JP2007277730A - Sputtering apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sputtering apparatus which forms a compound insulator film convenient for a gap layer of a magnetic head and a tunnel junction type GMR at an extremely thin thickness of several tens to several hundreds Å which are heretofore difficult with the conventional sputtering apparatus. <P>SOLUTION: A target 6 connected to a DC current 5 and a magnetron cathode 9 equipped with a magnet 7 behind the same and an RF coil 8 to enhance ionization efficiency in front of the same are disposed within a vacuum chamber 1 into which sputtering gas and reactive gas are respectively introduced. The target is connected to the DC current via an abnormal discharge prevention circuit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sputtering apparatus for forming an extremely thin insulating film applied to a hard disk magnetic head or the like.

Conventionally, thin-film heads and magnetoresistive (MR) heads have been used as magnetic heads for reading hard disks. Al ₂ O ₃ films with a thickness of about 1000 to 2000 mm are used as gap insulation for these heads. It is provided as a film. In order to form this Al ₂ O ₃ film, an RF magnetron sputtering method using Al ₂ O ₃ as a target is generally employed. However, when importance is placed on the productivity, Al is used as a target, and sputtering is performed. A reactive sputtering method is also employed in which an O ₂ gas is introduced into the inside atmosphere and an Al ₂ O ₃ film is formed using plasma oxidation while sputtering Al.

In addition, as a sputter cathode, an inductively coupled RF plasma assisted magnetron cathode in which a magnet is provided behind the target and an RF coil is provided in front of the target has been proposed by the applicant.
JP-A-6-41739

The cathode described in Patent Document 1 has the advantage that it can sustain the generation of plasma in a high vacuum and generates less impurities and secondary products.

There is a demand for improving the recording density of hard disks, and it is considered that the magnetic head for reading is also replaced with a giant magnetoresistive (GMR) head using a spin valve film, a multilayer film, and a tunnel effect. It is expected that an insulating film to be used also requires a compound insulating film such as Al ₂ O ₃ or AlN of several tens to several hundreds of liters. However, when such an extremely thin Al ₂ O ₃ film, for example, is produced by an RF magnetron sputtering method or a reactive sputtering method using a conventional Al ₂ O ₃ target, the leakage current is 10 ⁻⁶ A / mm ² or less. A high-quality insulating film having electrical characteristics with a dielectric strength of 5 MV / cm or more cannot be formed. This is believed to be based on the following reasons. That is, since the underlying metal film and Al ₂ O ₃ are not “wetting”, the Al ₂ O ₃ layer in the region in contact with the metal film is likely to have defects, but as the Al ₂ O ₃ film is deposited, this defect is likely to occur. It is considered that a thin Al ₂ O ₃ layer becomes a healthy Al ₂ O ₃ layer, and that a thick film of about 1000 mm has satisfactory electrical characteristics. Therefore, an extremely thin Al ₂ O ₃ film of several tens to several hundreds of mm In the case of forming the insulating layer, it is considered that the influence of the portion having many defects in the vicinity of the interface layer appears remarkably, and the insulating film having the above-mentioned electrical characteristics cannot be formed.

  The present invention proposes a sputtering apparatus for forming a compound insulating film that is convenient for a gap layer of a magnetic head or a tunnel junction type GMR with an ultrathin thickness of several tens to several hundreds of millimeters, which was difficult with a conventional sputtering apparatus. It is intended.

  The sputtering apparatus of the present invention includes a target connected to a direct current and a magnet behind the target and a RF coil for increasing ionization efficiency in front of the target in a vacuum chamber into which a sputtering gas and a reactive gas are respectively introduced. A sputtering apparatus provided with a magnetron cathode is characterized in that the target is connected to the direct current via an abnormal discharge force prevention circuit.

