Method And Apparatus To Apply Surface Release Coating For Imprint Mold
A surface coating apparatus for preparing a work piece having a working surface for imprint lithography, wherein the work piece comprises either a mold or a substrate. The apparatus includes a vacuum chamber and a generator to produce chemical reaction radicals for cleaning the working surface. The generator may be located inside said vacuum chamber and connected to an inner surface of said vacuum chamber or external to the vacuum chamber and connected thereto via suitable couplings. A fixture within the vacuum chamber is configured to hold the work piece with the working surface accessible by the chemical reaction radicals, and a means is provided for depositing a molecular layer of surfactant on the working surface inside the vacuum chamber.
The present application is a continuation of, and claims priority to, U.S. patent application Ser. No. 11/945,470 filed on Nov. 27, 2007 which in turn claims the benefit of U.S. Provisional Patent Application Ser. No. 60/867,498 filed on Nov. 28, 2006 and U.S. Provisional Patent Application Ser. No. 60/869,981 filed on Dec. 14, 2006, all of which are herein incorporated by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCHNot Applicable.
FIELD OF THE INVENTIONThis invention relates to treating molds and substrates for imprint lithography, and in particular, to an integrated cleaning/deposition process and related apparatus.
BACKGROUND OF THE INVENTIONLithography is a key process in the fabrication of semiconductor integrated circuits and many optical, magnetic, biological, and electro-mechanical devices. Lithography creates a pattern on a substrate-supported moldable film so that, in subsequent process steps, the pattern can be replicated in the substrate or in another material that is added onto the substrate.
Conventional lithography, referred to as photolithography, involves applying a thin film of photosensitive resist to a substrate, exposing the resist to a desired pattern of radiation and developing the exposed resist to produce a physical pattern on the substrate. The resolution of patterns produced by photolithography is limited by the wavelength of the exposing radiation. Moreover, as pattern features become smaller, increasingly expensive shorter wavelength equipment is required.
Imprint lithography, based on a fundamentally different principle, offers high resolution, high throughput, low cost and the potential of large area coverage. In imprint lithography, a mold with a pattern of projecting and recessed features is pressed into a moldable surface, typically a thin film, deforming the shape of the film and forming a relief pattern in the film. The film is hardened, as by UV or thermal curing, and the mold and imprinted substrate are separated. After the mold is removed, the thin film can be processed, as by removing the residual reduced thickness portions to expose the underlying substrate for further processing. Imprint lithography can be used to replicate patterns having high resolution features in the microscale and nanoscale ranges. Details of nanoscale imprint lithography (“nanoimprint lithography”) are described in U.S. Pat. No. 5,772,905 issued Jun. 30, 1998 and entitled “Nanoimprint Lithography”. The '905 patent is incorporated herein by reference.
A significant factor for commercial imprint lithography is the useful life of the imprint mold. The mold lifetime directly affects cost of the products and throughput of the production. The lifetime of the imprint mold is limited by wearing of the mold surface release coating and damage to the mold material. The material damage, such as breaks, surface feature rupture, and surface indentation is caused by the stress and strain of imprinting. Wearing of the surface release coating depends on the surface chemistry, bonding strength and the coverage of the surface release layer. It is also affected by how well the release layer is applied on the mold surface. Reliable methods of applying a surface release layer are much needed for imprint lithography.
BRIEF SUMMARY OF THE INVENTIONIn imprint lithography, the mold is coated with a surface release layer for a non-sticking separation. Bonding strength of the release layer to the mold depends on the cleanness of the surface and the process of release layer deposition. In accordance with the invention, the mold is disposed in an evacuable chamber, cleaned to remove surface organic contamination and coated with the surface release layer in a chamber, all without relocation or undesired time delay. The chamber encloses a support chuck for the mold or substrate, a surface cleaner unit adjacent the support, a heating source adjacent the support, and advantageously, sensors for measuring chamber pressure, vapor partial pressure and moisture concentration. A vapor source connected to the chamber supplies release surfactant vapor. The mold is cleaned, and the cleaning is followed by vapor phase deposition of the surfactant. The mold is advantageously heated. Typical ways of cleaning include exposure to ozone or plasma reactive ion etch. Surfactant vapor may be generated by liquid surface vaporization, liquid injection or spray vaporization. A surface adhesion promoter can be coated on the substrate by a similar method with the same apparatus.
