Optical integrated circuit microbench system

Information

  • Patent Grant
  • 6187515
  • Patent Number
    6,187,515
  • Date Filed
    Thursday, May 7, 1998
    26 years ago
  • Date Issued
    Tuesday, February 13, 2001
    23 years ago
Abstract
The invention relates to an optical integrated circuit microbench system for accurately aligning optical fiber and waveguides to efficiently couple energy between optical devices. This is accomplished by using the anisotropic etch characteristics of III-V semiconductor materials in two orthogonal directions. One etch direction serves to provide a channel for precise fiber-positioning; the other direction, which is orthogonal provides a reflecting surface for directing the optical energy onto optical devices.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates to a monolithically integrated optical microbench system for coupling optical energy between optical devices and a method for producing the same by using the anisotropic etch characteristics of m-V semiconductors where one orthogonal etch direction provides a natural channel for fiber positioning and the other orthogonal etch direction provides a reflecting surface for the redirection of optical energy between a fiber or waveguide and optical devices.




2. Description of the Prior Art




Compact and simple optical coupling systems for micro-optical devices are essential in optical communication systems. In addition, simplified assembly processes in packaging micro-optical coupling systems are very important in manufacturing low cost and reliable systems. An increasingly popular method for the coupling of optical energy between optical devices and systems is through the use of fiber and micro-optical lenses. Fiber provides an efficient transfer medium between optical devices by providing improvements in coupling efficiency and communication lag. Micro-optical lenses provide additional coupling efficiency by focusing divergent optical energy output from an optical fiber end. Present optical coupling systems use a variety of coupling schemes to obtain efficient coupling between micro-optical devices.




The publication “Packaging Technology for a 10-Gb/a Photoreceiver Module”, by Oikawa et al., Journal of Lightwave Technology Vol. 12 No. 2 pp.343-352, February 1994 discloses an optical coupling system containing a slant-ended fiber


10


secured in a fiber ferrule


12


where the fiber ferrule


12


is welded to a side wall


14


of a flat package


16


and a microlens


18


is monolithically fabricated on a photodiode


20


where the photodiode


20


is flip-chip bonded to the flat package


16


, as illustrated in FIG.


1


. An optical signal


22


enters horizontally and is reflected vertically at the fiber's


10


slant-edge. The microlens


18


then focuses the optical signal


22


on the photodiode's


20


photosensitive area.




In the Olkawa publication, maintaining alignment between the fiber and the photodiode chip is essential for optimal coupling of the optical signal. Misalignment can occur as a result of mechanical stress to the fiber ferrule or thermal fluctuations of the entire system. In an attempt to overcome these factors, complex assembly and fabrication techniques are used. The fiber attachment is a complex ferrule attachment which seeks to optimize the mechanical strength of the attachment and therefore minimize the effects of fiber displacement Because the photodiode chip is flip-chip bonded on the flat package a complex bonding machine is required for high-precision alignment. Finally, in order to provide a high optical coupling efficiency wide misalignment tolerances must be built in to the photodiode chip during fabrication to compensate for both displacement by the fiber attachment and deformation by temperature fluctuation.




Disclosed in U.S. Pat. No. 5,346,583 is a monolithic coupling system for optical energy transfer between a microlens and a fiber, as illustrated in FIG.


2


. The configuration disclosed in patent '583 contains at least one preshaped photoresist (PR) microlens


24


formed on a surface


33


of a substrate


34


by standard photolithography steps and on an opposing surface


31


of the substrate


34


an optical fiber guide


26


is formed through standard photolithography steps. The fiber guide


26


is used to mount an optical fiber


28


such that the central axis


30


of the optical fiber


28


is substantially coincident with the central axis


32


of the PR microlens


24


. While the proximity of the fiber


28


to the microlens


24


allows for efficient coupling of optical energy between the fiber


28


and an optical device, there are some significant disadvantages. First, the system is not very compact because of the orientation of the fiber


28


to the surface


31


of the substrate


34


. More importantly, the PR microlens


24


cannot withstand variable temperature cycles and long-term reliability of the system would be an issue.




In many cases external lenses are used to couple optical energy between optical fibers or waveguides and optical devices. Examples of such coupling techniques are disclosed in U.S. Pat. Nos.: 5,247,597; 4,653,847; 4,433,898; 4,875,750; and 5,343,546. Using external microlenses makes coupling extremely complex and in most cases unreliable.




