KR102012726B1 - Hexavalent Chrome Plating Solution And Crack Free Pulse-Reverse Electroplating Method Using of The Same - Google Patents

Abstract

The present invention relates to a hexavalent chromium plating solution and a pulse-reverse electroplating method optimized for the same, which can form a chromium plating layer with excellent corrosion resistance without a crack. According to the present invention, the plating method is applied to a semiconductor manufacturing process, conventional expensive palladium or nickel plating is substituted to manufacture a diamond tool for a semiconductor process for diamond that is inexpensive and has excellent adhesion and corrosion resistance.

Description

Hexavalent Chrome Plating Solution And Crack Free Pulse-Reverse Electroplating Method Using of The Same}

The present invention relates to a hexavalent chromium plating solution and a crack-free pulse-reverse electroplating method using the same. More specifically, the present invention relates to a crack free chromium plating method using a chrome sulfate bath optimized for forming a crack free plating layer for diamond tools and a pulse-reverse electroplating method optimized for forming a crack free plating layer for diamond tools using the chrome sulfate bath. .

Due to the rapid growth of the global mobile device market such as smartphones and tablet PCs, the demand for technology development related to semiconductor manufacturing is increasing. The semiconductor industry is an equipment industry and requires high technology. The domestic semiconductor industry is weak in technology and has a high external dependency on production equipment and manufacturing technology.

The semiconductor processing process among the semiconductor technologies is one of the technologies that can be localized, the importance of which is becoming more important. Diamond tools are mainly used in semiconductor processing. The diamond tool has a conditioner in which diamond is electrodeposited by plating nickel (Ni) on a disk-shaped plate on which diamond particles are electrodeposited and a SUS substrate. In the diamond tool, the fixed metals used for plating or eluting diamonds or binders may be eluted during processing. The eluted fixed metal causes the wafer to be contaminated to lower the yield, and the dropped diamond particles or the binder cause scratches on the semiconductor surface or cause excessive pressure to block the micropores, causing enormous cost loss.

In order to overcome the problems of the diamond processing tools for semiconductor processing, additional plating is performed as a fixed metal or nickel (Ni) is used to deposit metals such as silver (Ag), copper (Cu), indium (In), and titanium (Ti). Various methods have been tried. Among these methods, a method of minimizing the dissolution of the fixed metal and the dropping of diamond particles and binders by electroplating nickel on the SUS substrate to fix diamond in the form of a composite plating, and additionally plating nickel or palladium (Pd), etc. It is pushing ahead. However, the additional plating process of the nickel or palladium is expensive and the situation is required to replace the plating process.

In some manufacturing processes, a method of performing additional plating using inexpensive chromium (Cr) in place of palladium or nickel has been proposed. The chromium plating has an advantage of improving the surface properties such as high hardness and corrosion resistance of diamond tools due to its high hardness. However, when the thickness of the chromium plating layer increases in the chromium deposition process, there is a problem that an internal stress occurs and cracks are generated. When cracks occur in the chromium plated layer, various chemicals used in the semiconductor production process penetrate into the tool, thereby lowering the corrosion resistance of the diamond tool.

Therefore, if the chromium plating solution and chromium plating process for diamond tools that solve the problem of deterioration of corrosion is solved because no cracks are generated and chemicals do not penetrate, it is possible to replace expensive nickel or palladium plating, thereby inexpensive and high performance diamond tools for semiconductor processing. It is expected to be able to produce.

The patents and references mentioned herein are incorporated herein by reference to the same extent as if each document was individually and clearly specified by reference.

In order to solve the problem of corrosion caused by crack formation of the chromium plating layer for diamond tools, the present invention provides an optimal hexavalent chromium plating solution and an optimal chromium plating solution for forming a chromium plating layer for diamond tools without cracks. An object of the present invention is to provide a pulse-reverse plating method.

Other objects and technical features of the present invention are more specifically shown by the following detailed description, claims and drawings.

In the hexavalent chromium plating method using a chromium sulfate bath and a pulse-reverse electroplating method, the anode current direction plating is performed under conditions of a current density of 38 to 60 A / cm ² and a plating time of 10 msec. One set is performed under the conditions of 12 to 30 A / cm ² density and 0.4 to 1 msec of plating time, and if the total plating time is repeated to 10 to 20 minutes, the crack free chromium is performed. Provided is a hexavalent chromium plating method using a chromium sulfate bath and a pulse-reverse electroplating method, wherein a plating layer is formed.

The optimal chromium sulfate bath used in the chromium plating method of the present invention is 200 to 250 g / L chromic anhydride (CrO ₃ ), 2 to 2.7 g / L sulfuric acid (H ₂ SO ₄ ), 3 to 5 g / L EDTA compound , 50 to 100 g / L ammonium compound, 0.01 to 0.1 g / L polyoxyethylene polymer compound, 5 to 20 g / L oxalic acid compound, 13 to 20 g / L boron compound.

