JP2010121151A - Method for treating surface - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent local dissolution of aluminum or an aluminum alloy. <P>SOLUTION: A method for treating a surface includes: performing a desmutting treatment by immersing the surface of an electrode formed on the surface of a semiconductor substrate and containing aluminum as a main component into a nitric acid solution having a nitric acid concentration of 9-20 mol/L (step S3); forming a film substituted with zinc on the surface of the electrode by applying a first zincate treatment to the surface of the electrode (step S4); exfoliating the film substituted with zinc by immersing the electrode into a nitric acid solution having a nitric acid concentration of 9-20 mol/L (step S5); forming a film substituted with zinc on the surface of the electrode by applying a second zincate treatment to the surface of the electrode (step S6); and forming a plating film on the surface of the film substituted with zinc by an electroless plating treatment (step S7). <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a surface treatment method, and more particularly to a surface treatment method for forming a metal film on an aluminum electrode of a semiconductor element by an electroless plating method.

  Conventionally, a method of joining a semiconductor device to a mounting substrate or a package through bumps such as solder has been performed. Here, the electrode of the element is often made of aluminum or an aluminum alloy. However, since these are poor in wettability with solder and cannot firmly adhere to the solder, it is necessary to form an under bump metal film in order to join the solder bump to the electrode of the element.

  The under bump metal film is formed, for example, by plating nickel (Ni) or the like on the surface of an aluminum electrode that is a surface electrode of a semiconductor device. An electroless plating method is known as a plating treatment method. The electroless plating method is a method in which, for example, nickel ions in a solution are reduced and deposited on the surface of a material to be plated with a reducing agent such as hypophosphorous acid. However, if the electroless plating process is directly performed without any treatment on the aluminum electrode, the adhesion between the aluminum electrode and the plating film is poor. This is because the surface of the aluminum electrode is oxidized and an aluminum oxide film is present on the surface of the aluminum electrode. Therefore, there is a problem that a plating film having practical adhesion cannot be formed.

  The following three examples are generally given as plating pretreatment methods for improving the adhesion between the aluminum electrode and the plating film. As a first conventional example, a method has been proposed in which a zincate treatment is performed on the surface of an aluminum electrode, and after aluminum and zinc are replaced, an electroless nickel plating treatment is performed (for example, see Non-Patent Document 1 below).

  As a second conventional example, a method of performing electroless nickel plating after activating the surface of an aluminum electrode with palladium has been proposed (for example, see Non-Patent Document 2 below). As a third conventional example, a method of performing autocatalytic electroless nickel plating after directly replacing an aluminum electrode with nickel has been proposed (for example, see Non-Patent Document 3 below).

  Of the three examples described above, the first conventional example is the most prevalent method as a pretreatment method for the electroless plating treatment on the aluminum electrode. In the first conventional example, the zincate treatment is to immerse the surface of the aluminum electrode in an alkaline solution (zincate solution) such as zinc oxide. Thus, the aluminum oxide film on the surface of the aluminum electrode is removed, and aluminum is replaced with zinc, thereby forming a zinc film on the surface of the aluminum electrode.

  In the first conventional example, in a state where zincate treatment is performed and aluminum is replaced with zinc, it is immersed in an electroless nickel plating solution, and nickel is deposited in synchronization with the dissolution of the zinc film. By doing so, since the aluminum oxide film is not interposed at the interface between the nickel and the aluminum electrode, a nickel plating film having good adhesion to the aluminum electrode and good electrical and thermal conductivity is formed. The

However, when the zincate treatment is performed only once, the particles become large and rough zinc film, and the adhesion strength of the nickel plating film to be formed subsequently is not practical. Accordingly, the zincate film (zinc film) formed by the first first zincate process is peeled off using a nitric acid (HNO ₃ ) solution, and the second second zincate process is performed again, whereby the particles become finer. A method for forming a dense zinc film has been proposed. This method of performing the zincate treatment twice is called a double zincate method, and a nickel plating film having practical adhesion strength can be formed by this.

