JPH0361355A - Formation of thin garnet film - Google Patents

Abstract

PURPOSE:To obtain a thin garnet film of superior quality at low temp. with superior reproducibility by carrying out sputtering in an electron cyclotron resonance plasma by the use of a garnet material as a target and depositing grains composed of garnet components onto a substrate. CONSTITUTION:Microwaves of 2.456Hz are introduced 1 into a plasma formation chamber 2. At this time, solenoid coils 3A, 3B are disposed around the chamber 2 and electric power is supplied to the coils 3A, 3B from electric power sources 11A, 11B, respectively, to produce 875G as resonant magnetic field in the chamber 2, and a plasma 4 obtained in the chamber 2 is accelerated by means of a divergent magnetic field in a direction of a substrate 8 disposed in a specimen chamber 10. As a result, negative voltage is impressed on a plate target 5A disposed in the chamber 2 and an octagonal cylindrical target 5B disposed at the outlet from the chamber 2 to the chamber 10, respectively, and sputtering is carried out. On the other hand, a gaseous mixture of Ar and O2 is generally used as an electric discharge gas. By this method, grains composed of garnet components as raw materials constituting the targets 5A, 5B are deposited on the substrate 8, and a thin garnet film of superior quality can be formed at low temp. with superior reproducibility.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention is for forming high-quality garnet thin films at low temperatures with good reproducibility, which are widely used in optical isolators, magneto-optical recording media, magnetic sensors, etc. The invention relates to a novel method for

[Prior Art] Garnet thin films have been widely studied as magnetic bubble materials, magnetic memory materials, and optical communication materials.
And it has been put into practical use. The forming method generally includes liquid phase epitaxial method (LPE), sputtering method, etc.

The LPE method is a technology in which a garnet raw material is melted at high temperature using a flux such as PbO, and a thin garnet film is grown epitaxially on a crystal substrate from a liquid phase state.It is a technology that allows for the high-speed formation of a single crystal film with excellent crystallinity. He has a lot of technical experience. This method has been the most common method for forming garnet thin films.

On the other hand, the sputtering method is generally a vapor phase film formation method in which sputtering is performed in plasma using a garnet raw material as a target, and the resulting particles of garnet components are deposited on a substrate to form a garnet thin film. .

[Problem to be solved by the invention] As mentioned above, as a method for forming a garnet thin film, L
The PE method has been the most common until now, but this method
Since the raw materials are melted and the film is grown from a liquid phase, it is difficult to control the composition, and there are problems in that the controllability of the film thickness in the thin film region is greatly inferior. Moreover, since this method is essentially a thermal equilibrium technology, the substrate temperature required to obtain a good quality film is usually as high as 900°C or higher (for example, Tamaki, Tsushima, 38th Society of Applied Magnetics Research Conference Materials, No. , 38-5
, 1985, p. 23), the substrates used were limited to specific heat-resistant substrates or substrates in which the lattice constants of the film and substrate were precisely matched. Moreover, impurities (PB, PT, etc.) from flux and crucibles are inevitably mixed into the film, and when used for optical communication, for example, light absorption due to the impurities increases. , there were major problems such as deterioration of the figure of merit.

On the other hand, since sputtering is a non-thermal equilibrium technology, it is possible to form a garnet thin film with relatively low 7 crystals compared to the above-mentioned LPE method. , the film was severely damaged, and high temperatures of over 700°C were required to obtain a good quality garnet thin film (for example, Miyazaki, 38th Society of Applied Magnetics Research Materials, No. J8-15, 1985, p. 81).
.

In addition, as the degree of oxidation of the film decreases, metal ions (
For example, there are problems in that light absorption increases and crystallinity deteriorates due to changes in the valence of Fe ions), and it is difficult to say that this method is superior in terms of controllability of such reactivity.

Therefore, in order to form a high-quality garnet thin film at low temperatures, a method with less damage and high activity has been strongly desired.

Therefore, an object of the present invention is to provide a method for forming a high-quality garnet thin film at low temperatures and with good reproducibility.

[Means for Solving the Problems] In order to solve the conventional problems, the present invention forms a garnet thin film by a sputtering method using electron cyclotron resonance (ECR) plasma (ECR sputtering).

That is, the present invention is characterized in that sputtering is performed in an electron cyclotron resonance plasma using a garnet raw material as a target, and particles made of garnet components are deposited on a substrate to form a garnet thin film.