When the hexavalent chromium plating method using the chromium sulfate bath of the present invention is used, there is no crack on the nickel strike plated stainless steal sheet (SUS) substrate and a chromium plating layer having a thickness of 0.926 to 3.39 μm can be formed.

The hexavalent chromium plating solution of the present invention and the pulse-reverse electroplating method optimized thereto have the advantage of forming a chromium plating layer having excellent corrosion resistance since there is no crack.

When the plating method of the present invention is applied to a semiconductor manufacturing process, it is possible to manufacture a diamond tool for semiconductor processing, which is inexpensive but has excellent diamond adhesion and excellent corrosion resistance, replacing conventional expensive palladium or nickel plating.

Figure 1 shows the results of the hull cell test (Hull Cell Test) according to the addition of a complexing agent (Complex Agent).
Figure 2 shows the results of the hull cell test according to the addition of the ion conductor (Ionic Conductor).
Figure 3 shows the results of the hull cell test with the addition of organic additives (Organic additive).
Figure 4 shows the results of the hull cell test according to the addition of a reducing agent (Reducing Agent).
5 shows selected Examples 19, 25, 27, 32, and 35 (Compound Mix -19, Compound Mix-1) in which non-uniform plating and spot plating occurred and Examples showing uniform deposition and gloss. 25, 27, 32, 32, 35) shows the results of the hull cell test.
6 shows a diamond tool manufactured using the plating solution of Comparative Plating Solution (Comparative Example), Examples 25, 26, 30, 32, 35.
Figure 7 shows a method of applying a current in the positive and negative current direction of the pulse-reverse plating process.
8 shows a diamond tool prepared in Example 39 of the present invention. Panel A) shows a photograph of a diamond tool. Panel B shows a photograph of the surface of the diamond tool under an optical microscope. Panel C) shows the results of observation of the surface of the diamond tool with a scanning electron microscope.
9 shows a diamond tool prepared in Example 40 of the present invention. Panel A) shows a photograph of a diamond tool. Panel B) shows the results of the observation of the surface of the diamond tool with an optical microscope and panel C) shows the results of the observation of the surface of the diamond tool with a scanning electron microscope.
10 shows a diamond tool prepared in Example 41 of the present invention. Panel A) shows a photograph of a diamond tool. Panel B) shows the results of the observation of the surface of the diamond tool with an optical microscope and panel C) shows the results of the observation of the surface of the diamond tool with a scanning electron microscope.
11 shows a diamond tool prepared in Example 42 of the present invention. Panel A) shows a photograph of a diamond tool. Panel B) shows the results of the observation of the surface of the diamond tool with an optical microscope and panel C) shows the results of the observation of the surface of the diamond tool with a scanning electron microscope.

In the hexavalent chromium plating method using a chromium sulfate bath and a pulse-reverse electroplating method, the anode current direction plating is carried out under the conditions of current density of 38 to 60 A / cm ² and plating time 10 msec, and then the cathode current direction. Plating is carried out under a condition of current density of 12 to 30 A / cm ² and plating time of 0.4 to 1 msec as a set, and the set is repeated and crack-free when the total plating time is performed for 10 to 20 minutes. The present invention provides a hexavalent chromium plating method using a chromium sulfate bath and a pulse-reverse electroplating method characterized by forming a chromium plating layer.

The pulse-reverse electroplating method refers to a method of plating by repeatedly alternating anode and cathode currents, and the anode and cathode currents are applied one time at a time and the set is a predetermined number of times. The plating is performed by repeating the method.

In the present invention, an anode current condition and a cathode current condition having current density and plating time optimized for crack-free chromium plating were established through examples. The conditions are current density of 38 to 60 A / cm ² and plating time 10 msec for the anode current and current density of 12 to 30 A / cm ² and plating time 0.4 to 1 msec for the cathode current. It is confirmed that cracks occur in the chromium plating layer outside the above conditions, and if the total plating time performed by repeating the above set is within 10 minutes, the plating layer is formed to be less than 0.9269 μm in thickness and the plating layer is formed even if the total plating time exceeds 20 minutes. It was confirmed that the thickness did not exceed 3.39 mu m.

The crack refers to a crack due to stress generated in the chromium plating layer. When the crack occurs, various corrosive solutions used for semiconductor processing may penetrate into the plating layer, which leads to corrosion of the substrate inside the plating layer. Therefore, if the formation of the cracks is suppressed, the corrosion resistance of the plated substrate may be improved, thereby providing an excellent diamond tool having excellent stability.

The crack may be formed as a crack having a depth and a width that can be identified by an eye or an optical microscope, or a fine crack which cannot be identified by an optical microscope may be generated in a network form. In the present invention, in order to identify a micro crack network formed finely and difficult to identify with an optical microscope, the occurrence of cracks was confirmed using a scanning electron microscope together with the optical microscope.

