Patent Application
20190263023
The present invention relates generally to the fabrication of miniature structures and, more particularly, to the construction of miniature structures using nanoimprint lithography.
Nanoimprint lithography, or NIL, is a nanofabrication technology that relies upon the direct physical deformation of a designated surface on a particular material to create nanometer-scale structures. Specifically, a stamp, also commonly referred to in the art as an imprint mold or template, has a relief surface with patterns that are often micrometer or nanometer in scale, the patterns being formed using high precision formation techniques, such as electron beam lithography, focused ion beam milling, dry etching and the like.
To manufacture nanostructures through nanoimprint lithography, the patterned surface of the imprint mold is drawn into direct contact with imprint resist which is coated on a substrate, typically through a spin coating process. As a result of physical contact with the imprint mold, the resist deforms in the particular pattern defined by the complementary imprint mold. Through a designated curing process (e.g. through the application of heat or light), the resist is hardened in the specific deformation pattern. Subsequently, a pattern transfer process, such as reactive ion etching, is undertaken to transfer the pattern in the resist onto the substrate.
As a result, nanoimprint lithography enables nanoscale structures to be fabricated on a variety of different substrate materials through a pattern transfer process that operates in an inexpensive and highly precise fashion, which is highly desirable.
Often, the imprint mold, or stamp, serves as a critical factor in the overall success in fabricating miniature structures using nanoimprint lithography.
For instance, the ultimate resolution of patterns fabricated through nanoimprint lithography is largely is dependent upon the precision of the features that can be formed on the NIL stamp. Although current techniques allow for template patterning with relatively high precision, these techniques are generally laborious, time consuming and expensive to implement. As a result, there is currently no high yield, low cost solution for fabricating NIL stamps.
Additionally, the durability and reliability of a NIL stamp can directly affect fabrication costs, with many stamps having a limited lifespan in the order of 500 stamping cycles. Accordingly, it has been found that in order to generate millions of products using nanoimprint lithography, thousands of complementary NIL stamps are typically required.
Lastly, NIL imprint molds are commonly constructed as limited-sized discs or plates. To improve throughput, multiple individual patterned discs are often laser welded together to form a larger imprint mold. However, the connection of multiple individual discs can create seams which, in turn, can compromise output quality.
In response to many of limitations set forth above in conjunction with traditional NIL stamps, roller-type nanoimprint lithography, or RNIL, has recently been developed to allow for continuous patterning and, as a result, greater throughput. In roller-type nanoimprint lithography, an externally patterned, cylindrical roller, or master, is drawn into direct physical contact with a web as part of a continuous, roll-to-roll, pattern transfer process with nanoscale capabilities.
However, as with most NIL stamps, it has been found that roller-type masters are similarly difficult to construct with precise features in an inexpensive manner. Additionally, as with most NIL stamps, roller-type masters have a limited lifespan and therefore require frequent replacement in high-throughput applications.
It is an object of the present invention to provide a new and improved system and method for constructing a roller-type nanoimprint lithography (RNIL) master.
It is another object of the present invention to provide a system and method as described above that is capable of producing an RNIL master having a relief surface with a highly precise feature pattern.
It is yet another object of the present invention to provide a system and method as described above that is capable of producing an RNIL master with a relief surface in the absence of seams.
It is still another object of the present invention to provide a system and method as described above that is capable of producing a durable RNIL master in a simple and inexpensive manner.
Accordingly, as a feature of the invention, there is provided a method of manufacturing a roller-type nanoimprint lithography (RNIL) master, the method comprising the steps of (a) mounting an RNIL master on a rotatable axle, the rotatable axle having a longitudinal axis, (b) applying a layer of photoresist on the RNIL master, (c) positioning a writing instrument in relation to the RNIL master, the writing instrument being adapted to emit pulses of light of a first wavelength, and (d) exposing the photoresist in a defined pattern on the RNIL master using pulses of light emitted from the writing instrument.
Various other features and advantages will appear from the description to follow. In the description, reference is made to the accompanying drawings which form a part thereof, and in which is shown by way of illustration, an embodiment for practicing the invention. The embodiment will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.
In the drawings, wherein like reference numerals represent like parts:
Referring now to
As shown herein, system 11 comprises an RNIL master 13 and a master fabrication tool 15. As will be described in detail below, master fabrication tool 15 includes a unique collection of instruments that allow for nanoscale patterns to be formed onto master 13 as part of a novel RNIL master construction process.
For purposes of simplicity and ease of illustration, all of the various instruments that are used to perform the novel master fabrication process are shown as being integrated into a unitary, single-station, master fabrication tool 15. However, it is to be understood that one or more of these instruments could be disassociated therefrom and positioned at separate master fabrication stations without departing from the spirit of the present invention.
