Socket and a system for optoelectronic interconnection and a method of fabricating such socket and system

It is an object of the present invention to disclose a socket that is easy in use for optoelectrical interconnection. The socket of the invention can be handled as a compact device that allows the interconnection between electrical signals and external apparatus for transmitting the optical signals, preferably via a high density of optical channels. The socket of the invention has features and markers for attachment and alignment of optical transfer media such as optical fibers, optical fiber bundles and optical imaging fiber bundles. The alignment features and markers allow to align the optical transfer media to the connection for electrical signals. The markers can be integrated in or can be provided on a fiber optic face plate substrate forming part of the socket.

FIELD OF THE INVENTION
 The present invention relates to the field of semiconductor device
 structures, and more in particular to optoelectrical or optoelectronic
 devices. More precisely the present invention is related to a socket, and
 to a system for optoelectronic interconnection. The present invention is
 also related to a method of fabricating such sockets and such systems.
 BACKGROUND OF THE INVENTION
 The increased integration of transistors on single chips made possible by
 the submicron CMOS technology raises the problem of speed and performance
 limitation of electronic systems through the interconnect structures
 between chips or with other structures. A possible solution to this
 problem of CMOS interconnect bottlenecks could be the use of optical links
 or interconnects between chips. In a number of applications, especially to
 achieve high density interconnects, optical interconnects are advantageous
 over electrical interconnects. For instance, optical interconnects can
 reach a higher interconnect density and lower power consumption than
 electrical interconnects.
 In order to achieve high density optical interconnects, it is necessary to
 realize high density arrays of light sources and light detectors, and
 furthermore to use an optical path or channel between sources and
 detectors which sustains a high density of optical channels. The light
 sources used to send the optical signals through the optical interconnect
 channels receive their input and possibly at least part of their power
 from electrical signals. These electrical signals can originate from an
 integrated circuit, or from a board. Furthermore, at the other end of the
 optical interconnect channel are detectors, which also require electrical
 power to operate, and which convert the received optical signals into
 electrical signals. Hence, it is clear that high density optical
 interconnects require a high density of electrical or optical devices to
 possibly deliver at least part of the required electrical power to run the
 optical interconnect, as well as to send and retrieve the signals.
 Obviously, the foregoing analysis can be applied as well to interconnect
 systems that make use of another form of electromagnetic radiation than
 light.
 In many optical applications, it is required to have a transparent
 substrate for an optoelectronic device such as a light-emitting device, a
 photodetector, a modulator or a CCD sensor. An application example is when
 an optoelectronic device is contacted from the front side by flip-chip
 mounting, while the light has to be transported through the substrate.
 Many substrates are poorly or not transparent for the light emitted or
 detected in the active semiconductor layers grown on them. For example,
 Gallium-Arsenide (GaAs) or Aluminium-Gallium-Arsenide (AlGaAs) or InGaP or
 InAlGaP active layers emit and detect light with a peak wavelength that is
 strongly absorbed by the GaAs substrate on which they are typically grown.
 Hence, light-emission or light-detection through the original substrate is
 not possible. A possible solution to this problem is to remove the
 original substrate in a process such as described in U.S. Pat. No.
 5,578,162. Another possible solution is to replace the original substrate
 by a transparent substrate, such as a glass plate.
 U.S. Pat. No. 5,093,879 discloses an optoelectrical connector for
 accommodating high density applications. This patent specification however
 does not disclose and does not enable to fabricate integration neither
 alignment of a connection for the electrical signals to the devices for
 emitting and/or detecting electromagnetic radiation, wherein the
 functioning of said devices is being controlled by said electrical
 signals.