The chromium sulfate bath used in the hexavalent chromium plating method using the chromium sulfate bath is 200 to 250 g / L chromic anhydride (CrO ₃ ), sulfuric acid (H ₂ SO ₄ ) 2 to 2.7 g / L, EDTA compounds 3 to 5 g / L, ammonium compound 50-100 g / L, polyoxyethylene polymer compound 0.01-0.1 g / L, oxalic acid compound 5-20 g / L, and boron compound 13-20 g / L. The EDTA compound may be EDTA or an EDTA compound including EDTA.

The EDTA compound is used as a complexing agent and is preferably EDTA-4NA or EDTA-2NA. The EDTA compound has the effect of reducing the metal ions and precipitation potential to increase the current density range, thereby advantageously metal deposition. Among the EDTA compounds, the use of EDTA-4NA or EDTA-2NA showed the best plating results. In addition, when the EDTA compound is used at less than 3 g / L, metal deposition may be reduced and staining may occur, and even if the EDTA compound exceeds 5 g / L, the improvement of the metal electrodeposition effect is insignificant and the plating result is not further improved.

The ammonium compound is used as an ion conductor and is preferably ammonium chloride, ammonium sulfate, or ammonium nitrate. The ammonium compound has an electrical conductivity in the plating solution has the effect of favoring the metal electrodeposition. When the ammonium compound is used at less than 50 g / L, metal electrodeposition is lowered and stains are formed on the plating layer, making it difficult to obtain gloss. Even when the ammonium compound is used in excess of 1000 g / L, the effect of improving the electrical conductivity is insignificant. It doesn't work.

The polyoxyethylene polymer compound means a polyoxyethylene polymer and a polymer compound using the same, and is used as an organic activator. The organic activator increases the current density and reduces the dendritic growth precipitated during the plating process, thereby improving the smoothness of the plated surface. Glossiness is improved when the smoothness is improved. When the polyoxyethylene polymer compound is used at less than 0.01 g / L, the dendritic precipitated during the plating process may grow to reduce the smoothness of the plating layer, and the polyoxyethylene polymer compound may have 0.1 g / L. If used excessively, staining occurs or a non-uniform plating layer is formed, thereby increasing the defective rate.

 The oxalic acid compound is used as a reducing agent to improve the adhesion of the plating layer. The oxalic acid compound may be a compound including oxalic acid and oxalic acid. If the oxalic acid is used less than 5 g / L there is a fear that the plating layer is non-uniform, even if the oxalic acid is used in excess of 20 g / L is the effect of improving the adhesion of the plating layer is insignificant.

The boron compound is used as a buffer. The buffer may be boric acid or a compound comprising boric acid.

The chromium sulfate bath and the pulse-reverse plating method are applied to a nickel strike plated stainless steal sheet (SUS) substrate to prevent dropping of diamond particles, separation of binders, and elution of a fixed metal in diamond tools with diamonds. Used to manufacture crack free chromium plating layers.

The diamond tool is a stainless steal sheet (SUS) substrate; A nickel plating layer plated on the SUS substrate by a nickel strike method; Diamond attached to the nickel plating layer by a composite plating; And a chromium plating layer formed on the nickel-attached nickel layer. The diamond tool is a diamond tool for a semiconductor processing process, and the chromium plating layer has a thickness of 0.926 to 3.39 μm and is crack-free.

The diamond tool manufactured by the hexavalent chromium plating method using the chromium sulfate bath of the present invention is excellent in corrosion resistance and has no problem due to the escape of diamond particles during use because the chromium plating layer having excellent hardness and no cracks is formed on the diamond particles. There is no advantage.

The following examples give a detailed description of the invention.

Example

1. Crack Free Chrome Plating Optimization

The present invention relates to crack-free chromium plating. To this end, a plating solution having a composition ratio of various kinds of metal ions and additives was prepared, and the plating state was confirmed using a hull cell test.

1) Metal ion composition

The optimum metal ion composition was established for crack free chromium plating. Table 1 below shows the metal ion composition of the crack free chromium plating solution.

CrO ₃ H ₂ SO ₄ Low Concentration Metal Ion 150 g / L 1 to 1.5 g / L Medium metal ion 200 to 250 g / L 2 to 2.7 g / L High concentration metal ion 400 g / L 3.5 to 4 g / L

In the case of crack free chromium hard plating, chromium ion (CrO ₃ ) proceeds at a low concentration of 150 g / L. Using the low concentration of chromium ion has the advantage of reducing cracks and standard deviation. However, in the plating solution used in the present invention, since the chromium ion and the sulfate ion proceed at a ratio of 100: 1 (CrO ₃ : H ₂ SO ₄ ), the concentration of sulfate ion corresponds to 1 to 1.5 g / L to supply and manage sulfuric acid. There is a drawback that significant difficulties arise. In addition, when chromium ions are used at a high concentration of 400 g / L, a significant amount of chromium ions are released during dragging out during the plating process.

Therefore, the metal composition of the crack free chromium plating solution of the present invention was determined to be chromium ion (CrO ₃ ) at a medium concentration of 200 to 250 g / L. Preferably 250 g / L was used. According to the concentration of the chromium ion, sulfate ions were used in an amount of 2 to 2.7 g / L, which is about 1/100 of the chromium ion. The plating temperature was set to 35 to 50 ℃, the current density was set to 7 to 80 A / cm ² , the voltage was set to 4 to 5 V.

