JP2006045666A - Sputtering target for thin film formation, dielectric thin film, optical disk, and method for producing the dielectric thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the diffusion of water and oxygen from a dielectric protective film by eliminating free oxygen from a thin oxide film without detriment to the characteristics of the film as a dielectric protective film. <P>SOLUTION: A thin film of a mixed oxide comprising niobium oxide and silicon oxide or comprising niobium oxide and titanium oxide is used as a dielectric material for forming a dielectric protective film for an optical disk etc. In a desirable example, a target comprising niobium oxide as a main component and 1 to 30 wt.% of silicon oxide is used in the formation of an oxide thin film by sputtering. In this case, the oxide thin film is formed desirably in a nitrogen atmosphere. A nitrogen-containing oxide thin film is made by sputtering an oxygen-deficient target in the presence of a small amount of added nitrogen. By this way, it is possible to make a thin film having low reducibility and consequent high barrier properties as well as properties equivalent to those of a perfect oxide. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming an oxide thin film.

  In recording optical discs such as inorganic write-once discs, phase change discs, and magneto-optical discs, the recording film made of inorganic material reacts with oxygen or water and changes to oxide or hydroxide, so that it cannot be used over time. In order to prevent this, the optical disc is provided with a transparent dielectric protective film. Similarly, display elements of flat panel displays such as plasma displays and electroluminescent displays are provided with a transparent protective film in order to suppress corrosion due to reaction with oxygen or water. The recording film and the display element film as described above are collectively referred to as a medium film.

  The oxide thin film is an effective thin film as a dielectric protective layer for recording disks and a protective layer for flat panel displays. Although various methods are used as the film formation method, the sputtering method is often used because the film formation time is shortened and the film formation apparatus is simple. At that time, in order to shorten the film formation time, instead of using an oxide with a low sputtering rate, oxygen was partially lost in advance from the oxide to prepare a target with high sputtering efficiency, and oxygen was introduced during film formation. Thus, a method for producing the above thin film by reactive sputtering has been widely used. Further, such a target deficient in oxygen also has the advantage that DC sputtering is possible because the conductivity as a metal is improved, and the equipment can be made cheaper.

  Conventionally, when forming an oxide thin film, any one of the following methods has been adopted as standard.

(A) Method of forming an oxygen thin film by depositing while reacting in an atmosphere containing oxygen using a metal target (B) Adding a small amount of oxygen as it is or filling an oxygen deficiency using an oxide target Then, a method of forming a thin film while compensating for deficient oxygen However, both of the above methods (A) and (B) use an oxide thin film because the amount of oxygen in the oxide thin film is excessive and unstable. In application fields such as a dielectric protective layer of an optical disk, a flat panel display, and a semiconductor, deterioration with time and characteristic change of an oxide film in which oxygen is excessive or unstable is a problem.

  For example, in an oxygen-rich oxide thin film, excessive oxygen is liberated, so if the oxide thin film is active with adjacent metal layers and other layers, the interface with those layers A phenomenon occurs that reacts to form a product and degrades useful properties between layers.

  In order to avoid this, a method of forming a film by nitriding nitrogen of nitride or oxygen of oxide in a reducing atmosphere is known (see Patent Document 1). However, if nitrogen or oxygen is lost until a sufficient effect is obtained by this method, the optical characteristics of the protective film change. Specifically, there is a problem that light absorption by the protective film increases and the effect as a transparent protective film is impaired.

  In addition, in the case of an oxygen deficient state, since the reducing action works more, there is a problem that the amount of oxygen deficiency increases with time and does not bring about an effect suitable for the purpose of forming an oxide film, or it does not continue. Resulting in.

  From this point of view, various devices have been applied to the manufacturing apparatus and forming material for forming an oxide thin film, but there has not yet been obtained a technique that is essentially improved. Remains as.

JP-A-1-133229

  Examples of the problems to be solved by the present invention include the above. It is an object of the present invention to eliminate free oxygen in an oxide thin film and to suppress diffusion of water and oxygen present in the transparent dielectric protective film while maintaining characteristics as a transparent dielectric protective film.

  The invention according to claim 1 is characterized in that the thin film forming sputtering target contains titanium oxide as a main component and oxygen-deficient niobium oxide.

  According to a fourth aspect of the present invention, the dielectric protective film is mainly composed of titanium oxide or niobium oxide, and oxygen is deficient from the stoichiometric composition.

