JPH02229414A - Formation of magnetic-garnet thin film - Google Patents

Abstract

PURPOSE:To form a magnetic-garnet thin film whose Curie temperature is proper and whose recording sensitivity is excellent by a method wherein a high-frequency sputtering operation is executed while a bias voltage is being applied to a substrate. CONSTITUTION:An oxide containing a component element of a magnetic garnet is used as a target; while a bias voltage is being applied to a substrate, a high- frequency sputtering operation is executed. When the bias voltage is applied to the substrate, argon ions or oxygen ions, which are provided with a positive charge, in a plasma are attracted by a potential of the substrate and hit the surface of the substrate. The ions which have collided give a kinetic energy to sputtering atoms composed of Fe and rare-earth element which have reached the substrate. Thereby, it is possible to enhance a crystal property and a crystal orientation property of a formed thin film without heating the substrate as well as the magnetic characteristic and a photomagnetic characteristic can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for forming a magnetic garnet thin film mainly used as a recording material for magneto-optical disks, and in particular, it relates to a method for forming a magnetic garnet thin film mainly used as a recording material for magneto-optical disks. This invention relates to improving the properties, particularly the magneto-optical properties, of the magnetic garnet thin film. [Prior art and its problems] Magneto-optical disks have been actively developed and put into practical use as a recording material with a large recording capacity in recent years. The most promising recording materials for magneto-optical disks that are about to be put into practical use are non-quality rare earth transition metals such as TbFsC'SGdCo. This material has an excellent magneto-optic effect and can produce a magneto-optical disk with good sensitivity and C/N. However, poor quality rare earth transition metals are chemically unstable, and magneto-optical disks using these materials have poor weather resistance.
Furthermore, amorphous rare earth transition metals have the problem of being expensive. On the other hand, rare earth metals, which are magnetic garnets,
Oxide magnetic materials, such as iron garnet (hereinafter referred to as RIG), are relatively chemically stable and inexpensive, do not have the problems associated with non-quality rare earth transition metal materials, and have excellent magneto-optical effects. Because of its excellent properties, it is being researched as a material for magneto-optical disks. As a method for creating the RIG thin film, for example, as disclosed in Japanese Patent Application Laid-Open No. 60-200887,
Drying a film obtained by applying a solution containing a metal element as a component of the RIG, by a spunter method using the RIG as a target, or as disclosed in Japanese Patent Application Laid-open No. 61-222109, There is a method of thermal decomposition, or a liquid phase epitaxial method of forming a single crystal film on a single crystal substrate as disclosed in Japanese Unexamined Patent Publication No. 103603/1983.

In any of the conventional methods described above, in order to improve the crystallinity of the thin film formed on the substrate and obtain sufficient magnetic and magneto-optical properties, the substrate must be heated to a high temperature of 500°C or higher during or after film formation. It had to be heated. For this reason, heat resistance was required for the substrate, which greatly restricted the selection of substrates, which was a major obstacle in particular to using polymer-based substrates. On the other hand, as disclosed in Japanese Patent Application No. 63-156388, a method capable of forming a high-quality oxide film at a relatively low temperature involves vapor deposition while irradiating the substrate with an ion beam.
There is a method of forming a film using the super sota method. However, this method has the problem of increasing manufacturing costs because the ion gun is expensive. In addition, no bias voltage is applied to the substrate in any of these methods. [Problems to be Solved by the Invention] The present invention solves the problems of the prior art as described above, and in order to obtain a magneto-optical disk with good magneto-optical characteristics and a high C/N, The purpose of this study is to provide a method for forming a magnetic garnet thin film with good crystallinity and excellent squareness in the magnetic hysteresis curve and coercive force without requiring heat treatment. A further object of the present invention is to provide a method for forming a magnetic Garnet thin film having an appropriate Curie temperature and excellent recording sensitivity.

[Means for solving problems]

The object of the present invention is to form a thin film of magnetic garnet on a substrate by a sputtering method, in which an oxide containing a component element of magnetic garnet is used as a target and high-frequency sputtering is performed while applying a bias voltage to the substrate. This is achieved by a method of forming a magnetic garnet thin film that is characterized by the following properties. [Embodiment] Unlike conventional methods in which a bias voltage is not usually applied to the substrate, the method of the present invention applies a bias voltage to the substrate so that positively charged argon ions and Oxygen ions are attracted to the potential of the substrate and strike the surface of the substrate. The collided ions give kinetic energy to the supersota atoms mainly composed of Fe and rare earth elements that have reached the substrate, and as a result, the crystallinity and crystal conformation of the thin film that is formed without heating the substrate are improved. It is possible to obtain a magnetic garnet thin film with excellent magnetic and opto-magnetic properties. In the method of the present invention, in order to apply a bias voltage to the substrate, the output terminal of a DC constant voltage power supply and the substrate holder are connected, and the substrate is maintained at a predetermined potential with respect to ground potential. Furthermore, the current flowing through the substrate during the Svanter is proportional to the applied bias voltage, RF discharge power, and target area.