2) additive composition

An additive composition test was performed based on the plating solution. As the metal ion composition of the plating solution, 250 g / L of chromium ion and 2.7 g / L of sulfate ion were used. The plating state evaluation was used a hull cell test. The temperature of the hull cell test was in the range of 45 to 50 ° C., and brass, copper, and the like were used as a cathode, and a 20 A current was applied for 5 minutes to observe a metal electrodeposition (plating) shape formed on the cathode specimen. As a result of the experiment, it was confirmed that the current density range of 10 A / cm ² or more.

Six kinds of complexing agents, six kinds of ionic conductors, 24 kinds of organic additives, six kinds of reducing agents, and one kind of buffering agent in the plating solution To each was sequentially added to prepare a plating solution and subjected to the hull cell test to evaluate the plating state.

The complexing agent serves to inhibit the polymerization, the ion conductor serves to increase the conductivity, the organic active agent serves to increase the gloss, the reducing agent serves to increase the adhesion, the buffer Serves to maintain the pH of the plating liquid.

Table 2 below shows the types of complexing agents, ion conductors, organic active agents, reducing agents, buffers used in the present invention, and evaluation criteria for the plating layer after the hull cell test.

additive Kinds Evaluation standard Complexing agent EDTA compound Uniform plating and spotting Ion conductor Ammonium compounds Whether current efficiency is improved by improving electrical conductivity Organic activator Polyoxyethylene Polymer Compound Glossy Plating Conditions and Expanded Smoothing Range reducing agent Oxalic acid compound Improved adhesion range of plating layer Buffer Boron compounds Rapid pH Change Suppression

When the complexing agent is included in the plating solution, the free metal ions are reduced and the precipitation potential is lowered, thereby increasing the current density range, which favors metal electrodeposition. As a result of the experiment, it was confirmed that the plating solution containing the complexing agent 1 or 2 showed the plating result with the most uniform and few stains. Uneven plating and partial staining were observed for complexing agents 3-6. Figure 1 shows the results of the hull cell test according to the addition of the complexing agent.

When the ion conductor is included in the plating solution, it dissociates into ions and exhibits electrical conductivity, thereby facilitating electrodeposition of the metal. As for the ion conductor, it was confirmed that the plating liquid containing 4 was the best. Except for the ion conductor 4, the milky or misty plating occurred in the low and high current portions, respectively. Figure 2 shows the results of the hull cell test according to the addition of the ion conductor.

The organic activator interferes with the dendritic growth of the deposited metal during the plating process, contributes to the smoothing of the plating surface, increases the current density and hardens the plating layer to increase the gloss. Too much organic active agent causes many defects. As a result, it was confirmed that non-uniform plating and stain plating occurred in all of the organic activators 1 to 6, and it was confirmed that non-uniform plating and stain plating occurred in a wide current density. The organic activators 7, 17 and 18 showed uniform and glossy plating, and the organic activator 23 showed the best plating result in the gloss. Figure 3 shows the results of the hull cell test according to the addition of the organic active agent.

The reducing agent has the effect of improving the adhesion and range by promoting the reducing action of the plating layer. Reducing agents 1, 2, 5, and 6 were all non-uniform plating and stain plating was confirmed, but reducing agents 3 and 4 were uniform and stainless plating results. Figure 4 shows the results of the hull cell test according to the addition of the reducing agent.

3) Crack-free Hexavalent Chromium Plating Solution

Based on the results, 36 kinds of crack-free chromium plating solutions were prepared by combining metal ions and additives showing excellent plating results, and a plating solution showing excellent plating characteristics was selected through a hull cell test.

Table 3 shows a hull cell test for Comparative Examples, which are plating baths prepared using only chromic anhydride and sulfuric acid, and Examples 1 to 35, which are plating baths prepared using chromic anhydride, sulfuric acid, a complexing agent, an ion conductor, an organic active agent, and an original agent. Show results. In the above example, chromic anhydride (CrO ₃ ) was used at 250 g / L, sulfuric acid (H ₂ SO ₄ ) at 2.5 g / L, and 3 to 5 g / L of EDTA compound as a complexing agent, and 50 to ammonium compound as an ion conductor. Appropriate amounts in the range of 100 g / L, 0.01 to 0.1 g / L polyoxyethylene polymer compound as organic activator, 5 to 20 g / L oxalic acid compound as reducing agent, and 13 to 20 g / L boron compound as buffer Was used.

