Methods for fabricating microstructures by imaging a radiation sensitive layer sandwiched between outer layers

Microstructures are fabricated by imaging a microstructure master blank that includes a radiation sensitive layer sandwiched between a pair of outer layers, on an imaging platform, to define the microstructures in the radiation sensitive layer. At least one of the outer layers is then removed. The microstructures that were defined in the radiation sensitive layer are developed. The radiation sensitive layer sandwiched between the pair of outer layers may be fabricated as webs, to provide microstructure master blanks.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to application Ser. No. 10/661,916, entitled Systems and Methods for Fabricating Optical Microstructures Using a Cylindrical Platform and a Rastered Radiation Beam to the present inventors, filed concurrently, and application Ser. No. 10/661,917, entitled Systems and Methods for Mastering Microstructures Through a Substrate Using Negative Photoresist and Microstructure Masters So Produced to the present inventors, also filed concurrently, both of which are assigned to the assignee of the present application, the disclosures of both of which are hereby incorporated herein by reference in their entirety as if set forth fully herein.

FIELD OF THE INVENTION

This invention relates to microfabricating methods and systems, and more particularly to systems and methods for fabricating microstructures and microstructures fabricated thereby.

BACKGROUND OF THE INVENTION

Optical microstructures are widely used in consumer and commercial products. As is well known to those having skill in the art, optical microstructures may include microlenses, optical gratings, microreflectors and/or other optically absorbing, transmissive and/or reflective structures, the individual sizes of which are on the order of microns, for example on the order of about 5 μm to about 1000 μm in size.

The fabrication of large arrays of optical microstructures is currently being investigated. As used herein, a large array of optical microstructures contains at least about one million optical microstructures and/or covers an area of at least about one foot square. For example, large arrays of microlenses may be used in computer displays (monitors) and/or projection televisions. It will be understood that an array can have uniform and/or nonuniform spacing of identical and/or nonidentical microstructures.

Unfortunately, however, severe scaling barriers may be encountered in attempting to fabricate large arrays of optical microstructures. These scaling barriers may make it difficult to efficiently produce large arrays of optical microstructures with acceptable manufacturing yields.

Several barriers may be encountered in attempting to scale optical microstructures to large arrays. First, the time to master a large array may be prohibitive. In particular, it is well known that optical microstructures may be initially imaged in a “master”, which may then be replicated in one or more second generation stampers to eventually produce large quantities of end products. Unfortunately, it may be difficult to produce a master for a large array of optical microstructures within a reasonable time. For example, calculations may show that it may take years to create a single master for large screen rear projection television. These mastering times may be prohibitive for viable products.

It also may be difficult to image certain optical microstructures that may be desired for many applications. For example, computer displays or projection televisions may employ large arrays of microlenses, wherein each microlens comprises a hemispherical section, which can include a sub-hemisphere (subtends less than 180°), hemisphere (subtends about 180°) or super-hemisphere (subtends more than 180°). However, it may be difficult to master a large array of hemispherical sections using conventional photolithographic techniques. Finally, it may be difficult to efficiently replicate masters containing large arrays of optical microstructures to produce stampers, so as to enable high volume production of optical microstructure end products for display, television and/or other applications.

SUMMARY OF THE INVENTION

Some embodiments of the present invention fabricate microstructures by imaging a microstructure master blank that includes a radiation sensitive layer sandwiched between a pair of outer layers, on an imaging platform, to define the microstructures in the radiation sensitive layer. At least one of the outer layers is then removed. The microstructures that were defined in the radiation sensitive layer are developed. The developed microstructures can produce a microstructure master. The microstructures may comprise optical and/or mechanical microstructures. Subsequent steps can form second generation stampers from the microstructure master, and can fabricate end product microstructures from the stampers. In some embodiments, prior to imaging, the radiation sensitive layer that is sandwiched between a pair of outer layers is fabricated, for example as a web, and is placed on the imaging stage. Some embodiments of the present invention can thereby provide mass production of large microstructure masters.

In some embodiments, the pair of outer layers includes a first outer layer adjacent the imaging platform and a second outer layer remote from the imaging platform. After imaging, the second outer layer is removed from the radiation sensitive layer and the radiation sensitive layer is developed to create a master. A second generation stamper is then created from the microstructure master, by contacting the microstructures in the radiation sensitive layer to a stamper blank.

In particular, some embodiments of the present invention remove the imaged microstructure master from the imaging platform, and use the removed microstructure master to create the stampers. In particular, in some embodiments, the first outer layer is separated from the imaging platform, to thereby remove the imaged microstructure master from the imaging platform. The first or second outer layer is then separated from the radiation sensitive layer and the radiation sensitive layer is developed. A second generation stamper is then created from the microstructures that were developed in the radiation sensitive layer by contacting the microstructures in the radiation sensitive layer to a stamper blank. In some embodiments, the microstructures are pressed against the stamper blank. In other embodiments, the microstructures are rolled against the stamper blank.

Moreover, some embodiments of the present invention can use combinations of planar and/or nonplanar imaging and/or stamping platforms. More specifically, in some embodiments, the imaging platform is a planar imaging platform, and the second generation stamper is created from the microstructures that were developed in the radiation sensitive layer by pressing the microstructures in the radiation sensitive layer against a stamper blank. In other embodiments, the imaging platform is a cylindrical imaging platform and the second generation stamper is created by rolling the microstructures that were developed in the radiation sensitive layer against a stamper blank. Thus, these embodiments can also use the imaging platform itself as a stamping platform. Moreover, in other embodiments, the radiation sensitive layer that has been removed from the imaging platform is developed and is then attached to a planar or nonplanar stamping platform for creating stampers.

In some embodiments of the present invention, mass production and mass replication of masters may be provided. In particular, after a first microstructure master that comprises a radiation sensitive layer sandwiched between a pair of outer layers, is removed from the imaging platform, a second microstructure master that comprises a radiation sensitive layer sandwiched between a pair of outer layers, is imaged on the imaging platform, to define microstructures in the radiation sensitive layer. Imaging of the second microstructure master can at least partially overlap in time with creation of stampers from a previously imaged first microstructure master.

Embodiments of the invention have been described above primarily with respect to methods of fabricating microstructures. However, it will be understood by those having skill in the art that other embodiments of the invention can provide analogous systems for fabricating microstructures.

Apparatus for fabricating a blank for a microstructure master, according to some embodiments of the present invention, include a radiation sensitive material coating station that is configured to coat a layer of radiation sensitive material that is configured to accept an image of microstructures, on a first flexible web. A laminating station also is provided that is configured to laminate a second flexible web to the layer of radiation sensitive material that is configured to accept an image of microstructures, opposite the first flexible web. The radiation sensitive layer is a negative photoresist layer in some embodiments. The first and second flexible webs are identical in some embodiments. In other embodiments, the negative photoresist layer is sensitive to radiation at a predetermined frequency, the first flexible web is transparent to radiation at the predetermined frequency. In yet other embodiments, the second flexible web is opaque to radiation at the predetermined frequency. Analogous methods of fabricating a blank for a microstructure master also may be provided.

