TWI525225B - Electrolyte for electrodepositing molybdenum and method for forming molybdenum-containing layer - Google Patents

Description

Molybdenum-plated electrolyte and method for forming molybdenum-containing coating

The invention relates to a molybdenum-plated electrolyte and a method for forming a molybdenum-containing plating layer, and in particular to a non-aqueous solution molybdenum-plating electrolyte and a method for forming a molybdenum-containing plating layer using the non-aqueous solution molybdenum-plating electrolyte.

Molybdenum metal is one of high melting point refractory metals, which has good electrical conductivity, thermal conductivity, low coefficient of thermal expansion (similar to glass for electron tubes), high hardness, and the like. In terms of components, molybdenum and molybdenum alloys have advantages over tungsten, so they are often added to plates, strips, foils, tubes, rods, wires and profiles in tubes (gates and anodes), and electric sources (support materials). ) Production of parts, metalworking tools (die-casting and extrusion dies, forging dies, perforated plugs, liquid metal screens) and turbine discs. In terms of aerospace, molybdenum alloys can withstand pressure and corrosion resistance and can be used as components for space shuttles and aircraft.

In addition, it can be applied to the lithography electroforming (German Lithographie Galvanoformung Abformung, LIGA) process. Although this process has been industrialized, it is limited to metals deposited by aqueous solution such as copper, gold, nickel and Nickel-iron alloy. Refractory metal has been It is expected that the application will be applied to this process to help improve the performance and reliability of the MEMS.

Current techniques for depositing molybdenum include electrochemical deposition, vapor deposition (PVD, CVD), evaporation, sputtering, ion implantation, spray coating, electroless plating, and melt-gel, among which electrochemical deposition has simple equipment, low deposition temperature, high deposition rate, and low equipment cost. It is easy to operate and learn, and can be applied to large-scale production in the industry, which has led to extensive research.

Electrochemical deposition technology can be divided into aqueous solution electrolysis and non-aqueous solution electrolysis according to the type of electrolyte used. Electrolyte electrolysis is easy to produce toxic substances such as cyanide in the electrolysis process. In addition, the reduction potential of many metals in aqueous solution is less than the hydrogen standard potential. It is impossible to deposit by aqueous solution electrolysis, such as a high melting point metal such as molybdenum or tungsten. In the non-aqueous solution electrolysis, a molten salt is often used as an electrolyte, and the molten salt electrolyte has a high electrolysis efficiency and a high deposition rate as compared with the aqueous solution electrolyte, and a plating layer having good corrosion resistance can be formed.

Scholars Senderoff and Mellors deposited molybdenum with alkali metal oxide at 700 ° C to 850 ° C. Girginov, Tzvetkoff and Bojinov deposited metal molybdenum with fluorochloride at 500 ° C. In recent years, scholars have deposited at temperatures between 200 ° C and 350 ° C. The metal molybdenum is formed, but the temperature required for the electrochemical deposition is still high, and the energy consumed by the electrochemical deposition cannot be effectively reduced, so that the cost of depositing molybdenum is high.

Accordingly, it is an object of the present invention to provide a molybdenum-plated electrolyte which is a non-aqueous electrolyte and which can be subjected to a temperature of less than or equal to 130 ° C. An electrochemical reaction is performed to form a molybdenum-containing coating, thereby saving energy, avoiding high temperature corrosion, and avoiding thermal deformation or damage of the substrate.

Another object of the present invention is to provide a method for forming a molybdenum-containing plating layer, wherein the method for forming a molybdenum-containing plating layer uses the aforementioned molybdenum-plated electrolyte, thereby saving energy, avoiding high temperature corrosion, being highly operable, and avoiding heat of the substrate. Deformed or damaged, and can improve the quality of the molybdenum-containing coating.

One embodiment according to an aspect of the present invention provides a molybdenum-plated electrolyte that excludes fluorine-containing salts, and the molybdenum-plated electrolyte contains 0.01 mol% to 1 mol% of molybdenum pentachloride (MoCl ₅ ), 0.01 mol. The percentage of ears is up to 25 mole percent zinc chloride (ZnCl ₂ ) and the remaining amount of dimethyl hydrazine (C ₂ H ₆ O ₂ S, DMSO ₂ ).

