JP5999738B2 - Immersion imprint method - Google Patents

Description

  The present invention relates to an imprint method for transferring a fine concavo-convex structure on the surface of a molding material, and more particularly to defect prevention in a thermal imprint technique for thermoplastic materials.

Nanoimprinting is a technology that can easily transfer large quantities of nanometer-sized patterns by combining replication technology for plastic materials and precision molds and templates produced by applying semiconductor manufacturing technology.
Various technologies related to nanoimprinting have been developed, and their application ranges are diverse.
Among them, since there are many choices of molding materials, thermal nanoimprint has been incorporated into manufacturing methods for electronic devices, optical devices, biochips and the like.

In the above-described device, a thermoplastic material of bulk material is often processed, but when used as a masking layer for dry etching, a thermoplastic material thin film applied on a Si substrate is imprinted. In thermal imprinting, a thermoplastic material that has been heated to a temperature higher than the glass transition temperature and obtained fluidity flows into the concavo-convex structure of the mold pattern in conjunction with the press operation of the mold.
At that time, the molding material softened from the peripheral portion flows into the concave mold pattern, and the air remaining in the central portion is gradually compressed by a high pressure, and finally disappears and completely filled.
However, if the flowing material is insufficient, defects in the molding pattern are likely to occur. In particular, unlike bulk materials that are thick and contain abundant molding materials, the thin film formed on the Si substrate is thin and tends to have a shortage of flow, so that the molding pattern is not completely filled with the molding material. There is a high possibility of forming defects due to the remaining bubbles.

As means for preventing such molding defects, when manufacturing a mold, the pattern arrangement is designed in advance in consideration of the filling time of the molding material, or a micro-trench for storing residual gas is provided inside the mold pattern. Methods are disclosed in Patent Documents 1 and 2 below.
Further, a technique for improving the fluidity of a molding material by molding under a reduced pressure environment or ultrasonic vibration is described in Non-Patent Document 1 and Patent Document 3 below, and a gap between the mold and the molding material is positively formed. Patent Document 4 below discloses a method for preventing bubble defects caused by gas filling by replacing air with a condensable gas.

However, there are some technical problems when using the method described above.
When there is a restriction during the design of the mold pattern as in the methods disclosed in Patent Documents 1 and 2 below, the type of device that can be manufactured by applying the imprint technology is limited, so the versatility of the imprint technology is impaired. There is a risk that. Further, a vacuum pump, an ultrasonic generator, or the like must be added to the imprint apparatus in order to realize a reduced pressure environment and to apply ultrasonic vibration as disclosed in Non-Patent Document 1 and Patent Document 3 below.

  This leads to complicated equipment and processes and increased manufacturing costs. Moreover, the bubble defect prevention method by gas enclosure disclosed by the following patent document 4 is suitable for the optical nanoimprint method which made the ultraviolet curable resin the shaping | molding object. In this method, a condensable gas (for example, pentafluoropropane) is poured between a template and an ultraviolet curable resin layer spin-coated on a Si substrate, and pressure is applied to the condensable gas. Prevent bubble defects. However, pentafluoropropane has a high saturated vapor pressure in a general molding temperature region in thermal nanoimprint, and a gas liquefaction effect cannot be expected.

JP 2010-171338 A JP 2007-042715 A Japanese Patent No. 3619863 Japanese Patent No. 3700001

N. Roos et al., Proc. SPIE, vol. 5037, p. 211 (2003)

FIG. 1 shows a conventional thermal imprint process. When thermal imprinting is performed in the atmosphere, the atmosphere between the mold 3 and the molding material 2 (thermoplastic material thin film) is filled with air (FIG. 1A). As described above, when the mold 3 is pressed onto the molding material 2 in the air, air is taken into the gaps between the concave portions of the pattern formed on the mold 3 and the molding material 2, and the mold pattern is developed as the pressing process proceeds. It is compressed by the molding material 2 flowing into the inside (FIG. 1B).
However, when the total amount of the molding material 2 is relatively small, such as a thin film, and the inflow amount of the molding material necessary for completely filling the mold pattern cannot be secured, the shape of the mold pattern is accurately placed on the molding material. Transfer becomes impossible, and the defect 4 that causes defective molding occurs in the uneven structure on the surface of the molding material 2 (FIG. 1C).
In view of the above technical problems, in the present invention, the gas constituting the atmosphere during the imprint process is taken into the gap between the mold 3 and the molding material 2 without using a vacuum pump or an ultrasonic generator in the thermal imprint. It is an object of the present invention to provide an imprint method in which a replacement step with a high boiling point liquid is added in order to prevent a decrease in transfer accuracy due to the above.

