Anodic oxidation device, anodic oxidation process and method for producing the cathode of the anodic oxidation device

Abstract

Anodic oxidation device for forming a porous layer on a substrate to be treated, comprising: an electrolyte bath filled with an electrolyte solution; an anode and a cathode arranged in the electrolyte solution; and a power supply for applying current between the anode and the cathode in the electrolyte solution, wherein the anode is the substrate to be treated and the cathode is a silicon substrate with a surface on which a nitride film is formed.

Description

[0001] The present invention relates to an anodic oxidation device, an anodic oxidation process and a method for Manufacturing the cathode of the anodic oxidation device. STATE OF THE ART

[0002] Porous silicon enables the surface area of ​​silicon to be increased and is used for various purposes. For example Patent document 1 discloses a use as a gas sensor for detecting gas from nitrogen-containing molecules.

[0003] For uses other than the gas sensor, porous silicon is considered a promising electrode material for batteries. and has attracted attention in recent years, with various uses being disclosed and proposed (Patent Document 2).

[0004] In addition, uses are also being considered as a device structure that utilizes the fine structure of porous silicon (FET). (Patent document 3), or as a light-emitting device (Patent document 4), etc. proposed.

[0005] Therefore, porous silicon is expected to be used for a wide range of applications. Porous silicon will generally formed by anodic oxidation (for example, patent document 5). In particular, porous silicon is formed by a Silicon substrate for forming porous structures on the anode side and a metal electrode on the cathode side are arranged in a hydrofluoric acid solution. An electrochemical reaction is applied. Platinum is used as the cathode material, taking into account its resistance to RF. or a metal with high conductivity, such as copper, with a platinum coating is used.

[0006] To create a porous layer on the silicon substrate on the anode side, uniformly over the entire surface of the substrate To form a cathode, the opposite electrode must also be of a similar size. For this purpose, an electrode with a requires a comparatively large area.

[0007] Forming such a large-area electrode with platinum is extremely expensive. On the other hand, in the case of the coating, hydrofluoric acid seeps through gaps. it penetrates the coating layer and etches the underlying metal. In this case, not only is the cathode material degraded, but also the material produced by the The porous silicon formed by anodic oxidation becomes contaminated by metal because impurities dissolve in the chemical solution, leading to a Deterioration of the properties occurs if a sensor or a FET is subsequently formed.

[0008] As described, the choice of cathode material is extremely difficult, since hydrofluoric acid is used for anodic oxidation. There are Processes using carbon or silicon, which apparently do not etch, but in the case of carbon, impurities tend to accumulate. to dissolve, and in the case of silicon, silicon dissolves in the chemical solution, leading to fluctuations in the anodic Oxidation rate.

[0009] In particular, in the application of the device, patent document 6 suggests, for example, combining a metal such as platinum with silicon, to cover carbon or a non-metallic resin to create an electrode material for a low-metallic anodic oxidation process to prevent contamination. This covering can reduce contamination. However, this covering is a procedure that... metal electrodes are inserted into silicon or other materials, and there are concerns about an insertion process prior to anodic oxidation treatment. is required, and about seepage of the chemical solution from the introduced part, etc. Furthermore, the electrochemical reaction This is an extremely strict condition in an RF solution, and there are concerns regarding surface roughening or seepage. contained substances, etc., even in these materials. LITERATURE LIST PATENT LITERATURE Patent document 1: WO 2015 / 189889 A1 Patent document 2: JP 2018-065734 A Patent document 3: JP 2005-093664 A Patent document 4: JP H08-083940 A Patent Document 5: JP 2008-71782 A Patent Document 6: JP 2011-26638 A BRIEF DESCRIPTION OF THE INVENTION TECHNICAL PROBLEM

[0010] As described above, there are expectations regarding porous silicon in various applications. However, in order to qualitatively To obtain high-quality porous silicon, it is necessary to use a cathode with resistance to electrochemical reactions in an RF solution. and without metallic to avoid contamination, etc. Furthermore, there is the problem that a cost-effective cathode material cannot be obtained.

