Patent Application
20110006035
The present invention relates to a method for modifying a surface in selective areas and, more particularly, to a method of a plasma-induced modification in selective areas of a surface.
Nanotechnology has been developed as a reliable technology for producing minimal components for enabling performance of very precise functions. For instance, the availability of nanolithography processes is important in the fields of photonics, electronics, and biotechnology. Among the available nanolithography processes, nanoimprint and soft lithography are two alternatives to conventional photolithography for enabling the manufacture of devices with micrometer, nanometer, or centimeter-sized features.
The first-mentioned nanoimprint method mechanically imprints nano-patterns of a rigid template to a specific soft polymer plate. The soft polymer plate is then hardened such that the nano-patterns are formed on its surface. On the other hand, soft lithography methods, such as the microcontact printing, use an elastomeric stamp as a template. The elastomeric stamp is coated with a specific material as the ink paste and then contacted with a substrate to convert patterns to the substrate. As an example, an elastomeric stamp coated with thiol in contact with a gold-electroplated substrate can form patterns having corrosion-resisted self-assembled monolayer (SAM).
Both nanoimprint and microcontact printing methods employ templates to convert patterns, which techniques can satisfy the needs of scalability, high throughput, and low cost; however, the integration of a large quantity of nanoscale objects into functional devices and structures can still be a challenge to be overcome. Many factors, such as varying or uneven flatness and pressing uniformity of the imprint machine, the separation step of the template, and characteristics of the polymer, may decrease the yield rate of a nanoimprint method. In addition, the ink paste used with a microcontact printing method must be limited to a material that can react with the surface of the substrate, and resolution may fall short of requirements due to the diffusion of the applied inks.
Therefore, it would be advantageous to provide a novel nanolithography process having superior process capability and resolution.
One object of the present invention entails the provision of a method for modifying a surface in selective areas and a method for forming patterns, whereby patterns comprising a modified area and an unmodified area are formed on the surface of a sample. The modified area and the unmodified area may have different properties and may interact with a specific substance, a biological molecule, or a metal particle.
Another object of the present invention is to provide a method for modifying a surface in selective areas and a method for forming patterns, thereby forming nanoscale or microscale patterns with small feature sizes and high resolution that can be used to produce minimized components to perform more precise functions.
Another object of the present invention is to provide a method for modifying a surface in selective areas and a method for forming patterns, thereby satisfying needs for producing components having different scales.
Another object of the present invention is to provide a method for modifying a surface in selective areas and a method for forming patterns, which can be carried out in a sample having a large area, thereby reducing the time and cost of pattern conversion.
Another object of the present invention is to provide a method for modifying a surface in selective areas and a method for forming patterns, which can be carried out in a sample without perfect flatness, thereby improving the process capability and protecting the sample from being damaged during the process.
Another object of the present invention is to provide a method for modifying a surface in selective areas and a method for forming patterns, which forms patterns of superior uniformity, selectivity, and resolution in combination with self-assembly technology. According to the objects, an embodiment of the present invention provides a method for modifying a surface in selective areas, comprising providing a sample having a surface, providing and attaching a template to the surface, and providing a plasma to contact and modify the selective areas of the surface by using the template to selectively isolate the plasma.
According to the objects, another embodiment of the present invention provides a method for forming patterns, comprising providing a sample, providing an elastic stamp having a relief structure and attaching it to a surface of the sample, and providing a plasma to selectively contact and modify the surface by using the elastic stamp to selectively isolate the plasma, thereby forming a modified area and an unmodified area on the surface wherein the plasma flows through the relief structure and modifies the surface, thus forming the modified area to comprise patterns of the relief structure.
According to the objects, yet another embodiment of the present invention provides a method for forming patterns, comprising providing a sample, providing an elastic stamp having a relief structure, the elastic stamp being attached to a surface of the sample, providing a plasma to selectively contact and modify the surface using the elastic stamp to selectively isolate the plasma thereby forming a modified area and an unmodified area on the surface, providing a self-assembled molecule to selectively interact with a specific area of the surface of the sample, and immersing the sample in a solution containing a substance, the substance selectively interacting with the self-assembled molecule.
Reference will now be made in detail to specific embodiments of the invention. Examples of these embodiments are illustrated in the accompanying drawings. While the invention will be described in conjunction with these specific embodiments, it will be understood that such description is not intended to limit the invention to these embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without some or all of these specific details. In other instances, well-known process operations and components are not described in detail in order not to unnecessarily obscure the present invention. While the drawings are illustrated in detail, it is appreciated that the quantity of the disclosed components may be more or less than that disclosed, except for instances expressly restricting the amount of the components. Wherever possible, the same or similar reference numbers are used in the drawings and the description to refer to the same or like parts.