  As a processing procedure of the double zincate method, first, after performing a degreasing process, an etching process is performed using an acid solution or an alkali solution. And after performing a desmut process using nitric acid, a 1st zincate process is performed. Next, after the zincate film is peeled off, a second zincate treatment is performed. In addition, the process which wash | cleans the surface of an electrode with water is included between a certain process and the following process.

  Further, as a pretreatment when directly performing electroless plating on the silicon surface, a method of immersing in a solution in which an oxidizing agent is mixed with hydrofluoric acid (see, for example, Patent Document 1 below), hydrofluoric acid, There has been proposed a method of dipping in a plating pretreatment solution containing nitric acid and a compound that generates oxygen in an aqueous solution (for example, see Patent Document 2 below). According to these methods, since the electroless plating process is performed after the silicon surface is activated, the adhesion between the silicon surface and the plating film is improved.

Japanese Patent No. 3975625 Japanese Patent Publication No. 6-5670 Hiroshi Yamada, three others, “Planar LSI Interconnection Technology”, IEICE Technical Report, September 25, 1987, Vol. 87, 37, p. . 13-18 Junji Yamakawa (Koji YAMAKAWA), 2 others, “Bump Formation by Electroless Plating (BUMP FORMATION BY ELECTROLES PLATING)”, IEICE Technical Report, September 25, 1987, Vol. 87, No. 40 , P. 31-36 Yuichi Saito and four others, “Electroless nickel plating using substitution method on aluminum alloy”, Abstracts of 112th Lecture Meeting, Surface Technology Association, 6B-9, p. 109-110

  However, aluminum is an amphoteric metal that dissolves in acid and alkaline solutions. Therefore, in the double zincate method, the aluminum electrode is dissolved and eroded in each step of etching treatment, desmut treatment, zincate treatment, and peeling treatment using an acid solution or an alkali solution.

  Since these dissolutions and erosion are insignificant, there is no problem when electroless plating is applied to general bulk aluminum materials. On the contrary, it becomes a factor that improves adhesion by appropriate roughening. . On the other hand, the aluminum electrode in a semiconductor device has been made finer and the thickness of the aluminum electrode has been reduced, and is generally about 1 μm thick. Thus, when the aluminum film is thin, depending on the pretreatment conditions of electroless plating, there is a problem that the aluminum electrode is dissolved and eroded, and is halved or locally lost.

  Here, since the aluminum electrode in the semiconductor device is formed by a sputtering method or a vapor deposition method, the cleanliness of the surface is high. For this reason, a degreasing process and an etching process are abbreviate | omitted, and melt | dissolution and erosion in these processes can be prevented. However, it is essential to immerse the aluminum electrode in the nitric acid solution in the desmutting treatment and the peeling treatment, and to immerse the aluminum electrode in the alkaline solution in the zincate treatment, and preventing the dissolution and erosion of aluminum in these steps. Can not.

  In general, a nitric acid solution used for desmutting treatment or peeling treatment is produced by diluting commercially available concentrated nitric acid (60 to 70 vol%) approximately twice. The reason is that in the concentrated nitric acid solution, the surface of aluminum is passivated and dissolution does not proceed. Here, if the concentration of nitric acid in the nitric acid solution is too thin, passivation becomes insufficient and dissolution and erosion proceed. On the other hand, if the concentration of nitric acid in the nitric acid solution is too high, the volatility of nitric acid becomes remarkable and the workability deteriorates. Therefore, there is a problem that it is necessary to use a nitric acid solution having an optimum concentration.

  In zincate treatment, aluminum is eluted because zinc is deposited by substituting the surface of aluminum. Theoretically, if the entire aluminum surface is replaced with zinc, the reaction stops and aluminum is eluted. Should be gone. However, in reality, electrons emitted when aluminum is dissolved are supplied from the portion that has become a recess due to the dissolution of aluminum to the projection on which zinc is deposited. For this reason, zinc will precipitate further in a convex part, and since zinc does not precipitate in a recessed part, melt | dissolution of aluminum will not stop. Therefore, if the time for immersing the surface of the aluminum electrode in the zincate solution is lengthened, there is a problem that the local dissolution of aluminum proceeds.

