SUPER HYDROPHOBIC SURFACE FABRICATION METHOD

Abstract

The present invention relates to a method for producing a super-hydrophobic surface, and to a stack having a super-hydrophobic surface prepared by the above method. The super-hydrophobic surface may be realized only by plasma etching and deposition. The super-hydrophobic surface according to the present invention has a very low work of adhesion less than or equal to 3 mJ/m.sup.2. This super-hydrophobic surface may be applied to various fields including self-cleaning surface, anti-fogging surface, automobile glass surface, and drug delivery device surface.

Claims

1. A method for forming a super-hydrophobic surface, the method comprising: a) preparing a substrate having a mask disposed thereon, wherein the mask has a two-dimensional pattern in which holes having a micrometer scale are arranged at regular intervals; b) treating said substrate having the mask with a plasma of a fluorocarbon containing gas such that a fluorocarbon layer is formed on inner faces of the holes of the mask; c) treating said substrate having the mask with a plasma capable of etching the fluorocarbon layer and the substrate such that vertical rods corresponding to the pattern of the mask are formed on the substrate; d) repeating the steps (b) and (c) to increase height of the vertical rods; and e) after the step (d), treating the substrate having the vertical rods formed thereon with a plasma of a fluorocarbon containing gas to form a fluorocarbon layer on outer faces of the vertically rods.

2. The method of claim 1, further comprising: a step of plasma ashing and a step of removing the mask, which are performed between the step (d) and the step (e).

3. The method of claim 1, wherein the step (d) are repeated 5 to 500 times.

4. The method of claim 1, wherein the fluorocarbon containing gas is at least one selected from a group consisting of C.sub.4F.sub.8, C.sub.4F.sub.6, C.sub.2F.sub.6, CF.sub.4, and CH.sub.2F.sub.2.

5. A stack structure having a super-hydrophobic surface, wherein the stack structure comprises: a substrate; and a plurality of vertically oriented rods formed on the substrate, wherein the rods are formed by the method of claim 1, wherein the plurality of vertically oriented rods are arranged in a two-dimensional pattern at regular intervals, wherein each of the rods has a diameter equal to or smaller than 4 micrometer.

6. The stack structure of claim 5, wherein the super-hydrophobic surface has a contact-angle equal to or larger than 160.

7. The stack structure of claim 5, wherein the super-hydrophobic surface has a work of adhesion equal to or smaller than 3 mJ/m.sup.2.

8. A stack structure having a super-hydrophobic surface, wherein the stack includes: a substrate; and a plurality of vertically oriented rods formed on the substrate, wherein the rods are formed by the method of claim 1, wherein the plurality of vertically oriented rods are arranged in a two-dimensional pattern at regular intervals, wherein each of the rods has a diameter equal to or smaller than 10 micrometer, wherein a height of each of the rods is equal to or larger than 7 micrometer.

9. The stack of claim 8, wherein the super-hydrophobic surface has a contact-angle equal to or larger than 160.

10. The stack of claim 8, wherein the super-hydrophobic surface has a work of adhesion equal to or smaller than 3 mJ/m.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is an SEM photograph of a specimen resulting from a silicon rod being formed repeatedly 48 times.

[0017] FIG. 2 shows the height of the silicon substrate according to the number of repetitions of silicon rods formation.

[0018] FIGS. 3 and 4 respectively show a contact angle image and a contact angle measurement of water relative to the surface as taken after dropping 0.5 l of water droplets on the substrate surface having silicon rods formed thereon.

[0019] FIGS. 5 and 6 respectively show a contact angle image and a contact angle measurement of water relative to the surface as taken after 0.5 l of water droplets were contacted on a silicon rod substrate having a fluorocarbon film deposited thereon.

[0020] FIG. 7 is a graph showing a change in the work of adhesion of specimen with and without deposition of a fluorocarbon film.

[0021] FIG. 8 is a photograph showing the adhesion between 0.5 l of water drops and a silicon rod substrate (diameter: 1.7 micrometer, height: 2 micrometer).