The advantages, nature and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments now to be described in detail in connection with the accompanying drawings.
In the drawings:
It is to be understood that the drawings are to illustrate the concepts of the invention and are not to scale.
DETAILED DESCRIPTION OF THE INVENTIONReferring to
The same procedure can be used to apply an adhesion promoter (another surfactant) on the substrate to be imprinted. Thus, the method and apparatus of the invention can treat both the mold and the substrate with the same equipment and is believed effective for applying any type of molecular surfactant on a general workpiece.
In operation, mold 309 is loaded onto the chuck 305 with the molding surface of imprinting features facing upward. Cleaner 303 starts to clean the mold surface. After cleaning, and with minimal delay beyond apparatus response time, vapor deposition begins. The chamber 301 is drawn to a selected level of vacuum. Then vapor of the surfactant is introduced into the chamber from the vapor generation unit 311. The vapor partial pressure in the chamber is measured by the vapor partial pressure sensor 317. A feedback loop may be established to adjust flow-in rate of the vapor in order to control the vapor partial pressure precisely. Since typical surfactant reactions are sensitive to moisture in ambient, the moisture level in the ambient is advantageously monitored by moisture sensor 319. The moisture level may be adjusted by an additional component (not shown) which will be discussed later.
During vapor deposition, the mold may be heated by turning on the heating source 307 to speed up the surface bonding reaction and the coverage of the mold surface by surfactant molecules. After vapor deposition, the chamber is pumped to remove residual vapor. The chuck may be cooled for next run. Finally, the mold can be cooled within the chamber before or after unloading or cooled outside the chamber after unloading.
The apparatus may have a single vapor generation source or multiple vapor generation sources for multiple surfactants. In operation, vapors of surfactants may be introduced one at a time or several at a time. When several vapors are introduced, one should consider in advance acceptable cross contamination of the different surfactants.
Any of several methods may be used to precisely control the moisture level in vapor deposition. One method is to use a source of air with predetermined moisture concentration to purge the chamber. Another is to use a water vapor source to input moisture and a water absorption source to extract moisture. The moisture level in the chamber can be adjusted by controlling alternative operations of the water vapor source and the water absorption source. A third method is to use a water vapor source to input only specific amount of moisture through a flow rate controller.
Referring to
Referring to
One embodiment of the vapor generation source can be a gas reservoir that contains a predetermined concentration of surfactant vapor. The gas preferably comprises nitrogen, argon, helium or air. The surfactant vapor can be generated by vaporizing the surfactant and mixing it with the gas at predetermined ratio. The mixture is then filled into the reservoir. Alternatively, a user could install a prefilled reservoir as from a commercial supplier.
In addition to the port connected to the vapor generation source, the coating apparatus may have a port in chamber 301 connected to a water vapor source. Water vapor can be introduced from the source through the connection line and the port into the chamber. By selecting the amount or flow rate of water vapor introduced into the chamber, the moisture density inside the chamber can be optimally controlled for good coating strength and uniformity. Furthermore, the quality of the mold surface coating treatment can be steadily maintained by controlling the moisture density. In one embodiment, the water vapor source can be a gas reservoir that contains a predetermined moisture concentration. The gas can be air or an inert gas such as nitrogen, argon, or helium. Other embodiments of the water vapor source can be similar to the embodiments described and illustrated in
The principle of the invention can be implemented on a nanoimprint tool to clean the mold and treat it with a surface release coating on the nanoimprint tool. For such case, the described embodiments in the invention will be part of the nanoimprint tool. Through such integration, cleaning and treating the mold on site can minimally interrupt imprinting throughput by saving mold exchange time. In addition, cleaning and treating the mold can be done during the imprinting process in order to achieve higher yield and longer mold lifetime.
