JP2011131453A - Method for manufacturing nanoimprint mold for manufacturing optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method capable of manufacturing a nanoimprint mold for manufacturing an optical element with high precision and coping with manufacturing of large-area products. <P>SOLUTION: The manufacturing method comprises applying a photosensitive resist 4 on one side of a substrate 1, carrying out laser lithography to the photosensitive resist 4, developing the drawn image to form a mask pattern 5 having a desired opening pattern 5a, and etching the substrate 1 through the mask pattern 5 to a desired depth to obtain a mold 11. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a nanoimprint mold for manufacturing an optical element, particularly an optical element provided on a light emitting surface of a light emitting diode.

Compared to conventional light bulbs and fluorescent lamps, light-emitting diodes (hereinafter referred to as “LEDs”) have the characteristics of being small, long-life, ultralight, and low heat generation. Also, in recent years, the luminous efficiency of LEDs has improved, and in response to the demands of a low-carbon society, scanning lamps with high response speeds, backlights for liquid crystal display devices, automobile control panel lighting, traffic lights, general lighting In application fields such as appliances, LEDs are being used in place of light bulbs and fluorescent lamps.
The LED has a structure in which an emissive layer is sandwiched between an n-type doped semiconductor layer and a p-type doped semiconductor layer, and electrons from the n-type doped semiconductor layer are regenerated in an electron hole and an emissive layer from the p-type doped semiconductor layer. Emits light when combined. However, the light emitted by the LED is reflected at the interface with the substrate on which the LED is disposed, the interface between the LED and the air layer, etc., so the external extraction efficiency is low, effectively improving the light emission efficiency of the LED. There was a problem that it could not be used.

  In order to increase the external extraction efficiency, a photonic crystal is used as an optical element provided on the light emitting surface of the LED. For example, it is proposed to produce a photonic crystal on the light emitting surface of the LED using a stepper. (For example, Patent Document 1). Fabrication of a photonic crystal using such a stepper can increase the area, and the manufacturing cost can be kept low. However, for example, a hexagonal unit as shown by a chain line in FIG. 7, a hexagonal unit as shown by a chain line in FIG. 8, where the pattern is located on the stepper shot boundary line, FIG. 9 by a chain line In recent years, photonic crystals having a structure in which the periodicity of the pattern is difficult to be taken, such as a quadrangular unit as shown in the figure where the pattern is located on the stepper shot boundary line, have been developed. The conventional method using a stepper was difficult to produce.

  On the other hand, nanoimprint technology has recently attracted attention as a fine processing technology. Nanoimprint technology is a pattern formation technology that uses a mold (mold member) in which a fine concavo-convex structure is formed on the surface of a substrate, and transfers the concavo-convex structure to a workpiece to transfer the fine structure at the same magnification (Patent Literature). 2). And formation of a photonic crystal by nanoimprint technology is also being studied.

JP 2005-208180 A US Pat. No. 5,772,905

  As a method for producing a nanoimprint mold for producing a photonic crystal, for example, there is a method of forming a mask pattern using a stepper on a substrate for a master plate and producing a master plate having a desired concavo-convex structure by etching. is there. However, in this case as well, there is a problem similar to the above in the master plate manufacturing process in the mold manufacturing for photonic crystals that is not a simple cycle. Further, in the production of a mold for a photonic crystal, the control of the stepper is required to have an accuracy of several nm, and there is a problem that it is difficult to increase the area of the mold due to the control limit of the stepper.

On the other hand, by performing mask pattern formation on the master plate by electron beam drawing, a nanoimprint mold for producing a photonic crystal that is not a simple cycle can also be produced. Here, the electron beam spot beam has a maximum diameter of about 30 nm and is not suitable for drawing with a size of several tens of nm or more. The electron beam rectangular beam is a quadrangle having a side of about 50 to 100 nm, and circular drawing using the electron beam rectangular beam is performed by drawing a polygon approximate to a circle. However, such polygonal electron beam drawing data has a large amount of data and takes a lot of time for drawing. For example, electron beam drawing in forming a mask pattern on a 4-inch diameter substrate requires several days. However, there was a problem that it was not at a practical level. Further, in the electron beam drawing, there is a problem that the drawing accuracy is deteriorated due to the effect of the proximity effect due to the charging of the mold substrate to be drawn or the electron beam scattering.
This invention is made | formed in view of the above situations, and it aims at providing the manufacturing method which can manufacture the nanoimprint mold for optical element manufacture with high precision, and can respond also to enlargement. .