 U.S. Pat. No. 5,625,811 discloses an optically interconnected multichip
 module. The patent shows a dense integration of thin layers of
 semiconductor material with devices (chips) integrated therein and which
 are bonded to a fiber optic face plate. These chips are integrated in a
 multichip module and the fiber optic face plate is providing the optical
 intraconnection or optical transmission medium between the chips. The
 optical intraconnection (waveguide) is not flexible and does not allow for
 communication between chips which are in the same plane or in a remote
 location. This patent does not address the problem of a connector to an
 external apparatus or external devices that is versatile in use and easy
 to use.
 The use of fiber optic face plates in combination with optoelectrical
 devices has further been proposed, e.g. in U.S. Pat. No. 5,074,683, and in
 U.S. Pat. No. 5,652,811, and in U.S. Pat. No. 5,578,162.
 U.S. Pat. No. 5,631,988 discloses an optical interconnect that couples
 multiple optical fibers to an array of optoelectrical devices. The
 connector comprises a holder, a plurality of optical fibers attached to
 the holder, and guiding means. This connector is quite elaborate and not
 compaction in providing the optical path of the interconnection signals.
 Moreover, the direct contact of the optical fiber bundles to the
 optoelectrical devices can degrade such devices, in particular because the
 optical connection is detachable.
 U.S. Pat. No. 5,367,593 provides an optical/electrical connector that
 includes a molded base with alignment guides and with a well for
 integrating an electronic circuit. Also this device is not compact and
 provides an optical interconnection path only for a 1-dimensional array.
 The teaching of this patent does not disclose nor does it suggest an
 optoelectrical interconnect in a dense and compact configuration which is
 flexible in use for a multitude of configurations such as 2-dimensional
 arrays of light-emitting devices on an electronic circuit.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to disclose a socket that is easy
 in use for optical or optoelectronic or optoelectrical interconnection.
 The socket of the invention provides an interconnection device that has a
 dense, compact configuration. In an embodiment of the invention, the
 socket of the invention can be handled as a stand-alone package that
 allows the interconnection between electrical signals and an external
 apparatus for transmitting the optical signals, preferably via a high
 density of optical channels. The socket of the invention allows for a
 flexible communication between devices being controlled by electrical
 signals such as integrated circuits. With the socket of the invention a
 communication between chips in an in-plane configuration or in any other
 configuration or dimension is feasible. A communication between chips in
 an in-plane configuration (a 2-dimensional array of chips) or in any other
 configuration or dimension (for instance a 1-dimensional or 3-dimensional
 array) is feasible.
 It is another object of the present invention to provide a socket for
 optoelectrical interconnection with a transparent substrate for
 high-density optical input/output applications in which the electrical
 input/outputs are connected to the optical input/outputs. But the
 electrical input/outputs are at another side of the socket, preferably
 opposite, to the optical input/outputs.
 It is a further object of the invention to disclose a socket with features
 and markers for attachment and alignment of optical transfer media such as
 optical fibers, optical fiber bundles and optical imaging fiber bundles.
 The alignment features and markers allow to align the optical transfer
 media to the connection for electrical signals. The markers can be
 integrated in or can be provided on a fiber optic face plate substrate
 forming part of the socket. The alignment features and markers in an
 embodiment of the invention can comprise magnetic means for alignment
 and/or attachment. The optical fibers, fiber bundles or imaging fiber
 bundles can then further be aligned and attached to detectors integrated
 in a silicon integrated circuit.
 Thus, here is provided a socket for optoelectrical interconnection,
 comprising a connection for electrical signals; an array of devices
 emitting and/or detecting electromagnetic radiation, the functioning of
 said devices being controlled by said electrical signals; and a connection
 to an external apparatus, the connection including a transmitter or a
 channel for said radiation. Said connection for electrical signals can be
 connected with at least a part of said devices of said array. Said
 connection for electrical signals can be aligned through at least one
 marker in or on said connection to said external apparatus with at least a
 part of said devices of said array. The marker can be aligned with at
 least part of said devices of said array. Said external apparatus can
 include a channel or a high density of channels for said electromagnetic
 radiation. The external apparatus can also include a detector and/or
 devices for emitting electromagnetic radiation. Said connection for
 electronic signals can be at a first side of said socket and said
 connection to said external apparatus can be at a second side of said
 socket.