  In addition, Patent Document 1 and Patent Document 2 describe pretreatment of electroless plating treatment, but these techniques are for etching the surface of silicon. Therefore, when the above-described solution is used when an aluminum film is formed on the surface of silicon, there is a problem that hydrofluoric acid in the solution inhibits the passivation of aluminum and dissolution of aluminum does not stop.

  An object of the present invention is to provide a surface treatment method capable of preventing local dissolution of aluminum or an aluminum alloy in order to solve the above-described problems caused by the prior art.

  In order to solve the above-described problems and achieve the object, the surface treatment method according to the first aspect of the invention first cleans the surface of a conductor mainly composed of aluminum. Next, the surface of the cleaned conductor is replaced with zinc, and the formed zinc replacement film is peeled off. The solution used for cleaning the surface of the conductor and stripping the zinc-substituted film is a nitric acid solution in which only nitric acid is diluted, and the nitric acid concentration of the nitric acid solution is 9 mol / liter or more and 20 mol / liter or less.

  In the surface treatment method according to the second aspect of the invention, first, the surface of the conductor mainly composed of aluminum is cleaned. Next, the surface of the cleaned conductor is replaced with zinc, and the formed zinc replacement film is peeled off. The solution used for cleaning the conductor surface and peeling the zinc-substituted film is a mixed solution in which an oxidizing agent that does not form a precipitate on the conductor surface by an oxidation-reduction reaction is added to the nitric acid solution. Furthermore, the nitric acid concentration of the mixed solution is 4 mol / liter or more and 20 mol / liter or less, and the concentration of the oxidizing agent added to the mixed solution is 0.005 mol / liter or more and the solubility of the oxidizing agent in the mixed solution or less. And

  The surface treatment method according to claim 3 is the surface treatment method according to claim 2, wherein the oxidizing agent added to the mixed solution is any one of potassium peroxodisulfate, hydrogen peroxide, and ozone gas. That's it. The total concentration of the oxidizing agent added to the mixed solution is 0.005 mol / liter to 1 mol / liter.

  Further, in the surface treatment method according to the invention of claim 4, in the invention of claim 3, when the oxidizing agent contains ozone gas, the concentration of the ozone gas contained in the oxidizing agent added to the mixed solution is 0.005 mol. / L or more and 0.2 mol / L or less.

  A surface treatment method according to a fifth aspect of the invention is characterized in that, in the invention according to any one of the first to fourth aspects, the conductor is aluminum or an aluminum alloy.

  According to a sixth aspect of the present invention, in the surface treatment method according to any one of the first to fifth aspects, after the zinc-substituted film is peeled off, the surface of the conductor is replaced with zinc again. Next, nickel is electrolessly plated on the surface of the formed zinc replacement film.

  According to each of the above-described inventions, before replacing the surface of the conductor mainly composed of aluminum with zinc, the surface of the conductor is washed with a nitric acid solution having an optimum nitric acid concentration, so that the conductor composed mainly of aluminum is cleaned. After replacing the surface with zinc, the zinc-substituted film can be peeled off using a nitric acid solution having an optimal nitric acid concentration. Thus, by optimizing the nitric acid concentration in the nitric acid solution, the oxidizing power of the nitric acid solution can be increased and the passivation of aluminum can be promoted. Thereby, when the surface of the conductor mainly composed of aluminum is immersed in a nitric acid solution in the cleaning step or the peeling step, dissolution of the exposed portion of the aluminum can be stopped.