The inventive concept of the present invention is to use plasma (e.g., an activated gas) to modify one or more selective (e.g., selected) areas of a surface of a sample. The modification can comprise, but is not limited to, one or more of surface activation, plasma polymerization, plasma deposition, plasma induced grafting, plasma etching, and the like. Due to plasma being an activated gas having excellent chemical reactivity and flow ability it is suitable for treating samples having different materials, shapes, and sizes, and it is capable of modifying only the surface of the sample while maintaining the internal properties of the sample. For example, the surface modification may comprise altering one or more of the reflective index, the hardness, and the functional group of the surface, and altering one or more of the capability of wetting, adhesion, coloring, compatibility to biologics, and passivating.
An embodiment of the present invention provides a method to modify one or more selective areas of a surface of a sample. The method comprises providing a sample, arranging a template on a surface of the sample, and providing a plasma to modify one or more selective areas of the surface of the sample, wherein the template is used as a mask to isolate the plasma. In other words, the embodiment chooses a kind of plasma according to the design requirement and employs the template to determine the area or areas of the surface to be modified, so that areas covered by the template can maintain one or more of the original function group, chemical composition, and property. Therefore, the modified areas and unmodified areas may have different properties, and patterns having different functions can be formed on the surface of the sample.
The above-mentioned template is arranged on the surface of the sample to construct at least a channel through which the plasma flows; hence the plasma contacts the surface, and the modification can be carried out. To construct the above-mentioned channel, the template may comprise one or more continuous or discrete relief structures. After the template is arranged on the surface of the sample, the plasma flows into an inlet and exits from an outlet of the channel. The inlet and outlet may be located at one or more of the top and the side of the template. Alternatively, the template may comprise a plurality of openings (through holes), whereby the plasma contacts the surface via the openings thus modifying the selective areas of the surface. It is projected that, according to another embodiment of the present invention, the above-mentioned relief structure(s) may be formed on the surface of the sample rather than the surface of the template, and the channel may be constructed after the template is attached to the surface of the sample.
Because the template functions as a mask to shield the plasma, it is preferably made of a material having good chemical resistance to the selected plasma for increasing its reliability after repeated usages. In addition, because rigid templates disadvantageously cannot completely be attached to the surface of the sample, and the plasma may penetrate through or around gaps between the template and the surface of the sample, the template of the embodiment is preferably made of an elastic material, such as PolyDiMethylSiloxane (PDMS); therefore, the template can be attached on the surface of the sample completely (e.g., flush at all locations) even though (e.g., to the extent that) the surface of the sample is a bit uneven, thus forming modified areas having superior resolution and preventing the sample from being damaged by the template.
In other embodiments of the present invention, the template may be made of polyurethanes, polyimides, or cross-linked Novolac resins in a condition that the feature size and the resolution are not strictly requested (e.g., specified or predetermined).
Another embodiment of the present invention provides a method for forming patterns.
After the elastic stamp 22 is produced, the embodiment of the present invention selects suitable plasma according to the designed needs. For example, by using the oxygen as the plasma source to treat a general polymer, a polar functional group may be formed on the surface of the polymer, and makes the polymer hydrophilic; in contrast, by using the fluorine as the plasma source to treat the polymer, the polymer is made hydrophobic. Because the embodiment of the present invention arranges the elastic stamp 22 to be completely attached to the surface of a sample, the plasma only contacts the areas of the surface exposed by the elastic stamp 22, and the other areas are isolated by the elastic stamp 22. Hence plasma-induced modifications are implemented in selective areas of the surface that the plasma contacts. A modified area is formed in selective area(s), and the other area(s) is unmodified area. Where the plasma modifies the surface of the sample through the relief structure 24 of the elastic stamp 22, and thus the modified area comprises the shape of the relief structure 24 of the elastic stamp 22.
In addition, the modified area and unmodified area may be treated to have different properties according to the requirements. A specific substance may be added to or interacted with the modified area or the unmodified area. The specific substance may comprise a molecule that can proceed with the self-assembly reaction. For example, immersing the sample into a solution comprising specific chemical or biological molecules or metal particles will result in the specific molecules or particles being selectively adsorbed in the modified area or the unmodified area by their interacting force, which comprises Van der Walls force, hydrogen bonding, Coulomb electrostatic force, dipole-dipole interaction, and the like. Hence a pattern having different functions in different areas can be obtained. Because the self-assembled molecule is to use a specific functional group to interact with a specific surface of the sample, the uniformity and selectivity can be highly satisfied, and consequently the pattern has better resolution. According to the present invention, the thickness of the self-assembled structure can be controlled by controlling the processing time of plasma treatment, and the self-assembly reaction is capable of treating a large quantity of integration of patterns.
Although the above-mentioned embodiment employs the conventional lithography to produce the photoresist 12′ mold, in other embodiments the photoresist 12′ mold can be produced by other methods such as electron beam lithography or focused ion beam lithography. Accordingly, the feature size of the mold determines the scale of the relief structure 24 of the elastic stamp 22. The scale of the embodiment may comprise micrometer, nanometer, centimeter, and other scales; hence the patterns of the present invention may comprise multiple feature sizes having different scales. In addition, the working area of the elastic stamp 22 can be adjusted for different application. For example, a bigger elastic stamp 22 is suitable for a larger area to decrease the time and cost for replicating patterns.
