Method of manufacturing electret material

Abstract

To provide a method of manufacturing an electret material, which can inhibit leakage of an electric charge.SOLUTION: A method of manufacturing an electret material includes: an ion implantation step of performing ion implantation to an insulator; a heat treatment step of heat-treating the insulator by supplying energy from the outside after the ion implantation step; and a charging step of imparting an electric charge to an ion within the insulator after the heat treatment step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for producing electret materials. [Background technology]

[0002] Materials that permanently retain an electric charge, like the magnetism of a magnet, are called electret materials, and are mainly used in microphones, motors, etc. Electret materials include those made of organic materials and those made of inorganic materials, and also those that retain an electric charge by inducing polarization through some kind of treatment of these materials, and those that capture the electric charge within the material itself. Various techniques have been proposed for producing electret materials such as those disclosed in Patent Document 1. Among them, there is a prior art technique that involves ion implantation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-021786 A Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional technology, the charge of the ions is used as it is to charge the electret material, so the charge is prone to leak through defects caused by ion implantation, etc. Although heat treatment can be considered to reduce the defects, the effect is insufficient because the charge already stored in the ions leaks due to heat treatment.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and has as its main object to provide a manufacturing method for an electret material capable of suppressing charge leakage. [Means for solving the problem]

[0006] That is, the present disclosure includes the following aspects. <1> an ion implantation step of implanting ions into the insulator; a heat treatment step of heat-treating the insulator by supplying energy from an outside after the ion implantation step; a charging step of imparting electric charge to ions in the insulator after the heat treatment step; A method for manufacturing an electret material comprising the steps of:

[0007] <2> In the ion implantation step, the ions are implanted into the insulator away from the surface of the insulator. <1> A method for producing the electret material according to claim 1.

[0008] <3> a lamination step of laminating an insulating protective film on a surface of the insulator on the side where the ions are implanted, after the ion implantation step or the heat treatment step; <1> A method for producing the electret material according to claim 1.

[0009] <4> When electrons are captured by the ions, the valence band of the insulating protective film is at a higher energy level than the valence band of the insulator. <3> However, it is preferable that the conduction band of the insulating protective film has a higher energy level than the conduction band of the insulator.

[0010] <5> When holes are trapped by the ions, the conduction band of the insulating protective film has a lower energy level than the conduction band of the insulator. <3> However, it is preferable that the valence band of the insulating protective film has a lower energy level than the valence band of the insulator. Effect of the Invention

[0011] The present disclosure can provide an electret material capable of suppressing charge leakage. [Brief description of the drawings]

[0012] [Figure 1]1 is a flowchart showing an example of a method for producing an electret material according to the present disclosure. [Diagram 2] FIG. 2 is a cross-sectional schematic diagram showing an example of an electret material obtained by the manufacturing method of the present disclosure. [Diagram 3] FIG. 3(1) is a schematic diagram showing an example of a case where ions injected into an insulator capture electrons, the insulating protective film is a single layer, and the valence band of the insulating protective film is at a higher energy level than the valence band of the insulator (SiO2 in FIG. 3(1)). FIG. 3(2) is a schematic diagram showing an example of a case where ions injected into an insulator capture electrons, the insulating protective film is a single layer, the valence band of the insulating protective film is at a higher energy level than the valence band of the insulator (SiO2 in FIG. 3(2)), and the conduction band of the insulating protective film is at a higher energy level than the conduction band of the insulator. [Figure 4] FIG. 1 is a schematic diagram showing an example of a structure in which (1) is a Si substrate / insulator SiO2 / first insulating protective film HfO2 / second insulating protective film Si3N4, (2) is a Si substrate / insulator SiO2 / first insulating protective film ZrO2 / second insulating protective film Si3N4, (3) is a Si substrate / insulator SiO2 / first insulating protective film Y2O3 / second insulating protective film Si3N4, and (4) is a Si substrate / insulator SiO2 / first insulating protective film AlxGa1-xO3 / second insulating protective film Si3N4, where ions injected into the insulator capture electrons, the insulating protective film is two-layered, the valence band of the first insulating protective film on the insulator side is at a higher energy level than the valence band of the insulator, and the valence band of the second insulating protective film on the outermost surface side is at a higher energy level than the valence band of the first insulating protective film. [Diagram 5]FIG. 5(1) is a schematic diagram showing an example of a case where an ion injected into an insulator captures a hole, the insulating protective film is a single layer, and the conduction band of the insulating protective film is at a lower energy level than the conduction band of the insulator (SiO2 in FIG. 5(1)). FIG. 5(2) is a schematic diagram showing an example of a case where an ion injected into an insulator captures a hole, the insulating protective film is a single layer, the valence band of the insulating protective film is at a lower energy level than the valence band of the insulator (SiO2 in FIG. 5(2)), and the conduction band of the insulating protective film is at a lower energy level than the conduction band of the insulator. [Figure 6] FIG. 1 is a schematic diagram showing an example in which (1) is substrate Si / insulator SiO2 / first insulating protective film Si3N4 / second insulating protective film Y2O3, (2) is substrate Si / insulator SiO2 / first insulating protective film Y2O3 / second insulating protective film HfO2, and (3) is substrate Si / insulator Si3N4 / first insulating protective film Y2O3 / second insulating protective film HfO2, where ions injected into the insulator capture holes, there are two insulating protective films, the conduction band of the first insulating protective film on the insulator side is at a lower energy level than the conduction band of the insulator, and the conduction band of the second insulating protective film on the outermost surface side is at a lower energy level than the conduction band of the first insulating protective film. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments of the present disclosure will be described. Note that matters other than those specifically mentioned in this specification and necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of the electret material that do not characterize the present disclosure) can be understood as design matters of a person skilled in the art based on the prior art in the field. The present disclosure can be implemented based on the contents disclosed in this specification and the technical common sense in the field. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships.