  Further, by stopping the dissolution of aluminum in the nitric acid solution, it is possible to promote the dissolution of zinc and other metals formed on the surface of the conductor mainly composed of aluminum. Therefore, it is possible to prevent the surface of the conductor immediately before the replacement step (or the replacement step) from being contaminated with zinc or other metals. As a result, in the replacement step (or re-replacement step), it is possible to minimize the nucleus that causes the formation of the concave portion and the convex portion. Therefore, when replacing the surface of the conductor mainly composed of aluminum with zinc In addition, local dissolution of aluminum can be prevented.

  Moreover, according to invention of Claims 2-6, the density | concentration of nitric acid solution is added to the nitric acid solution used for a washing | cleaning process and a peeling process by adding the oxidizing agent by which an oxidation deposit is not formed on the surface of aluminum by oxidation-reduction reaction. Can be lowered. And since the density | concentration of a nitric acid solution is low, melt | dissolution of aluminum can be suppressed significantly. Moreover, copper (Cu), iron (Fe), other contaminating metals, and the zinc-substituted film formed after the substitution process can be completely dissolved and removed. This can prevent local dissolution of aluminum, particularly in the re-substitution step.

  According to the surface treatment method of the present invention, there is an effect that local dissolution of aluminum or aluminum alloy can be prevented.

  Exemplary embodiments of a surface treatment method according to the present invention will be explained below in detail with reference to the accompanying drawings.

(Embodiment 1)
FIG. 1 is a flowchart showing the processing procedure of double zincate processing. In the flowchart of FIG. 1, first, degreasing treatment is performed on the surface of an electrode mainly composed of aluminum such as aluminum or an aluminum alloy (step S1), and oily dirt adhering to the surface is removed and cleaned. To do. Then, an etching process is performed using an acid solution or an alkali solution (step S2). In the flowchart of FIG. 1, step S1 and step S2 may be omitted. This can prevent dissolution and erosion of the electrode mainly composed of aluminum in the degreasing process and the etching process.

Next, a desmut process is performed using a nitric acid (HNO ₃ ) solution (step S3), and the smut generated by the etching process in step S2 is removed. In step S3, the nitric acid concentration in the nitric acid solution is, for example, not less than 9 mol / liter and not more than 20 mol / liter. The reason will be described later.

  Next, a first zincate process is performed (step S4), and a zincate film is formed on the surface of the electrode mainly composed of aluminum. And the zincate film | membrane formed in step S4 is peeled using a nitric acid solution (step S5). In step S5, the nitric acid concentration in the nitric acid solution is, for example, not less than 9 mol / liter and not more than 20 mol / liter. The reason will be described later. Note that the nitric acid solution used in steps S3 and S5 is not mixed with an acid that inhibits passivation of aluminum, such as hydrofluoric acid. The reason is that when an acid other than nitric acid is mixed with these nitric acid solutions, the passivation of aluminum is inhibited, and dissolution of the exposed portions of aluminum in the nitric acid solution cannot be stopped.

  Next, the second zincate process is performed (step S6). In step S4 and step S6, by performing zincate treatment (double zincate treatment) twice, aluminum in the electrode mainly composed of aluminum is replaced with zinc, and a zinc film is formed on the surface of the electrode mainly composed of aluminum. It is formed. Thereafter, electroless plating is performed (step S7), the zinc film is replaced with, for example, nickel, and nickel is continuously deposited to form a nickel plating film. Thus, by performing the electroless plating treatment after the double zincate treatment, the nickel plating film can be reliably formed on the surface of the aluminum electrode with strong adhesion. In the flowchart shown in FIG. 1, it is assumed that a process of rinsing the surface of an electrode mainly composed of aluminum with water is included between steps, that is, between a certain process and the next process.

(First verification)
Next, as the first verification, the concentration of nitric acid in the nitric acid solution used for the desmutting process and the stripping process is verified. In the first verification, an aluminum-silicon alloy (Al-Si) film having a thickness of 1 μm was formed on one surface of a 6-inch silicon wafer by sputtering. A silicon wafer cut out 30 mm long and 30 mm wide was prepared as a plating substrate. And the sample of Examples 1-3 and Comparative Examples 1 and 2 was created on the following conditions using this board | substrate for plating.

