JPS60250229A - Inspecting device of plastic substrate - Google Patents

Abstract

PURPOSE:To measure rapidly coefficient of complex refraction, by installing laser beam generating means, fixing and rotating means of a substrate, its displacement means, 1/2 wave length board, optical analyzer, means for converting light energy into an electric signal and means of displaying and recording the electric signal. CONSTITUTION:A specimen plastic substrate 9 is fastened to a fixing unit 10, and by driving rotating unit 11 and diametral direction driving unit 12, the measuring point on the board 9 is displaced to a position where a laser beam 1 of a random polarized ray passes. Further, the beam 1 is converted to an electric signal by a photodetector 6 through polarizer 3 having a transmission axis in the C direction located by counter-clockwise rotation through an angle of 45 deg., substrate 9, 1/2 wave length board 4 in which vibration element in the D direction lags behind that in the E direction, and optical analyzer 5 having a transmission axis in the F direction located by counter-clockwise rotation through an angle of 45 deg.. Further, an output of the detector 6 is introduced in a display and recording apparatus (not shown) for observation of a coefficient of complex refraction as a quantity proportional to 1-cos delta corresponding to a phase lag of the measured light intensity by the detector 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to which the Invention Pertains] The present invention relates to a plastic substrate inspection device, and more particularly to a plastic substrate inspection device for fully inspecting the birefringence of a plastic substrate for an optical disk.

[Prior art]

Conventionally, a visual inspection method using two polarizing plates or a precision quantitative measurement method using ellipsometry has been used to inspect the refractive index of a plastic substrate for an optical disk.

In the former method, the object to be measured is placed between two polarizing plates and the entire distribution of transmitted light amount caused by birefringence is visually inspected, and the measurement accuracy is low because it is a qualitative measurement.

On the other hand, in the latter case, the amplitude of polarized light with two orthogonal vibration components is 1.
] It measures the ratio and phase difference to determine the optical properties of the object, and quantitative measurements are possible, but the analyzer is rotated to measure the light intensity in each direction and requires extremely complicated calculation processing. The disadvantage is that the measurement time is long.

In general, in the injection molding method used to manufacture plastic substrates, the optimal molding conditions are often searched for while continuing molding due to its thermal cycle nature. It is extremely important to take measurements in a short period of time and provide prompt feedback to molding condition parameters, and the long measurement time is a fatal drawback.

In addition, the latter method requires complicated arithmetic processing functions, which has the disadvantage of making the device expensive.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive plastic substrate inspection apparatus that can quantitatively and accurately measure the birefringence of a plastic substrate for an optical disk in a very short period of time.

[Structure of the Invention] The plastic substrate inspection apparatus of the present invention includes means for generating a linearly polarized laser beam, holding and rotating means for holding and rotating the plastic substrate in an attitude in which the surface of the plastic substrate is perpendicular to the laser beam, and the holding and rotating means for The entire plastic substrate is loaded onto the laser beam and moved in a direction that intersects the optical axis of the laser beam and deviates from the direction of polarization by 45 degrees, and the laser sporatra scans the plastic substrate in the radial direction. a half-wave plate located behind the plastic substrate inserted above the laser beam and having an axis perpendicular to the laser beam and at an angle of 45° with the direction of polarization; an analyzer located behind the half-wave plate on the laser beam and having a transmission axis in the same direction as the polarization direction of the laser beam; The apparatus includes means for converting the optical energy of the laser beam into a total electric signal, and means for quantitatively displaying and recording the electric signal.

[Explanation of Examples]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view of an embodiment of the present invention.

FIG. 2 is a block diagram showing the electrical signal processing system of the same embodiment.

In FIG. 1, in order to simplify the explanation, the laser beam 1 is observed from the 7-otode detector 6 side, and the laser beam 1 is observed in the vertically upward direction.
The plastic substrate inspection apparatus shown in Figs. 1 and 2 has an axial direction A and a horizontal right direction as the X-axis direction B.
a laser tube 2; a polarizer 3 fixed on the optical axis of the laser beam 1 with its transmission axis in a direction C rotated 45 degrees counterclockwise from the X axis; a half-wave plate 4 located behind the polarizer 3 and fixed in an attitude in which the vibration component in the X-axis direction lags behind the vibration component in the y-axis direction E; and the light of the laser beam 1. An analyzer 5 located behind the half-wave plate 4 on the axis and fixed in a posture with its transmission axis in a direction F rotated by 45 degrees counterclockwise from the X axis, and the laser The polarizer 3. is located behind the analyzer 5 on the optical axis of the beam 1. Plastic substrate9. Said half wavelength plate4. A photodetector 6 receives the laser beam 1 that has passed through the analyzer 5 and converts the amount of light into an electrical signal a, and amplifies the electrical signal a'f from the photodetector 6 and converts it into a voltage output. A processing section 13, an oscilloscope 7 for displaying the temporal change in the voltage output obtained by the processing section, a pen writing recorder 8 for recording, and a laser beam 1 for the plastic substrate 9.
a holding section 10 that holds the plastic substrate 9 in a position perpendicular to the optical axis of the laser beam 1; a rotating section 11 that rotates the plastic substrate 9 about an axis parallel to and at the same height as the optical axis of the laser beam 1;
and a radial moving section 12 that mounts the rotating section 11 and moves in the X-axis direction.

