JPS6243257B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide a photosensitive recording medium suitable for recording information using light of at least two wavelengths inside and outside a photosensitive recording area.

In recent years, light has been focused on a minute area on a photosensitive recording medium, such as a silver halide film, a photographic plate, or a photoresist-coated substrate, and the brightness of the light spot is modulated by a recording information signal, and the recording surface is scanned at the same time. There is a need for a means for sequentially recording information and for reading and reproducing the information thus recorded. In this case, the information recorded includes coded digital information and analog information such as video signals and audio signals, but in both cases, it is necessary to record as much information as possible at a high density and to stably reproduce it. desired.

In such a recording/reproducing method, it is desirable that information be recorded by applying an appropriate amount of exposure to the recording medium. However, the appropriate exposure amount for the recording medium varies depending on the spatial position on the recording medium.

For example, consider the case where a photoresist (for example, AZ1350; manufactured by Shipley Co., Ltd.) is coated on a substrate made of glass or the like on which chromium (Cr) is vapor-deposited and used as a recording medium.

In this case, methods for applying the photoresist on the substrate include spin coating, dip coating, and spraying. However, with either of these methods, it is extremely difficult to stably coat a disk with a diameter of about 30 cm with a change in film thickness within 100 Å. For example, in the spin coating method, photoresist liquid is dropped through a filter onto the circumference from the center of the substrate placed on the turntable of a spinner, and the centrifugal force when the spinner is started is used to coat the substrate. However, the film thickness tends to be thicker near the inner periphery, and the current situation is that applying a uniform film thickness over the entire surface of the substrate has a very poor yield. . Furthermore, in terms of improving recording density, it is desired to record information as far as possible to the inner circumference. Therefore, changes in the coating film thickness on the inner periphery of the recording medium have become an unavoidable problem. Furthermore, due to non-uniformity in the amount of photoresist dropped on the circumference, uneven coating often occurs even at the same diameter after coating. Such unevenness in coating film thickness results in a change in the spatial position of the appropriate exposure amount for the recording medium.

On the other hand, in such a recording and reproducing system,
FM modulation is used as the information encoding method. The carrier frequency used is 7 to 8 MHz depending on various factors of the reproduced information signal. In this case, the actual recording length on the recording medium is 2 μm at the outer circumference and 0.6 μm at the inner circumference when recording is performed by rotating the recording medium at 1800 rpm. Here, as the recording length on the recording medium becomes shorter, such as at the inner circumference, fluctuations in the development time have a negative effect, but it is difficult to control the development time in order to uniformly develop the entire recording medium. Therefore, it is necessary to strictly control the exposure amount to an appropriate amount.

However, as mentioned above, the actual coating film thickness tends to become thicker near the inner periphery, and the film thickness in the same radial direction also changes significantly near the inner periphery.

However, when the film thickness of the photoresist changes in such a recording medium, the rate at which recording or automatic focus adjustment light is reflected through the photoresist, that is, the rate at which it is absorbed by the photoresist, depends on the film thickness and the amount of light. Since it changes in relation to the wavelength, the recording state changes when the film thickness changes, making it impossible to perform good recording.
An example of such a conventional system will be explained with reference to FIG.

FIG. 1 is a diagram showing calculation results of the thickness of a resist film coated on a chromium vapor-deposited film having a reflectance of 50% on a glass substrate and its reflectance.
In this calculation, the refractive index of the resist is 1.7, and the wavelength of the light used is 4416 Å for curve A and 4416 Å for curve B.
This is the case of 6328 Å.

For example, 4416 in the vicinity of resist film thickness 2000Å
Changes in film thickness and reflectance for light of Å are ±
It is 5% at 100 Å, 10% at ±200 Å, and 26% at ±300 Å. In this graph, the maximum reflectance is 50%, so if the relationship between the above and the required exposure amount is linear, the change in the required exposure amount is 10% at ±100 Å, and 10% at ±200 Å.
20% at ±300Å, and 52% at ±300Å. The change in photoresist film thickness due to current coating methods is ±200 to ±300
Since it is about .ANG., the amount of light needs to change by 20% to 52% or more. However, this amount of change is a very large change with respect to the amount of exposure, and moreover, it changes depending on the spatial position on the recording medium, making exposure extremely difficult in reality.

In order to minimize the change in the required exposure amount due to the photoresist film, it is desirable to lower the reflectance at the boundary between the substrate and the photoresist, but when recording information, the recording wavelength and focus detection wavelength are When used, there is a problem in that lowering the reflectance, particularly for the focus detection wavelength, leads to a decrease in the focus detection force, making it impossible to record desired information.