[0014] In the present disclosure, an ion implantation step of implanting ions into an insulator is performed. a heat treatment step of heat-treating the insulator by supplying energy from an outside after the ion implantation step; a charging step of imparting electric charge to ions in the insulator after the heat treatment step; The present invention provides a method for producing an electret material comprising the steps of:

[0015] Insulators such as SiO2 used in conventional technology have so-called defect levels (defects at various energy positions in the forbidden band), which act as a path for charges in the insulator, and electret materials formed by injecting ions into an insulator to capture charges have poor charge retention performance. In particular, it becomes difficult to retain charges under high electric fields such as those used to drive motors. The present disclosure relates to an electret material of a type that captures an electric charge, and this charge is susceptible to external influences, such as contact with an object or moisture in the surrounding area, causing the charge to be carried away (leaked). This disclosure proposes a method for preventing leakage of electric charge from an electret material by injecting ions into the material to be the electret material, and then reducing the defect level in the material to ensure insulation on the surface of the material to prevent leakage of electric charge. countermeasure)

[0016] FIG. 1 is a flowchart showing an example of a method for producing an electret material according to the present disclosure. As shown in FIG. 1, the method for producing an electret material of the present disclosure includes (1) an ion implantation step, (2) a heat treatment step, and (3) a charging step, and may further include (4) a lamination step after (1) the ion implantation step or after (2) the heat treatment step, as necessary. 2 is a schematic cross-sectional view showing an example of an electret material obtained by the manufacturing method of the present disclosure. The electret material has a substrate 10 and an insulator 20 arranged on the substrate 10, and the insulator 20 is charged with electric charges 30.

[0017] (1) Ion implantation process The ion implantation step is a step of implanting ions into an insulator. In the ion implantation process, it is preferable that the ions are implanted into the insulator away from the surface thereof. In order to suppress leakage of charges trapped in the insulator, the ions are implanted into the insulator at a position away from the surface thereof, and the distance between the ions and the insulator surface is sufficiently large to ensure insulation. Charges have a phenomenon called the tunnel effect, and electrons in particular will stochastically penetrate an insulator even if the insulator is thick. For this reason, it is better to have ions far from the insulator surface, and the ion implantation depth from the insulator surface is preferably 60 nm to 100 nm. Insulators are SiO2, Si3N4, HfO2, ZrO2, Y2O3, Al2O3, and Al x Ga 1-x O3, In x Ga 1-x Examples include As, GaSb, MoS2, and diamond. Ions to be implanted into the insulator include ions of elements such as Al, Ar, As, Au, B, Cl, F, K, N, Ne, and P. The ion implantation dose is 1×10 11 / cm 2 It may be more than that.

[0018] The insulator may be disposed on the substrate. The insulator may be disposed on one side of the substrate, on both sides of the substrate, or on the entire surface of the substrate. The substrate may be Si, Al2O3, diamond, etc. The thickness of the substrate is preferably 500 nm or more. The thickness of the insulator is preferably 200 nm or more. The substrate may be subjected to a HF cleaning process, a H2SO4 / H2O2 cleaning process, etc. prior to depositing the insulator on the substrate. In the case of SiO2, a method of disposing an insulator on a substrate includes a method of heating a Si substrate in a dry atmosphere to oxidize it, etc. The heating temperature is preferably, for example, 1100°C or higher. As a method for disposing an insulator on a substrate, in addition to the above, a method similar to the method exemplified in (4) Lamination step described later can also be used.

