JP5732724B2 - Nanoimprint method - Google Patents

Description

The present invention provides a nanoimprint method of forming a fine uneven pattern, about the excellent nanoimprint method releasability obtained by or no pattern defects by reducing resin.

  In recent years, especially for semiconductor devices, high speed operation and low power consumption operation are required due to further progress in miniaturization, and high technology such as integration of functions called system LSIs is required. Under such circumstances, the lithography technology that is necessary for producing the pattern of the semiconductor device has become very expensive as the exposure apparatus and the like as the pattern becomes finer, and the price of the mask used therefor also becomes expensive. Yes.

  On the other hand, the nanoimprint method proposed by Chou et al. In Princeton University in 1995 is attracting attention as a fine pattern forming technique having a high resolution of about 10 nm, although the apparatus price and materials used are inexpensive (patents) Reference 1).

  In the nanoimprint method, a mold (also referred to as a template, stamper, or mold) in which a nanometer-size uneven pattern is formed on the surface in advance is pressed against a resin (also referred to as a resist in the present invention) applied and formed on the surface of a workpiece. This is a technology that mechanically deforms and precisely transfers a fine pattern, and processes the workpiece using the patterned resin as a resist mask. Once the mold is made, the nanostructure can be easily and repeatedly molded, resulting in high throughput and economics, and because it is a nano-processing technology with little harmful waste, not only semiconductor devices in recent years, Application to various fields is expected.

  In such a nanoimprint method, a thermal nanoimprint method in which a concavo-convex pattern is transferred by heat using a thermoplastic resin, or a photo nanoimprint method in which a concavo-convex pattern is transferred by ultraviolet rays using a photocurable resin (see, for example, Patent Document 2) ) Etc. are known. As the resin as the transfer material, a thermoplastic resin is used in the thermal nanoimprint method, and a photocurable resin is used in the optical nanoimprint method. The optical nanoimprint method can transfer patterns at low applied pressure at room temperature, and does not require heating / cooling cycles like the thermal nanoimprint method and does not cause dimensional changes due to mold or resin heat. It is said that it is excellent in terms of sex.

  Molds used in the nanoimprint method are required to have pattern dimension stability, chemical resistance, processing characteristics, and the like. Taking the case of the optical nanoimprint method as an example, generally, quartz glass that transmits ultraviolet rays used for photocuring is used. In the nanoimprint method, the pattern shape of the mold must be faithfully transferred to a resin that is a transfer material. For this purpose, it is necessary to transfer the mold shape to the resin and then release the mold without changing the shape when the mold is released.

  However, a mold made of quartz glass or the like usually has a low mold releasability with a resin that is a pattern transfer material. Therefore, as a method for improving the mold releasability between the mold and the resin, for example, a fluororesin or the like on the surface of the concave / convex pattern of the mold A method for improving the releasability by applying a thin film of a release agent is proposed. FIG. 6 is a schematic diagram showing a state where a monomolecular film of a release agent having a fluoroalkyl group is formed on the surface of a synthetic quartz mold as an example.

  However, even if a mold release agent is used, the mold release agent is consumed by continuous imprinting and the mold release property is lowered, and the adhesion force and friction force between the resin and the mold are increased. There was a problem that pattern defects occurred.

  FIG. 7 shows a case where a nanoimprint mold 71 formed by applying and forming a release agent to form a release layer 72 is pressed against a resin 74 of a material to be transferred on a substrate to be processed 73 and separated after photocuring (FIG. 7A )) And a partial cross-sectional schematic diagram for explaining the state immediately after that (FIG. 7B). At this time, an adhesion force A and a friction force F act between the resin 74 and the mold 71. As shown in FIG. 7B, after the mold is pressed against the resin, a part of the resin adheres to the mold side when the mold is released, so that a chip defect 75 is generated in the uneven pattern of the resin. There was a problem. Further, there is a problem that the mold 71 to which the resin is attached cannot be used for subsequent pattern transfer unless the resin 76 attached to the mold 71 is removed.

  As described above, whether the mold unevenness pattern and the transfer material have good releasability is extremely important in determining the quality, yield, and productivity of the imprinted product. Even when the agent is used, the releasability varies depending on the type of the release agent, and it is difficult to determine in advance whether the release property of the release agent is good before imprinting.

