JPH059849B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming a barium ferrite layer, for example, a barium ferrite layer used in magnetic recording media such as magnetic tapes and magnetic disks.

2. Prior Art Conventionally, this type of magnetic recording medium has been widely used for recording various electrical signals such as video, audio, and digital signals. These have been developed as a system that uses magnetization in the in-plane longitudinal direction of a magnetic layer (magnetic recording layer) formed on a substrate. However, in recent years, with the increase in the density of magnetic recording, in recording systems that use magnetization in the longitudinal direction in the plane, as the wavelength of the recording signal becomes shorter, the demagnetizing field within the medium increases, resulting in attenuation and rotation of the residual magnetization. occurs, and the playback output decreases significantly. For this reason, it is extremely difficult to reduce the recording wavelength to submicron or less.

On the other hand, a perpendicular magnetization recording method that uses magnetization in the thickness direction of the magnetic layer of a magnetic recording medium (so-called perpendicular magnetization) has recently been proposed (for example, "Nikkei Electronics" August 7, 1978 issue No. .192).
According to this recording method, as the recording wavelength becomes shorter, the demagnetizing field that acts on the residual magnetization in the medium decreases, so it has favorable characteristics for increasing density, and is essentially suitable for high-density recording. This method is considered to be suitable for

Incidentally, in order to perform such perpendicular recording efficiently, the recording layer of a magnetic recording medium must have an axis of easy magnetization in the perpendicular direction (thickness direction of the magnetic layer). Such a magnetic recording medium is a coated type in which a magnetic coating mainly composed of magnetic powder and a binder is coated on a substrate (support), and the axis of easy magnetization is oriented in the perpendicular direction of the magnetic layer. The medium is known. This applied media includes Co,
Fe ₃ O ₄ , γ-Fe ₂ O ₃ , Co-added Fe ₃ O ₄ , Co-added γ-
Fe ₂ O ₃ , hexagonal ferrite (e.g. barium ferrite), MnBi, etc. are used as magnetic powders (JP-A-52-46803, JP-A-53-67406, JP-A-52-
Publications No. 78403, No. 55-86103, and No. 54-87202). However, in these coated media, there is a limit to increasing the packing density of magnetic powder due to the presence of a non-magnetic binder in the magnetic layer, and therefore it is difficult to increase the S/N ratio sufficiently. I can't. Moreover, the magnitude of the recorded signal is limited by the size of the magnetic particles, and thus a medium having a magnetic layer made of a magnetic coating is unsuitable for perpendicular magnetization recording.

Therefore, continuous thin film magnetic recording media, in which a perpendicularly magnetized magnetic layer is formed by continuously depositing a magnetic material on a support without using a binder, are attracting attention as suitable for high-density recording. ing.

As a result of studying the film formation of magnetic layers for perpendicular magnetic recording proposed so far, the present inventor found that
We have discovered a very useful method and have arrived at the present invention.

3. Purpose of the Invention The purpose of the present invention is to provide a method that allows stable sputtering to be performed continuously and is particularly effective in forming a barium ferrite layer suitable for perpendicular magnetic recording. .

4. Structure of the Invention That is, the present invention comprises disposing a substrate on the side between targets facing each other, sputtering the targets by supplying high frequency power to the targets, and depositing the generated particles on the substrate. A method for forming a barium ferrite layer, wherein the supplied high-frequency power density Pav is 8 W/cm ² or more, the total gas pressure Ptotal is 10 mTorr or more, and the sputter is placed approximately between the two targets. The present invention relates to a method for forming a barium ferrite layer, which is characterized in that it is carried out in such a manner that no phase difference occurs.

5 Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The method of the invention is particularly carried out using a high-frequency discharge type opposed target sputtering device.

FIG. 1 shows a high frequency discharge type facing target sputtering device.

In the drawing, 1 is a vacuum chamber, 2 is an evacuation system consisting of a vacuum pump etc. for evacuating the vacuum chamber 1, and 3 is an exhaust system that introduces a predetermined gas into the vacuum chamber 1 to raise the gas pressure to 10 ^-1 ~
This is a gas introduction system set at approximately 10 ^-4 Torr.

