JPH0562259A - Optical information recording medium and production thereof - Google Patents

Abstract

PURPOSE:To facilitate an initialization stage for previously converting a thin- film layer consisting of a phase transition material which is a recording layer to a crystalline state or to eliminate the need for the initialization stage in the process for production of the optical information recording medium to be used for recording information by utilizing the reversible phase transition between the crystalline layer and amorphous layer of the material. CONSTITUTION:A deposited surface 4 is photoirradiated by using a light source 5, etc., and the recording film is formed while uniformly heating the entire surface of the deposited surface 4 uniformly with light at the time of forming the thin-film layer of the phase transition material on a substrate 3 by a method, such as vapor depositing or sputtering. The transition temp. for crystallization is lowered without changing the compsn. of the amorphous thin film if the film is formed in such a manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change type optical information recording medium, that is, a material thin film provided on a substrate is irradiated with a high-density energy flux such as a laser beam so that the irradiated portion is reversible and local. Method for producing optical information recording medium which causes reversible structural change between amorphous and crystalline, and records and reproduces information by utilizing the accompanying optical change, and optical information recording formed by using this method It is about the medium.

[0002]

2. Description of the Related Art A technique of forming a phase change recording thin film represented by a chalcogenide thin film on a substrate by a method such as vacuum deposition and sputtering, irradiating a laser beam to the formed recording thin film, and a reversible structure between an amorphous and a crystal. A technique for causing a change and thereby performing rewritable and high-density information recording is already widely known as a phase change optical disk medium and a phase change optical recording technique. As for the composition of the recording film, it was emphasized that the amorphous state was easily obtained with a low melting point in the early 1970s.
Although the composition near the eutectic point of Te-based alloys such as e15Sb2S2 has been studied extensively, the focus of the research has since shifted to increasing the crystallization rate.
The composition in the vicinity of stoichiometric compounds such as e and Ge2Sb2Te5 is the target of research and development. Along with this, the laser irradiation method for rewriting is also a method of using two laser spots having different spot lengths on the medium during the recording operation (amorphization) and the erasing operation (crystallization). It is changing to a method of overwriting.

It is also well known that the manufacturing process of a phase change medium roughly comprises the following (1)-(4). That is, the phase change medium has (1) an optical guide groove for guiding a laser beam for recording / reproducing to a predetermined recording position,
A replica preparation step of preparing a substrate provided with an address signal or the like as a shape change of the concavo-convex, (2) a film forming step of forming a recording thin film on the substrate by a method such as a vacuum deposition method or a sputtering method, and (3) an adhesive. It is formed through four steps of an adhesion step of sticking a protective plate to the surface of the recording film by using it, and an initialization step of (4) converting the recording film formed in an amorphous state into a crystalline state in advance.

A resin substrate is often used as the first replica preparing step. The method of injecting a molten resin mass into a mold to solidify it (injection method) is the mainstream. A metal plate in which an information signal such as an address is carved by concavo-convex by a method such as etching is used as a master plate, and a replica is formed with a thermoplastic resin such as polycarbonate or PMMA. It is also possible to use a glass substrate. In this case, the photopolymer is coated on a glass plate and then exposed one by one through an optical mask in which a signal is recorded in advance. Then, a glass substrate on which signal irregularities are formed is obtained by etching.

As the second film forming step, a vapor deposition method using an electron beam and a sputtering method using plasma of argon gas are dominant. Since it is necessary to form an alloy thin film of 2 to 5 elements, a multi-source evaporation method is convenient in the case of the evaporation method (for example, National Technical Re
port Vol. 35 No. 2 Apr. 1989
p110)). That is, for a plurality of constituent elements having different vapor pressures, melting points, etc., an evaporation source, an electron gun, and an evaporation rate controller are independently prepared to control each evaporation rate. The substrate is rotated so that it passes over each source in turn. As a result, each component is gradually and repeatedly stacked on the substrate at a constant speed. In the case of the sputtering method, a method of sputtering from an alloy target is general and convenient even for a multi-component system. Also in this case, in order to make the distribution of the recording film thickness as small as possible, the film is formed while rotating the substrate.

The third bonding step is performed for the purpose of protecting the recording film from mechanical damage. The purpose is achieved by bonding a hard resin plate and a glass plate similar to the substrate. When both sides of the medium are used, the same substrates each having a recording film are stuck together with the recording film surface inside.

