JP5613125B2 - Method for producing aluminum anodic oxide film having high withstand voltage and excellent productivity - Google Patents

Description

  The present invention relates to a method for producing an aluminum anodized film that can be applied to an anodized film member that requires high voltage resistance. The aluminum anodic oxide film obtained by the production method of the present invention is a vacuum chamber such as a semiconductor or liquid crystal production facility such as a dry etching device, a CVD (Chemical Vapor Deposition) device, an ion implantation device, a sputtering device, etc. Also, an aluminum member having an anodized film based on an aluminum alloy that is useful as a material for components provided in the vacuum chamber, and an aluminum member having an anodized film for an insulating member for power device modules or an insulating portion For example, it is suitably used.

  An anodizing treatment in which an anodized film is formed on the surface of a member made of aluminum or an aluminum alloy as a base material and plasma resistance or gas corrosion resistance is imparted to the base material has been widely performed.

  For example, a vacuum chamber used in a plasma processing apparatus of a semiconductor manufacturing facility and various parts provided in the vacuum chamber are generally configured using an aluminum alloy. However, if the aluminum alloy is used without any treatment (innocent), plasma resistance, gas corrosion resistance, etc. cannot be maintained. For these reasons, plasma resistance, gas corrosion resistance, and the like are imparted by forming an anodized film on the surface of a member made of an aluminum alloy.

  On the other hand, in recent years, due to the miniaturization of the wiring width, with the increase in plasma density, the power input to generate plasma is increasing, and in the conventional anodic oxide film, it occurs when high power is input. High voltage can cause dielectric breakdown in the coating. Since the electrical characteristics change in the portion where such dielectric breakdown occurs, the etching uniformity and the film formation uniformity are deteriorated. Therefore, it is desired to increase the voltage resistance of the anodized film.

  Various techniques for increasing the voltage resistance of the anodized film have been proposed so far. For example, Patent Document 1 proposes a method in which an anodized film is formed in a mixed solution of oxalic acid and formic acid and then anodized again in an alkali borate. However, in this method, an anodizing treatment in an alkali borate requires an expensive rectifier corresponding to a high voltage of several hundred volts or more, and there is a problem in terms of equipment cost.

  Patent Document 2 proposes a method of coating an anodic oxide film on a anodic oxide film with a polyimide film formed using a polyimide precursor. However, this technique requires additional equipment such as electrodeposition of a polyimide precursor.

  Patent Document 3 proposes a method for forming a high voltage endurance barrier type anodic oxide film using an electrolytic solution in which a salt of an inorganic acid is dissolved in a solvent having an alcoholic hydroxyl group. However, even in this technique, there is a problem that the management of the change in the concentration of alcohol in the electrolytic liquid due to the anodizing treatment becomes complicated.

  On the other hand, Patent Document 4 is an anodized film containing sulfur (S), and includes a first film having a large S content on the surface side and a second film having a small S content on the substrate side. A method for forming anodic oxide films having different S concentrations has been proposed. In the above publication, in order to further improve the voltage resistance, a method of performing a cathode electrolytic treatment as a pretreatment before the first film forming step is also proposed. In 3a, in addition to the desmut treatment, the cathode electrolytic treatment is separately performed, so there is room for improvement such as a reduction in productivity.

JP-A-60-204897 JP 2004-59997 A JP 11-229157 A JP 2011-157624 A

  Conventionally, various surface treatment members with high voltage resistance of anodized films and production methods for obtaining such surface treatment members have been proposed, but the complexity of the production process, production cost, and productivity are reduced. There was room for improvement from the viewpoint of the above.

  The present invention has been made paying attention to the above-mentioned circumstances, and the object of the present invention is to increase the productivity without increasing the number of manufacturing steps and reducing the total processing time. The premise is to provide a method for producing an anodized film that is more excellent in voltage resistance.