JP-T-2004-504718 JP 2002-93748 A

Therefore, the present invention has been made in view of the above problems. That is, an object of the present invention is to provide a nanoimprint method that is excellent in mold releasability between a mold and a resin and that does not cause or reduces resin pattern defects.

In order to solve the above-described problem, the nanoimprint method according to the invention of claim 1 is a method in which a mold having a concavo-convex pattern is pressed against a photocurable resin on a substrate to be processed, and the photocuring is performed through the mold. A nanoimprint method for transferring the concavo-convex pattern by curing the photocurable resin by irradiating light that sensitizes the photosensitive resin, the surface free energy of the mold surface, and the cured photocurable resin any of the surface free energy of the surface, 5 mJ / m ² or more at 30 mJ / m ² Ri der hereinafter the mold of the concave-convex pattern, and a fluorine-based silane compound, or a release layer composed of octadecyl trimethoxysilane It is characterized by being covered with .

The nanoimprint method according to claim 2 is the nanoimprint method according to claim 1, wherein after the photocurable resin is cured and the concavo-convex pattern is transferred, the mold is separated from the cured photocurable resin. The mold release force when molding is 1.9 kPa or more and 2.7 kPa or less .

According to the nanoimprint method of the present invention, both the surface free energy of the mold surface and the surface free energy of the photocurable resin surface after curing are imprinted as 5 mJ / m ² or more and 30 mJ / m ² or less. Accordingly, a nanoimprinting method that is excellent in releasability from the resin and that does not cause or reduces resin pattern defects is possible.

It is a partial section schematic diagram showing an example of the nanoimprint method of the present invention. It is a figure explaining the adhesion work of a mold and the resist for nanoimprint. It is a schematic diagram explaining the force which acts on the resist for nanoimprint on the mold surface. It is a perspective appearance figure of a measuring instrument used for mold release force measurement of a mold and resin. It is a figure which shows the mold provided with various mold release layers, and mold release force. It is a schematic diagram which shows the state in which the monomolecular film of the mold release agent which has a fluoroalkyl group was formed in the quartz mold surface. It is a partial cross-sectional schematic diagram for demonstrating the force and resin defect which work when it presses and separates the mold which apply | coated and formed the mold release agent to resin.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a partial cross-sectional schematic view showing an example of a substrate to be processed on which a nanoimprint mold of the present invention and a photocurable resin are applied and formed. The nanoimprint mold 10 has an uneven pattern 12 on one surface of a substrate 11, and the uneven pattern 12 is covered with a release layer 13. The substrate 14 to be processed is coated with a photocurable resin 15 on the surface. In the example shown in FIG. 1, the nanoimprint method of the present invention includes both the surface free energy of the mold 11 in a state where it is covered with the release layer 13 and the surface free energy of the surface of the photocurable resin after curing. Is 5 mJ / m ² or more and 30 mJ / m ² or less. When the mold 11 is not covered with the release layer 12, the surface free energy of the mold itself may be set within the above numerical range.

In the present invention, when at least one surface free energy of the surface free energy of the mold 11 and the surface free energy of the photocurable resin 15 after curing exceeds 30 mJ / m ² , the mold and the cured photocurable resin This is because the releasability of the resin deteriorates and a resin pattern defect occurs. Moreover, when the surface free energy of the photocurable resin 15 after curing is less than 5 mJ / m ² , the adhesion between the substrate to be processed and the photocurable resin applied and cured on the substrate decreases, This is because the resin may be peeled off.

According to the nanoimprint method of the present invention, by measuring the surface free energy of the mold surface coated with the release layer and the surface free energy of the photocurable resin surface after curing, the mold surface and photocurable property are measured. It becomes possible to evaluate the releasability of the resin, and it becomes easy to evaluate and select a release agent suitable for the release layer or a photocurable resin having good releasability. Surface free energy is determined to have good releasability in some cases in the range of 30 mJ / m ² or less in the above 5 mJ / m ² or more, not to 30 mJ / m ² within the following range 5 mJ / m ² or more In such a case, the releasability is poor, and it is judged to be unsuitable for imprinting.

  In FIG. 1, a substrate 11 is a member for holding a concavo-convex pattern 12, and is required to have pattern dimension stability, chemical resistance, processing characteristics, and the like. As a material constituting the substrate 11, an optically polished synthetic quartz is used. Examples thereof include glass, soda glass, fluorite, and calcium fluoride. Generally, synthetic quartz glass that transmits ultraviolet rays used for photocuring is used. Synthetic quartz glass as a substrate material has been used as a photomask substrate and has a stable quality, and can have a light-transmitting structure in which the substrate 11 and the concavo-convex pattern 12 are integrated. It is more preferable because a rough pattern can be formed.

