector and said first photodetector obtained by said third percent #I4 photodetector;
The second takes the ratio of the electrical signal proportional to the intensity of the light beam of $12.
and a multiplier that multiplies the outputs of the first and second dividers, and the depth of the uneven shape is detected from the multiplication result of the multiplier. measuring device.