Blanks for microstructure masters according to some embodiments of the present invention include a pair of closely spaced apart, flexible webs, and a radiation sensitive layer that is configured to accept an image of microstructures between the pair of closely spaced apart, flexible webs. In some embodiments, the radiation sensitive layer contains therein a latent image of optical microstructures. In some embodiments, the radiation sensitive layer is a negative photoresist layer.

In some embodiments, the pair of flexible webs are identical. In other embodiments, the negative photoresist layer is sensitive to radiation at a predetermined frequency, and the pair of flexible webs are transparent to radiation at the predetermined frequency. In yet other embodiments, one of the pair of flexible webs is transparent to radiation at the predetermined frequency, and the other of the pair of flexible webs is opaque to radiation at the predetermined frequency. These blanks may be used to form large area masters for microstructures according to some embodiments of the present invention.

DETAILED DESCRIPTION

It will be understood that when an element such as a layer, region or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. Furthermore, relative terms such as “top” or “outer” may be used herein to describe a relationship of one layer or region to another layer or region relative to a base structure as illustrated in the figures. It will be understood that these relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. Finally, the term “directly” means that there are no intervening elements.

Embodiments of the present invention will be described herein relative to the fabrication of optical microstructures, which may include microlenses, optical gratings, microreflectors and/or other optically-absorbing transmissive and/or reflective structures, the individual sizes of which are on the order of microns, for example on the order of about 5 μm to about 1000 μm, in size. However, it will be understood that other embodiments of the present invention may be used to fabricate mechanical microstructures such as pneumatic, hydraulic and/or microelectromechanical system (MEMS) microstructures, which may be used for micro-fluidics, micro-pneumatics and/or micromechanical systems, the individual sizes of which are on the order of microns, for example on the order of about 5 μm to about 1000 μm, in size.

FIG. 1is a perspective view illustrating systems and methods of fabricating optical microstructures according to some embodiments of the present invention. As shown inFIG. 1, a cylindrical platform or drum100that includes a radiation sensitive layer110thereon, is rotated about an axis102thereof, for example in a direction shown by the arrow104. As used herein, the term “radiation sensitive” encompasses any photo-imageable material, including, but not limited to, photoresist. As also shown inFIG. 1, simultaneously, a radiation beam such as a laser beam120, generated by a laser122, is axially rastered or scanned in opposite axial directions shown by the arrows124, across at least a portion of the radiation sensitive layer110, to image optical microstructures132in the radiation sensitive layer110. The image so formed may also be referred to as a latent image. It will be understood that, although embodiments of the invention are generally described herein with respect to laser beams and laser sensitive photoresists, other coherent or incoherent radiation beams, such as electron beams, may be used, along with compatible radiation sensitive layers.

It will also be understood by those having skill in the art that the radiation sensitive layer110may be directly on the cylindrical platform100, as shown inFIG. 1, or one or more intervening layers may be provided between the radiation sensitive layer110and the cylindrical platform100, as will be described in detail below. Moreover, one or more layers may be provided on the radiation sensitive layer110, remote from the cylindrical platform100, as will be described in detail below. Other embodiments of the radiation sensitive layer110also will be described below. Moreover, the cylindrical platform100may be rotated about axis102at a constant angular velocity and/or at variable angular velocity.

Still referring toFIG. 1, in some embodiments, the laser122is a Continuous Wave (CW) laser that emits radiation at a frequency or frequency band to which the radiation sensitive layer110is sensitive. In some embodiments, the laser beam120may be rastered axially over the entire axial length of the cylindrical platform. However, in other embodiments, as will be described in more detail below, the laser beam124may be rastered over relatively small portions of the cylindrical platform100.

Finally, it will be understood that, although only a small number of optical microstructures132are shown for the sake of illustration, conventionally large numbers of optical microstructures132are fabricated to provide, in some embodiments, a large array of optical microstructures. Although optical microstructures132are shown inFIG. 1as being microlenses in the shape of a hemispherical section, in other embodiments other microstructures, such as optical grating structures, may be formed as a plurality of uniformly and/or non-uniformly spaced, identical and/or non-identical optical microstructures132. Combinations of different types of optical microstructures, with uniform and/or nonuniform sizes and/or spacings, also may be fabricated.

FIGS. 2–4illustrate other embodiments of the present invention wherein the cylindrical platform100and/or the laser beam120are translated axially relative to one another, simultaneous with the platform rotation and beam rastering, to image the optical microstructures across at least a substantial portion of the length of the cylindrical platform100. In some embodiments, the axial translation can allow optical microstructures to be formed across substantially the entire axial length of the cylindrical platform100. In some embodiments, the cylindrical platform100may be maintained at a fixed axial position and the laser122and/or the laser beam120may be translated along the axial direction. In other embodiments, the laser122and/or laser beam120may be maintained in a fixed axial location and the cylindrical platform100may be translated axially. In still other embodiments, both the laser122and/or laser beam122, and the cylindrical platform100, may be translated relative to one another axially. For example, the laser122may be fixed at one end of the cylindrical platform100and laser optics such as a mirror may be configured to translate the laser beam122relative to the cylindrical platform, for example by moving axially and/or rotating.

FIGS. 2–4illustrate embodiments of the present invention wherein the cylindrical platform100is translated axially relative to a fixed laser122. More specifically, referring toFIG. 2, the cylindrical platform100is translated axially along an axial translation direction shown by arrow224, by moving a support210relative to a base220using rollers222and/or other conventional mechanisms. As shown inFIG. 2, continuous translation of the cylindrical platform110along the translation direction224is provided, to thereby image the optical microstructures132in a continuous spiral pattern230in the radiation sensitive layer110.

FIG. 3illustrates other embodiments of the present invention wherein a stepwise translation of the cylindrical platform100relative to the laser beam120, along a translation direction324, is provided, to thereby image the optical microstructures132in discrete bands330in the radiation sensitive layer. In embodiments ofFIG. 3, continuous rotation of the cylindrical platform100in the rotation direction of arrow104may be provided and stepwise translation of the cylindrical platform may be provided along a translation direction324after an individual band330has been imaged. It will be understood that the cylindrical platform100may continue to rotate through less than one, one, or more than one complete revolutions during the stepwise translation of the cylindrical platform100.

InFIG. 3, imaging of each band330begins and ends at the same predetermined rotation angle of the cylindrical platform100, to thereby provide a pattern of aligned bands330in the radiation sensitive layer110. A guardband may be provided in a band, to separate the beginning and end of the band from one another. Alternatively, the beginning and end of a band may abut against one another.