  First, the surface of the Al—Si film on each plating substrate was immersed in normal temperature acetone for 5 minutes, and then sufficiently rinsed with deionized water having a specific resistance of 10 MΩ or more. Subsequently, a desmut treatment, a first zincate treatment, a peeling treatment, and a second zincate treatment were performed in this order.

  Here, the nitric acid concentration in the nitric acid solution used for the desmutting treatment and the peeling treatment was changed for each sample. FIG. 2 is an explanatory diagram showing the nitric acid concentration in the nitric acid solution used for each sample of the first verification and the treatment time. As shown in FIG. 2, the nitric acid solution used in the desmutting treatment and the stripping treatment has a nitric acid concentration of 9 mol / liter in Example 1, a 15 mol / liter sample in Example 2, and a 20 mol / liter sample in Example 3. Created as. In addition, a sample having a nitric acid concentration of 1 mol / liter in a nitric acid solution used for desmutting treatment and peeling treatment was prepared as Comparative Example 1, and a sample having 8 mol / liter was prepared as Comparative Example 2. In the desmutting process, each sample was immersed in the above nitric acid solution for 30 seconds, and in the peeling process, each sample was immersed in the above nitric acid solution for 60 seconds.

  In each sample, the composition of the zincate treatment solution used for the first zincate treatment and the second zincate treatment was as follows: sodium hydroxide 120 g / liter, zinc oxide 20 g / liter, sodium potassium tartrate 50 g / liter, second chloride chloride It shall contain 2 g / liter of iron and 1 g / liter of sodium nitrate. In the first zincate treatment, each sample was immersed in the above-described zincate solution at room temperature for 10 seconds. In the second zincate treatment, each sample was immersed in the above zincate solution at room temperature for 30 seconds. Note that between one treatment and the next treatment, the surface of the Al—Si film was sufficiently rinsed with deionized water having a specific resistance of 10 MΩ or more.

  Then, after the second zincate treatment, the surface of the Al—Si alloy of each sample was sufficiently rinsed with deionized water having a specific resistance of 10 MΩ or more, and then an electroless nickel plating treatment was performed. Thereby, a nickel-phosphorus alloy (Ni-P) plating film having a thickness of about 1 μm was formed on the surface of each sample. The plating solution used for the electroless nickel plating treatment of each sample was 25 g / liter of nickel nitrate, 25 g / liter of sodium hypophosphite, 40 g / liter of sodium malate, 20 g / liter of sodium lactate, and 10 g of glycine. A pH adjusting agent such as sulfuric acid or caustic sodium was added to the composition containing / liter to adjust the pH to 4.8 to 5.0.

  In the electroless nickel plating treatment, each sample was immersed in the above plating solution at a temperature of 82 ° C. to 86 ° C. for about 5 minutes. Then, each sample was completed by thoroughly rinsing with deionized water having a specific resistance of 10 MΩ or more and performing blow drying using nitrogen.

  Next, the surface state of each sample was verified. First, using the fluorescent X-ray method, the film thickness (Al residual film thickness) of the Al—Si film remaining on each of the samples on which the plating process was completed was measured. Then, an arbitrary portion was cleaved, and a width of about 100 μm at an arbitrary portion of the cross section was smoothed by the FIB (Focused Ion Beam) method, and the state of the cross section of the smoothed portion was observed.

  FIG. 3 is an explanatory diagram showing the results of observing the thickness of the Al—Si film and the state of the plating interface for each sample of the first verification. Here, the plating interface is an interface between the Al—Si film and the Ni—P plating film. In FIG. 3, the evaluation of the Al remaining film thickness was made good for samples in which the film thickness of the Al—Si film remaining on the sample exceeded 0.5 μm. In addition, the evaluation of the state of the plating interface was performed by defining a hole having a width to depth ratio of 1: 1 or more and a depth of 0.1 μm or more as pitting corrosion, and performing smooth processing by the FIB method. The presence or absence of pitting corrosion in about 100 μm was observed, and a sample having no pitting was considered good.

