JPH0697647B2 - Method for producing ferrite thin film - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a ferrite thin film that enables high density recording / reproduction.

2. Description of the Related Art In recent years, magnetic recording and magneto-optical hot air recording are progressing toward higher density. Among these, for magnetic recording, a magnetic recording method based on so-called in-plane magnetization, which has an easy axis of magnetization in the plane, has been the mainstream. However, in this method, as the recording density is increased, the magnetization directions in the magnetic recording medium are arranged so as to repel each other, which makes it difficult to achieve high density. Therefore, in recent years, as a new method of magnetic recording, a magnetic recording method by so-called vertical magnetization having an easy axis of magnetization in the direction perpendicular to the in-plane of the magnetic recording medium has been developed [eg, Iwasaki "High density using perpendicular magnetization. Magnetic recording "Nikkei Electronics (8.
7) No.192, P.100,1978] It has become possible to dramatically increase the recording density.

In magneto-optical hot air recording as well, perpendicular magnetization is required to achieve high-density recording as in perpendicular magnetic recording.

However, in the case of magneto-optical hot air recording, it is different from the magnetic recording method in that, in addition to the perpendicularly magnetized film, a change in magnetism due to heat is used during recording, and an optical effect associated with magnetism is used for reproduction. That is, the heat of the laser beam is used for recording, and the Kerr effect or Faraday effect of the magneto-optical recording medium is used for reproduction. [For example, Shutake Imamura, Television Society, Vol. 39, No. 4, 1985, pages 365-36.
8] When this medium is, for example, a magneto-optical disk, a large Kerr effect (large Kerr rotation angle) is required to improve the CN ratio (signal to noise ratio) of this disk. [For example, Masanori Abe, Journal of Japan Applied Magnetics Vol. 8 5
No. 1984, pages 366-372] So, in recent years, manganese bismuth (MnBi), gadolinium cobalt (GdCo), gadolinium terbium iron (GdTb
Magneto-optical recording media having a large Kerr rotation angle such as Fe) have been developed by the vacuum deposition method and the sputtering method.
[For example, Shumu Imamura, Vol. 39, No. 4 of the Television Society of Japan
1985, pages 365-368] However, all of these recording media use thin metal films, and metals such as Gd, Tb, and Fe are easily oxidized, and an external storage device for a computer, which requires reliability, is required. It is considered difficult to adapt to

On the other hand, there has been an attempt to use a chemically extremely stable oxide ferromagnet for magneto-optical recording [eg, Abe Journal of Applied Magnetics, Vol. 7, No. 2, 1983, pages 123-1].
26] A cobalt ferrite film is mainly formed by a heat treatment at 700 ° C to 800 ° C by a sputtering method or a vapor phase thermal decomposition method.

Problems to be Solved by the Invention In these magneto-optical recording media, MnBi, GdCo, Gd, TbF
e-alloy can be synthesized as a perpendicularly magnetized film and at a low temperature, but it has a problem of reliability deterioration due to oxidation of the film, and particularly when inexpensive substrates such as polycarbonate and polyimide are used, these substrates easily adsorb moisture. Therefore, there is a problem that the above-mentioned alloy is oxidized by the adsorbed water.

On the other hand, cobalt ferrite, which is an oxide, is stable without any problem of oxidation of the film, and is inexpensive, but this film is produced by the sputtering method or the vapor phase pyrolysis method to obtain a film having a large Kerr effect. In order to do so, heat treatment (crystallization) at 700 ° C. to 800 ° C. is necessary, and it is difficult to use a substrate made of low melting point glass, aluminum polycarbonate, polyimide or the like. Moreover, because cobalt ferrite has a spinel-type isotropic crystal structure, it does not form a perpendicular magnetization film due to crystal magnetic anisotropy unlike barium ferrite or Co-Cr, making it difficult to achieve high-density recording. There is a problem.

Further, a plasma CVD method can be considered as a ferrite film forming method which is replaced by a sputtering method or a vapor phase thermal decomposition method. With this method, a ferrite film can be synthesized at a relatively low temperature (350 ° C to 200 ° C) because it is usually formed under a reduced pressure of 10 Torr to 0.1 Torr, but the heat resistant temperature of acrylic or polyethylene terephthalate is 70%.
There is a problem that a ferrite film cannot be formed on a substrate having a temperature of ℃ or less.