 The socket of the invention can be configured as an interconnection device
 for optoelectrical interconnection, comprising a connection for electrical
 signals; an array of devices emitting and/or detecting electromagnetic
 radiation, the functioning of at least a part of said devices being
 controlled by said electrical signals; and connection to an external
 apparatus including a transmitter for said radiation, said connection to
 said external apparatus comprising a substrate with a plurality of light
 channels for said radiation. The connection can be such that essentially
 each device of said array is aligned with at least a subset of said light
 channels. In an embodiment of the invention, said substrate can be a fiber
 optic face plate. According to this embodiment of the invention, the
 different parts of the interconnection device or socket are brought
 together adjacent one to another in a dense, compact configuration. The
 different parts can however be spatially separated. According to a
 preferred embodiment, such dense configuration can be achieved with having
 the different parts of the socket integrated on a substrate such as a
 PCB-board with a mounting technique, such as a flip-chip technique for
 mounting the parts, providing the alignment of the different parts one to
 another.
 In an advantageous embodiment of the invention, the fiber optic face plate
 can include microlenses. The microlenses can be made according to the
 teaching of U.S. Pat. No. 5,871,888 or of any patent or reference cited
 within or with respect to this patent, U.S. Pat. No. 5,871,888 or any of
 the prior art teachings being incorporated herein by reference.
 The socket of the invention can also be configured as an integrated socket
 providing the socket of the invention in a compact, single interconnection
 device with each of the different parts of the socket is abutting at least
 one of the other parts of the socket.
 The socket of the invention can also have at least one marker in said
 connection to said external apparatus, said marker being aligned with at
 least part of said devices of said array.
 In a preferred embodiment of the invention, in the socket essentially each
 of said devices for emitting and/or detecting electromagnetic radiation of
 said array is being confined through form and functioning and essentially
 each of said devices for emitting and/or detecting electromagnetic
 radiation of said array is being aligned with at least a part of said
 connection for electronic signals. With the term confined through form and
 functioning it is meant that without additional means or without
 additional structural features such as extended, large isolation features
 in the array of devices, each of said devices can be addressed
 individually via the connection for electrical signals. Such confinement
 through form and functioning can be done e.g. when said devices are being
 integrated in a single thin film semiconductor. The term confined through
 form and functioning is also used more generally in this specification.
 For instance, in an embodiment of the invention, said connection for
 electronic signals can include an electrically conducting glue providing
 separate conduction paths. These paths can be confined through form and
 functioning which means that without additional means the glue is
 providing a separate conduction path to substantially each of the devices.
 Also detector devices can be used that are confined through form and
 functioning.
 In an embodiment of the invention, one can also use devices that can both
 emit and detect electromagnetic radiation. Examples of such devices are
 optical thyristors or p-n diodes.
 In a preferred embodiment of the present invention, said socket includes a
 thin-film semiconductor layer attached to a transparent fiber optic face
 plate substrate, such that optoelectrical devices processed in the thin
 film semiconductor layer are electrically contacted from the side opposite
 to the side of the face-plate attachment. Markers and marker features for
 alignment are made in or on the fiber optic face plate. In an aspect of
 the invention, two sockets are abutted one against the other and
 information is transmitted between the light emitters/detectors of the
 respective sockets. An example of such use is the information transmission
 to and from a board with electronic devices to a rack including a multiple
 of such boards.