As discussed, present optical coupling systems use a variety of coupling schemes to obtain efficient coupling between micro-optical devices. However, these schemes use many components, require a complicated assembly process, and are not compact. In addition, these components are typically made of different materials and have different thermal expansion coefficients. These differences can cause optical misalignment during temperature changes, which are common in military and space applications. Furthermore, when using discrete bulk optical components, the complexity of the assembly process is increased because there are more individual components to align. The greater the complexity the more assembly costs are increased and reliability decreased.




Based on techniques known in the art for optoelectronic coupling schemes, a monolithic optical microbench system for coupling optical energy between a fiber or a waveguide and an optical device is highly desirable.




SUMMARY OF THE INVENTION




It is an aspect of the present invention to provide a monolithic optical microbench system for the coupling of light between optical devices which includes a substrate wafer having a crystal plane; a mirror etched in the crystal plane of the substrate wafer; and a groove etched on a side of the substrate wafer intersecting the crystal plane of the mirror.




It is also an aspect of the present invention to provide a method for producing a monolithic optical microbench for the coupling of light between optical devices. The method comprises the steps of providing a substrate wafer having a first opposing surface, a second opposing surface, a first crystal plane, and a second crystal plane; lapping the entire first opposing surface of the substrate wafer and polishing the entire first opposing surface of the substrate wafer; coating a first layer of photoresist material over the entire first opposing surface of the substrate wafer and coating a second layer of photoresist material over the entire second opposing surface of the substrate wafer; baking the first opposing surface and the second opposing surface of the substrate wafer; providing a first mask to the first opposing surface and a second mask for the second opposing surface of the substrate wafer; selectively aligning the first mask to the first opposing surface and the second mask to the second opposing surface of the substrate wafer; exposing the first opposing surface of the substrate wafer coated with the first layer of photoresist material to a light source to form a first photoresist mask and exposing the second opposing surface of the substrate wafer coated with the second layer of photoresist material to a light source to form a second photoresist mask; developing the first opposing surface and the second opposing surface of the substrate wafer; etching the first opposing surface and the second opposing surface of the substrate wafer; removing the first photoresist mask and cleaning the first opposing surface of the substrate wafer and removing the second photoresist mask and cleaning the second opposing surface of the substrate wafer; and finally, metallizing the entire substrate wafer.











BRIEF DESCRIPTION OF THE DRAWINGS




Reference is now made to the following specification and attached drawings, wherein:





FIG. 1

is an illustration of a known optical coupling system which includes a mounted fiber assembly and a microlens monolithicaly integrated into a photodiode;





FIG. 2

is an illustration of another known optical coupling system which includes a plurality of microlenses formed on a surface of a substrate and corresponding optical fiber guides formed on an opposing surface of the substrate;





FIG. 3

is a side view illustration of the optical microbench system in accordance with the present invention;





FIG. 4

is an illustration of the natural crystal planes of III-V semiconductor substrates;





FIG. 5



a


is a side view illustration of the lapping and polishing of the substrate in accordance with the present invention;





FIG. 5



b


is a side view illustration of the substrate coated with a layer of photoresist material to begin the formation of a reflective surface through photolithography steps in accordance with the present invention;





FIG. 5



c


is a side view illustration of the substrate wafer which includes a layer of photoresist material on a surface of the substrate wafer and the layer of photoresist material is exposed by an ultra-violet light source through a mask to later form a reflective mirror in accordance with the present invention;





FIG. 5



d


is a side view illustration of the substrate wafer and a photoresist mask formed on the surface of the substrate following the exposure of the substrate wafer to the ultra-violet light source in accordance with the present invention;





FIG. 5



e


is a cross-sectional side view illustration of the preferentially etched surface of the substrate wafer where a flat reflective mirror is formed in accordance with the present invention;





FIG. 5



f


is a top view of the preferentially etched surface of the substrate wafer where a flat reflective mirror is formed in accordance with the present invention;





FIG. 5



g


is a cross-sectional side view illustration of the substrate of

FIG. 5



f


where the photoresist has been removed from the surface of the substrate.