  In the invention according to claim 14, the dielectric protective film manufacturing method includes, as a main component, niobium oxide deficient in oxygen, 1 to 30 wt% of silicon oxide, and a stoichiometric composition ratio of the niobium oxide. Includes a step of performing sputtering using a sputtering target having niobium atoms to oxygen atoms of 2 to 3.

In a preferred embodiment of the present invention, a mixed oxide thin film of niobium oxide and silicon oxide or titanium oxide is used as a dielectric material for forming a dielectric protective film such as an optical disk. As dielectric materials used for protective films of optical disks, etc., mixed oxides of zinc sulfide (ZnS) and silicon oxide (SiO ₂ ) are known, but they are oxidized as an alternative to zinc sulfide for environmental considerations. Niobium is used and zinc (Zn) is not used. In a preferred example, in forming an oxide thin film by sputtering, it is preferable to use a target in which niobium oxide is the main component and silicon oxide is added in an amount of 1 to 30% by weight.

The addition of silicon oxide has the effect of improving the transparency required for the transparent dielectric protective film, but the refractive index of the thin film when viewed with light having a wavelength of 400 nm is 2.4 for Nb ₂ O _5. Silicon oxide has only 1.7. FIG. 1 shows the relationship between the ratio of silicon oxide contained in the transparent dielectric protective film and the refractive index of the transparent dielectric protective film. In optical disk applications, a high refractive index of 2.0 or higher is required to ensure reflectivity, so it is desirable to add silicon oxide up to 30% by weight at the maximum. However, if the optical characteristics required for the transparent dielectric protective film allow, there is no problem even if silicon oxide in an amount exceeding 30% by weight is added.

The oxide thin film functioning as a dielectric protective film is a composite oxide comprising a low electrical resistance niobium oxide having a theoretical composition value of Nb ₂ O ₃ as a main component and containing at least one of silicon oxide and titanium oxide. It is preferable that it is a thing. By using Nb ₂ O ₃ having conductivity, a thin film can be formed by DC sputtering. Moreover, transparency required as a dielectric protective film can be obtained by containing silicon oxide or titanium oxide.

  The complex oxide is preferably thinned in a nitrogen atmosphere. The oxide thin film is preferably produced by reactive sputtering using a target deficient in oxygen and introducing oxygen during film formation from the viewpoint of the sputtering rate as described above. However, when the film is formed by reactive sputtering with oxygen introduced, the oxide thin film contains free oxygen or is in a peroxidized state. Since the oxide in the peroxidized state has a strong reducing action and free oxygen also has the oxidizing action of other adjacent metals, the recording film and the reflective film adjacent to the dielectric protective layer are oxidized in the optical disk or the like. Adverse effects such as reacting with the metal that constitutes, causing the storage durability to deteriorate significantly. Therefore, a nitrogen-containing oxide thin film is produced by sputtering using a target deficient in oxygen and adding a small amount of nitrogen. This makes it possible to produce a thin film that has the same characteristics as a perfect oxide but has a small reducing action and a high barrier property.

  The composite oxide produced in this way is suitable as a dielectric protective layer for optical disks. In particular, in an optical disc, when a layer adjacent to the dielectric protective layer contains at least one metal of Al and Ag, or a metal that is easily oxidized, such as Bi or Fe, is generated by use, such as recording / reproduction or light emission. In the case of having properties, by using a nitrogen-containing oxide thin film having a small reducing action as described above, reaction with those metals can be prevented, and deterioration of the characteristics of the optical disk can be prevented. Highly preferred.

  In a preferred embodiment of the present invention, the method for manufacturing an optical disk includes a step of forming a dielectric protective layer by sputtering that compensates for oxygen vacancies in the oxide thin film by mixing nitrogen. In this way, a nitrogen-containing oxide thin film is formed by adding nitrogen instead of adding a small amount of oxygen during the sputtering process to fill the valence deficient portion of the oxide with nitrogen. Oxide thin films in which nitrogen atoms are mixed in the valence deficient part of the oxide have a material property that maintains the required oxide characteristics in order to suppress the reducing action of the oxygen deficient oxide. Stabilization can be achieved. Therefore, by using this nitrogen-containing oxide thin film as a dielectric protective layer, a reaction with an adjacent recording film or reflection film can be prevented, and an optical disk with little deterioration even when recording and reproduction are repeated is manufactured. be able to.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