The target electrode is connected to a pair of targets T ₁ and T ₂ (with stoichiometric composition) by a target holder 4.
The electrodes are configured as opposed target electrodes in which electrodes (BaO.6Fe ₂ O ₃ ) are arranged vertically and in parallel to each other and separated from each other. A magnetic field (for example, a plasma convergence magnetic field of 150 Oe) is formed between these targets by a permanent magnet 10 serving as a magnetic field generating means. On the other hand, a substrate 6 on which a magnetic thin film is to be formed is placed between both targets (upper side in the drawing) and heated to a predetermined temperature by a heater 7. For both targets T ₁ and T ₂ ,
A high frequency power source R _f having a matching circuit is connected, and the vacuum chamber 1 is grounded. In addition, 14 in Figure 1
15 is an insulator for shielding, and 15 is a cooling inlet pipe and an outlet pipe.

Note that various materials can be used for the base body 6 as long as a magnetic material can be attached thereto. For example, plastics such as polyethylene terephthalate, polyvinyl chloride, cellulose triacetate, polycarbonate, polyamide, polyimide, polymethyl methacrylate, ceramics such as glass, etc. can be used. Furthermore, Mg,
Al, Si, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn,
Metals such as Ge, Zr, Nb, Mo, Ru, Te, Ta, Co, and W, semimetals, and alloys thereof can also be used.

In the sputtering apparatus configured as described above, a magnetic field is formed perpendicularly to the surfaces of both the targets T ₁ and T ₂ facing each other in parallel, and this magnetic field causes the cathode falling part (or rather, the target T ₁ - Plasma atmosphere generated between T ₂ and each target T ₁ and T ₂
The γ electrons emitted by the impact of the sputtering gas ions accelerated by the electric field on the target surface (area between the two targets) are trapped in the space between the targets and moved toward the other opposing target. The γ electrons that have moved to the other target surface are reflected by the cathode fall section nearby. In this way, the γ electrons repeatedly move back and forth between the targets T ₁ and T ₂ while being constrained by the magnetic field. During this reciprocating motion, the γ electrons collide with the neutral atmospheric gas to generate ions and electrons of the atmospheric gas, and these products promote the release of the γ electrons from the target and the ionization of the atmospheric gas. Therefore, the target
A high-density plasma is formed in the space between T ₁ and _{T 2} , and the target material is sufficiently sputtered and deposited on the upper substrate 6 as barium ferrite.

Compared to other flying methods, this facing target sputtering device enables film formation at a high deposition rate using high-speed sputtering, and the substrate is not directly exposed to plasma, allowing film formation at low substrate temperatures. This is advantageous for forming a perpendicularly magnetized film. Moreover, the incident energy of the magnetic film material sputtered onto the substrate by the facing target sputtering device is smaller than that of a normal sputtering device, so the material is easily deposited directionally in the desired direction, and the material can be deposited vertically. It becomes easier to obtain a film with a structure suitable for magnetization recording.

What should be noted in the sputtering method using this opposed target sputtering device is that high frequency power is supplied by a high frequency power source R _f during sputtering. This will be explained in detail next.

For example, IEICE Journal VOL.J66-C
As shown in Nos. 1p9-16, when a DC facing target sputter using a DC power source is used, a high voltage is applied between the targets to generate a glow discharge between them, and this continues. Sputtering is performed using ions in plasma, but especially when sputtering is performed at high speeds, a transition from normal abnormal glow discharge to arc discharge frequently occurs.
It is often impossible to maintain a stable spat. Particularly when a target made of barium ferrite is used, the above transition to arc discharge becomes noticeable.
As a countermeasure, an electronic fuse circuit is installed in the DC power supply to automatically reduce the applied voltage to the target to stop the arc discharge when it transitions to an arc discharge, and then a special operation is carried out in which the voltage is returned to its original state. must be carried out.

On the other hand, when a high frequency power source R _f as in this embodiment is used, the surface of the target is always at a positive voltage during one cycle, so the above measures when using a DC power source are not necessary at all, and Stable spattering can be continued.

In addition, when designing the above-mentioned sputtering apparatus for the purpose of high-speed sputtering, it is desirable to suppress power loss consumed in areas other than the sputtering area. These power losses can include (1) electromagnetic radiation loss, (2) matching circuit loss, and (3) intermediate diameter loss, among which, in order to minimize electromagnetic radiation loss,
It is necessary to ensure that the equipment is sufficiently grounded, and that all parts other than the ground level be completely shielded with ground potential.