A fourth initialization method is, for example, Japanese Patent Publication No. 2-45.
No. 247, the recording medium is crystallized,
This is done to set the reflectance and the transmittance to a certain level. The Ar laser beam was elongated and placed in a direction perpendicular to the direction of travel of the medium, so that a wide range of traces could be obtained with a single rotation, and the entire surface of the medium could be processed in a short time.

[0008]

The most time consuming step among the above steps is the initialization step. That is, the initialization process requires a process for each medium, for example, if it is a disk medium, it is rotated one by one and laser irradiation is performed on the entire surface, which is a bottleneck in manufacturing. An object of the present invention is to add a devise to the film forming step (2) in the above manufacturing steps, thereby facilitating the initialization step (4). Further, for example, when recording is performed in the overwrite mode, this initialization operation is made completely unnecessary.

[0009]

According to the present invention, in a film forming process for depositing a thin film of a phase change material on a substrate, the surface on which the phase change material is deposited is uniformly irradiated with light, whereby the phase change being deposited. The phase change material thin film is deposited while uniformly heating the entire surface of the recording thin film.

[0010]

[Function] The phase change material thin film deposited and formed while being heated by light is formed as an amorphous film having a lower initial crystallization temperature as compared with the phase change material thin film of the same composition deposited without being heated by light. It becomes possible to crystallize with smaller energy. Therefore, the initialization can be easily performed. When recording is performed in the so-called overwrite mode, the initialization process can be omitted and recording can be performed immediately.

[0011]

EXAMPLE FIG. 1 shows one example of the manufacturing method of the present invention.
It shows a simple arrangement of a film forming system when a sputtering method is applied as a deposition method of a phase change material thin film. The film forming method is not limited to the manufacturing method of the present invention, and the film forming method can be similarly performed whether it is a vacuum vapor deposition method or an ion plating method. In this embodiment, the vacuum chamber 1 is used in an ordinary sputtering apparatus. Inside, a sputtering target 2 having a diameter of 100 mm and a polycarbonate substrate 3 having a diameter of 130 mm, which are the same as those normally used, are arranged at an interval of 140 mm and a central axis. Are eccentrically arranged by 50 mm. In FIG. 1, the target and the substrate have a vertical relationship, but they may be upside down or left-right positional relationship. The optimum position is selected in consideration of the film thickness distribution and the deposition rate.

In this example, Ge-Sb-Te, which is a typical phase change material, was used as the phase change material. Although a ternary alloy of Ge ₂₂ Sb ₂₂ Te ₅₆ was used as a target, it is also possible to obtain the same composition by co-sputtering using a plurality of targets, for example, three targets of Ge, Sb, and Te. In addition, In-Sb-Te system, S
Various material compositions such as b-Te series are known, but they can be treated equally in manufacturing. That is, it can be carried out according to this example.

The essence of the present invention is to heat the surface on which the phase change material is being deposited (deposition surface 4) by irradiation with light, and to appropriately select the heating conditions to make the characteristics of the phase change material thin film desirable. It is a thing. Generally, a phase change material used as an optical recording material is in an amorphous state at the time of film formation. However, the amorphous state is not single but depends on the film forming conditions, for example, the substrate temperature. In other words, the present invention reduces the phase change rate (cooling rate) from the vapor phase to the solid phase by heating the deposition surface to form an amorphous film having a low crystallization temperature. As a heating method, in addition to light heating, a method of directly heating the substrate using a heater can be considered, but for the reason that the thin film itself absorbs light to raise the temperature, and it is easy to uniformly heat the whole. Light heating is excellent.

In this embodiment, the light source is about 30 mm ×
A halogen lamp lamp 5 having a size of 8 mm was used and arranged so that the longitudinal direction of the lamp coincided with the radial direction of the disk substrate. A nickel mirror plate 6 was also used in order to improve the uniformity and at the same time efficiently use the light of the lamp. The position of the lamp was set at almost the same height as the target so as not to affect the plasma. As the light source, a laser, a xenon flash, etc. can be used in addition to the halogen lamp. A metal plate made of aluminum, nickel, copper or the like is suitable as the mirror plate from the viewpoint of heat resistance. The terminal of the lamp was connected to an external power source through a hermetic seal, and the amount of irradiation light was controlled by adjusting the applied voltage. Although the substrate can be stationary, it can be rotated to obtain a more uniform film thickness distribution.

