Patent Application
20080054508
The invention is in the field of manufacturing optical elements, in particular refractive optical elements and/or diffractive micro-optical elements, using a replication process that includes embossing or moulding steps. More particularly, the invention features a replication tool for manufacturing a plurality of elements.
Replicated optical elements include diffractive and/or refractive micro-optical elements for influencing an optical beam in any pre-defined manner, refractive elements such as lenses, potentially at least partially reflecting elements etc.
When optical elements are produced by replication, there is often a basic configuration involving a substrate and replication material on a surface thereof, which replication material is shaped and hardened in the course of a replication process.
Of special interest are the wafer-scale fabrication processes, where an array of optical elements is fabricated on a disk-like (“wafer-”) structure, which subsequently to replication is separated (“diced”) into parts constituting the individual elements. ‘Wafer scale’ refers to the size of disk like or plate like substrates of sizes comparable to semiconductor wafers, such as disks having diameters between 2 inches and 12 inches.
In wafer-scale replication processes, a single blob of replication material for the replica is disposed on the substrate. However, in such process, depending on properties of the replication material, the aspect ratio of replicated structures in wafer-scale replication is limited. If the structures to be replicated are not flat and have a high aspect ratio, it is difficult to make sure that all structures are duly filled by replication material. Also for structures with a limited aspect ratio, one has to dispense a large amount of replication material in order to make sure that also in peripheral regions enough replication material remains so that all structures are replicated. Often, it will happen that air gets trapped against the replication surface, e.g., in the mould. This causes defects in the finished replicated elements. In the case of optical elements, defective elements are rejected.
The invention, in one embodiment, features a replication tool and process for manufacturing optical elements that can improve the quality of optical elements replicated and reduce the occurrence of defects.
In one aspect, the invention features a method of manufacturing a plurality of optical elements by replication. A replication tool includes a plurality of replication sections. Each replication section defines a negative structural feature that defines the shape of a respective optical element. A plurality of individual portions of a replication material are applied a substrate and/or the replication tool. Each individual portion is associated with a respective negative structural feature. The replication tool is moved relative to the substrate to shape the plurality of individual portions of the replication material. Each individual portion of the replication material is discrete and shaped according to the respective replication section. The replication material is hardened to form the plurality of optical elements. Each optical element is discrete, optically transparent, and attached to the substrate.
In another aspect, the invention features a method of manufacturing a plurality of optical elements by replication. A replication tool includes a plurality of replication sections. Each replication section defines a dome-shaped portion that defines the shape of a respective optical element. An individual portion of a replication material is dispensed into each dome-shaped portion. The replication tool and a substrate are moved toward each other until the replication material contacts a surface of the substrate. The replication material is hardened to form the plurality of optical elements. Each optical element is discrete and associated with a dome-shaped portion of the replication tool. The replication tool can be removed, and the substrate is separated between adjacent optical elements to form a plurality of discrete sections of the substrate. Each discrete section is associated with a dome-shaped portion of the replication tool and includes a single optical element.
In other examples, any of the aspects above, or any apparatus or method described herein, can include one or more of the following features. The replication material can be in at least one of a plastically deformable, viscous, or liquid state. Each optical element can be a refractive lens.
In some embodiments, the replication tool can be moved against the substrate to shape the plurality of individual portions of the replication material. In certain embodiments, the plurality of individual portions of the replication material can be applied to the plurality of replication sections of the replication tool. The replication material can be applied while the replication sections are facing downwards. The individual portions of the replication material can be applied to the negative structural features of the replication sections. In certain embodiments, the replication material is applied to the substrate.
In various embodiments, a dispensing tool is used to apply the plurality of individual portions of the replication material. The dispensing tool can include a plurality of replication material loading portions. A surface of the dispensing tool can be dipped into a volume of the replication material to cause the replication material to adhere to the replication material loading portions. In certain embodiments, the replication material is transferred to at least one of the substrate and the replication tool by bringing the replication material loading portions into contact with the substrate and/or the replication tool. The individual portions of the replication material can be sequentially applied using an automated dispensing tool.