The present inventors are one of the main factors governing the voltage resistance of the anodized film is a crystallized substance (intermetallic compound such as FeAl ₃ or CuAl ₃ ) existing on the surface of the aluminum alloy substrate, The size of the crystallized product was closely correlated with the voltage resistance, and it was found that the voltage resistance was improved if the crystallized product could be removed efficiently. As a result of intensive investigations on a method for efficiently removing the crystallized substance, the base material in which the size of the crystallized substance is appropriately controlled is generally performed as a pretreatment for the anodic oxide film treatment. Instead of desmut treatment (immersion treatment in an acidic solution such as nitric acid solution without applying electrolysis voltage), the cathode electrolysis treatment may be performed with a predetermined integrated electric quantity. In comparison with the anodized film withstand voltage improvement rate (for example, as shown in the examples described later, with a certain base material (crystallized material size) (cathode electrolysis pretreated anodized film withstand voltage-nitric acid desmut pretreated Anodized film withstand voltage) ÷ Nitrate desmut pre-treated anodized film withstand voltage) is improved by about 10% or more, and it is found that the film thickness for obtaining the desired withstand voltage can be reduced. . Furthermore, in the subsequent anodized film, it was also found that if an anodized film is formed using an anodizing solution containing at least oxalic acid, an anodized film with few cracks can be obtained while maintaining high withstand voltage. The present invention has been completed. Further, in order to improve the wet acid resistance of the film, it is possible to subject the anodized film to a sealing treatment.

That is, in the method for producing an aluminum anodic oxide film according to the present invention, an aluminum alloy base material on which crystallized matter having a crystallized size (average of major axis and minor axis) of 3 μm or more is exposed is degreased with an alkaline solution. Thereafter, the surface of the degreased base material is subjected to cathodic electrolysis with an accumulated electric quantity of 5000 C / dm ² or more without desmutting, and then the cathodic electrolysis using an anodizing solution containing at least oxalic acid. The main point is that an anodized film is formed on the surface of the applied substrate.

  According to the present invention, a crystallized material having a certain size or more is formed on the surface so that the crystallized material on the substrate surface, which is one of the main factors governing the voltage resistance of the anodized film, can be efficiently removed. The exposed base material is subjected to a cathode electrolytic treatment with a predetermined integrated electric quantity instead of the generally performed desmutting treatment before the anodic oxide film treatment, so that the anode can be processed without increasing the number of manufacturing steps. By shortening the oxidation treatment time, the total treatment time can be shortened, and an aluminum anodic oxide film having excellent productivity and high voltage resistance can be easily produced. In addition, according to the present invention, since the anodized film is formed using the anodizing solution containing at least oxalic acid after the cathode electrolytic treatment, a film with few cracks while maintaining high voltage resistance. Is obtained.

  The characteristic feature of the present invention is that, as a pretreatment for the anodic oxide film treatment, the cathode electrolysis is performed with a predetermined integrated electric quantity instead of the desmut treatment on a substrate including a crystallized substance exposed on the surface having a size of 3 μm or more. It is in the point of processing. According to the present invention, a high voltage endurance aluminum anodic oxide film can be easily obtained even if the conventional desmutting treatment is omitted, so that the productivity is further improved. Moreover, since the thickness of the anodized film for obtaining a desired withstand voltage can be reduced by applying a predetermined cathode electrolytic treatment, it is possible to prevent cracks that are factors that reduce the withstand voltage. But it is effective. Furthermore, in the anodic oxide film treatment after the cathode electrolytic treatment, anodization is performed using an anodizing solution containing at least oxalic acid, thereby maintaining aluminum with less cracks while maintaining excellent high voltage resistance. An anodized film can be produced with high productivity.

  In this specification, “without desmut treatment” means (a) after degreasing treatment with an alkaline solution, and (b) prior to cathodic electrolysis treatment, which is usually performed to remove smut. It means not to do it. In addition, between the above (a) and (b), a usual water washing process may be performed (see the examples described later), or a mild pickling process (smut is performed if necessary). Although it does not reach the extent of removal, a pretreatment such as a pretreatment performed before the cathode electrolytic treatment may be performed, and such a mode is of course included in the scope of the present invention.