In order to achieve such an object, the present invention applies a photosensitive resist to one surface of a substrate, performs laser drawing on the photosensitive resist, and then develops to have a desired opening pattern. The method includes a step of forming a mask pattern and a step of etching the substrate to a desired depth through the mask pattern.
As another aspect of the present invention, the opening pattern of the mask pattern has a circular opening, the circular target diameter D (unit: nm) of the opening, and the wavelength λ (unit: nm) of the laser to be used. The following formulas (1) and (2) between the regular N-square N (N is an integer of 4 or more) as the laser drawing data approximated to a circle and the refractive index n of the medium through which the laser passes. The laser wavelength λ and the regular N-shaped N of the laser drawing data are set so that the above relationship is established.
90 ≦ D ≦ 1000 (1)
λ / n <D <λN / (2n) (2)

As another aspect of the present invention, Lmax (unit: nm) is the maximum diagonal length of a regular N-gonal trajectory as drawing data approximated to a circle, and the perpendicular length from the center of the regular N-gon to one side of the trajectory The following equations (3) and (4) are established among Lmin (unit: nm), circular target diameter D (unit: nm), and laser spot shape diameter d (unit: nm). As described above, the diameter d of the laser spot shape, the maximum diagonal length Lmax and the normal length Lmin of the regular N-gon are set.
d ≧ 2Lmin Equation (3)
d + 2Lmin <D <d + Lmax Expression (4)
In the regular N-gon of the laser drawing data, N is in the range of 6 to 8.

  In the present invention, since the mask pattern is formed by performing laser drawing, the advantage is that the laser spot is circular and the spot diameter is approximately the same as or larger than the laser wavelength, It is possible to draw a circular shape close to a perfect circle in a short time with drawing data with a smaller amount of data compared to electron beam drawing. The influence of the proximity effect due to scattering and the reduction of the drawing accuracy are prevented, so that it is possible to form a mask pattern with high accuracy, and therefore the accuracy of the mold to be manufactured is high, and it is also compatible with a large area. it can. Furthermore, in the mold manufacturing method using electron beam drawing, the time required for manufacturing is long, and from the viewpoint of manufacturing cost, the produced mold is not used for nanoimprinting, but must be used as a master plate to produce a copy mold. It was. However, in the present invention, the manufacturing time of the mold can be greatly shortened, so that the manufacturing cost can be greatly reduced, and the manufactured mold can be directly used for nanoimprinting, which is superior in accuracy compared to the copy mold. The mold can be used.

  Further, the circular target diameter D of the circular opening of the mask pattern, the wavelength λ of the laser to be used, a regular N-gonal N as laser drawing data approximated to a circle, and the refractive index n of the laser drawing medium By setting the laser wavelength λ and the regular N-gon N of the laser drawing data so that a predetermined relationship is established between them, it becomes possible to draw a circle that is closer to a perfect circle. By making this range, it is optimal to achieve both a small amount of data and approximation to a perfect circle.

