FABRICATION OF BINARY MASKS WITH ISOLATED FEATURES

An environmentally benign method for producing binary microfabrication masks is disclosed. An optical target may be provided that includes a water-soluble polymer material in contact with an ultraviolet radiation transmittable substrate. A laser may be focused on a primary mask to produce a mask image, the mask image thereafter being reduced by demagnification optics to provide a reduced image. The optical target may be exposed to the reduced image to create features of reduced size from the primary mask. The water-soluble polymer exposed to the ultraviolet radiation may be ablated from the optical target. The optical target may be subsequently metalized using a metal vapor to coat the remaining polymer material and exposed substrate. The metalized optical target may be contacted with an aqueous fluid to remove the metalized polymer material leaving the binary mask.

BACKGROUND

Laser microfabrication masks with micron sized spatial features are used in a number of industrial processes including the fabrication of integrated circuits, MEMS devices, and materials with attractive optical properties. Such microfabrication masks may be fabricated by a number of processes to create masks with either continuous or isolated features. Masks having continuous features may be manufactured using photolithographic methods employing negative primary masks or by direct photo-writing on a substrate. Masks having isolated features, however, may typically be manufactured using photolithographic methods employing positive primary masks. Photolithography processes using positive primary masks are typically considered wet process techniques

Wet processing techniques typically use a polymer material fixed to a substrate material, thereby creating an optical target. The optical target may be exposed to an image created by a UV light source, such as a UV laser or other ionizing radiation sources (including, without limitation, e-beam or ion beam), directed through a primary mask. In a negative primary mask process, the polymer material may be chemically altered by exposure to the radiation to make it resistant to a subsequent developing (removal) step. In a positive primary mask process, the polymer material may be either ablated directly or chemically altered by exposure to the radiation to make it more susceptible to removal during a subsequent developing step. Isolated target features can be more readily fabricated using a positive primary mask process. Wet processing derives its name from the use of chemical washes used during the process, such as during substrate preparation, optical target developing, material removal/etching, and additional cleaning steps.

One potential drawback in wet fabrication processes is the type of chemicals that may be used both for a development stage and/or a final cleaning stage of the target. Typical polymer materials may use chemical solvents requiring special handling to prevent environmental contamination. It is therefore desirable to develop a wet process for fabricating binary masks having isolated features that may employ environmentally benign chemicals.

SUMMARY

In an embodiment, a method of fabricating a laser binary microfabrication mask includes providing a radiation transmittable substrate, contacting the substrate with a water-soluble polymer material, thereby forming an optical target, exposing at least a portion of the optical target to a mask image formed by passing radiation through a primary mask, thereby etching at least a portion of the water-soluble polymer material, contacting the optical target with a metal vapor, thereby forming a metalized target comprising at least one metalized substrate portion and at least one metalized polymer material portion, and exposing the metalized target to an aqueous fluid, thereby removing the metalized polymer material portion.

In an embodiment, a system for fabricating a laser binary microfabrication mask may include a laser radiation source; a metal vapor source; a primary mask having a first side and a second side, the primary mask configured to receive radiation from the laser radiation source on the first side and to emit the radiation on the second side to form a mask image; and an optical target holder configured to hold an optical target, the optical target comprising a radiation transmittable substrate and a water-soluble polymer material, wherein the optical target holder is configured to perform one or more of the following: expose at least a portion of the optical target to the mask image to etch at least a portion of the water-soluble polymer material; contact the optical target with metal vapor from the metal vapor source to form a metalized target comprising at least one metalized substrate portion and at least one metalized polymer material portion; and expose the metalized target to an aqueous fluid to remove the metalized polymer material portion.

DETAILED DESCRIPTION

Microfabrication techniques may find use in the production of many devices having micron and submicron features, such as integrated circuits, MEMS devices, and optical devices with unusual properties, such as photonic devices. Microfabrication methods may include both wet and dry processes. In wet processes, such as photolithography, a laser light beam may be focused on a primary mask to produce a mask image overlaid on an optical target coated with a polymer material. In photolithography, after exposure to the image, the polymer material may be solubilized to leave a blocking layer on the target which may thereafter be subjected to a succession of further steps, including, as one non-limiting example, exposure to a metal vapor to coat the target with a thin metal film.

