JPH03259440A - Production of master disk of optical disk - Google Patents

Abstract

PURPOSE:To obtain good signals by using two laser beams of linearly polarized light with the direction of polarization planes different from each other by 90 deg., making the one P-wave of the two beams to irradiate one of slopes of a V-shape groove where a photoresist film has larger film thickness, and making the other S-wave to irradiate the other slope having small film thickness. CONSTITUTION:Two laser beams of linearly polarized light, P-wave and S-wave, with direction of polarization planes different from each other by 90 deg. are used for recording signals on an optical disk substrate 1. The reflectivity of the interface between the photoresist and air differs for the P-wave and for the S-wave. Since the reflectivity for the P-wave is smaller than that for the S-wave, P-wave is made to irradiate one of slopes of a V-shpae groove where the photoresist film is thick, while S-wave is made to irradiate the other slope having small film thickness. Thus, both slopes of the V-shape groove can be used to record signals in good state.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing an optical disc master.Prior art Optical disc master 41 A glass or the like with a polished surface, or a V-shaped groove formed on the surface and polished. A photoresist is coated on a substrate made of glass, etc., and exposed to laser light whose intensity is modulated according to the information signal to be recorded. Signal pits corresponding to the sensitivity are formed to create a V-shape on the surface. The reason for forming the grooves in the mold is to prevent the pits of adjacent tracks from being read when reading signals. Although this figure mainly shows the laser beam irradiation configuration, the substrate 14 coated with photoresist is shown in FIG.
1 Rotationally driven by spindle 2 and
- The substrate 1 is transferred in the radial direction by the axis moving table 3.
Laser light 27i emitted by argon laser oscillator 4!
, Two lenses having different focal lengths are arranged so as to share a focal point, and receive intensity modulation according to the signal to be recorded by an intensity modulator 7 using an electro-optic effect etc. via a mirror 5.6. Hiro dichroic mirror 9 whose beam diameter has been expanded by a beam expander 8,
The laser beam from the helium neon laser 12 is focused and irradiated onto the substrate 1 by the lens actuator 11 after passing through the mirror 10, and is used for focus and tracking control, and is used for polarization beam splitter 13, 1/2.
4-wavelength plate 14, dichroic mirror 9, mirror 10
The reflected light from the substrate 1 of this helium neon laser light is narrowed down by the lens actuator 11 and irradiated onto the substrate 1. The reflected light from the substrate 1 is passed through the mirror IO, the dichroic mirror 9, and the 1/4 wavelength plate 14 to the polarizing beam splitter. -13 separates the incident light from the incident light and guides it to the focus and tracking detection light receiving element 15.
Even though focus control and tracking adjustment of the laser beam 27 with respect to the substrate 1 is performed, the photodetectors capable of focus control are collectively represented as focus detection light receiving elements in the figure.For example, in the Naifetsu method, the focus of the lens The tracking servo system includes a knife lens between the surface and a photodetector divided into two parts.In the astigmatism method, it includes a cylindrical lens X and a photodetector divided into four parts.The tracking servo system also includes a cylindrical lens
For example, in the push-pull method, a light receiving element for tracking detection includes a lens and a photodetector divided into two parts.

FIG. 6(b) is a side view of the part that irradiates the substrate 1 with laser light in FIG. 6(a).The lens actuator 11 is driven in accordance with the signal obtained by the light receiving element 15.
The focus of the laser beam 27 is controlled by the argon laser 4. Even if the substrate 1 is irradiated with focused light on the When applying a photoresist to a substrate with spiral or concentric circles formed on the substrate (concentrically or spirally), if the spin code method is used as is commonly practiced, It is rare that the thickness of the photoresist is the same on two slopes. In most cases, the thickness of the photoresist is different on the side slopes, as shown in the cross section of Figure 7. For example, if the same laser beam is irradiated on the thinner side of the film, ζ4, the depth of focus will be shallow because the laser beam is narrowed down to a small size during signal recording, so it will not reach the slope where the film is thicker. It becomes difficult to record, and if the intensity of the laser beam is matched to a slope with a thick film, the laser beam will be too strong for a slope with a thin film, and the width of the signal pit will widen, making it impossible to obtain a good signal. In order to solve these problems, the thickness of the photoresist coated on the optical disc substrate is measured in advance, and two linearly polarized lights with polarization planes different from each other by 90 degrees are generated. Based on the above measurement results, signals were recorded by irradiating the P wave of these two laser beams onto the thick slope of the photoresist film and the S wave onto the thin slope of the photoresist. Using two laser beams with different intensities U) The stronger one of these two laser beams is used to irradiate the thick slope of the photoresist film, and the weaker one is used to irradiate the thinner slope of the photoresist film. According to the first invention above, when recording a signal on an optical disk substrate, two laser beams, P wave and S wave, whose polarization planes are different from each other by 90 degrees are used. For waves, the reflectance at the interface between photoresist and air is different, and the reflectance of P waves is lower than that of S waves, so P waves are irradiated onto slopes with thick photoresist films to reduce the film thickness. By irradiating S waves on thin slopes, it is also possible to record equally good signals on both slopes forming grooves.
In the second invention, when recording signals on an optical disc substrate,
Using two laser beams with different intensities, t,% By irradiating the slope with a thick photoresist film with a high-intensity laser beam and the slope with a thin film thickness with a weaker laser beam, ■ Signals can be recorded in the same way on either slope forming the groove.Examples The embodiments of the present invention will be explained below with reference to the drawings. This is a diagram showing the configuration of an optical disk master preparation device in one embodiment. A substrate 1 coated with photoresist and having a V-groove formed thereon is rotated by a spindle 2 and moved in the radial direction of the substrate 1 by an axis moving table 3. The laser beam 22a emitted by the argon laser oscillator 4a has a polarization plane perpendicular to the plane of the drawing, and is intensity-modulated by the intensity modulator 7a according to the signal to be recorded through the mirrors 5a and 6a. Even though the beam diameter is expanded by the mold mirror 17 and reflected by the polarizing beam splitter 18, the laser beam 22b emitted by the argon laser oscillator 4b has a polarization plane parallel to the plane of the paper, and mirrors 5b and 6.
After the beam diameter is expanded by the beam expander 8b, the beam diameter is expanded by the beam expander 8b, and then the polarizing beam splitter
Two laser beams with polarization planes that differ by 90 degrees are reflected or transmitted by the polarizing beam splitter 18 and are stabilized.
16, force t focused on the substrate 1 by the lens actuator 11 Lens actuator 11
Since the angle of incidence on the laser beams is slightly different, the laser beams are focused at two different positions on the substrate 1. FIG.

