US20070205180A1 - Nanoimprint lithography having solvent-free liquid polymer resist - Google Patents

Abstract

A polymer resist having a good flow is used in a nanoimprint lithography. A residual layer remained is thus thinner. Hence, a time spent for etching the residual layer is reduced. And a pattern obtained after the nanoimprint lithography will not be ruined because of a long-time etching. Nevertheless, the present invention can be applied on a hard substrate, like a silicon chip, or a soft substrate, like PET.

Description

FIELD OF THE INVENTION
• The present invention relates to a nanoimprint lithography; more particularly, relates to obtaining a solvent-free liquid polymer resist having high fluidity for a NIL for obtaining a thinner residual layer, a shorter time for etching the residual layer, and a prevention of ruining the pattern by etching for over-time.
DESCRIPTION OF THE RELATED ARTS
• A prior art, as revealed in U.S. Pat. No. 5,772,905, “Nanoimprint lithography”, provides a method and a device for imprinting a mini-photograph onto a film coated on a substrate, where the mini-photograph is imprinted by a mold to obtain a concaved image on the film; then the residual layer remained on the film is removed; and the above process can be repeated continuously.
• In the early days, the development of nanoimprint lithography is focus on shrinking area, so that the polymer used is mainly some easily obtained thermoplastic, such as poly(methylmethacrylate) (PMMA). Yet, on fabricating an object having bigger surface, parameters like fluidity, pressure, temperature, heating curve, etc. become complex, and interactions in between gets more and more; thus, the yield is affected. In these parameters, fluidity is the most important. A polymer having good fluidity is easily flowed out in the imprinting process, so that a residual layer formed is thinner and the time spent for etching the residual layer is shorter. As a result, process time is reduced and resources, like etching gas, electricity, etc., used for etching with reactive ions is diminished. Furthermore, the etching with reactive ions does not differ in etch selectivity; thus, size and shape of the polymer resist image is remained after etching the residual layer. Yet, in modern hot-imprinting technology, substrate is heated up to exceed glass transition temperature (Tg) for imprinting with etching resist, which might deform or even decompose a part of the plastic substrate. Again, in some coating process for a conductive layer of a display may deform the substrate; and development of some optoelectrical products are thus hindered.
• Later, C. Grant Willson in University of Texas announced a step-and-flash of imprint lithography. A few monomers and an optical initiator are mixed; and a quartz mold and an aligner are used for opto-copolymerization for imprinting. However, not only the quartz mold is expansive, but also reactive ion etching or inductively coupled plasma reactive ion etching is slow. So, quartz mold is not obtained easily.
• M. Sagnes et al. revealed an imprint lithography using thermal polymerization of methyl methacrylate (MMA) monomer mixed with a thermal initiator of azobisisobutyronitrile (AIBN). During heating up, the thermal initiator drives free bond for polymerization to obtain solid polymer. The polymer monomer has a good fluidity and so an advantage of almost non-residual layer is achieved. This technology uses cheaper material than the quartz mold to reduce production cost.
• Nevertheless, the above prior arts have the following shortcomings:
• First, the reaction of polymerization is formed by chemical bonding. When chemical bonds are formed, atoms are drawn closer, bonds formed are getting more and more, and size is obviously shrunk. In a word, the rate of monomer occupied in the whole reaction has a direct ratio to the shrinkage.
• Second, the above two chemical reaction mixture have too good fluidity. Hence, on spin-coating, film forming property is worse and thick polymer layer is not obtained on a low rotating speed. That is to say, in the imprinting process, polymer may be wasted and high aspect-ratio imprint image may not be obtained.
• Hence, the prior arts do not fulfill users' requests on actual use.
SUMMARY OF THE INVENTION
• The main purpose of the present invention is to obtain a solvent-free liquid polymer resist having high fluidity for a NIL for obtaining a thinner residual layer, a shorter time for etching the residual layer, and a prevention of ruining the pattern owing to etching over-time.
