Process for fabrication of magneto-optic recording medium

Abstract: A process for fabrication of a magneto-optic recording medium is disclosed. The process is constituted such that Co and Pd or Co and Pt are arranged in plural numbers upon a target, isolating plates are installed between the mentioned element regions, and a base plate is moved over the target horizontally relative to the target. When moving the base plate, a voltage is supplied to the target, so that the Co and Pd or Co and Pt should alternately adhere on the base plate in a continuous manner.

Description: Field of the invention The present invention relates to a process for fabrication of a magneto-optic recording medium, and particularly to a thin multi-layer type magneto-optic recording medium including Co/Pd or Co/Pt layers. Background of the invention Generally, magneto-optic recording technique is constituted such that a thin film having a vertical magnetic polarity is magnetically oriented upwardly or downwardly, thereby making it possible to store binary digital information. Such an information recording is carried out in such a manner that : as shown in Figure 1A, a magnetic field of about 300 Oe is applied in the desired direction from the external ; at the same time, the medium is heated by means of laser beams up to the curie temperature at which the medium loses its magnetic property : and then, the laser beams are withheld so as for the scanned regions of the medium to be magnetized in the same polarity as the external magnetic field, thereby recording the information. As shown in Figure 1B, the reading of the recorded information is carried out by utilizing the Polar Kerr effect. That is, if rotational polarized light rays are scanned onto a vertically magnetized material, the reflected light rays are rotated around the polarizing direction of the incoming light rays. The magnitude of the rotational angle depends on the magnitude of magnetization, and the rotational direction is formed clockwise or the anticlockwise in accordance with the amgnetized direction. Therefore, the reflecting light rays which are reflected from the upwardly and downwardly magnetized spots are detected, thereby reading the information. Meanwhile, as shown in Figure 1C, the erasing of a recorded information is carried out in such a manner that : the external magnetic field is applied in a direction opposite to that of the recording magnetic field. Such recording, erasing and re-recording can be repeated infitely by reversing the applied magnetic field. In the currently used magneto-optic recording medium, a thin layer consisting of rare earth-transition metal alloy is employed, and the rare earth elements include Tb, Cd, Nd, Dy, while the transition metals include Fe, Co, and the like. Among them, the most superior recording medium is made of Tb-Fe-Co. Meanwhile, in manufacturing the rare-earth-transition metal alloy recording film, principally, sputtering and vacuum depositing method are used. In the case of the sputtering, an alloy target is employed, or a Co-sputtering in which the rare earth and the transition metal serve as plural targets respectively is adopted. In the rare earth-transitional metal alloy recording medium, oxidation happens very easily, because the rare earths have a close affinity to oxygen. Therefore, in order to prevent such a phenomenon, and to increase the rotational angle during a reading, dielectric media are formed on the opposite faces of the recording film as protecting layers. The materials for the protecting layer may be cited to be Si3N4, A1N and other nitrides. However, in the above described conventional technique, the rare earth-transitional metal alloy recording medium is liable to be oxidized due to the fact that the rare earths have gaeat affinity with oxygen. Although dielectric layers are employed in order to prevent the oxidizing phenomenon, the protecting function is not sufficient. Futher, the recording medium is sensitively affected by the manufacturing process, and the yield is only about 10%. In order to overcome the above described problems, a treaties " Megnetic-optical properties of Co/Pd superlating thin film " has been published in the Journal of Applied Physics, volume 67, Page 317 (1990). According to the technique as published in it, the magneto-optic recording medium includes a multi layer film of Co/Pd, and the thickness of the Co sub-layer is 1Å, while the thickness of the Pd sub layer is 6 - 15Å, with such layers being stacked repeatedly until the total thickness of the recording medium becomes 110 - 270Å. The manufacturing method for the multi-layer thin film is constituted such that : a vacuum chamber accommodates a rotary table having a plurality of partitions on it, with the partitions being formed by means of stainless steel plates ; a base plate is mounted upon the rotary table ; and plurality a of crucibles containing Co and Pd respectively are disposed below the rotary table. In such an apparatus, the Co and Pd of the crucibles are deposited onto the upper base plate by applying the thermal evaporation deposition method, and then, a second deposition is carried out by rotating the rotary table, in such a manner that Pd should be deposited on the Co, and that Co should be deposited on the Pd. Such depositions are repeated to form a multi-layer film of Co/Pd. However, in such a manufacturing method, the number of the stainless steel partitions is limited, and therefore, a continuous production becomes difficult. Further, the thermal deposition method makes it unsuitable to the high melting point materials such as Pt, as well as making it difficult to obtain a uniform deposition. Summary of the invention It is the object of the present invention to provide a process and an apparatus for fabrication of a magnetic-optic recording medium, in accordance with the appended Claims. Brief description of the drawings The above object and other advantages of the present invention will become more apparent by describing in detail the preferred embodiment of the present invention with refernce to the attached drawings in which : Figure 1A illustrates recording of information ; Figure 1B illustrates reading of information ; Figure 1C illustrates erasing of information ; and Figure 2 illustrates the structure of the target on which Co/PD or Co/Pt are deposited. Description of the preferred embodiment The process for fabrication of a magneto-optic recording medium according to the present invention is constituted such that : Co and Pd or Co and Pt are arranged in the cited order ; the elements are isolated by means of isolating plates ; a target is let to perform reciprocal horizontal movements over the element arrangement ; and a sputtering method is applied in such a manner as to deposit the Co and Pd or the Co and Pt onto the base plate. Referring to Figure 2, Co 1 and Pd 2 or Pt are arranged in the cited order in plural numbers within a vacuum chamber, thereby forming a target. Isolating plates 3 are installed between the Co 1 and the Pd 2 or Pt which are disposed on the target. A base plate 4 is installed over the isolating plates 3. In this state, if a voltage is supplied to the target, then argon gases are accelerated toward the charged target to be collided with the target, and materials are emitted from the target to be deposited onto the base plate 4. Under this condition, the base plate moves continuously to the right, and therefore, first the Co 1 is deposited. Then, if the base plate 4 passes the Co region, and if it arrives at the Pd region, then the Pd 2 is deposited upon the Co layer. This process is repeated, with the result that a muti -layer film consisting of repetitions of Co/Pd or Co/Pt is formed. That is, the base plate passes continuously over the arrangement of Co and Pd regions, and therefore, a multi-layer film can be obtained. The function of the isolating plates 3 is to prevent the simultaneous adherences of the Co, and Pd. The arrangement of the Co 1 and the Pd 2 or Pt can be constituted in accordance with the required number of the sub-layers. Further, the base plate 4 can be moved to the left and right in performing the depositions, and therefore, the arrangement of the Co 1 and the Pd 2 does not have to be too long. The width d of the Co or Pd regions between the isolating plates 3 is decided proportionately to d - V R , assuming that the sputtering rate is decided in relation with the velocity V of the base plate 4 and the power supplied to the target. Thus the width d can be decided based on the above formula. If V ≃ 1 cm/s , and R = Å/s , then d - V R - 1cm/Å. Accordingly, if the required thickness of Co is 1 Å, then d is 1 cm. According to the present invention as described above, the Co 1 and the Pd 2 or Pt are continuously arranged on a single target, with the isolating plates being installed between the elements. Therefore, a multi-layer thin film consisting of Co and Pd or Pt sub-layers can be formed by horizontally moving the base plate, with the result that the fabricating time is short, and that the process becomes simple.