For example, with an 81φ target, RF power of 600 W, and bias voltage of 200 volts, the current will be approximately IA.

Therefore, it is necessary to pay attention to the capacity of the DC power supply used. Further, when a bias voltage is applied, if there are protrusions on the surfaces of the substrate and substrate holder, abnormal discharge will occur, so it is desirable to keep the surfaces as flat as possible.

The method of the present invention will be explained below using an example using the high frequency magnetron sputtering apparatus shown in FIG. Exhaust the chamber 2 using a vacuum pump 1, and reduce the degree of vacuum in the chamber 2 to 10-”To
After reducing the temperature to below rr, an inert gas such as argon gas and an oxidizing gas such as oxygen gas as necessary are introduced through the inert gas inlet 3 and oxidizing gas inlet 4 installed on the inner wall of the chamber 2. A predetermined amount of inert gas and oxidizing gas are sent into the chamber 2 by controlling the flow rate through a mass flow controller so that the gas pressure in the chamber 2 during sputtering ranges from 'lwTorr to 3QaaTorr.
Make it so that Next, a predetermined bias voltage, preferably -100, is applied to the substrate 6 fixed to the substrate holder 5 from the DC power supply unit 7.
volts or less, preferably -200 volts or less, and then a predetermined sputtering power is applied from a high frequency power source IO for sputtering to a target 9 mainly composed of a component element of magnetic garnet with a magnet 8 arranged on the back side. A magnetic garnet thin film is formed on the substrate 6 by sputtering.
Note that cooling water is passed through the substrate holder 5 so that the temperature of the substrate 6 does not become too high during film formation. The magnetic garnet referred to in the present invention has the general formula R3-xAxF
e5-yMyo12 (R is at least one element selected from yttrium and rare earth elements. A is Bi, Pb, S r s C a % B a
At least one element of SC d. M is Fe
A I SG a sS C s I that can replace
n s C r % C u SZ n % N I
SS l sC' e ST At least one element among elements such as I and Zr. It can be expressed as 0≦x<3, 0≦y5). And specifically, as a target, Y! ．． ll
B l +, OFe 4, @Qal, 601gD Y
t. aB l l. oF 13 4. @A j! +.
RIG sintered body such as oO+t or Dy. o. , B i
．． o, , Fe, Os, A7! ! 03 or a mixture of oxides such as Fe+Dy+ Dy+. *B i z. aF
e a. eG a I. Combinations of metals such as oO+t and RIG sintered bodies can be used. It should also be noted that the bias voltage applied to the substrate increases the kinetic energy of atoms on the substrate surface, so atoms with weak bonding forces with other atoms are easily re-spuntered and ejected from the film surface. There is a certain point. For this reason, a compositional deviation may occur in the magnetic garnant thin film formed on the substrate, so this point should be taken into consideration when determining the composition of the target. As the oxidizing gas in the method of the present invention, a mixed gas in which oxygen is mixed in an inert gas such as argon can be used. The degree of oxidation during deposition is important to fully achieve the purpose, and for this purpose it is necessary to control the amount of oxygen in the mixed gas and the deposition rate. That is, as the amount of oxygen increases, the degree of oxidation increases, and as the film formation rate increases, the degree of oxidation decreases. If the degree of oxidation is too high, a nonmagnetic phase will appear in the thin film, impairing the magnetic properties and magneto-optical properties, which is undesirable. On the other hand, if the degree of oxidation is too low, the magnetic anisotropy becomes small and a sufficient squareness ratio in the magnetic hysteresis curve cannot be obtained. The gas pressure during sputtering is 2 to 30 m.
It is desirable that it be mTorr.

Further, although there is no particular limit to the bias voltage applied to the substrate, the magnetic properties of the obtained thin film are further improved by setting it to -200 volts or less. Also, -100
As it becomes larger than the volt and approaches 0, the magnetic properties and magneto-optical properties gradually decrease. Other conditions in the high frequency subasota method employed in the method of the present invention are the same as those in conventionally known conventional methods, and no special conditions are necessary to achieve the object of the present invention.

