Nano protrusion surface forming method and base material having nano protrusion surface formed by method

Abstract

The present invention relates to a nano-protrusion forming method and a base material having a nano-protrusion surface formed by the method. The method includes forming an anti-reflective layer including nano-protrusions having a width of several nm to several tens of nm, and/or an anti-glare layer including protrusions having a width of several tens of nm to several μm, by a wet etching process using an acid solution without using a nano-mask.

Claims

1. A method of forming protrusions on a surface of a base material, the method comprising: providing a glass or polymer film substrate base material; forming irregularly sized, irregularly shaped, and irregularly positioned nano-protrusions on the surface of the base material by wet etching without selective etch-blocking, wherein forming the nano-protrusions comprises either forming an anti-glare layer including protrusions having a width of several tens of nm to several hundreds of nm by the wet etching using an acid solution, or forming an anti-reflective layer including protrusions having a width of several nm to several tens of nm by the wet etching using an acid solution.

2. The method of claim 1, wherein the acid solution which is used in forming the anti-glare layer contains fluorine-based acid and nitric acid, and the acid solution which is used in forming the anti-reflective layer contains fluorine-based acid.

3. The method of claim 1, wherein the acid solution which is used in forming the anti-glare layer contains hydrogen fluoride and nitric acid, and further contains at least one of ammonium fluoride, phosphoric acid and hydrochloric acid, and the acid solution which is used in forming the anti-reflective layer contains hydrogen fluoride, and further contains at least one of ammonium fluoride, phosphoric acid, nitric acid and hydrochloric acid.

4. The method of claim 1, wherein the acid solution which is used in forming the anti-glare layer comprises, based on 100 wt % of the acid solution, 10 wt % or less of hydrogen fluoride, 5 wt % or less of ammonium fluoride, 10 wt % or more to 25 wt % or less of nitric acid, 5 wt % or less of phosphoric acid, 10 wt % or less of hydrochloric acid, and the remainder being water.

5. The method of claim 1, wherein the acid solution which is used in forming the anti-reflective layer comprises, based on 100 wt % of the acid solution, 10 wt % or less of hydrogen fluoride, 5 wt % or less of ammonium fluoride, 5 wt % or less of nitric acid, 5 wt % or less of phosphoric acid, 10 wt % or more to 40 wt % or more of hydrochloric acid, and the remainder being water.

6. The method of claim 1, wherein forming the nano-protrusions comprises: forming an anti-glare layer including protrusions having a width of several tens of nm to several hundreds of nm by first wet etching using an acid solution; and forming an anti-reflective layer including protrusions having a width of several nm to several tens of nm on the anti-glare layer by second wet etching using an acid solution.

7. The method of claim 3, wherein the content of hydrogen fluoride in the acid solution is 10 wt % or less.

8. The method of claim 7, wherein when forming the anti-glare layer, the content of nitric acid in the acid solution is 10 wt % or more and 25 wt % or less, and when forming the anti-reflective layer, the content of the nitric acid in the acid solution is 5 wt % or less.

9. The method of claim 3, wherein the acid solution contains ammonium fluoride or phosphoric acid, and the content of the ammonium fluoride or the phosphoric acid is 5 wt % or less.

10. The method of claim 7, wherein when forming the anti-glare layer, the content of hydrochloric acid in the acid solution is 10 wt % or less, and when forming the anti-reflective layer, the content of the hydrochloric acid in the acid solution is 10 wt % or more and 40% wt or less.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is an overall flow chart showing a protrusion forming method according to one embodiment.

(2) FIG. 2 shows a sectional view of a glass substrate in which an anti-glare layer is formed according to one embodiment.

(3) FIG. 3 is a scanning electron micrograph of a glass substrate in which an anti-glare layer is formed according to one embodiment, and FIG. 4 is an enlarged scanning electron micrograph of FIG. 3.

(4) FIG. 5 shows a sectional view of a glass substrate in which an anti-reflective layer is formed according to one embodiment.

(5) FIG. 6 is a scanning electron micrograph of a glass substrate in which an anti-reflective layer is formed according to one embodiment, and FIG. 7 is an enlarged scanning electron micrograph of FIG. 6.