  Hereinafter, the process of reaching the present invention will be described.

First, one of the main factors governing the voltage resistance of the anodized film was the crystallized material present on the surface of the aluminum alloy substrate, and the anodizing treatment was performed on the cathode electrolytically treated substrate. Anodized film withstand voltage improvement rate (anodized film withstand voltage pre-treated with cathode electrolysis-anodized film withstand voltage with nitric acid desmut pretreated) ÷ treated with nitric acid desmut pretreated with a certain substrate (crystal size) It has been found that the anodized film withstand voltage increases as the size of the crystallized substance increases. This crystallized product is a FeAl ₃ or CuAl ₃ intermetallic compound in which a conductive component or conductive impurity (iron, chromium, copper, etc.) contained in an aluminum alloy is bonded to aluminum, and is short-circuited. As a result, the voltage resistance decreases. As one of the means for removing the crystallized substance, the above-mentioned Patent Document 4 proposes a cathode electrolytic treatment, and the crystallized substance can be removed by the cathode electrolytic treatment. It is described that the withstand voltage of the aluminum member is further improved because the anodizing treatment can be performed without receiving, and in the examples, degreasing → desmut treatment → cathode electrolytic treatment is performed before the anodization treatment. Is disclosed.

  However, according to the results of subsequent studies by the present inventors, the cathode electrolytic treatment can remove only the crystallized material exposed on the surface of the aluminum alloy base material, and therefore the base material containing a crystallized material having a small size. Then, it was found that the effect of removing the crystallized substance by the cathode electrolytic treatment was small. As a result of examining in detail the relationship between the size of the crystallized product and the voltage resistance improvement effect of the anodized film after the cathode electrolytic treatment, the crystallized product size (average of the major axis and the minor axis) is larger than 3 μm. When the cathode electrolysis treatment is performed on the base material containing the crystallized substance with a predetermined integrated electric quantity, the withstand voltage can be improved by about 10% or more compared with the case where the cathodic electrolysis treatment is not performed. It has been found that the film thickness for obtaining can be reduced. Moreover, this cathode electrolytic treatment can be performed in place of the desmut treatment which is one of the pretreatments usually performed before the anodic oxide film treatment. In the general pretreatment process of degreasing → desmut treatment. If the cathode electrolysis treatment is performed instead of the desmut treatment, and then the anodization treatment is performed, a desired withstand voltage improving effect can be obtained. That is, the method of the present invention performs degreasing → (desmut treatment is omitted) → cathode electrolytic treatment as a pretreatment of the anodic oxide film treatment, and there is no problem of an increase in the number of manufacturing steps due to the cathode electrolytic treatment. As described above, according to the method of the present invention, the desmut process can be omitted, and the manufacturing process is different from the above-described embodiment of Patent Document 4 that adopts the desmut process as an essential element as in the past. . Furthermore, according to the above method, since the anodizing time can be shortened, the total treating time can be shortened and the productivity is further enhanced.

  In addition, as a method for removing the crystallized substance that adversely affects the withstand voltage improvement, in addition to the cathode electrolytic treatment, for example, a method for producing a substrate without crystallized substance, a method for minimizing the crystallized substance, etc. However, these are not realistic methods. That is, the crystallized product is a natural product in the aluminum alloy, and as long as an aluminum alloy base material is used, the generation of crystallized product is inevitable, and the former method is difficult to realize. As the latter method, in order to minimize the crystallized product, for example, it is necessary to increase the rolling rate. In this case, the plate thickness of the aluminum alloy substrate is reduced to form a desired anodic oxide film. It is not possible to ensure a predetermined thickness. In addition, when trying to obtain an aluminum alloy base material having a predetermined thickness, it is necessary to perform rolling from a plate having a large thickness, which necessitates a large-scale apparatus and a complicated manufacturing process, resulting in an increase in manufacturing cost. . Therefore, in the present invention, attention was paid to cathode electrolytic treatment as a method for efficiently removing crystallized substances from the surface of the aluminum alloy substrate.