  The film thickness of the release layer when the mold is covered with the release layer is preferably a thin layer in order to reduce the influence on the uneven pattern size of the mold by forming the release layer. The film thickness of the release layer can be measured with an atomic force microscope (AFM).

  Here, the adhesiveness indicating the degree of mold release between the mold and the photo-curable resin for nanoimprint (hereinafter also referred to as a resist) will be described. FIG. 2 is an explanatory diagram for obtaining the adhesion work between the mold and the resist. The uneven pattern on the drawing is omitted. In FIG. 2, 21 indicates a mold and 22 indicates a resist.

Here, as shown in FIG. 2A, the unit areas of the mold 21 and the resist 22 which are the two mediums in contact with each other, as shown in FIG. The adhesion work that shows the change is W _{mold / resist} as the adhesion work that separates the mold from the resist surface, γ _{mold is the mold} interface energy (surface free energy), γ _{resist is the resist} interface energy (surface free energy) When the interfacial energy between resists is γ _{mold / resist} , it is expressed by the following formula (1).
W _{mold / resist} = γ _mold + γ _resist −γ _{mold / resist} (1)

  On the other hand, the phenomenon between the resist and the solid surface of the mold is simply expressed by the degree of wetting of the resist onto the solid surface. In the present invention, the contact angle used to determine the surface free energy is the angle formed between the tangent line drawn on the droplet and the solid surface at the intersection of the surface of the droplet placed on the solid surface and the solid surface. The angle on the side containing the droplet is shown.

FIG. 3 is a schematic diagram for explaining the force acting on the resist on the mold surface. As shown in FIG. 3, when the resist 32 is formed on the surface of the mold 31, the surface free energy of the mold, which has the same sign as in FIG. 2, is expressed as γ with respect to the contact angle representing the degree of wettability, that is, hydrophilicity and hydrophobicity. _{If the mold} , the interface energy between the mold and the resist is γ _{mold / resist} , the resist surface free energy is γ _resist , and the contact angle is θ, the force relationship indicated by the three arrows is balanced, and the following Young-Dupre (Young-Dupre) ) (2) holds.
γ _mold = Γ _resist cosθ + γ _{mold / resist} (2)

From the above formulas (1) and (2), the adhesion work W _{mold / resist} is expressed by the following formula (3). Therefore, if γ _resist and θ are known, the adhesion work W _{mold / resist} for separating the mold from the resist surface can be obtained. γ _resist and θ can be obtained by measurement.
W _{mold / resist} = γ _resist (1 + cosθ) (3)

Therefore, in order to easily pull the mold away from the resist surface, it is necessary to reduce the adhesion work W _{mold / resist} from Equation (3), that is, to use a material having a small _resist surface free energy γ _resist (surface tension). From the formula (2), the mold surface free energy γ _mold can be reduced, for example, a release layer having a small surface free energy may be provided on the mold surface.

On the other hand, from the Owens equation (DKOwens et al., J. Appl. Polym. Sci., 13, 1741-1747 (1969)), surface free energy γ ^d and polarity due to dispersion interaction When the sum of the surface free energy γ ^p due to the interaction (γ = γ ^d + γ ^p ) is established, the following formulas (4) and (5) are established.
γ _{mold / resist} = γ _mold + γ _resist -2 (√ (γ ^d _resist γ ^d _asl ) + √ (γ ^p _resist γ ^p _asl ))
... (4)
W _{mold / resist} = 2√ (γ ^d _resist γ ^d _asl ) + 2√ (γ ^p _resist γ ^p _asl )
... (5)
However, γ ^d _resist and γ ^p _resist are the dispersion component and polar component of the surface free energy of the resist, respectively, and γ ^d _asl and γ ^p _asl are the release layer (the mold itself if there is no release layer). Is a dispersion component and a polar component of the surface free energy.

