Abstract:
A method for manufacturing an optical assembly comprises providing a first substrate having a first surface, providing a second substrate having a second surface facing the first surface, and forming a patterned microbump on at least a select one of the first surface and the second surface. The method further comprises applying an adhesive to the at least select one of the first surface and the second surface in a region proximate the patterned microbump, and attaching the first substrate to the second substrate by placing the first surface and the second surface in close proximity to one another such that the adhesive contacts both the first surface and the second surface, and wherein the adhesive is held within a preselected area by the patterned microbump.

Description:
Parts of this invention were made with government support under Agreement No. H98230-05-C-0429 awarded by Maryland Procurement. The government may have certain rights in some of the claims of the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates generally to optical element micropositioning systems and methods, and in particular to optical elements including glass-based laser ridges for adhesive confinement. 
     SUMMARY OF THE INVENTION 
     A first aspect of the present invention is a method for manufacturing an optical assembly that comprises providing a first substrate having a first surface, providing a second substrate having a second surface facing the first substrate, and forming at least one patterned microbump on at least a select one of the first surface and the second surface. The method further comprises applying an adhesive to the at least select one of the first surface and the second surface in a region proximate the patterned microbump, and attaching the first substrate to the second substrate by placing the first surface and the second surface in close proximity to one another such that the adhesive contacts both the first surface and the second surface, and wherein the adhesive is held within a given area by the at least one patterned microbump. 
     Another aspect of the invention is an optical assembly that comprises a first substrate having a first surface, and a second substrate having a second surface facing the first substrate, wherein at least a select one of the first surface and the second surface includes at least one patterned microbump. The optical assembly further comprises an adhesive located between and in contact with the first surface and the second surface, wherein the adhesive is held within a preselected area by at least a portion of the at least one patterned microbump. 
     The present inventive method of manufacturing an optical assembly and the resultant optical assembly are compatible with existing laser bump forming processes, and allow arbitrarily-shaped wells and channels to be co-fabricated with laser bumps formed for spacing purposes. The laser ridges or patterned microbumps may be formed relatively rapidly and to the necessary heights, controlled to narrow constraints. Further, the heights of these laser ridges may be set dynamically, based on glass composition variations and upper substrate placement variations. Moreover, the present advantages may be implemented in a wide variety of component types and configurations, provide flexibility in the associated manufacturing process and are particularly well adapted for the proposed use. 
     Additional aspects, features and advantages of the invention are set forth in the detailed description that follows, and in part, will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description that follows, the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of the specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principals and operations of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top perspective view of an optical assembly embodying the present invention; 
         FIG. 2  is a top perspective view of a base substrate including a plurality of spacing microbumps and a patterned microbump formed thereon; 
         FIG. 3  is a cross-sectional view of the optical assembly taken along the line III-III,  FIG. 1 ; 
         FIG. 4A  is a top plan view of the base substrate having a plurality of spacing microbumps and a patterned microbump formed thereon, wherein the patterned microbump is configured to retain an adhesive within a preselected area; 
         FIG. 4B  is a top plan view of the base substrate having a plurality of spacing microbumps and a plurality of patterned microbumps formed thereon, wherein the patterned microbumps surround associated spacing microbumps to prevent adhesive from contacting the spacing microbumps; 
         FIG. 5  is top plan view of the first substrate having a plurality of spacing microbumps, a patterned microbump, and a plurality of gap-filling microbumps formed thereon; 
         FIG. 6  is a cross-sectional view of the first substrate taken along the line VI-VI,  FIG. 7 , with the addition of a second substrate and an adhesive placed therebetween; and 
         FIG. 7  is a top plan view of the base substrate with a plurality of the spacing microbump and the patterned microbump formed thereon, wherein the patterned microbumps defines a preselected area within an adhesive zone and an adhesive reservoir zone located outside of the adhesive zone. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in  FIG. 1 . However, it is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings and described in the following specification are particular embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. 
     The present invention includes optical assemblies and methods that rely on the formation of one or more microbumps in supporting elements that support optical elements within optical assemblies. In the description below, various methods of forming microbumps in light-absorbing supporting elements are described. This is followed by a description of example embodiments of methods for channeling an associated adhesive within an optical element via the formation of one or more patterned microbumps in the light-absorbing alignment element. Example embodiments of optical assemblies formed using the microbump micropositioning methods of the present invention is also described. 