An object of the present invention is to eliminate such conventional drawbacks and provide an information recording medium that can easily perform almost uniform recording even when the brush thickness of the recording photosensitive material is uneven. It is something.

In order to achieve this object, the information recording medium according to the present invention includes a vapor-deposited film of a metal such as gold or copper or a dielectric material such as TiO ₂ , ZrO ₂ , SiO ₂ , MgF ₂ , etc. on a substrate such as glass, and further A film made of a photosensitive material such as a photoresist is formed thereon, and the film thickness of the vapor-deposited film is set to have a high transmittance to light of a recording wavelength within the photosensitive wavelength range to which the photosensitive material is exposed. The reflectance of the auxiliary light for automatic focus control having a wavelength outside the photosensitive wavelength range to which the photosensitive material is not exposed is selected and configured to be high.

In this way, the recording light is effectively absorbed without being reflected by the recording medium, so that good recording can be performed regardless of changes in the film thickness of the photosensitive material.
Further, since the auxiliary light is sufficiently reflected by the recording medium, a sufficient amount of reflected light for automatic focus control can be obtained, and the control operation can be performed satisfactorily.

Therefore, even if the film thickness of the photosensitive material becomes non-uniform when applied by spin coating or the like, good recording is possible without being affected much by the non-uniformity.

FIG. 2 shows a block diagram of essential parts when performing optical recording using the information recording medium of the present invention.

1 is an information recording medium, 2 is an objective lens, and 3 is a recording light beam whose intensity is modulated by a recording signal. The recording light beam 3 enters the objective lens 2 and is recorded on the information recording medium 1.
The light is focused on. Here, the NA of the objective lens is 0.5, the depth of focus is approximately 2 μm, and the recording light beam 3 has a wavelength of
This is a 4416 Å He-Cd laser beam. The information recording medium 1 has a high transmittance (low reflectance) for light having a wavelength of 4416 Å and is formed into a disk shape. 4 is an objective lens 2 and an information recording medium 1
This is an auxiliary light beam for detecting a signal for maintaining a constant distance between the two and the auxiliary light beam, and is incident on the objective lens 2 at an angle with respect to the optical axis via the auxiliary lens 5. When the distance between the objective lens 2 and the information recording medium 1 is equal to the focal length of the objective lens 2, the reflected light of the auxiliary light beam 4 from the information recording medium 1 enters the pair of photoelectric conversion elements 6 and 7 in equal amounts. If the information recording medium 1 moves in the a direction, the reflected light flux that enters the photoelectric conversion element 6 increases, and if it moves in the b direction, the reflected light flux that enters the photoelectric conversion element 7 increases. Therefore, it is possible to detect an error signal for keeping the distance between the objective lens 2 and the information recording medium 1 constant by using a circuit 8 that takes the differential output of both the photoelectric conversion elements 6 and 7, and this error signal can be detected. If the control circuit 9 generates a control signal and drives the voice coil 10 coupled to the objective lens 2, the distance between them can be maintained at the focal position of the objective lens 2. As the auxiliary light flux 4, a light flux having a wavelength outside the photosensitive area, for example,
If a 6328 Å He--Ne laser beam is used, the above-mentioned automatic focus adjustment function will work well because the information recording medium 1 has a high reflectance for light of wavelengths outside the photosensitive region.

Next, the information recording medium 1 of the present invention will be explained in detail. This information recording medium 1 is made of metal such as gold, copper, TiO ₂ , ZrO ₂ , etc. on a substrate such as a glass plate.
A dielectric film such as SiO ₂ or MgF ₂ is deposited, and a photosensitive material is coated on top. Here, AZ1350 manufactured by Shipley Co., Ltd. is used as an example of a photosensitive material, and its spectral sensitivity characteristics are shown in FIG. The vertical axis shows sensitivity, and the horizontal axis shows wavelength. From this figure,
It can be seen that the photosensitive area of AZ1350 is 4800 Å or less.