[0011] The present invention was made with regard to the problems described above, and one object of it is to a cathode material for anodic oxidation to form porous silicon through an electrochemical reaction in an RF solution to provide a cathode material that is resistant to electrochemical reaction in an RF solution and is not metallic exhibits impurities, etc., and is also more cost-effective than a conventional cathode material. It is also a task of the The present invention aims to provide high-quality porous silicon at lower costs than previously possible. SOLUTION TO THE PROBLEM

[0012] To achieve the object, the present invention provides an anodic oxidation device for forming a porous layer on a substrate to be treated, comprising: an electrolyte bath filled with an electrolyte solution; an anode and a cathode, which are in the are arranged in an electrolyte solution; and a power supply for applying current between the anode and the cathode in the electrolyte solution, where the anode is the substrate to be treated and the cathode is a silicon substrate with a surface on which a nitride film is formed.

[0013] Such an anodic oxidation device has a cathode which is a silicon substrate with a surface on which a A nitride film is formed. Therefore, the cathode exhibits resistance to electrochemical reactions in an RF solution and has no metallic properties. It is free of impurities, etc., and is also cost-effective. Therefore, high-quality porous silicon can be produced at a lower cost than before. be manufactured.

[0014] Furthermore, in this case the cathode is preferably a silicon substrate with a surface from which a natural oxide film is removed. and on which a nitride film is formed.

[0015] With such a cathode, high-quality porous silicon can be produced at lower costs than before.

[0016] In addition, the present invention provides an anodic oxidation process for applying current between an anode and a Cathode positioned in an electrolyte solution to form a porous layer on a substrate to be treated, arranged in the electrolyte solution, where The substrate to be treated is used as the anode and a silicon substrate with a surface on which a nitride film is formed is used as the cathode. is used.

[0017] In such an anodic oxidation process, a silicon substrate with a surface on which a nitride film is formed is used as the cathode is used. Therefore, the cathode exhibits resistance to electrochemical reactions in an RF solution and has no metallic components. It removes impurities, etc., and is also cost-effective. Therefore, a high-quality porous material can be produced using the anodic oxidation process. Silicon can be produced at lower costs than before.

[0018] In addition, in this case preferably a silicon substrate is used, which is obtained by removing a natural oxide film from a surface a silicon substrate obtained by heat treatment in a non-oxidizing gas atmosphere other than a nitrogen gas atmosphere is and a nitride film is then formed on its surface by heat treatment in a nitrating gas atmosphere, as a silicon substrate with the Surface used on which the nitride film is formed.

[0019] In this way, if a silicon substrate with a nitride film formed on a surface from which a natural oxide film The removed material, used as a cathode, provides a high-quality porous silicon at a lower cost than before with greater certainty. be manufactured.

[0020] Furthermore, the present invention provides a method for producing a cathode of an anodic oxidation device, wherein a silicon substrate is introduced into a heat treatment furnace, a temperature is increased to 1000 °C or more and 1350 °C or less A first heat treatment for less than 30 minutes in an atmosphere of a non-oxidizing gas other than nitrogen gas will be carried out during the An elevated temperature is used to remove a natural oxide film from a surface of the silicon substrate, and then a second Heat treatment is carried out with a nitriding gas atmosphere inside the heat treatment furnace to form a nitride film on the surface. to form the silicon substrate.

[0021] Such a method for producing a cathode of an anodic oxidation device makes it possible to produce a cathode of an anodic Oxidation device, resistance to exhibits electrochemical reactions in an RF solution and contains no metallic impurities, etc., at a lower cost than before to produce.

[0022] Furthermore, in this case, in the first heat treatment, preferably an H2 gas, an Ar gas or a mixture thereof is used as a non- Oxidizing gas is used.

[0023] If the non-oxidizing gas during the first heat treatment is such a gas, a natural oxide film can be formed with greater certainty. removed and a cathode of an anodic oxidation device that exhibits resistance to electrochemical reactions in an RF solution and contains no metallic impurities, etc., and can be produced at lower costs than before. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0024] As described above, in the anodic oxidation device and the anodic device according to the invention, The oxidation process uses a silicon substrate with a surface on which a nitride film is formed as the cathode. Therefore, the cathode exhibits resistance to electrochemical reactions in an RF solution, contains no metallic impurities, etc., and is also cost-effective. This means that high-quality porous silicon can be produced at a lower cost than before.