Means the present invention for solving the problems In order to solve the above problems, conventional sputtering or vapor phase pyrolysis method or, instead of the usual plasma CVD, low pressure under (10 ^-1 to 10 ^{- (4} Torr) plasma obtained by magnetron discharge or plasma obtained by electron cyclotron resonance (ECR), by flowing a reaction gas, and by plasma CVD method utilizing the activity of high-density plasma at these low pressures. Provided is a method of manufacturing a cobalt ferrite perpendicular magnetization film suitable for magneto-optical recording without heating a substrate.

Action The inventors have found that cobalt ferrite can be obtained at room temperature by using a plasma CVD method obtained by magnetron discharge or electron cyclotron resonance (ECR). That is, Co, Fe and M (however, M
Is a metal chelate containing Al, Cr, Fe, Gd, Mn, In), for example, Co (C ₅ H ₇ O) ₃ (cobalt acetylacetone) and Fe (C ₅ H ₇ O) ₃ (iron acetylacetone) vapor and oxygen as a reaction gas were mixed with 10 ^-1 Torr to 10 ^-4 To
It is introduced into a reaction vessel (chamber) whose pressure is reduced to rr, and high frequency or microwave plasma is generated to deposit cobalt ferrite crystals on the substrate.

In this way, it is possible to precipitate cobalt ferrite at room temperature because it causes a chemical reaction at low temperature in magnetron discharge under low pressure of 10 ^-1 to 10 ^-4 Torr) or in high-density plasma using ECR discharge. There are many chemical species such as active radicals and ions, and ordinary CVD (CVD that causes thermal decomposition and deposition) and ordinary plasma CVD (0.1 to several Torr
Plasma CVD without magnetron discharge or ECR discharge)
Then, it is because a reaction that cannot occur energetically can occur at room temperature. [For example, Nikkei Microdevice Spring 1985 Special Edition P.93-100] Generally, the plasma CVD method using magnetron discharge or ECR discharge has a lower temperature (around room temperature) than the ordinary thermal CVD method.
In addition to synthesizing high-melting substances such as oxides, carbides, and nitrides, a columnar structure film of high purity and good crystallinity can be obtained even at low temperature because of the thermal decomposition reaction.
Therefore, an isotropic crystal magnetized film (in-plane magnetized film) such as cobalt ferrite is perpendicularly magnetized at a low temperature (cobalt ferrite is an isotropic crystal, so that the perpendicular magnetic anisotropy due to the columnar structure of the film causes It is an optimal method for forming a perpendicular magnetization film by utilizing anisotropy.

Embodiment One embodiment of the present invention will be described below with reference to the drawings. The figure shows a schematic diagram of a magnetron discharge plasma CVD apparatus in one embodiment of the present invention. In the figure, 11 is a reaction chamber, 12 is a high-frequency electrode with a built-in magnet for performing magnetron discharge, 13 is a high-frequency power source, 14 is a substrate holder, 15 is a substrate, 16 is a chelate bubbler containing cobalt, and 17 is iron. Chelate bubbler containing, 18 is M (where M is Al, Cr, Gd, Mn, In
A bubbler of a chelate containing 19% of nitrogen (N ₂ ) carrier gas, 20 is a cylinder of O ₂ reaction gas, and 21 is a rotary pump.