In some embodiments, each individual portion of the replication material includes a single drop of replication material. The single drop of replication material can be applied to the substrate and/or the replication tool. In certain embodiments, each individual portion of the replication material includes a plurality of droplets of replication material. The plurality of droplets can be applied to the substrate and/or the replication tool. Each droplet of each individual portion of the replication material can be applied through a nozzle or orifice. For example, ink jet technology can be used to apply the droplets. In some embodiments, each droplet of an individual portion of the replication material remains discrete from an adjacent droplet after being applied. The plurality of droplets join together to form the optical element when the replication tool and the substrate are moved together.
In some embodiments, flow of the plurality of individual portions of the replication material is limited along a surface of the substrate. In some embodiments, the substrate is separated along dicing lines associated with lateral positions of the substrate where replication material is not present.
In certain embodiments, a predetermined volume of replication liquid is applied locally and individually to at least one of the tool or the substrate prior to pressing the tool against the substrate. This allows providing a plurality of cavities with an optimal amount of replication liquid, and reducing or eliminating the volume of surplus liquid that is removed or diverted from the critical areas of the substrate when a plurality of elements was formed from a single blob of replication liquid.
After replication, the replication tool can be removed, and the substrate with the replication material thereon can be separated (“diced”) into parts each containing an individual element. The invention features the additional advantage that it is possible to confine the replication material on the individual elements, e.g., to have regions on the individual elements where the substrate is not covered by replication material.
The replication section of the tool defines a replication surface or section with (concave or convex) negative structural features, being a negative of at least some of the structural features of the element to be produced.
While the replication tool and the substrate are in the replication position—in which the replication tool and the substrate are moved together, the replication material can be hardened. In some embodiments, the replication tool is placed on the substrate. Depending on the replication material chosen, it may be hardened by curing, for example, UV curing. As an alternative it may be hardened by cooling. Depending on the replication material chosen, other hardening methods are possible. Subsequently, the replication tool and the replication material are separated from each other. For most applications, the replication material remains on the substrate. The optical element typically is a refractive and/or diffractive optical element, but also may e.g. also have a micromechanical function at least in regions.
The tool can include a plurality of replication sections, e.g., cavities or protrusions, thus allowing for the simultaneous manufacturing of a plurality of elements on a common substrate, which on the substrate are preferably arranged in an array-like manner. The tool can include a plurality of replication sections, thus allowing for the simultaneous manufacturing of an array of elements on a common substrate. This common substrate can be part of an opto-electronic or micro-opto-electronic assembly having optical and electronic elements produced on a wafer scale and later diced into separate parts.
In certain embodiments, the portion of replication material is applied to the tool, namely to the replication section. Preferably, the replication section is filled, at least to a large part, so that the critical locations of the replication section corresponding to the highest feature of the future element, which are most sensitive and prone to defects, are filled.
In some embodiments, the flow or dispersion of replication material across the tool is limited by the replication section being a convex part of the lower tool surface, e.g., convex features protruding from a surface of the tool. For example, the tool can be kept in this orientation, i.e. facing downwards, while being moved to and against the substrate. The substrate to which the replication material is applied in this manner (each convex part carrying a droplet of the replication material) can: be flat and absent any particular structure of the flat surfaces, except, optionally, structures for alignment; have concave receiving sections arranged opposite to the convex parts that are filled with replication material by moving the tool against the substrate; or have flat, concave or irregularly structured receiving surface sections, with the tool applying the replication material droplets to these receiving surface sections. In this case, with the indices of refraction of the hardened replication material and the substrate are preferably of similar magnitude. Then the exact height and surface structure of the substrate has little or no optical influence, and the optical properties and location of the optical element being formed are defined by the location of the tool, which may be better to control than that of individual features or surfaces of the substrate. The receiving sections in both latter cases can be arranged in a grid that is the mirror image of the grid defined by the convex replication sections on the tool.