One disadvantage of some forms of wet processes may include the use of a polymer material that can only be removed from the optical target through the use of environmentally intrusive solvents. Examples of such solvents may include one or more of acetone, methanol, isopropanol, ethyl glycol acetate, cyclopentanone, dimethyl formamide, and dimethyl sulfoxide, among others. After use, such solvents may require appropriate storage techniques to keep them away from the environment. It may therefore be appreciated that a photolithography process that may use a polymer material removable by simple aqueous solutions may improve the potential ecological impact of micromachining binary masks.

It may be appreciated that a binary mask produced by the method and system disclosed below may be used for a variety of microfabrication techniques, including but not limited to photolithography, direct laser writing, e-beam lithography, and ion beam lithography. While the reflectivity and resistance to thermal degradation of such binary masks may preferentially suggest their use with direct laser microfabrication techniques, it may be appreciated that techniques requiring lower laser power may similarly benefit from the use of such binary masks.

In an embodiment, a system for fabricating a laser binary microfabrication mask may include a laser radiation source; a metal vapor source; a primary mask having a first side and a second side, the primary mask configured to receive radiation from the laser radiation source on the first side and to emit the radiation on the second side to form a mask image; and an optical target holder configured to hold an optical target, the optical target comprising a radiation transmittable substrate and a water-soluble polymer material. The optical target holder can be configured to perform one or more of the following: expose at least a portion of the optical target to the mask image to etch at least a portion of the water-soluble polymer material; contact the optical target with metal vapor from the metal vapor source to form a metalized target comprising at least one metalized substrate portion and at least one metalized polymer material portion; and expose the metalized target to an aqueous fluid to remove the metalized polymer material portion. The radiation transmittable substrate can for example be a UV radiation transmittable substrate. The primary mask can for example be a primary microfabrication mask.

In one embodiment, the system may further include a demagnification optics system having a focal length to receive the mask image and to emit a demagnified mask image, wherein the optical target holder is further configured to expose at least a portion of the optical target to the demagnified mask image.

In one embodiment, the system may further include at least one of an attenuator and a homogenizer, each configured to be optically coupled to radiation from the laser radiation source. In another embodiment, the system may further include at least one of a cylindrical lens, a spherical lens, a doublet lens, a triplet lens, a synthetic fused silica lens, and a lens with an anti-reflective coating, for focusing radiation from the laser radiation source on the first side of the primary mask.

FIG. 1illustrates one embodiment of a binary mask microfabrication system100having a laser110, a variety of optical elements, such as115-140a,b, in the beam path between the laser110and the primary microfabrication mask145, and demagnification optics160located between the primary mask145, and an optical target165. The optical target165may be mounted on a movable stage170, either directly or incorporated in a frame for stabilization. Both laser110and movable stage170may be controlled by computerized devices, such as a laser radiation output controller105to control the output radiation of the laser110and a computer175to control actuators associated with the movable stage170. In one embodiment, the functions associated with controllers105and170may be performed by a single control device. In an alternative embodiment, controllers105and170may be performed by separate devices. The separate devices may be stand-alone, or may be in mutual electronic communication.

Laser110may include any laser used for microfabrication processes. Non-limiting examples of such lasers include a variety of excimer lasers, such as ArF, KrF, XeBr, XeCl, XeF, KrCl, and F2, as well as non-excimer Nd:YAG, N2gas, and HeCd lasers. In some embodiments, the laser can be an ultraviolet (UV) laser. Depending on the laser used, the laser radiation output may lie within a radiation band of about 150 nm to about 1200 nm inclusive of endpoints. In some embodiments, the laser radiation output may lie within a radiation band of about 190 nm to about 360 nm inclusive of endpoints. In some non-limiting examples, the laser radiation output may include at least one wavelength of about 356 nm, about 308 nm, about 266 nm, about 248 nm, about 193 nm, or ranges between any two of these values. Table 1 provides examples of radiation wavelengths associated with some lasers.