FIG. 5



h


is a cross-sectional side view illustration of the substrate wafer coated with a layer of photoresist material to begin the formation of a groove through photolithography steps on the surface opposite where the flat reflective mirror is formed in accordance with the present invention;





FIG. 5



i


is a side view illustration of the substrate wafer which includes a layer of photoresist material on a surface of the substrate wafer and the layer of photoresist material is exposed by an ultra-violet light source through a mask to later form a groove in accordance with the present invention;





FIG. 5



j


is a top view illustration of the substrate wafer and a photoresist mask formed on the surface of the substrate following the exposure of the substrate wafer to the ultra-violet light source in accordance with the present invention;





FIG. 5



k


is a top view illustration of the substrate wafer with an etched groove intersecting the plane of the etched flat reflective mirror in accordance with the present invention;





FIG. 5



l


is a side view illustration of the substrate wafer with an etched groove intersecting the plane of the etched flat reflective mirror in accordance with the present invention;





FIG. 5



m


is an illustration of the substrate wafer metallization process in accordance with the present invention;





FIG. 6

is a cross-sectional side view illustration of an alternate embodiment of the present invention where a curved reflective mirror is formed in accordance with the present invention; and





FIG. 7

is an illustration of the microbench system in accordance with the present invention.











DETAILED DESCRIPTION OF THE INVENTION




Briefly, the present invention relates to III-V semiconductor monolithic optical microbench and a method for producing the same for coupling optical energy between optical devices. The microbench, which is a monolithic assembly, can accurately align optical fibers or waveguides, and redirect and focus optical energy to and from optical devices using a reflective surface. The construction of the microbench system is accomplished by using the anisotropic etch characteristics of III-v semiconductors. Etching in one direction creates a natural channel for precise fiber positioning; etching in another direction, which is orthogonal to the first direction, creates a reflective surface at one end of the fiber channel for redirecting and focusing optical energy. The ability to form a monolithic compact and simple optical coupling system for micro-optical devices has several advantages. First, because the microbench can be made of the same semiconductor material as the device, there is better thermal expansion match between the microbench and the micro-optical device. Having the best thermal expansion match is important for stability where differences in thermal expansion coefficients can cause optical misalignments during temperature changes. Further, efficient coupling can be accomplished between a fiber, reflective surface, and the device without the use of complex coupling and alignment schemes which require many components and complicated assembly processes. Other advantages include redirection and focusing of optical energy using one optical component, lower loss and spherical aberrations using front surface reflectors compared to refractive lenses, compact construction and reduced package profile, very accurate alignment of reflector to optical devices, decrease in the time required for alignment of the reflector to the micro-optical device by passive alignment, expandability to integrate multiple reflectors into one structure, and providing for more efficient packaging of optical electronics systems. Finally, very precise fabrication is possible by using standard photolithographic processes and wafer level fabrication can result in high volume manufacturing and high reproducibility.




As previously mentioned, the present invention relates to an improvement in the coupling of optical energy between optical devices. Present optical systems use a variety of coupling schemes which can be very complex and unreliable. In order to produce less complex more efficient coupling between optical fibers or waveguides and micro-optical devices, a reflective mirror and fiber groove can be formed monolithically from the same semiconductor material to form a microbench. Monolithic integration allows for accurate alignment of optical fibers to efficiently couple energy between the microbench and optical devices. Additionally, because the microbench material is the same material as the optical devices similar thermal expansion properties make the resulting optical coupling more reliable.




It should be understood by those of ordinary skill in the art that the principles of the present invention are applicable to many types of reflective mirrors and micro-optical devices, such as flat mirrors, paraboloidal mirrors, waveguide devices, diode laser devices, fiber optical devices, photodiode devices, and optical integrated circuits. The principles of the present invention are also applicable to many types of III-v semiconductors, such as indium phosphide (InP), gallium arsenide (GaAs), indium arsenide (InAs), and gallium phosphide (GaP) and/or silicon.




The present invention relates to an optical mircobench system and, more particularly, to an optical microbench system which includes a III-V semiconductor substrate


36


, such as indium phosphide (InP), a fiber groove


38


, and a reflective mirror


40


, as illustrated in FIG.


3


. An important aspect of the invention is the monolithic integration of the microbench system. The fiber groove


38


provides a natural channel for precise optical fiber positioning where optical energy


42


is emitted from an optical fiber


44


and redirected at the reflective mirror


40


for collection at an optical detector device


46


. It should be understood that the principles of the present invention are also applicable for coupling optical energy from a waveguide to an optical device. It should filter be understood that the reflective mirror can be used for redirecting and focusing the diverging output of optical energy from an emitter or waveguide, or it can be used for collecting the optical energy coming to the input of a waveguide or detector.