In contrast, inFIG. 4, the cylindrical platform100is stepwise translated axially along the translation direction324at staggered rotation angles of the cylindrical platform100, to thereby image the optical microstructures132in a staggered band pattern430. In some embodiments, the beginning and/or ends of a band may be uniformly staggered relative to one another, as shown by the band beginnings/ends432. In other embodiments, non-uniform staggering of band beginnings/ends, as shown at434, may be provided. Combinations of aligned (FIG. 3) and staggered (FIG. 4) band patterns also may be provided. It also will be understood that combinations of the imaging systems and methods ofFIGS. 1–4may be provided in a single radiation sensitive layer110. In some embodiments, the spiral/band structures ofFIGS. 2–4may not be detected after all the optical microstructures are imaged and developed so that uniformly spaced optical structures are produced. However, in other embodiments, at least some aspects of the spiral/band structures may be detected after development.

FIGS. 5A–5Cand6A–6C illustrate the rastering of a radiation beam, such as a laser beam120, across at least a portion of a radiation sensitive layer, such as a radiation sensitive layer110ofFIG. 1, to image optical microstructures, such as the optical microstructures132ofFIGS. 1–4, in the radiation sensitive layer, according to various embodiments of the present invention. For ease of illustration, only a portion of the radiation sensitive layer110and the microstructures132are shown.

FIG. 5Ais a top view of a portion of the radiation sensitive layer110andFIG. 5Bis a cross-sectional view of the radiation sensitive layer110taken through line5B–5B′ ofFIG. 5A. As shown inFIGS. 5A and 5B, the radiation beam, such as the laser beam120ofFIGS. 1–4, is axially rastered across at least a portion of the radiation sensitive layer110, to image the optical microstructures132in the radiation sensitive layer, by axially rastering the laser beam120across at least a portion of the radiation sensitive layer110, while varying the amplitude of the laser beam. More specifically, as shown inFIGS. 5A–5C, axial rastering takes place by axially rastering the laser beam120across at least a portion of the radiation sensitive layer110while varying the amplitude of the laser beam, to thereby image the optical microstructures132in the radiation sensitive layer110. In particular, as shown inFIG. 5A, in some embodiments, the rastering may provide three scans510,512,514across the radiation sensitive layer110in the axial direction124. The scans are spaced apart from one another due to the rotation of the cylindrical platform100. InFIG. 5A, the laser beam is rastered along a first axial direction, shown as to the right inFIG. 5A, to image the optical microstructures and then blanked, as shown by dashed lines520,522and524in a second axial direction that is opposite the first axial direction, shown as to the left inFIG. 5A. During the axial scans510,512,514, the amplitude of the laser beam may be varied as shown inFIG. 5C, to produce the optical microstructures132.

Thus, as shown inFIGS. 5A–5C, the amplitude of the laser beam120is continuously varied to image the optical microstructures132in the radiation sensitive layer110. Moreover, the axial rastering is performed at sufficient speed, relative to the rotating of the cylindrical platform100, such that the laser beam120images an optical microstructure132over a plurality of scans of the laser beam, shown as three scans510,512,514inFIGS. 5A–5C. It will be understood that, in some embodiments, an optical microstructure may be imaged in a single scan and, in other embodiments, two scans or more than three scans may be used. Moreover, in some embodiments, a plurality of lasers may be used to perform more than one scan simultaneously.

It also will be understood that the amplitude of the laser beam120may not be a linear function of the shape of the optical microstructure that is being imaged, due to nonlinear absorption/development characteristics of the radiation sensitive layer110and/or other well-known nonlinear effects. In particular, the prediction of the shape that will result from the imaging may involve a detailed understanding not only of the beam profile and intensity, and the way in which they vary in space and time, but also the manner in which the radiation sensitive layer responds to the radiation energy deposited in it (“exposure curves”). In addition to the parameters involved in the exposure, the response of the radiation sensitive layer can also be affected by various post-exposure development parameters. The desired amplitude of the laser beam120during a scan may be determined empirically by trial and error, to arrive at a desired amplitude that produces a desired image of an optical microstructure, by using simulators, by using a mathematical convolution function that defines the relationship between laser dose and a developed image in a radiation sensitive layer and/or by using other conventional techniques that need not be described in detail herein.

FIGS. 6A–6Cillustrate other embodiments of the invention wherein the radiation sensitive layer110is imaged during forward and return scanning of the laser beam rather than blanking the laser beam120during its return. Higher density and/or higher speed may thereby be obtained at the potential expense of greater complexity.

Thus, as shown inFIGS. 6A–6C, imaging is performed in a first (forward) axial direction, shown as to the right inFIG. 6Aby scan lines610,612and614, and in a second direction that is opposite the first direction, shown as to the left inFIGS. 6A–6C, during return scans620and622. As was the case with respect toFIG. 5, fewer or larger numbers of scans may be provided. It also will be understood that embodiments ofFIGS. 5and/or6may be combined with any of the embodiments ofFIGS. 1–4.

FIG. 7is a block diagram of other systems and methods for fabricating optical microstructures according to other embodiments of the present invention. As shown inFIG. 7, a continuous wave laser beam120is generated by a continuous wave laser710, and power control stabilization may be provided by a power control stabilizer712. In other embodiments, a “quasi-continuous wave” laser beam may be provided, using, for example, a switchable semiconductor laser. A modulator714, which in some embodiments may be an acoustooptical (AO) modulator714, is used to vary the amplitude of and raster the laser beam120. In some embodiments, separate modulators may be used to modulate the amplitude of the laser beam120and to raster the position of the laser beam120. The modulator714is capable of imparting angular deflection to the beam, to provide a limited range of motion, without having to move the platform100on which the radiation sensitive layer110is placed. Moreover, other conventional techniques for changing the amplitude and/or position of the laser beam120also may employed. For example, the amplitude of the laser beam may be changed at the laser710itself, and the position may be rastered using a conventional scanner that employs rotating and/or oscillating mirrors.

Continuing with the description ofFIG. 7, a mirror, prism and/or other optical element(s)716may be used to change the direction of the laser beam120if desired. Beam shaping optics718may be used to control the shaping of the laser beam120, to form an ellipsoidal (such as circular) and/or polygonal (such as square) beam with an intensity profile thereacross which may be constant, Gaussian and/or follow other conventional profiles. An auto-focus system722also may be provided to control the focal point of the laser beam120relative to the cylindrical platform100. The design and operation of Blocks710–722are well known to those having skill in the art and need not be described in detail herein. These blocks may be referred to collectively as an optical train, or as a radiation beam system. Moreover, it will be understood that some of the Blocks712–722need not be used in optical trains or radiation beam systems according to other embodiments of the present invention. Accordingly, embodiments ofFIG. 7can generate a continuous wave laser beam120and modulate the laser beam to vary an amplitude thereof, while simultaneously oscillating the laser beam to raster the laser beam across at least a portion of the radiation sensitive layer110.

