MANUFACTURING METHOD OF ULTRA-LARGE COPPER GRAINS WITHOUT HEAT TREATMENT

Abstract

A film of single crystal copper is manufactured by means of electrodeposition without heat treatment. The grains of the single crystal copper have an average size of at least 10 μm. The electrolytic solution used in the method contains chloride ions, a wetting agent, sulfuric acid, CuSO4.5H2O and alkanesulfonate sulfide. The ultra-large copper grains of the present invention contain very few impurities and thus possess low resistance, high conductivity, shining appearance and anti-fingerprint property.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a manufacturing method of ultra-large copper grains, an electrolytic solution employed therein, and a copper film composed of the copper grains. More particularly, this method comprises an electrodeposition process without heat treatment. The copper grains have an average size of at least 10 μm.

2. Prior Art

In general, the copper film is made by depositing copper on a conductive substrate through the electroplating or sputtering process. Such copper film is composed of fine copper grains with an average size less than 100 nm. The copper films with larger grain sizes possess better conductivity or reliability and can be applied to different fields. Traditionally, the large copper grains are manufactured through the heat treatment or calendaring process.

The known technologies relating heat treatment include:

U.S. Pat. No. 6,126,761 (CN1056613C) discloses a process of controlling grain growth in metal films, which comprises: (a) depositing the metal film onto the substrate to form a film having a fine-grained microstructure, and (b) heating the metal film in a temperature range of 70-100° C. for at least five minutes, wherein the fine-grained microstructure is converted into a stable large-grained microstructure of an average crystallite size greater than 1 micron.

US20150064496 (TWI507569, CN104419983A) discloses a method for manufacturing a single crystal copper, in which an electroplating is performed to grow a nano-twinned crystal copper pillar on a surface of the cathode. The nano-twinned crystal copper pillar comprises a plurality of nano-twinned crystal copper grains. The cathode with the nano-twinned crystal copper pillar is then annealed at 350-600° C. for 0.5-3 hours to obtain a single crystal copper. The single crystal copper has a [100] orientation and a volume of 0.1 μm³-4.0×10⁶ μm³.

US20160168746A1 (TWI545231) discloses a copper film with large grains. The grains are grown along a crystal axis direction [100], and an average size of the grains is 150-700 μm. A manufacturing method of the copper clad laminate comprises: growing copper grains on one surface of a laminate by electroplating to obtain a [111]-oriented nano-twinned copper film; and annealing the [111]-oriented nano-twinned copper film under a temperature of 200-500° C. to obtain a copper film with large grains.

To perform the heat treatment, heating equipment is necessary and time and temperature have to be controlled. The processes including electroplating and heat treatment are complex and increase the cost. In addition, the heat treatment may cause diffusion of impurity in the copper and thus reduce conductivity.

SUMMARY OF THE INVENTION

The manufacturing method of ultra-large copper grains according to the present invention is performed without heat treatment.

This method comprises steps of: A. providing an electrodeposit equipment; and B. performing an electrodeposition process using the electrodeposit equipment with a current density of 1-80 A/dm².

In step A, the electrodeposit equipment primarily comprises an anode, a cathode, an electrolytic solution, a power unit, a temperature controller, and a mixer. The anode and the cathode respectively connect to the power unit and are immersed in the electrolytic solution. The temperature controller contacts the electrolytic solution to control the electrolytic solution at 25-55° C. The mixer is used to fast agitate the electrolytic solution. The electrolytic solution is obtained by mixing and dissolving chemical components such as chloride ions, wetting agent, sulfuric acid, copper sulfate and sulfur-containing compound having the formula (1) together in deionized water,

R₁—S—C_nH_2n—R₂   (1)

wherein R₁═—H, —S—C_nH_2n—R₂ or —C_nH_2n—R₂;

• • R₂═SO₃⁻, PO₄⁻ or COO⁻;
  • n=2-10.