Laser beams 22a, 22b4;! By controlling the galvanomirror 16 and the lens actuator 11 using a focusing and tracking servo system using a helium neon laser 12, the beams are narrowed down to two slopes of the V-groove, respectively. Laser beam 22al from the argon laser oscillator 4a whose polarization plane is perpendicular to the paper plane
The laser beam 22bi from the argon laser oscillator 4b whose polarization plane is parallel to the plane of the paper is incident as a P wave on the slope of the V groove. Waves have different reflectances at the interface between photoresist and air, and P waves have lower reflectance than S waves, so P waves are applied to thick slopes of photoresist, and P waves are applied to thin slopes of photoresist. By irradiating S waves, it is possible to record equally good signals on both slopes forming the groove. A diagram showing the principle of the method for measuring film thickness is shown.

Figure (b) is an enlarged view of a portion PQR8 of the optical disc substrate shown in figure (a), and figure (c) is a sectional view taken along line AA in figure (b). In figure (b), arrows e and f2
The dashed lines indicated by g indicate LLl and Xuzhan of the ■groove, respectively. When measuring film thickness, for example, the vw of photoresist
By irradiating the area indicated by xy with laser light and exposing this area to remove the photoresist,
) is measured using an STM (tunneling microscope).

Based on this measurement result, the argon laser oscillators 4a, 4
By controlling the output of b, a signal is recorded by irradiating a thick slope with a P wave or a strong laser beam, and a thin slope with a thin film by irradiating an S wave or a weak laser beam. Other embodiments of the first invention are shown in a) and (b).

In Figure 1, two argon laser oscillators were used to obtain two recording laser beams with different polarization planes. You can also divide it into two (
t Laser light 221 from the argon laser oscillator 4 whose plane of polarization is perpendicular to the plane of the paper is split into two by the half mirror 20 through the mirror 5, and the light 23b is transmitted through the polarizing beam splitter 18! ! half mirror 2
1/2 wavelength plate 2 between 0 and polarizing beam splitter 18
In FIG. 3, the half-wave plate 21 is placed between the mirror 6b and the intensity modulator 7b. If it is between L%, there is no problem in other places.Also, use an argon laser whose polarization plane is parallel to the plane of the paper (＼ Install a 1/2 wavelength plate on the side of the light 23 that is reflected by the polarizing beam splitter 18. It's not inconvenient at all,
Figure 3(b) is a side view of the part where the laser beams 23a and 23b are irradiated onto the substrate 1.
3a, 23bC & After passing through dichroic mirror 〇 and galvano mirror 16, it is narrowed down to substrate 1 by lens actuator 11. Polarizing beam splitter
The laser beam reflected by 18 enters the slope of the groove 2aaliV as a P wave, so it irradiates the slope of the thicker photoresist film & -4 Polarizing beam splitter -
The laser beam 23bj that has passed through 18 enters the slope of the mV groove as an S wave, so it irradiates the slope of the photoresist with a thinner film thickness.