For illustration, a method for producing the monolithic optical microbench system is described and illustrated further in

FIG. 4

,

FIGS. 5



a


through


5




m


, and

FIG. 6

with a substrate wafer


48


, a groove


82


, and reflective mirrors


66


and


68


.




More specifically, and with reference to the drawings, the first steps of the microbench fabrication, as illustrated in

FIG. 4

,

FIGS. 5



a


through


5




m


, and

FIG. 6

, relate to the formation of a groove and a reflective mirror from semiconductor material by standard photolithography processes. The construction of the microbench is accomplished by exploiting the anisotropic etch characteristics of III-v semiconductors. The unique crystal plane properties, as illustrated in

FIG. 4

, of III-V semiconductor material allow for the preferential etching of reflective surfaces in one (111) crystal plane


47


of a substrate and to etch an intersecting groove on an opposite (100) crystal plan


35


of the substrate.




The first step of the microbench fabrication process involves lapping the entire first opposing surface


54


of an indium phosphide (InP) substrate wafer


48


and polishing the entire first opposing surface


54


to a thickness of from approximately 135 to 175 microns, as illustrated in

FIG. 5



a


. The lapping and polishing steps are performed to provide the substrate wafer


48


with a desired thickness and are performed while the substrate wafer


48


is secured by means such as the wax


52


on a carrier


50


.




Following the lapping and polishing steps are the reflective mirror fabrication steps. The first step of the reflective mirror fabrication process, as illustrated in

FIG. 5



b


, is coating a layer of photoresist material


56


over the entire first surface


54


of the indium phosphide (InP) substrate wafer


48


. The preferred photoresist material


56


is 2-ethoxpyethylacetate (60%) and n-butyl acetate (5%) in xylene and hexamethyldisilozane (HDMS), and is preferred for its suitability for use with a variety of etching techniques. The indium phosphide substrate wafer


48


is chosen for its crystallographic etching characteristics. It is important to note that other materials can be used for the substrate wafer


48


and the photoresist coating


56


. For example, the substrate wafer


48


may be any III-v semiconductor material and may include gallium arsenide (GaAs), indium arsenide (InAs), and gallium phosphide (GaP). The photoresist coating material


56


may include 2-ethoxyethylacetate+n-butyl acetate in xylene solvent, 2-ethoxyethylacetate+n-butyl acetate in xylene and silicon dioxide (SiO


2


), 2-ethoxyethylacetate+n-butyl acetate in xylene and silicon nitride (Si


3


N


4


), silicon dioxide (SiO


2


) and complex silicon nitride (Si


x


N


y


), or aluminum oxide (Al


2


O


3


).




After coating the layer of photoresist material


56


over the first surface


54


of the substrate wafer


48


, the substrate wafer


48


is soft baked at a temperature of approximately 100° C. and for a period of approximately 45 minutes to remove any solvent from the photoresist material


56


.




Next, as illustrated in

FIG. 5



c


, a pattern mask


58


is used to transfer a reflective mirror pattern


60


from the mask


58


to the substrate wafer


48


. The mask


58


is aligned to the substrate wafer


48


and the layer of photoresist material


56


is then exposed to an ultra violet UV light source


62


through the mask


58


to transfer the reflective mirror pattern


60


to the photoresist material


56


. Next, as illustrated in

FIG. 5



d


, the layer of photoresist material


56


of

FIG. 5



c


is developed to form a photoresist mask


64


on the first surface


54


of the substrate wafer


48


. The development of photoresist material is a standard step in photolithography processing. Alternatively, if the substrate wafer


48


is precoated using SiO


2


, Si


3


N


4


, Si


x


N


y


, Al


2


O


3


or similar materials, the portions of the precoat layer not covered by the photoresist material


56


must be etched away by plasma or buffer HF (buffer hydrogen flouride) etching before proceeding to the preferential etching steps which follow.




Following the previously mentioned photolithography steps, the substrate wafer


48


is preferentially etched in the areas not protected by the photoresist mask


64


, as illustrated in

FIGS. 5



e


and


5




f


, to form a flat reflective mirror


66


. This preferential etching step is done by a wet-chemical etch process where the substrate


48


is etched in an orthogonal direction along the (111) first crystal plane


47


illustrated in FIG.