  FIG. 2 schematically shows a sputtering apparatus according to an embodiment of the present invention. The sputtering apparatus 100 includes a cathode 11 and an anode 12 disposed in the chamber 10 so as to face each other. A target 20 such as a metal or an oxide is disposed on the cathode 11, and a substrate 13 to be a target for forming a thin film is disposed on the anode 12. The chamber 10 is provided with an introduction port 16 for introducing an inert gas such as argon, and a pipe 17 connected to a vacuum pump (not shown). A high voltage DC power supply 15 is connected to the cathode 11 and the anode 12.

In the sputtering process, the inside of the chamber 10 is evacuated by a vacuum pump, and a DC high voltage is applied between the cathode 11 and the anode 12 while introducing argon gas. As a result, ionized argon (Ar ⁺ ) 14 collides with the target 20, and the target material 22 repelled is formed as a thin film 21 on the substrate 13 disposed on the anode 12. Note that when reactive sputtering is performed, a small amount of oxygen (O ₂ ) or nitrogen (N ₂ ) is introduced into the chamber 10 together with the argon gas.

  FIG. 3 schematically shows the structure of the optical disc according to the embodiment. FIG. 3A shows the appearance of the optical disc 50, and FIG. 3B shows the layer structure of the optical disc 50. As shown in FIG. 3B, the optical disc 50 is formed by laminating a reflective film layer 52, a dielectric protective layer 53, a recording film layer 54, a dielectric protective layer 55, and a cover layer 56 on a substrate 51. . The oxide thin film according to the present invention is formed on the optical disc 50 as the dielectric protective layers 53 and 55.

  Next, each example and comparative example of the optical disc 50 will be described with reference to FIG. FIG. 4A shows the thickness of each layer of the optical disc according to the example and the comparative example. FIG. 4B shows the refractive index and extinction coefficient as the optical constants of the target composition and sputtering deposition atmosphere gas used in the formation of the dielectric protective layer according to each of the examples and comparative examples, and the prepared oxide thin film. Show. The extinction coefficient indicates the degree of light absorption by the thin film, and the larger the value, the greater the light absorption. For comparison, all the materials other than the dielectric protective layer were the same. A disk-shaped substrate 51 made of polycarbonate resin and having a thickness of 1.1 mm and a diameter of 12 cm is provided with spiral grooves having a pitch of 0.320 μm. On this substrate 51, a reflective film layer 52 made of a silver alloy, a dielectric protective layer 53, a recording film layer 54 made of Bi-Ge-N, and a dielectric protective layer 55 were laminated in this order by sputtering. Further, a polycarbonate sheet was bonded from above using an ultraviolet curable resin as an adhesive to produce a light incident side substrate (cover layer) 56 having a thickness of 0.1 mm.

In each of Examples 1-a to 1-c, a mixture of niobium oxide (Nb ₂ O ₃ ) and silicon oxide (SiO ₂ ) was used as a target in sputtering. In the target Nb ₂ O ₃ —SiO ₂ , the amount of SiO ₂ is 18% by weight.

  In Example 1-a, the atmospheric gas used in the sputtering process is obtained by adding 3% oxygen to argon at a gas pressure of 0.2 Pa, and in Example 1-b, 5% oxygen is added to the argon in an amount of 0.0. The gas pressure was 2 Pa. In Example 1-c, 5% nitrogen was added to argon at a gas pressure of 0.4 Pa.

In Examples 2-a and 2-b, a mixture of niobium oxide (Nb ₂ O ₃ ) and titanium oxide (TiO ₂ ) was used as a target in sputtering, and the amount of TiO ₂ was 96 wt. %. In addition, in Example 2-a, the atmospheric gas used in the sputtering process is obtained by adding 3% oxygen to argon at a gas pressure of 0.2 Pa, and in Example 2-b, 5% nitrogen is added to argon. It was added at a gas pressure of 0.4 Pa.

Comparative Example 1-a uses a mixture of niobium oxide (Nb ₂ O ₃ ) and silicon oxide (SiO ₂ ) as a target in sputtering, and the amount of SiO ₂ is 18% by weight. The atmospheric gas used in the sputtering process is a mixture of argon and 5% oxygen at a gas pressure of 0.4 Pa.