In step B, ultra-large single crystal copper grains having an average size of at least 10 μm are deposited on a surface of the cathode to form a layer of copper grains. The sulfur-containing compound preferably is alkanesulfonate sulfide (R—S—C_nH_2n—SO₃⁻).

Examples of the sulfur-containing compound include 3-Mercaptopropanesulfonate (MPS), Bis-(3-sulfopropyl)-disulfide (SPS), 3-(2-Benzthiazolylthio)-1-propanesulfonate (ZPS), 3-(N,N-Dimethyl-thiocarbamoyl)-thiopropanesulfonate (DPS), (O-Ethyldithiocarbonato) —S-(3-sulfopropyl)-ester (OPX), 3-[(Amino-iminomethyl)thio]-1-propanesulfonate (UPS) and 3,3-Thiobis(1-propanesulfonate (TBPS).

A copper film is manufactured by the method aforementioned. The copper film comprises a plurality of the ultra-large single crystal copper grains having an average size of at least 10 μm.

By performing an electrodeposition process in the electrolytic solution, the ultra-large single crystal copper grains having an average size of at least 10 μm are deposited on the cathode.

The sulfur-containing compound preferably is alkanesulfonate sulfide (R—S—C_nH_2n—SO₃⁻).

The present invention further comprises a connecting structure of electric elements comprising the ultra-large copper grains produced by the aforementioned method. The connecting structure of electric elements comprises:

a copper pad comprising the ultra-large copper grains having an average size of at least 10 μm;

a solder unit soldered on a surface of the copper pad; and

an intermetallic compound (IMC) layer formed between the pad and the solder unit, and containing no void at the interface between the copper pad and IMC, and between the IMC and the solder unit.

Through the electrodeposition process without heat treatment, ultra-large copper grains having an average size of at least 10 μm, and copper films with less impurities, lower electrical resistance, shining appearance and anti-fingerprint property can be manufactured with lower costs.

The product of the present invention can be applied to circuit boards, substrates for IC packaging, copper traces and bumps of semiconductor chips, and decorative electroplating.

Through the heat treatment at 200° C. for 1000 hours, the connecting structure of electric elements having less impurity, lower electrical resistance and better reliability can be manufactured without Kirkendall void in the intermetallic compound layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show the electrodeposition equipment used in the present invention.

FIG. 3 shows the appearance of the copper film of the present invention.

FIG. 4 shows the SEM image (100×) of the copper film of the present invention.

FIG. 5 shows the SEM image (500×) of the copper film of the present invention.

FIG. 6 shows the SEM image (3000×) of the copper film of the present invention.

FIG. 7 shows the FIB images (5000×) of (A) the ultra-large copper grains of the present invention and (B) traditional nano-twinned crystal copper.

FIG. 8 shows the FIB image (1400×) of the ultra-large copper grains of the present invention.

FIG. 9 shows the size of the ultra-large copper grains of the present invention by the linear intercept method.

FIG. 10 shows the TEM images and SAD patterns of the ultra-large copper grains of the present invention.

FIG. 11 illustrates the connecting structure of electric elements including the ultra-large copper grains of the present invention.

FIG. 12 shows the FIB image of the connecting structure of electric elements including the ultra-large copper grains of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, the manufacturing method of ultra-large copper grains, the copper film and connecting structure of electric elements comprising the ultra-large copper grains are discussed in detail in conjunction with the accompanying figures.

In the present invention, the electrodeposition process for manufacturing the copper film of ultra-large single crystal grains can be the electroforming process or the electroplating process.

FIGS. 1 and 2 shows an electrodeposition equipment used in the present invention, which includes a cathode 1, an anode 2, an electrolytic solution 4, a mixer 5, a temperature controller 6 and a power unit 7. The anode 2 and the cathode 1 respectively connect to the power unit 7 and are immersed in the electrolytic solution 4.