(6) FIG. 8 shows a sectional view of a glass substrate in which both an anti-glare layer and an anti-reflective layer are formed according to one embodiment.

(7) FIG. 9 is a scanning electron micrograph of a glass substrate in which both an anti-glare layer and an anti-reflective layer are formed according to one embodiment.

(8) FIG. 10 shows a sectional view of a glass substrate in which an anti-reflective layer is additionally formed on protrusions and grooves having a size of several μm to several hundreds of formed on the glass substrate according to a conventional method which is not the present invention.

(9) FIG. 11 is a scanning electron micrograph of a glass substrate in which anti-reflective protrusions having a size of several nm to several tens of nm are additionally formed on anti-glare protrusions having a size of several μm to several hundreds of μm.

(10) FIG. 12 is a photograph of a smart phone comprising a glass or polymer film in which an anti-reflective layer is formed by a protrusion forming method according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(11) The above and additional aspects will become more apparent from embodiments which will be described with reference to the accompanying drawings. It is understood that the components of each embodiments may be combined in various manners in one embodiment, unless otherwise stated or mutually contradictory. Furthermore, the proposed invention may be embodied in various different forms and is not limited to the embodiments described herein.

(12) In the drawings, parts not related to the description are omitted in order to clearly describe the proposed invention, and like reference numerals designate like parts throughout the specification. Furthermore, it is understood that, when any part is referred to as “comprising” any component, it does not exclude other components, but may further comprise other components, unless otherwise specified. For example, although the present invention is described below with an emphasis on a glass substrate, it also includes a polymer film having glassy characteristics as described above.

(13) FIG. 1 is an overall flow chart showing a protrusion forming method according to one embodiment of the present invention.

(14) In one embodiment, the protrusion forming method comprises the steps of: (S610) cleaning a glass substrate; (S620) forming protrusions on the glass substrate by wet etching; and (S630) neutralizing the glass substrate.

(15) In one embodiment, the step (S610) of cleaning the glass substrate removes organic matter from the glass substrate, so that acid treatment with an acid solution the step (S620) of forming protrusion on the glass substrate by wet etching which is a subsequent process will be performed uniformly throughout the substrate. For cleaning of the glass substrate, IPA (isopropyl alcohol) or ethanol is used. After the glass substrate is cleaned with IPA (isopropyl alcohol) or ethanol, it is cleaned with water. In the cleaning process, the glass substrate may be cleaned using ultrasonic waves or a brush.

(16) According to one embodiment, the step (S620) of forming protrusions on the glass substrate by wet etching is performed by dipping the glass substrate in an acid solution or spraying the acid solution onto the glass substrate. In the step (S620) of forming protrusions, protrusions are formed on the glass substrate or a polymer film substrate having glassy characteristics by wet etching using an acid solution in the absence of a mask. The step (S620) of forming protrusions on the glass substrate by wet etching will be described later in detail.

(17) According to one embodiment, in the step (S630) of neutralizing the glass substrate, the surface of the glass substrate with reduced pH, which results from the step (S620) of forming protrusions on the glass substrate by wet etching, is maintained at neutral pH. For example, the glass substrate with reduced pH, which results from the step (S620) of forming protrusions on the glass substrate by wet etching, is immersed in a water bath, thereby neutralizing the acid.

(18) FIG. 2 shows a sectional view of a glass substrate in which an anti-glare layer is formed according to one embodiment.

(19) In one embodiment, the step of forming the protrusions comprises a step of forming an anti-glare layer including protrusions having a width (W.sub.1) of several tens of nm to several μm by wet etching using an acid solution. As shown in FIG. 2, the protrusions include concave and convex surfaces. The width (W.sub.1) is the width of the convex surface. The protrusions having a width (W.sub.1) of several tens of nm to several μm, formed by wet etching using an acid solution, have a height (h.sub.1) of several tens of nm to several μm. If the protrusions having a width (W.sub.1) of several tens of nm to several μm are present on the surface of the glass substrate, light irradiated onto the glass substrate will be scattered by the protrusions having a width (W.sub.1) of several tens of nm to several μm, and thus the reflectance of the glass substrate will be lowered, thereby reducing glare.