According to another embodiment of the present invention, there is provided a method of forming a molybdenum-containing plating layer comprising the steps of: providing molybdenum pentachloride, zinc chloride and dimethyl hydrazine, performing a water removal step, forming a plating The molybdenum electrolyte is subjected to an electrochemical reaction. The water removal step is carried out by placing molybdenum pentachloride, zinc chloride and dimethyl hydrazine in a vacuum environment for a period of time, so that the moisture content of molybdenum pentachloride, zinc chloride and dimethyl hydrazine is 2 wt. %the following. Forming a molybdenum-plated electrolyte system uniformly mixing molybdenum pentachloride, zinc chloride and dimethyl ruthenium, wherein the molybdenum-plated electrolyte excludes fluorine-containing salts, and the molybdenum-plated electrolyte contains 0.01 mol% to 1 mol% of pentachlorinated Molybdenum, 0.01 mole percent to 25 mole percent zinc chloride and the remaining amount of dimethylhydrazine. The electrochemical reaction is performed to form a molybdenum-containing coating.

According to the foregoing method for forming a molybdenum-containing plating layer, the water removal step can be carried out at 25 ° C to 120 ° C for 12 hours to 72 hours. Step of forming a molybdenum-plated electrolyte It can be carried out at 110 ° C to 150 ° C under a nitrogen atmosphere. The step of performing the electrochemical reaction can be carried out at 115 ° C to 130 ° C under a nitrogen atmosphere.

According to the foregoing method for forming a molybdenum-containing plating layer, wherein the step of performing the electrochemical reaction may use alternating current, direct current or pulsed electricity, the voltage may range from 10V to -10V, and the current density may range from ±0.1mA/cm ² to ±200mA/cm. ^2, and the energization amount may range from 1C / cm ² to 250C / cm ^2.

According to the foregoing method for forming a molybdenum-containing plating layer, the step of performing the electrochemical reaction is pulsed electricity, and the operating condition of the pulsed electricity may be T _on /(T _on +T _off )=0.1 to 0.9.

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210‧‧‧Molybdenum-plated electrolyte

220‧‧‧ cathode

230‧‧‧Anode

240‧‧‧ reference electrode

241‧‧‧Zinc wire

242‧‧‧Zinc-containing electrolyte

243‧‧‧ glass tube

250‧‧‧ Thermocouple Thermometer

260‧‧‧ gas filling port

270‧‧‧ gas discharge

280‧‧‧Reaction tank

1 is a flow chart showing the steps of forming a molybdenum-containing plating layer according to an embodiment of the present invention.

2 is a schematic view showing an electrochemical system used in a method of forming a molybdenum-containing plating layer according to an embodiment of the present invention.

Figure 3 is an SEM image of Example 1 in accordance with the present invention.

Figure 4 is an SEM image of Example 2 in accordance with the present invention.

Fig. 5 is an SEM image of Comparative Example 1.

Fig. 6 is an SEM image of Comparative Example 2.

Fig. 7 is an SEM image of Comparative Example 3.

Molybdenum plating electrolyte

The molybdenum-plated electrolyte contains molybdenum pentachloride, zinc chloride, and the remaining amount of dimethylhydrazine.

Specifically, the molybdenum-plated electrolyte uses dimethylhydrazine as a solvent, and the content of dimethylhydrazine varies depending on the total content of other components in the molybdenum-plated electrolyte. In the presence of other components, dimethyl group is added. The content of the molybdenum-plated electrolyte is 100% by mole.