     PYREX, as referenced herein, is a registered trademark of Corning, Inc., of Corning, N.Y. The term “microbump” is broadly understood to include various shapes such as circular islands, elongated ridges, etc., as formed in an IR-absorbing glass substrate using the methods described below. The term “optical element” is understood to mean any type of optical component, such as an optical fiber, a planar waveguide substrate, a lens, a microlens, a grating, a beamsplitter, etc. The term “optical assembly” as used herein includes a system or structure that includes optical elements, whether alone or in combination with other types of elements, such as electrical, electro-optical, electromechanical or mechanical elements. The phrase “light-absorbing substrate” is understood to mean a substrate that absorbs light at an absorption wavelength such as at a visible, near-infrared and/or infrared wavelength, wherein local absorption of the light by the substrate at one or more of the absorption wavelengths locally heats the substrate. 
     The reference numeral  10  ( FIG. 1 ) designates an optical assembly embodying the present invention. In the illustrated example, the optical assembly comprises a base substrate  12 , an upper substrate  14 , and an optical element (not shown) wherein the base substrate  12  and the upper substrate  14  are coupled to one another via an adhesive  16 . The base substrate  12  comprises a light-absorbing material, and preferably an IR light-absorbing glass, such as the family of IR-absorbing PYREX glasses available from Corning, Inc. In the present example, the base substrate  12  includes certain IR-absorbing species such as metal dopants, e.g. Cu, Fe, Co and/or V, that cause the glass to experience a dramatic and local reduction in density when heated rapidly at a given location, resulting in glass expansion. Alternatively, either or both of the substrates  12 ,  14  may comprise the light-absorbing material. The base substrate  12  may be configured to support the optical element thereon, wherein the optical element comprises optical and electro-optical elements/devices as known in the art. 
     The present inventive process generally includes forming spacing microbumps  18  ( FIG. 2 ) and at least one patterned microbump  22  on an upper surface  20  of the base substrate  12  prior to attachment of the upper substrate  14  to the base substrate  12 . In the illustrated example, the base substrate  12  comprises a monolithic light-absorbing glass and may be supported by a movable support stage (not shown) during processing such that the substrate  12  is translatable in the substrate plane relative to either a fixed light or a heat energy source. In a preferred embodiment, the base substrate  12  comprises a glass capable of absorbing light or heat energy in a localized region and in response thereto, rapidly expanding or swelling in the localized heated region. 
     The method of forming both the spacing microbumps  18  and the patterned microbump  22  on the upper surface  20  of the base substrate  12  includes locally heating the base substrate  12 . In the present example, this involves directing a light beam  24  to a localized region of the base substrate  12  as defined by a beam spot  26  formed by the light beam on the upper surface  20  of the base substrate  12 . In an example embodiment, the light beam  24  is convergent. The position of beam spot  26  on the upper surface  20  is selectable either by moving the support stage (not shown) or by adjusting the position of light beam  24  or both. In the present example, a laser generating a light beam  24  having an IR wavelength is utilized, such as a CO 2  laser that emits radiation (e.g., at 10.6 μm). Alternatively, light beams in the near infra-red wavelength (810 nm) may be utilized, so that the relatively long Rayleigh range of a laser-generated light beam  24  ensures that even minor variations in beam focus do not strongly influence the size of beam spot  26  during stage translation. In another alternative embodiment, the light beam  24  includes at least one of a visible wavelength, an NIR wavelength and an IR wavelength. In an example embodiment, visible wavelengths range from ˜400 nm to ˜750 nm, NIR wavelengths range from ˜750 nm to ˜1100 nm, and IR wavelengths include wavelengths in the range from ˜1100 nm to ˜1680 nm. 