A gas inlet 7 for introducing a sputtering gas is opened in the chamber, and is connected to an Ar gas cylinder through a variable leak valve 8. The chamber is evacuated by rotary pump 10
It is carried out by a cryopump connected through the main valve 9 after being pulled to about minus the first power of Pascal. 5 in the chamber from 10 -4 Pascal
After evacuating to a vacuum of about Pascal, the main valve was closed and Ar gas was introduced. A gas introduced by applying an electric field of DC 300 W between the target and the substrate surface was turned into plasma and sputtered under a pressure of 10 −1 Pascal to form a thin film of a phase change material having a thickness of 40 nm.

Table 1 shows the results of examining the characteristics of the phase change material thin film when the irradiation power (applied voltage) of the halogen lamp was changed.

[0017]

[Table 1]

In Table 1, the crystallization temperature was measured using a glass disk sample having a diameter of 8 mm and a thickness of 0.3 mm, which was attached on a polycarbonate substrate. The sample is heated at a constant rate (100 ° C./min), and the change in transmittance at that time is monitored using a He—Ne laser beam and a solar cell. Here, the temperature at which the transmittance changes by about half of the final change is defined as the crystallization temperature (for example, Japanese Patent Laid-Open No. 60-218442). As can be seen from (Table 1), the voltage is 0 V, that is, the crystallization temperature t in the case of forming a film without light heating was measured as 185 ° C., but the crystallization temperature T in the case of light heating was 30, 50, 70
It gradually decreases to 178, 170, and 160 ° C. as V is increased. That is, by forming a film while irradiating light, T
It was observed that the relationship of <t was established and crystallization was facilitated. When the voltage was further increased to 90 V, the crystallization temperature t dropped further, and a value of 120 ° C. was observed. In this case, the polycarbonate substrate was thermally damaged and deformed. It was observed that the crystals had already crystallized. When the crystallization temperature drops and partial crystallization occurs, the light absorption coefficient of that part becomes larger than that of other parts that have not yet been crystallized, and it becomes easier to raise the temperature, and it is thought that the deformation occurred at an accelerated rate. Be done. That is, when the resin substrate is used, it is not preferable to perform light heating that is strong enough to cause crystallization during film formation, and it is important to complete the film formation in an amorphous state. Since a change in the film composition can be considered as a factor for changing the crystallization temperature, it was confirmed by the plasma emission spectrometry (ICP) method that there was no composition change.

Next, an embodiment in which an optical disk is actually constructed and the effect of the manufacturing method of the present invention is examined will be described. Figure 2
Four optical disks having the configuration (cross section) shown in were prepared. Spiral groove for guiding the laser beam (depth 0.07
μm, width 0.65 μm, pitch 1.6 μm) on a 1.2 mm-thick polycarbonate substrate 10 with a thickness of 150 nm as a lower dielectric protection layer 11 ZnS—Si
Ge ₁₂ Sb ₃₉ Te as the O ₂ mixture thin film layer and recording layer 12
₄₉ phase change material thin film layer, 20n as upper dielectric protection layer 13
m ZnS—SiO ₂ mixture thin film layer, and a 100 nm Al reflection layer as the reflection layer 14 are sequentially sputtered to form an adhesive layer 15.
The protective plate 16 is attached to the protective plate 16 via the. Four
Of the two, two were discs formed by irradiating light with a voltage of 70 V during sputtering of the phase change material (disc A), and the other two were discs formed without irradiating light (disc B). Is. Here, the layer structure of the disk and the material of each layer are typical structures of the current phase change optical disk, and do not restrict the present invention. As the dielectric layers 11 and 13, oxides such as SiO ₂ , Ta ₂ O ₅ and Al ₂ O ₃ , AlN and S.
Needless to say, nitrides such as i ₃ N ₄ , carbides such as SiC, and materials such as DLC that are usually used for optical disks are used. Also, as the material of the reflective layer 15, in addition to Au, Al, Ni-Cr, Au-Cr, Al-Cr, Al-
Naturally, Ti, Ni, etc. are used, and further, a structure without a reflection layer can be constructed. First of all, without initializing, the disks of A and B are set to a constant speed of 1.
Overwrite recording was tried by rotating at 3 m / s. A semiconductor laser beam having a wavelength of 780 nm was used for recording, and an objective lens (NA = 0.5) was used to irradiate the phase change material layer as a light spot having a spot diameter of 0.8 μm (half value). As shown in FIG. 3, the laser output has a peak level of 17
(Here, 12 mW) and bias level 18 (here 6 mW) were modulated between two power levels, and recording was first performed at a frequency of 720 KHz (duty 50%). When reproducing with a laser power of 1 mW, C / N of 52 dB was obtained with disc A, but with disc B
Then, a little noise was generated and a C / N ratio of 45 dB was obtained.