In the molybdenum-plated electrolyte, the content of molybdenum pentachloride is from 0.01 mol% to 1 mol%. When the content of molybdenum pentachloride is less than 0.01 mol%, the concentration of molybdenum ions in the molybdenum-plated electrolyte is too low, which will cause a decrease in the reaction rate, which is disadvantageous for the formation of the molybdenum-containing coating. When the concentration of molybdenum ions is higher, the conductivity of the solution will be higher, which is beneficial to the conduction of molybdenum ions in the solution, thereby accelerating the reaction rate. Theoretically, it is necessary to add molybdenum pentachloride to the current temperature to achieve the optimum content. However, The higher the amount of molybdenum chloride added, the longer the required dissolution time will be. Considering the benefit ratio of dissolution amount to dissolution time, the maximum concentration in the dissolution time ≦1 hr (magnet stirring ≧215 rpm) was selected as the content of molybdenum pentachloride in the molybdenum-plated electrolyte.

In the molybdenum-plated electrolyte, the content of zinc chloride is from 0.01 mol% to 25 mol%, and the addition of zinc chloride helps to improve the quality of the molybdenum-containing coating, for example, improves the flatness and molybdenum content of the molybdenum-containing coating. , thickness, deposition rate and corrosion resistance (higher protection efficiency). When the content of zinc chloride is less than 0.01 mol%, the effect of improving the quality of the molybdenum-containing coating is limited. When the content of zinc chloride is more than 25 mol%, the zinc content in the molybdenum-containing coating is greatly increased (formation of Zn) -W alloy).

Method for forming a copper-containing plating layer

Please refer to FIG. 1 , which is a flow chart showing the steps of forming a molybdenum-containing plating layer according to an embodiment of the present invention.

Step 110 is to provide molybdenum pentachloride, zinc chloride and dimethyl hydrazine.

Step 120 is a water removal step of placing molybdenum pentachloride, zinc chloride and dimethyl hydrazine in a vacuum environment for a period of time to make molybdenum pentachloride, zinc chloride and dimethyl hydrazine. The moisture content is below 2% by weight. Specifically, in step 120, molybdenum pentachloride, zinc chloride and dimethyl hydrazine are placed in a vacuum environment at a vacuum of 1 Pa at 25 ° C to 120 ° C for 12 hours to 72 hours to make five The moisture content of molybdenum chloride, zinc chloride and dimethylhydrazine is 2% by weight or less. The aforementioned moisture content measurement can be carried out using a card type moisture analyzer (Karl-Fischer Titrator, available from Mettler-Toledo Pac Rim AG, model DL 31/38).

Step 130 is to form a molybdenum-plated electrolyte by uniformly mixing the above-mentioned water-containing molybdenum pentachloride, zinc chloride and dimethyl hydrazine to form a molybdenum-plated electrolyte. Please refer to the above for the composition of the molybdenum-plated electrolyte, and will not be repeated here. Specifically, the step 130 can be carried out under a nitrogen atmosphere, for example, in a glove box which is evacuated and filled with nitrogen, and the dimethyl hydrazine is placed on an electromagnetic stirring heater to be heated and melted, and then molybdenum pentoxide and chlorine are added. The zinc is added to the dimethyl hydrazine and placed on an electromagnetic stirring heater to be heated, stirred by a magnet, and uniformly mixed. According to an embodiment of the invention, the temperature is set to 110 ° C to 150 ° C and heated for 0.01 to 12 hours.

Step 140 is to carry out an electrochemical reaction whereby a molybdenum-containing coating can be formed.

Please also refer to FIG. 2, which is a schematic diagram showing an electrochemical system used in the method of forming a molybdenum-containing plating layer according to an embodiment of the present invention. In the second diagram, the electrochemical system includes a cathode 220, an anode 230, a reference electrode 240, a thermocouple thermometer 250, a gas filling port 260, a gas discharge port 270, a reaction tank 280, and a molybdenum-plated electrolyte 210.