It is process drawing for demonstrating the manufacturing method of the nanoimprint mold for optical element manufacture of this invention. It is process drawing for demonstrating the manufacturing method of the nanoimprint mold for optical element manufacture of this invention. It is a figure for demonstrating laser drawing at the time of setting a regular square orbit. It is a figure for demonstrating laser drawing at the time of setting a regular hexagonal orbit. It is a figure for demonstrating laser drawing at the time of setting a regular octagonal orbit. It is process drawing for demonstrating an example of the optical imprint method using the nanoimprint mold manufactured by this invention. It is a figure for demonstrating the relationship between the shot of a stepper and the periodicity of a pattern. It is a figure for demonstrating the relationship between the shot of a stepper and the periodicity of a pattern. It is a figure for demonstrating the relationship between the shot of a stepper and the periodicity of a pattern.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2 are process diagrams for explaining a method for producing a nanoimprint mold for producing an optical element of the present invention. First, a photosensitive resist 4 is applied to one surface of the substrate 1 (FIG. 1A), then laser drawing is performed on the photosensitive resist 4, and then developed, and a curing process is performed as necessary. Then, a mask pattern 5 having a desired opening pattern 5a is formed (FIG. 1B). The laser drawing in the present invention will be described later.
In the illustrated example, the substrate 1 is provided with a metal film 3 as a hard mask on one surface 2 a of a base material 2, and a photosensitive resist 4 is applied on the metal film 3. As the base material 2, for example, a material made of an inorganic material such as glass, quartz, or silicon can be used, or a material made of a resin material may be used. The thickness of the base material 2 can be set as appropriate, and can be set, for example, in the range of about 0.5 mm to 7 mm. The metal film 3 is intended to function as a hard mask for etching the base material 2 or to prevent laser reflection from the back surface when the base material 2 is transparent. A material such as chromium may be used, and the thickness can be appropriately set within a range of about 10 nm to 110 nm, for example. Such a metal film 3 can be formed by a known vacuum film forming method.

  The photosensitive resist 4 has a photosensitive wavelength region in the wavelength region of the laser to be used. For example, a G-line resist, an I-line resist, a DUV resist, a chemically amplified resist, or the like may be used. it can. The photosensitive resist 4 can be applied by, for example, spin coating, blade coating, bar coating, slit coating, die coating, roll coating, dip coating, spray coating, dispenser coating, and the like. . Further, the coating thickness (thickness after drying) of the photosensitive resist 4 affects the thickness of the mask pattern 5 and is, for example, in the range of 0.2 μm to 0.6 μm, preferably 0.3 μm to 0.5 μm. Can be set as appropriate. If the coating thickness of the photosensitive resist 4 is less than 0.2 μm, it is difficult to etch the metal film 3, and if it exceeds 0.6 μm, it is difficult to resolve the desired photonic crystal structure, which is not preferable. .

  Next, the substrate 1 is etched to a desired depth through the mask pattern 5 (FIG. 1C), and then the mask pattern 5 is removed to produce a mold 11 having a desired recess structure 12 (FIG. 1). 1 (D)). In the etching of the substrate 1, first, the metal film 3 is etched. The metal film 3 can be etched by a wet process using an etchant. However, since the pattern is fine, a dry process is preferable. As a process gas in the dry process, for example, when the metal film 3 is chromium, it is preferable to use oxygen and chlorine.

Next, the substrate 2 is etched to a desired depth. Here, for example, when the substrate is quartz, a dry process is preferable, and a fluorine-based gas is preferably used as the process gas. The depth of the concave structure 12 formed by such etching can be appropriately set according to the optical element manufactured using a mold. For example, in the case of a photonic crystal manufacturing application, the depth is 100 nm. It can set in the range of about ~ 2000 nm. Through the above steps, a nanoimprint mold for producing an optical element is produced.
In the above-described mold 11, the metal film 3 is left, but usually there is no metal film 3, and when the metal film 3 is unnecessary, the metal film 3 is etched using an etchant for the metal film. The film 3 is removed by a wet process to form a mold 11.