  According to the present invention, a magnetron cathode provided with an RF coil for increasing the ionization rate is provided, and the input power to the target and the RF coil and the flow rates of the inert gas and the reactive gas for sputtering introduced into the vacuum chamber are controlled. Since the metal film is formed on the substrate and the metal film is made into an insulating compound alternately, the substrate has excellent electrical characteristics, which is difficult with a conventional sputtering apparatus of several tens to several hundreds of liters. A thin insulating film can be formed, and it is advantageous in that it can be advantageously applied to the manufacture of a high-density hard disk magnetic head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, an embodiment of the present invention will be described. FIG. 1 shows a sputtering apparatus used for carrying out the present invention. Reference numeral 1 in FIG. 1 shows a vacuum chamber provided with an inlet 3 and a reactive gas inlet 4 for introducing a reactive gas such as O ₂ or N ₂ . In the vacuum chamber 1, a metal target 6 made of Al or the like connected to a DC power source 5 through an abnormal discharge prevention circuit 10, a magnet 7 behind it, and an RF coil 8 that increases the ionization rate in front of the target 6. A magnetron cathode 9 is provided. The cathode 9 is known as the above-described inductively coupled RF plasma assisted magnetron cathode, and the RF coil 8 is provided so as to surround the front periphery of the metal target 6. Is supplied. Reference numeral 13 denotes a substrate having a diameter of, for example, 2 inches provided to face the target 6 so as to form an extremely thin insulating film of a compound on the surface. It is formed in advance as a base film. The RF coil 8 is made of, for example, Al made of the same material as that of the metal target 6. If necessary, cooling water is circulated inside the RF coil 8.

  In order to form an extremely thin compound insulating film on the substrate 13 by reactive sputtering using the apparatus of FIG. 1, first, the inside of the vacuum chamber 1 is evacuated, and argon gas for sputtering is introduced from the inlet 3 near the cathode 9. After an appropriate amount is introduced and the pressure is adjusted, DC power is supplied to the metal target 6 and high-frequency power is supplied to the RF coil 8. As a result, plasma is generated in front of the target 6, the target 6 is sputtered by the ions, and the sputtered metal particles are deposited on the substrate 13. When the metal is deposited extremely thin, for example, about several tens of millimeters, the reaction gas is introduced from the reaction gas introduction port 4 in a state where the input power to the target 6 is set to zero and only the high-frequency power is applied to the RF coil 8. As a result, the target 6 is hardly sputtered, and the introduced reactive gas is excited and ionized by the plasma of the RF coil 8, so that it reacts quickly with the deposited metal film and becomes a compound insulating film. Since the deposited metal film is extremely thin, it becomes a compound film that is almost completely combined up to the inside of the thin film.

Thereafter, the sputtering process of the target 6 and the compounding process by introduction of the reaction gas are repeated, and an ultrathin compound insulating film of about 100 mm, for example, is formed on the substrate 13. The resulting compound insulation film is extremely thin, has a low leakage current and a high dielectric breakdown voltage, has a good insulation resistance, can form a compound insulation film with no variation in insulation, and reads high-density recording It can be conveniently applied to magnetic heads. Various metals that form an insulating film by combining with the target 6 can be used. For example, if Si is used, a very thin insulating film of SiO ₂ can be formed, and the target is made of Al and N _{2 is used as a} reactive gas. Can be used to form an ultra-thin insulating film of AlN, and various ultra-thin insulating films can be formed by appropriately selecting a target material and a reactive gas.

The deposition rate of the metal on the substrate 13 mainly depends on the DC power supplied to the target 6, and the degree of ionization and excitation of the sputtered metal particles and reactive gas mainly depends on the high frequency power supplied to the RF coil 8. To do. This is considered to be due to a post ionization mechanism similar to ion plating in which the sputtered neutral metal particles are ionized when passing through the plasma zone formed by the RF coil 8. This tendency becomes more remarkable under a low pressure of 2 × 10 ⁻³ Torr or less. When depositing the metal target 6, not only direct current power to the target 6 but also high frequency power is simultaneously applied to the RF coil 8, so that the ionization efficiency is improved and the substrate 13 is densely coated with good coverage. Thus, an extremely thin metal film having a good crystallinity of about several tens of millimeters can be deposited. When the reactive gas is introduced in a state where the direct current power to the target 6 is zero and only the high frequency power to the RF coil 8 is introduced, there is almost no metal to be sputtered, and it is excited and ionized by the plasma from the RF coil 8. The deposited ultra-thin metal film reacts quickly to almost completely form a compound insulating film.

  In the compounding process using the RF coil 8, since the metal film is not coated on the surface of the RF coil 8 by the sputtered particles from the target 6, the exposed surface of the RF coil 8 is subjected to inductively coupled plasma discharge. Contamination is considered that the sputtered particles of the coil material adhere to the surface of the substrate 13. Such contamination can be prevented by preparing the RF coil 8 with the same material as the target 6.

