JP4531145B2 - Ultra-thin insulating film formation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming an extremely thin insulating film applied to a hard disk magnetic head or the like.
[0002]
[Prior art]
Conventionally, thin film heads and magnetoresistive (MR) heads have been used as magnetic heads for reading hard disks, and Al ₂ O ₃ films with a thickness of about 1000 to 2000 mm are used for 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.
[0003]
Further, 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 as a sputter cathode (Japanese Patent Laid-Open No. 6-41739). This cathode has the advantage that it can sustain the generation of plasma in a high vacuum and has less generation of impurities and secondary products.
[0004]
[Problems to be solved by the invention]
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 or a tunnel effect. It is expected that an insulating film to be used will require an extremely thin 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 the RF magnetron sputtering method or the 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 “wet”, the Al ₂ O ₃ layer in the region in contact with the metal film is likely to have defects, but this defect is deposited as the Al ₂ O ₃ film is deposited. It is considered that a thin Al ₂ O ₃ layer becomes a healthy Al ₂ O ₃ layer, and a thick film of about 1000 mm is considered to satisfy its 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.
[0005]
It is an object of the present invention to propose a method for forming a compound insulating film that is extremely thin, several tens to several hundreds of millimeters, which is difficult for conventional sputtering, and is convenient for a magnetic head gap layer or a tunnel junction type GMR. To do.
[0006]
[Means for Solving the Problems]
In the present invention, a magnetron cathode provided with a metal target connected to a DC power source, a magnet behind it and an RF coil for increasing the ionization rate in front of the target is provided in a vacuum chamber, and the target and RF for plasma generation are provided. and power applied to the coil, the vacuum introduced into the chamber by controlling the flow rate of the sputtering inert gas and a reactive gas, on a Si substrate opposed to the target or a metal underlying film is formed on the substrate In addition, the above-mentioned object is achieved by alternately forming a metal film and forming an insulating compound of the metal film by plasma of only the RF coil in this order . Further, the metal target and the RF coil are made of aluminum, the argon gas is controlled and introduced into the vacuum chamber, the pressure is adjusted, and power is supplied to the metal target and the RF coil from the DC power source and the RF power source, respectively. After an aluminum film of about 30 mm or less is formed on the Si substrate or the substrate on which the metal underlayer is formed , the power supply to the target is stopped and O _{2 in} addition to the argon gas in the vacuum chamber. Introducing a gas or N ₂ gas to oxidize or nitride the aluminum film with plasma using only an RF coil, and then repeat this film formation and oxidation or nitridation to form an ultrathin insulating film of about 100 mm on the substrate. Thus, an ultrathin insulating film suitable for a gap layer of a magnetic head or an insulating film of a tunnel junction type GMR can be formed. The first compound layer is formed by forming a metal film on a Si substrate provided opposite to the target or a substrate on which a metal underlayer is formed, and forming the metal film into an insulating compound by plasma of only the RF coil. It is also possible to form the compound by reactive sputtering, in which the metal sputtering and the formation of an insulating compound by a reactive gas are simultaneously performed on the first compound layer .
[0007]
DETAILED DESCRIPTION OF THE INVENTION
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 in the practice of the present invention. Reference numeral 1 in the figure denotes an exhaust port 2 connected to a vacuum pump, and sputtering gas such as argon gas. 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 is shown. 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, and is supplied with power from the RF power source 12 via the matching box 11. 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 compound insulating film on the surface. In the case of a thin film head or MR head, a metal film is formed 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 the metal target 6, and if necessary, cooling water is circulated therein.
[0008]
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 adjusting the pressure by introducing an appropriate amount, DC power and high frequency power are input to the metal target 6 and the RF coil 8, respectively. 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.
[0009]
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 insulating film is very thin, has a low leakage current and a high dielectric breakdown voltage, has a good insulation resistance, can form a compound insulating film with no variation in insulation, and reads high-density recording It can be conveniently applied to magnetic heads. Using a variety of metal to the target 6 and compound to form an insulating film are possible, for example, be used to Si, can form a very thin insulating film of SiO _2, N ₂ target Al, the 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.
[0010]
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.
[0011]
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.
[0012]
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.
[0013]
【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 on a low resistance silicon substrate 13 was formed. 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. In addition, 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.
[0014]
Prior to the formation of the compound insulating film, the argon sputtering gas pressure in the vacuum chamber 1 is set to 8 × 10 ⁻⁴ Torr, the target input power is kept constant at 40 W DC, and the input power to the RF coil 8 is changed to change the power on the Si substrate 13. 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.
[0015]
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.
[0016]
Specifically, the direct current power to the target 6 is 130 W, the 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 direct current power to the target is kept at 0 V, the high frequency power to the RF coil 8 is kept at 50 W, the flow rate of the sputter argon gas is kept at 15 sccm, and O ₂ gas is introduced into the 30 sccm vacuum chamber. The Al metal film deposited by generating only the inductively coupled plasma of No. 8 for 60 seconds was plasma oxidized to obtain an Al ₂ O ₃ film. Further, a next metal film was deposited on the Al ₂ O ₃ film with 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 manner, the sputtering step and the compounding step were repeated three times to form an Al ₂ O ₃ film of about 100 mm on the substrate.
[0017]
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.
[0018]
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 the reactive sputtering method are also shown. The reactive sputtering condition is obtained by adding 130 W of direct current power to a target which is one of the conditions for sputtering Al in the compounding condition of the method of the present invention.
[0019]
When the characteristics of the film obtained by the method of the present invention (metal deposition / plasma oxidation lamination method) and the conventional reactive sputtering method are compared, the reactive sputtering film has more variation, and the dielectric breakdown of the film can be reduced with a small voltage. I am waking up. 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 metal deposition / plasma oxidation lamination method of the present invention, an Al film having good wettability with Si is first formed densely on the entire surface of the Si base, and then formed into Al ₂ O ₃ by plasma oxidation. The Al ₂ O ₃ film is presumed to have a good quality film with few defects even in the vicinity of the interface. When a thick film of about 1000 mm was deposited by the method 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. This value also confirms that the film obtained by the method of the present invention is an excellent film comparable to bulk Al ₂ O ₃ .
[0020]
Similar to the method 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.
[0021]
In the embodiment, the example of the Al ₂ O ₃ film is shown, but it can be applied to various insulating films and compound materials such as SiO ₂ and AlN. 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. 9B. It can be implemented by a tripolar or quadrupole type sputtering apparatus capable of forming plasma by ECR (electron cyclotron resonance) or an ECR or microwave sputtering apparatus capable of generating plasma by microwaves 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.
[0022]
【The invention's effect】
As described above, 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 sputtering inert gas and the reactive gas introduced into the vacuum chamber. In this way, a metal film is formed on the substrate and an insulating compound is alternately formed on the substrate, so that the electrical characteristics that were difficult with the conventional sputtering method of about several tens to several hundreds of meters on the substrate Can be formed and can be advantageously applied to the manufacture of high-density hard disk magnetic heads.
[Brief description of the drawings]
FIG. 1 is a cut side view of an apparatus used for carrying out the method of the present invention. FIG. 2 is a characteristic diagram of a voltage applied to the cathode of FIG. 1. FIG. 3 is a relationship diagram between RF coil power and film deposition rate. 4] Diagram of the procedure for carrying out the method of the present invention. [Fig. 5] Chemical composition analysis diagram of the film obtained by the method of the present invention by Auger electron spectroscopy (30Å).
FIG. 6 is a chemical composition analysis diagram (45 mm) of the film obtained by the method of the present invention by Auger electron spectroscopy.
FIG. 7 is a diagram showing the relationship between the leakage current and voltage of the film obtained by the method of the present invention. FIG. 8 is a diagram showing the relationship between the leakage current and dielectric breakdown voltage of the film obtained by the method of the present invention. Explanation of other sputtering equipment that can carry out [Explanation of symbols]
1 vacuum chamber, 3 sputter gas inlet, 4 reactive gas inlet, 5 DC power supply, 6 metal target, 7 magnet, 8 RF coil, 9 magnetron cathode, 10 abnormal discharge prevention circuit, 13 substrate,