  In the present invention, as described below, the mold produced as described above may be used as a master plate, a copy mold may be produced from the master plate, and the copy mold may be used as a nanoimprint mold for optical element production. That is, the imprint material 23 is applied onto the copy mold substrate 22 by, for example, spin coating, blade coating, bar coating, slit coating, die coating, roll coating, dip coating, spray coating, and dispenser. Supply is made by a coating method or the like, and the mold 11 is pressed against the imprint material 23 (FIG. 2A). Then, the imprint material 23 is cured to release the mold 11 (FIG. 2B), and the remaining film portion 23a of the formed imprint material is removed to form a mask pattern using the imprint material. The mold substrate 22 is selectively exposed. Next, the exposed portion of the copy mold substrate 22 is dry-etched to form the recess 22a, and then the imprint material 23 functioning as a mask pattern is removed. Thereby, a copy mold 21 having a reversal pattern of the mold 11 is produced (FIG. 2C). A predetermined optical element may be manufactured using the copy mold 21.

Here, laser drawing of the photosensitive resist 4 will be described.
In the present invention, the circular target diameter D of the opening pattern 5a to be formed in the mask pattern 5 (diameter of a perfect circular opening as a formation target, unit: nm), the wavelength λ (unit: nm) of the laser to be used, The relation of the following formulas (1) and (2) between the regular N-gon N (N is an integer of 4 or more) as the laser drawing data approximated to a circle and the refractive index n of the laser drawing medium. The laser wavelength λ and the regular N-gon N of the laser drawing data are set so as to be established. If the circular target diameter D is less than 90 nm, laser drawing cannot be performed because it is less than the limit of the diameter of the laser spot, and if it exceeds 1000 nm, it is too large compared to the diameter of the laser spot. It is necessary to set N of the regular N-gon large, which is not preferable in design. In addition, it is not preferable to use a laser or drawing data that does not hold the relationship of formula (2) because the roundness described later increases. When the medium through which the laser passes is air, the refractive index n is 1.
90 ≦ D ≦ 1000 (1)
λ / n <D <λN / (2n) (2)

  If there is a laser having a diameter d that matches the circular target diameter D of the opening pattern 5a formed in the mask pattern 5 among the usable lasers, the laser is brought to a desired position. It can be drawn by spot irradiation.

When the circular target diameter D is larger than the diameter d of the laser spot shape that can be used, a regular N-gonal trajectory is set as drawing data approximated to a circular shape, and the trajectory is drawn with the laser. In this case, when the maximum diagonal length of the regular N-gonal trajectory is Lmax (unit: nm), and the perpendicular length from the center of the regular N-gonal to one side of the trajectory is Lmin (unit: nm), the circular target The following equations (3) and (4) are established among the diameter D (unit: nm), the laser spot shape diameter d (unit: nm), the maximum diagonal length Lmax, and the perpendicular length Lmin. Thus, the diameter d of the laser spot shape and a regular N-gon (maximum diagonal length Lmax, perpendicular length Lmin) are set as drawing data. If this relationship is not established, an undrawn part remains in the region drawn on the regular N-gonal trajectory, and the roundness rate described later increases, which is not preferable.
d ≧ 2Lmin Equation (3)
d + 2Lmin <D <d + Lmax Expression (4)

  As the laser drawing machine used in the present invention, a drawing machine capable of controlling the minimum unit (address size) for drawing with several nm is preferable. This is because it is necessary to draw a circular pattern for each coordinate position of several nm. As described above, since the circular target diameter D of the present invention is in the range of 90 nm to 1000 nm, DUV (deep ultraviolet light) is suitable as the wavelength of the laser drawing machine to be used.

  FIG. 3 is a diagram for explaining laser drawing when a regular quadrangle (N = 4) trajectory is set. In this case, the diagonal length of the regular rectangular orbit 31 is the maximum diagonal length Lmax, and the perpendicular length Lmin corresponds to half the length of one side of the regular square (FIG. 3A). In the illustrated example, the laser spot 41 having a diameter d is indicated by hatching. Then, by scanning the laser spot 41 (scanning clockwise in the illustrated example) on the regular square orbit 31, the region surrounded by the outline 51 is drawn (FIG. 3B). In the illustrated example, the laser spot 41 when positioned at the four apexes of the regular tetragonal orbit 31 is indicated by a chain line. As shown in FIG. 3C, the laser-drawn region (the region surrounded by the outline 51 and is shaded) and the true circle with the diameter D (two-dot chain line) 2), the drawing area at the portion corresponding to each vertex of the regular tetragonal trajectory 31 protrudes outside the perfect circle, and the portion corresponding to the central portion of each side of the regular tetragonal trajectory 31. The drawing area in is located inside the perfect circle.