Laser controller105may control a variety of laser output parameters via laser control lines102. For example, the laser output may be pulsed, continuous, or a combination of pulsed and continuous beams. In a non-limiting example, the irradiance of the laser output in continuous mode may be less than or equal to about 10 W/cm2. In another non-limiting example, the laser output in pulsed mode may have a pulse energy fluence less than or equal to about 25 mJ/cm2. In one non-limiting embodiment, the laser pulses may have a pulse width of about 1 ps to about 1 μs. In another non-limiting embodiment, the laser pulses may have a pulse width of about 1 ps to about 100 ns. Non-limiting examples of laser pulse widths may include a pulse width of about 1 ps, about 5 ps, about 10 ps, about 50 ps, about 100 ps, about 500 ps, about 1 ns, about 5 ns, about 10 ns, about 50 ns, about 100 ns, or ranges between any two of these values. The pulse width may be fixed for the duration of a particular machining process or may be dynamically varied according to process parameters. For example, pulse shaping may be useful for clean exposure of the optical target to the features of the primary mask image depending on the target material (substrate material and/or polymer material) and feature size. In another embodiment, the pulse width may be fixed at a specific width, such as at about 20 ns. The pulse frequency may also be fixed or dynamically adjusted during machining. In one embodiment, the pulse frequencies may be about 1 Hz to about 50 Hz. Examples of pulse frequency may include, without limitation, about 1 Hz, about 5 Hz, about 10 Hz, about 20 Hz, about 30 Hz, about 40 Hz, about 50 Hz, and ranges between any two of these values. In another embodiment, the pulse frequency may be about 10 Hz. Pulse frequency may be chosen to optimize the exposure of the optical target based on the composition of the substrate material and/or the polymer material, laser power, and laser wavelength.

The laser radiation output can travel an optical path such as the one illustrated inFIG. 1by beam path107a-1. Beam path107ais a path from the laser output to attenuator115which may be used to reduce the beam power as required by the materials composing optical target165. The output of attenuator115may be further directed through a series of focusing optical elements127a-cof focusing optics system125, along beam path107d. The focusing elements127a-cmay include any of a variety or combination of elements, including but not limited to cylindrical lenses, spherical lenses, doublet lenses, triplet lenses, synthetic fused silica lenses and lenses with optical coatings, such as anti-reflective coatings. In one example, the focusing optics may comprise a group of two cylindrical lenses and a spherical lens. In one embodiment, the laser light output from the focusing optics may then be directed through a homogenizer135along beam path107gto provide a uniform intensity beam to illuminate one side of the primary microfabrication mask145. In one embodiment illustrated inFIG. 1, the output beam from attenuator115may pass through additional optical elements such as right angle prisms120and130along beam paths107b-c, and107e-f. Such right angle prisms may be used to maintain the required optical path length within a reasonably sized footprint for a manufacturing facility. Additional optical elements also may include field lenses140a,bcoupled by beam path107h.

The primary microfabrication mask145includes features that will be imaged on optical target165. The primary microfabrication mask may be fabricated from any of a number of materials or combination of materials, including metal sheets, polymer films, or metalized polymer films. Non-limiting examples of metallic sheets include stainless steel, chromium, aluminum or copper, although other malleable metals may also be used. In one embodiment, the metal sheets may have a thickness of about 15 μm to about 1 mm. In another embodiment, the metal sheet thickness may be from about 100 μm to about 150 μm. The metal sheets may be composed of a single metal. Alternately, the metal sheets may comprise layered metals or metals with polymer or metallic coatings. Polymer films may include, without limitation, polyimide, polythene and polytetrafluoroethylene. The primary microfabrication mask may be fabricated by a number of methods. Some non-limiting methods for manufacturing the primary mask may include CNC milling, electrical discharge machining, electro-chemical machining, laser microfabrication, laser etching, electronic beam machining, ion beam machining and plasma beam machining. The primary microfabrication mask may also be fabricated by direct laser etching that uses demagnifying optics to create a binary mask with reduced features from another binary mask.

As disclosed above, the output radiation from laser110can be focused on the upstream side of the primary mask145. On illumination, the features machined in the primary mask may produce an image projected from the downstream side of the primary mask. The image may then be projected through demagnification optics160onto optical target165. In one embodiment, the image from primary mask145may pass directly to the demagnification optics. In another embodiment, the image may be directed along optical path107ito a dichroic mirror/beam splitter150. One image from the dichroic mirror may be directed along beam path107kto a camera155—comprising, for example, a CCD camera with a phosphor screen—to record and/or analyze the image. The camera155may be positioned at an angle with respect to the mirror in order to obtain a useful image. In one non-limiting embodiment, the image data output produced by the camera may be used to program the laser output controller. In an alternative embodiment, the CCD output image may be used to control the position of a movable stage (see below) on which the optical target165is affixed. A second image from dichroic mirror150may be directed along beam path107jto the demagnification optics160.

