JP2761276B2 - Optical disk substrate evaluation system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for evaluating residual stress and transferability of information pits of an optical disk molded under general molding conditions (particularly, injection molding). Related to the device.

[Conventional technology]

Under the conventional molding conditions of an optical disc (especially injection molding), there is a close relationship between the residual stress of the molded disc and the transferability of information pits. It is required to meet the conditions. However, in general, when the residual stress, that is, the birefringence of the disk substrate is suppressed to a low level, the transferability of the pits is deteriorated. The stress tends to increase. Therefore, it is necessary to evaluate both for determining whether or not the molding of the disk is performed under preferable conditions.

For this reason, there are conventionally a birefringence measuring device for evaluating the residual stress of the disk substrate and a first-order diffracted light intensity measuring device for simply evaluating the transferability of information pits, and these devices are individually evaluated. Has been done.

FIG. 4 shows an example of an optical system of the birefringence measuring device. In the figure, reference numeral 1 denotes an inspection laser beam, 2 denotes a half mirror for splitting the inspection laser beam 1 in two directions, 3 denotes a light-source-light-quantity monitoring light-receiving sensor (hereinafter, referred to as a light source sensor) that receives one of the split beams. 4 receives the other split light and sets P
A polarizing plate 5 that allows direct polarized light of only the component to pass, and a linearly polarized light 5 from the polarizing plate 4 is converted into a circularly polarized light,
A quarter-wave plate, 7 is a quarter-wave plate that converts circularly-polarized light of light that has traveled straight through the disk 6 to be inspected into linearly polarized light, and 8 is a birefringent component that passes through the light that has passed through the quarter-wave plate 7. Polarizer, 9
Denotes a birefringent component light receiving sensor (hereinafter, referred to as a birefringent sensor) for receiving birefringent component light as light passing through the polarizing plate 8;
Reference numerals 0 and 10 'denote diffracted light beams which are generated and branched by the presence of pits on the disk 6 to be inspected. Here, I ₁ represents the birefringence component light amount, and I ₃ and I ₃ ′ represent the first-order diffraction light amounts.

The operation of the above configuration will be described. The inspection laser beam 1 is composed of a half mirror 2, a polarizing plate 4 and a quarter.
The light passes through the wave plate 5 to become circularly polarized light and enters the inspection target disk 6. When birefringence exists in the disk 6 to be inspected,
The light that has passed through the disk 6 to be inspected passes through the quarter-wave plate 7, passes through the polarizing plate 8, and is captured by the birefringence sensor 9. That is, only the birefringent component of the inspection laser beam 1 whose polarization state has changed due to the birefringence of the inspection target disk 6 is captured. On the other hand, when there is no birefringence, the inspection laser beam 1 cannot pass through the polarizing plate 8 and therefore does not reach the birefringence sensor 9.

Now, _assuming that the inspection light beam amount is Is, the maximum birefringence optical path difference Δ of the inspection target disk 6 can be expressed by the following equation.

Here, λ is the wavelength of the light source. Here, if the light amount branched by the half mirror 2 and received by the light source sensor 3 is I ₀ , and the light amount of the non-birefringent component not passing through the polarizing plate 8 is I ₂ , the inspection is performed. I _s in consideration of the attenuation of light intensity caused by light transmittance of the test disc 6, which is a major attenuation of the optical path of the laser beam 1, when the attenuation factor and _{α, I s = I 1 +} I 2 = It is indicated by αI ₀ . However, since I ₂ is shielded from light by the polarizing plate 8, actual capture is impossible.

Further, the inspection laser light 1 passing through the disk 6 to be inspected
If the order to be branched resulting diffracted light 10, 10 'by the influence of the presence of pits, the amount sum of the diffracted light and I _d, (1)
The actual calculation of the equation can be performed by substituting the I _s = αI ₀ -I _d. Therefore, in order to perform strict measurement in the conventional method, it is necessary to obtain the light transmittance (amount of light attenuation α) and the sum of the amounts of diffracted light (I _d ) of the above-described disk 6 to be inspected, and then obtain the equation (1). We need to find more birefringence.