In particular, it may be difficult to fabricate microstructures with uniform and/or varying profiles and/or heights with high accuracy. Some embodiments of the present invention can use continuously varying intensity radiation beam, such as a laser beam120, to form optical microstructures. This can allow creation of arbitrary three-dimensional profiles of optical elements in real time with high accuracy. In order to produce features at a high enough rate to permit the mastering of large numbers of optical microstructures using multiple exposures per optical microstructure, the laser beam120may be modulated in intensity and spatially at a rate of at least about 1 kHz and, in some embodiments, at MHz rates. AO modulation can provide this capacity, since the beam can be rastered and amplitude modulated at these frequencies. The focal plane or other aspects of the beam profile also may be changed rapidly, to vary the depth in the radiation sensitive layer110at which a maximum amount of radiation energy is deposited.

Still continuing with the description ofFIG. 7, a control system and/or method, also referred to herein as a controller, also may be provided. The controller730may include dedicated hardware and/or one or more enterprise, application, personal, pervasive or embedded computer systems that may be interconnected via a network, to execute one or more computer programs. The controller730may be centralized and/or distributed. The controller730may be used to control some or all of blocks710–722using conventional control techniques. In addition, the controller730may be designed to control the angular rotation6of the cylindrical platform100, the translation X of the cylindrical platform100, and the amplitude and position of the laser beam120relative to time, to image optical microstructures according to any of the embodiments that are described herein, or combinations thereof. The design of a controller is well known to those having skill in the control art, and need not be described further herein.

In some embodiments, the controller730is capable of synchronizing the beam exposure and placement as provided by Blocks710–722, with the desired physical location on the radiation sensitive layer110where the exposure is to take place. In some embodiments, systems/methods ofFIG. 7may be in operation for periods of up to about 24 hours or more at a time, so that the controller730should be capable of maintaining parameters within their desired tolerances over this period of time.

Moreover, in some embodiments of the present invention, the controller730can control an auto-focus system722, to perform additional functions. In particular, in some embodiments, the focal length of the laser beam120may be varied simultaneous with the rotation of the cylindrical platform100and the axial rastering the laser beam120, to at least partially compensate for radial variation in the cylindrical platform100and/or thickness variation in the radiation sensitive layer110. In other embodiments, the focal length of the laser beam120also may be varied to image portions of the optical microstructures at varying depths in the radiation sensitive layer110. In still other embodiments, the focal length of the laser beam120is varied to vary the exposure of the radiation sensitive layer110, to provide the desired optical microstructure. Combinations and subcombinations of these focal length control mechanisms may be provided, alone or in combination with amplitude control of the laser beam120.

In some embodiments, the optical microstructures132that is imaged in the radiation sensitive layer110ofFIGS. 1–7is developed at a developing station, as will be described in detail below. The developed radiation sensitive layer can provide a master for optical microstructure end products, which may be used, for example, in computer displays and/or televisions.

Additional discussion of embodiments of the present invention that were illustrated inFIGS. 1–7now will be provided. In particular, as was described above, conventional approaches for mastering optical microstructures may encounter severe scaling barriers when applied to at least about one million elements and/or covering at least about one foot square in area. In these structures, it may be difficult to image a master in a reasonable time. In sharp contrast, some embodiments of the present invention can perform on the order of one million separate exposures per second, with sufficient resolution and accuracy to produce on the order of 10,000 optical microstructures per second, so that a master for a large rear screen projection television can be fabricated in hours, rather than years using conventional technologies.

Some embodiments of the present invention can place a small laser beam, for example of diameter of about 5 μm, of sufficient intensity to expose a radiation sensitive layer, and modulate this beam in intensity and location at, for example, MHz speeds. A cylindrical platform on which the radiation sensitive layer can be placed or mounted, can be moved accurately and quickly by computer control. A control system synchronizes the placement of the modulated beam on the platform, to expose the proper portion of the radiation sensitive layer with the correct amount of radiation.

Dimensions and speeds according to some embodiments of the present invention will now be provided, to provide an appreciation of the scale in which some embodiments of the present invention may operate. However, these dimensions and speeds shall be regarded as examples, and shall not be regarded as limiting. In particular, in some embodiments of the present invention, the cylindrical platform100may be about three feet in length and about five feet in circumference. The radiation sensitive layer110may be between about 10 μm and about 150 μm thick. A band of the rastered laser beam124may be between about 1 μm and about 1000 μm in axial length. A hemispherical section lens that is about 75 μm in diameter may be fabricated using 10 scans per lens, wherein return scans are blanked. The cylindrical platform100may rotate at an angular velocity of about 60 revolutions/minute and the rastering may be performed at a frequency of about 500,000 scan/sec. Given these parameters, it may take about 2 hours to fabricate about 200 million microlenses.

FIG. 8is a cross-sectional view of systems and methods for fabricating optical microstructures according to other embodiments of the present invention. As shown inFIG. 8, a radiation beam such as a laser beam820from a laser822, which may correspond to the laser110and/or710ofFIGS. 1–7, is impinged through a substrate800that is transparent thereto into a radiation sensitive layer810thereon, which may correspond to the radiation sensitive layer110ofFIGS. 1–7, to image optical microstructures832, which may correspond to optical microstructures132ofFIGS. 1–7, in the radiation sensitive layer810. As was already described, the radiation beam may be coherent and/or incoherent. Moreover, as used herein, a “transparent” substrate allows at least some of the incident radiation to pass therethrough. Imaging of a radiation beam through a substrate that is transparent thereto into a radiation sensitive layer810on the substrate may be referred to herein as “back-side” imaging or “substrate incident” imaging. It will be understood by those having skill in the art that, inFIG. 8, although the substrate800is shown above the radiation sensitive layer810, other orientations of the substrate800, radiation sensitive layer810, laser beam820and laser822may be used to provide back-side imaging, according to various embodiments of the present invention.

Moreover, in providing back-side imaging of radiation sensitive layers810to fabricate optical microstructures832according to some embodiments of the present invention, many systems and methods may be used to move the laser beam820and the substrate800relative to one another. Some of these systems and methods are illustrated inFIGS. 9–11.

In particular, referring toFIG. 9, a cylindrical platform900, which may correspond to the platform100ofFIGS. 1–7, may be used according to any of the embodiments that were described above in connection withFIGS. 1–7. Thus, as shown inFIG. 9, a laser beam820is impinged through a cylindrical substrate800into a cylindrical radiation sensitive layer810that is on a cylindrical platform900. The substrate800may be flexible. In yet other embodiments, the structure ofFIG. 9may be used independent of any of the embodiments ofFIGS. 1–7. Moreover, in still other embodiments, the laser beam820may be produced and/or directed inside the cylindrical platform900, and the cylindrical platform900may constitute a transparent substrate.

FIG. 10illustrates other embodiments wherein a laser beam820is impinged through a polygonal substrate800′ into a polygonal-shaped radiation sensitive layer810′ that is on a polygonal platform1000. In some embodiments, the substrate800′ is rectangular or square, the radiation sensitive layer810′ is rectangular or square, and the polygonal platform1000is a rectangular or square high precision X–Y table that can be translated continuously and/or in a stepwise manner along orthogonal X and/or Y directions, as shown inFIG. 10.