In some embodiments, the replication material is applied to the convex replication sections by dipping the replication sections into the surface of a volume of replication material. The volume may be a pool in a container, or an amount of replication material spread over a surface. The replication sections are preferably dipped only as far to wet only the replication sections, leaving the rest of the tool surface free from replication material. Alternatively, the rest of the tool surface may be non-wetting with respect to the replication material, such that, when removing the lower surface of the tool from the volume of replication material, it remains free from replication material. The convex replication sections may be treated chemically or mechanically, or may be made of another material, in order to have a better wetting property, causing a droplet of replication material to adhere to each of replication sections.
In certain embodiments, a dispensing tool is used for dispensing the replication material on the substrate and/or the replication tool. The dispensing tool, according to this embodiment is based on the above principle. The dispensing tool can include a plurality of protruding replication material loading portions, which are arranged in an array corresponding to the array of replication sections of the replication tool. The replication material loading portions can be dipped into the surface of a volume of replication material. The protruding portions are preferably dipped only as far to wet only portions themselves, leaving the rest of the tool surface free from replication material. Then, the dispensing tool is brought into contact with the surface of the replication tool or the substrate, so that amounts of replication material stick to the replication tool or substrate surface, respectively. Instead of or in addition to being protruding, replication material loading portions may be made of another material than the surrounding surface of the dispensing tool to have a better wetting property, causing a droplet of replication material to adhere to each of the replication material loading portions. Dispensing in individual portions can be a fully parallel process.
In some embodiments, the portion of replication material is applied to the substrate. The replication material forms a droplet isolated from other droplets of replication material. The droplet can have a convex shape.
Applying the replication material in individual portions can, depending on the material properties of the replication material, provide an advantage when replicating structures with a high aspect ratio (deep cavities). When the tool with the replication section is moved against the droplet, the convex surface of the droplet reaches into the replication section, and can displace air at the critical location, before the tool touches the substrate. This is in contrast to the state of the art, where the entire surface of the substrate is covered with replication material, such that, when spacers surrounding the replication sections reach the replication material, the replication material can block air trapped in the replication section from escaping. This approach can be combined with any variant of the previous approach, e.g., the replication material may be applied to both the tool and the substrate.
The flow limiting means can be include an edge and/or an area of reduced wetting surrounding a material receiving area of the substrate. Such an area of reduced wetting is created by mechanical and/or chemical treatment of the surface of the substrate. Alternatively or in addition, such an area is created by an inlay of other material arrange in the surface of the substrate. The surface of the material receiving area may be treated as well, to increase its wetting capability.
Further, preferably, the replication tool can include spacer portions, which can allow for an automated and accurate thickness control of the deformable material on the substrate. The spacer portions can include “leg like” structures built into the tool. In addition, the spacers prevent the deformation of the micro optical topography since the spacers protrude further than the highest structural features on a tool.
The spacer portion is preferably available in a manner that it is ‘distributed’ over at least an essential fraction of the replication tool, for example, over the entire replication tool or at the edge. This means that features of the spacer portion are present in an essential fraction of the replication tool, for example, the spacer portion include a plurality of spacers distributed over the replication surface of the replication tool. The spacers allow for an automated and accurate thickness control of the deformable material layer.
As an alternative or in addition to spacers abutting the substrate surface, the replication tool can include a “floating spacer”, e.g., spacers that remain at a certain distance from the substrate surface during the replication process. The spacers can rest against a portion of the replication material. Floating spacers and/or contact spacers can surround a dome-shaped cavity that defines the shape of a refractive lens to be replicated.
The replica (for example, a micro-optical element or micro-optical element component or an optical micro-system) can be made of epoxy, which is cured, e.g., UV cured, while the replication tool is still in place. UV light curing is a fast process that allows for a good control of the hardening process. Depending on the replication material used, also other hardening processes are possible, for example by cooling, chemical reaction, delay time, etc. For most applications, the replication material is transparent.
Further preferred embodiments are evident from the dependent patent claims. Features of the method claims may be combined with features of the device claims and vice versa.
