JPH021222B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a protective film for protecting the active surface of a metal thin film, a semiconductor thin film, etc. from the surrounding environment, and particularly relates to a method for forming a protective film for protecting the active surface of a metal thin film, a semiconductor thin film, etc. from the surrounding environment. The present invention relates to a method suitable for protecting the surface of a thin film magnetic recording medium.

2. Description of the Related Art In various functional elements, recording media, etc. that utilize metal thin films, semiconductor thin films, etc., thin and stable protective films are required in various fields to protect the surfaces of these devices from the surrounding environment. Metal thin film magnetic recording media are required to minimize the distance between the medium and the magnetic head in order to take advantage of their characteristic high-density recording, but when the metal thin film itself is exposed to the surrounding environment, it is exposed to moisture, The surface is easily corroded by the action of corrosive gases, etc., and abrasion is likely to occur due to sliding with the magnetic head, so it is necessary to form a protective film on the surface.In this case, the above requirements should be taken into account. In order to reduce spacing loss, the film thickness must be 1000 Å or less, preferably several hundred Å or less. In the past, several proposals have been made to use ion bombardment to form a protective film on a metal or inorganic compound as a target, and we have investigated the application of these methods to metal thin film magnetic recording media using plastic films as substrates. However, most of them were poor in flexibility, cracked when the magnetic head ran on them, or were not compatible with the magnetic head and were easily scraped. It is also known to form a protective film on the surface of a material using tetrafluoroethylene polymer as a target, and this was investigated as a surface protective layer for a metal thin film type magnetic recording medium.
It was found that the corrosion resistance was poor. Therefore, as a result of trying to target other polymers that had never been used before, we found that the imide bond of the following general formula It has become clear that the desired protective film can be formed when sputtering a polymer containing in the main chain in an inert gas as a target.

Here, a polymer containing an imide bond in its main chain is 1 Polyimide For example, there is Kapton film manufactured by Dubon (USA).

2 Polyesterimide For example, there is a polymer obtained by curing isomide varnish manufactured by Schenectaday Chemical Company (USA).

3 Polyamideimide For example, there is a polymer made by hardening AI-10 varnish manufactured by Amco (USA).

It is a heat-resistant polymer represented by

A polymer containing this imide bond in its main chain is formed into a film or baked as a coating on an aluminum plate, and the above-mentioned properties are subjected to ion bombardment in an inert gas such as argon, krypton, or xenon. The target is vaporized and deposited on the surface to be protected. In other words, it sputters. Sputtering methods include regular radio frequency (RF) or DC sputtering, and magnetron-type RF.
Alternatively, known methods such as DC sputtering and ion beam sputtering are possible, but magnetron RF sputtering is most suitable for forming a protective film on a metal thin film magnetic recording medium using a plastic film as a substrate. In the case of this magnetron type RF sputtering method, the inert gas pressure is 10 ^-4 ~
10 ^-2 Torr, board temperature 20~200℃, target power
Under conditions of 0.5 to 5 W/ ^cm2 , it is applied directly onto a ferromagnetic metal thin film made of Fe, Co, Ni, their alloys, or their alloys with other metals, or via a nonmagnetic layer such as Al or Cr. film thickness at a deposition rate of 1 to 50 Å/sec.
When a protective film of 50 to 1000 Å is formed, the corrosion resistance of the metal thin film and the wear resistance against the magnetic head are significantly improved.

This will be explained below using a specific example.

Example A Co ferromagnetic thin film with a thickness of 0.2 μm was formed on a long polyester film with a thickness of 15 μm by continuous vacuum oblique evaporation method and cut into a tape shape, which was designated as Sample A. This sample A was sputtered under the following conditions, and the thickness
A protective film of 1000 Å was formed, and this was designated as Sample B.

Target: Kapton film (polyimide film manufactured by DuPont) thickness
75μm Atmosphere: 4×10 ^-2 Torr Ar Substrate temperature: 40℃ Target power: 2.5W/cm ² Sputtering time: 60sec Using another sample A, sputtering was performed under the following conditions to form a protective film with a thickness of 50Å. This was designated as sample C.

Target: Isamide varnish (polyester imide varnish manufactured by Schenectady Chemical Co.) baked onto a 0.5 mm thick Al plate to a film thickness of approximately 50 μm.

Atmosphere: 4×10 ^-2 Torr Ar Substrate temperature: 100℃ Target power: 2.5W/cm ² Sputtering time: 30sec Using another sample A, sputtering was performed under the following conditions to form a protective film with a thickness of 100 Å. was designated as sample D (comparative example).

Target: Teflon sheet (polytetrafluoroethylene sheet manufactured by DuPont) thickness 0.5 mm Atmosphere: 4 x 10 ^-2 Torr Ar Substrate temperature: 40°C Target power: 2.5 W/cm ² sputtering time: 60 sec These samples were As a result of a humidity test by leaving the sample in a temperature of 90% RH, the number of days required for rust to be observed on the magnetic surface using an optical microscope was as follows.

Sample A: 12 days (Comparative example) Sample B: 80 days Sample C: 75 days Sample D: 10 days (Comparative example) In addition, each of the above samples was separately prepared with the same functions as a commercially available home video tape recorder. The mass still time was measured using a still tester and the results were as follows.

Sample A: 30 minutes (Comparative example) Sample B: 60 minutes Sample C: 65 minutes Sample D: 50 minutes (Comparative example) Note that if the temperature of the substrate during sputtering falls below 20°C, the sputtered film will soften and the machine The contact angle with water decreases as the target strength decreases. This reduces the effectiveness of the protective film in humidity. Increasing the temperature of the substrate during sputtering also increases the contact angle and improves the mechanical strength of the sputtered film, but at a constant value e.g.
When the temperature exceeds 200-250℃, the protective film made of organic matter decomposes. From these points, this type of sputter has an optimal range for the substrate temperature, which ranges from 20 to
It was confirmed that the temperature was 180℃.

As is clear from the above examples, according to the method for forming a protective film of the present invention, the corrosion resistance and abrasion resistance of a ferromagnetic thin film can be greatly improved by forming a sputtered film with a thickness of about 100 Å. Furthermore, this method can also be applied to the protection of other metal thin films, semiconductor thin films, etc., making it very useful industrially.

Claims (1)

[Claims] 1. A target made of a polymer containing an imide bond of the general formula [formula] in its main chain is evaporated by bombardment with inert gas ions and deposited on the surface of a substrate to be protected. How to form a protective film. 2. The method for forming a protective film according to claim 1, wherein the inert gas ion bombardment is performed by high-frequency sputtering. 3 Claim 2, characterized in that the high frequency sputter is a magnetron type high frequency sputter.
A method for forming a protective film as described in . 4. The method of forming a protective film according to claim 1, wherein the bombardment with inert gas ions is performed while the temperature of the surface of the substrate is maintained at 20 to 180°C.