  As shown in FIG. 3, in Examples 1 to 3, the film thickness of the Al—Si film remaining on the sample exceeded 0.5 μm, and in Comparative Examples 1 and 2, the Al—Si film remaining on the sample was The film thickness was 0.5 μm or less. Moreover, in Examples 1-3, there was no pitting corrosion in the interface of a plating film, and pitting corrosion was observed in Comparative Examples 1 and 2.

  Thus, when the nitric acid concentration of the nitric acid solution is lower than 9 mol / liter, the Al-Si film on the sample was eluted by 1/2 or more and pitting corrosion occurred, but the nitric acid concentration of the nitric acid solution was 9 mol / liter. In the above case, aluminum elution was suppressed and no pitting corrosion occurred. In addition, the higher the concentration of nitric acid in the nitric acid solution, the more the passivation of aluminum is promoted. However, when the concentration is higher than 20 mol / liter, the volatility becomes remarkable and the workability deteriorates, which is inappropriate. Therefore, it was found that the nitric acid concentration in the nitric acid solution used for the desmut treatment and the stripping treatment is preferably 9 mol / liter or more and 20 mol / liter or less.

  According to the surface treatment method according to the first embodiment, the concentration of nitric acid in the nitric acid solution used for the desmutting treatment and the peeling treatment in the double zincate method is increased to 9 mol / liter or more and 20 mol / liter or less, so that the nitric acid solution The oxidizing power can be strengthened. Thereby, the passivation of aluminum is promoted, and when the surface of the electrode mainly composed of aluminum is immersed in a nitric acid solution, dissolution of the exposed portion of the aluminum can be stopped.

  Further, according to the surface treatment method according to the first embodiment, dissolution of zinc and other metals on the surface of the aluminum electrode can be promoted by stopping dissolution of aluminum in the nitric acid solution. Therefore, it is possible to prevent the surface of the electrode mainly composed of aluminum immediately before the zincate treatment from being contaminated with zinc or other metals. Thereby, in the zincate treatment, the core that causes the formation of the concave portion and the convex portion can be minimized, so that local dissolution of aluminum in the zincate treatment can be prevented.

(Embodiment 2)
Next, a surface treatment method according to the second embodiment will be described. In the second embodiment, the solution used for the desmut process (step S3) and the strip process (step S5) shown in FIG. 1 is a mixed solution in which an oxidizing agent is added to a nitric acid solution. Other processes are the same as those in the first embodiment, and a description thereof is omitted.

  In Embodiment 2, the nitric acid concentration in the mixed solution used for the desmutting treatment and the peeling treatment is preferably 4 mol / liter or more and 20 mol / liter or less. The reason will be described later. The oxidizing agent added to the mixed solution is an oxidizing agent that does not form oxygen precipitates on the surface of aluminum by the oxidation-reduction reaction. Specifically, for example, at least one of potassium peroxodisulfate, hydrogen peroxide, and ozone gas is added. Here, the lower limit of the total added concentration of the oxidizing agent is preferably 0.005 mol / liter or more. The reason will be described later. Further, the upper limit of the total added concentration is set to be equal to or lower than the solubility of the added oxidizing agent in the nitric acid solution. Specifically, for example, when ozone gas is added, it is 0.2 mol / liter or less, and when other oxidizing agent is added, it may be 1 mol / liter or less.

(Second verification)
Next, as the second verification, the type of oxidant and the addition concentration are verified. In 2nd verification, the sample of Examples 4-7 and Comparative Examples 3-5 was created on the following conditions using the board | substrate similar to the board | substrate for plating used for 1st verification. In addition, about the processes other than the desmut process and the peeling process, the same process as the first verification was performed.