FIG. 5 shows an example of an optical system of a first-order diffracted light intensity measuring device. In the drawing, reference numeral 11 denotes an inspection laser beam incident on the disk 6 to be inspected, 12 denotes a 0th-order diffracted light (straight traveling light) which travels straight after passing through the disk 6 to be inspected, and 13 and 13 'denote 0 due to the track pitch of information pits. A first-order diffracted light generated at both ends of the second-order diffracted light 12 with a diffraction angle θ, a zero-order diffracted light receiving sensor (hereinafter referred to as a zero-order sensor) that receives the zero-order diffracted light 12, and a first-order diffracted light 15 that receives the first-order diffracted light 13 1 shows a diffracted light receiving sensor (hereinafter, referred to as a primary sensor).

In the above, the first-order diffracted light intensity D is evaluated by calculating the intensity ratio between the zero-order diffracted light 12 and the first-order diffracted light 13. now,
Assuming that the light quantity captured by the primary sensor 15 is I ₃ and the light quantity captured by the zero-order sensor 14 is I ₄ , the primary diffracted light intensity D is obtained by the following equation.

In order to measure the birefringence and the first-order diffracted light intensity on the same inspection optical axis, FIG.
When a zero-order diffracted light can be captured by the light-receiving sensor 9, only the birefringent component can be captured by the light-receiving sensor 9 as described above. Impossible.

Next, FIG. 6 shows a specific signal processing circuit for measuring birefringence from the birefringent component light and the light source light amount captured by the optical system, and the first-order diffracted light intensity from the zero-order diffracted light 12 and the first-order diffracted light 13. 7 are shown in FIG. 7 respectively.

In FIG. 6, the birefringent component light captured by the birefringent sensor 9 is converted into a voltage by a current-voltage converter 31a, amplified by the amplifier 32a, and then passed through a band-pass filter 33a and AC-DC. The converter 34a removes noise components due to extraneous light from the measurement signal, which is an AC signal optically modulated by the optical chopper, and converts the signal into a DC signal. After the DC converter, then amplified to a required level by the amplifier 35a, converted into a digital signal by the A / D converter 36a, is inputted to the configured external computing device 37 from the CPU as the birefringent component signal S _1. On the other hand, the light source light amount captured by the light source sensor 3 is subjected to the same signal processing and the birefringent component light, is input to the external computing device 37 as a light source intensity signal S _0.

In FIG. 7, the primary sensor 15 and the zero-order sensor
First-order diffracted light and 0-order diffracted light is captured by 14 is also processed in configuration Naru similar to the signal processing circuit is input as first-order diffracted light signal S ₃ and 0-order diffracted light signal S ₄ to the external computing device 37.

Based on each of the input signals, the external calculation device 37 performs the following calculation to measure the birefringence and the first-order diffracted light intensity.

However, the S ₀ performs correction by α decay rate described above.

[Problems to be Solved by the Invention] As described above, the conventional apparatus has evaluated the measurement of the birefringence and the intensity of the first-order diffracted light by using separate apparatuses, but both apparatuses have been analyzed off-line. Therefore, the disk substrate has to be measured photoelectrically, and the data has to be processed and obtained by an external arithmetic unit.

For this reason, the birefringence and the intensity of the first-order diffracted light cannot be quickly evaluated at the molding site, and the molding conditions are overlooked.

The present invention has been made in order to eliminate the problems of the conventional apparatus as described above, and an object of the present invention is to easily and quickly reduce the birefringence and the first-order diffracted light intensity at a disk molding site. An object of the present invention is to provide an evaluation device which can measure and can confirm and maintain suitable molding conditions.