In operation of the apparatus, a substrate, for example a mold or wafer for imprint lithography, is loaded on to the chuck when the door is pulled out. After that, the door is pushed back against front surface of chamber wall. Then, a magnetic solenoid door lock 921 is electrically turned on to hold the door in position. After choosing and installing a program to run process, a user can press a button on the display to run the process. After the process is complete, the door is unlocked and pulled out to unload the substrate. The door shown in
A detailed example of the operation can now be described step by step. The first step is to load the work piece such as a mold or substrate. The second step is to turn on UV lamp to generate ozone to clean mold or substrate. The cleaning step may take from tens seconds to several minutes. During the cleaning step, the mold or substrate may be heated to facilitate cleaning reaction. The third step is to turn off UV lamp and exhaust the chamber for several minutes to remove residual ozone. The fourth step is to pump the chamber. Normally, a vacuum better than 1000 mTorr is needed for vapor coating. The vacuum can be reached in 30 seconds. The purging step typically lasts 1-3 minutes to achieve a better vacuum. The base vacuum of less than 50 mTorr can be achieved after 10-15 minutes pumping.
During steps 3 and 4, the mold or substrate is heated to vapor coating temperature, which is typical 60-100 ° C. Surfactant contained inside the vapor generation source is heated to vapor generation temperature. Higher temperatures provide higher vapor density of surfactant. The vapor generation temperature is typically set at 80° C. The fifth step is to coat mold or substrate with surfactant vapor. The temperature that is reached in the previous step is maintained during the coating step.
The coating starts with turning on control valve of vapor line. The vapor of surfactant is introduced into the chamber. The coating process on mold or substrate surface begins immediately. Coating typically takes several minutes to twenty minutes. An experimental study of five minutes coating deposition time showed that good surface release coating was obtained on a quartz mold. The vacuum pumping may be turned off to rely on good chamber seal to maintain vacuum. In such case, surfactant vapor pressure inside chamber is higher than maintaining vacuum pumping.
The sixth step is to close vapor line to stop flow-in of surfactant vapor and pump residual vapor out of the chamber. The pumping may take several minutes to remove most of residual vapor. The seventh step is to vent the chamber. After the chamber is vented to atmosphere, the coated mold or substrate is unloaded. The process was performed on various mold/substrate materials, such as quartz, glass, silicon, III-IV semiconductors, and polymers. Surfactants that were tested include surface release surfactant (1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane) for mold treatment and surface adhesion promoter ((3-Acryloxypropyl)-trichlorosilane) for substrate treatment.
Examples of surfactants which can be used in the apparatus comprise perfluorohexyl-trichlorosilane, perfluorooctyl-trichlorosilane, perfluorodecyl-trichlorosilane, perfluorodecyl-trichlorosilane, perfluorohexylpropyl-trichlorosilane, perflurordecyl-trichlorotitanium, perfluorodecyl-dichlorobromosilane, polydimethylsiloxane-trichlorosilane, perfluorodecyl-dichlorobromogermanium, perfluorodecyl-dichlorobromomochromium, acryloxypropyl-trichlorosilane, and the like. The apparatus works for any type of surfactant, especially for surfactant having liquid phase at room temperature and higher vapor pressure at a reasonable elevated temperature.
It is to be understood that the above-described embodiments are illustrative of only a few of the many possible specific embodiments which can represent applications of the invention. Numerous and varied other arrangements can be made by those skilled in the art without departing from the spirit and scope of the invention.
Claims
1. A surface coating apparatus for preparing a work piece having a working surface for imprint lithography, wherein the work piece comprises either a mold or a substrate, comprising:
- a vacuum chamber;
- a generator to produce chemical reaction radicals for cleaning the working surface, said generator located inside said vacuum chamber and connected to an inner surface of said vacuum chamber;
- a fixture within said vacuum chamber configured to hold the work piece with the working surface accessible by said chemical reaction radicals, said fixture connected to said inner surface of said vacuum chamber; and,
- a means for depositing a molecular layer of surfactant on said working surface inside said vacuum chamber.
2. The surface coating apparatus of claim 1 wherein said means comprises a vapor generator configured to produce a molecular vapor of surfactant and a means for deliver said molecular vapor of surfactant to said working surface.
3. The surface coating apparatus of claim 2 wherein said fixture includes a heater to heat said working surface.
4. The surface coating apparatus of claim 2 further comprising a means to increase a temperature of said working surface.
5. The surface coating apparatus of claim 2 further comprising a lamp to radiate light upon the work piece to increase a temperature of said working surface.
6. The surface coating apparatus of claim 2 wherein said vapor generator comprises:
- a reservoir to contain said surfactant, said reservoir comprising an internal volume to contain said surfactant and a port to dispense said molecular vapor of surfactant from said reservoir; and
- a heater to increase a temperature of said surfactant, wherein said heater is either connected to said reservoir or embedded inside said internal volume.