  In order to solve the above-mentioned problems, the present inventors replaced the air existing between the mold and the molding material with a high-boiling liquid that does not vaporize at the molding temperature in advance and does not ignite, and the fluidity increased by heating. The idea is that defects caused by the presence of residual air can be easily prevented by extruding the boiling point liquid to the outside of the mold pattern instantaneously by the molding pressure and filling the mold pattern with a softened molding material without inserting a gap. The present invention has been reached.

  That is, the present invention is an invention of an imprinting method, and in order to transfer the uneven structure on the mold surface to the thermoplastic material thin film formed on the substrate without defects, the air remaining between the mold and the molding material is a high-boiling liquid. The liquid whose fluidity has been improved by replacement is heated and completely filled with a thermoplastic material which is pressed out and extruded to the outside of the mold to soften the mold pattern.

More specifically, the imprint method of the present invention, by heating to a temperature in excess of the glass transition temperature is the molding material molding temperature coated on the substrate surface and pressed the molding material against motor Rudo In the imprint method comprising the step of transferring the concavo-convex structure formed on the mold surface, prior to the pressing step of pressing the molding material against the mold, inside the concavo-convex structure formed on the mold surface, Filled with an inert liquid that has a boiling point and ignition point higher than the molding temperature of the molding material and does not cause a chemical reaction with the thermoplastic material used as the molding material so as to exclude air inside the concavo-convex structure. A liquid filling step, wherein in the pressing step, the molding material flows into the recesses of the concavo-convex structure, the inert liquid is extruded, and the mold With a step that is discharged from the end.

  According to the present invention, a high boiling point liquid that does not evaporate even at a molding temperature is inserted between a mold and a molding material for a thermoplastic material thin film coated on a substrate that is difficult to prevent defects in thermal imprinting, and residual air By substituting with a high boiling point liquid, the uneven pattern on the mold surface can be completely transferred onto the molding material.

Process drawing of the conventional thermal imprint method. The process drawing of the liquid immersion imprint method which concerns on this invention. Sectional drawing at the time of experiment arrangement | positioning of the liquid immersion imprint method which concerns on this invention. The optical microscope photograph of the shaping | molding pattern on the PMMA thin film spin-coated on Si substrate. (A) A state in which defects are prevented by molding by the liquid immersion imprinting method according to the present invention, and (b) a state in which defects are generated by molding by a conventional thermal imprinting method. The cross-sectional profile of the white line part in a confocal microscope of the shaping | molding pattern on the PMMA thin film spin-coated on Si substrate, and a figure. (A) The state which shape | molded with the conventional thermal imprint method, and the defect generate | occur | produced, (b) The state which shape | molded with the liquid immersion imprint method which concerns on this invention, and the defect was prevented is shown. The curve which shows the aspect which the kinematic viscosity of the florinate FC-43 based on this invention reduces with a temperature rise. The curve which shows the aspect which drops the fluorinate FC-43 which concerns on this invention on the Si substrate by which the mold release process was performed, and the contact angle of the florinate FC-43 with respect to a board | substrate increases with a temperature rise.

  Embodiments of the present invention will be described below with reference to the drawings.

The imprint process according to the present invention will be described with reference to FIG. The molding material 2 applied to the solid substrate 1 such as a Si wafer is arranged so that the surface thereof is opposed to the concavo-convex pattern formed on the surface of the mold 3.
Next, the distance between the mold 3 and the molding material 2 is reduced, and the residual gas such as air existing in the gap is replaced with the liquid 5 described later (FIG. 2A).