Finally,FIG. 11illustrates other embodiments wherein a laser beam820is impinged through an ellipsoidal substrate800″ into an ellipsoidal radiation sensitive layer810″ on an ellipsoidal platform1100. In some embodiments, the ellipsoidal substrate800″ is a circular substrate800″, the ellipsoidal radiation sensitive layer810″ is a circular radiation sensitive layer, and the ellipsoidal platform1100is a circular platform that is mounted on a spindle1104for rotation, as shown by arrow1102.

In any of the embodiments ofFIGS. 9–11, an optical train or system corresponding, for example, to elements710,712,714,716,718and/or722ofFIG. 7may be provided, along with a controller such as controller730ofFIG. 7. Similarly, in any of the embodiments ofFIGS. 9–11, the laser beam may be maintained stationary and/or may be rastered, and relative translation between the radiation sensitive layer and the laser beam may be provided by translation of the laser822, the laser beam820and/or the platform100,1000or1100, as was already described in connection withFIGS. 1–7.

FIG. 12is a cross-sectional view of other embodiments of the present invention. In these embodiments, a negative photoresist layer1210is used as a radiation sensitive layer, with or without a substrate1200, and a radiation beam such as a laser beam820is impinged into the negative photoresist layer. Embodiments ofFIG. 12may be used in combination with any of the embodiments described above or which will be described below.

As is well known to those having skill in the art, photoresist is available in two tones: positive and negative. Positive photoresist is designed so that the areas of photoresist that are exposed to radiation are removed in the development process. Negative photoresist is designed so that the areas of photoresist that are exposed to radiation remain after development and the unexposed portions are removed. Both types have been used in conventional integrated circuit fabrication, although positive photoresist now may be more commonly used due to its ease of adaptation to integrated circuit fabrication. Conventionally, negative photoresist may not be regarded as being applicable for fabricating optical microstructures. See, for example, U.S. Published Patent Application 2002/0034014 entitled Microlens Arrays Having High Focusing Efficiency, to Gretton et al., published Mar. 21, 2002.

In particular, in a negative photoresist, only the portion of the photoresist which is exposed will remain after developing. Thus, in a thick film of photoresist, such as may be used to fabricate optical microstructures, only a shallow portion of an outer layer of the photoresist layer may be exposed. The latent image that is formed by exposure may then be washed away when the unexposed photoresist beneath it is removed during development. Some embodiments of the present invention may arise from a realization that negative photoresist may indeed be used in fabricating optical microstructures. In fact, some embodiments of the invention may arise from a realization that negative photoresist may provide advantages in fabricating optical microstructures, especially when coupled with back-side imaging. One example of a negative photoresist that can be used is SU-8™, which is a negative photoresist formed of epoxy novolac polymers and marketed by MicroChem Corp.

FIGS. 13A–13Bare cross-sectional views of embodiments of the present invention that combine back-side imaging of, for example,FIG. 8, along with the use of negative photoresist of, for example,FIG. 12. In particular, as shown inFIG. 13A, a radiation beam such as a laser beam820is impinged through a substrate800that is transparent thereto into a negative photoresist layer1310on the substrate800, to image optical microstructures132therein. Accordingly,FIG. 13Aalso illustrates optical microstructure products, according to some embodiments of the invention, which include a substrate800and an exposed layer of negative photoresist1310on the substrate800, which is exposed to define thereon optical microstructures132.FIG. 13Billustrates the imaged negative photoresist layer1310after development, to form optical microstructures132′. Accordingly,FIG. 13Balso illustrates optical microstructure products1350, according to some embodiments of the invention, which may provide an optical microstructure master, and which include a substrate800and a patterned layer of negative photoresist on the substrate800, which is patterned to define optical microstructures132′ thereon. It will be understood that any of the embodiments ofFIGS. 1–11may be used to fabricate embodiments ofFIGS. 13A and 13B.

Back-side imaging into a negative photoresist layer according to some embodiments of the present invention may provide many potential advantages with respect to the fabrication of an optical microstructure master. Some potential advantages now will be described in detail.

In particular, as is well known to those having skill in the art, once a master is created, a conventional replication process may then be employed to make multiple copies from the master. Each generation of replica generally is a negative of the previous generation. Referring toFIG. 14, a master1400may be created using back-side imaging through a substrate800into a layer of negative photoresist thereon, to create optical microstructures132′, for example as was described in connection withFIGS. 13A and 13B. A large number, for example on the order of up to about 1,000 or more, second generation stampers1420may be produced from a single master, using conventional techniques. As seen inFIG. 14, the stampers1420are negative replicas of the master1400with convexities turned into concavities and vice versa. Then, a large number, such as on the order of up to about 1,000 or more, end products1430, such as microlenses for computer displays or televisions, may be created from each stamper1420. The end products1430are the mirror image of the stampers1420, so that they correspond to a positive image of the master1400.

Accordingly, in the example shown inFIG. 14, on the order of up to one million or more end products1430may be created from a single master1400using only two generations of replication. In contrast, when using a positive photoresist, the master may be a negative of the desired shape, so that the first generation of replicas will be positives. In order to produce positive end products, second and third generations of replication may need to be provided. Unfortunately, third generation replicas may not be sufficiently faithful to the original pattern to be commercially viable. In contrast, a negative photoresist can be used to make a positive copy of the desired shapes in two generations of replication, as shown inFIG. 14, so that up to millions or more of high-quality end products1430may be produced from a single master1400, according to some embodiments of the invention.

FIGS. 15 and 16illustrate other potential advantages of back-side imaging combined with negative photoresist according to some embodiments of the present invention. In particular,FIG. 15illustrates an example of optical microstructures on a substrate1500. As shown inFIG. 15, it generally may be desirable to form optical microstructures having walls that are orthogonal to the substrate1500, as shown by microstructure1522, or lens or prism microstructures1524and1526, respectively, having bases1532adjacent the substrate1500and vertices or tips, generally referred to herein as “tops”,1534, remote from the substrate1500, wherein the bases1532are wider than the tops1534. Moreover, it may be desirable to form some microstructures, such as microstructure1528, that are short relative to other taller microstructures1522,1524and/or1526.

As shown inFIG. 16, some embodiments of the invention arise from the recognition that it may be difficult to form these shapes using conventional positive photoresist1610and conventional photoresist-incident (“front-side”) exposure. In particular, as shown inFIG. 16, when using positive photoresist1610and front-side exposure1630as is conventionally used, for example, in the semiconductor industry, the radiation acts as a “punch” to image the outer surface of the photoresist1610opposite the substrate1600. This relationship tends to form images1620a,1620bwhich are the opposite in shape as those which may be desired for optical microstructures (FIG. 15). Moreover, as also shown inFIG. 16, relatively shallow images1620cmay exist only at the exposed surface of the photoresist layer1610and may be washed away during development. See, for example, Paragraphs56–67of the above-cited U.S. Published Patent Application 2002/0034014.