  Thus, as a pretreatment for the anodic oxide film treatment, desmut treatment is performed after degreasing the aluminum alloy base material on which the crystallized material including the crystallized material having a crystallized size of 3 μm or more is exposed on the surface. By performing a predetermined cathode electrolytic treatment instead, the action of removing a crystallized substance by the cathode electrolytic treatment can be efficiently exhibited. As a result, there is no need to increase the rolling rate when obtaining an aluminum alloy substrate, the voltage resistance of the anodized film is improved, and the thickness of the anodized film for obtaining the desired voltage resistance can be reduced. Such an anodized film can be manufactured at low cost. Further, according to the present invention, in the degreasing treatment using an alkaline solution and the subsequent desmutting treatment that are generally performed before the preparation of the anodic oxide film, the cathode treatment can be performed instead of the desmutting treatment. Since the anodizing time can be shortened without increasing, the total processing time can be shortened, and as a result, the productivity can be further improved.

  In addition, by applying a predetermined cathode electrolytic treatment, the thickness of the anodized film for obtaining a desired withstand voltage can be reduced, but this prevents cracks, which are factors that lower the withstand voltage. It is also effective in doing.

  Furthermore, in the present invention, since an anodizing solution containing at least oxalic acid is used in the anodized film treatment after the cathode electrolytic treatment, the crack resistance is further enhanced while maintaining high voltage resistance.

  Hereinafter, the production method of the present invention will be described in detail in the order of steps.

  First, an aluminum alloy base material (hereinafter, referred to as an aluminum alloy base material) in which a crystallized product containing a crystallized product having a crystallized size (average of major axis and minor axis) of 3 μm or more is exposed may be used. ).

  In addition, even when the same treatment was performed using an aluminum alloy substrate having a crystallized size of less than 3 μm, a remarkable effect was not recognized in terms of the improvement rate of withstand voltage (Examples described later) See). A significant effect is observed even with a large crystallized product having a crystallized size of 5 μm or more. From the standpoint of improving the withstand voltage rate, the larger the size of the crystallized substance, the better the effect.However, if it is too large, the withstand voltage itself decreases too much. Since the anodized film for obtaining takes time and productivity is lowered, the size of the crystallized product is preferably 40 μm or less, and more preferably 20 μm or less.

  In the present invention, an aluminum alloy is used as the base material. The said aluminum alloy will not be specifically limited if it is normally used for formation of an anodic oxide film, For example, aluminum alloys, such as 6061 and 5052 prescribed | regulated to JISH4000, can be used. A commercially available aluminum alloy can also be used as the aluminum alloy.

  Next, the aluminum alloy base material is immersed in an alkaline solution, and etching of 10 μm or less is performed mainly for degreasing. The degreasing treatment is a method that is usually used before the anodic oxide film treatment in order to remove processing oil or the like attached during the processing of the aluminum member. In the present invention, as the alkaline solution, for example, sodium hydroxide, potassium hydroxide, etc. Is preferably used. The concentration of the alkali solution may be appropriately controlled based on the surface properties of the aluminum member so that a desired removal action can be obtained, but is preferably about 1 to 30% by mass. Moreover, it is preferable to control the immersion temperature (treatment temperature) of the alkaline solution to approximately 15 to 70 ° C. In order to efficiently carry out the etching with the alkaline solution, it is more preferably controlled to approximately 30 to 50 ° C. preferable. The treatment time with the alkaline solution may be appropriately controlled from the viewpoints of productivity, etching amount, etc., but is generally preferably about 1 to 10 minutes.

  The aluminum alloy after the degreasing treatment is preferably sufficiently washed with water. As a method for washing the aluminum alloy with water, shower washing or ultrasonic washing in water is suitable. Moreover, you may perform preliminary processes, such as a pickling process, as needed.