[0019] (2) Heat treatment process The heat treatment step is a step of heat treating the insulator by supplying energy from an outside after the ion implantation step. Generally, defects (broken bonds between atoms) can be activated by applying energy such as heat from outside the material, causing them to recombine with nearby atoms. After ion implantation into the insulator, defects occurring in the insulator can be reduced by subjecting the insulator to a heat treatment by supplying energy from outside the insulator. The heat treatment may be performed in a nitrogen-based gas (N2 annealing). In addition, H2 gas may be added to the rare gas during the heat treatment (also called hydrogen sintering). In addition to recombining the broken bonds between atoms, hydrogen sintering also promotes the effect of eliminating defects by bonding the added H with atoms. The heat treatment temperature varies depending on the material, but is preferably 200°C or higher and 600°C or lower. The heat treatment time is preferably 5 minutes or more.

[0020] (3) Charging process The charging step is a step of imparting electric charge to the ions in the insulator after the heat treatment step. Heat treatment causes some of the charge of the injected ions to leak out, but because the ions injected into the insulator act as charge traps, charge leakage from the electret material can be suppressed by performing a charging process that transfers charge from outside the insulator to the charge traps. The charging treatment can be performed using corona discharge, electron beam (electron beam irradiation), photoionization (soft X-rays), or the like.

[0021] (4)Lamination process The lamination step is a step of laminating an insulating protective film on the surface of the insulator on the side where the ions have been implanted, after the ion implantation step or the heat treatment step. To prevent leakage of charges trapped in the insulator, an insulating protective film may be formed and bonded onto the ion-implanted insulator. The insulator can be laminated by a sol-gel method, chemical vapor deposition (CVD), atomic layer deposition (ALD), or the like, and among these, CVD or ALD, which provides good quality of the insulator film, may be used. The insulating protective film is SiO2, Si3N4, HfO2, ZrO2, Y2O3, Al2O3, Al x Ga 1-x O3, In x Ga 1-x Examples of the insulating protective film include As, GaSb, MoS2, etc. The insulating protective film and the insulator may be made of the same material or different materials. The insulating protective film may be laminated on the surface of the insulator on the side into which ions have been implanted. If ions have been implanted on both sides of the insulator, the insulating protective film may be laminated on both sides of the insulator. If ions have been implanted on the entire surface of the insulator, the insulating protective film may be laminated on the entire surface of the insulator. The insulating protective film may be a single layer film made of one type of material layer, or a multilayer film in which two or more layers of different types of materials are laminated. The thickness of the insulating protective film is preferably 100 nm or more.

[0022] When electrons are captured by the ions, a material is used in which the valence band of the insulating protective film has a higher energy level than the valence band of the insulator. However, it is preferable that the conduction band of the insulating protective film has a higher energy level than the conduction band of the insulator. As a method for controlling whether electrons or holes are captured by ions, for example, in the (3) charging step, a method using corona discharge as a charging treatment can be mentioned.