In sharp contrast, as was shown, for example, inFIGS. 13A and 13B, back-side imaging combined with negative photoresist, according to some embodiments of the invention, can produce optical microstructures132′ that include bases1302adjacent the substrate800and tops1304that are narrower than the bases1302, remote from the substrate800. Moreover, as shown inFIG. 17, embodiments of the present invention that image through the substrate800and use negative photoresist1310can provide a photoresist layer1310that is thicker than the desired heights of the optical microstructures1732, so that the radiation beam may be impinged through the substrate800into the negative photoresist layer1310to image buried optical microstructures1732in the negative photoresist layer1310, adjacent the substrate800. As long as the negative photoresist layer1310is at least as thick as the thickest optical microstructure1732that is desired to be fabricated, relatively thick and relatively thin microstructures may be fabricated in one negative photoresist layer, adjacent the substrate800, and may not be washed away during the development process.

FIG. 18illustrates other embodiments of the present invention that may use negative photoresist1310and imaging by a laser beam822through the substrate800. As shown inFIG. 18, when forming a layer of negative photoresist1310over a large substrate800, the photoresist may have non-uniform thickness. However, as shown inFIG. 18, as long as the minimum thickness of the negative photoresist layer1310is thicker than the optical microstructures1832, then buried optical microstructures1832may be imaged in the photoresist layer1310of variable thickness, adjacent the substrate800, that may be independent of the variable thickness of the negative photoresist layer1310.

Other potential advantages of the use of back-side exposure and negative photoresist, according to some embodiments of the present invention, are shown inFIG. 19. As shown inFIG. 19, the negative photoresist layer1310may include impurities1910thereon. When using conventional front-side imaging rather than back-side imaging, these impurities1910may interfere with the front-side imaging. However, when using back-side imaging as shown inFIG. 19, the laser beam822need not pass through or focus on, the outer surface1310aof the negative photoresist1310, remote from the substrate800. Thus, impurities1910need not impact the formation of optical microstructures1832. Accordingly, imaging may take place in a non-clean room environment in some embodiments of the present invention.

Other potential advantages of the use of negative photoresist may include the fact that its chemistry involves a cross-linking of polymers during the exposure and development processes, which may provide added mechanical, chemical and/or thermal stability to the master during the replication process. In addition, since development may remove the bulk of the negative photoresist layer1310from the substrate800, there can be less internal stress remaining in the developed master. A protective layer also may be provided on the negative photoresist layer, opposite the substrate, as will be described below.

Additional discussion of the use of back-side imaging and/or negative photoresist according to some embodiments of the present invention now will be provided. In particular, as was described above, it may be difficult to create desired shapes for optical microstructures using standard lithographic approaches, particularly when applied to thick films of photoresist, i.e., layers of photoresist that are thicker than about 10 μm. Issues of uniformity of the thickness of the photoresist and quality of the photoresist surface can also interfere with the process. Given its base application in integrated circuit fabrication, photolithography has conventionally been performed on substrates such as silicon or other semiconductors which generally are not transparent to the wavelengths of radiation used in the photolithographic process. Accordingly, front-side exposure is conventionally made from the air or free side of the coating of photoresist, remote from the substrate.

In contrast, some embodiments of the present invention expose photoresist through the substrate. Since some embodiments of the present invention need not be concerned with the electrical properties of the substrate that form the master, material such as plastics that are transparent to the wavelengths of radiation that are being employed, may be used. Thus, the photoresist can be exposed through the substrate. Although back-side exposure is applicable in principle to both positive and negative photoresists, it may be particularly beneficial when using negative photoresist.

When exposed through the substrate, negative photoresist can naturally form shapes with their bases adjacent the substrate. In contrast, front-side exposures generally involve some attenuation of the beam energy as it penetrates through the photoresist film. This attenuation generally provides more exposure on the top of the photoresist than at the base thereof, resulting in undercutting. With back-side exposure, there also may be attenuation, but the attenuation can be in the desired direction, with the base of the structure receiving more exposure than the top.

Using back-side exposure, the height of the feature to be formed also can be rendered independent of the thickness of the photoresist. This may be difficult with front-side exposure, since the exposure may need to proceed all the way through the photoresist, from the outer surface of the photoresist to the base thereof, in order to not be washed away. Accordingly, some embodiments of the present invention can make shapes of varying heights, and the uniformity of the thickness of the photoresist and the quality of the photoresist surface need not play a critical role in determining the quality of the optical microstructures.

FIG. 20illustrates optical microstructures according to some embodiments of the present invention. As shown inFIG. 20, these optical microstructures include a substrate2010and a patterned layer of negative photoresist2020on the substrate2010, which is patterned to define therein optical microstructures2032. In some embodiments, the negative photoresist2020is sensitive to radiation at an imaging frequency, and the substrate2010is transparent to the imaging frequency.

In some embodiments, the optical microstructures comprise a plurality of optical microstructures2032including bases2034adjacent the substrate2010and tops2036remote from the substrate2010that are narrower than the bases2034. In some embodiments, the substrate2010is a flexible substrate. In other embodiments, the optical microstructures comprise a plurality of hemispherical sections including bases2034adjacent the substrate and tops2036remote from the substrate. In some embodiments, the substrate2010and the patterned layer of negative photoresist2020provide an optical microstructure master2000.

In some embodiments, the substrate2010is cylindrical, ellipsoidal or polygonal in shape. In other embodiments, the substrate2010is at least one foot long, one foot wide and/or one square foot in area. In yet other embodiments, the microstructures comprise microlenses. In still other embodiments, the optical microstructures comprise at least about one million optical microstructures2032. In still other embodiments, the photoresist2020may be a negative photoresist. Optical microstructures ofFIG. 20may be fabricated according to any of the methods that were described above in connection withFIGS. 1–14and/or17–19.

Embodiments of the present invention that can allow mass production of optical microstructure masters, which can be used to master large numbers of optical microstructures, now will be described. In particular,FIG. 21is a flowchart of operations that may be performed to fabricate optical microstructures. As shown in Block2110, an optical microstructure master that comprises a radiation sensitive layer sandwiched between a pair of outer layers is imaged on an imaging platform. Any of the imaging platforms and/or techniques that were described in any of the previous figures may be used. Moreover, other embodiments of imaging platforms and/or techniques will be described below. In some embodiments the pair of outer layers comprises a first outer layer adjacent the imaging platform and a second outer layer remote from the imaging platform. It will be understood that, as used herein, the terms “first” and “second” are merely used to denote two different outer layers, and that the positions and/or functions of the first and second outer layers may be reversed from those described herein.