Further, since it is necessary for the other target to act as a reflector for the γ electrons emitted from one target, it is preferable to perform sputtering in a state where no phase difference occurs between the two targets. In order to realize this, as shown in FIG. 1, both target holders 4 are made completely symmetrical, and the matching circuit is also arranged at the center position between the two targets. By symmetrically arranging the left and right targets in this manner, sputtering can be performed with almost no phase difference.

Next, a specific example of producing a magnetic recording medium using the above sputtering apparatus will be described.

The preparation conditions were as follows.

target material
Barium ferrite (BaO・6Fe ₂ O ₃ ) sintered at 1300℃ Substrate Distance between glass facing targets 100 mm Magnetic field in sputtering space 150 Oe Target shape 85 mm diameter disk (5 mm thickness) Distance between substrate and target end 40 mm In vacuum chamber Pre-exhaust pressure 8×10 ^-7 Torr Introduced gas Ar＋O ₂ (10:1) Introduced gas pressure 0.7×10 ^-3 Torr～20×10 ^-3 Torr Sputter input power Power density 0～20W/cm ² (High frequency 13.56MHz) In this way, a magnetic recording medium having a magnetic layer 21 made of barium ferrite on the base film 6 was obtained, as shown in FIG. The thickness of the magnetic layer of this medium was, for example, 1500 Å (by a stylus-type film thickness meter: Talystep, manufactured by Rank-Taylor-Hobson), and its composition was identified by EPMA.

FIG. 3 shows the dependence of the plasma potential V _p and the potential V _w induced on the substrate surface on the supplied power density P _av during the sputtering described above.

According to this, in the case of high frequency (R _f ) discharge as in this example, the absolute values of both V _p and V _w decrease monotonically as P _av increases, but in the case of direct current ( dc ) discharge, Both V _p and V _w become very small and do not change much with P _av . Furthermore, in the high-frequency discharge, the impact potential V _d is larger than that in the de discharge because the impact is applied at the potential of the difference V _d (=V _p −V _w ) between V _p and V _w . this
Although V _d becomes smaller as P _av becomes higher, it reaches a nearly constant value in the power density range; P _av ≧8W/cm ² .

Figure 4 shows the dependence of V _p and V _w on gas pressure. According to this, in the case of de discharge, V _d
is small, but V _d is large in R _f discharge (however, high P _av
It turns out that the smaller the value becomes, the smaller it becomes.

From the above facts, the impact potential V _d largely depends on the sputtering conditions (that is, the film quality also largely depends on the same conditions), and it is necessary to effectively utilize this characteristic.

Next, FIG. 5 shows the P _av dependence of the Ba composition X of the sputtered film (barium ferrite film), and FIG. 6 shows the gas pressure dependence. barium ferrite layer
When expressed as Ba _x Fe ₁₂ O _y , it can be seen that the Ba composition X largely depends on P _av and gas pressure. This corresponds well to the change curves shown in FIGS. 3 and 4.

That is, it is desirable to obtain a barium ferrite film with a stoichiometric composition (X = 1.0) as a magnetization film, but in order to achieve this, from the results shown in Figure 5, it is clear that P _av
It is clear that it is desirable to set the power to 8 W/cm ² or more (particularly 12 W/cm ² or more). In this case, high P _av
V _d becomes smaller as the value increases (see Figures 3 and 4).
This is because sputtering by R _f discharge is essentially a high-speed formation method.

Also, from Figure 6, the total gas pressure Ptotal is
It can also be seen that the Ba composition X can be made 1.0 if it is 11 mTorr or more.

In the above-mentioned example (see FIG. 1), the substrate 6 is fixed in position as a flat plate, but various changes can be made to the arrangement of the substrate.

For example, as shown in FIG. 7, the substrate 6 is formed into a film and is sequentially wound onto the take-up roll 13 from the unwind roll 11 to the circumferential surface of the back-up roll 12 above the two targets. During this time, the magnetic material may be sequentially deposited on the surface. This allows barium ferrite to be continuously deposited on the substrate.

Note that the above-mentioned backup roll 12 may have a structure as shown in FIGS. 8 and 9,
The wall portion may be a double wall that can guide the cold/hot medium 17 in one direction along the circumferential surface. In order to uniformly distribute the coolant/hot medium 17 to the outer circumferential side, the inlet port 18 (for example, it may be provided through the rotating shaft; the same applies to the outlet port 19) extends radially in the outer circumferential direction. The cylindrical passage 20 communicates with the cylindrical passage 20 of the The coolant to be used is, for example, ethylene glycol at -several tens of degrees Celsius when the substrate 6 has poor heat resistance (for example, in the case of a polymer film), and oil, etc. at 250 degrees Celsius when promoting the crystal growth of the magnetized film. can be mentioned. In addition, also in the example described later, the cooling/heating medium may be caused to flow in a structure similar to that shown in FIGS. 8 and 9.