The liquid 5 may be dropped in advance on either or both of the mold 3 and the molding material 2, or after the mold 3 and the molding material 2 are brought close to each other, the liquid is forcibly sent to extrude the air. Good.
Moreover, you may make it immerse the press mechanism itself containing the mold 3 and the molding material 2 in the container filled with the liquid. The physical properties required of the liquid 5 to be replaced with air do not evaporate even when heated up to the molding temperature, and remain in a chemically stable liquid state without igniting at this temperature. The material 3 has no solubility or erosion.

Next, the mold 3 and the molding material 2 are heated to a temperature equal to or higher than the glass transition temperature of the molding material 2, and the uneven structure formed on the surface of the mold 3 is pressed against the surface of the molding material 2.
Along with the progress of the pressing process, the softened molding material 2 flows into the recesses of the mold pattern, and the liquid 5 filled in the mold pattern is discharged to the outside of the mold pattern so as to be pushed out. It is discharged to the outside from the department.
Due to the presence of the liquid 5, the molding material 2 can be completely filled inside the mold pattern without being obstructed by residual gas such as air (FIG. 2B).
After the mold 3 and the molding material 2 are cooled below the glass transition temperature of the molding material, the mold 3 and the molding material 2 are separated from each other, and the concavo-convex structure in which the concavo-convex structure of the mold pattern is inverted is completely formed on the surface of the molding material 2 (FIG. 2 (c)).

  In addition, this liquid is required to have a fluid characteristic so that air inside the uneven structure of the mold pattern is surely eliminated during filling and to be smoothly discharged during the pressing process, but it is not necessarily completely at the end of the pressing process. However, it may remain as a very thin and uniform layer between the molding material and the uneven surface of the mold pattern.

Specific examples will be described in detail below.
In this example, polymethyl methacrylate (PMMA) was used as a molding material, and a fluorine-based inert liquid was used as a liquid filled in the uneven structure of the mold pattern formed on the surface of the mold 13.
FIG. 3 shows the arrangement of the molding material 11 and the Si mold 13 in an actual imprint experiment. Preparation of the molding material 11 and mold release processing of the mold 13 were performed according to the following procedure.
(Step 1)
An ultraviolet curable resin (OEBR = 1000) manufactured by Tokyo Ohka Kogyo Co., Ltd. in which polymethyl methacrylate (PMMA) was dissolved in an ethyl cellosolve acetate solution was spin-coated on the Si substrate 10 at a rotational speed of 4000 rpm. By heating in an oven at 170 ° C. for 20 minutes, the molding material 11 having a PMMA thin film layer having a thickness of 460 nm is formed on the Si substrate 10.
(Step 2)
A fluorine mold release agent Optool HD-1101 manufactured by Daikin Industries, Ltd. is applied to the surface of the concavo-convex pattern formed on the Si mold 13 by a dipping method.
(Step 3)
The outer peripheral end of the Si substrate 10 coated with the molding material 11 that is a PMMA thin film layer is fixed by a bolt 8 so as to be sandwiched between the flat washer 9 and the aluminum sample holder 6.
(Step 4)
The aluminum sample holder 6 is physically fixed to the upper ceramic heater 7a of the thermal imprint apparatus by the upper spring hook 16a so that the molding material 11 which becomes the PMMA thin film layer is on the lower side.
(Step 5)
The Si mold 13 is adhered to the glassy carbon plate 15 by a heat-resistant double-sided tape 14 composed of a polyimide base material and a silicone adhesive.
(Step 6)
The glassy carbon plate 15 is physically fixed to the lower ceramic heater 7b of the thermal imprint apparatus by the lower spring hook 16b so that the uneven pattern formed on the surface of the Si mold 13 is on the upper side.
(Step 7)
As described above, after the placement of the Si mold 13 and the molding material 11 that has become the PMMA thin film layer is completed, the fluorine-based inert liquid fluorinate FC-43 (boiling point) manufactured by 3M, whose main component is perfluorotributylamine. : 174 ° C.) 12 is dropped onto the concavo-convex structure formed on the surface of the Si mold 13 using a pipette.
(Step 8)
The upper and lower ceramic heaters 7a and 7b are energized to heat the Si mold 13 and the molding material 11 formed of the PMMA thin film layer to 145 ° C. exceeding 105 ° C. which is the glass transition temperature of PMMA.
(Step 9)
When the temperature of the molding material 11 that has become the Si mold 13 and the PMMA thin film layer reaches a set value, the molding material 11 that has become the PMMA thin film layer with respect to the concavo-convex structure formed on the surface of the Si mold 13. The surface is pressed at a pressure of 1 MPa to 5 MPa.
(Step 10)
When the molding pressure reaches the set value, hold for 10 to 60 seconds.
(Step 11)
The energization of the upper and lower ceramic heaters 7a and 7b is stopped, and natural cooling is performed until the temperature of the molding material 11 that becomes the Si mold 13 and the PMMA thin film layer becomes 95 ° C. below the glass transition temperature of PMMA.
(Step 12)
The Si mold is released from the PMMA thin film.