As seen most clearly in
A motor (not shown) precisely controls movement of spindle 23 (and, as such, drum 19 and sleeve 21 mounted thereon) along both (i) a rotational path about the longitudinal axis of spindle 23, as represented by arrow R, and (ii) a linear path in parallel with the longitudinal axis of spindle 23 (i.e. along its Z-axis), as represented by arrow Z. In this manner, a controller (not shown) can be used to position any location on nickel sleeve 21 relative to the various instruments of tool 15, as will be explained further in detail below.
Referring back to
Master fabrication tool 15 comprises an inverted U-shaped frame, or base, 33 that is fixedly mounted onto support structure 31. Additionally, as referenced above, tool 15 includes a plurality of individual instruments that are mounted onto frame 33 and are utilized at various stages of the novel master fabrication process to be described in detail below.
More specifically, tool 15 comprises, inter alia, a diamond cutting instrument 35, a laser writing instrument 37, an inkjet head 39, an infrared (IR) heater 41, and a collection tray, or pan, 43 that is removably mounted onto a base plate 45 which is coupled to frame 33. One or more controllers (not shown) regulate operation of the various instruments of tool 15 and provide means for user interaction.
As will be explained further in detail below, laser writing instrument 37 is preferably designed to pulse highly focused spots of ultraviolet (UV) light onto RNIL master 13. In this manner, UV light generated from laser writing instrument 37 can be used to assist in both the acute alignment and patterning of RNIL master 13.
As seen most clearly in
More specifically, optical system 115 comprises a collimating lens 121 and beam expander 123 that direct light produced from light source 113 onto a polarizing beam splitter 125. In turn, polarizing beam splitter 125 transmits p-polarized light, while reflecting s-polarized light. The p-polarized light is directed through a quarter-wave plate 127 and one or more focusing lenses 129 to yield a focused, spot-sized, pulse of light onto the desired surface, as will be explained further in detail below. The s-polarized light is directed through at least one lens 131 and onto a quad-focus detector 135. As will be explained further below, detector 135 assists in the acute alignment, or registration, of instrument 37 relative to RNIL master 13, thereby affording system 11 with great precision in writing patterns onto master 13.
Light source 113 is represented herein as a UV laser diode that emits light capable of modulation within a designated UV frequency range. Preferably, light produced from light source 113 falls within a specific range of relatively short wavelengths, as shorter wavelength light is preferred in order to write with the high level of precision and resolution required to create nanoscale features. For instance, in the present application, light source 113 is preferably designed to emit 405 nm light. However, it is to be understood that shorter wavelength light (e.g., 365 nm, 255 nm, or 190 nm light) could be used in place thereof to achieve even greater resolution and accuracy.
As referenced briefly above, laser writing instrument 37 is designed to pulse highly focused spots of UV light. As seen most clearly in
D=(0.6*λ)/NA
Accordingly, with a laser writing instrument 37 that emits 405 nm light and has a numerical aperture of approximately 0.65, spots of UV light can be generated that have a width, or diameter, of approximately 400 nm. By shortening the wavelength of light emitted from light source 111 (e.g. to 190 nm) and increasing the numerical aperture of optical system 115 (e.g. to as much as 2.0 through the integration of immersion optics, as shown in
To minimize the presence of any particulates created during the fabrication of RNIL master 13 (e.g. as a result of diamond turning processes), it is envisioned that system 11 may be enclosed within an environment that is specifically designed to remove such contaminants. For instance, in
Referring now to
As set forth in detail below, the master fabrication method comprises the principal steps of (i) setting up RNIL master 13 for subsequent patterning, the aforementioned set-up step being identified generally by reference numeral 201 in
Further details with respect to each step of the aforementioned master fabrication method are set forth below. Specifically, in step 201, RNIL master 13 is first set up, or registered, for subsequent patterning. Accordingly, as seen most clearly in
With drum 19 affixed to spindle, electroformed nickel sleeve 21 is then axially mounted onto drum 19. Preferably, sleeve 21 has a reduced thickness in the order of approximately 125 microns to 150 microns. Due to its limited thickness, a supply of air is utilized to expand sleeve 21 to permit fitted axial mounting on drum 19.
More specifically, inlets 61 on air drum 19 are adapted to receive air from a designated pneumatic device (not shown). A circumferential array of air holes 63 is provided at each end of drum 19, with each air hole 63 in fluid communication with inlets 61. As a result, the supply of air delivered to drum 19 ultimately exits through the array of air holes 63 which, in turn, causes nickel sleeve 21 to expand to the extent necessary to axially mount onto drum 19. Upon withdrawal of the air supply, sleeve 21 resiliently retracts and is thereby fittingly mounted onto drum 19 (i.e. in conformance therewith). In this capacity, air supplied to inlets 61 can be used to easily mount sleeve 21 on/off drum 19 (or other similarly sized drums utilized at other fabrication stations).