When the recording portions of the two discs were observed with a microscope, elliptical amorphous mark portions were arranged in order in the uniform crystallized portion of the disk A, but in the disc B, the crystallized portions were not uniform. there were.

Next, a 196 kHz signal was overwritten at the same location with a similar modulation waveform. 196 for disk A
A C / N ratio of 52 dB was observed for the KHz signal component, and at the same time the 720 KHz signal component was attenuated by 30 dB,
The signal was rewritten. On the other hand, for disc B, 196
The KHz component was recorded at a C / N ratio of 50 dB,
It was found that the 720 KHz signal component was attenuated by 20 dB. When recording was repeated alternately at two frequencies, the same C /
The N ratio and the erasing rate are shown. That is, in the disc B, the recording characteristics are different between the first time and the second time and it is necessary to perform the recording operation several times in order to reach a certain level of the signal quality, whereas the disc A is required. It was found that high quality signals can be obtained from the first recording.

Next, a bulk eraser LK105A (laser spot diameter 0.85 × 55, manufactured by Shibasoku Co., Ltd.)
Initialization was performed on the remaining disks A and B by using a half-width at half maximum. As a result, it was found that the laser irradiation power required for the initialization of the disk B was about 70% of the laser irradiation power required for the initialization of the disk A, in other words, the initialization was easy. Initialized 2
Good recording was performed from the first time on each of the disks A and B.

[0023]

According to the present invention, there is provided a phase change optical recording medium which can be initialized with a smaller laser power, or a high quality signal can be overwritten from the first time without undergoing an initialization process, and a manufacturing method thereof. Was done.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a method for manufacturing an optical information recording medium of the present invention.

FIG. 2 is a cross-sectional view of a general optical information recording medium formed to investigate the effects of the present invention.

FIG. 3 is a waveform chart of a laser irradiation waveform performed to investigate the effect of the present invention.

[Explanation of symbols]

1 Vacuum Chamber 2 Sputter Target 3 Substrate (Polycarbonate) 4 Deposition Surface 5 Light Source (Halogen Lamp) 6 Mirror Plate 7 Gas Inlet 8 Variable Leak Valve 9 Main Valve 10 Disk Substrate (Polycarbonate Substrate) 11 Dielectric Protective Layer (ZnS-SiO) ₂ mixture thin film layer) 12 recording layer (Ge ₁₂ Sb ₃₉ Te ₄₉ phase change material thin film layer) 13 dielectric protective layer (ZnS-SiO ₂ mixture thin film layer) 14 reflective layer (Al reflective layer) 15 adhesive layer 16 protective plate 17 Peak level 18 Bias level

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenichi Nagata 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Nobuo Akabira, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A method of manufacturing an optical information recording medium, which comprises depositing a thin film of a phase change material which causes a reversible phase change between an amorphous phase and a crystalline phase upon irradiation with a high density energy flux on a substrate. Then, in the step of depositing the phase change material thin film on the substrate,
The phase change material thin film is deposited while uniformly irradiating the phase change material deposition surface with light and uniformly heating the entire surface of the phase change recording thin film that is being deposited. Method of manufacturing information recording medium. 2. A phase change material thin film deposited while irradiating light is formed as a thin film in an amorphous state having an initial crystallization transition temperature T, and the initial crystallization transition temperature T is
2. The relationship of T <t is satisfied as compared with the initial crystallization transition temperature t of the amorphous thin film obtained when the phase change material thin film is deposited without light irradiation. Of manufacturing the optical information recording medium of. 3. An optical information recording medium comprising a phase change material thin film which causes a reversible phase change between an amorphous phase and a crystalline phase upon irradiation with a high density energy flux, wherein the phase change material thin film comprises: An optical information recording medium, characterized in that a film is formed while the deposition surface is heated by light irradiation at the time of its formation.