阅读说明：本技术 在表面具备微细凹凸结构的塑料元件的制造方法 (Method for manufacturing plastic element having fine uneven structure on surface ) 是由 谷边健志 山本和也 于 2019-06-11 设计创作，主要内容包括：本发明提供在表面具备微细凹凸结构的塑料元件的制造方法,其能够通过反应性离子蚀刻工艺在塑料元件的表面直接生成所期望的间距和所期望值的深度的微细凹凸结构。一种在表面具备微细凹凸结构的塑料元件的制造方法,其包括下述步骤：第1步骤,通过第1气体气氛的反应性离子蚀刻在该塑料元件的表面生成0.05微米至1微米范围的特定值的平均间距的微细凹凸结构；以及第2步骤,通过第2气体气氛中的反应性离子蚀刻在大致维持平均间距的该特定值的同时使该微细凹凸结构的平均深度为0.15微米至1.5微米范围的特定值,该第2气体对该塑料元件的反应性比该第1气体对该塑料元件的反应性低。(The invention provides a method for manufacturing a plastic element having a fine uneven structure on the surface, which can directly generate the fine uneven structure with a desired pitch and a desired depth on the surface of the plastic element by a reactive ion etching process. A method for manufacturing a plastic element having a fine uneven structure on a surface thereof, comprising the steps of: a step 1 of forming a fine textured structure having an average pitch of a specific value in a range of 0.05 to 1 μm on the surface of the plastic member by reactive ion etching in a1 st gas atmosphere; and a 2 nd step of making the average depth of the fine textured structure to a specific value in a range of 0.15 to 1.5 μm while substantially maintaining the specific value of the average pitch by reactive ion etching in a 2 nd gas atmosphere, the 2 nd gas being less reactive with the plastic element than the 1 st gas.)

1. A method for manufacturing a plastic element having a fine uneven structure on a surface thereof, comprising the steps of:

a step 1 of forming a fine textured structure having an average pitch of a specific value in a range of 0.05 to 1 μm on the surface of the plastic member by reactive ion etching in a1 st gas atmosphere; and

and a 2 nd step of making the average depth of the fine textured structure to a specific value in a range of 0.15 to 1.5 μm while substantially maintaining the specific value of the average pitch by reactive ion etching in a 2 nd gas atmosphere, the 2 nd gas being less reactive with the plastic element than the 1 st gas.

2. The method for manufacturing a plastic device having a fine uneven structure on a surface thereof according to claim 1, wherein said 1 st gas is sulfur hexafluoride (SF)₆) Sulfur hexafluoride and oxygen (O)₂) Or a mixture of at least one of argon (Ar), or oxygen.

3. The method for manufacturing a plastic device having a fine uneven structure on a surface thereof according to claim 1 or 2, wherein the gas used in the 2 nd step is trifluoromethane (CHF)₃) A mixture of trifluoromethane and at least one of oxygen or argon, carbon tetrafluoride (CF)₄) Carbon tetrafluoride and at least one of oxygen or argon.

4. The method for producing a plastic member having a fine uneven structure on a surface thereof according to any one of claims 1 to 3, further comprising a 3 rd step of bonding fluorine radicals to the surface of the fine uneven structure without causing ion etching by plasma treatment in a 3 rd gas atmosphere.

5. The method for manufacturing a plastic device having a fine uneven structure on a surface thereof according to claim 4, wherein the 3 rd gas is trifluoromethane, carbon tetrafluoride, or sulfur hexafluoride.

6. The method for producing a plastic element having a fine textured structure on a surface thereof according to any one of claims 1 to 5, wherein the plastic element is an optical element.

7. The method for producing a plastic element having a fine uneven structure on a surface thereof according to any one of claims 1 to 6, wherein the fine uneven structure is a fine uneven structure for antireflection.

Technical Field

The present invention relates to a method for manufacturing a plastic element having a fine uneven structure on a surface thereof. The plastic member includes an optical member made of plastic. The optical element includes a lens, a diffraction grating, a prism, a microlens array, a diffusion plate, and a protective window.

Background

An optical element uses an antireflection structure formed of a fine uneven structure arranged at a small pitch (period) equal to or less than the wavelength of light. As a method for manufacturing a mold for forming such a fine uneven structure, a method of patterning a resist using an interference exposure apparatus or an electron beam writing apparatus to perform etching or electroforming is known. However, it is difficult to form a fine uneven structure on a large-area flat surface or curved surface by these methods.

Therefore, a manufacturing method has been developed in which a mold having a fine uneven structure is manufactured by a reactive ion etching process without patterning (for example, patent document 1). According to this method, a molding die having a fine uneven structure on a large-area plane or curved surface can be manufactured without patterning. However, when a plastic element is produced from a molding die produced by the above method, it is not easy to transfer the fine uneven structure of the molding die to a plastic material with high accuracy.

In addition, a method of directly forming a fine uneven structure on the surface of a plastic element such as a lens by a reactive ion etching process has been developed (for example, patent document 2). However, there has not been established a method for directly forming a fine uneven structure having a pitch and a depth suitable for preventing reflection of light in the visible light region on the surface of a plastic element by a reactive ion etching process. Specifically, in the conventional method, it is difficult to set the pitch and depth of the fine uneven structure formed on the surface of the plastic element to desired values.

Thus, the following production methods have not been developed: the method is a method for manufacturing a plastic element having a fine uneven structure on the surface, and the method can directly form the fine uneven structure with a desired pitch and a desired depth on the surface of the plastic element by a reactive ion etching process.

There is therefore a need for a manufacturing method that: the method is a method for manufacturing a plastic element having a fine uneven structure on the surface, and the method can directly form the fine uneven structure with a desired pitch and a desired depth on the surface of the plastic element by a reactive ion etching process.

Documents of the prior art

Patent document

Patent document 1: WO2014/076983A1

Patent document 2: DE10241708A1

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in an effort to provide a method for manufacturing a plastic element having a fine uneven structure on a surface thereof, which can directly form a fine uneven structure having a desired pitch and a desired depth on the surface of the plastic element by a reactive ion etching process.

Means for solving the problems

The method for manufacturing a plastic element having a fine uneven structure on the surface of the plastic element according to the present invention comprises the steps of: a step 1 of forming a fine textured structure having an average pitch of a specific value in a range of 0.05 to 1 μm on the surface of the plastic member by reactive ion etching in a1 st gas atmosphere; and a 2 nd step of making an average depth of the structure a specific value in a range of 0.15 to 1.5 μm in a 2 nd gas atmosphere having a lower reactivity with the plastic member than the 1 st gas.

According to the present invention, the fine uneven structure having a desired average pitch can be generated in the 1 st step, and then the average depth of the fine uneven structure can be set to a desired value while substantially maintaining the specific value of the average pitch by reactive ion etching in the 2 nd gas atmosphere having a reactivity with respect to the plastic element lower than that of the 1 st gas in the 2 nd step, so that the fine uneven structure having the desired pitch and the desired depth can be directly generated on the surface of the plastic element.

In the method for manufacturing a plastic component having a fine uneven structure on a surface according to embodiment 1 of the present invention, the 1 st gas is sulfur hexafluoride (SF)₆) Sulfur hexafluoride and oxygen (O)₂) Or a mixture of at least one of argon (Ar), or oxygen.

In the method for manufacturing a plastic element having a fine uneven structure on the surface according to embodiment 2 of the present invention, the gas used in the 2 nd step is trifluoromethane (CHF)₃) A mixture of trifluoromethane and at least one of oxygen or argon, carbon tetrafluoride (CF)₄) Carbon tetrafluoride and at least one of oxygen or argon.

The method for manufacturing a plastic element having a fine uneven structure on the surface according to embodiment 3 of the present invention further includes a 3 rd step of bonding fluorine radicals to the surface of the fine uneven structure without causing ion etching by plasma treatment in a 3 rd gas atmosphere.

According to the present embodiment, the water repellent treatment of the plastic element having the fine uneven structure can be performed by the plasma treatment. The 3 rd step can also be performed by using a device in which the connection between the high-frequency power supply device and the electrode of the reactive ion etching device for performing the 1 st and 2 nd steps is changed.

In the method for manufacturing a plastic device having a fine uneven structure on a surface according to embodiment 4 of the present invention, the 3 rd gas is trifluoromethane, carbon tetrafluoride, or sulfur hexafluoride.

In the method for manufacturing a plastic element having a fine uneven structure on the surface according to embodiment 5 of the present invention, the plastic element is an optical element.

In the method for manufacturing a plastic element having a fine uneven structure on the surface according to embodiment 6 of the present invention, the fine uneven structure is a fine uneven structure for antireflection.

According to the present embodiment, a plastic element having a fine uneven structure with an appropriate average pitch and average depth according to the wavelength of light desired to be prevented from being reflected can be manufactured.

Drawings

Fig. 1 is a diagram showing a configuration of a Reactive Ion Etching (RIE) apparatus 100A used in an etching method according to an embodiment of the present invention.

Fig. 2 is a Scanning Electron Microscope (SEM) image of the fine uneven structure obtained by etching under condition 1.

Fig. 3 is an SEM image of the fine uneven structure obtained by etching under condition 2.

Fig. 4 is a flowchart illustrating an etching method according to an embodiment of the present invention.

Fig. 5A is a diagram for explaining an etching method according to an embodiment of the present invention.

Fig. 5B is a diagram for explaining an etching method according to an embodiment of the present invention.

Fig. 5C is a diagram for explaining an etching method according to an embodiment of the present invention.

Fig. 6 is a flowchart illustrating a method of determining the etching conditions in step 1.

Fig. 7 is a flowchart illustrating a method of determining the etching conditions in step 2.

Fig. 8 is a flowchart illustrating a method of determining target values of the average pitch and the average depth of the fine uneven structure.

Fig. 9 is an SEM image of the fine uneven structure for antireflection for visible light generated by the above method.

Fig. 10 is a graph showing the relationship between wavelength and reflectance.

Fig. 11 is a graph showing a relationship between wavelength and transmittance.

FIG. 12 shows the use of trifluoromethane alone (CHF)₃) SEM image of the surface of the etched plastic element.

FIG. 13 shows sulfur hexafluoride (SF) alone₆) SEM image of the surface of the etched plastic element.

Fig. 14 is an SEM image of the surface of the plastic member after etching using only oxygen.

Fig. 15 is a graph showing a relationship between wavelength and transmittance.

Fig. 16 is an SEM image of the fine uneven structure for antireflection for visible light generated by the method shown in table 4.

Fig. 17 is a graph showing the relationship between wavelength and reflectance.

Fig. 18 is a graph showing a relationship between wavelength and transmittance.

Fig. 19 is a diagram showing the structure of a water-repellent treatment apparatus 100B used for water-repellent treatment according to an embodiment of the present invention.

Fig. 20 is a photograph of water droplets formed on the surface of a plastic element having a fine uneven structure without being subjected to a water repellent treatment.

Fig. 21 is a photograph of water droplets formed on the surface of a plastic element having a fine uneven structure subjected to the water repellent treatment of condition 1 in table 6.

Fig. 22 is a photograph of water droplets formed on the surface of a plastic element having a fine uneven structure subjected to the water repellent treatment of condition 2 in table 6.

Detailed Description

Fig. 1 is a diagram showing a configuration of a Reactive Ion Etching (RIE) apparatus 100A used in an etching method according to an embodiment of the present invention. The reactive ion etching apparatus 100A has a reaction chamber 101. The reaction chamber 101 after vacuum evacuation is supplied with gas from the gas supply port 111. The amount of gas supplied can be adjusted. A gas outlet 113 is provided in the reaction chamber 101, and a valve, not shown, is attached to the gas outlet 113. By operating the valve, the gas pressure in the reaction chamber 101 can be set to a desired pressure value. The reaction chamber 101 is provided with an upper electrode 103 connected to the ground and a lower electrode 105 connected to a high-frequency power supply 107, and can generate plasma by applying a high-frequency voltage between both electrodes by the high-frequency power supply 107. The plastic element 200 is disposed on the lower electrode 105. The plastic element 200 is, for example, a lens made of plastic. The lower electrode 105 may be cooled to a desired temperature using a cooling device 109. The cooling device 109 is a device using a water-cooled cooler for cooling, for example. The lower electrode 105 is cooled in order to control the etching reaction by setting the temperature of the substrate 101 to a desired temperature.

The reactive ion etching apparatus described with reference to fig. 1 is a capacitively-coupled ion etching apparatus, but other types of ion etching apparatuses, for example, an inductively-coupled ion etching apparatus, may be used.

When a high frequency voltage is applied to the lower electrode 105 on which the plastic element 200 is disposed, ions or radicals in the plasma are accelerated toward the plastic element 200 and collide with the plastic element 200. At this time, the sputtering by the ions and the chemical reaction of the etching gas occur simultaneously, and etching is performed. The plastic of the plastic member 200 is formed of a plurality of molecular chains, and dense portions and sparse portions of the molecular chains are randomly present on the surface of the plastic member 200. Since portions with dense molecular chains are not easily etched and portions with sparse molecular chains are easily etched, a fine uneven structure is generated on the surface of the plastic element 200 by etching.

Table 1 is a table showing the etching conditions and the average pitch and average depth of the fine uneven structure produced by etching under the etching conditions. The plastic member 200 is made of polycarbonate. In table 1 and other tables, the RF power is the power supplied from the high-frequency power supply 107, the machining temperature is the temperature controlled by the cooling device 109, and the machining time is the time during which the treatment is performed while supplying the power.

[ Table 1]

Condition 1 differs from condition 2 only in the processing time. In general, the longer the processing time (etching time), the larger the values of the average pitch and the average depth of the fine textured structure, and therefore, by changing the processing time, the values of the average pitch and the average depth of the fine textured structure can be changed in the same manner. According to table 1, the values of the average pitch and the average depth of the fine uneven structure obtained by the etching of condition 2 in which the processing time is long are larger than the values of the average pitch and the average depth of the fine uneven structure obtained by the etching of condition 1 in which the processing time is short, respectively.

On the other hand, since the antireflection function of the fine uneven structure is determined by the average pitch and the average depth, it is necessary to set the average pitch and the average depth to desired values in order to obtain a desired antireflection function. However, it is difficult to make the average pitch and the average depth respectively desired values only by the processing time. For example, as described below, the depth of the fine uneven structure obtained by the etching under the condition 1 is too small for obtaining a desired antireflection function with respect to visible light, and the depth of the fine uneven structure obtained by the etching under the condition 2 is appropriate for obtaining a desired antireflection function with respect to visible light, but the average pitch is too large, and cloudiness occurs due to reflection of light of various wavelengths of visible light.

The average pitch and the average depth can be changed by the power supplied from the high-frequency power supply 107, but in this case, the average pitch and the average depth similarly increase with the magnitude of the power, and it is difficult to set the average pitch and the average depth to desired values, respectively.

Fig. 2 is a Scanning Electron Microscope (SEM) image of the fine uneven structure obtained by the etching under condition 1.

Fig. 3 is an SEM image of the fine uneven structure obtained by the etching under condition 2.

The inventors have observed the formation process of the fine textured structure by etching, and have found that the fine textured structure is formed at a small pitch and a small depth in an early stage, and the pitch and the depth are increased with the passage of time in a later stage. Therefore, the inventors tried to divide the etching into an early stage (i.e., the 1 st step) and a subsequent stage (i.e., the 2 nd step), and suppress the etching in the 2 nd step. As a result, the inventors have newly found the following: if an atmosphere gas having lower reactivity than the atmosphere gas in the 1 st step is used in the 2 nd step, the depth can be increased without increasing the pitch in the 2 nd step. That is, it was found that the pitch and depth of the fine uneven structure can be made to be desired values by dividing the etching into the 1 st step and the 2 nd step using an atmosphere gas having lower reactivity than the atmosphere gas in the 1 st step.

Fig. 4 is a flowchart illustrating an etching method according to an embodiment of the present invention.

Fig. 5A to 5C are diagrams for explaining an etching method according to an embodiment of the present invention.

In step S1010 of fig. 4, a fine uneven structure of an average pitch of a specific value is generated on the surface of the plastic element 200 by Reactive Ion Etching (RIE) in the 1 st gas atmosphere. Fig. 5A is a diagram showing plastic member 200 before step S1010 is performed, and fig. 5B is a diagram showing plastic member 200 after step S1010 is performed.

In step S1020 in fig. 4, the average depth of the fine uneven structure is set to a desired value while maintaining the average pitch of the fine uneven structure by Reactive Ion Etching (RIE) in the 2 nd gas atmosphere having lower reactivity than the 1 st gas. Fig. 5C is a diagram showing the plastic member 200 after step S1020 is performed.

The target value P of the average pitch of the fine uneven structure for antireflection needs to be set so as to satisfy the following equation, where λ is the wavelength of light, n is the refractive index of the plastic element, and θ is the incident angle of light to the surface of the plastic element.

[ number 1]

When the wavelength of light is λ 0.4 μm, the refractive index of the plastic element is N1.5, and the incident angle of light on the surface of the plastic element is θ 30 °, the target value P needs to be less than 0.2 μm. In general, the target value of the average depth of the fine uneven structure for antireflection needs to be 0.35 times or more the wavelength λ of light. The average depth is about 0.25 μm or more with respect to the maximum wavelength of visible light of 0.7 μm.

Fig. 6 is a flowchart illustrating a method of determining the etching conditions in step 1.

In step S2010 of fig. 6, Reactive Ion Etching (RIE) is performed in the 1 st gas atmosphere under specific etching conditions.

In step S2020 in fig. 6, the generated fine uneven structure is observed, and it is determined whether or not the average pitch is a desired value, that is, a target value. If the average pitch is a desired value, the process is terminated. If the average pitch is not the desired value, the process proceeds to step S2030.

In step S2030 of fig. 6, the set values of power and time are changed so that the average pitch of the fine uneven structure becomes a desired value. To increase the average pitch, the set value of power or time is increased; to reduce the average pitch, the power or time set point is reduced. After step S2030 ends, the process returns to step S2010.

Fig. 7 is a flowchart illustrating a method of determining the etching conditions in step 2. After step 1 is performed using the etching conditions determined by the method shown in the flowchart of fig. 6, the etching conditions of step 2 are determined using the method shown in the flowchart of fig. 7.

In step S3010 of fig. 7, Reactive Ion Etching (RIE) is performed in a 2 nd gas atmosphere under predetermined etching conditions.

In step S3020 of fig. 7, the generated fine uneven structure is observed, and it is determined whether or not the average depth is a desired value, that is, a target value. If the average depth is a desired value, the process is terminated. If the average depth is not the desired value, the process proceeds to step S3030.

In step S3030 in fig. 7, the power or time setting value is changed so that the average depth of the fine uneven structure becomes a desired value. To increase the average depth, the power or time setting is increased; to reduce the average depth, the power or time set point is reduced. After step S3030 ends, the process returns to step S3010.

Fig. 8 is a flowchart illustrating a method of adjusting the target values of the average pitch and the average depth of the fine uneven structure.

In step S4010 in fig. 8, a fine uneven structure having a desired average pitch and a desired average depth is generated by the method shown in the flowcharts in fig. 6 and 7.

In step S4020 in fig. 8, the reflectance and transmittance of the plastic element are evaluated.

In step S4030 in fig. 8, it is determined whether the reflectance and transmittance of the plastic element are satisfactory. If satisfactory, the process is terminated. If not, the process proceeds to step S4040.

In step S4040 of fig. 8, the target value of at least one of the average pitch and the average depth is changed. After step S4040 ends, the process returns to step S4010.

Table 2 is a table showing the etching conditions of the etching method according to the embodiment of the present invention and the average pitch and the average depth of the fine uneven structure produced by the etching method. The plastic member 200 is made of polycarbonate.

[ Table 2]

The 1 st gas as the atmosphere gas of the 1 st step is oxygen and sulfur hexafluoride (SF)₆) The mixed gas of (1). The 2 nd gas as the atmosphere gas of the 2 nd step is oxygen and trifluoromethane (CHF)₃) The mixed gas of (1). The 2 nd gas is less reactive with the plastic component than the 1 st gas. After step 1, the average pitch was 0.06. mu.m, and the average depth was 0.1. mu.m. In step 2, the average depth was increased from 0.1 μm to 0.3 μm, but the average pitch was maintained at 0.06. mu.m. This provides a fine uneven structure having an average pitch and an average depth suitable for antireflection of visible light.

Fig. 9 is an SEM image of the fine uneven structure for antireflection for visible light generated by the method shown in table 2. As shown in Table 2, the average pitch was 0.06. mu.m, and the average depth was 0.3. mu.m.

Fig. 10 is a graph showing the relationship between wavelength and reflectance. The horizontal axis of fig. 10 represents wavelength, and the vertical axis of fig. 10 represents reflectance. The solid line shows the reflectance of the plastic element having the fine uneven structure obtained by the method of the present invention shown in table 2. The dashed line labeled "conventional method" indicates the reflectance of the plastic element having the fine uneven structure obtained by the method shown in condition 2 of table 1. The dotted line marked "raw" indicates the reflectance of the plastic element without the fine textured structure.

Fig. 11 is a graph showing a relationship between wavelength and transmittance. The horizontal axis of fig. 11 represents wavelength, and the vertical axis of fig. 11 represents transmittance. The solid line shows the transmittance of the plastic element having the fine uneven structure obtained by the method of the present invention shown in table 2. The broken line labeled "conventional method" indicates the transmittance of the plastic element having the fine uneven structure obtained by the method shown in condition 2 of table 1. The dotted line marked "raw" indicates the transmittance of a plastic element that has not been subjected to etching treatment and has no fine uneven structure.

The plastic element on which the measurement of reflectance shown in FIG. 10 and the measurement of transmittance shown in FIG. 11 were performed was a plate-shaped element having a thickness of 5 mm.

According to fig. 10, the reflectance of the plastic element having the fine uneven structure obtained by the method of the present invention is 1% or less in the visible light range of 400 nm to 700 nm, and is lower than the reflectance of the plastic element having the fine uneven structure obtained by the method shown in condition 2 of table 1.

According to fig. 11, the transmittance of the plastic element having a fine uneven structure obtained by the method of the present invention is 90% or more in the visible light range of 400 nm to 700 nm, which is higher than the transmittance of the plastic element having a fine uneven structure obtained by the method shown in condition 2 of table 1. In addition, the transmittance of the plastic element having a fine uneven structure obtained by the method of the present invention is about 5% higher than that of a plastic element having no fine uneven structure in the visible light range of 400 nm to 700 nm.

Next, etching in a single gas atmosphere will be described.

Table 3 is a table showing the etching conditions of the etching in the single gas atmosphere and the average pitch and average depth of the fine uneven structure produced by the etching. The plastic member 200 is made of polycarbonate.

[ Table 3]

FIG. 12 is trifluoromethane (CHF) alone₃) SEM image of the surface of the treated plastic element of (a).

FIG. 13 is sulfur hexafluoride (SF) only₆) SEM image of the surface of the treated plastic element of (a).

FIG. 14 is oxygen (O) only₂) SEM image of the surface of the treated plastic element of (a).

The average pitch of the fine uneven structure formed after the treatment in the gas atmosphere of only sulfur hexafluoride is larger than the average pitch of the fine uneven structure formed after the treatment in the gas atmosphere of only trifluoromethane, and the average depth of the fine uneven structure formed after the treatment in the gas atmosphere of only sulfur hexafluoride is larger than the average depth of the fine uneven structure formed after the treatment in the gas atmosphere of only trifluoromethane. Therefore, it is found that sulfur hexafluoride has higher reactivity with plastic parts made of polycarbonate than trifluoromethane.

According to fig. 14, no fine uneven structure was generated on the surface of the plastic element after the treatment in the gas atmosphere of only oxygen.

Fig. 15 is a graph showing a relationship between wavelength and transmittance. The horizontal axis of fig. 15 represents wavelength, and the vertical axis of fig. 15 represents transmittance. The thick solid line indicates the transmittance of the plastic element having the fine uneven structure obtained by the method of the present invention shown in table 2. The dotted line indicates sulfur hexafluoride (SF) alone as shown in Table 3₆) The transmittance of the plastic element having a fine uneven structure obtained after the treatment in the gas atmosphere of (2). The dotted line indicates that trifluoromethane (CHF) alone is contained as shown in Table 3₃) The transmittance of the plastic element having a fine uneven structure obtained after the treatment in the gas atmosphere of (2). The chain double-dashed line indicates that oxygen (O) alone is contained as shown in Table 3₂) The transmittance of the plastic element having a fine uneven structure obtained after the treatment in the gas atmosphere of (2). The thin solid line epitope labeled "unprocessed" was not treated and was not microfineTransmissivity of the relief-structured plastic element.

According to fig. 15, the transmittance of the plastic element having a fine uneven structure obtained after the treatment in the gas atmosphere of trifluoromethane alone and the transmittance of the plastic element having a fine uneven structure obtained after the treatment in the gas atmosphere of oxygen alone are substantially the same as those of the plastic element having no fine uneven structure without the treatment, and are lower by about 4% to 5% in the visible light range of 400 nm to 700 nm than those of the plastic element having a fine uneven structure obtained by the method of the present invention. The transmittance of the plastic element having a fine uneven structure obtained after the treatment in a gas atmosphere containing only sulfur hexafluoride is at most about 1% lower than the transmittance of the plastic element having a fine uneven structure obtained by the method of the present invention in the range of 600 nm or less.

The above description relates to plastic components made of polycarbonate. The invention can also be applied to elements of other plastic materials. Next, a case where the plastic material is an acrylic resin will be described.

Table 4 is a table showing the etching conditions of the etching method according to the other embodiment of the present invention and the average pitch and the average depth of the fine uneven structure produced by the etching method. The plastic element 200 is made of polymethyl methacrylate (PMMA) as an acrylic resin.

[ Table 4]

Fig. 16 is an SEM image of the fine uneven structure for antireflection for visible light generated by the method shown in table 4.

Fig. 17 is a graph showing the relationship between wavelength and reflectance. The horizontal axis of fig. 17 represents wavelength, and the vertical axis of fig. 17 represents reflectance. The solid line shows the reflectance of the plastic element having the fine uneven structure obtained by the method of the present invention shown in table 4. The dotted line marked "raw" indicates the reflectance of the plastic element without the fine textured structure and without treatment.

Fig. 18 is a graph showing a relationship between wavelength and transmittance. The horizontal axis of fig. 18 represents wavelength, and the vertical axis of fig. 18 represents transmittance. The solid line shows the transmittance of the plastic element having the fine uneven structure obtained by the method of the present invention shown in table 4. The dotted line marked "raw" indicates the transmittance of the plastic element without treatment and without the fine textured structure.

As shown in fig. 18, the transmittance of the plastic element having a fine uneven structure obtained by the method of the present invention is 92% or more in the visible light range of 400 nm to 700 nm, and is about 3% to 4% higher than that of the plastic element not having a fine uneven structure.

Table 5 is a table showing the etching conditions of the etching method according to the other embodiment of the present invention and the average pitch and the average depth of the fine uneven structure produced by the etching method. The plastic member 200 is made of polymethyl methacrylate (PMMA).

[ Table 5]

In the present embodiment, it is shown that the reactivity of oxygen to polymethyl methacrylate is higher than that of a mixed gas of trifluoromethane and argon to polymethyl methacrylate by using oxygen in the 1 st step and a mixed gas of trifluoromethane and argon in the 2 nd step to obtain a fine textured structure having a desired average pitch and average depth.

After the completion of step 1 in table 5, when the etching was continued in the oxygen atmosphere, the average depth did not change significantly, the average pitch increased, and the desired average pitch and the desired average depth could not be obtained.

It is considered that the reason why the fine uneven structure is not formed when the polycarbonate is etched in the atmosphere of only oxygen gas shown in table 3 is that the entire surface is etched because the power and the etching time are long, not because the etching is not performed. The reactivity with plastic materials is generally considered to be in the order of oxygen, sulfur hexafluoride and trifluoromethane. Carbon tetrafluoride (CF4) may also be used instead of trifluoromethane as the relatively less reactive gas for the plastic material.

The atmosphere gas used in the 1 st step of the etching method of the embodiment of the present invention contains sulfur hexafluoride, a mixture of sulfur hexafluoride and at least one of oxygen or argon, or oxygen. The atmosphere gas used in the 2 nd step of the etching method of the embodiment of the invention includes trifluoromethane, a mixture of trifluoromethane and at least one of oxygen or argon, a mixture of carbon tetrafluoride, carbon tetrafluoride and at least one of oxygen or argon.

In the present invention, the average pitch of the fine uneven structure is determined in the 1 st step, and the processing is performed in the 2 nd step using an atmosphere gas having a lower reactivity with respect to the plastic element than the atmosphere gas in the 1 st step, whereby the average depth of the fine uneven structure can be increased while maintaining the average pitch. As described above, according to the present invention, a plastic element having a fine uneven structure with a desired pitch and a desired depth can be manufactured.

Next, a novel method of water repellent treatment of a plastic element having a fine uneven structure will be described. Conventionally, in order to waterproof a plastic element having a fine uneven structure, the surface of the element is coated with a waterproof film by immersing the element in a waterproof coating liquid. However, it is difficult to coat a fine uneven structure on the surface of a lens having a complicated shape with a uniform water-repellent film. In addition, the treatment requires time and labor, and the waterproof coating liquid is very expensive, so that the treatment cost is high.

In a new water repellent treatment method, a water repellent treatment is applied to a fine uneven structure on the surface of a plastic element using an apparatus having a structure similar to that of the reactive ion etching apparatus 100A shown in fig. 1.

Fig. 19 is a diagram showing the structure of a water-repellent treatment apparatus 100B used for water-repellent treatment according to an embodiment of the present invention. The waterproof processing apparatus 100B has a reaction chamber 101. The reaction chamber 101 after vacuum evacuation is supplied with gas from the gas supply port 111. The amount of gas supplied can be adjusted. A gas outlet 113 is provided in the reaction chamber 101, and a valve, not shown, is attached to the gas outlet 113. By operating the valve, the gas pressure in the reaction chamber 101 can be set to a desired pressure value. The reaction chamber 101 is provided with a lower electrode 105 connected to the ground and an upper electrode 103 connected to a high-frequency power supply 107, and can generate plasma by applying a high-frequency voltage between both electrodes by the high-frequency power supply 107. A plastic element 200 having a fine uneven structure on the surface is disposed on the lower electrode 105. The plastic element 200 is, for example, a lens made of plastic. The lower electrode 105 may be cooled to a desired temperature using a cooling device 109. The cooling device 109 is a device using a water-cooled cooler for cooling, for example. The lower electrode 105 is cooled to control the reaction by setting the temperature of the substrate 101 to a desired temperature.

In the reactive ion etching apparatus 100A shown in fig. 1 and the water-repellent treatment apparatus 100B shown in fig. 19, only the high-frequency power source 107 is connected to the upper and lower electrodes differently. In the water repellent treatment apparatus 100B, the lower electrode 105 of the plastic element 200 having a fine uneven structure on the surface thereof is grounded so as not to be etched by ions. In the water repellent treatment apparatus 100B, fluorine radicals generated by plasma are bonded to the surface of the fine uneven structure, thereby performing water repellent treatment. The atmosphere gas is selected so that the radicals do not damage the fine uneven structure, and the electric power and the processing time of the high-frequency power supply are adjusted. The etching treatment and the water repellent treatment may be performed by using a single apparatus configured to be capable of changing the connection between the high-frequency power supply and the upper and lower electrodes.

Table 6 is a table showing the water repellent treatment conditions. The plastic member 200 is made of polymethyl methacrylate (PMMA).

[ Table 6]

	Pressure of gas	Gas species-flow	RF power	Processing temperature	Working time
						Condition 1	5Pa	CHF3：50mL/min	100W	10℃	300sec
Condition 2	1Pa	CHF3：50mL/min	50W	10℃	300sec

As the atmosphere gas for the water repellent treatment, carbon tetrafluoride or sulfur hexafluoride may be used instead of trifluoromethane.

Fig. 20 is a photograph of water droplets formed on the surface of a plastic element having a fine uneven structure without being subjected to a water repellent treatment. In a cross section perpendicular to the surface of the plastic member, the angle formed by the tangent to the surface of the water droplet and the surface of the plastic member, i.e., the contact angle, was 38.3 degrees.

Fig. 21 is a photograph of water droplets formed on the surface of a plastic element having a fine uneven structure subjected to the water repellent treatment of condition 1 in table 6. The contact angle was 139 degrees. By the water repellent treatment, the contact angle is significantly increased.

Fig. 22 is a photograph of water droplets formed on the surface of a plastic element having a fine uneven structure subjected to the water repellent treatment of condition 2 in table 6. The contact angle was 137 degrees. By the water repellent treatment, the contact angle is significantly increased.