number name Uniformity Glossiness Stain Plating Result Example 1 Compound Mix-1 Heterogeneity lowness O Bad Example 2 Compound mix-2 Uniformity lowness O Bad Example 3 Compound mix-3 Uniformity lowness O Bad Example 4 Compound mix-4 Heterogeneity lowness O Bad Example 5 Compound mix-5 Heterogeneity lowness O Bad Example 6 Compound mix-6 Heterogeneity lowness O Bad Example 7 Compound mix-7 Heterogeneity lowness O Bad Example 8 Compound mix-8 Uniformity lowness X Bad Example 9 Compound mix-9 Uniformity lowness X Bad Example 10 Compound Mix-10 Heterogeneity lowness O Bad Example 11 Compound mix-11 Heterogeneity lowness O Bad Example 12 Compound mix-12 Uniformity middle X Bad Example 13 Compound Mix-13 Heterogeneity lowness O Bad Example 14 Compound mix-14 Heterogeneity middle O Bad Example 15 Compound mix-15 Heterogeneity middle O Bad Example 16 Compound mix-16 Uniformity lowness X Bad Example 17 Compound Mix-17 Heterogeneity lowness O Bad Example 18 Compound Mix-18 Heterogeneity lowness O Bad Example 19 Compound Mix-19 Uniformity height X good Example 20 Compound Mix-20 Uniformity height X good Example 21 Compound Mix-21 Heterogeneity lowness O Bad Example 22 Compound Mix-22 Heterogeneity lowness O Bad Example 23 Compound Mix-23 Heterogeneity lowness O Bad Example 24 Compound Mix-24 Heterogeneity lowness O Bad Example 25 Compound Mix-25 Uniformity height X good Example 26 Compound Mix-26 Heterogeneity height O Bad Example 27 Compound Mix-27 Uniformity height X good Example 28 Compound Mix-28 Heterogeneity lowness O Bad Example 29 Compound Mix-29 Heterogeneity lowness O Bad Example 30 Compound mix-30 Uniformity height X good Example 31 Compound Mix-31 Heterogeneity height O Bad Example 32 Compound Mix-32 Uniformity height X good Example 33 Compound Mix-33 Heterogeneity lowness O Bad Example 34 Compound Mix-34 Heterogeneity lowness O Bad Example 35 Compound Mix-35 Uniformity height X good

It was confirmed that the plating solutions of Examples 1 to 18, 21 to 24, 28, 29, 31, 33, 34, and 35 had non-uniform plating and spot plating. In contrast, it was confirmed that Examples 19, 20, 25 to 27, 30, 32, and 35 showed uniform deposition and gloss. In Examples 19, 20, 25 to 27, 30, 32, and 35, complexing agents, ion conductors, organic activators, reducing agents, and buffers were found to show excellent plating results through suitable combinations. 5 shows the results of the hull cell test of Examples 19, 25, 27, 32, and 35 selected from Example 1 where uneven plating and stain plating occurred and examples showing uniform deposition and gloss.

4) Diamond tool manufactured using crack free hexavalent plating solution

The diamond tool for actual wafer processing was prepared using the plating solution of Example showing excellent chromium plating results through the above examples, and the plating results were confirmed. The diamond tool is a stainless steal sheet (SUS) substrate, a nickel plated layer plated on the SUS substrate by a nickel strike method, a diamond plated on the nickel plated layer by a composite plating, and a chrome plated layer formed on the diamond layer. It is composed.

As a result, it was confirmed that the basic plating solution containing only chromium ions and sulfate ions (comparative example) could be chromium plated, but the stability of the plating layer was inferior, and very large cracks were generated.

In addition, diamond tools manufactured using the chromium plating solutions of Examples 19, 20, 25 to 27, 30, and 35 except for Example 32 were found to have partial unevenness and yellowing because the conditions were not met. 6 shows a diamond tool manufactured using the plating solution of Comparative Plating Solution (Comparative Example), Examples 25, 26, 30, 32, 35. Therefore, the chromium plating solution of Example 32 was selected as an optimal crack free chromium plating solution.

2. Establish optimal pulse-reverse electroplating conditions

1) Condition search through hull cell test

First, as a result of performing a hull cell test using a basic chromium plating solution (sargent bath), in the case of a sample plated at 10 A for 1 minute, plating with bright luster occurs at a current density of 0.05 to 0.6 A / cm ² . It was confirmed that as the current density increases, the crack density increases.

The increase in crack density may be due to a phenomenon in which the plating layer is thickened and the hydrogen evolution reaction (HER) reaction is active in proportion to the increase in the current density, thereby increasing the formation of chromium hydrogen compounds.

2) Exploration of pulse-reverse elctroplating conditions

Dielectric current electroplating (Dicrect Current electroplating) method has the advantage of easy to obtain a plating having a gloss, but it is difficult to obtain crack-free plating due to an increase in the crack density with the increase of the current density.

Therefore, in the present invention, the pulse-reverse electroplating method was used. Whereas the direct current electroplating method is to perform a plating by applying a constant current for a predetermined time, the pulse-reverse electroplating method is a method of repeatedly alternating the positive and negative currents. 7 shows a method of applying a current in the direction of the positive current (constant current) and the negative current (reverse current) of the pulse-reverse plating process.