The temperature controller 6 contacts with the electrolytic solution 4 which is fast agitated with the mixer 5. The mixer 5 is a jet mixer located between the cathode 1 and the anode 2. The cathode 1 can be a rotary cylinder complimentary to the anode 2, as shown in FIG. 1. Alternatively, the cathode 1 and the anode 2 can be plate-shaped, as shown in FIG. 2. The anode 2 can be soluble or insoluble, and made by platinum, iridium dioxide/titanium, iridium dioxide/tantalum pentoxide/titanium, copper, or copper-phosphorus alloy. The cathode 1 can be made by any conductive material such as metal and conductive carbon. The cathode 1 and the anode 2 are separated by a distance of 1-12 cm. The product is deposited on the surface of the cathode 1. The equipment in FIG. 1 is usually defined as an electroformer since the product 3 on the cylindric cathode 1 is collected by a delivery band over the roller 8. The equipment in FIG. 2 can be defined as an electroplating if the product 3 remains on the plate cathode 2, or an electroformer if the product 3 is separated from the cathode 2.

The electrolytic solution is obtained by mixing and dissolving chloride ions, wetting agent, sulfuric acid, copper sulfate pentahydrate (CuSO₄.5H₂O) and sulfur-containing compound having the formula (1) together in deionized water,

R₁—S—C_nH_2n—R₂   (1)

wherein R₁═—H, —S—C_nH_2n—R₂, or —C_nH_2n—R₂;

• • R₂═SO₃⁻, PO₄⁻, or COO⁻;
  • n=2-10.

The electrolytic solution is controlled at 25-55° C. The copper sulfate pentahydrate in the electrolytic solution has a concentration of 125-320 g/L. The low concentration of copper sulfate pentahydrate (125 g/L) is operated at low temperature (25 degree), vice versa. The sulfuric acid in the electrolytic solution has a concentration of 17.6-176 g/L. The chloride ions are supplied by sodium chloride or hydrochloric acid and have a concentration of 30-60 ppm in the electrolytic solution. The wetting agent is polyethylene glycol (PEG) with a molecular weight of 200-2000, and has a concentration of 10-200 ppm in the electrolytic solution. The sulfur-containing compound is alkanesulfonate sulfide (R—S—C_nH_2n—SO₃⁻) and has a concentration of 0.1-5 ppm in the electrolytic solution. The alkanesulfonate sulfide includes but is not limited to 3-Mercaptopropanesulfonate (MPS), Bis-(3-sulfopropyl)-disulfide (SPS), 3-(2-Benz-thiazolylthio)-1-propanesulfonate (ZPS), 3-(N,N-Dimethyl-thiocarbamoyl)- thiopropanesulfonate (DPS), (O-Ethyl dithiocarbonato)-S-(3-sulfopropyl)-ester (OPX), 3-[(Amino-iminomethyl)thio]-1-propanesulfonate (UPS) and 3,3-Thiobis-(1-propanesulfonate (TBPS).

In a preferred embodiment, the DC power source with an output 100 A/10V is used for the power unit 7.

The current density of the current provided by the power unit 7 is 1-80 A/dm², and the current efficiency is 94%.

By means of electrodeposition, ultra-large copper grains (ULG) having an average size of at least 10 μm are deposited on the cathode. The thickness is determined according to Faraday's law (δ=0.003445×j×t; wherein δ is thickness (μm), j is current density (A/dm²), and t is time for electrodeposition (second)). In a preferred embodiment, the deposit of ultra-large copper grains each have a size of 18 cm×21 cm×30 μm (thickness).

FIG. 3 shows the ultra-large copper grains of the present invention, which has a rough surface and shining appearance caused by reflection of the single crystals. The surface roughness is determined by a surface measuring machine (SURFCOM 130 A of ZEISS). The ten point height of irregularities (Rz) is 29.40±8.40 μm, and the arithmetical mean deviation (Ra) is 4.67±6.14 μm. The high roughness can reduce the area contacting with fingers, so that almost no finger-print remains.

FIG. 4 shows the SEM image (100×) of the ultra-large copper grains, which indicates deep indents distributed over the surface.

FIGS. 5 and 6 show the SEM images (500× and 3000×, respectively) of the ultra-large copper grains, which indicate the copper crystals with sharp edges.