As described above, each component (γ ^d ; γ ^p ) of the surface free energy γ of the solid can be obtained by measuring contact angles with two types of liquids having different surface tensions on the same solid surface. The surface free energy γ is obtained as the sum of the surface free energy γ ^d due to the dispersion interaction and the surface free energy γ ^p due to the polar interaction (γ = γ ^d + γ ^p ). As a preferable embodiment of the present invention, pure water and diiodomethane (CH ₂ I ₂ ) are mentioned as the above two kinds of liquids.
Hereinafter, the present invention will be described in more detail with reference to examples.

Table 1 shows the measured contact angle of each material used in the nanoimprinting method of the present invention and the value of the surface free energy γ (γ = γ ^d + γ ^p ) determined from the contact angle. Contact angle is measured by using an optical microscope with a goniometer that can read the angle, directly observing the droplet from the side and measuring the contact angle directly, or measuring the angle by image analysis of the droplet outline For example, a conventionally known method is used. In this example, Drop Master manufactured by Kyowa Interface Science Co., Ltd. was used as the contact angle measuring device. Pure water and diiodomethane (CH ₂ I ₂ ) were used as the two liquids used to determine the contact angle. As a measurement sample, there are a mold coated with four types of release layers, a mold without a release layer, and one type of resist.

In Table 1, the four release layers include trade names OPTOOL DSX (Optool: manufactured by Daikin Industries, Ltd.), octadecyltrimethoxysilane (ODS: CH ₃ (CH ₂ ) ₁₇ Si) mainly composed of a fluorine-based silane compound. (OCH ₃ ) ₃ ) and hexamethyldisilazane (HMDS) were each formed on a synthetic quartz substrate by vapor phase epitaxy to prepare a measurement sample as a release layer. HMDS uses two types with different coating conditions, and HMDS-1 and HMDS-2 are samples in which a release layer is provided with a vapor phase growth time of 30 minutes and 5 minutes, respectively. The mold without the release layer uses a synthetic quartz substrate (Qz: 6 inch square, thickness 0.25 inch) after washing with sulfuric acid / hydrogen peroxide solution (H ₂ SO ₄ / H ₂ O ₂ ). . The resist used was the trade name PAK-01 (manufactured by Toyo Gosei Co., Ltd.). In Table 1, among the two types of liquids used to determine the contact angle, pure water is γ = 72.8, γ ^d = 21.8, γ ^p = 51.0 (unit: mJ / m ² ). Yes, diiodomethane is γ = 50.8, γ ^d = 48.5, γ ^p = 2.3 (unit: mJ / m ² ).

  Among the measurement samples shown in Table 1, the surface free energy γ = 12.4 is the smallest in the OPTOOL DSX (Optool) whose main component is the fluorine-based silane compound of the release layer 1. On the other hand, a synthetic quartz substrate mold (Qz) without a release layer exhibits a high surface free energy γ = 72.4.

Next, the quartz mold surface is respectively coated with the release layer 1 to the release layer 4 to prepare samples 1 to 4, and five types of molds are made using the quartz mold without the release layer as the sample 5. A sample was used, and the mold release force of each mold was measured. For the measurement of mold release force, the measurement device shown in FIG. 4 proposed by Taniguchi et al. Was prepared and used (J. Taniguchi et al., Jpn. J. Appl. Phys. Vol. 41 (2002) pp. .4194-4197). A light (ultraviolet) curable resin 42 was applied onto a silicon wafer 41 serving as a substrate to be processed, and the resin was placed in the measuring apparatus shown in FIG. 4, the mold 43 was pressed, and each mold sample was irradiated with ultraviolet rays. As the photocurable resin 42, PAK-01 (manufactured by Toyo Gosei Kogyo Co., Ltd.) was used, and the ultraviolet irradiation amount was 200 mJ / cm ² , and the irradiation amount for curing the photocurable resin 42 was irradiated.

Next, a load 44 was applied to the silicon wafer 41 side by the measuring device shown in FIG. 4 to determine the separation force of each sample. The result is shown in FIG. A commercially available force gauge DPS-50R (manufactured by Imada Co., Ltd.) was used for measurement of the release force. The mold release force (MPa) is a force required to release the mold and the cured photo-curing resin adhering to the mold, and is expressed by the following mathematical formula (6), per unit area (mm ² ). It is indicated by the maximum load (N) required for mold release. Further, a quartz mold without a release layer was measured as a sample 5 for comparison.
Release force per unit area (MPa) = Release force (maximum load, N) / resin area (mm ² )
...... (6)

  In FIG. 5, the black dots in the release force (vertical axis) of each sample (horizontal axis) indicate the variation in the measured values depending on the number of samples of each measured sample, and the horizontal solid line and the numerical values next to it indicate the release force (kPa). The average value is shown. As shown in FIG. 5, a synthetic quartz substrate mold (Ref Qz / Pak) without a release layer shows a high release force of 14.6 kPa, but four types of molds with a release layer are provided. In both cases, the release force of OPTOOL DSX (Optool) and octadecyltritoxylsilane (ODS) is low at 2.7 kPa and 1.9 kPa, respectively. It was shown that it is a suitable mold release agent with good moldability.