Claims: A method for producing a magneto-optical recording medium with a recording layer consisting of alternately stacked Co and Pd or Co and Pt layers within a multi layered structure by arranging at least one region (1) consisting essentially of cobalt and at least one region (2) consisting essentially of palladium or platinum in substantially alternating areas on a single target, applying a voltage to said targets to induce sputtering of said cobalt, palladium and/or platinum from said targets, positioning a substrate (4) towards those targets and subjecting said substrate (4) to said sputtering so that said layers are alternately deposited on said substrate (4), characterized in that said substrate being repeatedly reciprocated between a position above a cobalt region and a position above a region of platinum or palladium linearly arranged one behind the other, and isolating each region (1) of cobalt from each adjacent region (2) of palladium or platinum by means of vertical steel plates. The method of claim 1, characterized in that said vertical plates (3) retard depositing a mixture of cobalt and platinum or a mixture of cobalt and palladium on said substrate (4). The method of claims 1 or 2, characterized in that said method is conducted at a pressure less than atmospheric pressure in a gaseous atmosphere consisting essentially of argon. Apparatus for carrying out the method according to one of the preceding claims, comprising a single target which comprises at least one region (1) of cobalt and at least one other region (2) of palladium or platinum to be sputtered on a substrate (4) movable with regard to said targets, characterized in that said regions (1,2) are separated by an isolating steel plate (3) extending from said single target towards said substrate (4) being moved repeatedly reciprocated with regard to said target.

Inventors: KIM JIN HONG, SHIN SUNG CHUL, KIM, JIN HONG, SHIN, SUNG CHUL
Applicants: LG ELECTRONICS INC, LG ELECTRONICS INC.
Application year: 1991
Main classification: G11B11
IPC codes: H01F41, C23C14, H01F10, G11C13, G11B11