  When the obtained molding pattern was observed with an optical microscope, no defects were observed as shown in FIG. 4A, and high transfer accuracy was realized. As described above, when the molding material 11 that has become the PMMA thin film layer is thermally imprinted in the atmosphere, a high-boiling fluorine-based inert liquid is used between the Si mold 13 and the molding material 11 that has become the PMMA thin film layer. It has been confirmed that it is effective to insert a certain florinate FC-43.

FIG. 5 shows the result of observing the molding pattern of PMMA with a confocal microscope Optelics S130 (manufactured by Lasertec).
The lower diagram shows the cross-sectional shape of the portion indicated by the white line in the upper diagram.
In the case of imprinting by the conventional method in which Fluorinert FC-43 shown in FIG. 5A was not dropped, a considerably large depression and a raised structure were confirmed as compared with the size of the mold pattern.
The difference between the maximum value and the minimum value indicated by the two dotted lines is 532 nm, which is more than twice the pattern height of the convex Si mold 200 nm.
On the other hand, when Fluorinert FC-43 shown in FIG. 5B is dropped, the difference between the maximum value and the minimum value is measured as 32 nm. This value is higher or lower than in the conventional method not using Fluorinert FC-43. Only 6% of the difference means that the transfer accuracy has been dramatically improved.

In this example, fluorinated inert liquid Fluorinert FC-43 was used as the liquid, and was dropped onto the concavo-convex structure formed on the surface of the Si mold 13 by a pipette. Immediately before the process or at an appropriate timing during the pressing process, the dropping device is automatically positioned on the concavo-convex structure formed on the surface of the Si mold 13, and an optimum amount capable of reliably filling the inside is pumped and supplied. You may do it.
In particular, in order to form a plurality of elements at once, when using a mold with a large number of uneven structures for each element, the position of the dropping device and the liquid supply amount are automatically programmed and controlled to the required location. It is preferable that an optimal amount is supplied.

  The liquid itself is almost completely discharged at the end of the pressing process, but can be reused any number of times when an inert liquid such as fluorinated inert liquid Fluorinert FC-43 is used. . Therefore, if the liquid overflowing from the outer periphery of the Si mold 13 is collected by a liquid receiving portion provided on the lower outer periphery of the Si mold 13 and recirculated to the liquid supply tank or the like, the manufacturing cost is minimized. It can be suppressed to the limit.

  In addition, in order to reliably fill the liquid into the concave-convex structure formed on the surface of the Si mold 13, a liquid holder that slightly protrudes from the surface is attached over the entire outer periphery of the mold 13, and interlocked with the pressing process. It is also preferable to evacuate downward.

[Comparative Example 1]
In order to demonstrate the effect of the present invention, in the above-described embodiment, the fluorine-based inert liquid fluorinate FC-43 is not dropped on the uneven pattern formed on the surface of the Si mold 13, but under exactly the same molding conditions. The result of imprinting is shown in FIG. In most of the convex space area around the pattern area, a defect was observed in which the residual air compressed by pressurization exploded during decompression.
In general, in thermal nanoimprinting, conditions such as molding temperature, cooling temperature, molding pressure, press speed, and holding time have a great influence on molding accuracy. Therefore, in this experiment, the heating temperature and the cooling temperature were fixed at 145 ° C. and 95 ° C., respectively, and other molding conditions were increased / decreased, but the disappearance of defects could not be confirmed under either condition.