  FIG. 4 is a diagram for explaining laser drawing when a regular hexagonal (N = 6) trajectory is set. In this case, the maximum diagonal length Lmax of the regular hexagonal orbit 32 is the length of the diagonal passing through the center (FIG. 4A). In the illustrated example, the laser spot 42 having a diameter d is indicated by hatching. Then, by scanning the laser spot 42 on the regular hexagonal orbit 32 (scanning clockwise in the illustrated example), the region surrounded by the outline 52 is drawn (FIG. 4B). In the illustrated example, the laser spot 42 at the six apexes of the regular hexagonal orbit 32 is indicated by a chain line. As shown in FIG. 4C, the laser-drawn region (the region surrounded by the outline 52 and is shaded) and the perfect circle with the diameter D (two-dot chain line) 2), the drawing region at the portion corresponding to each vertex of the regular hexagonal trajectory 32 protrudes outside the perfect circle, and the portion corresponding to the center of each side of the regular hexagonal trajectory 32. The drawing area in is located inside the perfect circle.

  Further, FIG. 5 is a diagram for explaining laser drawing when a regular octagonal (N = 8) trajectory is set. In this case, the maximum diagonal length Lmax of the regular octagonal orbit 33 is the length of the diagonal passing through the center (FIG. 5A). In the illustrated example, the laser spot 43 having a diameter d is indicated by hatching. Then, by scanning the laser spot 43 (scanning clockwise in the illustrated example) on the regular octagonal orbit 33, the region surrounded by the outline 53 is drawn (FIG. 5B). In the illustrated example, the laser spot 43 when located at the eight vertices of the regular octagonal orbit 33 is indicated by a chain line. As shown in FIG. 5C, the laser-drawn region (the region surrounded by the outline 53 and is hatched), and a perfect circle with a diameter D (two-dot chain line) 2), the drawing region at the portion corresponding to each vertex of the regular octagonal trajectory 33 protrudes to the outside of the perfect circle, and the portion corresponding to the central portion of each side of the regular octagonal trajectory 33. The drawing area in is located inside the perfect circle.

The roundness of the contour lines 51, 52, and 53 in such a drawing region is obtained by measuring the deviation of the pattern observed with a scanning electron beam microscope (SEM) from the perfect circle by the mean square error method. In the specification, this roundness ratio indicates that when the value is small, the deviation from the perfect circle is small and the formed pattern is close to the perfect circle, whereas when the value is large, the deviation from the perfect circle is large. , And an index indicating that the formed pattern is far from a perfect circle. In the present invention, the roundness is calculated as follows, and the case where the roundness is 3% or less is regarded as a practical level. Usually, when the N of the regular N-gon as the laser drawing data is 6 or more, the roundness is 3% or less, and the larger N is, the lower the roundness is. However, as N increases, the amount of data increases and the time required for laser drawing increases. For this reason, by setting N in the range of 6 to 8, both the small amount of data and the approximation to the perfect circle are optimal.
(Calculation of roundness)
From the obtained SEM image, the ideal perfect circle radius is R (θ), the radius obtained by SEM measurement is R ′ (θ), and the perfect circle ratio Δ (θ) is
Δ (θ) = [| R (θ) −R ′ (θ) | / R (θ)] × 100
The average value of Δ (θ) calculated at each θ position is taken as the roundness.

