US20110011148A1

US20110011148A1 - Method for forming patterned modified metal layer

Info

Publication number: US20110011148A1
Application number: US12/585,721
Authority: US
Inventors: Sun-Zen Chen; Tai-Bor Wu; Ching-Wen Chang; Wen-Feng Kuo; Ruo-Ying Wu
Original assignee: National Tsing Hua University NTHU
Current assignee: National Tsing Hua University NTHU
Priority date: 2009-07-15
Filing date: 2009-09-23
Publication date: 2011-01-20
Also published as: TWI473726B; TW201102189A

Abstract

A method for forming a patterned modified metal layer is disclosed, which comprises the following steps: (A) providing a metal base which is in the form of either a bulk metal or a metal coated substrate, and a mold with patterns; (B) applying the mold onto the metal base to transfer the patterns of the mold to the metal surface; (C) removing the mold; and (D) modifying the whole metal base or the, surface and a certain depth beneath the surface of metal base to form a modified metal layer with designated patterns.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a method for forming a modified metal layer and, more particularly, to a method combining direct imprint and surface modification for forming a modified metal layer.
2. Description of Related Art
As progressing in fabrication techniques, several patterning methods have been developed to form micro- or nano-patterns on the surface of the materials. Currently, the patterning methods used to form nano-patterns can be e-beam lithography, ion-beam lithography, DUV (deep ultraviolet)/EUV (extreme ultraviolet) photolithography, soft X-ray lithography, and nanoimprint lithography. Among the aforementioned patterning techniques, the nanoimprint technique has advantages of high resolution, rapid manufacturing rate, and low cost, so it is widely applied in various fields.
FIGS. 1A to 1E are the process scheme for forming a patterned metal layer onto a substrate by using nanoimprint. First, as shown in FIG. 1A, a substrate 10, and a mold 11 are provided, wherein the substrate is covered with a photoresist layer 101, and the mold 11 has determined patterns of recesses 111 and protrusions 112. Then, as shown in FIG. 1B, the mold 11 is applied onto the photoresist layer 101 coated on the substrate 10 at elevated temperature, which is usually above the T_gof the photoresist. The photoresist layer 101 becomes less viscous and easy to flow at this temperature with applying a suitable load, so the photoresist layer 101 can sufficiently fill the recesses 111 of the mold 11. After cooling to the room temperature and then releasing the load and the mold 11 is finished, the determined patterns are transferred to the photoresist layer 101, as shown in FIG. 1C. The patterned photoresist layer 101 is used as an etching mask to etch the substrate 10. After the photoresist layer 101 is removed, a patterned substrate 10 is obtained, as shown in FIG. 1D. Finally, a metal layer 12 is deposited on the surface of the patterned substrate, and a metal layer 12 with patterns is obtained.
Nanoimprint can prepare a patterned substrate with high resolution in a cheap and rapid way. However, when a patterned metal layer is desired, the processes of etching and deposition have to be performed. Sometimes, due to the control of the parameters of these processes being difficult, the patterns of the metal layer are different from the original patterns on the mold, which causes the resolution of patterns to decrease and further causes the failure in processes.
In addition, metal oxides can be widely applied in various fields. For example, titanium oxide can be applied in electronic devices such as electrode material of dye-sensitized solar cells (DSSCs), photocatalyst, and biomaterials, i.e. bio-implant material. When the titanium oxide layer (i.e. modified metal layer) is finely patterned, the photoelectric conversion efficiency of DSSC or bioactive efficiency of bio-implant can be improved greatly. In addition, the ordinarily used photocatalyst is mostly in powder form, which could cause damage to respiratory systems. If the patterned titanium oxide layer is used as the photocatalyst, not only the catalytic efficiency of the photocatalyst can be improved, but also the problem of dust in the air can be solved.
In conclusion, the modified metal layer can be applied to various fields, and the patterned modified metal layer can further increase the efficiency of the products. Therefore, it is desirable to provide a simple method for forming a patterned modified metal layer, especially focusing on the potential of mass production, and reducing the process complexity and cost.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for forming a patterned modified metal layer, which can prepare a patterned modified metal layer in a simple way, to decrease both the cost and the complexity of the process and also increase the application or functionality of products.
To achieve the object, the method for forming a patterned modified metal layer of the present invention comprises the following steps: (A) providing a metal base, and a mode with patterns; (B) applying the mold onto the metal base to transfer the patterns of the mold to a surface of the metal base; (C) removing the mold; and (D) modifying the metal base to form a modified metal layer with the patterns.
According to the method of the present invention, the imprinting process is performed to the metal base directly, so the pattern on the mold can be transferred to the metal base without the using of series complex processes, such as pattern exposing and developing, deposition, and etching etc. Hence, the production cost and the complexity of the process can be reduced greatly. In addition, in order to increase the applications of the metal base, the patterned metal base is modified to form a patterned modified metal layer in the present invention. Therefore, the method of the present invention combines the metallic direct imprinting process with modification treatment to form a patterned modified metal layer, which can be applied widely to various fields.
