JPH0630175B2 - Method of making substrate of flat information recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a substrate of a flat information record carrier having grooves and pit rows having different depths.

2. Description of the Related Art Optical discs can record and reproduce information by using a minute laser spot with a diameter of 1 μm or less, which enables high-capacity and high-density recording. Therefore, an image that requires a large amount of information is required. It has been put to practical use as a file system for documents and documents.

On the information recording surface of this optical disc, concentric or spiral grooves or pit rows are formed, and information is read by irradiating the laser spot along the grooves and pit rows. In a read-only optical disc such as a video disc, information is recorded as fine pits and projections, and in a write-once optical disc that allows additional recording of information, information is recorded as a change in physical properties of a film on the recording surface. However, even in this case, guide grooves are formed on the recording surface so that information can be recorded at a high density at regular intervals. If the spacing between the pit row and the guide groove is narrowed, the recording density will increase, but if the spacing becomes close to the size of the laser spot, the data will be read over the groove (or pit row) that is being read when reading information. Even if the laser spot is irradiated, a part of the light flux is applied to the adjacent groove (or pit row), so that the influence appears as crosstalk of the reproduction signal. In order to reduce this crosstalk, alternating depths of adjacent grooves and pit rows are attracting attention as a method for increasing the density of optical disks. (See Japanese Patent Laid-Open No. 54-136303) A conventional method for forming such grooves and pit rows having different depths on one disk will be described with reference to FIG.

First, the photoresist 2 is uniformly applied to the surface of the glass plate 1 that has been highly accurately polished (FIG. 2A). After that, the photoresist 2 is exposed by the laser light 3 which is modulated in accordance with the desired pit row and groove structure (FIG. 2B). At this time, when the laser intensity is changed and the exposure is performed, the amount of the photoresist 2 removed in the developing step changes depending on the exposure amount, and accordingly the depth of the groove formed differs (see FIG. 2c). ). By transferring this concavo-convex pattern to the metal plate 4 (Fig. 2d) and further transferring it to the substrate 5 of acrylic or the like (Fig. 2e), an optical disk substrate having a desired structure and depth can be manufactured. .

Problems to be Solved by the Invention However, in such a conventional creating method,
Since the development amount of the photoresist is very sensitive to changes in the state of the developing solution and the external environment, there is a problem that it is very difficult to control the development amount to obtain a predetermined groove depth.

Means for Solving the Problems In order to solve the above problems, the present invention causes a plasma gas to react with substrates provided with masks having different widths to form grooves or pit rows having different depths. It is characterized by doing so.

Operation The operation of this means is as follows. When a plasma-like gas is applied to a substrate whose surface is masked with photoresist or the like, the unmasked portion of the substrate surface is etched due to the collision of plasma and the chemical reaction between the substrate and plasma. The shape of this etching pattern actually changes greatly from the original mask pattern, but this is due to the effect of the isotropic reaction process and the change in the etching amount with respect to the incident angle of the plasma ion beam. .

These influences vary depending on the type of gas used as plasma, pressure, discharge power for generating plasma, time for which plasma is applied, etc., but by appropriately selecting these factors, the mask pattern changes. It is possible to find etching conditions such that the depth of the etching pattern formed with respect to is changed. By utilizing this, by changing the width of the mask pattern formed on the substrate, it is possible to form grooves or pit rows having different depths on the same substrate.

Example Hereinafter, an example of the present invention will be described with reference to FIG.

Laser light 3 on glass plate 1 coated with photoresist 2
The process of irradiating is similar to the conventional method (Fig. 1a,
b). However, in this example, the width of the exposed region is changed by changing the spot diameter of the irradiated laser light. If a positive photoresist is used as the photoresist 2, the exposed portion is removed by development. At this time, the development is allowed to proceed until the surface of the glass plate 1 is exposed, so that the surface of the glass plate 1 is predetermined. A mask pattern having a width of is formed.

Next, this glass plate with a mask pattern is placed on the cathode electrode in the dry etching apparatus, and after being evacuated, gas is introduced to cause discharge to perform etching. In this embodiment, CHF ₃ is used as the etching gas.
In this case, the plasma generated by the dissociation of CHF ₃ by the discharge collides with the surface of the glass plate 1 to sputter the glass, and at the same time, selectively reacts with SiO ₂ which is the main component of the glass to decompose it. With. Therefore, the etching rate of the glass plate 1 can be made higher than the etching rate of the photoresist 2 and a deeper groove can be formed. The glass plate 1 used in this example is
A normal soda glass material is used, and even in this case, a sufficient etching rate can be obtained.

Etching was advanced to a predetermined depth (Fig. 1d).
After that, if the remaining photoresist 2 is removed by plasma ashing with O ₂ gas, grooves and pit rows having different depths are formed on the surface of the glass plate 1 (first
Figure e).

As the substrate of the flat information record carrier, other than using the glass plate 1 as it is, it is also possible to use the one obtained by transferring the concavo-convex pattern from the glass plate 1 as in the conventional method.

As the gas for etching, in addition to CHF ₃ in the present embodiment, and the like can be used _{CF 4, C 2 F 6,} C 3 F 8, NF 3. When an inert gas such as Ar is used, SiO ₂
Since there is no decomposition effect of (1), the etching rate of the glass plate 1 becomes small, but a pattern can be formed.

Further, as the glass plate 1, inexpensive soda glass as in this embodiment can be used, and quartz glass or the like having a high etching rate can be used to form a deeper groove.

EFFECTS OF THE INVENTION As described above, according to the present invention, by applying a plasma gas to a flat substrate provided with masks having different widths to form grooves and pit rows having a depth corresponding to the mask width, It is possible to easily create an optical disk substrate having grooves and pit rows having different depths on the substrate.

[Brief description of drawings]

FIG. 1 is a process drawing showing a method of manufacturing a flat information recording medium substrate according to an embodiment of the present invention, and FIG. 2 is a process drawing showing a conventional method of manufacturing a flat information recording medium substrate. 1 ... glass plate, 2 ... photoresist, 3 ... laser light, 4 ... metal plate, 5 ... acrylic substrate.

Claims (6)

[Claims] 1. A groove having a different depth corresponding to the width of the opening by causing a gas in a plasma state to act on a flat substrate provided with a mask having continuous or intermittent openings having different widths. A method for producing a substrate for a flat information record carrier, which comprises forming a pit row. 2. The method for producing a substrate for a flat information record carrier according to claim 1, wherein a positive photoresist is used as the mask. 3. The flat plate-like substrate according to claim 1, wherein at least a portion where a groove or a pit row is formed is formed of a material containing SiO ₂ as a main component. Method of making substrate of information recording carrier. 4. The flat plate-shaped substrate is formed of a material containing SiO ₂ and Na ₂ O as main components at least in a portion where a groove or a pit row is formed.
Item 6. A method for producing a substrate for a flat information record carrier according to the item. 5. CHF ₃ , CF ₄ , C ₂ F as gas in plasma state
_{6. The} method for producing a substrate for a flat information record carrier according to claim 1, wherein at least one of ₆ , C ₃ F ₈ and NF ₃ is used. 6. The method for producing a substrate for a flat information record carrier according to claim 1, wherein Ar 2 is used as the gas in the plasma state.