  FIG. 4C shows the characteristics (jitter) of the optical discs according to the respective examples and comparative examples. As measurement conditions, an optical disk on which the oxide thin film is formed as the dielectric protective layers 53 and 55, a guide groove surface convex toward the light incident side, a wavelength of 405 nm at a linear velocity of 4.92 m, and an aperture of the objective lens. A random pattern of 1-7 modulation was recorded using an optical head of several 0.85. A multi-pulse type strategy was used for recording, and the window width was 15.15 nsec.

  As can be understood from FIG. 4C, good jitter is obtained in all the examples, and no significant deterioration of jitter is observed even when continuous reproduction is performed.

  On the other hand, in Comparative Example 1-a, the jitter value has deteriorated due to continuous reproduction, and the initial jitter ratio has deteriorated by 20%, and a good value cannot be maintained. As can be seen from FIG. 4B, in Comparative Example 1-a and Example 1-b, the pressure of the sputtering film forming atmosphere gas is higher in the comparative example (Example 1-b: 0.2 Pa, Comparative Example). 1-a: 0.4 Pa), and in Comparative Example 1-a, it is understood that the oxide thin film is in a state in which oxygen is excessive (peroxidation state), and thus the characteristics are deteriorated. That is, in this recording disk, metal bismuth which is easily oxidized is generated in the recording film by recording. Therefore, in the optical disk manufactured so that the oxide is in a peroxidized state by the film forming method of the comparative example, it is free. It is clear that oxygen reacts abruptly with the metal bismuth produced immediately after recording to form a reaction product, which deteriorates the characteristics of the disc.

  On the other hand, in the optical disk produced by adding an appropriate amount of oxygen as in Examples 1-a and 1-b, deterioration of characteristics can be suppressed as shown in FIG. It was confirmed that the film has a sufficient performance as a dielectric protective film.

  However, as can be understood by comparing the film formation atmosphere gases of Examples 1-a and 1-b and Comparative Example 1-a, in the film formation method by sputtering in which oxygen is introduced, the oxygen introduction flow rate and the gas pressure are Adjustments must be made strictly. Therefore, instead of finely adjusting the oxygen introduction amount and the gas pressure, in Example 1-c, when a film was formed by adding a small amount of nitrogen instead of oxygen, the produced oxide thin film was The characteristic as a dielectric protective layer is maintained, and the characteristic is not deteriorated. In the oxide thin film formed by sputtering in which nitrogen is introduced in this manner, nitrogen atoms are mixed in the valence deficient portion of the oxide, and the nitrogen contained suppresses the reducing action of the oxide in the oxygen deficient state. Thereby, the reaction at the interface with the film in contact with the dielectric protective layer can be effectively suppressed, and material stabilization can be realized while maintaining the required oxide characteristics.

In Examples 1-a to 1-c, a mixture of niobium oxide (Nb ₂ O ₃ ) and silicon oxide (SiO ₂ ) was used as a target, but Examples 2-a and 2-b were used as targets. A mixture of niobium oxide (Nb ₂ O ₃ ) and titanium oxide (TiO ₂ ) is used. Example 2-a is formed by sputtering with addition of oxygen, and Example 2-b is formed by sputtering with addition of nitrogen. As shown in FIG. 4 (c), the optical disks of Examples 2-a and 2-b do not show deterioration in characteristics (jitter) due to continuous reproduction. Therefore, it can be seen that even when a mixture of titanium oxide is used as the target, the formed oxide thin film satisfies the performance as the dielectric protective layer.

[Modification]
The present invention produces an oxide thin film that functions as a protective layer for a recording medium such as an optical disk by a sputtering method using a target mainly composed of niobium oxide and containing any one of silicon oxide and titanium oxide. It has the characteristics. Therefore, in the recording medium to which the oxide thin film according to the present invention is applied, there is no limitation on the type of other films. For example, a rewritable recording disk using a phase change material such as SbTe for the recording film or a dye film for the recording film. The present invention can be applied to various optical disks having a protective layer, such as organic dye-type recording disks. Further, the present invention can be applied to a disk using an Al alloy as a reflective film.