• To achieve the above purpose, the present invention is a nanoimprint lithography having a solvent-free liquid polymer resist, comprising steps of: (a) mixing at least one polymer material, at least one monomer and a thermal initiator to obtain a solvent-free liquid polymer resist; (b) coating or dropping the polymer resist on a substrate to obtain a polymer resist layer; (c) applying a pressure to the polymer resist layer to process a NIL through an imprint machine under a coordination of a mold having a space pattern; (d) heating the imprint machine to a first temperature while remaining the pressure; (e) after the polymer resist layer is hardened, cooling down to a second temperature and releasing the mold from the hardened polymer resist layer to obtain a polymer imprinted pattern; and (f) etching a remained residual layer of a sunken area on the polymer imprinted pattern, where the polymer material is a thermoplastic polymer, or an oligomer having single or dual double bond, such as poly(methylmethacrylate) (PMMA); the monomer is a monofunctional group acrylic monomer having single double bond, a bifunctional group acrylic monomer having dual double bond, or a multi-functional group acrylic monomer having multi-double bond; the acrylic monomer is MMA or nomal-butylacrylate (n-BA); and the thermal initiator is 2,2′-AIBN. Accordingly, a novel nanoimprint lithography having a solvent-free liquid polymer resist is obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
• The present invention will be better understood from the following detailed description of the preferred embodiment according to the present invention, taken in conjunction with the accompanying drawings, in which
• FIG. 1 is the flow view showing the preferred embodiment according to the present invention;
• FIG. 2A is the first SEM view showing the polymer imprinted pattern;
• FIG. 2B is the second SEM view showing the polymer imprinted pattern
• FIG. 3 is the third SEM view showing the polymer imprinted pattern;
• FIG. 4 is the fourth SEM view showing the polymer imprinted pattern;
• FIG. 5A is the view showing the state of releasing the substrate from the mold;
• FIG. 5B is the view showing the check points for the residual layer; and
• FIG. 5C is the view showing the result of checking the residual layer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
• The following description of the preferred embodiment is provided to understand the features and the structures of the present invention.
• Please refer toFIG. 1, which is a flow view showing a preferred embodiment according to the present invention. As shown in the figure, the present invention is a nanoimprint lithography (NIL) having a solvent-free liquid polymer resist, comprising the following steps:
• (a) Obtaining polymer resist11: At least one polymer material, at least one monomer and a thermal initiator are mixed to obtain a polymer resist. The polymer resist is a solvent-free liquid polymer resist, which is a thermoplastic polymer, or a oligomer having single or multi double bond. The monomer is a monofunctional group acrylic monomer having single double bond, a bifunctional group acrylic monomer having dual double bond, or a multi-functional group acrylic monomer having multi-double bond, where the acrylic monomer is methyl methacrylate (MMA) or nomal-butylacrylate (n-BA). And the thermal initiator is 2,2-azobisisobutyronitrile (AIBN).
• (b ) Obtaining polymer resist layer12: The above polymer resist is coated or dropped on a substrate to obtain a polymer resist layer, where the substrate is polyethylene terephthalate (PET), PET/indium tin oxide (ITO), or other transparent substrate; or the substrate is a silicon chip or a glass.
• (c) Processing NIL13: A pressure is applied to the polymer resist layer through an imprint machine to process a NIL under a coordination of a mold having a space pattern, where the pressure is between 2 kilograms per square centimeter (Kg/cm²) and 60 Kg/cm².
• (d) Heating imprint machine14: The imprint machine is heated to a first temperature while remaining the pressure, where the first temperature is between 70 Celsius degrees (° C.) and 150° C.
• (e) Obtaining polymer imprinted pattern15: After the polymer resist layer is hardened, the temperature is cooled down to a second temperature and then the mold having the space pattern is released from the hardened polymer resist layer to obtain a polymer imprinted pattern, where the second temperature is between 15° C. and 25° C.
• (f) Etching residual layer16: A residual layer remained in a sunken area of the polymer imprinted pattern is etched.
• In step (a), to obtain the polymer resist, the polymer material and the monomer are well mixed at first and then the thermal initiator is added for stirring. Yet the stirring is operated at a third temperature lower than 25° C. to avoid a premature thermal polymerization due to over-heat.
• Besides, step (c) together with step (d) can be done through injection molding. The present invention uses a solvent-free liquid polymer resist, which has high fluidity, as the polymer resist so that the residual layer is thinner and time spent for etching the residual layer is shorter. Hence, fabrication time is reduced and the polymer imprinted pattern is not ruined owing to a long time spent in etching the residual layer.
EXAMPLE
• (a) The following components are mixed to be stirred for obtaining a clear and homogeneous solution: 10 grams (g) of poly(methylmethacrylate) (PMMA) having a 990K molecular weight (Mw), 10 g of PMMA having a 110K Mw, 50 g of MMA acrylic monomer, and 10 g of nomal-butylacrylate (n-BA) acrylic monomer. The solution is stored still for one day and is confirmed that no PMMA powder or particles remains. Then 3 g of 2,2′-AIBN as a thermal initiator is added to be stirred at a third temperature until being completely dissolved in the solution. And then the solution is stored still in a refrigerator to obtain a polymer resist. Therein, the third temperature is lower than 25° C.