  The circular target diameter D of the present invention is preferably in the range of 90 nm to 1000 nm as described in the above formula (1). For example, in the case where the optical element to be manufactured is a photonic crystal provided on the light emitting surface of the LED, the external extraction efficiency of the LED by the photonic crystal is reduced when the optical element is out of the range. In addition, it is difficult to produce a pattern in this range with a conventional electron beam drawing in a short time and with high accuracy, and the advantage of employing laser drawing is more exhibited. In addition, since the influence of the proximity effect is suppressed by using laser drawing in the present invention, the distance between the centers of adjacent patterns can be designed to be several nm or less, It is possible to form a more functional optical element using the obtained mold. Further, in the present invention, even when the pattern density is high by using laser drawing, it is not necessary to perform an electron beam proximity effect correction necessary for electron beam drawing, and the drawing data production time can be shortened.

As described above, in the present invention, since the mask pattern 5 is formed by performing laser drawing, the advantage is that the laser spot is circular and the spot diameter is approximately the same as or larger than the laser wavelength. Thus, it is possible to draw a circular shape close to a perfect circle in a short time with drawing data having a smaller amount of data than electron beam drawing. Further, charging of the mold substrate, which is a drawing target, which occurs in electron beam drawing, the influence of the proximity effect due to electron beam scattering, and a reduction in drawing accuracy are prevented. Therefore, the mask pattern can be formed with high accuracy. Therefore, the accuracy of the mold 11 to be manufactured, or the accuracy of the copy mold 21 to be manufactured using the mold 11 as a master plate is also high. It can cope with area increase.
In addition, the above-mentioned embodiment is an illustration and this invention is not limited to this.

Next, an example of the optical imprint method using the nanoimprint mold manufactured according to the present invention will be described with reference to FIG. 6 using the above-described mold 21 as an example.
First, the photocurable resin layer 72 is formed on one surface of the substrate 71 which is a target for forming a desired uneven structure (FIG. 6A). The material of the substrate 71 can be appropriately selected according to the optical element to be manufactured, and is not particularly limited. For example, in the case of a photonic crystal manufacturing application, silicon, sapphire, silicon silicon carbide, spinel, and the like can be given. be able to.

  Next, the mold 21 is pressed against the photocurable resin layer 72, and the photocurable resin layer 72 is irradiated with light through the mold 21 to be cured (FIG. 6B). Thereafter, the mold 21 is released to obtain a resin layer 72 ′ having a concavo-convex structure 72a in which the concavo-convex structure 22 of the mold 21 is inverted (FIG. 6C). Then, using the resin layer 72 ′ as a mask, the substrate 71 is dry-etched (FIG. 6D), and then the resin layer 72 ′ is removed to obtain the substrate 71 having a desired concavo-convex structure 74. (FIG. 6 (E)).

Next, the present invention will be described in more detail by showing more specific examples.
[Example 1]
A quartz base material (diameter 6 inches, thickness 6.35 mm) having a chromium thin film (thickness 60 nm) on one side as a metal film is prepared as a substrate, and a photosensitive resist (Fuji Film Co., Ltd.) is formed on the chromium thin film of the substrate. Manufactured FEP-171 resist) was applied by spin coating and dried at 120 ° C. for 10 minutes. The thickness of the photosensitive resist after drying was 0.3 μm.
Next, using a laser drawing apparatus (ALTA4300 manufactured by ETEC Co., Ltd.), the diameter D (circular target diameter D) of the perfect circular opening which is the formation target is set to 500 nm, and the photosensitive resist is formed under the following conditions. Laser drawing. This condition satisfied the relationship of the above formula (1), formula (2), formula (3), and formula (4). In addition, a region where laser drawing is performed under the following conditions is a circular region having a diameter of 4 inches at the center of the substrate.
(Conditions for laser drawing)
・ Laser used: Argon ion laser (double harmonic, wavelength 257 nm)
・ Laser spot diameter d: 250 nm
-Laser drawing medium: Air-Regular N-gon of drawing data: N = 6
Maximum diagonal length Lmax = 277nm
Perpendicular length Lmin = 120nm
The time required for laser drawing under such conditions was 1.5 hours.