Demagnification optics160may comprise a number of optical elements. Some non-limiting examples include spherical lenses, Fresnel lenses, diffractive optics systems, doublet lenses, triplet lenses, synthetic fused silica lenses and coated lenses. Spherical lenses may further include corrections for spherical aberrations, coma and astigmatism. Lens coatings may include anti-reflective coatings among others. The demagnification optics may be used to project a reduced image of primary mask145onto the optical target165based on the focal length of the demagnification optics.

One metric to measure the amount of image reduction due to the demagnification optics is the demagnification ratio. The demagnification ratio is the ratio of the object distance divided by the image distance. The object distance is the optical distance from the primary microfabrication mask145to the demagnifying optics160(for example, a distance measured inFIG. 1as the length of beam path107i+beam path107j). The image distance is the optical distance from the demagnifying optics160to the optical target165(for example, the distance of beam path107l). A demagnification ratio greater than 1 indicates that the image on the target has smaller features than those on the primary micromachining mask. In a non-limiting example, the demagnification ratio may be about 2 to about 25. In another non-limiting example, the demagnification ratio may be about 2 to about 12. In another non-limiting example, the demagnification ratio may be about 10. Non-limiting examples of the demagnification ratio may include about 2, about 5, about 10, about 15, about 20, about 25, or ranges between any two of these values.

AlthoughFIG. 1illustrates an embodiment that incorporates a variety of optical elements configured in a specific order, it may be appreciated that other embodiments may include alternative and/or additional optical elements such as slits, collimators, and shutters. Further, alternative embodiments may lack certain of the optical elements illustrated inFIG. 1, or distribute the elements in a different order along the optical beam path. It should be understood that all such variations in optical elements and arrangements may be contemplated by this disclosure.

The optical target165may require sufficient exposure time to the mask image to expose the polymer materials to produce the necessary features. The laser output controller105may be programmed in any number of ways to provide sufficient exposure time to the laser radiation. In some embodiments, the exposure time may be a fixed period of time. In another embodiment, the exposure time may be based on the material composition of the optical target or its thickness. In another embodiment, exposure time may be based on the size of the primary mask features. In yet another embodiment, the exposure time may be based on the output power of the laser. In still another embodiment, the exposure time may be based at least in part on the intensity of an image obtained by camera155.

In order to stabilize the optical target165during laser exposure, the optical target may be fixed within a frame that is mounted on a movable stage170. Alternatively, the optical target may be fixed onto the stage without the use of a frame. The stage motion may be controlled in any one or more of an “x”, a “y”, and a “z” direction. One or more actuators may be provided to move the stage. As non-limiting examples, the actuators may comprise any one or more of a linear motor, a piezoelectric actuator, a pneumatic actuator, or a hydraulic actuator. A combination of actuators may move the target horizontally to provide multiple areas that may be sequentially exposed to the first target image, thereby creating a target of repeating features. In addition, the stage may be moved vertically to focus the demagnified image on the target surface. The actuators may be controlled directly by a computer controller175through a user interface or via appropriate data and power connections177. The computer controller175may also have a user interface to permit a user to program the motion of the actuators.

In some embodiments, a method of fabricating a laser binary microfabrication mask may include providing a radiation transmittable substrate; contacting the substrate with a water-soluble polymer material, thereby forming an optical target; exposing at least a portion of the optical target to a mask image formed by passing radiation through a primary mask, thereby etching at least a portion of the water-soluble polymer material; contacting the optical target with a metal vapor, thereby forming a metalized target comprising at least one metalized substrate portion and at least one metalized polymer material portion; and exposing the metalized target to an aqueous fluid, thereby removing the metalized polymer material portion. The radiation transmittable substrate may be an ultraviolet radiation transmittable substrate. The radiation can be UV radiation.