• (b) The polymer resist is taken out to obtain a room temperature (about 20° C.) and then is coated or dropped on a substrate to form a polymer resist layer.
• (c) A NIL with a mold having a space pattern is processed under a pressure of 10.18 kilograms per square centimeter (Kg/cm²) at a speed of 1 kilogram per minute (Kg/min).
• (d) An imprint machine is heated to a first temperature while remaining under the pressure of 10.18 Kg/cm², where the first temperature is 95° C. and the temperature is remained for 1.5 hours.
• (e) The first temperature is remained until the polymer resist layer is hardened. Then the solution is cooled down to a second temperature, which is about 20° C. Then the mold having the space pattern is released from the hardened polymer resist layer to form a polymer imprinted pattern.
• (f) In the end, a residual layer remained in a sunken area of the polymer imprinted pattern is etched.
• Please refer toFIG. 2A andFIG. 2A, which are a first SEM view and a second SEM view showing the polymer imprinted pattern. As shown in the figures, a polymer imprinted pattern obtained according to the present invention is photographed by a scanning electron microscopy (SEM). A first SEM view is obtained at a voltage of 15 kilo-volts (kV) with a magnification of 10K, where line width to space width (line/space) is 500 nm/500 nm; and a second SEM view is obtained at a voltage of 15 kV with a magnification of 20K, where line/space is 300 nm/300 nm. From the first and the second SEM views, it is clearly seen that the polymer imprinted pattern is intact. Hence, the polymer resist used in the present invention is suitable for hard substrate.
• Please refer toFIG. 3, which is a third SEM view showing a polymer imprinted pattern. As shown in the figure, a PET substrate is used to obtain a polymer imprinted pattern. A third SEM view for the polymer imprinted pattern is obtained at a voltage of 15 kV with a magnification of 100, where line/space is 20 um/400 um. From the third SEM views, it is clearly seen that the polymer imprinted pattern is intact. Hence, the polymer resist used in the present invention is suitable for soft substrate.
• Please refer toFIG.4, which is a fourth SEM view showing a polymer imprinted pattern. As shown in the figure, a fourth SEM view is obtained at a voltage of 15 kilo-volts (kV) with a magnification of 1.5K. From the fourth SEM view, it is seen that the mold used is clearly stamped on a surface of a polymer imprinted pattern. Although the mold is originally obtained through an inductively coupled plasma reactive ion etching and so its surface is rough, the polymer resist used in the present invention has a high fluidity and thus sunken areas made by the mold is filled with the polymer resist by adding a certain pressure.
• Please refer toFIG. 5A,FIG. 5B andFIG. 5C, which are a view showing a state of releasing a substrate from a mold; a view showing check points for a residual layer; and a view showing a result of checking the residual layer. As shown in the figures, for examining aresidual layer221, a releasing layer is coated on asubstrate21 before a polymer resist layer is formed on thesubstrate21. After the NIL, a mold releasing is processed, where the polymer imprinted pattern is adhered on themold23 and themold23 together with the polymer imprintedpattern22 is released from the substrate21 (as shown inFIG. 5A). Then nine check points are obtained on a surface where the polymer imprintedpattern22 is separated from thesubstrate21, including afirst check point31, asecond check point32, athird check point33, afourth check point34, afifth check point35, asixth check point36, aseventh check point37, aeighth check point38 and aninth check point39. Thicknesses of the residual layer at the check points are examined through an Alpha-step profilometer; and results include 176 nm for thefirst check point31, 195 nm for thesecond check point32, 175 nm for thethird check point33, 186 nm for thefourth check point34, 188 nm for thefifth check point35, 148 nm for thesixth check point36, 195 nm for theseventh check point37, 165 nm for theeighth check point38, 152 nm for theninth check point39. In the above data, the thicknesses of the residual layer are all thinner than 200 nm. From the thicknesses for theninth check point39 at center together with thefifth check point35, thesixth check point36, theseventh check point37 and theeighth check point38, it is seen that the thicknesses of the polymer resist layer do not get thicker as long as the flow path gets longer; since the polymer resist used for forming the polymer resist layer has a high fluidity.
• To sum up, the present invention is a nanoimprint lithography having a solvent-free liquid polymer resist, where a polymer resist used to form a polymer resist layer has a high fluidity so that a residual layer is thinner and time spent for etching the residual layer is shorter, and a polymer imprinted pattern is not ruined owing to a long-time etching of the residual layer.
• The preferred embodiment herein disclosed is not intended to unnecessarily limit the scope of the invention. Therefore, simple modifications or variations belonging to the equivalent of the scope of the claims and the instructions disclosed herein for a patent are all within the scope of the present invention.