In addition to the above-mentioned Ar gas, there are also other gases for spatsuta.
There are Kr, Ne, He, etc., but this sputtering gas can be introduced alone, or the above-mentioned O ₂ , N ₂ , H ₂ O
A mixed gas with the like may also be used.

Next, for comparison, as a result of supplying DC power (300V x 0.4A) to the sputtering device shown in Figure 1,
The time that stable spatter without arcing can be maintained has become as short as 5 minutes. On the other hand, when using the high frequency discharge of this example, the duration of stable sputtering could be extended to several hours.

FIG. 10 shows another example, and shows the seventh
Unlike the example shown in the figure, the locations of targets T ₁ and T ₂ with respect to the roll 12 are different (they are rotated by 90 degrees), and the targets T 1 and T 2 are placed above the upper end of target T ₁ on the left side of the drawing. A mask plate 22 is stretched. Due to the existence of this mask plate 22,
Among the particles from between the targets, the component 23 that is about to enter the substrate 6 obliquely is blocked by the mask plate 22, and only the vertically incident component 23' enters the substrate 6 and is deposited in the vertical direction. Become. In this way, when the substrate 6 is moved after the grains have grown vertically on the substrate 6, even if the next grain component 23'' is incident obliquely, it will be deposited on the grains that have already grown vertically, resulting in epitaxy. As a result, the magnetic film formed on the substrate 6 becomes a good film in which the grains are aligned in the vertical direction, and has excellent perpendicular anisotropy.

FIG. 11 shows an example in which plasma particles between the targets are first deposited in the vertical direction 23' by placing the target _T1 below the center of the roll 12. This also allows epitaxial growth in the vertical direction as described in FIG. 11. Furthermore, by moving the targets T ₁ and T ₂ as shown by arrows 24, the spatter conditions can be controlled. Alternatively, the conditions may be controlled by rotating the target _T2 as shown by the dashed line.

Note that each of the above-mentioned examples can be further modified based on the technical idea of the present invention.

For example, the part to which high frequency is applied is the target T ₁ ,
The cooling water does not need to be added directly to T ₂ , for example, it may be added to the cooling water inlet pipe and the outlet pipe 15 . Further, the arrangement and number of targets, the arrangement and shape of the substrate, etc. may be varied in various ways.

6 Effects of the Invention According to the present invention, a high performance barium ferrite layer suitable for perpendicular magnetic recording can be efficiently formed.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, in which Fig. 1 is a schematic cross-sectional view of a sputtering device, Fig. 2 is a cross-sectional view of a magnetic recording medium, and Fig. 3 is a diagram showing the plasma potential and the power of the induced potential on the substrate surface. A graph showing the density dependence, FIG. 4 is a graph showing the gas pressure dependence of the plasma potential and the induced potential on the substrate surface,
Figure 5 is a graph showing the power density dependence of the Ba composition of barium ferrite, Figure 6 is a graph showing the total gas pressure dependence of the same Ba composition, Figure 7 is a front view of the main parts of another sputtering device, and Figure 7 is a graph showing the dependence of the Ba composition on the power density. Figure 8 is a cross-sectional view of the backup roll, Figure 9 is a cross-sectional view taken along line X-X in Figure 8,
10 and 11 are schematic diagrams of still other sputtering devices. In addition, in the symbols shown in the drawings, 1...vacuum chamber, 2...exhaust system, 3...gas introduction system, 4...holder, 6...substrate, 10...permanent magnet, 21...
... Barium ferrite layer, T ₁ , T ₂ ... Target, R _f ... High frequency power source.

Claims (1)

[Claims] 1. A method of forming a barium ferrite layer by disposing a substrate on the side between mutually facing targets, sputtering the targets by supplying high frequency power to the targets, and depositing the generated particles on the substrate. The supplied high frequency power density Pav is 8 W/cm ² or more, the total gas pressure Ptotal is 10 mTorr or more, and the sputtering is performed so that there is almost no phase difference between the two targets. A method for forming a barium ferrite layer characterized by: