US20220090282A1

US20220090282A1 - Manufacturing method of aluminum nitride

Info

Publication number: US20220090282A1
Application number: US17/465,877
Authority: US
Inventors: Kun-Cheng Peng; Chun-Ying Lee; Chi-Ting CHUNG
Original assignee: Ming Chi University of Technology
Current assignee: Ming Chi University of Technology
Priority date: 2020-09-22
Filing date: 2021-09-03
Publication date: 2022-03-24
Also published as: TWI765358B; TW202212252A

Abstract

The present disclosure provides a manufacturing method of aluminum nitride, including: providing an electrolyte including choline chloride, urea, aluminum chloride, boric acid, and ascorbic acid; disposing a workpiece, wherein at least a part of the workpiece is in contact with the electroplating solution; heating the electrolyte to within 60° C.-95° C.; applying an operating current to electroplate aluminum onto the workpiece; and annealing the aluminum on the workpiece to form aluminum nitride.

Description

CROSS REFERENCE TO RELATED DISCLOSURE

This disclosure claims the priority benefit of Taiwan Patent Disclosure Number TW109132791, filed on Sep. 22, 2020, the full disclosure of which is incorporated herein by reference.

BACKGROUND

Technical Field

The present disclosure is related to an electroplating technique, and in particular, a manufacturing method of aluminum nitride.

Related Art

Aluminum nitride (AlN) is the wurtzite structure which belongs to the hexagonal crystal system. The bonding thereof is covalent bond, and the melting point thereof is up to 2700° C. AlN is the material having the highest bandgap (about 6.2 eV) among the group of III-V compound semiconductors and is transparent in the visible lights. AlN may be used as an optical thin film. Moreover, AlN has excellent physical properties such as high thermal conductivity (285 W/mK), high dielectric constant (es=8.5), good piezoelectric activity, high surface acoustic wave speed (may be up to 5600˜6000 m/s in the preferred orientation of c-axis), and high electromechanical coupling coefficient, etc.
Based on the characteristics mentioned above, AlN is widely used. For example, AlN may be used as a packaging substrate of semiconductors and microelectronics, a substrate for carrying high brightness LED chips, automotive electronics, lighting components, heat-dissipating material for high-power electronic components, IC packaging material, surface acoustic wave (SAW) components, bulk acoustic wave (BAW) components, light-emitting diode, gate dielectric layer for high-temperature disclosure, etc.
In the present, for manufacturing of AlN coating, chemical vapor deposition (CVD) is generally used to form AlN on substrate or workpiece. However, CVD has a lot of process limitations and is difficult to correspond to the workpiece with complicated shapes. Therefore, CVD is not conducive to large-scale production. In addition, due to the CVD equipment is expensive and the deposition rate of CVD is low, the cost of AlN remains high.

SUMMARY

The embodiments of the present disclosure disclose a manufacturing method of aluminum nitride, in order to solve the problem of the high cost due to the complex process when the aluminum nitride coatings are manufactured by chemical vapor deposition.
In order to solve the above technical problems, the present disclosure is implemented as follows.
The present disclosure provides a manufacturing method of aluminum nitride, which including: providing an electrolyte including choline chloride, urea, aluminum chloride, boric acid, and ascorbic acid; disposing a workpiece, wherein at least a part of the workpiece is in contact with the electroplating solution; heating the electrolyte to within 60° C.-95° C.; applying an operating current to electroplate aluminum onto the workpiece; and annealing the aluminum on the workpiece to form aluminum nitride.
In the embodiment of the present disclosure, the aluminum is electroplated on the workpiece by the electrolyte with specific compositions, then the electroplated workpiece is annealed to obtain an AlN coating. The process of the present disclosure is simple and may be applied to large-area production. Moreover, the composition of the electrolyte used in the electroplating process is safe and non-toxic, and the electrolyte may be reused to reduce the waste of resources.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures described herein are used to provide a further understanding of the present disclosure and constitute a part of the present disclosure. The exemplary embodiments and descriptions of the present disclosure are used to illustrate the present disclosure and do not limit the present disclosure, in which:

FIG. 1 is the flowchart of the manufacturing method of aluminum nitride according to an embodiment of the present disclosure;

FIG. 2 to FIG. 6 respectively are the surface morphologies of the AlN according to the first embodiment of the present disclosure;

FIG. 7 to FIG. 10 respectively are the surface morphologies of the AlN according to the second embodiment of the present disclosure;

FIG. 11 is the element analysis diagram of the AlN according to the second embodiment of the present disclosure;

FIG. 12 is the X-ray diffraction spectrum of the AlN according to the second embodiment of the present disclosure;

FIG. 13 is the X-ray diffraction spectrum of the AlN according to the third embodiment of the present disclosure; and

FIG. 14 is the spectrum of electron spectroscopy for chemical analysis (ESCA) of the AlN according to the third embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In order to make the objectives, technical solutions, and advantages of the present disclosure clearer, the technical solutions of the present disclosure will be described clearly and completely in conjunction with specific embodiments and the figures of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of this disclosure.
The following description is of the best-contemplated mode of carrying out the present disclosure. This description is made for the purpose of illustrating the general principles of the present disclosure and should not be taken in a limiting sense. The scope of the present disclosure is best determined by reference to the appended claims.
Moreover, the terms “include”, “contain”, and any variation thereof are intended to cover a non-exclusive inclusion. Therefore, a process, method, object, or device that comprises a series of elements not only includes these elements, but also comprises other elements not specified expressly, or may include inherent elements of the process, method, object, or device. If no more limitations are made, an element limited by “include a/an . . . ” does not exclude other same elements existing in the process, the method, the article, or the device which comprises the element.
The manufacturing method of AlN of the present disclosure includes a plurality of steps and is applied to any electroplating and annealing equipment recognized by a person of ordinary skill in the art.
In some embodiments, electroplating equipment may include an electroplating tank, target, and power supply. The power supply includes the anode and cathode. The target is electrically connected to the anode of the power supply. The target includes aluminum metal or alloy to be the source of aluminum ions. In some embodiments, the electroplating equipment may further include an absorbent component. The absorbent component is electrically connected to the power supply and generates static electricity by the current provided by the power supply to absorb carbon ions generated during the electroplating process.
In some embodiments, the annealing equipment may be a rapid thermal annealing (RTA) furnace, which may be applied to anneal the product or workpiece just electroplated with aluminum to reduce the internal stress generated during the electroplating process of the products or workpieces. Furthermore, the annealing process may make the atomic in the aluminum coating diffusion to form new grains.
FIG. 1 is the flowchart of the manufacturing method of aluminum nitride according to an embodiment of the present disclosure. As shown in the figure:
Step S1: Providing the electrolyte includes choline chloride, urea, aluminum chloride, boric acid, and ascorbic acid. The electrolyte is disposed in the electroplating tank and at least a part of the target is submerged in the electrolyte. In some embodiments, the absorbent component included in the electroplating equipment may also be submerged in the electrolyte.
The purpose of adding choline chloride and urea is to form deep eutectic solvent. More specifically, the mixture of choline chloride and urea with a specific ratio is liquid at room temperature. In some embodiment, the concentration of choline chloride in the electrolyte is 560 g/L. According to the molar concentration formula (molar concentration=mass of solute (g)/molecular mass of solute (g)/solution volume (L)), the molar concentration of choline chloride is 4 M. The concentration of urea in the electrolyte is 480 g/L, or the molar concentration thereof is 8 M. In other words, the molar ratio of choline chloride and urea in the electrolyte is 1:2. The electrolyte with the present molar ratio has the lowest melting temperature of 12° C. However, the present disclosure is not limited thereto. The concentration of choline chloride in the electrolyte may be within 460 g/L to 660 g/L and the concentration of urea may be within 380 g/L to 580 g/L. The preferred mixing ratio in the electrolyte is 560 g of choline chloride and 480 g of urea per litter. In some embodiments, 560 g of choline chloride and 480 g of urea are mixed and heated to 80° C. to form the ionic liquid. The ionic liquid is the main ingredient of the electrolyte of the present disclosure.
The purpose of adding aluminum chloride is to provide the source of aluminum ions in the electrolyte. In some embodiments, the molar concentration of aluminum chloride may be within 0.005 M to 1 M. For example, the concentration of aluminum chloride added to the electrolyte is 120 g/L or 0.5 M. However, the present disclosure is not limited thereto. The concentration of aluminum chloride in the electrolyte may be within 90 g/L to 150 g/L, and the preferred adding amount is 120 g/L.
The purpose of adding ascorbic acid is to eliminate the oxygen bubbles in the electrolyte, therefore the quality of electroplating is improved. In some embodiments, the molar concentration of ascorbic acid may be within 0.025 M to 0.15 M. For example, the concentration of ascorbic acid in the electrolyte is 2 g/250 mL or 0.05 M. However, the present disclosure is not limited thereto. The concentration of ascorbic acid in the electrolyte may be within 1 g/250 mL to 6 g/250 mL, and the preferred adding amount is 2 g/250 mL.
The purpose of adding boric acid is to stabilize the pH value of the electrolyte, i.e. adjust the concentration of hydrogen ions. The electrolyte after adding oric acid becomes weakly acidic and has a pH value of about 4. In some embodiments, the molar concentration of boric acid may be within 0.7 M to 2 M. For example, the concentration of boric acid in the electrolyte is 20 g/200 mL or 1.62 M. However, the present disclosure is not limited thereto. The concentration of ascorbic acid in the electrolyte may be within 15 g/200 mL to 25 g/200 mL, and the preferred adding amount is 20 g/200 mL.
In some embodiments, the electrolyte may further include saccharin (C₇H₅NO₃S). The purpose of adding saccharin is to refine the grain size, adjust the internal stress, and improve the surface finish of plated coating. In some embodiments, the molar concentration of saccharin may be within 0.03 M to 0.2 M. For example, the concentration of saccharin in the electrolyte is 2 g/200 mL or 0.05 M. However, the present disclosure is not limited thereto. The concentration of saccharin in the electrolyte may be within 2 g/200 mL to 7 g/200 mL, and the preferred adding amount is 2 g/200 mL.
In some embodiments, the electrolyte may further include graphene or graphene oxide. The purpose of adding graphene or graphene oxide is to improve the corrosion potential (E_corr) and the corrosion current (I_corr). In some embodiments, the molar concentration of graphene or graphene oxide may be within 0.005 M to 0.05 M. For example, the concentration of graphene in the electrolyte is 0.05 g/200 mL or 0.02 M. Alternatively, the concentration of graphene oxide is 0.05 g/200 mL or 0.02 M
In some embodiments, the electrolyte may further include brightener, stabilizer, softener, wetting agent, leveling agent, or any combinations thereof according to different requirements.
In general, the electrolyte of the present disclosure is ionic liquid and may contain no water. Therefore, the overall liquid temperature does not rise too much after electroplating, thus delaying the degradation rate of the electrolyte of the present disclosure.
Step S2: Disposing the workpiece, and at least a part of the workpiece is in contact with the electrolyte. The workpiece is electrically conductive or at least partially conductive and is electrically connected to the cathode of the power supply. In some embodiments, the workpiece may be metal or other material coated with a metallic layer on the surface. For example, the workpiece may include copper or alloys thereof.
In some embodiments, the workpiece may be polished by using emery paper or rinsed by using diluted hydrochloric acid to remove the rust on the surface. Then, the de-rusted workpiece is degreased by rinsing with sodium hydroxide solution. Finally, the workpiece is rinsed with distilled water, disposed in the electroplating equipment, and electrically connected to the power supply and in contact with electrolyte.
Step S3: Heating the electrolyte up to 60° C. to 95° C. The electrolyte is anhydrous ionic liquid, so the electrolyte has a certain viscosity. The viscosity decreases as the temperature increases. When the temperature is lower than 60° C., the viscosity is too high to impedes the flow of the electrolyte. When the temperature is lower than 60° C., the viscosity of the electrolyte is too high. Therefore, aluminum ions do not flow easily, and the deposition rate is too low. In contrast, when the temperature is higher than 95° C., the surface structure of the aluminum coating is damaged and the quality of the coating is reduced. Therefore, the preferred working temperature for the electrolyte is within 60° C. to 95° C. For example, the working temperature for the electrolyte may be 60° C., 65° C., 70° C., 75° C., 80° C., 85° C., 90° C., 95° C., or any temperature within the range mentioned above.
Step S4: Applying an operating current to electroplate aluminum onto the workpiece. When the power switch is on, the power supply provides direct current to the workpiece and the target to perform electroplating. During the electroplating process, the reaction at the anode is Al→Al³⁺+3e⁻, while the reaction at the cathode is Al³⁺+3e⁻→Al. Specifically, the aluminum of the target releases electrons and becomes aluminum ion Al^e+ dissolved in the electrolyte. The Al³⁺ in the electrolyte receives the electrons from the target and is reduced into aluminum metal. Then, the aluminum metal is deposited on the surface of the workpiece at the cathode. In some embodiments, the working current may be within the range of 1 mA to 10 mA. For example, the working current may be 1 mA, 2 mA, 3 mA, 4 mA, 5 mA, 6 mA, 7 mA, 8 mA, 9 mA, 10 mA, or any current within the range mentioned above.
Step S5: Annealing the workpiece to form aluminum nitride by nitriding the aluminum on the workpiece. To prevent the aluminum coating from oxidation with oxygen in the surrounding at high temperature, a certain degree of vacuum has to be secured inside the annealing equipment before annealing. The annealing belongs to a thermal activation process. When the annealing temperature is lower than 250° C., the effect of the stress relief is limited and the crystallization of AlN is formed difficult. In contrast, when the annealing temperature is higher than 450° C., the grains of the crystallization are too coarse. The quality of the coating is worse, and the coating may even crack due to thermal stress. Therefore, the preferred annealing temperature range is within 250° C. to 450° C. For example, the annealing temperature may be 250° C., 300° C., 350° C., 400° C., 450° C., or any temperature within the range mentioned above.
During the annealing process, the aluminum coating on the workpiece reacts with the residual nitrogen atoms from urea and choline chloride. Therefore, AlN is formed. More specifically, an AlN coating is formed. In other words, no additional nitrogen gas has to be supplied in the annealing equipment and the process coat is reduced. However, the present disclosure is not limited thereto. The introduction of additional nitrogen gas in the annealing equipment may also be a feasible option.
In some embodiments, in addition to vacuuming the annealing equipment, nitrogen may also be introduced to anneal the workpiece in a nitrogen environment. In this way, the aluminum coating on the workpiece may react with more nitrogen atoms to form a uniform aluminum nitride coating. More specifically, the volumetric flow rate is within 10 sccm to 30 sccm. For example, the flow rate may be 10 sccm, 15 sccm, 20 sccm, 25 sccm, 30 sccm, or any flow rate within the range mentioned above.
Hereinafter, the aluminum nitride manufactured according to the method of the present disclosure will be discussed. Wherein, the parameters of the first embodiment to the third embodiment are shown in Table 1:

TABLE 1

	1^st	2^nd	3^rd
Parameters	embodiment	embodiment	embodiment

Choline chloride	560	g	560	g	560	g
Urea	480	g	480	g	480	g
Aluminum	120	g	120	g	120	g

chloride

Boric acid	10	g	10	g	10	g
Ascorbic acid	4	g	4	g	4	g
Graphene	0	g	0.05	g	0	g
Electrolyte	85°	C.	85°	C.	85°	C.

temperature

Working current	0.01	A	0.01	A	0.01	A
Working voltage	1	V	1	V	1	V
Plating duration
	2	hr	2	hr	2	hr
Coating thickness	7	um	7.3	um	7	um
Annealing	350°	C.	350°	C.	300°	C.

temperature

Annealing

30

min

30

min

40

min

duration

Nitrogen flow

20

sccm

20

sccm

0

sccm

rate

FIG. 2 to FIG. 6 respectively are the surface morphologies of the AlN according to the first embodiment of the present disclosure. More specifically, these figures are at different magnifications, respectively: 1 kX for FIG. 2, 10 kX for FIG. 3 and FIG. 4, 40 kX for FIG. 5 and FIG. 6. As shown in the figures, the surface of the AlN coating manufactured from the first embodiment has rectangular and polygonal grains which distribute uniformly over the surface. In addition, the sizes of the grains are roughly within 100 nm-200 nm.
FIG. 7 to FIG. 9 respectively are the surface morphologies of the AlN according to the second embodiment of the present disclosure More specifically, these figures are at different magnifications, respectively: 1 kX for FIG. 7, 10 kX for FIG. 8, 40 kX for FIG. 9. As shown in the low magnification figures, the larger grains distribute on the surface due to graphene is doped. In the high magnification figures, the smaller equiaxial grains distribute uniformly on the surface of the workpiece. In addition, the sizes of the grains are also roughly within 100 nm-200 nm.
FIG. 10 and FIG. 11 respectively are the surface morphologies of the AlN and the element analysis diagram of the AlN according to the second embodiment of the present disclosure Specifically, FIG. 11 presents the measured compositions from a certain region in FIG. 10. As shown in the figure, that the coating includes aluminum may be confirmed from the composition weight percent (wt. %) or atom percentage (at. %).
FIG. 12 is the X-ray diffraction spectrum of the AlN according to the second embodiment of the present disclosure The diffraction peaks corresponding to the AlN are clearly identified in the figure. The appearance of (111), (200), (220), and (311) crystalline planes clearly demonstrates the existence of crystalline AlN. In other words, the presence of aluminum nitride coating may be confirmed from the elemental analysis diagram and X-ray diffraction chart.
FIG. 13 and FIG. 14 respectively are the X-ray diffraction spectrum and the spectrum of electron spectroscopy for chemical analysis (ESCA) of the AlN according to the third embodiment of the present disclosure. The XRD spectrum clearly shows the peaks of (111), (200), and (220) corresponding to crystalline AlN. A similar confirmation may be also obtained from the ESCA measurement. In other words, the presence of aluminum nitride coating may be confirmed from the XRD spectrum and ESCA measurement. Furthermore, the present embodiment demonstrates that without additional supply of nitrogen in the annealing equipment, the aluminum coating may still react with the residual nitrogen from choline chloride and urea to form the desired AlN.
In summary, in the embodiment of the present disclosure, the aluminum is electroplated on the workpiece by the electrolyte with specific compositions, then the electroplated workpiece is annealed to obtain an AlN coating. The process of the present disclosure is simple and may be applied to large-area production. Moreover, the composition of the electrolyte used in the electroplating process is safe and non-toxic, and the electrolyte may be reused to reduce the waste of resources.
