JPS63118340A - Treatment of plastic substrate and device therefor - Google Patents

Abstract

PURPOSE:To remove water in a plastic substrate effectively and to make it possible to form a high-quality recording thin film, by irradiating the plastic substrate with high frequency of specific number of cycles in a high vacuum before a recording thin film or a reflecting film is formed. CONSTITUTION:Before a recording thin film or a reflecting thin film is formed, a plastic substrate is irradiated in high vacuum of 1X10<-7>-10<-8>Torr with high frequency of number of cycles (1-50GHz number of cycles) which does not excite plastic molecules and selectively excites only water molecules in the plastic in order to remove water in the plastic substrate and water in the substrate is rapidly removed without thermally damaging the plastic substrate.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a processing method and recording performed before forming a recording thin film on a plastic substrate used in an optical disk for recording information, a floppy disk used in a personal computer, a magnetic tape, etc. The present invention relates to a thin film forming apparatus. More specifically, the present invention provides a method and apparatus for removing moisture from plastic substrates, which provides high quality and is suitable for mass production.

[Conventional technology]

2. Description of the Related Art Recently, optical recording technology in which recording bits with a diameter of several microns are recorded on a recording thin film on a substrate using a laser beam or the like and read out is being actively researched.

Recording media for optical recording, for example, in the case of disk substrates, are divided into read-only types such as laser video discs and compact discs, and recordable types on which the user can record arbitrary information. Ru.

The former type is injection molded in a mold with recording pits formed in advance, and then a reflective film is provided.The latter type is a write-once type, which allows recording but cannot erase data. They are subdivided into phase change type rewritable optical disks that can record and erase data, and magneto-optical type rewritable optical disks. However, the basic structure of any type of optical disk is that a recording thin film or a reflective film is provided on a substrate.

This basic structure is shown in FIG. In FIG. 1, // indicates a substrate made of plastic or glass, and /2 indicates a recording thin film or reflective film made of metal. /3 indicates a track guide groove.

[Problem that the invention seeks to solve]

The biggest problem with recording media having such a structure is that the recording thin film or reflective film is oxidized by moisture in the atmosphere. This is because the recording thin film and the reflective film must have appropriate light reflectance, but when the recording thin film is oxidized, the light reflectance decreases and efficiency deteriorates.

Therefore, conventionally, as shown in Fig. 2, the side of the recording thin film 7.2 facing the outside is coated with a protective film/g to protect the recording thin film 2 reflective film from moisture, gas, etc. from the external atmosphere. is customary.

On the other hand, amorphous materials such as glass have conventionally been used as the substrate in contact with the recording thin film/2, but glass has high thermal conductivity, so when writing with laser light, it is necessary for writing. It was inefficient because it allowed heat to escape. This has led to the use of plastics with lower thermal conductivity to improve efficiency.

However, when plastic is used for the substrate, a phenomenon has been discovered in which moisture contained within the plastic permeates into the recording thin film or reflective film, oxidizing the recording thin film or reflective film.

This kind of deterioration due to moisture in the plastic substrate is T
b-Fe-C, o magneto-optical rewritable media, T
This is particularly noticeable in recording thin films for phase change type rewritable media made mainly of e-based alloys, and has become an important problem in stabilizing the characteristics of optical discs and in preventing changes over time.

In order to solve such problems, conventionally, as shown in FIG. 3, a separation layer /j is provided between the substrate /l and the recording thin film 12, or, although not shown, the plastic substrate // is connected to the recording thin film. Before manufacturing 7.2, a method of sufficiently dehydrating and drying in a vacuum was used.

In the former, a separation layer is used to prevent moisture from entering. as 5i
A 5i02 sputtered film or the like is used, but it is necessary to form a separation film by sputtering or vapor deposition before forming a recording thin film or a reflective film, which increases the number of steps and is complicated, and the high thermal conductivity of the 5i02 film makes it difficult to use laser light. When recording on a thin recording film, the separation film releases the heat necessary for writing, resulting in a disadvantage that the writing efficiency is reduced, similar to when a glass substrate is used.

Separation membrane again/! When it becomes thick, cracks and peeling may occur due to internal stress, etc.

On the other hand, the latter method is essentially a method for removing moisture within the substrate, but when dehydrating and drying a plastic substrate processed into a disk shape, the heating temperature is usually used to suppress deformation and warping of the plastic substrate. Tg of plastic base material
(glass transition point) or less.

This temperature is normal for plastic materials! O°C~70
``C is the limit, and at this temperature the degree of vacuum is 7O-8 Tor.
Even if the substrate is dried at a temperature of about r, the processing time is long, for example, about 3 days for polycarbonate substrates and 7 days or more for acrylic substrates, which is a fatal drawback for mass production.

[Means for solving problems]

In order to improve the above-mentioned conventional drawbacks, the present invention removes moisture in the plastic substrate before forming a recording thin film or a reflective film, so that the plastic molecules are not excited in a high vacuum, and only the water molecules contained in the plastic are removed. The plastic substrate is irradiated with a high frequency wave of a specific frequency that selectively excites the
Moisture inside the plastic substrate can be quickly removed without causing thermal damage to the substrate.

[For production]

The principles and effects of the optical plastic substrate processing method according to the present invention will be described below.

First, the principle of the present invention is that only the water contained in the plastic substrate is selectively excited and heated.

In conventional technology, plastic substrates are heated and dried in a vacuum, so the temperature limit that does not cause deformation or warping is RO.
'c~70'C. PMMA (acrylic resin) is a material normally used for plastic substrates for optical discs.
, PC (polycarbonate resin), etc. are adjusted to a low humidity state before disc processing, and in the case of PMMA, the moisture content is 0.3-0. In the case of μchi and PC, the moisture content is 0. /Tachi level.