[0025] Furthermore, the inventive method for producing a cathode of an anodic oxidation device enables a cathode an anodic oxidation device that exhibits resistance to electrochemical reactions in an RF solution and is non-metallic to produce items containing impurities, etc., at a lower cost than before. List of characters Fig. 1 is a diagram showing an example of a heat treatment sequence in the manufacture of a cathode of an anodic An oxidation device according to the present invention is shown. Fig. 2 is a schematic view showing an example of an anodic The oxidation device according to the present invention is shown. Fig. 3 is a SEM image of the surface of the cathode material after anodic oxidation. Oxidation treatment in an example. Fig. 4 is a SEM image of the surface of the cathode material after anodic oxidation treatment in Comparative example 1. DESCRIPTION OF THE EXECUTION FORMS

[0026] As described above, there are expectations regarding porous silicon in various applications, but in order to qualitatively To obtain high-quality porous silicon, it is necessary to use a cathode with resistance to electrochemical reactions in an RF solution. and to obtain one without metallic contamination, etc. Furthermore, no cost-effective cathode material can be procured. Therefore, a An anodic oxidation device is desired that can produce high-quality porous silicon at a lower cost than before.

[0027] The inventors of the present invention have thoroughly investigated the problems described above and found that using a silicon substrate with a formed nitride film, wherein the nitride film is a passive film exhibiting high resistance exhibits resistance to hydrofluoric acid and can withstand an electrochemical reaction as the cathode of an anodic oxidation device, high-quality porous silicon can be produced at lower costs than before, and completed the present invention.

[0028] The present invention is described in detail below, but is not limited thereto.

[0029] The present invention provides an anodic oxidation device for forming a porous layer on a substrate to be treated. ready, comprising: an electrolyte bath filled with an electrolyte solution; an anode and a cathode arranged in the electrolyte solution; and a power supply for applying current between the anode and the cathode in the electrolyte solution, wherein the anode is the component to be treated The substrate is and the cathode is a silicon substrate with a surface on which a nitride film is formed.

[0030] Such an anodic oxidation device has a cathode which is a silicon substrate with a surface on which a A nitride film is formed. Therefore, the cathode exhibits resistance to electrochemical reactions in an RF solution and has no metallic properties. It removes impurities, etc., and is also cost-effective. Thus, according to the anodic oxidation device, a high-quality porous surface can be produced. Silicon can be produced at lower costs than before.

[0031] Furthermore, in this case the cathode is preferably a silicon substrate with a surface from which a natural oxide film is removed and applied to which forms a nitride film.

[0032] Such a cathode does not contain any impurities that are present in the natural oxide film, and exhibits a coating formed on it, solid and fine nitride film, and therefore high-quality porous silicon can be produced with greater certainty at lower costs than before. be manufactured.

[0033] Here, the anodic oxidation device according to the present invention is described in more detail with reference to Fig. 2. Fig. Figure 2 is a schematic view showing an example of the anodic oxidation device according to the present invention. In the anodic Oxidation device 6 according to the present invention comprises a silicon substrate as the substrate 2 to be treated (anode) and a cathode 1 in arranged in an electrolyte bath 5, wherein the electrolyte bath 5 is filled with an electrolyte solution 4 such as an RF solution, such that the The substrate to be treated, 2, is completely immersed. A silicon substrate with the same shape as the substrate to be treated serves as cathode 1. 2 and a surface on which a nitride film is formed. This prevents metallic contamination from the cathode.

[0034] A porous layer can be formed on the surface of the substrate 2 to be treated by applying the substrate 2 to be treated and The cathode 1 is connected by a power supply 3, as shown in Fig. 2, and current is applied.

[0035] In addition, the present invention provides an anodic oxidation process for applying current between an anode and a Cathode positioned in an electrolyte solution to form a porous layer on a substrate to be treated, arranged in the electrolyte solution, where The substrate to be treated is used as the anode and a silicon substrate with a surface on which a nitride film is formed is used as the cathode. is used.

[0036] In such an anodic oxidation process, a silicon substrate with a surface on which a nitride film is formed is used as the cathode is used. Therefore, the cathode exhibits resistance to electrochemical reactions in an RF solution and has no metallic components. It removes impurities, etc., and is also cost-effective. Therefore, a high-quality porous material can be produced using the anodic oxidation process. Silicon can be produced at lower costs than before.