[Means for solving the problem]

In order to achieve the above object, an optical disk substrate evaluation apparatus according to the present invention includes a polarizing beam splitter that passes linearly polarized light of only a P component from a light beam emitted from a light source, and that converts the linearly polarized light into circularly polarized light. A half-wave plate, a light-receiving sensor for irradiating the disk to be inspected with the circularly polarized light and capturing first-order diffracted light obtained from the disk to be inspected, and a linearly polarized light that travels straight through the disk to be inspected 4 A quarter-wave plate, a polarizing beam splitter that splits the output light of the quarter-wave plate into birefringent component light and non-birefringent component light, and a light receiving device that captures one of the branched light, the birefringent component light Sensor for
A light-receiving sensor that captures the non-birefringent component light that is the other branch light; and further, output signals of the birefringent component light, the non-birefringent component light, and the first-order diffracted light captured by the optical system. A current-to-voltage converter for converting current to voltage, a preamplifier for amplifying the output of the current-to-voltage converter, a band-pass filter for removing noise from the amplified signal, An AC-DC converter for converting the output of a pass filter into direct current, wherein the AC-D of each of the birefringent component light, the non-birefringent component light and the first-order diffracted light.
At the output of the C converter, an adder for adding the birefringent component light output and the non-birefringent component light output, and the birefringent component light output and the first-order diffracted light output are selected and switched by a signal selection control clock and output. An analog signal selector, the adder output and the analog signal selector output as inputs,
An A / D converter having a ratio-metric conversion function for obtaining a ratio A of the birefringent component light output to the adder output or a ratio B of the first-order diffracted light output; and outputting the A / D converter output to the signal selection control clock. And a latch circuit A and B for holding the signals of the output ratios A and B, respectively, and a memory for selecting and outputting a value for the output signal of the latch circuit A based on a predetermined conversion table stored in advance. And means are provided.

[Action]

The optical disk substrate evaluation apparatus of the present invention includes an optical system for measuring the birefringence and the intensity of the first-order diffracted light on the same inspection optical axis, and a processing system for a sensor signal obtained thereby.

In the optical system, light emitted from the inspection laser light is converted into circularly polarized light by the polarizing beam splitter and the quarter-wave plate, and is incident on the disk to be inspected. After passing through the disk to be inspected, the straight-ahead light becomes linearly polarized light by a quarter-wave plate, and is split into birefringent component light and non-birefringent component light by another polarizing beam splitter. Is captured by On the other hand, the first-order diffracted light generated after passing through the inspection target disk is also captured by another light receiving sensor. The birefringence and the first-order diffracted light intensity are measured from the amounts of light captured by these light receiving sensors.

Next, the respective light quantity signals obtained by the light receiving sensor are respectively converted into a current-voltage converter, a preamplifier, and a band amplifier.
The signal is processed by a pass filter and an AC-DC converter and converted into a DC signal. Next, the DC voltage-converted birefringent component signal and the non-birefringent component signal are added to obtain a component serving as a base when obtaining the birefringence and the first-order diffracted light intensity. This base component is input to the reference voltage input terminal of an A / D converter with ratiometric conversion function (hereinafter referred to as A / D converter), while the birefringent component signal and the first-order diffracted light signal are input to the analog signal input terminal. Are alternately switched by the signal selection control clock by the analog signal selector and input, so that the value obtained by dividing the birefringence component signal or the first-order diffracted light signal by the base component is output to the output terminal of the A / D converter. can get.

Then, by holding each output of the A / D converter in a latch circuit in synchronization with the signal selection control clock, the first-order diffracted light intensity can be directly obtained, while the birefringence is obtained by the A / D converter. A correct value can be obtained by calling a value corresponding to the output value of the A / D converter as a measurement result from a ROM (read only memory) storing a conversion table of the output value and the correct value.