[0023] FIG. 3 is a schematic diagram showing an example in which (1) ions injected into the insulator capture electrons, the insulating protective film is a single layer, and the valence band of the insulating protective film is at a higher energy level than the valence band of the insulator (SiO2 in FIG. 3(1)), and (2) is a schematic diagram showing an example in which ions injected into the insulator capture electrons, the insulating protective film is a single layer, the valence band of the insulating protective film is at a higher energy level than the valence band of the insulator (SiO2 in FIG. 3(2)), and the conduction band of the insulating protective film is at a higher energy level than the conduction band of the insulator. Si shown in FIGS. 3(1)-(2) is the substrate. In the insulator, there are electrons captured by the implanted ions, but at the same time, there may be holes in the insulator. In this case, since the electrons and holes are in the same insulator, they are physically close to each other and may recombine. To prevent this, if a material is selected in which the valence band of the insulating protective film is at a higher level than that of the insulator, as shown in Figure 3(1), the holes will tend to move in a direction that is energetically stable (upward in Figure 3(1)). Therefore, the holes will move into the insulating protective film while diffusing (moving) through the insulator. When holes move from the insulator to the insulating protective film, that is, when the holes move to the insulating protective film, which is more energetically stable, they release energy such as heat. Therefore, since holes that have once moved to the insulating protective film need to be supplied with energy from an external source in order to move back to the insulator, the greater the difference in the valence band levels, the more difficult it becomes for the holes to return to the insulator. In the case of Figure 3(1), the electrons captured in the insulator tend to move in the direction of lower energy (downward in the figure), in contrast to the holes, and so it is probabilistic (quantum mechanical) that they will move to the insulating protective film in the same way as the holes. On the other hand, if the conduction band of the insulating protective film is higher than that of the insulator, as in Figure 3(2), the electrons cannot move to the forbidden band (the energy level where electrons cannot exist) of the insulating protective film, and so tend to remain in the insulator without moving to the insulating protective film. Therefore, recombination of electrons and holes is less likely to occur. In the explanation of FIGS. 3(1) and 3(2) above, it is assumed that the insulator into which ions are implanted is sufficiently thick, since it is possible that holes and electrons move toward the Si substrate side. When the implanted ions are present inside the insulator and away from its surface, and when the ions are far enough away from the Si substrate, if the insulating properties of the insulator are good, the probability of electrons moving to the substrate becomes negligible. On the other hand, the holes may move to the Si substrate side, which is advantageous because it is expected to have the effect of preventing the recombination of electrons. Since holes do not have an electric charge, the electret material does not lose its electric charge even when they recombine with electrons. However, electret materials may come into contact with H2O, ions, pollutants, etc. present in the atmosphere. These substances in the atmosphere may transfer electric charge when they come into contact with the electret material, so if the electrons injected into the insulator are not fixed in the insulator, 1) the electrons that recombine with the holes become able to move within the insulator and the insulating protective film, 2) the electrons move to H2O, etc. adsorbed on the surface of the electret material, and 3) when the H2O, etc. that has received these electrons leaves the electret material, they end up taking away the electric charge from the electret material. Materials that satisfy the conditions shown in Figure 3(1) include SiO2 for the insulator and Si3N4, HfO2, ZrO2, Y2O3, Al2O3, or Al for the insulating protection film. x Ga 1-x Combinations such as O3 are included. Materials that satisfy the conditions shown in Figure 3(2) include SiO2 for the insulator and In for the insulating protective film. x Ga 1-x Examples of such combinations include As, GaSb, and MoS2.

[0024] FIG. 4 shows the cases where ions injected into the insulator capture electrons, where there are two insulating protective films, where the valence band of the first insulating protective film on the insulator side is at a higher energy level than the valence band of the insulator, and where the valence band of the second insulating protective film on the outermost surface side is at a higher energy level than the valence band of the first insulating protective film. (1) is substrate Si / insulator SiO2 / first insulating protective film HfO2 / second insulating protective film Si3N4, (2) is substrate Si / insulator SiO2 / first insulating protective film ZrO2 / second insulating protective film Si3N4, (3) is substrate Si / insulator SiO2 / first insulating protective film Y2O3 / second insulating protective film Si3N4, and (4) is substrate Si / insulator SiO2 / first insulating protective film Al. x Ga 1-x FIG. 13 is a schematic diagram showing an example of O3 / second insulating protective film Si3N4. When ions injected into the insulator have captured electrons and the insulating protective film is two-layered, the same reasoning can be applied as for the single-layered insulating protective film described above. However, because the insulating protective film is two-layered, the holes move from the insulator to the first insulating protective film on the insulator side in search of an energetically stable location, and as they further diffuse from the first insulating protective film to the second insulating protective film on the outermost surface side, the holes become physically separated from the insulator into which the ions were injected, making it difficult for them to recombine with electrons. The case in Figure 4(4) shows an example of using a material whose forbidden band becomes slanted when the composition ratio (x) is gradually changed (grade band gap). In Figures 4(1) to (4), Si3N4 is used for the second insulating protective film, which is the outermost layer. However, since Si3N4 has low moisture permeability and is therefore difficult for moisture to pass through, the outermost second insulating protective film may also be made of Si3N4, as this makes it difficult for moisture to reach the insulator and carry away the charge.

[0025] When holes are trapped by the ions, a material is used in which the conduction band of the insulating protective film has a lower energy level than the conduction band of the insulator. However, it is preferable that the valence band of the insulating protective film has a lower energy level than the valence band of the insulator.