According to the method of the present invention, the metal base may be a bulk metal, or a substrate with a metal layer formed/coated thereon (i.e. metal-layer-coated substrate). Herein, the material of the substrate is unlimited. Preferably, the substrate is a silicon substrate, a glass substrate, or a quartz substrate. In addition, the material of the bulk metal and the metal layer is unlimited, as long as the material of the bulk metal and the metal layer is soft metal. Preferably, the material of the bulk metal and the metal layer is Al, Ti, Zn, Cu, Ag, Ni, Au, Pt, or an alloy thereof. More preferably, the material of the bulk metal and the metal layer is Al, Zn, Au, or Ti. Hence, the method of the present invention can pattern the metal base by performing the imprinting process on the metal base directly, due to the flexibility of the soft metal.
According to the method of the present invention, the surface of the metal base, which is to be patterned, is not limited to a flat surface. The surface of the metal base also can be a curved surface, such as a concave surface, a convex surface, or a wave surface.
According to the method of the present invention, the pattern of the mold may be transferred to the surface of the metal base through a thermal nanoimprint process in the step (B). In addition, the metal base may be modified by using the well known techniques, such as heat treatment, plasma treatment, laser treatmemt, pulse laser treatment, or rapid thermal annealing/processing (RTA or RTP) etc., in the step (D). Herein, the plasma treatment may be oxygen-plasma treatment, nitrogen-plasma treatment, or mixture-plasma treatment, such as oxygen-argon plasma treatment and nitrogen-argon plasma treatment. When the metal layer is treated with nitrogen plasma or nitrogen-argon plasma, a metal nitride layer is obtained. When the metal layer is treated with oxygen plasma or oxygen-argon plasma, a metal oxide layer is obtained. Furthermore, when the heat treatment, laser treatment, pulse laser treatment, or rapid thermal annealing/processing is used to modify the metal layer, the inlet gas can be a single component gas, such as O₂, N₂, H₂, and Ar, or mixture-gases, such as N₂—Ar, O₂—Ar, and H₂—O₂. Also, the heat treatment, laser treatment, laser pulse laser treatment, or rapid thermal annealing/processing can be performed in a vacuum. When the modification is performed under an O₂atmosphere, a metal oxide layer is obtained. When the modification is performed under an N₂atmosphere, a metal nitride layer is obtained. When the modification is performed under an atmosphere of inert gas such as Ar atmosphere, or in a vacuum, the crystalline structure or the micro-structure of the metal layer can be changed. Preferably, the modified metal layer formed by the method of the present invention can be an Al₂O₃layer, an AlN layer, a TiO₂layer, a TiN layer, or a ZnO layer.
According to the method of the present invention, the thickness of the metal base is unlimited. When the metal base is a bulk metal, the modification process in the step (D) could be the whole bulk (i.e. entire modification), or only the surface of the bulk (i.e. partial modification). When the metal base is a metal-layer-coated substrate, the modified layer can be either entire metal layer or partial metal layer in the step (D). In the method of the present invention, the thickness of the metal layer is unlimited, which can be selected according to the application field. Preferably, the thickness of the metal layer is 1 nm˜5 μm. In addition, the thickness of the modified metal layer is also unlimited, which can be adjusted according to the application field. Preferably, the thickness of the modified metal layer is 1 nm˜5 μm. More preferably, the thickness of the modified metal layer is 2 nm˜2 μm.
According to the method of the present invention, the prepared modified metal layer has patterns of recesses and protrusions. Herein, the sizes of the recesses and protrusions of the patterns are unlimited, and can be adjusted according to the application field. Hence, the modified metal layer may have a nano-scale pattern, or a micro-scale pattern, even or a mixture-scale pattern. Preferably, the depth of the recesses is 1 nm˜3 μm, and the width of the recesses is 3 nm˜300 μm. More preferably, the depth of the recesses is 2 nm˜1 μm, and the width of the recesses is 3 nm˜10 μm.
The patterned modified metal layer, which is prepared by the method of the present invention, can be applied in various fields, such as electrode materials of DSSCs, photocatalysts, biomaterials such as bio-implant materials, and device elements with wear-resisting outer surfaces.
When the patterned TiO₂layer or ZnO layer is used as an electrode of DSSC, the photoelectric conversion efficiency of the DSSC can be improved.
In addition, the conventional TiO₂photocatalyst is formed by aggregation of nano-sized TiO₂particles, so the unbound nano-sized particle may cause damage to the respiratory system. On the contrary, when the patterned TiO₂layer prepared by the method of the present invention is used as a photocatalyst, the problem of dust in the air can be solved. At the same time, the patterned TiO₂layer can increase the reaction surface through patterning, so the catalytic efficiency can also be maintained.
Furthermore, when the patterned TiO₂layer or the patterned modified Ti layer is used in a biomedical device, the contact surface area of the biomedical device can be increased by the nano-sized pattern of the TiO₂layer or modified Ti layer. Hence, the reaction efficiency and the applicability of the biomedical device can be improved.
In addition, when the patterned Al₂O₃layer is used in light reflection material, the reflection coefficient can be increased by the pattern of the Al₂O₃layer.
TiN has the property of high hardness, so the patterned TiN layer formed by the method of the present invention can be used to increase the wear-resistance of the outer surface of the device elements in different application fields.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1E are the sectional views illustrating the process for forming a patterned metal layer through a nanoimprint process in the art;