 Still a further object of the invention is to disclose a system for
 transmitting information comprising at least one channel for
 electromagnetic radiation; a socket for optoelectronic interconnection,
 and said channel comprising a channel marker, said channel marker being
 aligned with a socket marker. The socket includes a connection for
 electronic signals; an array of devices emitting and/or detecting
 electromagnetic radiation, the functioning of said devices being
 controlled by said electronic signals, said connection being connected and
 aligned with at least a part of said devices of said array; a connection
 for said channel for said radiation; and at least one socket marker in
 said connection for said channel, said marker being aligned with at least
 part of said devices of said array. The system can further comprise an
 array of devices emitting and/or detecting electromagnetic radiation, said
 array of devices being connected to said channel, the detectors of said
 array being adapted for receiving said radiation and converting said
 radiation into electronic signals. Said detectors can further comprise
 detector markers such that said channel is aligned with said detector
 markers and such that specific parts of said array of radiation emitting
 devices are aligned with specific parts of said detector.
 Yet another object of the invention is to disclose a method of fabricating
 an optoelectrical structure wherein the optical devices forming part of
 the structure are controlled by electrical connections that can be aligned
 with an external channel for transmitting the optical information. The
 method of fabricating the optoelectrical structure provides a way of
 aligning the different parts of the optoelectrical structure one with
 respect to the other.
 In an embodiment of this object of the invention, a method of large-scale
 and wafer-scale fabrication of arrays of optoelectronic devices with
 above-mentioned transparent fiber optic face plate substrate is disclosed.
 A preferred embodiment of the invention reveals wafer scale fabrication of
 the optoelectronic devices on a fiber optic face plate including
 integrated socket features.
 Yet any combination can be made of any of the embodiments of the devices or
 methods of the invention, disclosed in the present patent application.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS OF THE PRESENT INVENTION
 The invention is described in the sequel through a detailed description of
 several embodiments of the invention. It is obvious that other embodiments
 of the invention can be configured according to the knowledge of persons
 skilled in the art without departing form the true sprit of the invention,
 the invention being limited only by the terms of the appended claims.
 FIG. 1 depicts a socket 1 according to one embodiment of the present
 invention. One surface 111 of a thin-film semiconductor 11 is attached to
 a fiber optic face plate 13. Optoelectrical or optoelectronic devices 121,
 122, etc., generally referred to as 12, are fabricated in the thin-film
 semiconductor 11. Means for electrically conductive bonding 14 are
 provided at the other surface 112 of the thin-film semiconductor, and
 perform the double function of mechanically attaching the thin-film
 semiconductor to a carrier 15, and providing electrical connection between
 said carrier and said optoelectronic devices.
 The carrier 15 can be an integrated circuit. It can, however, also be a
 multichip module, a board such as a printed circuit board, a part of a
 connector, or, in general, any carrier that provides electrical signals
 and/or electrical power to the optoelectronic devices 12.
 Examples of possible means for electrically conductive bonding 14 are metal
 bumps, solder balls, conductive epoxy, conductive polymers and
 equivalents. Said means include a combination of a means for electrical
 feed-through, such as metal bumps, with a means for mechanical attachment,
 such as underfill, glue, resist, epoxy, or equivalent products.
 Based on the knowledge of person skilled in the art, a glue can be chosen
 that is an electrically conducting glue which allows for separate
 conduction paths through form and functioning.
 The fiber optic face plate 13 transmits optical inputs and outputs of the
 optoelectronic devices 12. The attachment 16 of thin-film semiconductor 11
 to fiber optic face plate 13 has to be transparent for the light of the
 optoelectronic devices. Attachment 16 is preferably done by means of an
 epoxy, including EPO-TEK 353ND of Epoxy Technology Inc, or a polyimide,
 including PIQ-13 of Hitachi chemical, that withstand high temperatures
 (several hundreds degrees Celsius). However, the invention also covers the
 use of other means of attachments, such as soldering glass or direct
 bonding of the thin-film semiconductor 11 to the fiber optic face plate
 13.
 According to a preferred embodiment of the invention, depicted in the FIG.
 2a, fiber optic face plate 13 has markers 211 including grooves and holes.