The method of the present invention is particularly effective when the substrate is a resin substrate. [Effects of the Invention] As mentioned above, since the present invention applies a bias voltage to the substrate, the f of magnetic garnet can be increased without heating the substrate after film formation.
It is possible to increase the crystallinity and crystal orientation of IWA,
A magnetic garnet thin film with excellent properties can be obtained even on a resin substrate whose heat resistance is not very high.

Therefore, the substrate used in the method of the present invention is
In addition to glass, resin substrates such as polycarbonate, polymethyl methacrylate, polyolefin, and epoxy can be used.

Next, the novel effects of the present invention will be clarified by the following examples. [Example] A target having a composition of Dy2BlIFe4CalOl2 was used as the target 9 of the magnetron sputtering apparatus shown in FIG.
It is a barium borosilicate glass with a thickness of 0 nm and a thickness of 11 mm. A magnetic garnet thin film was formed using a Corning #7059 glass substrate under the following conditions. First, after reducing the degree of vacuum in the chamber 2 to 10-'' Torr or less by evacuation using the vacuum pump 1, the gas inlet 3 for the inert gas is inserted into the chamber 2.
Argon gas and oxygen gas were introduced from the oxidizing gas inlet 4 with flow rates controlled by mass flow controllers so that the sputtering gas pressure during sputtering was 10 mTorr. On the other hand, the glass substrate 6 includes the DC power supply unit 7.
Voltages of -90 volts, -180 volts, and 220 volts are applied to the target 9 of the magnetic Garnesoto.
A magnetic garnet thin film with a thickness of 0.5 μm was formed on the glass substrate 6 by applying a sputtering power of 0.5 μm. In addition, the flow rate of the gas and the amount of oxygen in the Supasota gas are 1.
It was set to 0% by volume. The Faraday hysteresis curve of each sample of the magnetic garnet thin film formed on the glass substrate 6 obtained as described above was measured under the following conditions. The results are shown in Figure 2 (in the case of an applied voltage of -90 volts applied to the substrate 6).
3 (applied voltage applied to the substrate 6 -130 volts) and FIG. 4 (applied voltage applied to the substrate 6 -22 volts)
(in case of 0 volts) is shown. To measure Faraday hysteresis, a semiconductor laser with a wavelength of 830 nm was irradiated from the surface of the magnetic Garnet thin film, and an external magnetic field was applied with a maximum magnetic field of 16 kOe. In order to make it easier to read, the sign of the Faraday rotation angle is reversed in the figure. In Figure 3, the squareness ratio was 0.76, and in Figure 4, the squareness ratio was almost 1.0, indicating that a magnetic garnet thin film with extremely good properties was obtained. on the other hand,
If the substrate bias voltage in Figure 2 is -90 volts, then
It was found that the Faraday hysteresis characteristics were somewhat reduced. From this, it has been found that the bias voltage applied to the substrate 6 is desirably -100 volts or less. [Comparative Example] A magnetic garnet thin film was formed on the glass substrate 6 under the same conditions as in the example except that no bias voltage was applied. FIG. 5 shows the Faraday hysteresis curve of the obtained sample.

It was found that if no bias voltage was applied to the substrate, the squareness ratio would drop significantly, making it no longer practical.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the main parts of a high-frequency magnetron spasota device used in the method of the present invention. FIG. 2 is a graph showing the Faraday hysteresis curve of the magnetic garnet thin film obtained in the example when the bias voltage applied to the substrate was -90 volts. FIG. 3 is a graph showing the Faraday hysteresis curve of the magnetic garnet thin film obtained in the example when the bias voltage applied to the substrate was -180 volts. FIG. 4 is a graph showing the Faraday hysteresis curve of the magnetic garnet thin film obtained in the example when the bias voltage applied to the substrate was -220 volts. FIG. 5 shows the magnetic garneso IJiWI! obtained in a comparative example in which no bias voltage was applied to the substrate in the example. It is a graph which shows the Faraday hysteresis curve of. 1 ... High frequency power supply for spatter 2 ...
...Chamber 3 ...Inert gas inlet 4 ... Oxidizing gas inlet 5 ...Substrate holder 6 ...Substrate 7 ...・ DC power supply unit 8 ... High frequency power supply for alloy target spanner of magnet F6 and CO

Claims (2)

[Claims] (1) A method for forming a magnetic garnet thin film on a substrate by sputtering, which is characterized by performing high-frequency sputtering while applying a bias voltage to the substrate using an oxide containing component elements of magnetic garnet as a target. Method for forming magnetic garnet thin film. (2) The method of forming a magnetic garnet thin film according to claim 1, wherein the bias voltage applied to the substrate is -200 volts or less.