Claims (14)

1. A nanoimprint lithography (NIL) having a solvent-free liquid polymer resist, comprising steps of:

(a) mixing at least one polymer material, at least one monomer and a thermal initiator to obtain a polymer resist;

(b) deposing said polymer resist on a substrate to obtain a polymer resist layer through a method selected from a group consisting of coating and dropping;

(c) applying a pressure to said polymer resist layer to process a NIL through an imprint machine under a coordination of a mold having a space pattern;

(d) heating said imprint machine to a first temperature while remaining said pressure;

(e) after said polymer resist layer is hardened, cooling down to a second temperature and releasing said mold from said polymer resist layer to obtain a polymer imprinted pattern; and

(f) etching a residual layer of a sunken area being remained on said polymer imprinted pattern.

2. The NIL according toclaim 1,

wherein said polymer resist is a solvent-free liquid polymer resist.

3. The NIL according toclaim 1,

wherein said monomer is selected from a group consisting of a monofunctional group acrylic monomer having single double bond, a bifunctional group acrylic monomer having dual double bond, and a multi-functional group acrylic monomer having multi-double bond.

12. The NIL according toclaim 3,

wherein said acrylic monomer is selected from a group consisting of methyl methacrylate (MMA) and nomal-butylacrylate (n-BA).

4. The NIL according toclaim 1,

wherein said polymer material is selected from a group consisting of a thermoplastic polymer, an oligomer having single double bond, and an oligomer having dual double bond.

5. The NIL according toclaim 1,

wherein said thermal initiator is 2,2′-azobisisobutyronitrile (AIBN).

6. The NIL according toclaim 1,

wherein said substrate is a transparent soft substrate selected from a group consisting of polyethylene terephthalate (PET) and polyethylene terephthalate/indium tin oxide (PET/ITO).

7. The NIL according toclaim 1,

wherein said substrate is selected from a group consisting of a silicon chip and a glass.

8. The NIL according toclaim 1,

wherein said pressure is between 2 kilograms per square centimeter (Kg/cm²) and 60 Kg/cm².

9. The NIL according toclaim 1,

wherein said first temperature is between 70 Celsius degrees (° C.) and 150° C.

10. The NIL according toclaim 1,

wherein said second temperature is between 15° C. and 25° C.

11. The NIL according toclaim 1,

wherein said polymer resist in step

(a) is obtained through steps of:

(a1) mixing at least one polymer material and at least one monomer to obtain a mixture;

(a2) after no polymer material powder and no polymer material particles are remained in said mixture, adding a thermal initiator to said mixture; and

(a3) stirring said mixture under a third temperature until said polymer material, said monomer and said thermal initiator are completely solved.

13. The NIL according toclaim 1,

wherein said third temperature is lower than 25° C.

14. The NIL according toclaim 1,

wherein said step (c) together with said step (d) is done through injection molding.

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