In the present invention, a sintered body having the composition of a thin film obtained by target binding used in the electron cyclotron resonance plasma method, a sintered body having a composition that compensates for the compositional deviation between the target and the thin film, or a composite thereof. During the formation of the garnet thin film, oxygen gas or a mixed gas of oxygen gas and an inert gas such as argon is introduced into a plasma generation chamber that generates electron cyclotron resonance plasma. It is preferable to do so.

Furthermore, in the present invention, the substrate is irradiated with ECR plasma using oxygen gas or a mixed gas of oxygen gas and an inert gas such as argon as the discharge gas immediately before the deposition of the garnet thin film. It is characterized by performing plasma cleaning.

Here, the ECR sputtering method is a method that combines ECR plasma and sputtering, and is known as one of the highly active sputtering methods (for example, Ono, Taka
hashi, & Matsuo, Jpn, J.Ap.
pl, Phys.

23 (1984) L534, Ya Matsuoka
& Ono, J., Appl.

Phys, 65 (1989) 4403).

[Function] According to the present invention, a high-quality garnet thin film, which is widely used in optical isolators, magnetic or magneto-optical recording media, magnetic sensors, etc., can be formed at low temperature with good reproducibility.

That is, the present invention provides a highly active electron cyclotron
! This method forms a garnet thin film at a low temperature by sputtering using % (ECR) plasma (ECR sputtering), and also performs substrate pretreatment and film deposition in the same process.

[Example] Hereinafter, the present invention will be explained in detail based on the drawings.

Examples 1 to 8 of the present invention are summarized in Table 1. In the above example, all mixed gases were introduced from the plasma generation chamber. GGG is GdGa garnet, SGG
indicates SmGa garnet, NGG indicates NdGa garnet, and all are (111) planes. A film can be formed on the (100) plane under almost the same conditions. Hydrogen reduction treatment of the target was performed in hydrogen at 400°C for 2 hours.
By imparting conductivity to the target, sputtering in DC mode was made possible.

Table 2 shows comparative examples of garnet thin film formation using the conventional sputtering method.

FIG. 1 is a configuration diagram showing an example of the configuration of an EcR sputtering apparatus used to form a garnet thin film according to the present invention.

Here, microwaves of 2.45 GHz are introduced into the plasma generation chamber 2 through the microwave introduction window 1. Solenoid coils 3^ and 3B are arranged around the plasma generation chamber 2, and are supplied with power from power sources 11A and 11B, respectively, so that both D! % magnetic field is 87
Make sure you get 5G. Here, the current flowing through the two solenoid coils 3A and 3B was set to 2OA. Plasma 4 obtained in the plasma generation chamber 2 is accelerated toward a substrate 8 placed in the sample chamber 10 by a divergent magnetic field.

A negative voltage is applied to each of the flat plate target 5A placed in the plasma generation chamber 2 and the '8 square cylinder target placed at the exit from the plasma generation chamber 2 to the sample chamber 1o,
The substrate 8 on which sputtering is performed can be heated.

As targets 58 and 5B, a combination of flat and cylindrical sintered bodies was used. Here, an octagonal cylindrical target is used as the cylindrical target 5B.

Sputter discharge modes include alternating current (f) and direct current (da
), but the dc mode is more desirable because it causes less damage to the film and has higher film formation efficiency. At this time, the target is reduced in hydrogen to facilitate direct current discharge sputtering of the target part.
It is better to make it conductive.

On the other hand, the discharge gas is generally a mixed gas of argon and oxygen, or a single gas of argon or oxygen.
It is preferable that the oxygen gas be introduced from the plasma generation chamber 2 through the gas introduction port 9A.

Figure 2 shows a case where oxygen gas is introduced from the plasma generation chamber 2 through the gas inlet 9^, and the sample chamber 10 is the same as in (a).
The results of a comparison of plasma emission spectra in the case (b) in which the gas is introduced through the gas introduction port 9B are shown. The reaction gas introduced from the plasma generation chamber 2 (a) is highly excited and has excellent reactivity.

Furthermore, when forming a thin film, especially when performing epitaxial growth on a single crystal substrate, if the surface of the substrate is covered with various impurities and oxides, not only will it not be possible to obtain a good quality thin film, but the epitaxial growth will be hindered. Therefore, before placing the substrate in a vacuum chamber, it is usually necessary to chemically treat the substrate or subject it to high temperature treatment in the vacuum chamber to remove the contaminant layer on the surface of the substrate. In fact, when using a substrate that is not cleaned, a temperature of 550°C is required to obtain a single crystal film.
It was necessary to heat the substrate to a higher degree (see Example 4).