To operate this, after fixing the plastic substrate 9 to be measured to the holding part 10, the rotating part 116 and the radial moving part 12 are fully driven so that the laser beam 1 passes through the point to be measured on the plastic substrate 9. Move to the desired position.

At this time, the moving direction is horizontal, and the measurement point can be moved in the radial direction of the plastic substrate 9. Furthermore, even if the measuring point is changed by rotation or movement, the radial direction of the plastic substrate 9 always corresponds to the X-axis direction A1 and the circumferential direction corresponds to the Y-axis direction B at the measuring point. Next, when the He-Ne laser 2 is turned on, each vibrational component of the laser beam 1 after passing through the polarizer 3 becomes the following equation (1) α').

EX = E□ exp(-iwt) (1) Ey =
E□ exp(-iwt) (1') where Ex,
BY are vibration components in the X-axis direction and the y-axis direction, respectively.

Next, when this laser beam 1 passes through the plastic substrate 9, birefringence occurs due to alterations caused by resin molding, such as material distortion and molecular orientation, resulting in a phase shift.

According to the general injection molding method used for resin molding of plastic substrates for optical disks, the resin is normally filled from the gate in the center of the plastic substrate toward the periphery, so the axis of birefringence is the axis of the plastic substrate 9. By measuring the phase shift of the vibration components in the radial direction and the circumferential direction, the total birefringence of the plastic substrate can be measured.

If a phase shift of δ occurs in the circumferential vibration component with respect to the radial vibration component due to birefringence in these two directions, the laser beam 1 after passing through the plastic substrate
is the formula (2) (a) EX = E□ exp(-i
wt) (2) Ey=E□ exp(-iwt)exp
iδ C) Furthermore, 1/2 with axes in the x and y axes directions
When transmitted through 4 wave plates, the formula (3) (3') is obtained.EX =
E□ exp(-iwt) (3)Ey =E□ e
xp(-iwt)exp i (δ1π)σ) When this laser beam passes through an analyzer with a transmission ring in a direction rotated 45 degrees counterclockwise from the X axis, only the component in this direction passes through. () Since the intensity of light is the sum of the squares of each amplitude, the intensity of light measured by the photodetector 6 is expressed by equation (5) σ).

I = 1/2 E□ ((1-cosδ) +stn
δ) (5) = Eo (1-cos δ) (a) Therefore, the intensity of the light measured by the photodetector 6 is an amount proportional to 1-cos δ corresponding to the phase shift δ, and this must be converted into a total electric signal. For example, the birefringence can be observed and recorded instantly using an oscilloscope 7 or a pen recorder 8.

Furthermore, by rotating the plastic substrate 9, changes in birefringence in the circumferential direction can be observed and recorded instantaneously.

Furthermore, by moving the plastic substrate 9 in the radial direction, changes in the birefringence index in the radial direction can be observed and recorded instantaneously.

〔Effect of the invention〕

The plastic substrate inspection apparatus of the present invention includes a rotating section 9-11 and a radial moving section, and rotates and moves the plastic substrate so that the radial direction and circumferential direction of the plastic substrate at the measurement point are always constant. , 1/2
By using the wave plate 4 and analyzer 5, only the most important phase shift between the radial and circumferential vibration components can be extracted (-) and can be observed and recorded instantly, eliminating the need for complex arithmetic processing. This method has the effect of being able to quantitatively and accurately measure the refractive index in a short period of time.

Furthermore, since the device has a simple configuration and does not require arithmetic processing functions, it has the advantage that the device can be provided at a low cost.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing one embodiment of the present invention, and FIG. 2 is a block diagram showing an electrical signal processing system of the same embodiment. 1... Laser beam, 2... He-Ne laser tube,
3...Polarizer, 4...Half wavelength plate, 5...Analyzer, 6...Photodetector, 7...Oscilloscope, 8...Pen t! Recorder, 9... Plastic substrate, 10... 10- Holding section, 11... Rotating section, 12... Radial direction moving section,
13... Processing part, a... Electric signal, b... Electric output. 11- % r Figure Z? figure

Claims (1)

[Claims] a means for generating a linearly polarized laser beam; a holding and rotating means for holding and rotating the surface of a plastic substrate in a posture orthogonal to the laser beam; and a moving means for moving in a direction making a 45° angle to the direction of polarization, inserting the plastic substrate onto the laser beam, and scanning the plastic substrate in the radial direction; a half-wave plate located behind the inserted plastic substrate and having its entire axis perpendicular to the laser beam and at a 45° angle with the direction of polarization;
an analyzer located behind the half-wave plate on the laser beam and having a transmission axis in the same direction as the polarization direction of the laser beam; A plastic substrate inspection apparatus comprising: means for converting optical energy of a laser beam into an electrical signal; and means for quantitatively displaying and recording the electrical signal.