Next, the aluminum alloy base material after degreasing is subjected to cathodic electrolysis with an accumulated electric quantity of 5000 C / dm ² or more without desmut treatment. Cathodic electrolytic treatment means that the aluminum alloy substrate is immersed in an acid, and an electrolytic voltage is applied to flow the current so that the aluminum member becomes a negative electrode, thereby treating the member. On the other hand, in the anodic oxide film treatment, an electrolytic voltage is applied to flow an electric current so that the aluminum member becomes an anode to oxidize the member, which is in a direction opposite to the cathode electrolytic treatment. It differs in that it performs processing.

  Examples of the acid used for the cathode electrolytic treatment include various acid solutions such as sulfuric acid, nitric acid, and oxalic acid. These acids may be used alone or in combination of two or more. Of these, nitric acid is preferred. When an aqueous nitric acid solution is used as the acid, the concentration is preferably 1% by mass or more (more preferably 10% by mass or more, more preferably 15% by mass or more), and 50% by mass or less (more preferably 40% by mass or less, further preferably Is preferably 30% by mass or less).

  The temperature (liquid temperature) at which the cathode electrolytic treatment is performed is preferably 5 ° C. or higher (more preferably 15 ° C. or higher). The higher the treatment temperature, the shorter the time required to remove the crystallized product, and the productivity is further improved. The higher the liquid temperature, the shorter the time required for removing the crystallized product. However, it is usually preferably 60 ° C. or lower (more preferably 50 ° C. or lower).

The current density of the current that flows during the cathode electrolytic treatment is preferably 1 A / dm ² or more (more preferably 3 A / dm ² or more, and even more preferably 5 A / dm ² or more), and 100 A / dm ² or less (more preferably 50 A / dm ² or less, more preferably 20 A / dm ² or less). Within the above range, if the current density is 50 A / dm ² or less, the crystallized product can be removed in a short time without using expensive equipment. Further, when the current density is 5 to 20 A / dm ² , the time required for removing the crystallized substance can be shortened.

In the present invention, it is important that the treatment time (energization time) of the cathode electrolytic treatment is 5000 C / dm ² or more in terms of accumulated electric quantity [current density (C / dm ² ) × time (seconds)]. As shown in the examples described later, when the cumulative amount of electricity in the cathodic electrolysis is less than 5000 C / dm ² , the crystallized product cannot be sufficiently removed, and the desired withstand voltage improvement effect cannot be obtained. It was. A preferable integrated quantity of electricity in the cathode electrolytic treatment is 10,000 C / dm ² or more. In addition, although the upper limit is not specifically limited, when productivity etc. are considered, it is preferable to control to 30000 C / dm < ² > or less in general.

  Examples of the electrode used at the time of the cathode electrolytic treatment generally include electrodes such as platinum, carbon-based, and titanium. From the viewpoint of high voltage resistance, low cost, long life, and the like, glassy carbon It is preferable to use a dense amorphous carbon electrode as described above. Glassy carbon includes carbon fiber and the like. That is, the titanium electrode is not suitable for production management because the resistance of the electrode and further the voltage increase when the anodic oxide film is formed. In addition, the platinum electrode is expensive and inappropriate from the viewpoint of cost. In addition, a graphite-based electrode is generally used as the carbon-based electrode, but the solution soaks into the electrode during cathode electrolytic treatment, and gas is generated inside the electrode. The graphite material is pulverized from the electrode by the force due to volume expansion at this time. Since it peels as a body, volume reduction is large and life is short. On the other hand, if a glassy carbon electrode is used, all the above-mentioned problems can be solved, and an anodic oxide film having a high withstand voltage and a long life can be produced at a low cost.

  The aluminum alloy after the cathode electrolytic treatment is preferably sufficiently washed with water. As a method for washing the aluminum alloy with water, shower washing or ultrasonic washing in water is suitable.

  By the above pretreatment (degreasing step with an alkaline solution and cathodic electrolysis treatment), crystallized substances that adversely affect the voltage resistance are effectively removed from the surface of the aluminum alloy substrate.