  Further, the recording medium to which the oxide thin film according to the present invention is applied is not limited in its layer structure. For example, in addition to a recording medium having a light incident side substrate or a cover layer, a protective layer, a recording film layer, and a reflective layer. One or more recording medium configurations are added to the position of the recording medium having a structure in which another material layer is added, the recording film having two reflective film layers, or the substrate on the light incident side or the light reflecting side. The present invention can be applied to various recording media such as a recording medium capable of multilayer recording, a recording medium such as a read-only disk, and a shape other than a disk, for example, a card-type recording medium.

  In the above embodiment, the oxide thin film according to the present invention is applied to an optical disk. However, the oxide thin film according to the present invention can also be applied as a transparent protective film for flat panel displays and semiconductor elements. This is because the performances required for the protective layer (transparency, oxidation prevention, reduction prevention, etc.) are almost the same.

  Moreover, in the above embodiment, an example of performing sputtering using one target containing niobium oxide and silicon oxide or titanium oxide was shown. Instead, niobium oxide and silicon oxide or titanium oxide were respectively used. It is also possible to adopt a method of forming a film from a plurality of targets at the same time by co-sputtering as a target.

It is a graph which shows the relationship between the silicon oxide ratio contained in a transparent dielectric protective film, and the refractive index of the transparent dielectric protective film. 1 schematically shows a sputtering apparatus according to an embodiment of the present invention. The structure of the optical disk based on an Example is shown typically. 4A shows the thickness of each layer of the optical disk according to the example and the comparative example, and FIG. 4B shows the target composition and sputtering film formation used in the formation of the dielectric protective layer according to each example and the comparative example. The atmospheric gas and the optical constant of the produced oxide thin film are shown, and FIG. 4C shows the characteristics (jitter) of the optical discs according to the examples and comparative examples.

Explanation of symbols

10 Chamber 11 Cathode 12 Anode 13 Substrate 15 High Voltage DC Power Supply 20 Target 21 Thin Film

Claims (18)

  A sputtering target for forming a thin film comprising titanium oxide as a main component and oxygen-deficient niobium oxide.   2. The sputtering target for forming a thin film according to claim 1, wherein the stoichiometric composition ratio of niobium atoms and oxygen atoms is 2 to 3 in the niobium oxide deficient in oxygen.   The thin film-forming sputtering target according to claim 1 or 2, wherein the titanium oxide content is about 96 wt%.   A dielectric protective film comprising titanium oxide or niobium oxide as a main component and having oxygen deficient due to a stoichiometric composition.   5. The dielectric protective film according to claim 4, comprising titanium oxide as a main component, containing 96 wt% of the titanium oxide, and containing niobium oxide.   5. The dielectric protective film according to claim 4, comprising niobium oxide as a main component and containing 1 to 30% by weight of silicon oxide.   The dielectric protective film according to any one of claims 4 to 6, comprising nitrogen.   An optical disc comprising the dielectric protective film according to any one of claims 4 to 7.   A flat panel display comprising the dielectric protective film according to claim 4.   The dielectric protective film manufacturing method including the process of performing sputtering using the sputtering target as described in any one of Claims 1 thru | or 3.   The method of manufacturing a dielectric protective film according to claim 10, wherein the sputtering is performed in an atmosphere in which nitrogen or oxygen is mixed in an inert gas.   The method for manufacturing a dielectric protective film according to claim 11, wherein the atmosphere is an inert gas to which 3% of oxygen is added.   The dielectric protective film manufacturing method according to claim 11, wherein the atmosphere is an inert gas to which 5% of nitrogen is added.   Using a sputtering target containing mainly niobium oxide deficient in oxygen, containing 1 to 30% by weight of silicon oxide, and having a stoichiometric composition ratio of niobium oxide of 2 to 3 of niobium atoms to oxygen atoms. A dielectric protective film manufacturing method including a step of performing sputtering.   15. The dielectric protective film manufacturing method according to claim 14, wherein the sputtering is performed in an atmosphere in which nitrogen or oxygen is mixed in an inert gas.   The dielectric protective film manufacturing method according to claim 15, wherein the atmosphere is an inert gas to which 5% of oxygen is added, and the pressure is 0.2 Pa or less.   The dielectric protective film manufacturing method according to claim 15, wherein the atmosphere is an inert gas to which 3% of oxygen is added, and the pressure is 0.4 Pa or less.   The dielectric protective film manufacturing method according to claim 15, wherein the atmosphere is an inert gas to which nitrogen is added at 5%, and the pressure is 0.4 Pa or less.

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