DETAILED DESCRIPTIONS

[0022] Examples of various embodiments are illustrated and described further below with reference to the drawings. It will be understood that the description herein is not intended to limit the claims to the specific embodiments described. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the present disclosure as defined by the appended claims. For simplicity and clarity of illustration, elements in the figures are not necessarily drawn to scale. The same reference numbers in different figures denote the same or similar elements, and as such perform similar functionality. Also, descriptions and details of well-known steps and elements are omitted for simplicity of the description. Furthermore, in the following detailed description of the present disclosure, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be understood that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present disclosure.

[0023] It will be understood that, although the terms first, second, third, and so on may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section described below could be termed a second element, component, region, layer or section, without departing from the spirit and scope of the present disclosure.

[0024] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms a and an are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms comprises, comprising, includes, and including when used in this specification, specify the presence of the stated features, integers, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, operations, elements, components, and/or portions thereof. As used herein, the term and/or includes any and all combinations of one or more of the associated listed items. Expression such as at least one of when preceding a list of elements may modify the entire list of elements and may not modify the individual elements of the list.

[0025] Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive concept belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0026] 1. Preparation of Si Thin Film Patterned with SiO.sub.2 Mask

[0027] A silicon specimen surface patterned with a SiO.sub.2 mask in a cylindrical shape was used. The SiO.sub.2 masks were 1.7, 4, 8, and 10 m in diameter, respectively, and the spacing between the masks were 2, 4, 8, and 10 m, respectively. The height of each of the masks was 2 m.

[0028] Although this example uses silicon, the present invention is not limited thereto. Depending on the application, various samples made of insulating film, semiconductor, and conductive polymer may be used. The present invention can be accomplished by performing the etching of a specimen with a plasma capable of etching such a specimen according to the material of the specimen.

[0029] In addition, this example uses SiO.sub.2 as an etching mask. The present invention is not limited thereto. Any etching mask may be used as long as a material thereof has a high etching selectivity to a substrate material. Therefore, the etching mask of the present invention is not limited to SiO.sub.2.

[0030] The diameter of the etching mask (SiO.sub.2) may be chosen according to the diameter of the rod to be formed on the specimen to be etched. For example, the diameter of the etching mask (SiO.sub.2) can range from tens of nanometers to hundreds of micrometers.

[0031] 2. Formation of a Structure Comprising a Plurality of Vertically Oriented Rods

[0032] The specimen prepared in the above step was etched. Subsequent deposition and etching were repeated to form a structure comprising a plurality of vertically oriented rods.

[0033] In the deposition step, the specimen on which the mask is formed is treated with a plasma of a fluorocarbon-containing gas to form a fluorocarbon layer on the inner side face and the top face of the mask pattern. This was carried out under the process conditions of Table 1 below.

TABLE-US-00001 TABLE 1 Flow Source Bias voltage rate Pressure Temperature Time Gas power (W) (V) (sccm) (mTorr) ( C. ) (s) C.sub.4F.sub.8 800 0 30 30 5 10

[0034] The etching step comprises etching the specimen on which the fluorocarbon layer is formed, using a plasma of a gas capable of etching the fluorocarbon layer and the specimen. This etching step forms a rod corresponding to the mask on the substrate. This etching step was performed under the process conditions shown in Table 2 below.

TABLE-US-00002 TABLE 2 Source power Bias Flow rate Pressure Temperature Time Gas (W) voltage (V) (sccm) (mTorr) ( C. ) (s) SF.sub.6 800 50 30 10 5 40

[0035] The number of repetitions of the deposition and etching processes was set at 6, 12, 24, 36 and 48 cycles. As a result, rods having various heights were formed.

[0036] The structure including the rods thus formed was cleaned in the following manner. [0037] 60 minute ashing in temperature 500 C. furnace, [0038] treatment (SiO.sub.2 mask removal) in 20 vol % HF aqueous solution for 2.5 minutes,

[0039] DI water washing: 5 minutes.