To account for any non-uniformity in its thickness, sleeve 21 is preferably diamond turned using diamond cutter 35 to ensure that the roughness of cylindrical RNIL master 13 is less than 5 nm root mean square (RMS) surface finish. As such, prior to patterning, RNIL master 13 is rendered fully concentric with an ideal surface finish, thereby minimizing the risk of any patterning inaccuracies during subsequent steps.
With RNIL master 13 mounted and prepared as such, set-up step 201 further requires laser writing instrument, or head, 37 to be properly aligned relative to RNIL master 13. As seen most clearly in
With instrument 37 positioned relative to RNIL master 13, alignment fiducials are written into master 13 to ensure proper alignment during subsequent patterning steps. It should be noted that quad-focus detector 135 in instrument 37 is specifically designed to utilize astigmatic focus error signals from the feedback of light reflected from the surface of RNIL master 13 to ensure proper image focus. In other words, the two pairs of diagonally arranged quadrants of the image reflected from the surface of RNIL master 13 are focused on opposing sides of detector 135 using infinite conjugate astigmatic lenses, with one pair of diagonally arranged quadrants of the image focused behind quad-focus detector 135 and the other pair of diagonally arranged quadrants of the image focused the same distance in front of quad-focus detector 135. As a result, optical focus is achieved when the light beam size for each quadrant pair is equal.
As seen most clearly in
A more detailed explanation of the fiducial marking process is set forth below. Specifically, drum 19 is preferably rotated at nominal alignment speed, such that mark detection accuracy is less than 10% of minimum mark length. For instance, with 1 MHz detector bandwidth and one million marks per revolution, then drum 19 preferably rotates at 0.1 revolution per second, or 6 rotations per minute (RPM).
Fiducial marking is accomplished by pulsing laser writing instrument 37 at high power to mark the circumference of sleeve 21 with an intermittent bit pattern of one or multiple frequencies. Adjacent tracks 73 are preferably written with one focused spot diameter of separation (i.e. approximately (0.6*laser wavelength)/(focusing lens numerical aperture)). As seen most clearly in
Additionally, laser writing instrument 37 pulses at high power to write one long marking (not shown) at a spindle encoder index zero location or another fixed circumferential target location. This index marking is used to find the absolute clocking alignment of sleeve 21. The length of index marking can be selected to differentiate between spurious marks or noise and the actual location of the sleeve index marking. The edges of the index marking (or, in the alternative, its center, as detected by the modulated reflection signal read in detector 135) can therefore be used for subsequent rotational alignment.
Upon completion of set-up, or alignment, step 201, nickel sleeve 21 is coated with photoresist 203 as part of step 205 shown in
As seen most clearly in
Upon completion of photoresist coating step 205, photoresist 203 is pre-baked using infrared (IR), or convection, heat 207, as part of step 209 shown in
Upon completion of pre-bake step 209, laser writing instrument 37 exposes photoresist 203 in the desired feature pattern 211, as part of laser writing step 215 shown in
In order to laser write in the desired feature pattern 211, images to be written onto sleeve 21 are preprocessed, with target encoder positions calculated relative to known location information for fiducials 71. For patterning at different heights, each layer would have its own image to be written at a specific stage. The collection of images represents each patterning layer for RNIL master 13 in sequence from the bottom layer to the top layer.
The collection of images to be written into photoresist 203 on sleeve 21 are then loaded into a buffer for the controller of laser writing instrument 37. Using the images, laser writing instrument 37 pulses, with overlap and at a power level corresponding to rotation speed of drum 19, to provide the targeted photoresist exposure energy.
It should be noted that the laser writing process can be triggered by (i) comparison to spindle 23 and/or the Z axis encoder position of drum 19 while in targeted focus for pixels or bits to be written, or (ii) sequentially through incremental counting of encoder ticks correlating to a particular bit pattern. For instance, rotational and axial displacement of drum 19 could be regulated so that printing occurs basically along a single, acute, helical path (i.e. thread). Very high writing speeds are obtainable using this technique, thereby significantly reducing the time requirement associated with the overall fabrication process, which is a principal object of the present invention.