FIGS. 2A-Dillustrate one embodiment of a method for processing the optical target during and after radiation exposure. InFIG. 2A, the UV radiation225may impinge on a primary mask220producing a mask image230. Although not shown inFIG. 2A, additional optics, such as demagnifying optics, may be placed between the primary mask220and the optical target as illustrated inFIG. 1. The optical target may include a UV transmittable substrate material210in contact with a water-soluble polymer material215. The substrate material210may comprise any suitable UV transmittable material. In one non-limiting example, the substrate material210may transmit radiation having at least one wavelength of about 190 nm to about 360 nm with a transmittance of greater than or about 85%. In another non-limiting example, the substrate material210may transmit radiation having at least one wavelength of about 190 nm to about 360 nm with a transmittance of greater than or about 90%. The substrate material210may be contacted by a water-soluble polymer material215on at least one side of the substrate. Non-limiting examples of such substrate material210may include fused silica, calcium fluoride, magnesium fluoride, and fused quartz.

The physical characteristics of the substrate material210can provide good optical qualities of the resulting mask at the wavelength for which the substrate may be used. Such physical characteristics may include, as non-limiting examples, surface flatness, wedge angle, and scratch and dig figures. If the mask substrate210has a variation of flatness/thickness across the surface, there may be a phase variation at some wavelength of light across the substrate as measured by interferometry. The phase variability may affect the focusing by the substrate210in a non-trivial manner. The phase variability may be reported as lambda/“n” in which lambda is the wavelength of the light used to examine the substrate surface210, and “n” is an even integer related to the number of interference fringes observed in the flatness measurement. In some non-limiting examples, a measurement of lambda/6 as measured using the UV wavelength at which the mask may be used may be a useful amount of flatness. Alternatively, a substrate210having a flatness measurement of lambda/6 as measured at 633 nm may also be useful. Substrate material210having a flatness of lambda/n, in which n is greater than about six, may also be useful in this application.

The surface characteristics of the substrate material210may also include “scratch and dig” values. Such values may indicate the maximum sizes of scratches or pits (digs) present on the polished substrate. The imperfections may be specified by a designation such as “20-10”, “60-40”, or “80-50”, in which the first number indicates the maximum width allowance for a scratch measured in microns, and the second number is the maximum diameter for a dig in hundredths of a millimeter. A substrate material210having a scratch and dig value of about 60-40 or better (such as a value of 20-10) may be useful for the applications disclosed above. Additional surface imperfection requirements may include a combined length of the largest scratches on each surface not exceeding about a quarter of the diameter of the substrate210. Further, in one non-limiting example, the maximum number of digs may be about one or fewer for any 20 mm diameter section on a single surface of the substrate210.

Yet another useful physical characteristic of the substrate material210may include a value of a wedge angle, which represents a deviation of the top and bottom surfaces of the substrate from a true parallel orientation. For an application as substantially disclosed above, a substrate210having a wedge angle less than or about 10 arc minutes may be useful.

The water-soluble polymer material215may be applied to the substrate material210according to any appropriate method including, but not limited to, spin coating, dip coating, evaporative deposition, and cladding. The water-soluble polymer material215may comprise any suitable water-soluble material include one or more of polyvinyl pyrrolidone and polyvinyl alcohol. Such water-soluble polymer materials215may comprise polymers having a molecular weight of about 10,000 daltons to about 150,000 daltons. Non-limiting examples of such water-soluble polymer materials215may have a molecular weight of about 10,000 daltons, about 20,000 daltons, about 40,000 daltons, about 50,000 daltons, about 100,000 daltons, about 125,000 daltons, about 150,000 daltons, or ranges between any two of these values. In one embodiment, the water-soluble polymer material215may have a thickness of about 200 nm to about 500 nm. Non-limiting examples of such water-soluble polymer materials215may have a thickness of about 200 nm, about 250 nm, about 300 nm, about 350 nm, about 400 nm, about 450 nm, about 500 nm, or ranges between any two of these values. In another embodiment, the water-soluble polymer material215may have a thickness of about 20 nm to about 10 μm.

During the fabrication process, the optical target may be exposed to a mask image230formed by the laser output radiation225impinging on the primary mask220. At least a portion of the polymer material215component of the optical target may be exposed to the mask image230. The result of the exposure to the incident image may be to remove the polymer material215, for example by ablation.