First, cobalt acetylacetone [Co (C ₅ H ₇ O) ₃ ], iron acetylacetone [Fe (C ₅ H ₇ O) ₃ ] and aluminum acetylacetone [Al (C ₅ H ₇ O) ₃ ] were bubbler heated to 150 ℃. , 16, 17 and 18, respectively, and N ₂ gas 19 for bubbles was flowed at 80 cc / min, 120 cc / min and 4 cc / min, respectively, and these vapors were evacuated in the reaction chamber 11 by the rotary pump 21. The aluminum substrate 15 is introduced. Next, the same reaction gas, oxygen (O ₂ ) 20, was flown on the same aluminum substrate at a flow rate of 200 cc / min, and the reaction was performed for about 25 minutes. At this time, the gas pressure is 1.1 × 10 ^-2 Torr and the substrate temperature is 40.
The high frequency power (13.56MHz) at 500 ° C was 500W (5W / cm ² ). The magnetic force of the magnet was about 400 gauss near the substrate. At this time, the film thickness of cobalt ferrite deposited on the substrate was 2250Å. Next, for this film, analysis of the crystal structure by X-ray and measurement of Kerr rotation angle (wavelength
Laser light of 780 nm was made incident on the ferrite film, reflected on the aluminum surface, and again measured by detecting the laser light that has passed through the ferrite film). The result at that time is shown in Sample No. 1 in the table. Similarly, the substrate temperature, chelate type, bubbler amount (N ₂ flow rate), reaction chamber pressure (changed by rotary pump valve operation) magnet strength, plasma generation method, etc. were changed. The X-ray analysis and Kerr effect (size of Kerr rotation angle) at that time are shown in sample numbers 2 to 24 in the table. Further, sample numbers 25 to 26 are comparative examples outside the present invention.

Here, the X-ray analysis was conducted on the crystal structure of cobalt ferrite, the orientation of the film, and the additive M (where M is Al, Cr, Fe, Gd, M).
The solid solution state of any one of n and In) was investigated. The Kerr effect (size of Kerr rotation angle) is calculated by the polarization plane modulation method [eg, Imamura Television Society, Vol. 39, No. 4, 1985 366.
Page]. In addition, whether or not the cobalt ferrite film is a perpendicular magnetization film was examined from the magnetic characteristics (BH curve) of the film by VSM (vibrating sample magnetometer).

The pressure inside the chamber was set to 10 ^-1 Torr to 10 ^-4 Torr because the mean free path of various particles (neutral, radicals, ions, etc.) in the chamber is short when the pressure is higher than 10 ^-1 Torr. This makes it difficult for various particles to contribute to the reaction with some kinetic energy. Therefore, it is difficult to synthesize cobalt ferrite at low temperature. Also, if it is 10 ⁻⁴ Torr or less, it is difficult to maintain magnetron discharge, and the growth rate of the ferrite film becomes low.

EFFECTS OF THE INVENTION As described above, according to the present invention, the activity of low-pressure plasma can be skillfully utilized to form a vertical film of cobalt ferrite having a large magneto-optical effect at a low temperature of 50 ° C. or lower. It is a very useful invention for achieving high density magneto-optical recording.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a plasma CVD apparatus in one embodiment of the present invention. 11 ... Reaction chamber, 12 ... High-frequency electrode with built-in magnet for magnetron discharge, 13 ... High-frequency power supply, 14 ... Substrate holder, 15 ... Substrate, 16 ... Cobalt containing chelate bubbler, 17 …… Chelate bubbler containing iron, 18 …… M (where M is Al, Cr,
Chelating bubbler containing any one of Gd, Mn and In), 19 ... Nitrogen (N ₂ ) carrier gas cylinder, 20
…… O ₂ reaction gas cylinder, 21 …… Rotary pump.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI Technical display location G11B 5/706 7215-5D 5/85 Z 7303-5D (72) Inventor Hideyuki Okinaka Kadoma, Osaka Prefecture No. 1006 within Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-57-117225 (JP, A) JP-A-60-124901 (JP, A) JP-A-62-275761 (JP, A)

Claims (1)

[Claims] 1. Cobalt (Co), iron (Fe) and M [where M is aluminum (Al), chromium (Cr), iron (F)
e), gadolinium (Gd), manganese (Mn), or indium (In)] and the oxygen gas (O ₂ ) as a reaction gas at 10 ^-1 Torr
Introduced into a chamber depressurized to ~ 10 ^-4 Torr, these vapors are decomposed in plasma using magnetron discharge or plasma generated by electron cyclotron resonance, and the general formula CoFe _2-X M _X O ₄ [However, M is A
Any one element of l, Cr, Fe, Gd, Mn, In, X
Is a number of 0 to 1.0], and a ferrite thin film is produced.