4


. The unique crystal plane properties of III-V semiconductor material allows for the preferential etching of flat angled reflective surfaces of between


36


and


53


degrees, as illustrated in the preferred embodiment. For the purposes of the preferred embodiment, the surface


54


of the substrate wafer


48


shown in

FIG. 5



e


is wet-chemically etched in a deionized water:potassium dichromate:acetic acid:hydrobromic acid (H


2


O:K


2


Cr


2


O


7


:H


3


CCOOH:HBr), 450 ml:66 g:100 ml:300 ml solution at a temperature of from 40° C. to 60° C. Alternative wet-chemical etch solutions may include bromine:methanol (Br


2


:H


3


COH), bromine:isopropanol (Br


2


:H


5


C


2


OH), deionized water:hydrobromic acid:acetic acid (H


2


O:HBr:H


3


CCOOH), deionized water:potassium dichromate:sulfuiic acid:hydrochloric acid (H


2


O:K


2


Cr


2


O


7


:H


2


SO


4


:HCl), phosphoric acid:hydrochloric acid (H


3


PO


4


:HCl), phosphoric acid:hydrochloric acid:deionized water (H


3


PO


4


:HCI:H


2


O), phosphoric acid:hydrochloric acid:hydrogen peroxide (H


3


PO


4


:HCl:H


2


O


2


), iron chloride:hydrochloric acid (FeCl


3


:HCl) under illumination, potassium periodide:hydrochloric acid (KIO


3


:HCl), hydrochloric acid: acetic acid:hydrogen peroxide (HCl:acetic acid:H


2


O


2


), hydrochloric acid:hydrogen peroxide:deionized water (HCl:H


2


O


2


:H


2


O), sulfuric acid:hydrogen peroxide:deionized water (H


2


SO


4


:H


2


O


2


:H


2


O), citric acid:hydrogen peroxide:deionized water (citric acid:H


2


O


2


:H


2




0


), bromine:methanol (Br


2


:CH


3


OH), nitric acid:hydrofloric acid:deionized water (HNO


3


:HF:H


2


O), or hydrogen peroxide:amonium hydroxide:deionized water (H


2


O


2


:NH


4


OH:H


2


O).




Alternatively, as illustrated in

FIG. 6

, a curved reflective mirror


68


can be formed by non-selective etching the substrate wafer


48


using the same wet-chemical etch solution previously mentioned at a temperature of from approximately 60 to 65° C. The photoresist layer used for non-selective etching is baked at a temperature of approximately 150° C. so that the photoresist mask can withstand high etching temperatures where the etching temperatures are greater than approximately 60° C.




Following the etching of the surface


54


of the substrate wafer


48


to form the flat reflective mirror


66


, the photoresist mask


64


is removed from the surface


54


of the substrate wafer


48


, as illustrated in

FIG. 5



g


. The photoresist mask


64


is removed and the surface


54


of the substrate wafer


48


is cleaned by first removing the photoresist mask


64


using acetone. Following the removal of the photoresist mask


64


, the acetone is removed from the surface


54


of the substrate wafer


48


with isopropanol and the isopropanol is removed from the surface


54


of the substrate wafer


48


using deionized water. Finally, oxides and photoresist residual are removed from the surface


54


of the substrate wafer


48


using potassium hydroxide (KOH) and etch residue is removed from the surface


54


of the substrate wafer


48


using a solution of sulfuric acid:hydrogen perodixe:deionized water (H


2


SO


4


:H


2


O


2


:H


2


O).




As previously mentioned, the monolithic integration of a reflective surface and a groove is significant. Monolithic integration allows for more reliable and less complex optical alignment between optical devices. To complete the monolithic integration, a groove is formed on a surface of a substrate wafer opposite the surface where the reflective mirror has been formed.




As illustrated in

FIG. 5



h


, the substrate wafer


48


is demounted from the carrier


50


, and remounted to the carrier


50


using the wax material


52


, thereby exposing the surface


70


of the substrate wafer


48


. The surface


70


of the substrate wafer


48


is cleaned using solvent to remove any wax residue. The first steps in the fabrication of the groove are photolithography steps. The first photolithography step includes coating a layer of photoresist material


72


over the entire surface


70


of the substrate wafer


48


opposite the surface


54


of the substrate wafer


48


where the flat reflective mirror


66


has previously been formed. The preferred photoresist material


72


is 2-ethoxyethylacetate+n-butyl acetate in xylene. Next, the substrate wafer


48


is soft baked at a temperature of approximately 100° C. for a period of approximately 45 minutes to remove solvents from the photoresist material


72


.




As further illustrated in

FIG. 5



i


, a mask


74


is used to transfer a groove pattern


76


to the layer of photoresist material


72


. The mask


74


is selectively aligned to the substrate wafer


48


. Using standard photolithography steps, the layer of photoresist material


72


is exposed with an ultra-violet light source


78


through the mask


74


.




The layer of photoresist material


72


is developed creating a photoresist mask


80


on the surface


70


of the substrate wafer


48


, as shown in

FIG. 5



j


. The surface


70


of the substrate wafer


48


containing the photoresist mask


80


is wet-chemically etched in the areas not protected by the photoresist mask


80


to form the groove


82


, as shown in

FIGS. 5



k


and


5




l


. The groove


82


is etched on the (100) crystal plane


35


, shown in

FIG. 4

, of the substrate wafer in an orthogonal direction such that the end


84


of the groove


82


intersects the plane of the flat reflective mirror


66


. Because of the anisotropic etch characteristics of the substrate wafer


48


, the groove


82


is formed in a semi-circular shape, as shown in

FIG. 5



k


. The semi-circular shape of the groove


82


allows for increased stability during thermal expansion of the microbench system because the semi-circular groove


82


allows more surface area contact with round optical fibers than equivalent v-groove structures.




Following the formation of the groove


82


, the photoresist mask


80


is removed from the surface


70


of the substrate wafer


48


and the surface


70


of the substrate wafer


48


is cleaned, using the same steps illustrated in the formation of the flat reflective mirror.




To secure the microbench system to a micro-optical device, the entire substrate


48


is metallized by first evaporating


92


a layer


86


of titanium (Ti) over the entire substrate wafer


48


, evaporating


92


a layer of platnium (Pt)


88


over the layer


86


of titanium, evaporating


92


a layer


90


of gold (Au) over the layer


88


of platnium, and applying a standard alloy treatment to the metal layers to bond the layers for better adhesion, as illustrated in

FIG. 5



m.






Finally, as shown in

FIG. 7

, an optical fiber


92


and the substrate wafer


48


are secured using eutectic bonds


100


. The optical fiber


92


is secured in the groove


82


and the substrate wafer


48


is mounted to optical devices


94


. An optical signal


96


is emitted from the optical fiber


92


and is reflected at the flat reflective mirror


66


to an optically active area


98


.




Obviously, many modifications and variations of the present invention are possible in light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.