The pulse-reverse electroplating method has a disadvantage in that it is difficult to obtain gloss unlike the direct current electroplating method, but it is mainly used for crack-free plating in hexavalent chromium plating. The reason is that hydrogen is not contained in the chromium plating due to the anodic current applied during the chromium plating for a short time. This is because the plating is performed in the shape of a body centered cubic lattic (BCC) structure. When chromium is plated with a body-centered cubic crystal, it is less stressed due to phase change and thus has less cracks.

In the present invention, the plating is performed by changing the current density, the current time, the number of pulses, and the like, and the optimum crack-free pulse-reverse chromium electroplating method is derived.

Table 4 below shows the experimental conditions for deriving the optimal crack-free pulse-reverse chromium electroplating method.

Kinds Condition Plating amount Basic Chrome Plating Solution (Sargent Bath) + HY-30 Temperature 50 ℃ working electrode Cu plate (2 x 2 cm ² ) counter electrode Pb plate (2 x 2 cm ² ) reference electrode Ag / AgCl Gap 1 cm Anode current density 0.15 to 0.6 A / cm ² Cathode Current Density 0.075 to 0.3 A / cm ²

(1) Influence of cathodic current density

First, all other conditions (see Table 4) were fixed constantly, and the anode current density was adjusted in the range of 0.15 to 0.6 A / cm ² to determine the effect.

As a result of the experiment, it was found that the gloss surface was obtained in all samples, but the edge effect occurred as the anode current density was increased and the edges of the samples lost the gloss to gray. This is because the current draw phenomenon occurs due to the edge effect, whereby chromium hydride is formed.

It was also confirmed that the crack density increased as the anode current density increased. If the anode current density is higher at the same anode current time condition, thicker plating will be obtained. To determine whether the increase in crack density was influenced by the coating thickness, the anode current time was adjusted to maintain the plating of similar thickness even though the anode current density was different, and then the crack density was compared. As a result of the comparison, no crack density was found.

The same amount of charge was applied by adjusting the time to minimize the effect of the plating thickness and to analyze the effect on the cathodic current. As a result, it was confirmed that at low current density, the plating deposition rate was considerably low and that it had fewer cracks. However, there was no significant difference in hardness.

As a result of analyzing the current efficiency effect by the cathodic current density, it was confirmed that the current density was less than 10% at the low anode current density and similar current density at the anode current density above. This means that at low anodic current densities, most of the charge is mostly used for chromium plating and to form an electric double layer.

As a result, although the current efficiency is low at a low anode current density, it is determined that the use of a low anode current density is required for crack-free chromium plating. However, since the proper range of the anode current density may be affected by the cathode current density, the experiment for the proper cathode current density was further performed.

(2) Influence of anode current density

All other conditions (see Table 4) were fixed constant and the cathode current density was adjusted in the range of 0.075 to 0.3 A / cm ² , and the effect was observed. As a result of the experiment, all samples maintained gloss, and crack density did not show a big difference.

The thickness of the plating tends to have a similar overall thickness because of the same amount of charge in the cathode current and the anode current, but a slight difference occurs because the amount of charge in the oxidation reaction increases with the cathode current density. . When the anodic current increases to increase the charge of the oxidation reaction, a reaction to ionize the plated chromium occurs again. Accordingly, the thickness of the plating layer is gradually reduced.

It was confirmed that the hardness of the plated layer also showed a slight difference. In general, chromium plating using the DC current electroplating method has a higher hardness than plating using the pulse-reverse electroplating method. Therefore, when the anode current density is lowered, plating may be formed close to the DC current electroplating method, thereby forming a plating layer having a high hardness.

It is expected that the higher the cathode current density, the greater the amount of charge in the oxidation reaction, resulting in a lower current efficiency. This is because samples with a constant reduction reaction charge amount have only a very small difference in oxidation current charge amount.

(3) Effect of number of pulses

All other conditions (see Table 4) were constant, fixed, and experimented with varying number of pulses.

As a result of the experiment, the smaller the number of pulses, the lower the crack density. The thickness of the plated layer did not change with the number of pulses, but the hardness of the plated layer was inversely proportional to the number of pulses. When the number of pulses was small, high hardness (4H) was shown, but as the number of pulses increased, it was confirmed that the hardness decreases rapidly. Current efficiency was found to be inversely proportional to the number of pulses.

Electroplating is performed by the formation of an electric double layer on the electrode surface, followed by reaction of electrons and ions in the electric double layer on the electrode surface. As the number of pulses increases, the electrical double layer on the electrode surface is formed at the cathodic current density and then disappears at the anodic current density, which causes a huge loss of charge. Therefore, the current efficiency decreases as the number of pulses increases.

(4) Influence of anode and cathode current time

In general, when the anode current time is reduced while applying a certain amount of charge in the pulse-reverse electroplating method, the number of pulses increases, which leads to a decrease in current efficiency.

Since the change in the current efficiency affects the crack generation, in order to remove it in the present invention, a certain amount of DC current electroplating was first performed, followed by pulse-reverse electroplating.