 The markers 2111, 2112 can also be fabricated upon the fiber optic face
 plate instead of in the fiber optic face plate as shown on the drawings 2b
 and 2c. The FIGS. 2b and 2c show a piece 23 for attachment and alignment
 containing markers. The piece 23 can be attached, for instance with a glue
 24, on the face plate 13 while in alignment to the structures 112 that are
 already processed. Shown in the FIGS. 2b and 2c are the piece (23) for
 attachment and alignment containing at least one marker (2121, 2131) for
 alignment and at least one cavity (2122, 2132) for attachment including at
 least one structure (2123, 2133) for clamping the feature of the external
 apparatus meant for fixing the external apparatus.
 Thus the markers generally labelled as 21 include markers 2111, 2121, 2131
 for aligning and features 2112, 2122, 2132 for attaching an external
 apparatus through a plug. The markers can also be receptacles for pins.
 With markers 21 in or on fiber optic face plate 13, the structure can be
 used as a socket. The socket can comprise a thin semiconductor film with
 optoelectronic devices therein and is attached to a carrier at one side
 and to a fiber optic face plate at another side. An advantage of providing
 markers 21 preformed in or on face plate 13 is that alignment of the
 optoelectronic devices 12 to said features can be obtained during the
 fabrication of the socket. This will be further clarified below.
 In the preferred embodiments of the invention (FIGS. 2a, 2b, 2c), the
 optoelectronic devices for emitting radiation are confined through form
 and functioning. Each of said devices is aligned with at least a part of
 said connection for electrical signals. The confinement through form and
 functioning is shown in detail in FIG. 2d where the confinement is
 realized through mesa etch confinement and current confinement by a
 limited lateral oxidation 28. The technique of mesa etching is known to
 the person skilled in the art. Ways of realizing the confinement can be
 current confinement, proton confinement or oxide confinement. In essence,
 an extended space charge layer is to be defined in order to isolate the
 devices one from another and to realize in this way the confinement
 through form and functioning of the device. Each of the devices can be
 addressed individually through the metal grid structure 27 on one side of
 the thin semiconductor layer and the solder balls 14 on the other side of
 the semiconductor layer. In general, every optoelectronic device 12 has
 two electrodes. Arrays of optoelectronic devices can be operated with one
 electrode common to all devices of the array, or with separate electrodes
 for each device of the array.
 FIGS. 3a and 3b depict the use of a plug 311, 312 connected to a socket.
 Plugs 311, 312 have means for alignment 3111, 3121 and means for
 attachment 3112, 3122. In an embodiment of the invention shown in FIG. 3a,
 the plug 311 can have means for alignment 3111 and means for attachment
 3112 that mate to markers 211 and 212 of a socket according to the
 invention, respectively. Plug 311 can be the termination 311 of a
 light-guiding device 33, that could, for example, be an imaging fiber
 bundle or a bundle of optical fibers. The plug-terminated light-guide will
 henceforth be referred to as structure 34. By plugging structure 34 into
 the socket, the optical inputs and outputs of the optoelectronic devices
 12 can be transported to a remote location. Moreover, because
 optoelectronic devices 12 can be aligned to the markers 2111 of the socket
 during fabrication, and because markers 2111 mate to markers 3111 of plug
 311, plug 311 automatically aligns to the optoelectronic devices 12 when
 it is snapped into the socket.
 FIG. 3b shows the alignment and the attachment of a plug 312 to the socket
 of FIG. 2b. More particularly is shown a fiber bundle 33 terminated by a
 plug 312. Plug 312 includes a part that slides into the cavity 2122 and,
 when pushed, the structure 35 will snap behind the structure 2123 such
 that the plug 312 cannot slide out of the structure 23 any more. To
 release it, the spring 36 has to be pressed and simultaneously the fiber
 33 has to be pulled out. The alignment is automatically arranged by the
 marker 3121 that is guided in the alignment cavity 2121. A minimum
 distance of the fiber end to the face plate 13 can be set by the stud 37.