FIG. 7 compares the FIB (focused ions beam) images (5000×) of the ultra-large copper grains of the present invention (A) and the traditional twinned copper crystals (B). Obviously, the copper grains of the present invention have a size about 10-50 times of the traditional twinned copper.

FIG. 8 shows the FIB image (1400×) of the ultra-large copper grains of the present invention, which indicates that the microstructure is consistent within a profile of 100 μm.

In FIG. 9, the linear intercept method is used to determine the average size of the ultra-large copper grains and the mean grain intercept is measured as 10 μm.

FIG. 10 shows the TEM (transmission electron microscope) images and the SAD (selected area diffusion) patterns of the ultra-large copper grains, which verify that each of the ultra-large grains is a single crystal.

In the present invention, the ultra-large copper grains having an average size of at least 10 μm, less impurities and lower electrical resistance can be manufactured through the electrodeposition (electroforming or electroplating) process without any heat treatment.

FIG. 11 illustrates the connecting structure of electric elements including the ultra-large copper grains of the present invention. The connecting structure of electric elements primarily includes a first dielectric layer 11, a second dielectric layer 12, copper pads (or copper traces) 13, 14 and a solder unit 15. The copper pads 13, 14 are respectively formed on the opposite surfaces of the first dielectric layer 11 and the second dielectric layer 12. The copper pads 13, 14 are made by the electrodeposition process aforementioned and thus include the ultra-large copper grains having an average size of at least 10 μm. The solder unit 15 is formed between the copper pads 13, 14, and can be made by pure tin, tin/silver/copper alloy, tin/silver alloy or other solder materials. The intermetallic compound (IMC) layers 16 (Cu₃Sn), 17 (Cu₆Sn₅) existing between the copper pads 13, 14 and the solder unit 15 are formed by metal diffusion and shifting.

FIG. 12 shows the FIB images of the connecting structures of electric elements including the ultra-large copper grains after heated at 200° C. for 72 hours (A) and 1000 hours (B), and then cut with ion beams. As shown in FIG. 12, there is no void at the interface between the copper pad 13 and IMC 16, and between the IMC 17 and the solder unit 15 after high heat treatment. In addition, the intermetallic compound layers 16, 17 between the copper pad 13 and the solder unit 15 are solid without Kirkendall void. It is known that the Kirkendall void is adverse to electron transport and thus reduce conductivity. The connecting structure of electric elements of the present invention contains no Kirkendall void, and the ultra-large copper grains contain very few impurities and have low resistance. Therefore, the present invention can provide a connecting structure of electric elements with superior reliability.

Claims

1. A manufacturing method of ultra-large copper grain without heat treatment, comprising: A. providing an electrodeposit equipment which comprises an anode, a cathode, an electrolytic solution, a power unit, a temperature controller and a mixer; wherein the anode and the cathode respectively connect to the power unit and are immersed in the electrolytic solution; the temperature controller contacts with the electrolytic solution to control the electrolytic solution at 25-55° C.; the mixer agitates the electrolytic solution; and the electrolytic solution is obtained by mixing and dissolving chloride ions, wetting agent, sulfuric acid, copper sulfate and sulfur-containing compound having the formula (1) together in deionized water, R1—S—CnH2n—R2 wherein R1═—H, —S—CnH2n—R2 or —CnH2n—R2; R2═SO3−, PO4− or COO−;n=2-10;B. performing an electrodeposition process using the electrodeposit equipment with a current density of 1-80 A/dm2 to deposit ultra-large single crystal copper grains having an average size of at least 10 μm to form a layer of copper grains on a surface of the cathode.