The gas discharge port 270 may include a gas condensing device (not shown). The material of the reaction tank 280 may be a container such as Pyrex glass or a crucible. The cathode 220 may be a metal such as stainless steel, copper or nickel, and in the present embodiment, a stainless steel wire (SS304, diameter 0.6 mm) is used. The reference electrode 240 includes a zinc wire 241, a zinc-containing electrolyte 242, and a glass tube 243. The bottom of the glass tube 243 is filled with porous glass (not shown) to separate the zinc-containing electrolyte 242 from the molybdenum-plated electrolyte 210. The reference electrode 240 is assembled in the following manner: a zinc-containing electrolyte 242 is prepared in a glove box. The composition of the zinc-containing electrolyte 242 is DMSO ₂ : ZnCl ₂ = 50 mole%: 50 mole%, and the zinc-containing electrolyte 242 is placed in the glass tube 243. Then, one end of the zinc wire 241 is placed in the glass tube 243 and immersed in the zinc-containing electrolyte 242, and one end of the zinc wire 241 soaked into the zinc-containing electrolyte 242 can be curled into a spiral shape (not shown), thereby increasing the zinc wire. The contact area of 241 with the zinc-containing electrolyte 242. The anode 230 may be an inert electrode such as a molybdenum rod or platinum, and a molybdenum rod (diameter: 6 mm) is used in this embodiment.

Specifically, when step 140 is performed, the electrochemical system is first assembled: the molybdenum-doped electrolyte 210 is added to the reaction tank 280, and the cathode 220, the anode 230, the reference electrode 240, the thermocouple thermometer 250, and the gas filling port are inserted. 260 is filled with nitrogen into the molybdenum-doped electrolyte 210 to remove moisture and oxygen, and the cathode 220 is a substrate for electrolytically molybdenum plating.

After the assembly of the electrochemical system is completed, after the cathode 220, the anode 230, and the reference electrode 240 are connected to the power source, a molybdenum-containing plating layer can be formed on the cathode 220 by electrochemical reaction.

The foregoing power source can provide alternating current, direct current or pulsed electric power, preferably direct current, more preferably pulsed electric.

The temperature at which the electrochemical reaction is carried out may be from 115 ° C to 130 ° C.

The voltage for performing the electrochemical reaction may range from 10V to -10V, preferably -0.5V.

The current density for performing the electrochemical reaction may range from ±0.1 mA/cm ² to ±200 mA/cm ² , preferably from ±5 mA/cm ² to ±20 mA/cm ² .

Through an electrochemical reaction amount may range from 1C / cm ² to 250C / cm ^2, preferably 10C / cm ² to 225C / cm ^2, more preferably 25C / cm ^2.

When the electrochemical reaction is performed using pulsed electricity, the operating condition of the pulsed electricity may be T _on /(T _on +T _off )=0.1 to 0.9, preferably _Ton /(T _on +T _off )=0.25 to 0.75, More preferably, T _on /(T _on +T _off ) = 0.75.

According to the above embodiment, specific examples and comparative examples will be described in detail below.

Examples 1 to 2 and Comparative Examples 1 to 3

According to the composition and dosage of Table 1, the molybdenum pentachloride, zinc chloride and dimethyl hydrazine are placed in a vacuum environment and heated for a period of time to make the moisture of molybdenum pentachloride, zinc chloride and dimethylhydrazine. The content was 2 wt% or less, and the above-described water-removed molybdenum pentachloride, zinc chloride and dimethyl hydrazine were uniformly mixed to form the molybdenum-plated electrolytes of Examples 1 to 2 and Comparative Examples 1 to 3.

The molybdenum-plated electrolytes of Example 1, Example 2 and Comparative Example 2 were placed in the aforementioned electrochemical system, and electrochemically reacted by pulsed electricity to form a molybdenum-containing plating layer, wherein the electrochemical reaction was operated at a temperature of 130 ° C and a reduction voltage. It is -0.5 V and T _on /(T _on +T _off ) = 0.75.

The molybdenum-plated electrolyte of Comparative Example 1 was placed in the aforementioned electrochemical system, and electrochemically reacted by pulsed electricity to form a molybdenum-containing plating layer, wherein the electrochemical reaction was operated at a temperature of 130 ° C, a reduction voltage of -0.5 V, and _Ton / (T _on +T _off )=0.5.