Although the present disclosure has been explained in relation to its preferred embodiment, it does not intend to limit the present disclosure. It will be apparent to those skilled in the art having regard to this present disclosure that other modifications of the exemplary embodiments beyond those embodiments specifically described here may be made without departing from the spirit of the invention. Accordingly, such modifications are considered within the scope of the invention as limited solely by the appended claims.
A person of ordinary skill in the art will understand current and future manufacturing processes, method and step from the content disclosed in some embodiments of the present disclosure, as long as the current or future manufacturing processes, method, and step performs substantially the same functions or obtain substantially the same results as the present disclosure. Therefore, the scope of the present disclosure includes the above-mentioned manufacturing process, method, and steps.
The above descriptions are only examples of this disclosure and are not intended to limit this disclosure. This disclosure may have various modifications and changes for a person of ordinary skill in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this disclosure shall be included in the scope of the claims of this disclosure.

Claims

What is claimed is:

1. A manufacturing method of aluminum nitride, comprising:

providing an electrolyte comprising choline chloride, urea, aluminum chloride, boric acid, and ascorbic acid;

disposing a workpiece, wherein at least a part of the workpiece is in contact with the electrolyte;

heating the electrolyte to within 60° C. to 95° C.;

applying an operating current to electroplate aluminum onto the workpiece; and

annealing the aluminum on the workpiece to form aluminum nitride.

2. The manufacturing method of aluminum nitride of claim 1, wherein in the step of annealing the workpiece, 10 sccm to 30 sccm of nitrogen gas is introduced to anneal the workpiece in a nitrogen environment.

3. The manufacturing method of aluminum nitride of claim 1, wherein an annealing temperature is within 250° C. to 450° C.

4. The manufacturing method of aluminum nitride of claim 1, wherein a current density of the operating current is within 1 mA/cm²to 10 mA/cm².

5. The manufacturing method of aluminum nitride of claim 1, wherein a molar ratio of choline chloride to urea in the electrolyte is 1:2.

6. The manufacturing method of aluminum nitride of claim 1, wherein a molar concentration of aluminum chloride in the electrolyte is from 0.005 M to 1 M.

7. The manufacturing method of aluminum nitride of claim 1, wherein a molar concentration of boric acid in the electrolyte is from 0.7 M to 2 M.

8. The manufacturing method of aluminum nitride of claim 1, wherein a molar concentration of ascorbic acid in the electrolyte is from 0.025 M to 0.15 M.

9. The manufacturing method of aluminum nitride of claim 1, wherein the electrolyte further comprises saccharin, and a molar concentration of saccharin is from 0.03 M to 0.2 M.

10. The manufacturing method of aluminum nitride of claim 1, wherein the electrolyte further comprises graphene or graphene oxide, and molar concentrations of graphene and graphene oxide both are from 0.005 M to 0.05 M.