Claims (3)

A magnetron cathode provided with a metal target connected to a DC power source, a magnet behind the vacuum source, and an RF coil for increasing the ionization rate in front of the target in a vacuum chamber is provided, and the target and the RF coil are generated for plasma generation. power and, by controlling the flow rate of the sputtering inert gas and a reactive gas introduced into the vacuum chamber, the metal film on the substrate Si substrate or a metal undercoating was provided opposite to the target has been formed A method of forming an ultrathin insulating film, wherein film formation and formation of an insulating compound of the metal film by plasma of only an RF coil are alternately performed in that order . The metal target and the RF coil are made of aluminum, argon gas is controlled and introduced into the vacuum chamber and the pressure is adjusted, and plasma is generated by supplying power from the DC power source and the RF power source to the metal target and the RF coil, respectively. After forming an aluminum film of about 30 mm or less on a Si substrate or a substrate on which a metal underlayer is formed , power supply to the target is stopped, and in addition to argon gas, O ₂ gas or Introducing N ₂ gas to oxidize or nitride the aluminum film with plasma using only an RF coil, and then repeat this film formation and oxidation or nitridation to form an ultrathin insulating film of about 100 mm on the substrate. The method for forming an ultrathin insulating film according to claim 1. A magnetron cathode provided with a metal target connected to a DC power source, a magnet behind the vacuum source, and an RF coil for increasing the ionization rate in front of the target in a vacuum chamber is provided, and the target and the RF coil are generated for plasma generation. The power and the flow rate of the inert gas and reactive gas for sputtering introduced into the vacuum chamber are controlled so that the metal film is formed on the Si substrate provided opposite to the target or on the substrate on which the metal underlayer is formed. the insulating compound of said metal film by only the plasma membrane and the RF coil to form a compound layer of the first layer I a row, the insulating compound into a first layer of compound layer by sputtering and reactive gases metal A method for forming an ultrathin insulating film, wherein the compound is formed by reactive sputtering performed simultaneously.

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