The molybdenum-plated electrolyte of Comparative Example 3 was placed in the aforementioned electrochemical system, and electrochemically reacted by pulsed electricity to form a molybdenum-containing plating layer in which the operating temperature of the electrochemical reaction was 110 ° C, the reduction voltage was -0.5 V, and _Ton / (T _on +T _off ) = 0.75.

SEM results

The surface morphology of the molybdenum-containing coating layers of Examples 1 and 2 and Comparative Examples 1 to 3 was observed using an SEM (Model: Jeol JSM-6700F), and the results are shown in Figs. 3 to 7 and Figs. 3 and 4 Is respectively according to embodiment 1 of the present invention With respect to the SEM image of Example 2, FIGS. 5 to 7 are SEM images of Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively, wherein (a) of FIG. 3 to FIG. 7 are enlarged. The magnification is 10,000 times, and the figure (b) in FIGS. 3 to 7 has a magnification of 50,000.

It can be seen from Fig. 3 to Fig. 6 that when an appropriate amount of zinc chloride is added to the molybdenum-plated electrolyte, the formed molybdenum-containing coating has no cracks, has good flatness, and can form crystal grains, which can be formed by Fig. 3 It is seen that the grain size of Example 1 is from 0.1 μm to 0.2 μm, and it can be seen from Fig. 4 that the grain size of Example 2 is from 0.15 μm to 0.3 μm. When zinc chloride is not added to the molybdenum-plated electrolyte, the surface of the molybdenum-containing coating is liable to be cracked and the crystal grains are not conspicuous. When the zinc chloride in the molybdenum-plated electrolyte is excessively added, the surface of the molybdenum-containing plating layer is rough and uneven, and no crystal grains are generated.

Please compare Example 2 with Comparative Example 3 at the same time. When the operating temperature of the electrochemical reaction is 130 ° C, the formed molybdenum-containing coating has no cracks, has good flatness, and can form crystal grains when the operation of electrochemical reaction At a temperature of 110 ° C, the surface of the molybdenum-containing coating formed is uneven and the cracks are increased.

Energy dispersive spectrometer measurement results

The molybdenum-containing plating layers of Examples 1 and 2 and Comparative Examples 1 to 3 were subjected to elemental composition analysis by an energy dispersive X-ray spectrometer (EDS) attached to a SEM, and the results are shown in Table 2.

It can be seen from Table 2 that when the operating temperature of the electrochemical reaction is the same (130°C in both Examples 1-2 and Comparative Examples 1-2), the molybdenum content in the molybdenum-containing coating can be effectively improved by adding an appropriate amount of zinc chloride. The molybdenum content of Example 1 was as high as 61.34 wt%, and the molybdenum content of Example 2 was as high as 60.17 wt%. When the zinc chloride is added in excess, the content of zinc in the molybdenum-containing coating is much larger than that of molybdenum.

In addition, comparing Example 2 with Comparative Example 3, when the operating temperature of the electrochemical reaction is 130 ° C, the molybdenum content in the molybdenum-containing coating is as high as 60.17 wt%, and when the operating temperature of the electrochemical reaction is 110 ° C, in the molybdenum-containing coating The molybdenum content is only 24.95 wt%.

3D surface profiler measurement results

The molybdenum-plated electrolyte component of Comparative Example 4 was 0.01 mol% of molybdenum pentachloride and 99.99 of dimethylhydrazine. The foregoing components were placed in an electrochemical system, and electrochemically reacted by pulsed electricity to form a molybdenum-containing plating layer in which electrolysis was performed. The operating temperature of the reaction was 130 ° C, the reduction voltage was -0.5 V and T _on /(T _on +T _off ) = 0.75.

The molybdenum-containing plating layers of Examples 1 to 2 and Comparative Example 4 were measured by a 3D surface profilometer (TM) to measure the height difference of the molybdenum-containing plating layer (having a boundary between the plating layer and the uncoated layer) to obtain the thickness of the molybdenum-containing plating layer. The results are shown in Table 3.