In the present invention, in order to further remove these trace amounts of water, the plastic substrate is irradiated with high frequency waves in a vacuum to selectively excite and heat only the water molecules (1-120 molecules) in the substrate. After diffusing and moving within the substrate, it reaches the substrate surface and is evaporated into vacuum and removed. Also, the phenomenon is used that since the plastic molecules of the substrate are not excited at the above-mentioned specific frequency, no heating occurs as a result other than heat conduction of heat generated by water molecules.

The most desirable high frequency for irradiating H20 molecules in the substrate is 1420's original absorption region 0GH2. However, the frequency of 2.0 is high enough to generate heat due to dielectric loss of H20 molecules. ≠! GHz
can also be used, and in fact /G1-Iz-! r O
GI (area of z is available.

On the other hand, considering an apparatus that irradiates a plastic substrate with the above-mentioned high frequency waves, the substrate processing chamber also serves as a mode stabilizing waveguide for the high frequency waves to be irradiated, so its size is an integral multiple of //2 of the wavelength used. Good to have.

For example, in the case of a high frequency of 4tOGH2, the wavelength is λ-3×1
0106n÷Hiro0×10=0.7! ;Because it is a mouth, λ/
, 2=0.37o(7).

Also, in the case of high frequency of / GHz, λ=jX1010cm
Since ÷/×/θ9=30α, λ/2−/!
cm.

〔Example〕

Examples of the present invention will be described below.

〔Example/〕

FIG. 3 shows an embodiment of an optical disk manufacturing apparatus equipped with a substrate processing apparatus of the present invention. In the figure, 27 is a preliminary exhaust chamber, 2
2 is a substrate processing chamber, 23 is a high frequency magnetron tube,
2'A is a high frequency power supply, 2 is a thin film forming chamber, 2 is a vapor deposition device, 27 is a sputtering device, 2g is a substrate take-out chamber, and 2 is a substrate transfer device having a substrate holder.

The structure of the substrate transfer device from each chamber to the next chamber is substantially similar to the sample transfer device of an electron microscope.

Using this equipment, a Te thin film was deposited on the acrylic substrate of the same lot through the processing time shown in the table.
To prevent deterioration, 5iQ2 was sputter-coated to 7000 on the opposite side of the thin film to the substrate.

Experimental data are shown in Table/.

Table 7 × Frequent occurrence of pinholes Δ I I Slightly ○ l l Almost none ◎ I I None In the substrate processing process according to the present invention, the occurrence of pinholes was clearly small, and no substrate deformation occurred.

[Example 2] Polycarbonate (PC
) A magneto-optical film of Te-Fe-Co was fabricated on a type substrate.

Experimental data are shown in Table.

In the Examples shown in Table 1 and above, it is clear that the substrates subjected to the treatment process of the present invention are less likely to produce pinholes and can be treated in a short time.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to almost completely dehydrate plastic substrates used for manufacturing optical disks in a short period of time.

In addition, since high-frequency heating is applied which mainly acts only on the moisture in the plastic substrate, it has the effect of penetrating into the interior of the substrate and removing moisture without causing almost any thermal damage to the plastic constituting the substrate. In addition, since a thin film and a protective film are formed immediately after removing moisture, there is no need to worry about deterioration after removal from the chamber.

This can be done using the traditional method with an acrylic board for about 10 days, and with polycarbonate! Considering that it was necessary for pre-production treatment on a scheduled basis, this is a very big advance, and the effect it has on mass production is extremely large.

In addition to mass production, the performance of the product has also been significantly improved.

Although the above description has been made of plastic substrates for optical disks, the present invention is not applicable only to them, but also applies to plastic substrates such as floppy disks used in word processors, personal computers, etc., magnetic tapes used in computers, etc. It is also applied to memory parts having a recording thin film or the like on the material, and its application range is wide.

[Brief explanation of the drawing]

1, λ, and 3 are sectional views showing the basic structure of an optical disk, and FIG. 3 is a schematic diagram of an optical disk manufacturing apparatus according to the present invention. //... Substrate, /2... Recording thin film or reflective film, /
3... Track guide groove, /llt... Protective film, /j
...Separation membrane 1.20...Plastic substrate, 2/...
...Preliminary exhaust chamber, 22...Substrate processing chamber,
23... High frequency magnetron included, 2≠... High frequency power source, 2... Thin film forming chamber, 2A... Evaporation device, 27... Sputtering device, 2g... Substrate take-out chamber, 2...・-Plastic substrate transfer device, 30...
・Vacuum exhaust system. Laser ゛-t Half 10% 2 times -' Figure

Claims (2)

[Claims] (1) Plastic board 1 x 10^-^7~10^-
^ Placed in a vacuum state of 8 Torr and with a frequency of 1 GHz
A method for processing a plastic substrate, comprising irradiating the plastic substrate with high frequency waves in the range of ~50 GHz to remove moisture in the plastic substrate. (2) a substrate processing chamber connected to a vacuum evacuation device;
a substrate holding unit that holds the substrate in the substrate processing chamber;
The substrate processing chamber consists of a magnetron tube that irradiates high frequency waves onto the plastic substrate held in the substrate holder, and a power source for the magnetron tube, and the substrate processing chamber has three internal dimensions that are an integer of 1/2 of the wavelength of the high frequency wave to be irradiated. A plastic substrate processing device characterized by double the size.