  Here, in the second verification, the composition of the mixed solution used for the desmut treatment and the peeling treatment was changed for each sample. FIG. 4 is an explanatory diagram showing the composition and processing time of the mixed solution used for each sample in the second verification. As shown in FIG. 4, in the desmutting treatment and the peeling treatment, the samples of the respective examples were immersed in a mixed solution having the following composition. The sample of Example 4 was immersed in a mixed solution having a nitric acid concentration of 4 mol / liter and an added concentration of potassium peroxodisulfate of 0.005 mol / liter. The sample of Example 5 was immersed in a mixed solution having a nitric acid concentration of 4 mol / liter and an added concentration of potassium peroxodisulfate of 0.1 mol / liter. The sample of Example 6 was immersed in a mixed solution having a nitric acid concentration of 4 mol / liter and a hydrogen peroxide addition concentration of 0.1 mol / liter. The sample of Example 7 was immersed in a mixed solution having a nitric acid concentration of 4 mol / liter and an ozone gas addition concentration of 0.1 mol / liter.

  Further, the sample of Comparative Example 3 was immersed in the same mixed solution as in Example 4 in the desmut treatment, but in the peeling treatment, the nitric acid concentration was 3 mol / liter and the addition concentration of potassium peroxodisulfate was 0.005 mol. / Lit was immersed in a mixed solution. The sample of Comparative Example 4 was immersed in a mixed solution having a nitric acid concentration of 4 mol / liter and an added concentration of potassium peroxodisulfate of 0.004 mol / liter in the desmutting treatment and the peeling treatment. The sample of Comparative Example 5 was immersed in a mixed solution having a nitric acid concentration of 4 mol / liter and a potassium chromate addition concentration of 0.1 mol / liter in the desmutting treatment and the peeling treatment.

  In addition, each sample of an Example and a comparative example was immersed in the above-mentioned nitric acid solution for 30 seconds in the desmut process, and was immersed in the above-mentioned nitric acid solution for 60 seconds in the peeling process.

  FIG. 5 is an explanatory diagram showing the results of observing the thickness of the Al—Si film and the state of the plating interface for each sample of the second verification. As shown in FIG. 5, in Examples 4-7, the film thickness of the Al—Si film remaining on the sample exceeded 0.5 μm, and in Comparative Examples 3 and 4, the Al—Si film remaining on the sample was The film thickness was 0.5 μm or less. Moreover, in Examples 4-7, there was no pitting corrosion in the interface of a plating film, and pitting corrosion was observed in Comparative Examples 3 and 4.

  Thus, it was found that when the solution used for the desmutting treatment and the stripping treatment was a mixed solution in which an oxidizing agent was added to a nitric acid solution, a lower nitric acid concentration was sufficient than using a nitric acid solution to which no oxidizing agent was added. Specifically, the nitric acid concentration in the mixed solution may be 4 mol / liter or more. Moreover, it turned out that the addition density | concentration of the oxidizing agent added to a mixed solution should just be 0.005 mol / liter or more.

  Further, the higher the concentration of nitric acid in the mixed solution, the more the passivation of aluminum is promoted. However, when the concentration is higher than 20 mol / liter, the volatility becomes conspicuous and the workability deteriorates. Therefore, it was found that the composition of the mixed solution used for the desmutting treatment and the peeling treatment preferably has a nitric acid concentration of 4 mol / liter to 20 mol / liter and an oxidizing agent addition concentration of 0.005 mol / liter or more.

  In addition, the upper limit of the addition concentration of an oxidizing agent is below the solubility of the nitric acid solution of each oxidizing agent. Specifically, for example, when adding ozone gas, the addition concentration may be 0.2 mol / liter or less. Moreover, when adding oxidizing agents other than ozone gas, an addition density | concentration should just be 1 mol / liter or less.

  Further, in the sample of Comparative Example 5, since the insoluble chromium oxide compound film (chromate film) was formed on the aluminum surface by chromic acid, the elution of aluminum was remarkably suppressed. However, a zincate film or an electroless nickel-phosphorous plating film could not be deposited in the subsequent steps. Thus, it has been found that the oxidant added to the nitric acid solution may be any oxidant that does not form an oxide precipitate on the surface of aluminum by the oxidation-reduction reaction.