(Example of the invention)

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. The same parts as those in the above-described conventional example are denoted by the same reference numerals, detailed description thereof will be omitted, and different parts will be mainly described. In FIG. 1, the difference from the conventional polarizing plate is that
By providing a pair of polarizing beam splitters 16 and 17 instead of 4 and 8, it is possible to capture birefringent component light and non-birefringent component light, and a light receiving sensor 18 for capturing non-birefringent component light.
And a light receiving sensor 15 for capturing the first-order diffracted light.

In the figure, the amount of light captured by the birefringence sensor 9 is I ₁ ,
Assuming that the amount of light received by the non-birefringent component light receiving sensor (hereinafter, referred to as a non-birefringent sensor) 18 is I ₂ , I ₂ is the amount of light that could not be captured by the polarizing plate 8 in the conventional optical system. It is. That is, by using the polarizing beam splitter 17, birefringent component light and non-birefringent component light can also be captured, so that the maximum birefringent optical path difference Δ can be obtained by the following equation.

When this method is compared with the conventional example, the value of I ₁ + I ₂ is (1)
It is possible to test light amount I _s shown by the formula, occurs following advantages.

There is no need to consider the light transmittance α of the disk to be inspected.

I ₁ and I ₂ are the amounts of light obtained by branching the straight traveling light (zero-order diffracted light) by its birefringent component. If I ₁ + I ₂ is treated as the inspection light beam amount and I ₁ is treated as the birefringent component light amount, Sum of the amount of diffracted light
There is no need to consider I _d .

That is, by capturing I ₁ and I ₂ , accurate measurement of birefringence becomes possible without being affected by the light transmittance and diffracted light of the disk to be inspected.

Further, the amount of light I ₃ which is captured by the primary sensor 15, the first-order diffracted light intensity can be obtained by the following equation.

Here, I ₁ + I ₂ is the sum of light obtained by branching the light that has traveled straight through the disk to be inspected into two components, I ₁ and I ₂ , according to the polarization state, and this sum corresponds to the 0th-order diffracted light Needless to say.

As described above, in the conventional example, it is impossible to appropriately capture the 0th-order diffracted light only by adding the primary sensor 15, but as shown in FIG. 1, the polarization beam splitter 17 is used.
By capturing both I ₁ and I ₂ and summing the sum as the light amount of the 0th-order diffracted light, the intensity of the 1st-order diffracted light can be measured using the same inspection optical axis that shares a part of the birefringence measurement optical system. Becomes
Further, since the optical elements can be partially shared, the configuration is simplified.

FIG. 2 shows a circuit for processing a signal captured by the optical system. The point that the measurement signal, which is an AC signal of each of the birefringent component light, the non-birefringent component light, and the first-order diffracted light obtained by the optical system, is converted into a DC signal as in the related art. In the figure, reference numeral 38 denotes an adder for adding the outputs of the AC-DC converters 34a and 34b, and 39 alternately outputs the outputs of the AC-DC converters 34b and 34c in synchronization with a signal selection control clock supplied to a terminal A. The analog signal selector 40 has a function of converting the output of the adder 38 into a digital signal while performing division by inputting the output of the adder 38 to the reference voltage input terminal B and the output of the analog signal selector 39 to the analog signal input terminal C. A / D converter with ratio metric conversion function, 41a, 41b
A latch circuit for latching the output of the A / D converter 40 in synchronization with the signal selection control clock, 42 is an inverter for synchronizing the latch operation of the latch circuit 41b with the signal selection control clock, and 43 is a latch circuit 41b. A ROM that outputs a value corresponding to the output value based on the conversion table stored in advance based on the output, 44 is a display that displays the output of the latch circuit 41a, and 45 is an output that is read as data from the ROM 43. Display. Note that the portion within the broken line in the figure is the calculation unit in the present invention.

Now, AC-DC converters 34a, 34b, respectively non-birefringent component signal output 34c (hereinafter, referred to as S _6), the birefringence component signal (hereinafter referred to as S ₅₎ and first-order diffracted light signal (hereinafter, S ₇ ), it can be seen that the maximum birefringence optical path difference Δ and the first-order diffracted light intensity D can be obtained by the following equations.

