JP2009292703A - Method for manufacturing die for forming optical element, and method for forming optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a die for forming an optical element, where a rugged structure is formed on the forming surface of the die by a simple technique, and the like. <P>SOLUTION: This method for manufacturing a die 10 for forming an optical element comprises a step of film-forming a masking film 12 on a matrix material 11; a step of forming a self-assembled film 13 formed of a block polymer and composed of two phases on the masking film 12; a first etching step of removing a dispersed phase 15 in the self-assembled film 13; a second etching step of removing parts of the masking film 12 corresponding to the dispersed phase 15 removed in the first etching step; a third etching step of forming a rugged structure on the matrix material 11 by removing the surface parts of the matrix material 11 corresponding to the masking film 12 removed in the second etching step. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a mold for molding an optical element, and more particularly to a method of manufacturing a mold for molding an optical element suitable for manufacturing an optical element having an antireflection structure.

  Anti-reflection measures are often taken for optical elements that need to prevent reflection of incident light. As an antireflection measure, a method of forming a single layer film having a low refractive index or a multilayer film having a low refractive index and a high refractive index as an antireflection film by a method such as vapor deposition, sputtering, or painting is used. . This antireflection film causes interference of light, whereby the optical element can have an antireflection function. Such an antireflection film is widely used because it can be formed by a general technique such as vapor deposition or sputtering. However, it is difficult to design optically optimal conditions because various factors such as material selection, optical element shape, and light wavelength to be used are involved. In addition, a complicated process is required for film formation, and the cost is disadvantageous.

  Therefore, a technique for giving an antireflection effect by giving a very fine uneven shape on the surface of the optical element instead of the antireflection film has been widely studied. This utilizes the phenomenon that when light is incident on the surface of an uneven structure having an aspect ratio of 1 or more at a pitch shorter than the wavelength of light, light having a wavelength longer than the pitch of the structure is almost transmitted.

For example, in Patent Document 1, an electron beam drawing apparatus is used to form a metal mask in the form of a dot array on an optical element, and then reactive ion etching is performed. At that time, the metal mask diameter gradually decreases, A method of forming a weight shape on an optical element by etching the optical element until it finally disappears is described.
As another method, it is conceivable that the optical element is manufactured by a press molding method using a mold, and a concavo-convex structure is formed on the surface of the mold as a shape transfer source. As a method for forming such a concavo-convex structure on a mold, for example, Patent Document 2 discloses a step of simultaneously forming a nickel and nickel phase-separating material on a nickel substrate, and a nickel obtained by the film forming step. And a matrix region containing a material surrounding the plurality of cylinders and phase-separated from nickel, and at least one of the first and second materials contains nickel. A method for producing a mold for an optical element having a concavo-convex structure including a step of producing a mold made of nickel or a nickel alloy by etching away a matrix portion from a mixed film is described.

JP 2001-272505 A JP 2008-37089 A

However, the method using electron beam drawing requires a very long drawing time, and the drawing apparatus is very expensive, resulting in a significant increase in production cost. Therefore, there is a problem that it is not suitable for production of an optical element for which cost reduction is desired.
In addition, in the method of manufacturing an optical element mold using a phase-separating material, when an alloy is used as the phase-separating material, the pattern size of the concavo-convex structure is determined by the combination of metals constituting the alloy. Therefore, in order to match the target pattern size, various combinations of alloys need to be selected, but the selection is not easy.

In view of the above problems, an object of the present invention is to provide a method for producing a mold for molding an optical element in which a concavo-convex structure such as a transfer structure of an antireflection structure is formed by a simple method.
Furthermore, another object of the present invention is to provide a method for manufacturing an optical element having a concavo-convex structure such as an antireflection structure on its surface in a large amount and at a low cost.

  As a result of intensive studies, the present inventors have used a self-assembled film made of a block polymer as a material for phase separation, and by using this self-assembled film, the uneven structure can be used as a mold for molding optical elements. Based on this finding, the present invention was completed. That is, the gist of the present invention is as follows.

  The optical element molding die manufacturing method of the present invention includes a step of forming a mask film on a base material, a step of forming a two-phase self-assembled film formed of a block polymer on the mask film, A first etching step of removing a portion of one phase of the self-assembled film, and a first etching step of a portion corresponding to the portion of one phase of the self-assembled film removed by the first etching step A second etching step for removing the mask film exposed by the step, and a surface corresponding to the mask film removed by the second etching step, by removing the surface portion of the base material exposed by the second etching step, And a third etching step for forming the structure.

  Here, the concavo-convex structure is preferably a transfer structure having an antireflection structure. The block polymer is preferably a combination of a hydrophobic polymer and a hydrophilic polymer, more preferably a diblock polymer. The diblock polymer is preferably a combination of polystyrene and polymethyl methacrylate, and the polymethyl methacrylate is more preferably contained in a proportion of 20 mol% to 30 mol%.

  Moreover, it is preferable that the part which consists of one phase among self-organization films | membranes makes a substantially cylindrical shape, and at least 1 process is performed by dry etching among a 1st etching process, a 2nd etching process, and a 3rd etching process. The dry etching is more preferably reactive ion etching.

  The optical element manufacturing method of the present invention includes a step of forming a mask film on a base material, a step of forming a self-assembled film formed of a block polymer on the mask film and comprising two phases, and a self-assembly. A first etching step for selectively removing a portion made of one phase of the film; and a second etching step for removing a mask film of a portion corresponding to the portion made of one phase of the self-assembled film. And a third etching step for removing the surface portion of the base material corresponding to the removed mask film, and press-molding the heat-softened optical element base material using the optical element molding die manufactured by the third etching step By doing so, an uneven structure is formed on the surface of the optical element.

  Here, the uneven structure is preferably an antireflection structure.

  According to the present invention, it is possible to manufacture a mold or the like for molding an optical element in which an uneven structure such as a transfer structure having an antireflection structure is formed by a simple method.

FIGS. 1A to 1F are diagrams illustrating a method for manufacturing a mold for molding an optical element having a concavo-convex structure on a molding surface according to the present embodiment.
First, the mask film 12 is formed on the surface of the base material 11 made of glassy carbon (FIG. 1A). The mask film 12 functions as a mask when dry etching is performed as will be described later. In this case, the material is not particularly limited as long as it is difficult to be etched. For example, it is selected from chromium (Cr), molybdenum (Mo), tantalum (Ta), tungsten (W), and silicon (Si). It is possible to use at least one kind of simple substance, alloy, nitride or oxide-containing material. In this embodiment, the mask film 12 made of chromium is formed with a thickness of 20 nm by a sputtering method.

Next, a self-assembled film 13 made of a block polymer and having two phases is formed on the mask film 12 (FIG. 1B). As will be described in detail later, this block polymer has a structure in which the dispersed phase 15 grows in the matrix phase 14 by self-organizing and separating into two phases by heating after film formation. In the present embodiment, the dispersed phase 15 is preferably substantially cylindrical.
In the present embodiment, a block polymer in which PS (polystyrene) and PMMA (polymethyl methacrylate) are bonded is used. In the present embodiment, it is possible to use a diblock polymer containing PMMA at a ratio of 20 mol% to 30 mol% and the rest being PS. The total molecular weight of this diblock polymer is, for example, about 40,000. Film formation can be performed by spin-coating a slurry in which toluene is used as a solvent and PS-PMMA is dispersed at a weight ratio of 1%. After the film formation, if annealing is performed at 170 ° C. for 24 hours, a self-assembled film 13 having a thickness of 1 μm is formed.
Here, FIG. 2 is a perspective view illustrating the self-assembled film 13. As shown in FIG. 2, the self-assembled film 13 has a structure in which a dispersed phase 15 having a substantially cylindrical shape mainly containing PMMA is grown in a honeycomb shape on a matrix phase 14 mainly containing PS.

Next, dry etching by reactive ion etching (RIE) using RF plasma is performed to remove a portion composed of one phase of the self-assembled film 13 (first etching step) (FIG. 1C )). This dry etching is performed by using oxygen gas as a processing gas. At this time, the etching rate ratio between the disperse phase 15 mainly composed of PMMA and the matrix phase 14 mainly composed of PS is about 3: 1. That is, in this step, the dispersed phase 15 is removed first, and a substantially cylindrical void portion 16 arranged in a honeycomb shape is formed. Then, a portion of the mask film 12 corresponding to the portion composed of the dispersed phase 15 is exposed.
In the present embodiment, the reactive ion etching is performed by setting the pressure of the oxygen gas to 30 Pa, the RF power to 500 W, and the processing time to 20 minutes.

Next, using the remaining matrix phase 14 as a mask, dry etching is performed by ion etching using argon as a processing gas (second etching step) (FIG. 1D). Thereby, the mask film 12 exposed by the first etching step in the portion corresponding to the portion made of one phase removed by the first etching step in the self-assembled film 13 can be removed. In the dry etching in the present embodiment, the etching rate ratio between the matrix phase 14 mainly composed of PS and the mask film 12 made of chromium is about 5: 1. That is, by this step, the portion of the mask film 12 where the dispersed phase 15 exists is removed, and a part of the surface of the base material 11 is exposed. Further, the matrix phase 14 is also removed.
In the present embodiment, the ion etching was performed by setting the argon pressure to 1 Pa, the RF power to 500 W, and the processing time to 6 minutes.

Next, dry etching is performed by reactive ion etching using RF plasma (third etching step) (FIG. 1E). This dry etching is performed by using oxygen gas as a processing gas. By this dry etching, the mask film 12 made of chromium is hardly etched, but the base material 11 made of glassy carbon is etched. For this reason, the surface portion of the base material 11 exposed by the second etching step in the portion corresponding to the mask film 12 removed by the second etching step can be removed. As a result, a recess 17 is formed in the base material 11, and an uneven structure is formed in the base material 11.
In the present embodiment, the reactive ion etching is performed by setting the pressure of the oxygen gas to 30 Pa, the RF power to 500 W, and the processing time to 20 minutes.

Finally, when the remaining mask film 12 is removed using a chromium etching solution, a mold 10 for molding an optical element having a fine concavo-convex structure can be manufactured (FIG. 1 (f)).
In the present embodiment, the center-to-center distance (P) of this concavo-convex structure is about 100 nm. Further, the average height (H) from the bottom surface of the concave-convex structure to the top surface of the convex portion was about 200 nm. In this way, an optical element molding die having an antireflection structure transfer structure on the molding surface, which is a fine concavo-convex structure having an aspect ratio of 1 or more, can be produced.

On the other hand, FIGS. 5A to 5F are views for explaining a method for producing a concavo-convex structure in an optical element by a method using a conventional electron beam drawing apparatus.
First, an electron beam resist 52 is formed on a substrate 51 made of quartz or glass by spin coating (FIG. 5A).
Next, the electron beam lithography is performed by irradiating the electron beam resist 52 with an electron beam drawing apparatus, and the electron beam resist 52 is exposed to a predetermined pattern 53 (FIG. 5B). This pattern can be drawn with a width of about several tens of nanometers, for example.
Next, the exposed portion of the exposed electron beam resist 52 is removed by development (FIG. 5C).
Next, a metal 54 is formed (FIG. 5D). The metal 54 is made of, for example, chromium (Cr) or aluminum (Al), and can be formed by vapor deposition.
Next, the electron beam resist 52 is removed by lift-off (FIG. 5E). As a result, the metal 54 deposited on the substrate 51 remains.
Next, etching is performed by reactive ion etching using the metal 54 as a metal mask. Here, a mixed gas of C ₄ F ₈ and CH ₂ F ₂ can be used as the reaction gas. Then, if etching is performed until the metal mask disappears, weight-shaped protrusions are obtained (FIG. 5 (f)).

  In the method using the electron beam drawing apparatus as described above, a long drawing time is required in the step of exposing the predetermined pattern 53 described with reference to FIG. On the other hand, in the method using the block polymer as in the present embodiment, a fine concavo-convex structure can be produced without requiring a long drawing time.

Next, the block polymer used in the present embodiment will be described in detail.
The block polymer formed in this embodiment is not particularly limited as long as it is spontaneously separated into two phases by annealing treatment or the like. However, in order to easily cause phase separation, a hydrophobic polymer and a hydrophilic polymer are preferably combined. More specifically, in addition to the AB type diblock polymer made of PS (polystyrene) -PMMA (polymethyl methacrylate), the AB type diblock polymer made of PP (polypropylene) -EPR (ethylene propylene). ABA type triblock polymer composed of PS (polystyrene) -PEO (polyethylene oxide) -PS (polystyrene) can be used.

When an alloy is used as the material for phase separation, the pattern size is determined by the combination of metals constituting the alloy. Therefore, in order to match the target pattern size, it is necessary to select different combinations of alloys, but the selection is not easy. On the other hand, when a block polymer is used, the pattern size can be easily changed to a desired one by changing the chain length of the polymer constituting the block polymer.
Furthermore, to change the pattern size, it is only necessary to change the type of the solution in which the block polymer is dispersed. Therefore, it becomes easy to improve the productivity of an optical element molding die having a transfer structure of an antireflection structure on the molding surface, and it becomes easy to manufacture a large amount of optical elements at low cost.

  In the present embodiment described with reference to FIG. 1, the uneven structure is finally formed in the base material 11 by selectively removing the portion of the dispersed phase 15 by etching. However, it is also possible to produce a concavo-convex structure in the base material 11 by a method in which the matrix phase 14 is selectively removed by etching. For this purpose, for example, a diblock polymer is used in which PS (polystyrene) and PMMA (polymethyl methacrylate) have a component ratio of PS of 15 mol% to 25 mol%, and the remainder is PMMA. By using a diblock polymer having such a component ratio, a disperse phase 15 having a substantially cylindrical shape mainly containing PS is grown in a honeycomb shape on the matrix phase 14 mainly containing PMMA. In the step described with reference to FIG. 1C, the matrix phase 14 mainly composed of PMMA is selectively removed by etching.

In addition, the method of performing reactive ion etching using capacitively coupled RF plasma as dry etching has been described. However, the present invention is not limited to this, and for example, ECR (Electron Cyclotron Resonance) etching method, inductively coupled plasma etching method, etc. Is available.
Further, the etching is not limited to dry etching, and can be applied by a method using wet etching.

Next, an apparatus for performing reactive ion etching (RIE), etching conditions, and the like will be described in detail.
FIG. 3 is a diagram illustrating a processing apparatus that performs reactive ion etching using capacitively coupled RF plasma.
The processing apparatus 30 that performs the reactive ion etching shown in FIG. 3 includes an installation table 32 on which an object to be processed 31 is installed, and a counter electrode 33 arranged to face the installation table 32. Further, the processing apparatus 30 includes a processing gas introduction valve 34 that introduces a predetermined processing gas into the environment around the workpiece 31, a high frequency power source 35 that applies a high frequency voltage between the installation table 32 and the counter electrode 33, It has an exhaust valve 36 and an exhaust pump 37 for exhausting air or processing gas from the surrounding environment.

  The installation base 32 is made of a conductive material such as stainless steel having a strength capable of mounting the workpiece 31. The installation table 32 is connected to the high frequency power source 35 together with the counter electrode 33.

  The counter electrode 33 is made of, for example, a conductor such as stainless steel. The counter electrode 33 is disposed opposite to the installation table 32 so that the counter electrode 33 is substantially parallel to the installation table 32 on which the workpiece 31 is mounted.

  In the processing gas introduction valve 34, an exhaust valve 36 and an exhaust pump 37, which will be described later, exhaust air from the environment around the workpiece 31 formed between the installation base 32 and the counter electrode 33, and have a predetermined degree of vacuum. After reaching, process gas is introduced.

  The high frequency power source 35 applies a high frequency voltage between the installation base 32 and the counter electrode 33. The applied high frequency has such a frequency and voltage that the processing gas introduced by the processing gas introduction valve 34 is excited to generate plasma.

  The exhaust valve 36 and the exhaust pump 37 exhaust air from the environment around the workpiece 31 formed between the installation base 32 and the counter electrode 33 until a predetermined degree of vacuum is reached. The exhaust valve 36 and the exhaust pump 37 are used when exhausting the processing gas after the processing is completed.

A method of performing reactive ion etching using the processing apparatus 30 having the above configuration will be described below.
First, the workpiece 31 is mounted at a predetermined position on the installation table 32. In the present embodiment, the object 31 to be processed is one in which the mask film 12 and the self-assembled film 13 are formed on the base material 11 described in FIG. 1B, or in FIG. This corresponds to the case where the mask film 12 partially remains on the base material 11 described.
Next, the exhaust valve 36 and the exhaust pump 37 cooperate to exhaust air from the environment around the workpiece 31 until a predetermined degree of vacuum is reached. After reaching a predetermined degree of vacuum, the processing gas is introduced from the processing gas introduction valve 34.
A high frequency voltage is applied between the installation base 32 and the counter electrode 33 by the high frequency power source 35. The processing gas is decomposed by the applied high-frequency voltage, and radicals and ions are generated. Etching is performed by the generated radicals and ions colliding with the object to be processed 31, causing a chemical reaction with the metal oxide to be vaporized and removed.

Next, an apparatus and a method for press-molding an optical element using the mold 10 manufactured by the manufacturing method described above will be described below.
FIG. 4 is a configuration diagram showing a press molding apparatus 100 using the mold 10 in which the transfer structure of the antireflection structure is manufactured according to the present embodiment.
The press molding apparatus 100 includes a lower mold 10a and an upper mold 10b for press-molding optical elements, and a lower temperature equalizing plate 114 and an upper temperature equalizing plate 116 for maintaining the lower mold 10a and the upper mold 10b at predetermined temperatures. And a lower heater 118 and an upper heater 120 for raising the temperature of the lower mold 10a and the upper mold 10b. The press molding apparatus 100 also includes a pressure cylinder 124 that moves the upper mold 10b, a nitrogen inlet 126 and a nitrogen exhaust 128 that control the molding environment of the optical element, a lower mold 10a, an upper mold 10b, and the like. And a sleeve 132 for restricting the operation of the upper mold 10b.

Both the lower mold 10a and the upper mold 10b are the mold 10 having the transfer structure of the above-described antireflection structure on the molding surface. The lower die 10a and the upper die 10b are placed and softened to form a glass lens by molding the optical element base material 122 softened.
Lower soaking plate 114 and upper soaking plate 116 are mounted on lower heater 118 and upper heater 120, respectively. The lower soaking plate 114 and the upper soaking plate 116 serve as a thermal buffer (thermal buffer) so that the heat received from the lower heating heater 118 and the upper heating heater 120 does not interfere with the production of the optical element. A uniform state is transmitted to the lower mold 10a and the upper mold 10b. Here, the lower heater 118 and the upper heater 120 are controlled using control means (not shown) so that the surfaces of the lower mold 10a and the upper mold 10b have temperatures suitable for press molding.

The optical element base material 122 is made of, for example, low-melting glass containing silica as a main component and added with alumina, sodium, lanthanum fluoride, or the like. The optical element base material 122 may be, for example, a low-melting glass having a softening temperature of about 600 ° C. or lower or an ultra-low melting glass having a softening temperature of about 400 ° C. or lower.
The pressure cylinder 124 is a drive system that moves the upper mold 10b fixed to the upper heater 120 and the upper soaking plate 116 up and down. The operation is controlled by a control means (not shown).
The nitrogen inlet 126 and the nitrogen outlet 128 use nitrogen as the mold atmosphere during molding to prevent oxidation at high temperatures.

A manufacturing process in which the press molding apparatus 100 having the above configuration press-molds the optical element base material 122 to manufacture an optical element will be described below.
First, the optical element base material 122 is placed between the lower mold 10 a and the upper mold 10 b, and the optical element base 122 is placed in the press molding apparatus 100.

Next, nitrogen is introduced from the nitrogen inlet 126 using an exhaust pump and a processing gas introduction pump (not shown), and the air inside the press molding apparatus 100 is replaced with nitrogen gas. Then, the temperature of the lower heating heater 118 and the upper heating heater 120 is increased, and the optical element base material 122 is sufficiently heated to the transition point (transition temperature) Tg of the optical element base material 122 in a nitrogen atmosphere. The temperature is increased to a deformation temperature (At), and the optical element base material 122 is softened.
When the temperature becomes near the yield temperature At, the upper die 10b is moved by the pressure cylinder 124, and the optical element base material 122 is pressed by the lower die 10a and the upper die 10b.

The optical element base material 122 spreads outward by the pressure applied by the lower mold 10a and the upper mold 10b during pressing, and is accommodated in a gap formed between the lower mold 10a and the upper mold 10b, and is press-molded. Is done. At the same time, the optical element base material 122 is filled in the transfer structure recesses of the antireflection structure on the surfaces of the lower mold 10a and the upper mold 10b.
Thereafter, the press molding apparatus 100 is cooled to near the transition temperature Tg while the pressure is applied, and then the pressure of the upper mold 10b is released, for example, cooled to room temperature, and the optical element is taken out.
Through this series of steps, the concavo-convex structure on the surfaces of the lower mold 10a and the upper mold 10b is transferred to the optical element, and an optical element having a concavo-convex structure such as an antireflection structure formed on the surface is manufactured.

It is a figure explaining the manufacturing method of the metal mold | die for optical element shaping | molding which has an uneven structure in the molding surface by this Embodiment. It is the perspective view explaining the self-organization film | membrane. It is a figure explaining the processing apparatus which performs reactive ion etching by capacitive coupling type RF plasma. It is a block diagram which shows the press molding apparatus using the metal mold | die with which the transfer structure of the antireflection structure was produced by this Embodiment. It is the figure explaining the method of producing an uneven structure in an optical element by the method using the conventional electron beam drawing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Mold, 10a ... Lower mold, 10b ... Upper mold, 11 ... Base material, 12 ... Mask film, 13 ... Self-assembled film, 14 ... Matrix phase, 15 ... Dispersed phase, 30 ... Processing apparatus, 100 ... Press molding equipment

Claims (11)

A method for producing a mold for optical element molding,
Forming a mask film on the base material;
Forming a two-phase self-assembled film formed of a block polymer on the mask film;
A first etching step of removing a portion of one phase of the self-assembled film;
A second etching step of removing the mask film exposed by the first etching step in a portion corresponding to the portion made of the one phase removed by the first etching step in the self-assembled film;
A third etching step of forming a concavo-convex structure on the base material by removing a surface portion of the base material exposed by the second etching step at a portion corresponding to the mask film removed by the second etching step; ,
The manufacturing method of the metal mold | die for optical element shaping | molding characterized by having this.   The method for producing a mold for molding an optical element according to claim 1, wherein the uneven structure is a transfer structure having an antireflection structure.   The method for producing a mold for molding an optical element according to claim 1, wherein the block polymer is a combination of a hydrophobic polymer and a hydrophilic polymer.   The method for producing a mold for molding an optical element according to claim 1, wherein the block polymer is a diblock polymer.   5. The method for producing a mold for molding an optical element according to claim 4, wherein the diblock polymer is a combination of polystyrene and polymethyl methacrylate.   The said polymethyl methacrylate is contained in the ratio of 20 mol%-30 mol%, The manufacturing method of the metal mold | die for optical element shaping | molding of Claim 5 characterized by the above-mentioned.   The method for producing a mold for molding an optical element according to claim 1, wherein a portion of one phase of the self-assembled film has a substantially cylindrical shape.   The method for manufacturing a mold for molding an optical element according to claim 1, wherein at least one of the first etching step, the second etching step, and the third etching step is performed by dry etching. .   The method for producing a mold for molding an optical element according to claim 8, wherein the dry etching is reactive ion etching. A method for manufacturing an optical element, comprising:
A step of forming a mask film on a base material, a step of forming a self-assembled film formed of a block polymer on the mask film and comprising two phases, and a portion of the self-assembled film comprising one phase. Corresponding to the first etching step to selectively remove, the second etching step to remove the mask film in the portion corresponding to the portion composed of one phase of the self-assembled film, and the removed mask film An optical element by press-molding the heat-softened optical element base material using the optical element molding die manufactured by the third etching step for removing the surface portion of the base material of the part to be processed An uneven structure is formed on the surface of the optical element.   The method of manufacturing an optical element according to claim 10, wherein the uneven structure is an antireflection structure.

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