7. The surface coating apparatus of claim 2 wherein said vapor generator comprises:
- a reservoir to contain said surfactant, said reservoir comprising an internal volume to contain said surfactant and a port to dispense said molecular vapor of surfactant from said reservoir; and
- a bubbler to flow inert gas through said surfactant within said internal volume.
8. The surface coating apparatus of claim 7 wherein said vapor generator further comprises a heater to increase a temperature of said surfactant, wherein said heater is either connected to said reservoir or embedded inside said internal volume.
9. The surface coating apparatus of claim 2 wherein said vapor generator comprises:
- a reservoir defining an internal volume;
- a port to dispense said molecular vapor of surfactant from said reservoir; and,
- a dropper to deliver a plurality of droplets of surfactant into said internal volume of said reservoir.
10. The surface coating apparatus of claim 9 further including a controller operatively connected to said dropper, said controller configured to precisely control a volume of each droplet and to count droplets delivered by said dropper.
11. The surface coating apparatus of claim 1 further comprising a means for controlling moisture partial pressure inside said vacuum chamber.
12. The surface coating apparatus of claim 1 wherein said generator is a plasma generation electrode.
13. The surface coating apparatus of claim 1 wherein said generator is an ozone generation ultraviolet lamp.
14. The surface coating apparatus of claim 13 wherein said fixture includes a heater to heat said working surface.
15. The surface coating apparatus of claim 14 wherein said means comprises a vapor generator to produce a molecular vapor of surfactant and a means to deliver said molecular vapor of surfactant to said working surface.
16. A surface coating apparatus for preparing a work piece having a working surface for imprint lithography, wherein the work piece comprises either a mold or a substrate, comprising:
- a vacuum chamber;
- a generator to produce chemical reaction radicals for cleaning said working surface, said generator disposed outside of said vacuum chamber and connected to said vacuum chamber through a gas passing line for feeding said chemical reaction radicals into said vacuum chamber;
- a fixture to hold the work piece with said working surface accessible by said chemical reaction radicals within said vacuum chamber, said fixture connected to an inner surface of said vacuum chamber; and,
- a means for depositing a molecular layer of surfactant on said working surface inside said vacuum chamber.
17. The surface coating apparatus of claim 16 further comprising a means to increase a temperature of said working surface.
18. An surface cleaning and coating tool comprising:
- a base;
- a vacuum chamber fixed to said base, said vacuum chamber having an opening on a front side for loading and unloading;
- a sliding guidance system connected to either an outer surface of said chamber or to said base;
- a door panel to seal said opening, said door panel connected to said sliding guidance system, said sliding guidance system configured to engage said door panel in contact with said front side in a closed position;
- a seal surrounding said opening between said door panel and said front side when said door panel is in contact with said front side;
- a chuck with a heating means fixed to said door panel, said chuck inside said vacuum chamber when said door panel is at said closed position;
- wherein said sliding guidance systems is configured to displace said door panel away from said front side at an substantial extent for loading or unloading said chuck;
- an ozone generation UV lamp installed inside said vacuum chamber, said UV lamp adjacent to said chuck when said door panel is at said closed position; and
- a vapor generator coupled to said base comprising a vapor generation reservoir and a vapor discharge port, said vapor discharge port coupled to said vacuum chamber through a vapor passing line with ON/OFF control.
19. The surface cleaning and coating tool of claim 18 further comprising:
- a pneumatic line system connected to said chamber for drawing a vacuum within said chamber and for discharging gas into said vacuum chamber; and
- an electronic control system configured to operate said UV lamp, said heating means of said chuck, said vapor passing line, and said pneumatic line system.
20. The surface cleaning and coating tool of claim 19 further comprising a user interface mechanically connected to said base and operatively connected to said electronic control system.
Type: Application
Filed: Feb 15, 2011
Publication Date: Jun 30, 2011
Inventors: Wei Zhang (Newtown, PA), Lin Hu (Livingston, NJ), Hua Tan (Princeton Junction, NJ), Linshu Kong (Plainsboro, NJ), Stephen Y. Chou (Princeton, NJ)
Application Number: 13/027,530
International Classification: C23C 16/513 (20060101);