[Comparative Example 2]
Next, instead of fluorine-based inert liquid fluorinate FC-43, fluorine-based inert liquid fluorinate FC-3283 (boiling point: 128 ° C.) mainly composed of perfluorotripropylamine having a relatively low boiling point is used as a Si mold. Although it was dropped on the uneven pattern on the surface and imprinted under exactly the same molding conditions as in Example 1, all Fluorinert FC-3283 evaporated during the pressing process, and the effect of preventing defects could be confirmed. There wasn't.

[Comparative Example 3]
Furthermore, in order to verify the influence of the temperature rise on the fluidity of the fluorinated inert liquid Fluorinert FC-43, the relationship between the heating temperature by the ceramic heater 7, the kinematic viscosity, and the contact angle accompanying the surface tension was examined.
As the molding material 11 that becomes the Si mold 13 and the PMMA thin film layer is heated, the Fluorinert FC-43 that fills the gap between the Si mold 13 and the molding material 11 that becomes the PPMMA thin film layer also has a heat transfer effect. It will be heated by and will affect its physical properties.
One of the important properties indicating the fluidity of a liquid is kinematic viscosity. According to FIG. 6, the kinetic viscosity of Fluorinert FC-43 decreases from 25 cSt at room temperature to 0.33 cSt when heated to 145 ° C.
Another factor that affects fluidity is the interaction of surface tension. That is, the relative magnitude relationship of the surface tension between the substrate and Fluorinert FC-43 changes the fluidity of Fluorinert FC-43.
FIG. 6 shows the results of measuring the temperature dependence of the contact angle by dropping Fluorinert FC-43 onto a Si substrate that has been subjected to a release treatment as an alternative to the Si mold 13. When the Si substrate temperature was heated to 145 ° C., the contact angle of the Fluorinert FC-43 droplet on the substrate increased from 7.9 ° at room temperature to 22.3 °. From this, it is expected that the interfacial tension between Fluorinert FC-43 and the Si mold is reduced in an environment around the molding temperature, and the fluidity is improved.
Therefore, it is desirable that the high boiling point liquid used in the imprinting method according to the present invention has a characteristic that the fluidity improves as the temperature rises while maintaining a stable liquid state near the molding temperature.

  In addition, various liquids can be used as the liquid to be filled in the concavo-convex structure formed on the mold surface, depending on the material of the molding material. When the mold is heated to the molding temperature, it will boil and vaporize. Viscosity characteristics, flow that has a stable chemical property to the molding material, does not ignite, and is smoothly discharged without mixing bubbles when the molding material is pressed against the mold. Those having characteristics can be used.

As described above, the liquid immersion imprint method according to the present invention can pattern a thermoplastic material thin film applied on a Si substrate at a high speed in a state in which defects due to residual air are eliminated, for example, after molding. This thermoplastic material layer is used as a mask layer for dry etching, and can be expected to be widely applied as a mass production technique for processing a wiring pattern of a semiconductor element on a Si substrate.
Defects caused by air bubbles are also present when micro / nano structures are formed on relatively brittle materials that cannot be subjected to excessive molding load or on substrates with multiple layers of different thermal properties. It is expected to reduce the generation of defects and to demonstrate its power as a low-load molding technology.

1 Substrate 2 Molding material (thermoplastic material thin film)
3 Mold 4 Defect 5 High-boiling liquid 6 Aluminum sample holder 7 Ceramic heater 8 Bolt 9 Flat washer 10 Si substrate 11 Molding material 12 PMMA thin film layer Fluorinert FC-43
13 Si mold 14 Polyimide double-sided tape 15 Glassy carbon plate 16 Spring hook

Claims (1)

The molding material applied on the substrate surface is heated to a temperature in excess of the glass transition temperature is the molding temperature, and press the molding material against motor Rudo, a step of transferring an uneven structure formed on the mold surface In the imprint method provided,
Prior to the pressing step of pressing the molding material against the mold, the concavo-convex structure formed on the mold surface has a boiling point and an ignition point higher than the molding temperature of the molding material, and as the molding material A liquid filling step of filling an inert liquid that does not cause a chemical reaction with the thermoplastic material to be used so as to exclude air inside the concavo-convex structure;
In the pressing step, the molding material flows into the concave portion of the concavo-convex structure, and the inert liquid is pushed out and discharged from an end of the mold.

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