[0037] In addition, in this case preferably a silicon substrate is used, which is obtained by removing a natural oxide film from a surface a silicon substrate is obtained by heat treatment in an atmosphere of non-oxidizing gas other than nitrogen gas and on whose surface then forms a nitride film through heat treatment in a nitrating gas atmosphere, as a silicon substrate with the surface used, on which the nitride film is formed.

[0038] When such a silicon substrate with a surface on which a nitride film is formed is used as a cathode, there are few Impurities are removed because the natural oxide film is eliminated and the adhesion of the nitride film to the silicon substrate is improved. Therefore, a High-quality porous silicon can be produced at lower costs than before.

[0039] Furthermore, the present invention provides a method for manufacturing a cathode of an anodic oxidation device, wherein a silicon substrate is introduced into a heat treatment furnace, a temperature is increased to 1000 °C or more and 1350 °C or less A first heat treatment for less than 30 minutes in an atmosphere of a non-oxidizing gas other than nitrogen gas will be carried out during the An elevated temperature is used to remove a natural oxide film from a surface of the silicon substrate, and then a second Heat treatment is carried out with a nitriding gas atmosphere inside the heat treatment furnace to form a nitride film on the surface. to form the silicon substrate.

[0040] Such a method for producing a cathode of an anodic oxidation device makes it possible to produce a cathode of an anodic Oxidation device that exhibits resistance to electrochemical reactions in an RF solution and contains no metallic impurities, etc. exhibits the ability to produce at lower costs than before.

[0041] The method for producing a cathode of an anodic oxidation device according to the present invention is described below Described with reference to Fig. 1.

[0042] Fig. 1 is a diagram showing an example of a heat treatment sequence in the manufacture of a cathode of an anodic The oxidation apparatus according to the present invention is shown. First, a silicon substrate is introduced into a heat treatment furnace. (substrate loading), the temperature is increased to 1000 °C or more and 1350 °C or less, and a treatment (first heat treatment) for less than 30 minutes in an atmosphere of a non-oxidizing gas other than nitrogen gas at the elevated temperature. In this way, the natural oxide film, etc., on the surface of the silicon substrate is removed, so that the substances contained in the natural oxide film are exposed. Impurities can be removed, and at the same time the surface of the silicon substrate is activated. The process described here... “Activating” means exposing the unsaturated bonds of silicon, rather than covering the surface of the silicon substrate with to passivate hydrogen or oxygen. Furthermore, in this case, the time required to perform the initial heat treatment is not particularly significant. The duration is limited as long as it is less than 30 minutes, however, the treatment is preferably carried out for 1 minute or longer.

[0043] Next, the gas introduced into the heat treatment furnace is switched to a nitriding gas such as nitrogen in order to to form a nitride film on the activated surface of the silicon substrate (second heat treatment). In this way, a fine and strong Nitride film is formed.

[0044] Subsequently, the temperature in the heat treatment furnace is lowered and the silicon substrate with the formed nitride film is removed. removed (substrate discharge).

[0045] One function of the non-oxidizing gas during the first heat treatment is to remove the natural oxide film, etc., from the surface to remove, and the gas is preferably a hydrogen gas, an argon gas, or a mixture thereof. Argon is generally non-explosive and therefore a readily identifiable material. Gas to be handled.

[0046] The use of such a gas as the non-oxidizing gas in the first heat treatment makes it possible to create a cathode an anodic oxidation device that exhibits resistance to electrochemical reactions in an RF solution and is non-metallic to produce products containing impurities, etc., at lower costs than before and with greater certainty.

[0047] If a cathode material formed in this way is used as a cathode material at the time of anodic oxidation, an anodic Oxidation can be carried out without degrading the cathode, even if the cathode is used for a long time, due to its resistance. The resistance of the nitride film formed at high temperatures to hydrofluoric acid is extremely high.

[0048] It should be noted that a nitride film is an insulating film, but it is thin and undergoes anodic oxidation using a Since a comparatively high voltage is to be used, anodic oxidation can be carried out using the nitride film. although there is a parasitic resistance component.