Moreover, in the above embodiment the relief structure 24 is located in the surface of the elastic stamp 22, but this should not be limited. If the PDMS liquid gel 20 is poured into the mold with a height smaller the height of the mold, perforated openings will be formed in the relief structure, and the plasma contacts and modifies the surface of the sample through the openings.
Furthermore, in the above embodiment the elastic stamp is made of PolyDiMethylSiloxane (PDMS), but in other embodiments it can be made of other elastic materials in a condition that the elastic stamp can be attached completely with the surface of the sample, thus forming modified area having superior resolution in selective areas, and preventing the surface of the sample from being damaged by the elastic stamp. More, the elastic stamp is preferably made of a material having good chemical resistance to the selected plasma, so that it has good reliability after repeated usages.
First, a sample 30, for example, a silicon substrate, is provided. The surface of the silicon substrate may be naturally oxidized to form a silicon oxide layer in an environment having oxygen and water. Or, hydroxyl groups may be formed on the surface of the silicon substrate by treatment of plasma or sulfuric acid; the hydroxyl groups will be used later for forming a uniform self-assembled monolayer. In this exemplary embodiment, the silicon substrate is cleaned with acetone, alcohol, and deionized water in sequence. The cleaned silicon substrate is treated in a plasma chamber having condition power 12 W, 0.6 torr for 10 minutes with air as the plasma source, and the surface of the silicon substrate is activated by the air plasma. The activated silicon substrate is then immerged in 0.5 mM OctadecylTrichloroSilane (OTS, H3C(CH2)17SiCl3, Aldrich, product no. 104817) solution with toluene as the solvent, resulting in that an OTS monolayer 32 is formed in the activated surface of the silicon substrate by self-assembled reaction between the OTS molecule and activated surface, as shown in
In this embodiment, because the inlet and outlet holes A, B (
After the plasma treatment is finished, the PDMS elastic stamp 22 is separated from the sample 30. The sample 30 is then cleaned by acetone, alcohol, and deionized water in sequence. Accordingly, the sample 30 with OTS monolayer 32′ having modified area 34 and unmodified area 34′ is obtained.
Referring to
The above experiments prove that the combination of the plasma and the elastic stamp is capable of modifying the selective surface of the sample. In other embodiments, other gases or mixture of gases, such as oxygen or water vapor or oxygen-contained gas, can be or comprise a part of the plasma source. The plasma source should not be limited to the disclosed examples in interpreting the present invention.
Referring to
In addition, in this embodiment a self-assembled molecule may be further provided to selectively interact with a specific area of the surface of the sample 30. As an example, the sample 30 with modified OTS monolayer in selective areas is immersed in a 3-AminoPropylTriMethoxySilane (APTMS), 97 wt % solution for 24 hours. The APTMS (H2N(CH2)3Si(OCH3)3) may be obtained from Aldrich, product no. 281778. Referring to
Further, the sample 30 being adsorbed with APTMS molecules 44 is immersed in an aqueous solution containing gold nanoparticles (for example, Sigma, product no. G1527, ca., 10 nm mean particle size) for 30 minutes. The terminal of the APTMS molecule 44 is an amino group (—NH2), which will be protonated to a positively charged amino group (NH3+) in the solution. The APTMS molecules 44 can be used to electrically attract the negatively charged gold nanoparticles 46, and thus a multilayer structure of gold nanoparticle/APTMS/OTS can be formed in the modified area 34′, as shown in
In other embodiments, the gold nanoparticles 46 may comprise or consist of sizes in any part or all of the range from 1 to 1000 nm and/or may be uniformly distributed in a colloidal solution. For instance, the colloidal particles of the colloidal solution may comprise nanoscale and microscale gold particles. The embodiment employs the self-assembled monolayer (or multilayer) as the linker layer, the self-assembled monolayer being oppositely charged to the colloidal particles and the self-assembled monolayer electrically attracting the gold nanoparticles to form a uniform, two dimensional gold nanoparticle array. This embodiment can be applied in one or more of the fields of nanocatalyst, chemistry, biosensor, and nanophotonics.
In addition, the positively charged APTMS molecule can selectively adsorb one or more of other negatively charged particles such as (e.g., selected from) protein, antigen, antibody, ribonucleic acid, deoxyribonucleic acid, and the like.
According to the disclosed embodiments of the present invention, the number of the modification in selective areas of the surface of the sample is not intended to be limited; the sample can be repeatedly modified according to design requirements. The generated pattern may comprise multilayer structure(s). For precisely positioning the PDMS elastic stamp on the sample, markers may be formed on the sample, and the PDMS elastic stamp and a photo camera may be used to check the markers before positioning.
Although specific embodiments have been illustrated and described, it will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the present invention, which is intended to be limited solely by the appended claims.