As a result, it was confirmed that the crack density decreases as the anode current time and cathode current time decrease. In particular, it was confirmed that the cathode current time had a greater effect on the reduction of the crack density than the anode current time.

2) Development of crack-free pulse-reverse elctroplating process

As the chromium plating solution used in the development of the crack-free pulse-reverse electroplating process, the plating solution of Example 32 determined above was used, and the plating temperature was set to 35 to 50 ° C.

For the development of crack-free pulse-reverse electroplating process, optimization of anode, optimization of pretreatment method and optimization of pulse-reverse electroplating condition were performed.

(1) Optimization of anode

In the crack-free pulse-reverse electroplating of the present invention, an insoluble anode was used. An insoluble anode refers to a cathode in which a very small amount of electrolyte and plating solution do not melt or melt when a current flows. The use of an insoluble anode allows the metal ions to be directly supplied to the solution, which facilitates the concentration control of the metal ions used for plating. When the anode is used as an insoluble metal, it can be manufactured in various shapes, which is advantageous for current distribution, and is preferred for high quality plating because it enables thickness deviation management and high-speed plating.

Therefore, the positive electrode of the present invention did not use chromium, which is a soluble metal, but used an insoluble metal such as platinum (Pt), lead-tin (Pb-Sn), or lead-antimony (Pb-Sb) alloy. Preferably lead-tin (Pb-Sn) or lead-antimony (Pb-Sb) alloy was used. The reason for using the alloy is that the alloy has lower solubility than pure metal.

In the crack-free pulse-reverse electroplating of the present invention, a hanger of sufficient thickness was used. If the hook is not thick enough, it can overheat. If overheated, power loss and current distribution may worsen, which may lead to the non-plating part, and the jig may melt. In addition, due to the characteristics of hexavalent chromium plating, which requires low current efficiency and requires high current density, the high current density part is easily burned and the unplated part easily occurs.

(2) Optimization of the pretreatment method

If the surface of the metal is non-uniform due to the presence of an oxide film on the metal surface, the incorporation of foreign matter, the crack of the surface, and the deviated direction of the surface structure, the plating quality is deteriorated. In particular, the oxide film on the metal surface lowers the plating adhesion and degrades the plating quality. The oxide film has a higher electrode potential than a target metal, is difficult to dissolve in acid, has a high density, and is difficult to remove. Since oxide layers are formed differently depending on the type of metal, the degree of treatment of the oxide film varies depending on the pretreatment process. In addition, even if the oxide film is removed through the pretreatment, an oxide film, which is difficult to see with the naked eye, may be instantaneously generated to degrade the plating quality. Therefore, optimization of the pretreatment process is very important.

In the present invention, by removing the metal oxide film through a pretreatment, the surface of the metal was processed into a reducing state that is easily plated. In the pretreatment of the present invention, the oxide film was removed using reducing acids such as hydrochloric acid, hydrofluoric acid, acetic acid, organic acid, and oxidizing acids such as nitric acid, chromic acid, phosphoric acid, persulfate, and sulfuric acid.

(3) Optimization of pulse-reverse electroplating conditions

The optimum pulse-reverse electroplating conditions were established while varying the voltage and current conditions applied during chromium plating. Using the chromium plating solution of Example 32, diamond tools were prepared by increasing the area and current density on the nickel strike plated actual SUS substrate. The diamond tool is a stainless steal sheet (SUS) substrate, a nickel plated layer plated on the SUS substrate by a nickel strike method, a diamond plated on the nickel plated layer by a composite plating, and a chromium plated layer formed on the diamond layer. The manufacturing process of the diamond tool of the present invention comprises an electrolytic degreasing process, a pretreatment process for removing an oxide film through acid treatment, a nickel strike process, a nickel plating process and a diamond composite plating process, and a chromium plating process.

First, a diamond tool was prepared by plating on the conditions of Examples 37 and 38 on a laboratory scale. As a result, it was confirmed visually that reverse peeling generate | occur | produced in unplated and peeled to the nickel layer. This may be because the allowable current density value is too low or the pulse-reverse plating time is too long.

anode cathode Total Plating Time
(min) Current (A / cm ² ) Time (msec) Current (A / cm ² ) Time (msec) Example 37 0.15 10 0.075 One 30 Example 38 18 10 9 One 30

Table 6 shows an example in which the diamond tool was manufactured by changing the current density value and the pulse-reverse plating time.

anode cathode Total Plating Time
(min) Plating thickness
(Μm) Cracking electric current
(A / cm ² ) time
(msec) electric current
(A / cm ² ) time
(msec) Example 39 25 10 12.5 One 36 ~ 1.71 O Example 40 38 10 19 One 10 0.926-1.25 X Example 41 60 10 30 0.5 20 2.53-2.93 X Example 42 60 10 12 0.4 18 2.65-3.39 X

In Example 39, the anode current density was increased by 39% and accordingly the cathode current density value was plated. As a result of the plating, it was visually confirmed that the chrome plating proceeded in the donut type and the maximum plating thickness was 1.71 μm. In addition, cracking of the plating was confirmed by using an optical microscope and a scanning electron microscope. 8 shows the results of observing the diamond tool prepared in Example 39 and its surface with an optical microscope and a scanning electron microscope.