FIG. 2Billustrates an example of the results the polymer material being ablated by exposure to the UV radiation. The result of the removal of the polymer material (through ablation is a feature235in the polymer material215that is the complement of the mask image (230inFIG. 2A). After the exposed polymer material215has been removed from the optical target (for example, by ablation), the optical target may then be composed of the exposed substrate210along with polymer material215incorporating the mask image feature235.

The optical target may then be metallized, as illustrated inFIG. 2C. Non-limiting examples of metal that may be deposited on the optical target may include one or more of aluminum, chromium, a nickel/iron alloy, and a nickel/chromium super-alloy. The metal film245deposited on the optical target may have a thickness of about 150 nm to about 200 nm. Non-limiting examples of metal film thickness may include about 150 nm, about 160 nm, about 170 nm, about 180 nm, about 190 nm, about 200 nm, or ranges between any two of these values. The optical target may be metalized by means of a coating system including, but not limited to, thermal vapor deposition, E-beam evaporation, coat sputtering, pulsed laser deposition, chemical vapor deposition, or other similar methods. It may be appreciated that the metallization step will result in a metal film245coating both the remaining polymer material215, as well as any exposed substrate material247.

After the optical target has been metallized, the remaining polymer material215, which may also be coated with a thin film245of metal, may be removed by exposing the optical target to an aqueous fluid. The aqueous fluid may solubilize the remaining polymer material215so it may readily be removed from the substrate material210. In one non-limiting example, the aqueous fluid may comprise distilled water. In other non-limiting example, the aqueous fluid may include one or more of a salt solution, an acidic solution, and a basic solution. Exposing the metalized target to an aqueous solution may include any appropriate means including, but not limited to, one or more of immersion and shaking the metalized target in the aqueous solution. Either or both of these steps may be accomplished for some period of time and/or at some controlled temperature. If both immersion and shaking occur, then the two steps may be run simultaneously or sequentially in any order. The two steps may be run under the same conditions (both time and temperature) or at different times or at different temperatures. In some non-limiting embodiments, the metalized target may be exposed to the aqueous fluid at a temperature of around 300° K. to about 340° K. Non-limiting examples of aqueous fluid temperatures may include about 300° K., about 310° K., about 320° K., about 330° K., about 340° K., or ranges between any two of these values. In one non-limiting example, the aqueous fluid may be at a temperature of around 300° K. In another non-limiting example, the metalized target may be exposed to the aqueous fluid for about 1 minute to about 2 minutes.FIG. 2Dillustrates an example of a non-limiting result of exposing the metalized optical target to the aqueous fluid. It may be observed that the binary mask formed at the end of the process may include the UV transparent substrate material210with the film representing the mask image feature247in contact with the substrate. It may be noted that the mask image feature247may be isolated from any other structure on the substrate material210. It may additionally be appreciated that a final binary mask may comprise one or more features physically isolated from each other.

Additional process steps may also be included in the method to produce a binary mask. In one non-limiting embodiment, the binary mask (which may be considered the optical target after the metalized polymer material has been removed by application of the aqueous fluid) may then be dried. In one non-limiting example, drying the binary mask may be accomplished by gently blowing a gas, such as dry nitrogen gas, over the binary mask. Other gases may be used in the step as well, including one or more of dry argon, dry helium, and dry carbon dioxide. The dry gas may be at any suitable temperature, such as at a temperature of around 300° K. to about 340° K. Non-limiting examples of dry gas temperatures may include about 300° K., about 310° K., about 320° K., about 330° K., about 340° K., or ranges between any two of these values. In one non-limiting example, the dry gas may be at a temperature of around 300° K. An additional step may include examining the binary mask for one or more flaws. Flaws may include one or more of metal film flakes, cracks in the metal film, and retained polymer. In one non-limiting example, the binary mask may be inspected through the use of light microscopy.