[0049] However, it should be noted that in the present invention, to achieve an anodic oxidation similar to that achieved by, If the cathode is a platinum electrode, a higher voltage is required than in the case of a platinum electrode if the current value is the same. The application time must be longer if the applied voltage is to remain the same. However, the exact magnitude of the change is not yet determined. depends on the actual anodic oxidation environment (conditions) such as the thickness of the nitride film or electrolyte solution, etc., and therefore It is advisable to carry out a test beforehand.

[0050] It should be noted that it is sufficient for the nitride film to have a thickness of about 0.1 nm to 10 nm. The present invention This is a process for the direct nitriding of silicon with nitrogen, and it is difficult to form an even thicker nitride film. The nitride film is preferably as thin as possible. EXAMPLES

[0051] The present invention is described in more detail below with reference to an example and comparative examples, but the present The invention is not limited to this. [EXAMPLES]

[0052] First, a p-type silicon substrate (boron-doped and with normal resistance) with a diameter of 200 mm was provided. The substrate was placed in a vertical oven and the temperature inside the oven was increased from 800 °C to 1200 °C at a rate of 5 °C / min. During this time, argon gas was introduced at a flow rate of 10 l / min. After reaching 1200 °C, the annealing process was continued for 10 minutes with The process was carried out with unchanged gas flow (first heat treatment), and then the interior of the furnace was switched to nitrogen gas and 10 A treatment was carried out for a period of minutes (second heat treatment). Afterwards, the gas was switched back to Ar-gas, and the temperature was adjusted. The temperature was reduced from 3 °C / min to 800 °C, and the silicon substrate with a nitride film formed on it was removed. The thickness The thickness of the nitride film at that time was approximately 1 nm.

[0053] Next, the silicon substrate with the nitride film formed as described above was immersed in an anodic The oxidation device was arranged as shown in Fig. 2 and was used as the cathode at the time of anodic oxidation. The substrate was incorporated into a mixed A solution of 50% HF:ethanol:water = 1:1:1 (1 L each) immersed according to the volume ratio. A p-type silicon substrate (with a A tube with normal resistance and a diameter of 200 mm was used as the anode. It should be noted that the distance between the two The electrodes were set at 5 cm. Additionally, anodic oxidation was accelerated by applying an electric current of 1.7 A for 30 minutes. The process was carried out. After applying an electric current, porous silicon was formed on the silicon substrate on the anode side, and the thickness The thickness of the formed porous layer was 10 µm when observed using SEM.

[0054] The surface of the cathode material after the anodic oxidation treatment was examined using SEM. Fig. 3 shows an SEM- Image of the surface of the cathode material after anodic oxidation treatment in the example. When considering the surface of the material acting as the cathode... The silicon substrate used with the nitride film formed according to the present invention after anodic oxidation treatment using SEM was No roughening of the surface, etc., is considered. [Comparison example 1]

[0055] A p-type silicon substrate (boron-doped and with normal resistance) with a diameter of 200 mm was provided.

[0056] The substrate was arranged in an anodic oxidation device and, at the time of anodic oxidation, without special The substrate was used as a cathode during treatment. It was immersed in a mixed solution of 50% HF:ethanol:water = 1:1:1 (1 L each) based on... The volume ratio was immersed. A p-type silicon substrate (with a normal resistance) with a diameter of 200 mm was also used. used as the anode. Note that the distance between the two electrodes was set to 5 cm. Additionally, the anodic Oxidation was carried out by applying an electric current of 1.7 A for 20 minutes. After applying the electric current, porous material was observed. Silicon was formed on the anode side, and the thickness of the porous layer formed was 10 µm when observed using SEM.

[0057] The surface of the cathode material after the anodic oxidation treatment was examined using SEM. Fig. 4 shows an SEM image. the surface of the cathode material after anodic oxidation treatment in comparative example 1. When considering the surface of the material as After anodic oxidation treatment of the silicon substrate used in the cathode by SEM, a roughening of the surface was observed due to the electrochemical reaction on the surface is considered. [Comparative example 2]

[0058] A p-type silicon substrate (boron-doped and with normal resistance) with a diameter of 200 mm was provided.