(20) In one embodiment, the acid solution contains fluorine-based acid and nitric acid. Examples of the fluorine-based acid include hydrogen fluorine (HF), ammonium fluoride (NH.sub.4F) and the like. By wet etching using an acid solution containing fluorine-based acid and nitric acid, protrusions having a width of several tens of nm to several μm can be formed on the glass substrate.

(21) In one embodiment, the acid solution contains hydrogen fluoride (HF) and nitric acid (HNO.sub.3), and may further contain at least one of ammonium fluoride (NH.sub.4F), phosphoric acid (H.sub.3PO.sub.4), hydrochloric acid (HCl), and water (H.sub.2O).

(22) In one embodiment, the content of the hydrogen fluoride may be more than 0 wt % and 10 wt % or less based on 100 wt % of the acid solution.

(23) The chemical reaction equations shown below theoretically explain a process in which nano-protrusions are formed according to the present invention. Even if a portion of the chemical reaction process differs, there is no change in the result of formation of nano-protrusions and the effect obtained therefrom.
SiO.sub.2+6HF.fwdarw.H.sub.2SiF.sub.6+2H.sub.2O  Chemical reaction equation 1

(24) As shown in chemical reaction equation 1 above, silicon dioxide reacts with hydrogen fluoride to cause etching of the surface of the glass substrate, and as a result, protrusions having a width of several nm to several tens of nm are formed on the glass substrate.

(25) In one embodiment, the content of the nitric acid may be 10 wt % or more and 25 wt % or less based on 100 wt % of the acid solution. The nitric solution whose content is 10 wt % or more and 25 wt % or less based on 100 wt % of the acid solution reacts with aluminum oxide, thereby forming protrusions having a width of several tens of nm to several μm on the glass substrate including the protrusions having a width of several nm to several tens of nm, formed by the above-described process.
6HNO.sub.3+Al.sub.2O.sub.3.fwdarw.2Al(NO.sub.3).sub.3+3H.sub.2O  Chemical reaction equation 2

(26) According to chemical reaction equation 2 above, nitric acid flows into the grooves produced by the etching according to the above-described chemical reaction equation 1, and reacts with aluminum oxide (Al.sub.2O.sub.3). According to this reaction, protrusions having a width of several tens of nm to several μm, which are greater than the protrusions formed by hydrogen fluoride, are formed on the glass substrate. As the content of the nitric acid increases in the range of 10 wt % or more to 25 wt % or less based on 100 wt % of the acid solution, protrusions having a greater height and a greater width can be formed on the glass substrate.

(27) In one embodiment, the acid solution contains ammonium fluoride, and the content of the ammonium fluoride may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution.
NH.sub.4F<.fwdarw.NH.sub.3+HF  Chemical reaction equation 3

(28) Although hydrogen fluoride decreases according to the above-described chemical reaction equation 1, hydrogen fluoride is produced according to chemical reaction equation 3. Accordingly, the content of hydrogen fluoride in the acid solution is maintained at a constant level. As the content of hydrogen fluoride is maintained at a constant level, the wet etching process can be stably performed.

(29) In one embodiment, the acid solution contains phosphoric acid, and the content of the phosphoric acid may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution.
2H.sub.3PO.sub.4+Al.sub.2O.sub.3.fwdarw.2Al(PO.sub.4)+3H.sub.2O  Chemical reaction equation 4

(30) According to chemical reaction equation 4 above, phosphoric acid reacts with aluminum oxide (Al.sub.2O.sub.3), thereby smoothing the surface of the protrusions having a rough surface. Phosphoric acid is more viscous than nitric acid, and thus can smooth the surface of the protrusions formed according to the chemical reaction of nitric acid.

(31) In one embodiment, the acid solution contains hydrochloric acid, and the content of the hydrochloric acid may be more than 0 wt % and not more than 10 wt % based on 100 wt % of the acid solution.
SiO.sub.2+4HCl.fwdarw.SiCl.sub.4+2H.sub.2O  Chemical reaction equation 5

(32) According to chemical reaction equation 5 above, hydrochloric acid reacts with silicon dioxide (SiO.sub.2), thereby smoothing the surface of the protrusions having a rough surface.

(33) In one embodiment, the acid solution contains water, hydrogen fluoride, ammonium fluoride, phosphoric acid, nitric acid, and hydrochloric acid. In this case, the content of the hydrogen fluoride may be more than 0 wt % and not more than 10 wt % based on 100 wt % of the acid solution; the content of the ammonium fluoride may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution; the content of the nitric acid may be 10 wt % or more and 25 wt % or less based on 100 wt % of the acid solution; the content of the phosphoric acid may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution; the content of the hydrochloric acid may be more than 0 wt % and not more than 10 wt % based on 100 wt % of the acid solution; and the remainder is water.

(34) By a wet etching process using the acid solution containing the above-described amounts (wt %) of water, hydrogen fluoride, ammonium fluoride, phosphoric acid, nitric acid and hydrochloric acid, protrusions having a width of several tens of nm to several μm are formed on the glass substrate. The water serves to dilute the acid solution.

(35) FIG. 3 is a scanning electron micrograph of a glass substrate in which an anti-glare layer is formed according to one embodiment. Protrusions formed on the glass substrate have a width of several tens of nm to several μm. FIG. 4 is an enlarged scanning electron micrograph of FIG. 3.

(36) FIG. 5 shows a sectional view of a glass substrate in which an anti-reflective layer is formed according to one embodiment.

(37) In one embodiment, the step of forming the protrusions comprises a step of forming an anti-reflective layer including protrusions having a width (W.sub.2) of several nm to several tens of nm by wet etching using an acid solution. As shown in FIG. 5, the protrusions include concave and convex surfaces. The width (W.sub.2) is the width of the convex surface. If the protrusions having a width (W.sub.2) of several nm to several tens of nm are present on the surface of the glass surface, the transmittance of light irradiated on the glass substrate will be increased by the protrusions, and the reflectance of the light will be lowered.

(38) In one embodiment, the acid solution contains fluorine-based acid. Examples of the fluorine-based acid include hydrogen fluoride (HF), ammonium fluoride (NH.sub.4F) and the like. By wet etching using the acid solution containing the fluorine-based acid, protrusions having a width of several nm to several tens of nm can be formed on the glass substrate.

(39) In one embodiment, the acid solution contains hydrogen fluoride, and may further contain at least one of ammonium fluoride, phosphoric acid, nitric acid and hydrochloric acid.

(40) In one embodiment, the content of the hydrogen fluoride may be more than 0 wt % and not more than 10 wt % based on 100 wt % of the acid solution.
SiO.sub.2+6HF.fwdarw.H.sub.2SiF.sub.6+2H.sub.2O  Chemical reaction equation 6

(41) As shown in chemical reaction equation 6 above, silicon dioxide reacts with hydrogen fluoride to cause etching of the surface of the glass substrate, and as a result, protrusions having a width of several nm to several tens of nm are formed on the glass substrate.

(42) In one embodiment, the acid solution contains ammonium fluoride, and the content of the ammonium fluoride may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution.
NH.sub.4F<.fwdarw.NH.sub.3+HF  Chemical reaction equation 7

(43) Although hydrogen fluoride decreases according to the above-described chemical reaction equation 6, hydrogen fluoride is produced according to chemical reaction equation 7. Accordingly, the content of hydrogen fluoride in the acid solution is maintained at a constant level. As the content of hydrogen fluoride is maintained at a constant level, the wet etching process can be stably performed.

(44) In one embodiment, the acid solution contains nitric acid, and the content of the nitric acid may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution. The nitric acid whose content is more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution functions to maintain the size of the protrusions formed by hydrogen fluoride in the range of several nm to several tens of nm.
6HNO.sub.3+Al.sub.2O.sub.3.fwdarw.2Al(NO.sub.3).sub.3+H.sub.2O  Chemical reaction equation 8

(45) According to chemical reaction equation 8 above, nitric acid flows into the grooves produced by the etching according to the above-described chemical reaction equation 6, and reacts with aluminum oxide (Al.sub.2O.sub.3). According to this reaction, protrusions having a width of several nm to several tens of nm are formed on the glass substrate. As the content of the nitric acid increases in the range of 10 wt % or more to 25 wt % or less based on 100 wt % of the acid solution, protrusions having a greater width of up to several μm can be formed on the glass substrate. On the other hand, the nitric acid whose content is more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution maintains the width of the protrusions, formed on the glass substrate, at a constant level in the range of several nm to several tens of nm.