FIG. 3is a flow chart of an embodiment of a method for manufacturing the binary mask as disclosed aboveFIG. 2. The method may include providing a substrate material310composed of a UV transmittable material as disclosed above. The substrate may be contacted with a water-soluble polymer material320including a polymeric material such as polyvinyl alcohol as disclosed above. The polymer material may be applied according the any number of methods including spin coating. For the spin coating method, the amount of polymer material applied to the substrate, as well as the spin rotation rate and time of substrate rotation, may depend on a number of parameters including the viscosity of the polymer material, the polymer material temperature, the desired final thickness of the polymer coating on the substrate, and the molecular weight of the polymer. The polymer material-coated substrate may be considered as an optical target available for exposure to UV radiation. The optical target may then be exposed to a mask image330provided by illuminating a primary mask with a source of UV radiation. A variety of optical elements may be used to provide a mask image having the desired size and luminous intensity. Exposure of the polymer material to the mask image may result in polymer material being ablated from the optical target as a result of impinging UV radiation.

After UV exposure resulting in polymer material removal (for example, by ablation), the resulting optical target may be composed of exposed substrate material and substrate material coated with the polymer. The optical target may then be contacted with a metal vapor340that may result in the optical target comprising portions that contain metalized substrate material and metalized polymer material. The optical target may then be exposed to an aqueous fluid350able to remove the metalized polymer material (or any additional polymer material) from the substrate. The resulting optical target, composed of either exposed or film-coated substrate material may form the binary mask.

It may be appreciated that the resulting binary mask may be used to create micromachined devices such as electronic components or MEMS components. Alternatively, such a binary mask may be used in an iterative process to create additional primary masks having reduced feature size.

EXAMPLES

Method for Fabricating Binary Masks

An optical target was fabricated from a fused silica substrate that may transmit UV radiation of about 175 nm to about 360 nm, inclusive of endpoints. A layer of a water-soluble poly vinyl pyrrolidone polymer material was spin-coated on the substrate to a thickness of about 200 nm to about 500 nm. A KrF excimer laser capable of producing 750 mJ pulses with a 25 us pulse width at 248 nm was used to provide the laser output radiation. A homogenizer comprising a pair of 8×8 fixed array insect eye lenses was included to create a uniform illumination field of 20 mm×20 mm at the upstream side of a primary mask. The primary mask was fabricated to have a grid of 100 μm holes. Demagnification optics were selected to provide a mask image having a demagnification ratio of about 10. The target was placed on a micro-machining 3-axis translator to position the target with respect to the demagnified mask image. The optical target was exposed to the mask image from the primary mask in a manner so that the polymer material exposed to the UV radiation was ablated from the optical target. An aluminum film having a thickness of about 150 nm to about 200 nm was deposited on the optical target using physical vapor deposition, thereby depositing the aluminum film of the exposed silica substrate as well as on the polymer material. The aluminum coated polymer material was then removed from the optical target using distilled water. The resulting binary mask had a grid of aluminized pillars or disks about 10 μm in diameter.

Compared to other positive mask photolithography processes, the process disclosed above may take fewer steps, in that only one exposure, one metallization, and one cleaning step may be required. Additionally, other lithographic methods, such as e-beam or X-ray methods, may use polymers like poly methyl-methacrylate or other polymers that may require additional organic etchant solvents like acetone, chlorobenzenes, chloroform, or ketones in the fabrication process. Such organic etchants may require special handling and storage as presenting potentially harmful contaminants to the environment. Further, other than X-ray and some photolithograpy processes, target features greater than about a micron in height may not be easily fabricated. The green process disclosed above may readily be used to fabricate such features.

Method of Contacting a Substrate with a Water-Soluble Polymer Material

Poly vinyl pyrrolidone (PVP) having an average molecular weight of about 40.000 daltons was dissolved in distilled water to make a solution having a concentration of about 100 mg/ml. The PVP solution was spin coated on a fused silica substrate at about 2000 RPM for about 40 sec. The resulting optical target was then baked at about 75° C. for about 50 sec resulting in a generally uniformly coated substrate.

With respect to the use of substantially any plural and/or singular terms in this disclosure, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth in this disclosure for sake of clarity.

It will be understood by those within the art that, in general, terms used in this disclosure, and especially in the appended claims (for example, bodies of the appended claims) are generally intended as “open” terms (for example, the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to.” etc.). While various compositions, methods, and devices are described in terms of “comprising” various components or steps (interpreted as meaning “including, but not limited to”), the compositions, methods, and devices can also “consist essentially of” or “consist of” the various components and steps, and such terminology should be interpreted as defining essentially closed-member groups.

From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed are not intended to be limiting, with the true scope and spirit being indicated by the following claims.