[0026] FIG. 5 is a schematic diagram showing an example in which (1) ions injected into the insulator capture holes, the insulating protective film is a single layer, and the conduction band of the insulating protective film is at a lower energy level than the conduction band of the insulator (SiO2 in FIG. 5(1)), and (2) is a schematic diagram showing an example in which ions injected into the insulator capture holes, the insulating protective film is a single layer, the valence band of the insulating protective film is at a lower energy level than the valence band of the insulator (SiO2 in FIG. 5(2)), and the conduction band of the insulating protective film is at a lower energy level than the conduction band of the insulator. Si shown in FIGS. 5(1)-(2) is the substrate. In the above-mentioned Figures 3 and 4, we have mentioned the case where an electron is captured by an ion, but there are also cases where an ion captures a hole instead of an electron, as shown in Figure 5. The difference between the case where an ion captures an electron and the case where an ion captures a hole is that the energy level of the hole captured by the ion is closer to the valence band. When an ion captures an electron, it is thought to be located at an energy level close to the conduction band of SiO2. If an electron is captured close to the valence band, the probability that this electron will recombine with SiO2 is high, so the probability that the electron can exist is thought to be low. When an ion has a hole trapped in it, the opposite concept can be applied, and it is considered that the energy level of the hole trapped in the ion is close to the valence band. Therefore, when the trapped object is a hole, the relative positions of the conduction band and the valence band are reversed from when the trapped object is an electron. In FIG. 5(1), the conduction band of the insulating protective film is at a lower energy level than the conduction band of the insulator, so that the recombination of electrons and holes can be suppressed by the movement of electrons from the insulator to the insulating protective film. In Figure 5(1), the valence band of the insulating protective film is at a higher energy level than the valence band of the insulator, so that holes in the insulator can move to the insulating protective film, causing the electrons and holes to recombine. On the other hand, in FIG. 5(2), the valence band of the insulating protective film is at a lower energy level than the valence band of the insulator, and the conduction band of the insulating protective film is at a lower energy level than the conduction band of the insulator. Therefore, even if electrons move from the insulator to the insulating protective film, the holes in the insulator tend to remain in the insulator without moving to the insulating protective film, and recombination of electrons and holes can be suppressed better. Materials that satisfy the conditions shown in Figure 5(1) include SiO2 for the insulator and Si3N4, HfO2, ZrO2, Y2O3, Al2O3, or Al for the insulating protection film. x Ga 1-x Combinations such as O3 are included. Materials that satisfy the conditions shown in FIG. 5(2) include a combination of Si3N4 for the insulator and HfO2, ZrO2, or Y2O3 for the insulating protective film.

[0027] FIG. 6 is a schematic diagram showing an example in which (1) is substrate Si / insulator SiO2 / first insulating protective film Si3N4 / second insulating protective film Y2O3, (2) is substrate Si / insulator SiO2 / first insulating protective film Y2O3 / second insulating protective film HfO2, and (3) is substrate Si / insulator Si3N4 / first insulating protective film Y2O3 / second insulating protective film HfO2, where ions injected into the insulator capture holes, there are two insulating protective films, the conduction band of the first insulating protective film on the insulator side is at a lower energy level than the conduction band of the insulator, and the conduction band of the second insulating protective film on the outermost surface side is at a lower energy level than the conduction band of the first insulating protective film. When the ions injected into the insulator capture holes and the insulating protective film is two layers, the same concept can be applied as in the case of a single-layer insulating protective film, but because the insulating protective film is two layers, as electrons move from the insulator to the first insulating protective film on the insulator side and then diffuse from the first insulating protective film to the second insulating protective film on the outermost surface side, the electrons physically move away from the ion-injected insulator, making it difficult for them to recombine with holes. Also, because the valence band of the second insulating protective film is at a lower energy level than the valence band of the first insulating protective film, even if the holes in the insulator move from the insulator to the first insulating protective film, they are unlikely to move from the first insulating protective film to the second insulating protective film, so the recombination of electrons and holes can be better suppressed. [Explanation of symbols]

[0028] 10. Substrate 20. Insulators 30.Charge

Claims

1. an ion implantation step of implanting ions into the insulator; a heat treatment step of heat-treating the insulator by supplying energy from an outside after the ion implantation step; a charging step of imparting electric charge to ions in the insulator after the heat treatment step; A method for manufacturing an electret material comprising the steps of:

2. The method for producing an electret material according to claim 1 , wherein in the ion implantation step, the ions are implanted into the interior of the insulator away from a surface of the insulator.

3. The method for producing an electret material according to claim 1 , further comprising a lamination step of laminating an insulating protective film on a surface of the insulator on a side where the ions have been implanted, after the ion implantation step or the heat treatment step.

4. The method for producing an electret material according to claim 3 , wherein, when electrons are captured by the ions, a valence band of the insulating protective film has a higher energy level than a valence band of the insulator.

5. The method for producing an electret material according to claim 3 , wherein, when holes are captured by the ions, the conduction band of the insulating protective film has an energy level lower than that of the conduction band of the insulator.

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