FIGS. 2A to 2D are the sectional views illustrating the process for forming a patterned modified metal layer in Embodiment 1 of the present invention; and

FIGS. 3A to 3C are the sectional views illustrating the process for forming a patterned modified metal layer in Embodiment 2 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinbelow, the present invention will be described in detail with reference to the Embodiments. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the Embodiments set forth herein. Rather, these Embodiments are provided to fully convey the concept of the invention to those skilled in the art.

Embodiment 1

FIGS. 2A to 2D are the sectional views illustrating the process for forming a patterned modified metal layer in the present embodiment.
First, as shown in FIG. 2A, a metal base 20 is provided, wherein the metal base 20 is a substrate 201 with a metal layer 202 formed thereon. Further, a mold 21 is provided, wherein the mold 21 has a determined pattern of recesses 211 and protrusions 212. In the present embodiment, the substrate 201 is a silicon substrate; the material of the metal layer 202 is Ti; and the thickness T of the metal layer 202 is 100 nm.
Next, as shown in FIG. 2B, the mold 21 is applied onto the metal base 20 through a hot embossing nanoimprint process. After removing the mold 21, the pattern on the mold 21 is transferred to the metal layer 202 of the metal base 20, as shown in FIG. 2C. Herein, the protrusions 2021 of the metal layer 202 correspond to the recesses 211 of the mold 21, and the recesses 2022 of the metal layer 202 correspond to the protrusions 212 of the mold 21.
Then, as shown in FIG. 2D, the metal layer 202 of the metal base 20 is modified to form a modified metal layer 23. Herein, a heat treatment is performed to modify the whole metal layer 202, and then a metal oxide layer is obtained. In the present embodiment, the material of the metal layer 202 is Ti, so the modified metal layer 23 is a TiO₂layer.
In addition, the modified metal layer 23 has a pattern of protrusions 231 and recesses 232, which is the same as the pattern of the metal layer 202 of the metal base 20. In the present embodiment, the recesses 232 of the modified metal layer 23 have a width W of 10 nm, and a depth D of 50 nm.