Example 40 increased the anode current density by 52% and shortened the plating time to 19 minutes, compared to Example 39. As a result of the plating, the thickness of the plating layer was confirmed to be the minimum thickness at the center of 0.926 ㎛, the side was confirmed to the maximum thickness of 1.25 ㎛. In addition, no crack was found when the surface was observed using an optical microscope and a scanning electron microscope. 9 shows the results of observing the diamond tool prepared in Example 40 and its surface with a scanning electron microscope.

In addition, after the plating temperature was fixed at 50 ° C. and the plating was performed as in Examples 41 and 42 by adjusting the current density and the plating time, the anode current density was allowed up to 60 A / cm ² and the cathode current density was 12 A / cm ^2. It was confirmed that cracks were not found even when allowed. It was also confirmed that the plating thickness was also improved to 2.53 to 3.39 mu m. FIG. 10 shows the results of observing the diamond tool prepared in Example 41 and its surface with a scanning electron microscope, and FIG. 11 shows the results of observing the diamond tool prepared in Example 42 and its surface with a scanning electron microscope.

Therefore, the most preferable pulse-reverse plating conditions are anodic current density 38 to 60 A / cm ² , anodic current direction plating with a plating time of 10 msec and a cathode current density of 12 to 30 A / cm ² and a cathode current with a plating time of 0.4 to 1 msec. Alternating aroma plating was found to be performed for 10-20 minutes of the total plating time.

As a result, the plating solution of Example 32 was subjected to the anodic current direction plating according to the plating process of the present invention, and the cathode current direction plating was performed after the current density was 38 to 60 A / cm ² and the plating time was 10 msec. It is carried out under the conditions of 30 to 30 A / cm ² and the plating time of 0.4 to 1 msec as a set, but if the set is repeated to a total plating time of 10 to 20 minutes, the plating thickness is 0.926 to 3.39 μm and there is no crack It has been confirmed that crack free diamond tools can be manufactured.

Specific embodiments described herein are meant to represent preferred embodiments or examples of the present invention, whereby the scope of the present invention is not limited. It will be apparent to those skilled in the art that variations and other uses of the invention do not depart from the scope of the invention described in the claims.

Claims (5)

In the hexavalent chromium plating method using a chromium sulfate bath,
The chromium sulfate bath is 200 to 250 g / L chromic anhydride (CrO ₃ ), 2 to 2.7 g / L sulfuric acid (H ₂ SO ₄ ), 3 to 5 g / L EDTA compound, 50 to 100 g / L ammonium compound, poly A chromium sulfate bath containing 0.01 to 0.1 g / L of an oxyethylene polymer compound, 5 to 20 g / L of an oxalic acid compound, and 13 to 20 g / L of a boron compound;
Anodic current direction plating is performed under the conditions of current density of 38 to 60 A / cm ² and plating time of 10 msec, and cathodic current direction plating is performed under the condition of current density of 12 to 30 A / cm ² and plating time of 0.4 to 1 msec. One set, but repeating the set is carried out for a total plating time of 10 to 20 minutes, a crack free chromium plating method using a chromium sulfate bath characterized in that the crack-free chromium plating layer is formed.
delete The hexavalent chromium plating method according to claim 1, wherein the crack-free chromium plating layer is formed to a thickness of 0.926 to 3.39 μm.
The hexavalent chromium plating method according to claim 1, wherein the crack-free chromium plating layer is formed on a nickel strike plated stainless steal sheet (SUS) substrate.
Stainless steal sheet (SUS) substrate; A nickel plating layer plated on the SUS substrate by a nickel strike method; In the diamond tool for a semiconductor processing process consisting of a diamond attached to the nickel plated layer by a composite plating; and a chromium plated layer formed on the nickel layer to which the diamond is attached;
The chromium plated layer is 200 to 250 g / L chromic anhydride (CrO ₃ ), 2 to 2.7 g / L sulfuric acid (H ₂ SO ₄ ), 3 to 5 g / L EDTA compound, 50 to 100 g / L ammonium compound, polyoxyethylene using a chromium sulfate bath containing 0.01 to 0.1 g / L of a (polyoxyethylene) polymer compound, 5 to 20 g / L of an oxalic acid compound, and 13 to 20 g / L of a boron compound,
Anodic current direction plating is performed under the conditions of current density of 38 to 60 A / cm ² and plating time of 10 msec, and cathodic current direction plating is performed under the condition of current density of 12 to 30 A / cm ² and plating time of 0.4 to 1 msec. It is a semiconductor, characterized in that one set, which is manufactured by a hexavalent chromium plating method of repeating the set for a total plating time of 10 to 20 minutes, the thickness is 0.926 to 3.39 ㎛ and is crack-free Diamond tools for the machining process.

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