In addition, when the reactive gas is excited and ionized by plasma, the surface of the target 6 also reacts to form a compound layer there, and the DC discharge in the next sputtering process may become unstable. This is because when a compound or insulator with low electrical conductivity is formed on the target surface, a positive charge is charged on the surface in DC discharge, and the potential difference between the cathode (target) and the anode (substrate) disappears. As a result, the discharge becomes unstable or the discharge stops. In order to eliminate this state, the positive charges accumulated on the surface of the target may be neutralized with electrons from the plasma. Therefore, an abnormal discharge prevention circuit 10 is interposed in the DC power source 5 of the target 6 as shown in FIG. Thus, a positive potential is generated at a constant rate, and when this positive potential is reached, electrons from the plasma are drawn into the target surface to neutralize the positive charges accumulated on the target surface.
(Example)
Using the apparatus with the inductively coupled RF plasma assisted magnetron cathode shown in FIG. 1, an extremely thin Al ₂ O ₃ compound insulating film of about 100 mm was formed on a low resistance silicon substrate 13. The RF coil 8 is made of water-cooled Al, and the DC power source 5 is connected to the Al target 6 via the abnormal discharge prevention circuit 10. Further, argon gas as a sputtering gas can be introduced from the inlet 3, and O ₂ gas as a reactive gas can be introduced from the reactive gas inlet 4. The diameter of the cathode 6 is 2 inches.

Prior to the formation of the compound insulating film, the argon sputtering gas pressure in the vacuum chamber 1 is 8 × 10 ⁻⁴ Torr, the target input power is kept constant at 40 W DC, the input power to the RF coil 8 is changed, and The changes in the Al film deposition rate and the ionic current flowing into the substrate were measured. Note that −50 V was applied to the substrate 13 so that the ion current flowing into the substrate could be measured. The result is as shown in FIG. 3, and it can be seen that the deposition rate of the Al film does not depend much on the input power to the RF coil 8. The Al film deposition rate is proportional to the electric power applied to the target 6 as in the normal magnetron sputtering. On the other hand, the ion current flowing into the substrate 13 increases rapidly with the input power to the RF coil 8, indicating that this inductively coupled RF plasma assisted magnetron sputtering method is extremely effective in promoting ionization of sputtered particles. . The ions flowing into the substrate are Al ions and Ar ions.

Based on this result, the sputtering process for depositing the Al metal film and the compounding process for compounding the film by plasma oxidation are repeated according to the procedure shown in FIG. An Al ₂ O ₃ compound insulating film having excellent electrical characteristics was formed. The sputtering argon gas pressure was 8 × 10 ⁻⁴ Torr, and the temperature of the Si substrate was room temperature.

Specifically, DC power to the target 6 is 130 W, high-frequency power to the RF coil 8 is 50 W, Ar gas is 15 sccm, O ₂ gas is 0 sccm, and sputtering is performed for 18 seconds under these conditions. First, the thickness is about 30 mm. An Al metal film was deposited on the substrate. Subsequently, the DC power to the target is maintained at 0 V, the high frequency power to the RF coil 8 is maintained at 50 W, the flow rate of the sputter argon gas is maintained at 15 sccm, and O ₂ gas is introduced into the 30 sccm vacuum chamber. The Al metal film deposited by generating only inductively coupled plasma by No. 8 for 60 seconds was plasma oxidized to obtain an Al ₂ O ₃ film. Further, the next metal film was deposited on the Al ₂ O ₃ film at a thickness of about 30 mm under the sputtering conditions of the Al metal film, and the next metal film was deposited under the same conditions as the compounding conditions. In this way, the sputtering process and the compounding process were repeated three times to form an Al ₂ O ₃ film of about 100 mm on the substrate.

  When the composition analysis in the depth direction of the film produced here was evaluated using Auger electron spectroscopy, the film composition was stable in the depth direction of the film, and the detected Al spectral peak was all oxygen and It was the energy value obtained in the combined state. The analysis result is shown in FIG. For comparison, a metal film having a thickness of about 45 mm was similarly deposited under the sputtering conditions of the Al metal film, and a sample produced by plasma oxidation was evaluated. The film contained oxygen in the depth direction. There was variation in the amount, and the detected peak of Al was detected not only in the energy value obtained in the state of binding to oxygen but also in the energy value from Al in the metallic state (FIG. 6). This is presumably because the film thickness of Al deposited as a metal film was too thick, and the entire metal Al film was not oxidized during plasma oxidation, and the next metal Al layer was deposited.

Then, in order to measure the electrical characteristics of the obtained Al ₂ O ₃ film, a Cu electrode of 500 μm □ was specifically deposited on the film by a sputtering method. The VI characteristics of the film thus obtained are shown in FIG. It can be seen that the Al ₂ O ₃ film has a VI characteristic peculiar to an insulator, although the film thickness is as extremely thin as about 100 mm. Further, FIG. 8 plots the measured leakage current and dielectric breakdown voltage of the insulating film. The dielectric breakdown voltage and leakage current here are obtained when the insulation of the film was broken in the previous VI measurement. Defined as voltage and current. For comparison, the measurement results of the Al ₂ O ₃ film having the same film thickness prepared by reactive sputtering are also shown. This reactive sputtering condition is obtained by adding 130 W of DC power to a target that is one of the conditions for sputtering Al in the compounding condition in the sputtering apparatus of the present invention.