Claims
  • 1. A method for producing a monolitic optical microbench for the coupling of light between optical devices, said method comprising the steps of:providing a III-V semiconductor substrate wafer having a first surface, a second surface opposite the first surface, a first crystal plane, and a second crystal plane; lapping the entire first surface of the substrate wafer and polishing the entire first surface of the substrate wafer; coating a first layer of photoresist material over the entire first opposing surface of the substrate wafer and coating a second layer of photoresist material over the entire second opposing surface of the substrate wafer; baking first layer and the second layer of photoresist material at a temperature of substantially 150° C.; providing a first mask for the first opposing surface and a second mask for the second opposing surface of the substrate wafer; selectively aligning the fist mask to the it opposing surface and the second mask to the second opposing surface of the substrate wafer; exposing the first opposing surface of the substrate wafer coated with the first layer of photoresist material to a light source to form a first photoresist mask and exposing the second opposing surface of the substrate wafer coated with the second layer of photoresist material to a light source to form a second photoresist mask; developing the first opposing surface and the second opposing surface of the substrate wafer; etching the first opposing surface of the substrate wafer at a temperature substantially from 60° C. to 65° C. to form a curved reflective mirror; etching the second opposing surface of the substrate wafer to form a groove intersecting a plane of the curved reflective mirror; removing the first photoresist mask and cleaning the first opposing surface of the substrate wafer and removing the second photoresist mask and clang the second opposing surface of the substrate wafer; and metallizing the entire substrate wafer.
  • 2. The method as recited in claim 1, wherein providing the substrate wafer further comprises providing the substrate wafer of a III-V semiconductor material selected from the group consisting of gallium arsenide (GaAs), gallium phosphide (GaP), indium phosphide (InP), or indium arsenide (INAs).
  • 3. The method as recited in claim 1, wherein providing the substrate wafer having the first and the second crystal planes further comprises providing the substrate wafer having a (100) first crystal plane.
  • 4. The method as recited in claim 1, wherein providing the substrate wafer having the first and the second crystal planes further comprises providing the substrate wafer having a (111) second crystal plane.
  • 5. The method as recited in claim 1, wherein etching the first opposing surface of the substrate wafer to form the curved reflective mirror farther comprises non-selectively etching the first opposing surface of the substrate wafer to form the curved reflective mirror.
  • 6. The method as recited in claim 5, wherein non-selectively etching the first opposing surface of the substrate wafer to form the curved reflective mirror further comprises etching on the second crystal plane of the substrate wafer.
  • 7. The method as recited in claim 1, wherein providing the second opposing surf etching the second opposing surface of the substrate wafer to form the groove further comprises forming the groove to intersect the second crystal plane of the substrate wafer.
  • 8. The method as recited in claim 7, wherein forming the groove further comprises providing the groove to position an optical fiber therein.
  • 9. The method as recited in claim 7, wherein forming the groove further comprises non-selectively etching the second opposing surface of the substrate wafer to form the groove.
  • 10. The method as recited in claim 9, wherein non-selectively etching the second opposing surface of the substrate wafer to form the groove further comprises non-selectively etching the second opposing surface of the substrate wafer to form the groove having a semi-circular cross-section.
  • 11. The method as recited in claim 1, wherein lapping and polishing the entire first opposing surface of the substrate wafer further comprises lapping the substrate wafer to a thickness of approximately 135 to 175 microns.
  • 12. The method as recited in claim 1, wherein selectively aligning the first mask to the substrate wafer over the first opposing surface and the second mask to the substrate wafer over the second opposing surface further comprises aligning the first and the second mask along the first crystal plane of the substrate wafer.
  • 13. The method as recited in claim 1, wherein etching the first and the second opposing surfaces of the substrate wafer further comprises wet-chemical etching.
  • 14. The method as recited in claim 1, wherein etching the first and the second opposing surfaces of the substrate wafer further comprises providing a wet chemical etch solution selected from the group consisting of deionized water:potassium dichromate:acetic acid:hydrobromic acid (H2O:K2Cr2O7:H3CCOOH:HBr), bromine:methanol (Br2:H3COH), bromine:isopropanol (Br2:H5C2OH), deionized water:hydrobromic acid:acetic acid (H2O:HBr:H3CCOOH), deionized water-potassium dichromate:sulfuric acid:hydrochloric acid (H2O:K2Cr2O7:H2SO4:HCl), phosphoric acid:hydrochloric acid (H3PO4;HCl), phosphoric acid:hydrochloric acid:deionized water (H3PO4:H2O), phosphoric acid:hydrochloric acid:hydrogen peroxide (H3PO4:HCl:H2O2), iron chloride:hydrochloric acid (FeCl3:HCl) under illumination, potassium periodide:hydrochloric acid (KIO3:HCl), hydrochloric acid:acetic acid:hydrogen peroxide (HCl:acetic acid:H2O2), hydrochloric acid:hydrogen peroxide:deionized water (HCl:H2O2:H2O), sulfuric acid:hydrogen peroxide:deionized water (H2SO4:H2O2:H2O), citric acid:hydrogen peroxide-deionized water (citric acid:H2O2:H2O), bromine:methanol (Br2:CH3OH), nitric acid:hydrofloric acid:deionized water (HNO3:HF:H2O), and hydrogen peroxide:ammonium hydroxide:deionized water (H2O2:NH4OH:H2O).
  • 15. The method as recited in claim 1, wherein the step of metallizing the entire substrate wafer comprises the steps of:evaporating a layer of titanium (Ti) over the entire substrate wafer; evaporating a layer of platinum (Pt) over the layer of titanium; evaporating a layer of gold (Au) over the layer of platinum; and applying an alloy treatment to the titanium layer, the platinum layer, and the gold layer to adhere the surface of the substrate wafer to the layer of titanium, the layer of titanium to the layer of platinum, and the layer of platinum to the layer of gold.
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