  According to the surface treatment method according to the second embodiment, the same effect as in the first embodiment can be obtained. Further, by adding an oxidizing agent that does not form oxidation precipitates on the surface of aluminum by oxidation-reduction reaction to the nitric acid solution used for the desmutting treatment and the peeling treatment in the double zincate method, the nitric acid concentration can be reduced as compared with the first embodiment. Can be lowered. And since nitric acid concentration is low, melt | dissolution of aluminum can be suppressed significantly.

  Moreover, according to the surface treatment method according to the second embodiment, copper (Cu), iron (Fe), other contaminating metals, and zinc formed after the first zincate treatment can be completely dissolved and removed. it can. This can prevent local dissolution of aluminum, particularly in the second zincate treatment.

  As described above, when this surface treatment method is applied to a method for manufacturing a semiconductor device, local dissolution of an electrode made of aluminum or an aluminum alloy can be prevented.

  As described above, the surface treatment method according to the present invention is useful for manufacturing a semiconductor device in which a plating film is formed on an electrode surface by an electroless plating process. It is suitable for manufacturing a semiconductor device for forming a bump metal film.

It is a flowchart shown about the process sequence of a double zincate process. It is explanatory drawing shown about the nitric acid concentration in the nitric acid solution used for each sample of 1st verification, and processing time. It is explanatory drawing which shows the result of having observed the film thickness of the Al-Si film | membrane, and the state of the plating interface about each sample of 1st verification. It is explanatory drawing shown about the composition and process time of the mixed solution used for each sample of 2nd verification. It is explanatory drawing which shows the result of having observed the film thickness of the Al-Si film | membrane, and the state of the plating interface about each sample of 2nd verification.

Claims (6)

A cleaning process for cleaning the surface of the conductor mainly composed of aluminum;
A replacement step of replacing the surface of the conductor cleaned by the cleaning step with zinc;
A peeling step for peeling the zinc-substituted film formed by the substitution step;
Including
The solution used in the cleaning step and the stripping step is a nitric acid solution obtained by diluting only nitric acid, and the nitric acid concentration of the nitric acid solution is 9 mol / liter or more and 20 mol / liter or less. A cleaning process for cleaning the surface of the conductor mainly composed of aluminum;
A replacement step of replacing the surface of the conductor cleaned by the cleaning step with zinc;
A peeling step for peeling the zinc-substituted film formed by the substitution step;
The solution used in the cleaning step and the stripping step is a mixed solution in which an oxidizing agent that does not form precipitates on the surface of the conductor by an oxidation-reduction reaction is added to a nitric acid solution, and the nitric acid concentration of the mixed solution is 4 mol / liter or more A surface treatment method, wherein the concentration is 20 mol / liter or less and the concentration of the oxidizing agent added to the mixed solution is 0.005 mol / liter or more and below the solubility of the oxidizing agent in the mixed solution.   The oxidizing agent is at least one of potassium peroxodisulfate, hydrogen peroxide, and ozone gas, and the total addition concentration of the oxidizing agent to the mixed solution is 0.005 mol / liter to 1 mol / liter. The surface treatment method according to claim 2, wherein the surface treatment method is provided.   4. The method according to claim 3, wherein when the oxidizing agent contains ozone gas, the concentration of ozone gas contained in the oxidizing agent to the mixed solution is 0.005 mol / liter to 0.2 mol / liter. The surface treatment method as described.   The surface treatment method according to claim 1, wherein the conductor is aluminum or an aluminum alloy. After the peeling step, a re-replacement step of substituting the surface of the conductor with zinc again,
A plating step of electrolessly plating nickel on the surface of the zinc replacement film formed by the resubstitution step;
The surface treatment method according to claim 1, further comprising:

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