[0059] Using the substrate as the anode and platinum as the cathode, these were arranged in an anodic oxidation device and An anodic oxidation was performed. The substrate was dissolved in a mixed solution of 50% HF:ethanol:water = 1:1:1 (11 each). immersed to the volume ratio. Note that the distance between the two electrodes has been set to 5 cm. Additionally Anodic oxidation was carried out by applying an electric current of 1.7 A for 12 minutes. After applying the electric current... Porous silicon was formed on the anode side, and the thickness of the porous layer formed was 10 µm when observed using SEM.

[0060] From a comparison of Example 1 and Comparative Example 1, no roughening of the surface was observed after the anodic oxidation treatment. The surface, etc., of the silicon substrate used as a cathode with the formed nitride film is considered in the example, while on the surface of the silicon substrate used as a cathode without any treatment after the anodic oxidation treatment, especially in Comparative example 1 considered surface roughening due to the electrochemical reaction. Accordingly, it was shown that that the silicon substrate used as the cathode, without special treatment in comparative example 1, has no resistance to electrochemical Reactions in an RF solution were observed, silicon was dissolved in the electrolyte solution, which caused a fluctuation in the anodic oxidation rate. caused, and that it was difficult to produce high-quality porous silicon.

[0061] Furthermore, when using the porous silicon substrate with the nitride film formed according to the present invention as Cathode material (example) compared to the use of platinum (comparative example 2) due to the electrode resistance, some time is needed to achieve a to obtain a porous silicon layer of the same thickness, but it was possible to produce an equivalent porous silicon.

[0062] Furthermore, there are problems regarding metallic contamination and high costs, etc., when platinum is used for the cathode. (Comparative example 2), whereas when using a silicon substrate with a nitride film formed according to the present invention as Cathode material (example) gives no concerns regarding metallic impurities, etc., and a High-quality porous silicon can be produced at lower costs.

[0063] It should be noted that the present invention is not limited to the embodiments described above. The embodiments are only examples, and all examples that have essentially the same feature and the same functions and effects. show how those in the technical concept disclosed in the claims of the present invention are in the technical scope contained in the present invention. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was generated automatically and is solely for the better information of the Readers' contributions were included. The list is not part of the German patent or utility model application. The DPMA assumes no liability whatsoever. for any errors or omissions. Cited patent literature

[0000] WO 2015 / 189889 A1

[0009] JP 2018065734 A

[0009] JP 2005093664 A

[0009] JP H08083940 A

[0009] JP 2008071782 A

[0009] JP 2011026638 A

[0009]

Claims

[1] Anodic oxidation device for forming a porous layer on a substrate to be treated, comprising: an electrolyte bath filled with an electrolyte solution; an anode and a cathode, which are arranged in the electrolyte solution; and a power supply for applying current between the anode and the cathode in the electrolyte solution, where the anode is the substrate to be treated and The cathode is a silicon substrate with a surface on which a nitride film is formed. [2] Anodic oxidation device according to claim 1, wherein the cathode is a silicon substrate with a surface of which a natural The oxide film is removed and a nitride film is formed on it. [3] Anodic oxidation process for applying current between an anode and a cathode in an electrolyte solution to form a porous layer on a substrate to be treated, arranged in the electrolyte solution, wherein the substrate to be treated is used as the anode a silicon substrate with a surface on which a nitride film is formed is used as the cathode. [4] Anodic oxidation process according to claim 3, wherein a silicon substrate obtained by removing a natural oxide film from a Surface of a silicon substrate by heat treatment in a non-oxidizing gas atmosphere other than a nitrogen gas atmosphere is obtained, and a nitride film is then formed on its surface by heat treatment in a nitrating gas atmosphere, as a silicon substrate. is used on the surface on which the nitride film is formed. [5] Method for producing a cathode of an anodic oxidation device, wherein a silicon substrate is placed in a heat treatment furnace is introduced, a temperature is increased to 1000 °C or more and 1350 °C or less, a first heat treatment for less than 30 minutes in an atmosphere of a non-oxidizing gas other than nitrogen gas at the elevated temperature to create a natural to remove the oxide film from a surface of the silicon substrate, and then a second heat treatment with a nitriding gas atmosphere inside the heat treatment furnace is used to form a nitride film on the surface of the silicon substrate. [6] A method for producing a cathode of an anodic oxidation device according to claim 5, wherein in the first heat treatment a H2 gas, an Ar gas or a mixture thereof is used as a non-oxidizing gas.