However, plasma cleaning of the substrate can be easily performed by irradiating the substrate with ECR plasma using oxygen gas or a mixed gas of oxygen gas and an inert gas such as argon as the discharge gas immediately before thin film deposition. This allows for epitaxial growth at lower temperatures. In Examples 1 to 3 and 5 to 8, oxygen gas (flow rate: 1105 ce,
Gas pressure 0.07D a 1 /rI L +, -h
Mayu i 4 boo y (mano/y rv -nrk 'ff -
h.

Plasma cleaning was performed by irradiating the substrate heated to 500° C. with 200 W) for 5 minutes. here,
Ar gas can also be used as the plasma cleaning gas, but in this case, the substrate surface may be damaged, so it is preferable to use only oxygen gas.

Next, a method for forming a garnet single crystal film having a composition of Y2B I1Fe5012 will be described. Y2BilFe50
When a sintered body having a composition of In order to obtain a film of 10%, it is necessary to use a target with a composition that compensates for this reduction in advance.

The third centroid shows the change in the composition of the thin film obtained at that time depending on the substrate temperature.

Here, Y and Bi compositions of 2.0 and 1.0 correspond to stoichiometric compositions, respectively.

At this time, as a discharge gas, 0.04% of argon and oxygen are mixed.
Both were introduced from the plasma generation chamber 2. The substrate 8 is garnet (GdGa garnet:
GGG) was used. Here, since the film becomes single crystal when the substrate temperature is approximately 400°C or higher, if a target with a composition of approximately Y2Bi, 4Fe50X (X is a value between 8 and 12) is used, the Y2B1+F
A thin film with a stoichiometric composition of e50+2 is obtained at a temperature of 400° C. or higher. The composition of the thin film thus obtained was approximately stoichiometric and was a high quality single crystal film.

Furthermore, it was confirmed that when the oxygen gas flow was increased, the shrimp critical temperature decreased and a single crystal film could be obtained even below 400°C.

In this embodiment, only a method using two targets was shown as an example of forming a garnet thin film by ECR sputtering, but this method uses only a cylindrical target and the same effect can be obtained. Similarly, the cylindrical target does not need to be an octagonal cylinder as in this embodiment, but may be a cylinder or a polygonal cylinder. That is,
If a garnet thin film is formed by a method combining ECR microwave plasma and sputtering, the same effects as those obtained in the embodiments of the present invention described above can be obtained regardless of the form.

[Effects of the Invention] As explained above, according to the present invention, a garnet thin film is formed by sputtering using highly active microwave plasma generated by electron cyclotron resonance, and a high-quality garnet thin film can be formed. It can be formed at low temperatures and with good reproducibility.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of an ECR sputtering apparatus used to form a garnet thin film according to the present invention, and Fig. 2 shows a case where oxygen gas is introduced from the plasma generation chamber and a case where oxygen gas is introduced from the plasma generation chamber. Figure 3 shows a wavelength-emission intensity characteristic diagram for explaining the difference in plasma emission spectra in comparison with the case where the plasma is introduced from the sample chamber. FIG. 2 is a characteristic diagram showing the substrate temperature dependence of the thin film composition obtained when a solid is used. DESCRIPTION OF SYMBOLS 1... Microwave introduction window, 2... Plasma generation chamber, 3A, 3B... Solenoid coil, 4... Plasma, 5A... Flat target, 5B-... Octagonal cylindrical target, 6 ...Vacuum waveguide, 7...Substrate heating mechanism, 8...Substrate, 9^, 9B...Gas inlet, 10...Sample chamber, 11A, IIB...Power source. My

Claims (1)

[Claims] 1) A garnet thin film characterized in that a garnet thin film is formed by sputtering in an electron cyclotron resonance plasma using a garnet raw material as a target and depositing particles made of garnet components on a substrate. How to form. 2) The target is a sintered body having the composition of the obtained thin film, a sintered body having a composition that compensates for the compositional deviation between the target and the thin film, or a composite thereof. Method of forming garnet thin film. 3) A claim characterized in that during the formation of the garnet thin film, oxygen gas or a mixed gas of oxygen gas and an inert gas such as argon is introduced into a plasma generation chamber that generates electron cyclotron resonance plasma. Item 2. The method for forming a garnet thin film according to item 1 or 2. 4) By irradiating the substrate with ECR plasma using oxygen gas or a mixed gas of oxygen gas and an inert gas such as argon as a discharge gas, immediately before depositing the garnet thin film, the plasma on the substrate is reduced. 2. The method for forming a garnet thin film according to claim 1, wherein cleaning is performed.