[0040] FIG. 1 is an SEM photograph of a specimen resulting from a silicon rod being formed repeatedly 48 times. As shown in FIG. 1, it can be seen that silicon rods having various diameters are formed according to the diameters of the holes defined in the mask pattern.

[0041] FIG. 2 shows the height of the silicon substrate according to the number of repetitions of silicon rods formation. As the number of cycles increases, the height of the rod increases linearly.

[0042] FIGS. 3 and 4 respectively show a contact angle image and a contact angle measurement of water relative to the surface as taken after dropping 0.5 l of water droplets on the substrate surface having silicon rods formed thereon. When the height of the rod was 0 to 7 micrometer, the contact angle of water decreased as the diameter of the rod increased. When the height of the rod was 7 micrometer or more, the contact angle of the water was defined to be about 94 degree except that the diameter of the rod was 10 micrometer.

[0043] 3. Plasma Treatment of a Structure Comprising a Plurality of Vertically Oriented Rods

[0044] A plurality of vertically oriented rods prepared as described above were treated with plasma of a fluorocarbon-containing gas. Thereby, a fluorocarbon layer was formed on outer faces of the above formed rods. The processing conditions of this treatment are shown in Table 3 below.

TABLE-US-00003 TABLE 3 Source Bias Flow Tem- power voltage rate Pressure perature Time Gas (W) (V) (sccm) (mTorr) ( C. ) (s) C.sub.4F.sub.8 800 0 30 30 5 10 (10 to (1 to 500) (1 to 5000) (1 to 100) 2000)

[0045] C.sub.4F.sub.8 gas is one embodiment of the gas used to deposit a fluorocarbon thin film. In addition to C.sub.4F.sub.8, a variety of fluorocarbon based gases such as C.sub.4F.sub.6, C.sub.2F.sub.6, CF.sub.4, CH.sub.2F.sub.2 may be used as the process gas. In addition, the process gas may include a hydrocarbon gas capable of realizing hydrophobic characteristics.

[0046] FIGS. 5 and 6 respectively show a contact angle image and a contact angle measurement of water relative to the surface as taken after 0.5 l of water droplets were contacted on a silicon rod substrate having a fluorocarbon film deposited thereon. When the diameter of the rod was 1.7 and 4 m, the contact angle of water was about 164 regardless of the height of the rod. This confirms that a super-hydrophobic surface is implemented. A super-hydrophobic surface (contact angle of 160 or more) was realized when the etching depth of the specimen were 7 and 15 m or more respectively when the rod diameters were 8 and 10 m.

[0047] FIG. 7 is a graph showing a change in the work of adhesion of specimen with and without deposition of a fluorocarbon film. The work of adhesion was calculated using the following equation:

Work of adhesion [mJ/m.sup.2]=.sub.LV(1+cos )

[0048] .sub.LV: surface tension of water on a solid surface [72.8 mN/m],

[0049] : contact-angle

[0050] The work of adhesion means the amount of work required to remove the water droplets attached to the specimen surface. The smaller the work adhesion, the easier it is to drop water from the surface. As shown in FIG. 7, when the diameter of the rod is 1.7 and 4 m, the work of adhesion is 3 mJ/m.sup.2 or less regardless of the height. When the diameter of the rod is 8 and 10 m, the height of the rod is 7 and 15 m or more, the work of adhesion is 3 mJ/m.sub.2 or less. These results indicate that droplets may easily be removed by depositing the fluorocarbon thin film on the silicon rod surface.

[0051] FIG. 8 is a photograph showing the adhesion between 0.5 l of water drops and a silicon rod substrate (diameter: 1.7 micrometer, height: 2 micrometer). In FIG. 8, the arrow indicates the direction of movement of the substrate. That is, by moving the substrate slowly upwards, droplets adhere to the substrate, and then the substrate moves downward again. Water droplets on a needle with a diameter of 200 m did not adhere to the substrate. This is because the work of adhesion of the substrate is very small.

[0052] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention as defined in the appended claims.