As referenced above, the design of laser writing instrument 37 allows for the emission of highly focused UV light spots, each spot having a width of approximately 400 nm. By intermittingly pulsing UV light spots of a limited width, light patterns can be emitted onto sleeve 21 with considerable precision and high resolution. Referring now to
By comparison, a diamond-based immersion lens (not shown) would preferably lie in near tangential contact with RNIL master 13. More specifically, the immersion lens would preferably be spaced away from photoresist 203 on RNIL master 13 a distance which is less than approximately one-quarter the wavelength of the UV light emitted from laser writing instrument 37 (e.g. approximately 100 nm for 405 nm UV light) so as to achieve evanescent coupling. As an added benefit, the near tangential positioning of a diamond-based immersion lens relative to RNIL master 13, as well as the hardness and strength of the diamond material, would allow for the immersion lens to shear, or shave, any irregularities or impurities from the surface of photoresist 203 (e.g. dust or other similar particulates that would otherwise interfere with certain steps in the RNIL master fabrication process).
Upon completion of laser writing step 215, the RNIL master manufacturing process pauses for approximately 30-120 minutes in a rest environment at greater than 50% humidity in order to rehydrate resist 203 to complete reaction. Thereafter, photoresist 203 is post-baked as part of step 219 shown in
Upon completion of post-baking step 219, a chemical developer solution is applied to RNIL master as part of step 223 shown in
Thereafter, as part of step 225 shown in
Upon completion of electroplating step 225, RNIL master 13 is diamond turned in step 227, as shown in
In final step 229, as shown in
It should be noted that the focus error signal may be used in situ at low power for (i) measuring heights and profiling the existing structure on sleeve 21 as an intermediate step or (ii) mapping the surface where the FES signal strength normalized by the sum of the detectors is directly proportional to height above the surface. Thus, calibration is achieved by moving the X axis relative to the cylinder surface.
The invention described in detail above is intended to be merely exemplary and those skilled in the art shall be able to make numerous variations and modifications to it without departing from the spirit of the present invention. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims.
For example, the master construction method could be modified, as needed, to allow for the manufacture of a NIL master 13 with highly precise, multi-dimensional, nanoscale features through a relatively simple and efficient alternative patterning process. Specifically, as set forth in detail in
The modified RNIL master manufacturing process is similar to the method set forth in
The modified RNIL master manufacturing process differs from the method set forth in
More specifically, using laser writing tool 37, photoresist 303 is illuminated with UV light 313. As can be appreciated, photoresist 303 becomes soluble when exposed to UV light 313 (i.e. chemical bonds are broken in photoresist 303 which allows for subsequent dissolution/removal). As shown in
As an inherent chemical property which is discovered and, in turn, exploited as part of the present invention, UV light 313 develops photoresist 303 at a depth H that is dependent upon the intensity and duration of the illumination of UV light 313 as well as the chemical attributes and thickness of photoresist 303. This effect is created because photoresist 303 is naturally opaque (due to the presence of a photodye) and only becomes transparent upon development. As such, UV light 313 is not initially able to penetrate through the entirety of photoresist 303. Rather, the interior portion of photoresist 303 cannot receive UV light 303 until the outermost regions first become developed. Accordingly, as part of the writing process shown in
In other words, precise UV light application can create different depths, or steps, of photoresist exposure. For instance, a multi-stepped photosensitizing process is shown in
For purposes of illustration only, it is envisioned that photoresist 303 has a thickness preferably in 2-10 microns range (e.g. 4.5 microns). Additionally, with respect to the Intensity and duration of UV light 313, it is envisioned that the energy of UV light 313 (i.e. the product of the UV light power and duration) be scaled dependent upon, inter alia, spot size, photoresist thickness, photoresist sensitivity/type as well as desired penetration depth (e.g. 10%, 25%, 50% of energy required to fully penetrate photoresist). For instance, the energy of UV light 313 is probably in the order of about 20-1000 mjoules/cm2.
Upon completion of the laser writing process, photoresist 303 is post-baked on RNIL master 13 using IR heat 317, the post-baking step being identified generally by reference numeral 319 in
Thereafter, chemical developer (e.g. Microposit™ Remover 1165 solution, which is manufactured by The Dow Chemical Company) is applied to the entire exposed outer surface of RNIL master 13, this developing step being identified generally by reference numeral 321 in
After completion of developer application step 321, non-sensitized photoresist 303 is further post-baked with IR heat 325 to achieve the necessary hardness, this additional post-baking step being identified generally by reference number 327 in
The present application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application No. 62/778,447, inventors John S. Berg et al., filed Dec. 12, 2018 and U.S. Provisional Patent Application No. 62/635,223, inventors John S. Berg et al., filed Feb. 26, 2018, both disclosures being incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62778447 | Dec 2018 | US | |
| 62635223 | Feb 2018 | US |