Embodiment 2

FIGS. 3A to 3C are the sectional views illustrating the process for forming a patterned modified metal layer in the present embodiment. In the present embodiment, the process for forming patterned modified metal layer is similar to that illustrated in Embodiment 1.
First, a metal base 20 and a mold 22 with a determined pattern are provided, as shown in FIG. 3A. In the present embodiment, the metal base 20 is a bulk metal, and the material of the metal is Al.
Next, the mold 22 is applied on the metal base 20, to transfer the pattern of the mold 22 to the metal base 20. After the mold 22 is removed, a patterned metal base 20 is obtained, as shown in FIG. 3B.
Finally, the metal base 20 is modified to form a patterned modified metal layer 23. Herein, an oxygen plasma treatment is performed to partially modify the surface of the metal base 20, and then a metal oxide layer is obtained. In the present embodiment, the material of the metal base 20 is Al, so the obtained modified metal layer 23 is an Al₂O₃layer.
In the present embodiment, the thickness T of the obtained modified metal layer 23 is about 100 nm. Herein, the modified metal layer 23 has a pattern of protrusions 231 and recesses 232. In the present embodiment, the recesses 232 of the modified metal layer 23 have a width W of 100 nm, and a depth D of 20 nm. Furthermore, the recesses 232 are in the forms of holes.

Embodiment 3

The process for forming patterned modified metal layer in the present embodiment is similar to that illustrated in Embodiment 1, except that the metal layer is modified with nitrogen plasma instead of heat treatment. Hence, a patterned TiN layer is obtained in the present embodiment.
In conclusion, according to the method for forming a modified metal layer of the present invention, the patterned metal layer is formed by imprinting the soft metal directly, without performing the process of etching and metal deposition. Hence, as compared with the conventional process, the method of the present invention can form a patterned metal layer in a simpler way, so the production cost and the complexity of the process can be reduced. Also, the applicability of products can be increased. In addition, the method of the present invention further combines the metallic direct imprinting process with a process of modification, in order to obtain a patterned modified metal layer, which can be applied to various fields.
Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.

Claims

1. A method for forming a patterned modified metal layer, comprising the following steps:

(A) providing a metal base, and a mode with patterns;

(B) applying the mold onto the metal base to transfer the patterns of the mold to a surface of the metal base;

(C) removing the mold; and

(D) modifying the metal base to form a modified metal layer with the patterns.

2. The method as claimed in claim 1, wherein the whole metal base, or the surface of the metal base is modified in the step (D).

3. The method as claimed in claim 1, wherein the metal base is a with bulk metal, or a substrate with a metal layer formed thereon.

4. The method as claimed in claim 3, wherein the material of the bulk metal and the metal layer is soft metals.

5. The method as claimed in claim 4, wherein the soft metal is selected from the group consisting of Al, Ti, Zn, Cu, Ag, Ni, Au, and Pt.

6. The method as claimed in claim 1, wherein the modified metal layer is a metal oxide layer.

7. The method as claimed in claim 6, wherein the metal oxide layer is an Al₂O₃layer, a TiO₂layer, or a ZnO layer.

8. The method as claimed in claim 1, wherein the modified metal layer is a metal nitride layer.

9. The method as claimed in claim 8, wherein the metal nitride layer is TiN.

10. The method as claimed in claim 1, wherein the metal layer is modified under an atmosphere of inert gas in the step (D).

11. The method as claimed in claim 1, wherein the metal layer is modified under vacuum in the step (D).

12. The method as claimed in claim 3, wherein the substrate is a silicon substrate, a glass substrate, or a quartz substrate.

13. The method as claimed in claim 1, wherein the metal base is modified through heat treatment, laser treatment, pulse laser treatment, plasma treatment, or rapid thermal annealing in the step (D).

14. The method as claimed in claim 13, wherein the plasma treatment is oxygen-plasma treatment, or nitrogen-plasma treatment.

15. The method as claimed in claim 1, wherein the thickness of the modified metal layer is 1 nm˜5 μm.

16. The method as claimed in claim 4, wherein the thickness of the metal layer is 1 nm˜5 μm.

17. The method as claimed in claim 1, wherein the modified metal layer comprises recesses.

18. The method as claimed in claim 17, wherein the depth of the recesses is 1 nm˜3 μm.

19. The method as claimed in claim 17, wherein the width of the recesses is 3 nm˜300 μm.

20. The method as claimed in claim 1, wherein the surface of the metal base is a flat surface, or a curved surface.