(46) In one embodiment, the acid solution contains phosphoric acid, and the content of the phosphoric acid may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution.
2H.sub.3PO.sub.4+Al.sub.2O.sub.3.fwdarw.2Al(PO.sub.4)+3H.sub.2O  Chemical reaction equation 9

(47) According to chemical reaction equation 9 above, phosphoric acid reacts with aluminum oxide (Al.sub.2O.sub.3), thereby smoothing the surface of the protrusions having a rough surface. Phosphoric acid is more viscous than nitric acid, and thus can smooth the surface of the protrusions formed according to the chemical reaction of nitric acid.

(48) In one embodiment, the acid solution contains hydrochloric acid, and the content of the hydrochloric acid may be 10 wt % or more and 40 wt % or less based on 100 wt % of the acid solution.
SiO.sub.2+4HCl.fwdarw.SiCl.sub.4+2H.sub.2O  Chemical reaction equation 10

(49) According to chemical reaction equation 10 above, hydrochloric acid reacts with silicon dioxide (SiO.sub.2), thereby smoothing the surface of the protrusions having a rough surface.

(50) In one embodiment, the acid solution contains water, hydrogen fluoride, ammonium fluoride, phosphoric acid, nitric acid and hydrochloric acid. In this case, the content of the hydrogen fluoride may be more than 0 wt % and not more than 10 wt % based on 100 wt % of the acid solution; the content of the ammonium fluoride may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution; the content of the nitric acid may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution; the content of the phosphoric acid may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution; the content of the hydrochloric acid may be 10 wt % or more and 40 wt % or less; and the remainder is water.

(51) By a wet etching process using the acid solution containing the above-described amounts (wt %) of water, hydrogen fluoride, ammonium fluoride, phosphoric acid, nitric acid and hydrochloric acid, protrusions having a width of several nm to several tens of nm are formed on the glass substrate. The water serves to dilute the acid solution.

(52) FIG. 6 is a scanning electron micrograph of a glass substrate in which an anti-reflective layer is formed according to one embodiment. Protrusions formed on the glass substrate have a width of several nm to several tens of nm. FIG. 7 is an enlarged scanning electron micrograph of FIG. 6.

(53) FIG. 8 shows a sectional view of a glass substrate in which both an anti-glare layer and an anti-reflective layer are formed according to one embodiment.

(54) In one embodiment, the step of forming the protrusions comprise the steps of: forming an anti-glare layer including protrusions having a width of several tens of nm to several μm by first wet etching using an acid solution; and forming an anti-reflective layer including protrusions having a width of several nm to several tens of nm on the anti-glare layer by second wet etching using an acid solution.

(55) In the steps of forming anti-glare and anti-reflective layers, an anti-glare layer including protrusions having a width of several tens of nm to several μm are first formed by first etching using an acid solution.

(56) The above-described acid solution contains water, hydrogen fluoride, ammonium fluoride, nitric acid, and hydrochloric acid. In this case, the content of the hydrogen fluoride may be more than 0 wt % and not more than 10 wt % based on 100 wt % of the acid solution; the content of the ammonium fluoride may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution; the content of the nitric acid may be 10 wt % or more and 25 wt % or less based on 100 wt % of the acid solution; the content of the phosphoric acid may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution; the content of the hydrochloric acid may be more than 0 wt % and not more than 10 wt % based on 100 wt % of the acid solution; and the remainder is water.

(57) In the steps of forming anti-glare and anti-reflective layers, after the step of forming the anti-glare layer, an anti-reflective layer including protrusions having a width of several nm to several tens of nm are formed on the anti-glare layer by second etching using an acid solution.

(58) The above-described acid solution contains water, hydrogen fluoride, ammonium fluoride, phosphoric acid, nitric acid and hydrochloric acid. In this case, the content of the hydrogen fluoride may be more than 0 wt % and not more than 10 wt % based on 100 wt % of the acid solution; the content of the ammonium fluoride may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution; the content of the nitric acid may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution; the content of the phosphoric acid may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution; the content of the hydrochloric acid may be 10 wt % or more and 40 wt % or less; and the remainder is water.