2. The method of claim 1, wherein the sulfur-containing compound is alkanesulfonate sulfide (R—S—CnH2n—SO3−).

3. The method of claim 1, wherein the sulfur-containing compound is selected from the group consisting of 3-Mercaptopropanesulfonate (MPS), Bis-(3-sulfopropyl)-disulfide (SPS), 3-(2-Benzthiazolylthio)-1-propanesulfonate (ZPS), 3-(N,N-Dimethylthiocarbamoyl)-thiopropanesulfonate (DPS), (O-Ethyldithiocarbonato)-S-(3-sulfopropyl)-ester (OPX), 3-[(Amino-iminomethyl)thio]-1-propanesulfonate (UPS) and 3,3-Thiobis(1-propanesulfonate (TBPS).

4. The method of claim 1, wherein the sulfur-containing compound has a concentration of 0.1-5 ppm in the electrolytic solution.

5. The method of claim 4, wherein the copper sulfate in the electrolytic solution has a concentration of 125-320 g/L.

6. The method of claim 5, wherein the sulfuric acid has a concentration of 17.6-176 g/L in the electrolytic solution.

7. The method of claim 6, wherein the chloride ions have a concentration of 30-60 ppm in the electrolytic solution.

8. The method of claim 7, wherein the wetting agent is polyethylene glycol (PEG) having a molecular weight of 200-2000 and a concentration of 10-200 ppm in the electrolytic solution.

9. The method of claim 1, wherein the anode and the cathode are separated from each other by a distance of 1-12 cm.

10. The method of claim 1, wherein the mixer is a jet mixer having a flow rate of 9-45 cm/s.

11. A copper film manufactured by the method of claim 1, comprising a plurality of the ultra-large single crystal copper grains having an average size of at least 10 μm.

12. An electrolytic solution employed in a manufacturing method of ultra-large copper grains without heat treatment, comprising: chemical components including chloride ions, a wetting agent, sulfuric acid, copper sulfate and a sulfur-containing compound having the formula (1), R1—S—CnH2n—R2   (1),wherein R1═—H, —S—CnH2n—R2 or —CnH2n—R2; R2═SO3−, PO4− or COO−;n=2-10; anddeionized water for mixing and dissolving the chemical components therein;wherein the manufacturing method performs an electrodeposition process in the electrolytic solution to deposit ultra-large single crystal copper grains having an average size of at least 10 μm to form a layer of copper grains on a work electrode.

13. The electrolytic solution of claim 12, wherein the sulfur-containing compound is alkanesulfonate sulfide (R—S—Cn—H2n—SO3−).

14. The electrolytic solution of claim 12, wherein the sulfur-containing compound is selected from the group consisting of 3-Mercaptopropanesulfonate (MPS), Bis-(3-sulfopropyl)-disulfide (SPS), 3-(2-Benzthiazolylthio)-1-propanesulfonate (ZPS), 3-(N,N-Dimethylthiocarbamoyl)-thiopropanesulfonate (DPS), (O-Ethyldithiocarbonato)-S-(3-sulfopropyl)-ester (OPX), 3-[(Amino-iminomethyl)thio]-1-propanesulfonate (UPS) and 3,3-Thiobis(1-propanesulfonate (TBPS).

15. The electrolytic solution of claim 12, wherein the sulfur-containing compound has a concentration of 0.1-5 ppm in the electrolytic solution.

16. The electrolytic solution of claim 15, wherein the copper sulfate in the electrolytic solution has a concentration of 125-320 g/L.

17. The electrolytic solution of claim 16, wherein the sulfuric acid has a concentration of 17.6-176 g/L in the electrolytic solution.

18. The electrolytic solution of claim 16, wherein the chloride ions has a concentration of 30-60 ppm in the electrolytic solution.

19. The electrolytic solution of claim 18, wherein the wetting agent is polyethylene glycol (PEG) having a molecular weight of 200-2000 and a concentration of 10-200 ppm in the electrolytic solution.

20. A connecting structure of electric elements including the ultra-large copper grains manufactured by the manufacturing method of claim 1, comprising: a copper pad including the ultra-large copper grains having an average size of at least 10 μm;a solder unit on a surface of the pad; andan intermetallic compound (IMC) layer formed between the copper pad and the solder unit, wherein no void is present at the interface between the copper pad and the IMC, and between the IMC and the solder unit.