  Next, the substrate subjected to the cathode electrolytic treatment is immersed in an anodizing solution containing at least oxalic acid to form an anode, and an electrolytic treatment is performed to form an anodized film on the surface of the substrate.

  In the present invention, it is important to use an anodizing solution containing at least oxalic acid as the anodizing solution. The factors governing the voltage resistance of the anodic oxide film are cracks in the film in addition to the crystallized substances described above. In order to significantly reduce the cracks in the anodic oxide film and further increase the voltage resistance, This is because it is preferable to apply an acid film.

  That is, as a general anodizing treatment liquid, organic acids such as oxalic acid and formic acid; inorganic acids such as phosphoric acid, chromic acid, and sulfuric acid can be mentioned, but the withstand voltage is improved while significantly reducing the occurrence of cracks. From this point of view, it is necessary to use a treatment liquid containing at least oxalic acid. The oxalic acid concentration in the anodizing solution may be appropriately controlled so that the desired effect can be effectively exhibited, but is generally controlled in the range of 20 g / L to 40 g / L. Is preferred.

  In the present invention, the anodic oxidation treatment liquid only needs to contain at least oxalic acid. Unless the desired effect is hindered, a mixed acid obtained by mixing other commonly used anodic oxidation treatment liquid other than oxalic acid with oxalic acid. It can also be. Examples of other anodizing treatment liquid used in the present invention include formic acid, phosphoric acid, chromic acid, sulfuric acid and the like, and these can be used alone or in combination of two or more. These acids are preferably used generally in the range of 0 g / L to 4 g / L.

  The temperature (liquid temperature) at which the anodizing treatment is performed is preferably about 10 ° C to 35 ° C. If the processing temperature is less than 10 ° C., the current density becomes small, the film forming speed becomes very slow, and the productivity may be deteriorated. On the other hand, when the treatment temperature exceeds 35 ° C., there is a risk of dissolution due to chemical reaction of the film depending on the shape of the aluminum alloy substrate. A more preferable treatment temperature is 15 ° C. or more and 25 ° C. or less.

  In addition, what is necessary is just to adjust suitably the electrolytic voltage (surface film formation voltage) and processing time when performing anodizing process suitably so that a desired anodized oxide film may be obtained. For example, regarding the electrolysis voltage, if the electrolysis voltage is low, the current density becomes small and the film formation rate becomes slow. On the other hand, if the electrolysis voltage is too high, the anodized film tends not to be formed due to dissolution of the film by a large current. Since the influence of the electrolysis voltage is related to the composition of the electrolytic treatment solution to be used, the temperature at which the anodizing treatment is performed, and the like, it may be set as appropriate.

  In the above, the manufacturing method of the anodic oxide film concerning this invention was demonstrated.

  The anodized film obtained by the production method of the present invention is excellent in voltage resistance and significantly reduces the occurrence of cracks. For example, it is provided in a vacuum chamber of a semiconductor or liquid crystal production facility, or in a vacuum chamber. It can be suitably used for a clamper, a shower head, a susceptor and the like.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and can be implemented with modifications within a range that can meet the above and the following purposes. These are all included in the technical scope of the present invention.

Example 1
(Preparation of aluminum alloy substrate)
In this example, a rolled material (base material) of 6061 alloy defined in JIS H 4000 was used as the aluminum alloy base material, and a test piece of size: 25 mm × 35 mm (rolling direction) × 1 mm ^t was cut out and its surface A plurality of samples that were subjected to chamfering were used. Specifically, the base materials having four types of crystallized material sizes shown in Table 1 are prepared from a base material having a different rolling rate and a surface portion and a center portion of the base material, By measuring the size, four types of substrates were obtained. In the cutting, the samples were cut so that the distances from the surface of the base material were equal, and the samples cut in this way were used as the same substrate.