It can be seen from Table 3 that the thickness of the molybdenum-containing coating increases as the concentration of zinc chloride increases, indicating that the deposition rate can be increased by adding zinc chloride in an appropriate amount.

Corrosion resistance analysis

The corrosion resistance analysis was carried out in Example 1 and Comparative Example 4, and the analysis method was as follows. A 3.5 wt% NaCl aqueous solution was used as the etching solution, a platinum wire was used as the counter electrode, a test object was used as the working electrode, and Ag/AgCl was used as the reference electrode. The reference electrode is manufactured as follows. The front end of the silver wire is spirally formed (10 turns, 0.2 cm per turn), and the platinum wire is used as a cathode and the silver wire is used as a cathode with a 3 M hydrochloric acid aqueous solution at a voltage of 3 V. After electroplating in a two-pole manner for 15 minutes, an Ag/AgCl electrode wire can be obtained. A saturated potassium chloride aqueous solution is prepared and placed in a porous glass, and the Ag/AgCl electrode wire is placed in the porous glass and saturated with chlorine at one end. A reference electrode can be obtained by using an aqueous solution of potassium. The scanning range was -0.7V to 1.2V, and the scanning rate was 1mV/s. The Taver polarization curves of Example 1 and Comparative Example 4 were obtained, respectively, and the corrosion obtained by the Taver polarization curve was obtained. The current further calculated the protection efficiency of the molybdenum-containing plating layer, and the protection efficiency of Example 1 was 74%, and the protection efficiency of Comparative Example 4 was 70%.

In summary, the molybdenum-plated electrolyte of the present invention can improve the flatness, molybdenum content, thickness, deposition rate and corrosion resistance of the molybdenum-containing coating by adding 0.01 mol% to 25 mol% of zinc chloride. High efficiency), In addition, compared with the conventional molybdenum deposition technology, the temperature of the electrochemical reaction in the method for forming a molybdenum-containing coating of the present invention is 115 ° C to 130 ° C, and the required temperature is significantly lower, which can effectively save energy and avoid high temperature corrosion. And to avoid deformation or damage to the substrate.

While the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and the invention may be modified and modified in various ways without departing from the spirit and scope of the invention. The scope is subject to the definition of the scope of the patent application.

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Claims (4)

A molybdenum-plated electrolyte, excluding fluorine-containing salts, comprising: 0.01 mole percent of molybdenum pentachloride (MoCl ₅ ); 10 mole percent to 20 mole percent of zinc chloride (ZnCl ₂ ); The remaining amount of dimethyl hydrazine (C ₂ H ₆ O ₂ S). A method for forming a molybdenum-containing plating layer, comprising: providing molybdenum pentachloride, zinc chloride and dimethyl hydrazine; performing a water removal step of placing the molybdenum pentachloride, the zinc chloride and the dimethyl hydrazine In a vacuum environment, heating is continued for a period of time, so that the moisture content of the molybdenum pentachloride, the zinc chloride and the dimethyl hydrazine is less than 2 wt%; forming a molybdenum-plated electrolyte, which is a molybdenum pentachloride, the chlorine Zinc is uniformly mixed with the dimethylhydrazine, wherein the molybdenum-plated electrolyte excludes fluorine-containing salts and contains 0.01 mol% of molybdenum pentachloride, 10 mol% to 20 mol% of zinc chloride, and the balance Dimethyl hydrazine; and performing an electrochemical reaction to form a molybdenum-containing plating layer, wherein the electrochemical reaction is performed at 130 ° C using a pulsed electric current under a nitrogen atmosphere, and the reduction voltage of the pulse electric current is -0.5 V, and The operating condition of this pulsed electric power is Ton / (Ton + Toff) = 0.75. The method of forming a molybdenum-containing plating layer according to claim 2, wherein the step of performing the water removal is carried out at 25 ° C to 120 ° C for 12 hours to 72 hours. A method of forming a molybdenum-containing plating layer as described in claim 2, wherein the step of forming the molybdenum-plated electrolyte is carried out at 110 ° C to 150 ° C under a nitrogen atmosphere.