Table 2 shows the release force (kPa) of the above samples 1 to 5 shown in FIG. 5, the value of work of adhesion (mJ / cm ² ) obtained by calculation, and visual inspection and visual inspection using an optical microscope. The result of the presence or absence of the pattern defect of the obtained resin is shown. The value of the adhesion work was obtained from the above formula (5).

  As shown in Table 2, the mold with octadecyltrimethoxysilane (ODS) of sample 1 and Optool DSX (Optool) of sample 2 with small adhesion work values can easily release the cured photo-curing resin. The pattern defect due to the resin did not occur due to the mold release. On the other hand, the mold in which the HMDS sample 4 was formed by the vapor phase method showed a relatively low release force of 3 kPa, but partially caused resin pattern defects at the time of release.

As shown in Table 1, the surface free energies of Optool DSX (Optool) which is the mold release agent of Sample 1 and octadecyltrimethoxysilane (ODS) of Sample 2 are 12.4 mJ / m ² and 29.64 mJ / respectively. m ² . Therefore, it is shown that the surface free energy of the mold is 30 mJ / m ² or less in order not to cause pattern defects due to the resin at the time of mold release.

On the other hand, even when the surface free energy on the surface of the photocurable resin after curing is not 30 mJ / m ² or less, not on the mold side, as explained in the above formulas (1) to (5), It is possible to prevent or reduce the pattern defects of the resin.

Therefore, in order to perform a nanoimprint method that is excellent in releasability from the resin and does not cause or reduce resin pattern defects, the surface free energy on the mold surface and the surface of the cured photocurable resin (resist) surface It is required that at least one of the surface free rubies with the free energy is 5 mJ / m ² or more and 30 mJ / m ² or less. If either one of the mold and the resist is 30 mJ / m ² or less, the work of adhesion can be reduced and the releasability can be improved. Moreover, the mold release property of a resist and a mold can be improved by making the surface of photocurable resin (resist) into a film in which alkyl and fluoroalkyl are densely arranged and having a surface free energy of 30 mJ / m ² or less. As explained above, the mold surface may be coated with a release layer.

According to nanoimprint method of the present invention, the surface free energy of the mold coated with a release layer, measuring the surface free energy of the photocurable resin cured with ultraviolet ray on the substrate to be processed, both the surface free energy of the If it is within the predetermined range, it can be determined that the releasability is good, and if it is not within the predetermined range, it can be determined that the releasability is poor and a pattern defect of the resin may occur. The suitability of the functional resin can be evaluated.

DESCRIPTION OF SYMBOLS 10 Mold 11 Substrate 12 Uneven pattern 13 Release layer 14 Substrate 15 Photocurable resin 21, 31 Mold 22, 32 Resist 41 Silicon wafer 42 Photocurable resin 43 Synthetic quartz substrate 44 Load 71 Mold 72 Release layer 73 Processed substrate 74 Resin 75 Chip defect 76 Adhered resin A Adhesive force F Friction force

Claims (2)

A mold having a concavo-convex pattern on the surface is pressed against a photocurable resin on a substrate to be processed, and the photocurable resin is cured by irradiating light that sensitizes the photocurable resin through the mold. A nanoimprint method for transferring the concavo-convex pattern,
Wherein the surface free energy of the mold surface, none of the surface free energy of the photocurable resin surface after the curing state, and are 30 mJ / m ² or less at 5 mJ / m ² or more,
The nanoimprint method, wherein the uneven pattern of the mold is coated with a release layer composed of a fluorine-based silane compound or octadecyltrimethoxysilane .   The mold release force when releasing the mold from the cured photocurable resin after curing the photocurable resin and transferring the uneven pattern is 1.9 kPa or more and 2.7 kPa or less. The nanoimprint method according to claim 1.

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