AZ-1350 (Sibley) diluted with AZ thinner to a volume ratio of 20% was used as a photoresist, and a final coat was applied to the V-groove at a rotational speed of 50 rpm using a laser with a wavelength of 458 nmlOmW at a linear velocity of 10 m/s. Signals were recorded on the thinner slope of the photoresist, but signals could be recorded for both P waves and S waves.
On the thicker slope, a signal could be recorded for P waves, but insufficient recording for S waves ■When the groove opening angle is 160 degrees, the incident angle is 10 degrees, and the signal is recorded at the interface between the photoresist and air. S-wave reflectance Rs and P-wave reflectance Rp it The refractive index of the photoresist is 1. 5, then Rs=4. 2
% Rp=3. 8% f-0 FIG. 4 shows an embodiment of the second invention.

In the figure, even though the two laser beams 24a and 24b with polarization planes different by 90 degrees are separated by the polarizing beam splitter 18 as in FIG. 1(a), the output ζ of the argon laser oscillator 4a is The laser light 24 is set so that the light 24a is stronger than the light 24b, and the laser light 24 is combined by the polarizing beam splitter 18.
a, 24b4L The light is converted into circularly polarized light by the 1/4 wavelength plate 25 and narrowed down to the substrate on which V grooves are formed with photoresist. By irradiating the strong laser beam 24a and irradiating the thin slope with the weaker laser beam 24b, it is possible to record similarly good signals on the two slopes forming the groove.

FIG. 5 shows another embodiment of the second invention.

In this embodiment, as shown in FIG. 3(a), the output from one argon laser oscillator 4 is divided into two laser beams 26a and 26b by a half mirror 20. The intensity of the two laser beams can be changed by shifting the ratio of transmission and reflection of the half mirror that separates the beams from 50:5 to the one that narrows down to the thick slope of the photoresist between the two slopes that form the V-groove. (°C) Also, in this case, as in the previous example, the two laser beams at the base should be connected to the 1/4 wavelength plate 25.
The light is converted into circularly polarized light by

AZ-1350 (Shipley) diluted with AZ thinner to a volume ratio of 20% was used as a photoresist, and a final coat was applied to the V-groove at a rotational speed of 500 rpm using a laser with a wavelength of 458 nm at a linear velocity of 10 m/s. The signal was recorded on the thin slope of the photoresist, where a signal could be recorded even with 10 mW.On the thick slope, 10 mW was insufficient to record the signal, but the signal could be recorded with 12 mW. By increasing the L laser power with
If the power of the laser beam applied to the thick slope of the V-groove is made about 20% stronger than the laser power applied to the thin slope, signals can be recorded on the side slopes of the V-groove in the same way.

In the above example, a polarizing beam splitter is used to combine two laser beams. In this case, the intensity of the laser beam is halved, so it is necessary to increase the intensity of the beam before combining.

More than just the effects of the invention, by irradiating the two sloped plates that form the V-groove of the optical disk substrate, by irradiating the slope with the thicker photoresist film with the P wave and the slope with the thinner film with the S wave. , Good signals can be recorded simultaneously on both slopes forming the groove.Similarly, by irradiating the slope with the thicker photoresist film with a strong laser beam, the slope with the thinner photoresist film can be recorded simultaneously. Good signals can be simultaneously recorded on the two slopes forming the kV groove by irradiating one slope with a weak laser beam.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) show the a precepts of an optical disc master manufacturing apparatus in an embodiment of the present invention. FIGS. 2(a) to (C) show the preparation of an optical disc master for measuring the photoresist film thickness. The configuration of the apparatus is as follows: Figure 7 is a cross-sectional view of an optical disk substrate coated with photoresist. 5.6, IOl 16, 17... ; Two 7... Intensity modulation edge 8... Beam expander, 9... Dichroic mirror 11... Lens actuator 12... Helium neon laser 13, 18 ...Polarizing beam splitter 14.25...
・1/4 wavelength plate 15, 19... Light receiving element for focus and tracking detection, 20... Half mirror 1 21... 1/2 wavelength plate

Claims (2)

[Claims] (1) A step of forming a groove with a V-shaped cross section in a spiral or concentric shape on one surface of a disk-shaped optical disk substrate, a step of polishing the surface on the same surface, and a step of applying photoresist on the same surface. and recording a signal by irradiating the V-shaped groove with a laser beam whose intensity is modulated according to the information signal, The measurement was carried out on two slopes forming the groove, using two linearly polarized laser beams with polarization planes different from each other by 90 degrees, and the S wave of the two laser beams was measured on the slope of the thinner film. A method for producing an optical disc master, characterized in that signals are recorded on both slopes of the V-shaped groove by irradiating P waves onto the slopes of the thicker film. (2) A step of forming a spiral or concentric groove with a V-shaped cross section on one surface of a disk-shaped optical disk substrate, a step of polishing the surface on the same surface, and a step of applying photoresist on the same surface. and recording the signal by irradiating a laser beam whose intensity is modulated according to the information signal. Using two laser beams with different intensities, the stronger laser beam of the two laser beams is irradiated on the slope with the thicker film thickness, and the weaker laser beam is irradiated with the thicker slope of the film thickness. A method for producing an optical disc master, characterized in that a signal is recorded on both slopes of the V-shaped groove by irradiating a thin slope.