Therefore, as the recording light beam 3, Hg with a wavelength of 4416 Å
-Cd lasers and 4560 Å Ar lasers can be used within the sensitive wavelength range. On the other hand, wavelength 6328
The He--Ne laser having a wavelength of 1.5 nm can be used as the auxiliary light beam 4 because it falls outside the sensitive wavelength region where the photosensitive material is not exposed. Therefore, by suppressing the reflectance at the interface between the base material and the photosensitive material to almost 0% at 4800 Å or less, the change in reflectance at the interface between the base material and the photosensitive material due to changes in the film thickness of the photosensitive material can be kept to below a few percent. It becomes possible to suppress the However, in this case, if the vapor deposited film is removed, the reflected light at wavelengths outside the sensitive wavelength range will also be approximately 4%, and if a 6328 Å He-Ne laser is used as the auxiliary light beam 4 for focus detection, the S/N will be poor. A problem occurs. Therefore, a vapor deposited film that has low reflectivity for wavelengths within the photosensitive region (4800 Å or less) of the photosensitive material and high reflectivity for wavelengths outside the photosensitive region (4800 Å or more) is used as a substrate and photoresist. It must be formed on the boundary of

For this purpose, in the present invention, for example, a vapor deposited film layer of copper or gold is formed between the substrate and the photosensitive material layer,
Alternatively, by forming a multilayer film layer of dielectric material such as TiO ₂ or MgF ₂ , the transmittance is high for the recording wavelength within the photosensitive wavelength range (e.g. 4416 Å), and the transmittance is high for the recording wavelength within the photosensitive wavelength range (e.g. 6328 Å). ) is provided with a vapor deposited film that increases the reflectance.

As a specific example of the structure of this vapor deposited film, a case where a metal film is used will be described. When using gold,
The reflectance near 4416 Å is about 40%, and the reflectance near 6328 Å is about 95%. Similarly, when copper is used, a reflectance of about 55% near 4416 Å and about 95% near 6328 Å can be obtained. The above characteristics can be sufficiently obtained with a deposited film thickness of several thousand angstroms or more.

Although the effects of the present invention can be obtained with the above-mentioned configuration example, in order to further improve the reflectance within the photosensitive wavelength region, it is necessary to add a high refractive index film (nH) and a low refractive index film (nL) on the glass substrate. ), with a film thickness that is an integer multiple of 1/4 of the desired wavelength, and by alternately laminating about 10 layers each, the reflectance is about 0% at the recording wavelength within the photosensitive area, and the reflectance is about 0% at the recording wavelength outside the photosensitive area. It is possible to secure a reflectance of 98% or more at any wavelength (see Figure 4). These techniques are already known as techniques for creating a three-color separation type dichroic mirror. In the case of an example of the present invention, the characteristics are almost the same as those of the blue reflective dichroic mirror. As the film constituent materials, TiO ₂ and ZrO ₂ are used for the high refractive index film, and SiO ₂ and MgF ₂ are used for the low refractive index film.

The thickness of the deposited film differs depending on the material, and the appropriate value also changes depending on the wavelengths of the recording and auxiliary light beams used. That is, since both the photosensitive film and the vapor-deposited film exhibit different properties as shown in FIGS. 1A and B depending on the optical path difference of their respective lights, they can be determined as appropriate depending on the light source and material used.

As described above, the present invention provides an information recording medium with a high transmittance for light having a recording wavelength in a part of the photosensitive wavelength range, and a high reflectance for light with a part of wavelength outside the photosensitive wavelength range. By configuring the structure to be as large as possible, it is less affected by uneven thickness of the photosensitive film, which simplifies the formation of the photosensitive film, improves recording accuracy and density through proper exposure, and facilitates mass production. It has great industrial value, such as homogenization of quality. In particular, in the present invention, since a photosensitive film with high transmittance to recording light is used, even if the thickness of the photosensitive film varies, it does not affect the exposure amount of recording light. , a good recording state can be stably obtained, and since a photosensitive film with a low reflectance to the recording light is used, standing waves of the recording light can be prevented. It is possible to prevent unevenness on the pit edge caused by the influence of standing waves, resulting in a good recording condition, and it is also possible to easily peel off the stamper. By using a large material, the automatic focus adjustment light reflected on the surface can be effectively used, and automatic focus adjustment can be performed satisfactorily, which has great practical effects.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing changes in film thickness and reflectance of the photosensitive film, Fig. 2 is a diagram showing the main part of an apparatus for recording using the information recording medium of the present invention, and Fig. 3 is a spectral diagram of the photosensitive material. FIG. 4 is a reflection characteristic diagram of the information recording medium.

Claims (1)

[Claims] 1. A vapor deposited film made of a metal or dielectric is formed on a substrate, and a film of a photosensitive material is further formed on the vapor deposited film, and the vapor deposited film is made of a material that the photosensitive material for recording information on the photosensitive material film is exposed to. It has a high transmittance for recording light with a wavelength that is recorded, and a low reflectance for auxiliary light for automatic focus adjustment that has a wavelength longer than the recording light and has a wavelength that does not sensitize the photosensitive material. An information recording medium characterized in that the film thickness is set so as to be large.