Next, the photosensitive resist subjected to laser drawing is post-baked (120 ° C., 10 minutes), developed, and subjected to a curing process (120 ° C., 10 minutes). A mask pattern having an opening pattern arranged as shown in FIG. 9 was formed. When the roundness of the circular opening of this opening pattern was measured and calculated using SEM as described above, it was 2.2%, and it was confirmed that it was at a practical level (roundness is 3% or less). It was done.
Next, the chromium thin film is etched through the mask pattern using a dry etching apparatus (process gas: oxygen, chlorine), and then the quartz substrate is similarly formed through the mask pattern using a dry etching apparatus (process gas: fluorine-based gas). The material was etched. Thereafter, the mask pattern was removed. As a result, a pattern was formed in which the concave structure having a depth of 500 nm from the chromium thin film on the surface was arranged in the same manner as the opening pattern of the mask pattern. Then, it was immersed in a cerium diammonium nitrate solution as an etchant, and the chromium thin film on the surface was removed to obtain a mold.

[Example 2]
A mask pattern was produced in the same manner as in Example 1 except that the laser drawing conditions were as follows. The laser drawing conditions satisfied the relationships of the above formulas (1), (2), (3), and (4).
(Conditions for laser drawing)
・ Laser used: Argon ion laser (double harmonic, wavelength 257 nm)
・ Laser spot diameter d: 250 nm
-Laser drawing medium: Air-Regular N-gon of drawing data: N = 8
Maximum diagonal length Lmax = 260nm
Perpendicular length Lmin = 120nm
The time required for laser drawing under such conditions was 1.6 hours.

When the roundness of the circular opening of the opening pattern of the mask pattern formed in this way was measured and calculated in the same manner as in Example 1, it was 1.3% and was at a practical level (roundness is 3% or less). It was confirmed.
Next, etching was performed in the same manner as in Example 1 through the formed mask pattern, and then the mask pattern was removed. As a result, a pattern was formed in which the concave structure having a depth of 500 nm from the chromium thin film on the surface was arranged in the same manner as the opening pattern of the mask pattern. Then, it was immersed in a cerium diammonium nitrate solution as an etchant, and the chromium thin film on the surface was removed to obtain a mold.

[Comparative Example 1]
A substrate similar to that of Example 1 was prepared, and a photosensitive resist (FEP-171 resist manufactured by Fuji Film Co., Ltd.) was applied on the chromium thin film of this substrate by a spin coating method and dried at 120 ° C. for 10 minutes. The thickness of the photosensitive resist after drying was 0.3 μm.
Next, using an electron beam drawing apparatus (JBX9000 manufactured by JEOL Ltd.), the diameter D (circular target diameter D) of the perfect circular opening which is the formation target is set to 500 nm as in Examples 1 and 2. The photosensitive resist was drawn with an electron beam under the following conditions.
(Conditions for electron beam drawing)
・ Exposure: 13μC / cm ²
Proximity effect correction parameters: η = 0.8, σ = 10
-Regular N-gon of drawing data: N = 8
The time required for electron beam drawing under such conditions was about 10 days.

Next, the photosensitive resist on which electron beam drawing was performed was developed and cured (120 ° C., 10 minutes), and circular openings with a diameter of 500 nm were arranged at a pitch of 550 nm as shown in FIG. A mask pattern having an opening pattern was formed. When the roundness of the circular opening of this opening pattern was measured and calculated in the same manner as in Example 1, it was 2.0%, and it was confirmed that it was at a practical level (roundness is 3% or less).
Next, etching was performed in the same manner as in Example 1 through the formed mask pattern, and then the mask pattern was removed. As a result, a pattern was formed in which the concave structure having a depth of 500 nm from the chromium thin film on the surface was arranged in the same manner as the opening pattern of the mask pattern. Then, it was immersed in a cerium diammonium nitrate solution as an etchant, and the chromium thin film on the surface was removed to obtain a mold.

  From the results of Examples 1 and 2 and Comparative Example 1 described above, Examples 1 and 2 that perform laser drawing form patterns with the same accuracy (roundness) as Comparative Example 1 that performs electron beam drawing. It was confirmed that the time required for drawing can be greatly reduced.