(59) As the protrusions having a width (W.sub.1) of several tens of nm to several μm are formed, the light transmittance and reflectance of the glass substrate decrease. Thereafter, as the protrusions having a width (W.sub.2) of several nm to several tens of nm are additionally formed on the protrusions having a width (W.sub.1) of several tens of nm to several the transmittance of the glass substrate relatively increases, and the reflectance further decreases. As a result, an anti-glare and anti-reflective glass substrate is produced.

(60) FIG. 9 is a scanning electron micrograph of a glass substrate in which both an anti-glare layer and an anti-reflective layer are formed according to one embodiment. The photograph at the bottom of FIG. 9 is a further enlarged photograph of the rectangular portion shown at the top of FIG. 9.

(61) FIG. 10 shows a sectional view of a glass substrate in which an anti-reflective layer is additionally formed on protrusions and grooves having a size of several μm to several hundreds of formed on the glass substrate according to a conventional method which is not the present invention.

(62) In one embodiment, the method of the present invention may further comprise a step of additionally forming an anti-reflective layer having a width of several nm to several tens of nm on an anti-glare layer having a size of several μm to several hundreds of formed on a glass substrate according to a conventional method which is not the present invention, by wet etching using an acid solution. FIG. 11 is a scanning electron micrograph of a glass substrate in which anti-reflective protrusions having a size of several nm to several tens of nm are additionally formed on an anti-glare layer including protrusions having a size of several μm to several hundreds of μm, formed according to a conventional method.

(63) The above-described acid solution contains water, hydrogen fluoride, ammonium fluoride, phosphoric acid, nitric acid and hydrochloric acid. In this case, the content of the hydrogen fluoride may be more than 0 wt % and not more than 10 wt % based on 100 wt % of the acid solution; the content of the ammonium fluoride may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution; the content of the nitric acid may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution; the content of the phosphoric acid may be more than 0 wt % and not more than 5 wt % based on 100 wt % of the acid solution; the content of the hydrochloric acid may be 10 wt % or more and 40 wt % or less based on 100 wt % of the acid solution; and the remainder is water.

(64) The photograph at the bottom of FIG. 11 is an enlarged scanning electron micrograph of the rectangular portion shown at the top.

(65) From the scanning electron micrographs of FIGS. 6, 9 and 11, it can be seen that, in the base material surface formed by the nano-protrusion method of the present invention, a state in which the protrusions are formed has no regularity in the mutual position of the protrusions and the size or shape of the protrusions, because the protrusions on the surface are formed by wet etching and the wet etching is performed without a process of forming a selective etch-blocking means such as a mask before the etching.

(66) The irregularity of the surface protrusions as described above can be regarded as an inherent characteristic obtained by mask-free wet etching.

(67) FIG. 12 is a photograph of a smart phone comprising a glass or polymer film in which an anti-reflective layer is formed by the protrusion forming method according to the present invention.

(68) Referring to FIG. 12, the left side of the glass included in the smart phone with respect to the central dotted line has an anti-reflection layer formed by the protrusion forming method according to the present invention. However, the right side of the glass included in the smart phone does not have the anti-reflection layer formed by the protrusion forming method according to the present invention. It can be seen that a fingerprint formed on the left side of the glass is not darker than that on the right side.

(69) Those skilled in the art can appreciate that the present invention may be embodied in other specific forms without departing from the technical idea or essential characteristics thereof. Therefore, it is to be understood that the above-described embodiments are illustrative only and not restrictive of the scope of the present invention. It is also to be understood that the flow charts shown in the figures are merely the sequential steps illustrated in order to achieve the most desirable results in practicing the present invention and that other additional steps may be provided or some steps may be omitted. The scope of the present invention is defined by the appended claims rather than the foregoing detailed description, and it should be interpreted that all changes or modifications derived from the meaning and scope of the claims and equivalents thereof are included within the scope of the present invention.

DESCRIPTION OF REFERENCE NUMERALS

(70) 100: glass substrate.