     The absorption of light by base substrate  12  from light beam  24  locally heats the base substrate  12  and initially raises the temperature of the portion of the base substrate  12  in proportion to intensity of the light beam  24 . If the light beam  24  has a circularly symmetric cross-sectional intensity distribution, such as a Gaussian distribution, then the beam spot  24  is circular and the substrate expansion occurs over a circular region as well. Absorption of the light by the base substrate  12  to form the patterned microbump  22  is accomplished by passing the light beam  24  over the upper surface  20  of the base substrate  12  in a set pattern. In both the formation of the spacing microbumps  18  and the patterned microbumps  22 , when light beam  24  is locally absorbed by base substrate  12 , a limited expansion zone is created within which the rapid temperature change induces a dramatic decrease in density of the base substrate  12 . Thus, an example embodiment of the method includes modifying the depth of the expansion zone by adjusting the intensity of the light beam  24 , the size of the beam spot  26  and/or the irradiation duration. In an example embodiment, the depth of the expansion zone is changed or made selectable by adjusting the concentration of the IR-absorbing materials in the substrate, as described above. 
     Since the expansion zone is constrained by unheated (and therefore unexpanded) regions of base substrate  12  surrounding the expansion zone, the substrate material within the expansion zone is compelled to relieve internal stresses by deforming upward, thereby forming the spacing microbump  18  or the patterned microbump  22 . In the illustrated example, the surface profile of spacing and patterned microbumps  18 ,  22  corresponds to the light beam intensity distribution, with the microbump peak corresponding to the location of the highest beam intensity. The light beam  24  may be scanned over any surface of the base substrate  12  and stopped at specific locations so as to form microbumps  18 ,  22  of various shapes and sizes. Bump profiles of various sizes and shapes can also be formed by adjusting the light beam power, sweep velocity and/or path during the course of the bump forming process for a single bump. In the instant example, the sweep velocity of the light beam  24  over the upper surface  20  of the base substrate  12  when forming the patterned microbump  22  is preferably greater than or equal to 1.0 mm/sec, while the height of the patterned microbump  22  is preferably maintained within 5% of the total height of the microbump  22 , more preferably within 3% of the total height of the microbump  22 , and most preferably within &lt;0.2 μm. 
     The method of forming the microbumps  18 ,  22  further includes fixing the microbump  18 ,  22  by rapidly cooling the heated region of the base substrate  12 . In an example embodiment, this is accomplished by terminating the irradiation of upper surface  20  of the base substrate  12  by the IR radiation beam  24 . 
     The location, spacing distance d, and height h of the patterned microbumps  18 ,  22  ( FIG. 3 ) are based on a precision characterization of the upper surface  20  of the base substrate  12  and a lower surface  30  of the upper substrate  14 . This characterization accommodates typical variations in the upper surface  20  and the lower surface  30  due to the surface mount process. The relative distance d between the upper surface  20  and the lower surface  30  and the height h may each be determined using one or more methods, including: scanning laser profilometry, image analysis of single-image or stereoscopic views of a coupling region; white light interferometric techniques; probing methods that establish offsets by detecting physical contact; and, combinations of these methods, and transversing a probe mounted on a precision stage though a coupling region and imaging the transversal to provide multiple calibration points in a coupling region. 
     It is noted that a detailed description of the methods and apparatus related to and incorporating the formation of the microbumps within electrical and electro-optical devices is set forth in U.S. patent application Ser. No. 11/365,391, filed Feb. 28, 2006 and entitled GLASS-BASED MICROPOSITION SYSTEMS AND METHODS, which is hereby incorporated by reference herein in its entirety. 
     In the illustrated example, three separate spacing microbumps  18  ( FIG. 1 ) are formed on the upper surface  20  of the base substrate  12 , thereby cooperating to form a platform upon which the upper substrate  14  is supported. The spacing microbumps  18  cooperate to define an adhesive zone or region  32  within which the adhesive  16  is preferably contained so as to avoid interference with the spacing microbumps  18 , or create other problems with the alignment between the base substrate  12  and the upper substrate  14 . The illustrated example further includes a square-shaped patterned microbump  22  that defines a preselected area or adhesive well  34  within the adhesive zone  32  and within which the adhesive  16  is more preferably contained. Subsequent to the formation of the spacing microbumps  18  and the patterned microbumps  22 , the predetermined amount of the adhesive  16  is placed within the preselected area  34  and the upper substrate  14  is lowered onto the base substrate  12  until the bottom surface  30  of the upper substrate  14  contacts an rests upon the spacing microbumps  18 . As is best illustrated in  FIG. 3 , the adhesive  16  is contained within the preselected area  34  by the patterned microbump  22 . It is noted that the height h of the patterned microbump  22  is slightly less than the height of the spacing microbumps  18 , thereby eliminating any interference caused by the abutment of the patterned microbump  22  with the bottom surface  30  of the upper substrate  14 . Further, the adhesive  16  is partially contained within the given area  34  by the cohesive properties within the adhesive  16 . In the illustrated example, the adhesive  16  includes a thin layer of low-shrinking UV curable and/or thermal curing adhesive. 