  The size of the crystallized material on the surface of the substrate was measured as follows. First, the substrate was embedded in a resin (acrylic resin) and the surface was polished. At this time, the polishing amount of the substrate surface was made as small as possible. Next, the surface of the substrate was observed with SEM, and among the crystallized substances observed in the field of view of 180 μm × 230 μm, three were selected in the order of large crystallized substances. The size of the crystallized product is the average of the major axis (the longest part of the crystallized substance) and the minor axis (the longest part in the direction perpendicular to the major axis) of each crystallized substance. The SEM observation was performed at three random locations, and the average size of a total of 9 crystallized products was defined as the crystallized product size of the substrate.

(Degreasing process)
Next, the sample cut out as described above was immersed in a 50 ° C.-15 wt% NaOH aqueous solution for 2 minutes and then washed with water to clean the surface.

(Cathode electrolysis process)
Next, a glassy carbon electrode was used for the anode, a nitric acid solution was used as the cathode electrolytic treatment solution, and the cathode electrolytic treatment was performed under the conditions shown in Table 1, followed by washing with water to prepare a sample whose surface was cleaned (degreasing → cathode Electrolytic treatment).

  For comparison, a sample whose surface was cleaned by washing with water after being immersed in a 40 ° C.-20 wt% HNO solution for 2 minutes as a desmutting step instead of the cathode electrolysis treatment was prepared ( Degreasing → desmut treatment).

(Anodizing process)
Next, each sample was anodized at a liquid temperature of 15 ° C. and a constant voltage of 80 V using a mixed acid of oxalic acid solution 25 g / L and sulfuric acid 0.1 g / L as an anodizing solution. Then, it washed with water and produced the anodic oxide film of the film thickness shown in Table 2. Further, the current value during the anodizing treatment was recorded together with the anodizing time.

(Measurement of anodized film thickness)
The film thickness of the anodized film in each sample was measured using an eddy current film thickness meter. The measurement is performed five times on the same part, and the average value is set as the film thickness of the part, and the same operation is performed on other parts so that the film thickness on the entire surface of the sample can be evaluated. The average film thickness at the part was defined as the film thickness of the anodized film (all samples were approximately 50 μm).

(Withstand voltage measurement)
With respect to the withstand voltage of each sample, a withstand voltage tester (“TOS5051A”, manufactured by Kikusui Electronics Co., Ltd.) is used, the + terminal is connected to a needle-shaped probe, and is brought into contact with the anodized film, and the − terminal is an aluminum alloy A voltage was applied to the substrate and a voltage when a current of 1 mA or more flowed was defined as a withstand voltage. Note that the evaluation of the withstand voltage was performed at the minimum withstand voltage. This is because, in the case of a semiconductor manufacturing apparatus, since dielectric breakdown occurs at the lowest withstand voltage in the substrate, it is preferable to evaluate at the minimum withstand voltage. In calculating the minimum low voltage, the voltage resistance was measured at 10 locations per sample as described above, and a total of 2 samples (10 locations / sample × 2 samples = 20 locations) were measured. Values and standard deviations were determined, and the average value −2 × standard deviation was determined as the minimum withstand voltage.

(Evaluation of voltage resistance and productivity)
In the evaluation of the withstand voltage, a case where the withstand voltage improvement rate at 50 μm was 10% or more was determined to be acceptable (◯), and a value less than 10% was determined to be unacceptable (×).

  Further, productivity was evaluated as follows. That is, for each sample (degreasing → cathode electrolytic treatment → anodic oxide film treatment or degreasing → desmut treatment → anodic oxide film treatment) having the anodized film (film thickness: about 50 μm) obtained as described above. The minimum withstand voltage is obtained, and if the minimum withstand voltage does not reach 2000V, the target film thickness is changed to 80 μm [original film thickness (about 50 μm) +30 μm], and the anodized film is again applied under the same conditions. The minimum withstand voltage was manufactured and measured (for example, No. 3 in Table 2).

  On the other hand, when the minimum withstand voltage of the anodic oxide film (film thickness: about 50 μm) in each sample reaches 2000 V, the target film thickness is set to 20 μm [original film thickness (about 50 μm) −30 μm], An anodized film was prepared under the same conditions, and the minimum withstand voltage was measured (for example, No. 1, 2, 4, 5 in Table 2).