Now, in the adder 38 adds the value of S ₅ and S _6, and inputs the reference voltage input terminal B of the A / D converter 40. On the other hand, S ₅ and S ₇ inputted to the analog signal selector 39 is switched alternately by the signal selection control clock the A / D converter 4
0 is input to the analog signal input terminal C. By the way, A
Since / D converter 40 has a dividing function, for example, when the output of the analog signal selector 39 is S _5, the digital output of the A / D converter 40 is an _{S 5 / (S 5 + S} 6) , in the case of S ₇
S ₇ / (S ₅ + S ₆ ).

Then, each output value is latched by the latch circuit 41 using the signal selection control clock and the inverted clock by the inverter 42.
a, 41b, and the held signal is supplied to the latch circuit 41a by the display 44.
Is displayed as the first-order diffracted light intensity value. On the other hand, the holding signal of the latch circuit 41b becomes an address signal of the ROM 43, and the output of the ROM 43 is displayed on the display 45 as a birefringence value. In this case, (2) is a function of the birefringence _{Δ S 5 / (S 5 +} S 6) In the equation, delta by the value of the _{S 5 / (S 5 + S} 6) is uniquely determined. Therefore, the relationship between S ₅ / (S ₅ + S ₆ ) and Δ is stored in the ROM 43 in advance, and the value of S ₅ / (S ₅ + S ₆ ) is input to the address input of the ROM 43 to obtain the corresponding Δ. Read from ROM43,
The birefringence value Δ can be easily obtained without performing a complicated operation such as the equation (2).

Further, since the data holding of the latch circuits 41a and 41b is performed alternately in synchronization with the signal selection of the analog signal selector 39, a single A / D converter 40 performs time-division and performs signal conversion. The values of S ₅ / (S ₅ + S ₆ ) and S ₇ / (S ₅ + S ₆ ) are correctly held in the latch circuits 41b and 41a, respectively.

By repeating the above operation alternately, the updated data of the birefringence value and the first-order diffracted light intensity are displayed on the respective displays 45, 4
4 can be displayed.

Note that n in the signal lines after the A / D converter 40 represents the number of signal lines due to the bit resolution n of the A / D converter used (for example, n = 8 for 8 bits).

FIG. 3 is a block diagram of the entire optical system according to the present invention. The difference from FIG. 1 is that the rotational driving force of the spindle motor 20 by the spindle 19 is applied to the disk 6 to be inspected.
And further modulates light from the light source laser 22 by an optical chopper 21 such as a rotating disk.

As shown by a two-dot chain line in FIG.
A screw shaft 24 is screwed onto 23, and the screw shaft 24 is supported by two columns 25 and a feed motor
By rotating 26, the support base 23 may be moved in the horizontal direction in the drawing. In this case, by moving the disk 6 to be inspected horizontally in the radial direction, it is possible to perform a point measurement at an arbitrary radial position or a measurement on the same circumference by rotating the spindle 9 at that position. Further, by measuring the feed pitch of the disk 6 to be inspected in the radial direction and one rotation of the spindle 9 in synchronization, the entire circumference of the disk 6 to be inspected can be inspected in a spiral.

〔The invention's effect〕

As described above, in an optical system, a pair of polarizing beam splitters is provided in place of a polarizing plate conventionally used, and a birefringent component light and a non-birefringent component light can be captured. Since the first-order diffracted light is configured to be captured by the same inspection optical axis which shares a part of the system, the birefringence and the first-order diffracted light intensity can be measured simultaneously.

In the signal processing system, A / A
Some arithmetic functions (ratio /
Metric conversion), and two types of arithmetic processing are performed in a time-division manner by a set of processing circuits.
The processing unit has been simplified, and the arithmetic processing method has also been simplified.

As described above, important conditions such as residual stress and pit transfer can be accurately and simply evaluated at the disk molding site, and thus it is easy to confirm and maintain suitable molding conditions. In addition, the size of the device can be reduced and the manufacturing cost can be reduced.