[Comparative Example 2]
An attempt was made to produce a mask pattern in the same manner as in Example 1 except that the diameter D (circular target diameter D) of the perfect circular opening as the formation target was set to 400 nm and the laser drawing conditions were as follows. It was. The laser drawing condition is that the wavelength of the laser to be used is large and satisfies the relationship of the above formulas (1), (3), and (4), but the relationship of the above formula (2) is not satisfied. Met.
(Conditions for laser drawing)
・ Laser used: He-Cd laser (wavelength 422 nm)
・ Laser spot diameter d: 300 nm
-Laser drawing medium: Air-Regular N-gon of drawing data: N = 6
Maximum diagonal length Lmax = 231 nm
Perpendicular length Lmin = 100nm
The time required for laser drawing under such conditions was 2.0 hours.
However, the opening pattern of the mask pattern was not obtained (not resolved), and the roundness could not be measured and calculated.

[Comparative Example 3]
An attempt was made to produce a mask pattern in the same manner as in Example 1 except that the laser drawing conditions were as follows. The conditions for this laser drawing are improper setting of the regular hexagon of drawing data (maximum diagonal length Lmax, perpendicular length Lmin), and the above equations (1), (2), and (3) Although the relationship was satisfied, the relationship of the above formula (4) was not established.
(Conditions for laser drawing)
・ Laser used: Argon ion laser (double harmonic, wavelength 257 nm)
・ Laser spot diameter d: 250 nm
-Laser drawing medium: Air-Regular N-gon of drawing data: N = 6
Maximum diagonal length Lmax = 139nm
Perpendicular length Lmin = 60nm
The time required for laser drawing under such conditions was 1.5 hours.
However, the opening pattern of the mask pattern was not obtained (not resolved), and the roundness could not be measured and calculated.

  It can be used for manufacturing an optical element using an optical imprint technique.

DESCRIPTION OF SYMBOLS 1 ... Board | substrate 4 ... Photosensitive resist 5 ... Mask pattern 5a ... Opening pattern 11 ... Mold 12 ... Recessed structure 21 ... Copy mold 22 ... Base material for mold formation 31, 32, 33 ... Orbit of regular N-angle of laser drawing data 41 , 42, 43 ... laser spot

Claims (4)

Applying a photosensitive resist on one surface of the substrate, performing laser drawing on the photosensitive resist, and then developing to form a mask pattern having a desired opening pattern;
And a step of etching the substrate to a desired depth through the mask pattern. A method for producing a nanoimprint mold for producing an optical element, comprising: The opening pattern of the mask pattern has a circular opening, the circular target diameter D (unit: nm) of the opening, the wavelength λ (unit: nm) of the laser to be used, and laser drawing approximated to a circle The laser is such that the following formulas (1) and (2) are established between the regular N-gon N (N is an integer of 4 or more) as data and the refractive index n of the medium through which the laser passes. The method of manufacturing a nanoimprint mold for manufacturing an optical element according to claim 1, wherein a wavelength λ of the laser beam and a regular N-gon N of the laser drawing data are set.
90 ≦ D ≦ 1000 (1)
λ / n <D <λN / (2n) (2) Lmax (unit: nm) is the maximum diagonal length of a regular N-gonal trajectory as drawing data approximated to a circle, and Lmin (unit: nm) is the perpendicular length from the center of the regular N-gon to one side of the trajectory. The diameter d of the laser spot shape so that the relationship of the following formulas (3) and (4) holds between the circular target diameter D (unit: nm) and the laser spot shape diameter d (unit: nm). The method for producing a nanoimprint mold for producing an optical element according to claim 2, wherein a maximum diagonal length Lmax and a perpendicular length Lmin of a regular N-gon are set.
d ≧ 2Lmin Equation (3)
d + 2Lmin <D <d + Lmax Expression (4)   4. The method for producing a nanoimprint mold for producing an optical element according to claim 2, wherein N is in the range of 6 to 8 in the regular N-gon of the laser drawing data.

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