Then, referring to Block2120, at least one of the outer layers is removed. As will be described in detail below, in some embodiments, the first outer layer is removed from the radiation sensitive layer, to thereby separate the radiation sensitive layer and the second outer layer from the imaging platform, while the first outer layer at least temporarily remains on the imaging platform. In other embodiments of the present invention, at least one outer layer is removed from the imaging platform by removing the optical microstructure master, including the radiation sensitive layer sandwiched between the first and second outer layers, from the imaging platform. Subsequent processing may be performed to develop the imaged radiation sensitive layer and to create second generation stampers and third generation end products from the developed radiation sensitive layer.

FIG. 22is a flowchart of operations that may be performed to fabricate optical microstructures according to other embodiments of the present invention. In particular, as shown inFIG. 22, at Block2210, an optical microstructure master blank or precursor is fabricated by sandwiching a radiation sensitive layer between a pair of outer layers. In some embodiments, a precursor or blank for an optical microstructure master includes a pair of closely spaced apart flexible webs and a radiation sensitive layer that is configured to accept an image of optical microstructures, between the pair of closely spaced apart flexible webs, as will be described in detail below.

Still referring toFIG. 22, at Block2220, the master blank is placed on an imaging platform. Many examples will be provided below. At Block2230, the master blank is imaged to define optical microstructures. At Block2240, at least one outer layer is removed, for example as was described in connection with Block2120ofFIG. 21. Many other examples will be provided below. At Block2250, a second generation stamper is created by contacting the optical microstructures in the radiation sensitive layer to a stamper blank. Then, at Block2260, end products, such as microlenses for computer displays or televisions, are created by contacting the stamper to final product blanks.

FIG. 23is a schematic diagram of systems and methods that may be used to fabricate optical microstructure master blanks according to some embodiments of the present invention, which may correspond to Block2210ofFIG. 22. As shown inFIG. 23, a first roller2340aor other conventional supply source contains thereon a flexible web of a first outer layer2310. A radiation sensitive layer coating station2350is configured to coat a radiation sensitive layer2320on the first outer layer2310using one or more conventional coating techniques. As was described above, for example in connection withFIG. 18, some embodiments of the present invention can allow optical microstructure masters to be imaged in the radiation sensitive layer2320independent of thickness variations of the radiation sensitive layer2320.

Still referring toFIG. 23, a second roller2340bor other conventional supply source contains thereon a web of a second outer layer2330. A lamination station, which can include a roller2340cand/or other conventional laminating devices, is used to laminate the second outer layer2330to the radiation sensitive layer2320opposite the first outer layer2310, which is then gathered on a take-up roller2340dor other storage device. Thus, as shown inFIG. 24, a blank or precursor structure2400for an optical microstructure master, according to some embodiments of the invention, includes a pair of closely spaced apart flexible webs2310and2330, and a radiation sensitive layer2320that is configured to accept an image of optical microstructures, between the pair of closely spaced apart flexible webs2310and2330.

Optical microstructure master precursors2400ofFIG. 24may be used in any of the embodiments described above in connection withFIGS. 1–22. In some embodiments, the radiation sensitive layer2320can embody the layers110,810,810′,810″,1210,1310,1610and/or2020that were described above. In some embodiments, the second outer layer2330can provide a flexible, optically transparent substrate, which may correspond to the substrate800,800′,800″,1200,1600and/or2010that were described above. The first outer layer2310can provide a release layer that may be placed adjacent an imaging platform in any of the preceding figures, to allow release of the optical microstructure master precursor2400from an imaging platform after imaging. The first outer layer2310may also function as a pellicle, which can protect the radiation sensitive layer2320from contaminants prior to, during and/or after imaging, so that fabrication, storage and/or imaging of the optical microstructure master precursors2400need not take place in a clean room environment. The first outer layer2310also may function as an optically absorbing, reflective or transmissive layer during the imaging process. Combinations of these and/or other properties also may be provided in the first outer layer2310. It also will be understood that the first outer layer2310and/or the second outer layer2330can comprise a plurality of sublayers.

Still referring toFIG. 24, in some embodiments of the present invention, the radiation sensitive layer2320is a negative photoresist layer, as was described extensively above. In other embodiments of the present invention, the first outer layer2310and the second outer layer2330are identical. In still other embodiments, the negative photoresist layer2320is sensitive to radiation at a predetermined frequency, and the second outer layer2330is transparent to radiation at the predetermined frequency. In still other embodiments of the present invention, the second outer layer2330is transparent to radiation at the predetermined frequency and the first outer layer2310is opaque to radiation at the predetermined frequency. As was also already described, the structure and/or functions of the first and second outer layers may be reversed.

In some embodiments of the present invention, the optical microstructure master blank or precursor2400includes a second outer layer2330that is transparent to the wavelengths of radiation used in exposure, is flat, relatively free of imperfections (i.e., of optical quality), clear and without haze, It may be desirable for the radiation sensitive layer2320to adhere well to the second outer layer2330, and it may be desirable for the second outer layer2330to be relatively impervious to the chemicals and thermal processes that may be involved in developing the radiation sensitive layer. In some embodiments, the second outer layer2330comprises plastic, such as polyester, polycarbonate and/or polyethylene. The first outer layer2310also may comprise plastic, such as polyester, polycarbonate and/or polyethylene.

Embodiments of the present invention as shown inFIGS. 23 and 24may be contrasted with conventional mastering approaches for optical microstructures, which generally have been performed on expensive and/or inflexible substrates such as glass, silica or silicon. These masters may not exceed 300 mm in diameter. In contrast, embodiments of the present invention as shown inFIGS. 23 and 24can fabricate large area master blanks from webs, which may be more than about a foot wide in some embodiments. The master blanks can be set up for exposure, and can permit rapid turnaround of the imaging platform or mastering machine. Thus, embodiments of the present invention as shown inFIGS. 23 and 24can be used where the imaging platforms may be expensive and/or require long lead time items. The master blanks can be placed on the imaging platform for imaging, and then taken off the imaging platform to free the imaging platform for another master blank, as will be described in detail below.

FIGS. 25A–25Eare cross-sectional views of systems and methods of fabricating optical microstructures according to some embodiments of the present invention. As shown inFIG. 25A, a flexible optical microstructure master blank or precursor2400ofFIG. 24is wrapped around a cylindrical imaging platform2500, which may correspond to one of the imaging platforms ofFIGS. 1–4,7and/or9that were described above. In some embodiments, imaging can take place through the second outer layer2330according to any of the techniques for back-side imaging that were described above, to produce an image of optical microstructures in the radiation sensitive layer2320. Accordingly,FIG. 25Aillustrates some embodiments of Blocks2110,2220and/or2230.

Then, referring toFIG. 25B, in some embodiments, the first outer layer2310can act as a release layer, which can permit removal of the second outer layer2330and the imaged radiation sensitive layer2320′ from the first outer layer2310. The imaged radiation sensitive layer2320′ is developed to produce optical microstructures2320″ as shown inFIG. 25C. Thus,FIG. 25Cillustrates another embodiment of a completed optical microstructure master2550, andFIGS. 25B and 25Cillustrate embodiments of Blocks2120and/or2240.