     As described above, the patterned microbumps or adhesive wells  22  may be formed within the adhesive zone  32  to ensure that the adhesive  16  does not wick between the substrates  12 ,  14  to undesirable locations. While a square-shaped pattern microbump  22  has been described, other shapes and patterns may also be utilized such as that as illustrated in  FIG. 4A , wherein a generally triangularly-shaped patterned microbump  22  is located within a triangularly-shaped adhesive zone  32 . This generally matched geometrical configuration between the patterned microbump  22  and the adhesive zone  32  prevents the flow of the low-viscosity adhesive  16  away from a central portion of the adhesive zone  32  during the adhesive application, while allowing coverage of a significant portion of the adhesive zone  32  upon assembly of the upper substrate  14  with the lower substrate  12 . 
     Alternatively, laser ridges  22   a  ( FIG. 4B ) may be formed around spacing microbumps  18   a  as a barrier structure to prevent the flow of the adhesive (not shown) into regions surrounding the spacing microbump  18   a . It is noted that since the patterned microbumps  22   a  are similar to the previously-described patterned microbumps  22 , similar parts appearing in  FIGS. 1-3  and  FIG. 4B , respectively, are represented by the same, corresponding reference numeral, except for the suffix “a” in the numerals of the latter. It is further noted that patterned microbumps may also be used to prevent adhesive flow to other regions of the associated substrates, such as those regions that include active or passive electronic or optical components. 
     Another alternative embodiment includes the formation of a plurality of gap-filling microbumps  40  ( FIG. 5 ) located within the adhesive well  34   b  as defined by the patterned microbump  22   b . As most of the elements in the present example are similar to those as previously described, similar parts appearing in  FIGS. 1-3  and  FIG. 5 , respectively, are represented by the same, corresponding reference numeral, except for the suffix “b” in the numerals of the latter. In the illustrated example, the space-filling microbumps  40  include a plurality of closely-spaced individual microbumps. As is best illustrated in  FIG. 6 , the space-filling microbumps  40  serve to fill the adhesive well  34   b , thereby decreasing the amount of adhesive  16   b  necessary to fill the adhesive well  34   b , and reducing the chances of misalignment due to an excess amount of adhesive being located between the lower substrate  12   b  and the upper substrate  14   b  during assembly. 
     In yet another alternative embodiment, the patterned microbump  22  defines the adhesive well  34   c , a reservoir portion  42 , and a capillary  44  extending therebetween. In the illustrated example, the reservoir portion  42  is generally square-shaped and is located outside of the adhesive zone  32   c , while the capillary  44  provides fluid communication between the adhesive well  34   c  and the reservoir portion  42 . In assembly, the predetermined amount of the adhesive  16   c  is placed within the reservoir portion  42 , and is forced via the capillary  44  into the adhesive well  34   c  as the upper substrate  14   c  is lowered onto the lower substrate  12   c . Alternatively, the adhesive  16   c  may originally be placed within the adhesive well  34   c  with any excess amount of the adhesive  16   c  being forced into the reservoir portion  42  via the capillary  44  as the upper substrate  14   c  is lowered onto the lower substrate  12   c.    
     The present inventive method of manufacturing an optical assembly and the resultant optical assembly are compatible with existing laser bump forming processes, and allow arbitrarily-shaped wells and channels to be co-fabricated with laser bumps formed for spacing purposes. The laser ridges or patterned microbumps may be formed relatively rapidly and to the necessary heights, controlled to narrow constraints. Further, the heights of these laser ridges may be set dynamically, based on glass composition variations and upper substrate placement variations. Moreover, the present advantages may be implemented in a wide variety of component types and configurations, provide flexibility in the associated manufacturing process and are particularly well adapted for the proposed use. 
     In the foregoing description, it will be readily appreciated by those skilled in the art, that modifications may be made to the invention without departing from the concepts as disclosed herein, such modifications are to be considered as included in the following claims, unless these claims by their language expressly state otherwise.