The subject matter of the invention will be explained in more detail in the following text with reference to preferred exemplary embodiments, which are illustrated in the attached drawings, which schematically show:
FIGS. 3-6: cross sections through further tools and substrates in various production stages;
FIGS. 7-11: details of cross sections of substrates and tools;
The first spacer portion 1 on the one hand can serve to define the shape or the boundary of the element 6 in the region close to a substrate body, henceforth simply referred to as substrate 7, and on the other hand to define the height of the element 6 with respect to the substrate 7. That is, the first spacer portion 1 comes to rest against the substrate 7 or at a controllable distance from the substrate 7. The latter distance, called “element spacer height difference”, is determined by the vertical extension of second spacer portions 2 relative to that of the first spacer portion 1. The second spacer portions are contact spacer portions protruding further than the first spacer portions and being, during replication, in direct contact with the substrate. In some embodiments, the local, first spacer portion 1 comes to rest on the substrate 7 without any residual replication material 5 in between, the element spacer height difference being zero, or all spacer portions are at a distance from the substrate, so that the spacer-to-substrate distance is determined by capillary forces and/or surface tension effects or by other means such as by active distance adjusters etc.
In this text, for the sake of convenience, the dimension perpendicular to the surface of the substrate 7, which comprises an essentially flat surface—is denoted as “height”. In actual practice, the entire arrangement may also be used in an upside down configuration or also in a configuration where the substrate surface is vertical or at an angle to the horizontal. The according direction perpendicular to the surface is denoted z-direction. The terms “periphery,” “lateral” and “sides” relate to a direction perpendicular to the z-direction. The terms “periphery” and “sides” of the element are thus understood when looking at the substrate from a direction perpendicular to the essentially flat substrate. The element covers a part of the substrate, and the surrounding other parts of the substrate, i.e. the region of space adjacent to both the substrate and the functional part of the element, in particular under the first spacer portions, may be covered with the replication material, without interfering with the function of the element.
The replication tool preferably is made of materials with some elasticity, for example PDMS (polydimethylsiloxane) or another elastic material. This results in a conformal thickness control of the element 6 produced, even if the substrate surface, on which the process is executed is not perfectly planar, or if the replication tool is not perfectly planar.
The tool 9 is preferably adapted to be used in wafer-scale processing, e.g., the substrate containing the array of replication sections may be disc-shaped. Thus, the diameter of the tool 9 preferably lies in a range from 5 cm to 30 cm. Wafer-scale combination of manufacturing with micro-electronics is possible, as is for example disclosed in WO 2005/083 789 by the same applicant, herewith incorporated by reference.
In the alternative step of
In another preferred embodiment of the invention, the first spacer portions 1 do not surround every replication section 3, but are e.g. separate pillars dispersed over the replication area 12. In this manner, a certain area of the substrate 7 can remain covered with a thicker section of the replication material 5 which is not functional, as compared to the elements 6.
Starting out from either the arrangement of
The tool-scale spacer portions 2 touch the substrate 7 without any replication material 5 in between, such that most of the weight of the tool 9 rests on the tool-scale spacer portions 2. The first spacer portions 1 can be separated from the substrate 7 by the element spacer height difference, the resulting volume being filled with replication material 5.
The replication material 5 is then hardened by thermal or UV or chemical curing.
In
In certain embodiments, the replication material 5 is applied to a plurality of convex replication sections 16 of the tool 9 simultaneously by dipping the tool 9 into the surface of the replication material 5. When drawing out the tool 9, droplets 19 of the replication material 5 can remain hanging from the convex replication section 16. This offers a significant advantage of speed and simplicity over the individual dosing with a syringe.
The tool 9 comprises spacers 23—which may be floating spacers or contact spacers—such that the tool 9 rests on the substrate 7 at a defined distance. The arrangement of
In
In
While the invention has been described in present preferred embodiments of the invention, it is distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practised within the scope of the claims.
This application is a continuation-in-part of U.S. patent application Ser. No. 11/384,563 filed Mar. 20, 2006, the disclosure of which is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11384563 | Mar 2006 | US |
| Child | 11943476 | Nov 2007 | US |