A second generation of optical microstructures, also referred to as a stamper, is created from the master2550that contains the optical microstructures2320″ in the developed radiation sensitive layer, by contacting the optical microstructures2320″ to a stamper blank. This may correspond to Block2250. In particular, as shown inFIG. 25D, contacting to a stamper blank may take place by mounting the master2550on a planar stamping platform2510, and pressing the planar stamping platform2510against a stamper blank2520in the direction shown by arrow2512. In other embodiments, as shown inFIG. 25E, the master2550is placed on a cylindrical stamping platform2540, and rolled in the direction of arrow2542against a stamper blank2520, to create a stamper.

FIGS. 26A and 26Billustrate other embodiments of the present invention, which may be formed in operations of Blocks2120and/or2240. InFIG. 26A, the step of removing at least one outer layer is performed by removing the entire imaged master blank2400from the imaging platform2500. Then, inFIG. 26B, the first outer layer2310is removed from the imaged radiation sensitive layer2320′, and the imaged radiation sensitive layer2320′ is developed, to provide the master2550.

FIG. 27illustrates yet other embodiments that may be formed in operations of Blocks2110,2220and/or2230, according to other embodiments of the present invention, wherein the optical microstructure master precursor2400is imaged on a planar imaging platform2700, which may correspond to the imaging platform1000or1100of respectiveFIG. 10or11. After imaging ofFIG. 27, removal (Blocks2120and/or2240) may take place as was described in connection withFIG. 25Band/orFIG. 26A. Moreover, stamping operations may take place as was described in connection withFIGS. 25Dand/or25E. Accordingly, imaging may take place on a planar or nonplanar imaging platform, and stamping may take place on a planar or nonplanar stamping platform, which may or may not be the same platform as the imaging platform, according to various embodiments of the present invention.

Additional discussion ofFIGS. 21–27, according to some embodiments of the present invention, now will be provided. In particular, an optical microstructure master blank or precursor2400may be held on a cylindrical imaging platform, such as platform2500ofFIG. 25A, or on a planar imaging platform, such as platform2700ofFIGS. 27, using electrostatic charge, vacuum chuck, adhesive tape and/or other conventional techniques which may be depend on the thickness, weight and/or flexibility of the master blank2400. Moreover, after imaging or exposure inFIGS. 25Aand/or27, the optical microstructure master precursor2400undergoes post-exposure development of the radiation sensitive layer, to create a master, such as the master2550ofFIGS. 25Cand/or26B.

It will be understood by those having skill in the art that removable optical microstructure master precursors2400can be used for both front-side and back-side exposures, and with both positive and negative photoresists. However, some embodiments of the present invention use back-side exposure and negative photoresist, as was described extensively above. When using back-side exposure and negative photoresist, the first outer layer2310may be removed after imaging. Removal of the first outer layer2310may take place on the imaging platform as was described, for example, inFIGS. 25A and 25B, or after removal of the imaged master from the imaging platform as was described inFIGS. 26A and 26B.

Accordingly, embodiments of the present invention that were described above in connection withFIGS. 21–27can provide for removing of the first outer layer2310from the imaged radiation sensitive layer2320′, to thereby remove the imaged radiation sensitive layer2320′ from the imaging platform2500or2700after imaging has taken place. A stamper may be created from the optical microstructures2320″ by contacting the optical microstructures2320″ to a stamper blank2520. In other embodiments, the first outer layer2310is separated from the imaging platform2500or2700after imaging has taken place. Then, the first outer layer2310is separated from the imaged radiation sensitive layer2320′. A stamper may be created from the optical microstructures2320″ by contacting the optical microstructures2320″ to a stamper blank2520. In some embodiments, the optical microstructures are pressed against a stamper blank (FIGS. 25D). In other embodiments, the optical microstructures are rolled against a stamper blank (FIG. 25E).

Removable optical microstructure master blanks as were described in connection withFIGS. 21–27may be particularly suitable for mass production of masters and stampers according to some embodiments of the present invention. In particular, as shown inFIGS. 28, imaging of an optical microstructure master precursor2400may take place, while creating stampers from an optical microstructure master2550that was previously imaged. Thus, imaging of an optical microstructure master precursor and creating stampers from a previously imaged microstructure master precursor at least partially overlap in time.

Thus, a potentially expensive and/or long lead time optical imaging platform2500may be used on an almost continuous basis for imaging, by removing an optical microstructure master precursor from the imaging platform2500, after imaging. However, in other embodiments of the present invention, the imaging platform also may be used as a stamping platform, by not removing the imaged optical microstructure master precursor from the imaging platform. It will be understood that inFIG. 28, cylindrical and/or planar imaging platforms may be used, and pressing and/or rolling of the master against the stamper blank may be used, as was described in connection withFIGS. 25–27.

Mastering on removable substrates can permit the same machine and/or platform to be used to form masters with a number of different radiation sensitive layers, coated on different substrates of varying thickness. The use of negative photoresist and exposure through the substrate can permit use of removable masters according to some embodiments of the present invention, since the surface of the photoresist that is attached to the imaging platform can be removed during developing and, thus, need not be involved in the final production of the optical elements. Similarly, it is possible to employ simple, rapid and/or relatively inexpensive techniques of coating photoresist onto the substrate when using negative photoresists and back-side exposure, according to some embodiments of the present invention.

Accordingly, some embodiments of the present invention can provide a master for replicating large numbers of optical microstructures that are formed by multiple exposures through a transparent, removable substrate, into negative photoresist on a removable substrate. This can provide commercially viable mastering systems, methods and products for large numbers of optical microstructures. In some embodiments of the present invention, masters of at least about one foot long, about one foot wide and/or about one foot square, containing up to about one million or more microstructures of about 100 μm or smaller in size, can be mastered in about 8 to 15 hours. Optical elements with arbitrary shapes can be formed by varying exposure from point to point in the master. The spacing of the elements in the master can be varied from widely separated to overlapping. The master can be created on a removable substrate, so that the mastering platform can be reconfigured for further mastering work.

Finally, it will be understood that embodiments of the present invention have been described herein relative to the fabrication of optical microstructures, which may include microlenses, optical gratings, microreflectors and/or other optically-absorbing transmissive and/or reflective structures, the individual sizes of which are on the order of microns, for example on the order of about 5 μm to about 1000 μm, in size. However, it will be understood that other embodiments of the present invention may be used to fabricate mechanical microstructures such as pneumatic, hydraulic and/or microelectromechanical system (MEMS) microstructures, which may be used for micro-fluidics, micro-pneumatics and/or micromechanical systems, the individual sizes of which are on the order of microns, for example on the order of about 5 μm to about 1000 μm, in size.