When the characteristics of the film obtained by the sputtering apparatus of the present invention and the sputtering apparatus of the conventional reactive sputtering method are compared, the reactive sputtering film has a larger variation, and the dielectric breakdown of the film is caused by a small voltage. When this is depositing _Al 2 _{O 3} film from the beginning by reactive sputtering, Si and _{the Al} 2 _{O 3} film of underlying "wet" poor, the _{the Al} 2 _{O 3} film in contact with the Si considered liable contains the defect It is done. On the other hand, in the sputtering apparatus of the present invention (metal deposition / plasma oxidation lamination method), first, an Al film having good wettability with Si is formed densely on the entire surface of the Si base, and thereafter Al ₂ O ₃ is formed by plasma oxidation. Therefore, it is presumed that the formed Al ₂ O ₃ film has a good quality film with few defects even in the vicinity of the interface. When a film having a thickness of about 1000 mm was deposited with the sputtering apparatus of the present invention and its refractive index was measured, the same value of 1.71 to 1.72 as that of bulk Al ₂ O ₃ was obtained. The rate value also confirms that the film obtained by the apparatus of the present invention is an excellent film comparable to bulk Al ₂ O ₃ .

  As with the sputtering apparatus of the present invention, an Al film having a required film thickness, for example, 100 mm, was first formed by sputtering, and then the Al film was oxidized by another plasma oxidation apparatus. Since only the degree is oxidized and not the inside of the film, the VI characteristic peculiar to the insulator could not be obtained.

In the embodiment, the example of the Al ₂ O ₃ film is shown, but the present invention can be applied to various insulating films such as SiO ₂ and AlN and compound materials. In principle, the method of the present invention has both a mechanism for sputtering metal and a mechanism for exciting atmospheric gas with plasma in the same chamber, and these can be controlled almost independently. It can be implemented. Therefore, in addition to the apparatus illustrated in FIG. 1, for example, a sputtering apparatus in which an RF coil is installed between the target and the substrate as shown in FIG. 9A, and thermoelectrons are generated by a hot filament as shown in FIG. It can be implemented by a tripolar or quadrupole type sputtering apparatus capable of forming plasma by an ECR (electron cyclotron resonance) or an ECR or microwave sputtering apparatus capable of generating plasma by a microwave as shown in FIG. 9C. In the embodiments, the insulating film sputtering process of the hard disk magnetic head has been described. However, the present invention can be applied to various electronic device device thin film manufacturing processes such as flat panel displays. Further, in this case, in order to obtain a thick film of the compound, the sputtering process and the compounding process were alternately repeated. However, only the first compound layer having poor “wetting” with the base was prepared by this method, After the layers, compound layers may be formed all at once by so-called reactive sputtering.

A cut side view of the sputtering apparatus used in the present invention, FIG. 1 is a characteristic diagram of a voltage applied to the cathode of the sputtering apparatus of FIG. Relationship diagram between RF coil power and film deposition rate, The diagram of the implementation procedure in the sputtering apparatus of the present invention, Chemical composition analysis chart (30 cm) by Auger electron spectroscopy of the film obtained by the sputtering apparatus of the present invention, Chemical composition analysis diagram (45 mm) by Auger electron spectroscopy of the film obtained by the sputtering apparatus of the present invention, Relationship diagram between leakage current and voltage of the film obtained by the sputtering apparatus of the present invention, Relationship between the leakage current and breakdown voltage of the film obtained by the sputtering apparatus of the present invention, It is explanatory drawing of the sputtering device in the modification of the sputtering device of this invention.

Explanation of symbols

1 Vacuum chamber 3 Sputtering gas introduction port 4 Reactive gas introduction port 5 DC power source 6 Metal target 7 Magnet 8 RF coil 9 Magnetron cathode 10 Abnormal discharge prevention circuit 13 Substrate

Claims (1)

  Sputtering apparatus provided with a magnetron cathode provided with a target connected to a direct current and a magnet and an RF coil for increasing ionization efficiency in front of the target in a vacuum chamber into which a sputtering gas and a reactive gas are respectively introduced In the sputtering apparatus, the target is connected to the direct current through an abnormal discharge force prevention circuit.

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