  For each sample, from the two minimum withstand voltages and film thicknesses obtained as described above, the film thickness at which the minimum withstand voltage is 2000 V is calculated by proportional calculation, and the anodizing treatment time at which the film thickness is obtained, and The cathodic electrolysis time (or desmutting time) was determined from current and time profile data calculated in advance by experiments.

  Then, the total processing time (cathode electrolysis process and anodization process) required to produce the anodized film thickness necessary for the withstand voltage (minimum withstand voltage) measured as described above to be 2000V. The total processing time in Table 2, B) in Table 2 is the total processing time when the desmutting treatment was performed instead of the cathode electrolytic treatment (the total processing time in the desmutting step and anodizing step, A in Table 2). ) (A> B) was determined to be acceptable (O), and the same or longer (A ≦ B) was determined to be unacceptable (X).

  In the rightmost column of Table 2, a “judgment” column is provided, the withstand voltage improvement rate at 50 μm is 10% or more, and the difference in processing time (AB in Table 2) is positive (> 0) ) Was determined to be acceptable (O), and those not satisfying either one were determined to be unacceptable (x). Here, in Table 2, A is the total processing time of “Degreasing → Desmutting → Anodizing” (comparative example), and B is the total processing of “Degreasing → Cathode electrolysis → Anodizing”. It's time.

  These results are also shown in Table 2.

  From these results, it can be considered as follows.

First, no. 1 to 3 are examples in which the production conditions of the present invention are adopted, and a base material on which a crystallized product including a crystallized product having a crystallized size of 3 μm or more is exposed is subjected to cathodic electrolytic treatment after degreasing. As shown in Table 2, the withstand voltage improvement rate at a thickness of 50 μm was 10% or more because the anodization was performed after the cathode electrolytic treatment was performed under the condition that the cumulative amount of electricity was 5000 C / dm ² or more. . Further, the total treatment time (see B in Table 2) when the minimum withstand voltage is 2000 V when degreasing → cathode electrolysis treatment → anodic oxidation treatment as in the present invention is not performed. The total processing time (see A in Table 2) when the desmut treatment was performed (degreasing → desmut treatment → anodizing treatment) was shortened. This is because the processing time of each step can be shortened by the method of the present invention, and according to the present invention, it has been confirmed that the productivity is remarkably improved.

  In contrast, no. 4 is an example using a base material having a crystallized material size of less than 3 μm (not including a crystallized material of 3 μm or more), and the withstand voltage improvement rate at 50 μm is less than 10%, which improves the withstand voltage. The effect was small. No. When a base material with a small crystallized size was used as in No. 4, the effect of the method of the present invention (the effect of adopting the cathode electrolytic treatment instead of the desmut treatment) was not effectively exhibited, and the desmut treatment was performed. Compared to the case, the processing time was almost the same. This is because the size of the crystallized material on the surface of the base material is too small, so that the crystallized material of only the surface layer of the aluminum alloy base material has been removed even if a predetermined cathode electrolytic treatment is performed.

No. No. 5 is a comparative example in which the cumulative amount of electricity in the cathode electrolysis treatment is less than 5000 C / dm ² , and the withstand voltage improvement rate at 50 μm is less than 10%, and the desired withstand voltage cannot be ensured. This is because the accumulated amount of electricity in the cathodic electrolysis treatment is small, so that the crystallized material on the substrate surface cannot be removed sufficiently.

Claims (1)

After degreasing the aluminum alloy base material on which the crystallized product size of 3 μm or more is exposed on the surface with an alkaline solution,
Without desmut processing
The surface of the degreased base material is subjected to cathode electrolytic treatment with an accumulated electric quantity of 5000 C / dm ² or more using an aqueous solution containing nitric acid ,
Then, the cathode electrolytic treatment to the substrate surface which has been subjected to, manufacturing method of an aluminum anodized film and forming a positive electrode oxide film by using an anodic oxidation treatment solution containing at least oxalic acid.