If the disk is configured to be movable in the radial direction, point measurement at an arbitrary radial position or measurement on the same circumference by moving the disk in the radial direction can be performed. By synchronizing the feed pitch with one rotation of the spindle and measuring, the whole circumference of the disk to be inspected can be inspected in a spiral manner.

[Brief description of the drawings]

FIG. 1 is a diagram showing an optical system for measuring birefringence and first-order diffracted light intensity by the evaluation device of the present invention. FIG. 2 is a diagram of a signal processing circuit for measuring birefringence and first-order diffracted light intensity by the evaluation device of the present invention. FIG. 3 is a block diagram of the entire optical system by the evaluation device of the present invention; FIG. 4 is a diagram showing an optical system for measuring birefringence by a conventional device; FIG. 6 is a block diagram of a signal processing circuit for measuring birefringence by a conventional device, and FIG. 7 is a block diagram of a signal processing circuit for measuring the intensity of first-order diffracted light by a conventional device. 1 ... Inspection laser beam, 5,7 ... Quarter wave plate, 6 ...
... Disc to be inspected, 9 ... Sensor for receiving birefringent component light,
15 ………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………,
a, 31b, 31c ... current-voltage converter, 32a, 32b, 32c ... preamplifier, 33a, 33b, 33c ... band-pass filter, 34
a, 34b, 34c AC-DC converter, 38 Adder, 39
... Analog signal selector, 40 ... A / D converter with ratio / metric conversion function, 41a, 41b ... Latch circuit, 43 ...
ROM, 44, 45 …… Display.

Claims (3)

(57) [Claims] 1. A polarizing beam splitter for passing linearly polarized light of only a P component from a light beam emitted from a light source, a quarter-wave plate for converting the linearly polarized light to circularly polarized light, and a disk to be inspected for converting the circularly polarized light to a disk to be inspected. Irradiating, the light receiving sensor that captures the first-order diffracted light obtained from the disk to be inspected, a quarter-wave plate that converts the light that has traveled straight through the disk to be inspected into linearly polarized light,
A polarizing beam splitter that splits the output light of the quarter-wave plate into birefringent component light and non-birefringent component light, a light-receiving sensor that captures one of the split birefringent component lights, and the other splitter An optical disk substrate evaluation apparatus, comprising: a light-receiving sensor that captures non-birefringent component light as a light; and measuring birefringence and first-order diffracted light intensity using the same inspection optical axis. 2. A current-voltage converter for converting a current into a voltage for each of output signals of a birefringent component light, a non-birefringent component light, and a first-order diffracted light captured by the optical disk substrate evaluation apparatus according to claim 1. A converter, a preamplifier for amplifying the output of the current-to-voltage converter, a band-pass filter for removing noise from the amplified signal, and an AC- for converting the output of the band-pass filter to DC. A DC converter, and at the output of the AC-DC converter for each of the birefringent component light, the non-birefringent component light, and the first-order diffracted light, an adder that adds a birefringent component light output and a non-birefringent component light output. An analog signal selector for selecting and switching between the birefringent component light output and the first-order diffracted light output by a signal selection control clock and outputting the selected signal; and the adder output and the analog signal selector output as inputs, A / D converter having a ratio metric conversion function for obtaining a ratio A of the birefringent component light output or a ratio B of the first-order diffracted light output to a device output, and selecting the A / D converter output by the signal selection control clock. Latch circuits A and B for holding the signals of the output ratios A and B, respectively, and storage means for selecting and outputting a value for the output signal of the latch circuit A based on a predetermined conversion table stored in advance. An apparatus for evaluating an optical disk substrate, comprising: simultaneously measuring birefringence and first-order diffracted light intensity. 3. The apparatus for evaluating an optical disk substrate according to claim 1, wherein a spindle for rotating said disk to be inspected is movable in a radial direction.