 Further, FIG. 4 illustrates the use and advantages of this alignment.
 According to this aspect of the invention, the plug can be used as holder
 for an array of optoelectronic devices that match with another array of
 optoelectronic devices. For example, in case the optoelectronic devices of
 one array are light-emitting devices, the plug can contain an array of
 detectors that are essentially aligned to the emitters when the plug is
 snapped into the socket.
 An application in a system for transmitting electrical information and for
 providing an optical interconnect between two chips is disclosed. The
 system is a basic building structure for parallel optical interconnects
 between chips. Imaging fiber bundles, well know from medical imaging, and
 used among others in endoscopes, transport an image from one place to
 another with a one to one correlation between light input and light output
 image.
 In detail, in FIG. 4 are shown a first socket structure containing emitters
 421 and detectors 431, aligned to markers 441 of a first fiber optic face
 plate, and a second socket structure, containing emitters 422 and
 detectors 432, aligned to markers 442 of a second fiber optic face plate.
 The arrays of light emitting devices are spaced very densely, in arrays on
 a pitch of 100 micron or even less. A light-guide 43 is also shown having
 both its ends terminated with a plug. A first plug fits into the first
 socket and aligns to the markers of said first socket. The second plug
 fits into the second socket and aligns to the markers of said second
 socket. Both ends of the plug-terminated light-guide 43 are to be snapped
 into their respective sockets. All light detectors 432 face corresponding
 emitters 421, and all light detectors 431 face corresponding emitters 422,
 by simple mechanical alignment. This is due to the cascade of alignments
 of the devices 421 and 431 to markers 441, markers 441 to plug 451, plug
 451 to light-guide 43, light-guide 43 to plug 452, plug 452 to markers
 442, and of markers 442 to devices 422 and 432.
 An example of the use of the socket of the invention is shown in FIG. 5. In
 this example, the carrier 15 is an integrated circuit die 51. Integrated
 circuit die 51 is attached to a package base 53. Electrical wires 52
 connect electrical input and output pads of the integrated circuit die to
 pins 54 of the package. Now, according to the present invention, the
 socket of FIG. 2 can be used for providing optical inputs and outputs to
 the integrated circuit. As shown in FIG. 5, more than one socket can be
 provided on the same integrated circuit die 51. The optoelectronic devices
 12 integrated on sockets can include light-emitters, such as
 Vertical-cavity Surface Emitting Lasers (VCSELs) or Light-Emitting Diodes
 (LEDs). They also can include detectors such as p-i-n diodes.
 Alternatively, the detectors can be integrated in the integrated circuit
 die 51 rather than in the thin-film semiconductor 11.
 As shown in FIG. 5, an integrated circuit die 51 mounted on and bonded to
 package base 53 can be further capped, for example with plastic moulding
 55, leaving sockets accessible for attachment of light-guides. In this
 way, the electrically and optically interconnected integrated circuit 51
 is completely protected from the environment, while still accepting
 optical inputs and outputs. Therefore, the described method results in the
 fabrication of a practical electrically and optically interconnected
 integrated circuit 51. Electrically and optically interconnected
 integrated circuit 51 can safely be shipped, mounted onto a board, and
 undergo other handling operations. It is more robust and practical to use
 and to mount than a pig-tailed chip--this is a chip which has light-guides
 attached to it--and than a partially-uncovered chip--in which a part of
 the integrated circuit which is intended to offer optical accessibility is
 naked and unprotected from the environment.
 As mentioned previously, the optoelectronic devices 12 can be aligned to
 circuitry of the integrated circuit die 51 during the application of the
 electrically conductive bonding 14. For example, if the electrically
 conductive bonding consists of solder balls, optoelectronic devices 12 are
 aligned during the flip-chip bonding process. Furthermore, as stated
 above, the optoelectronic devices can be aligned to the markers 21 of the
 fiber optic face plate 13 during the fabrication of the socket of the
 invention. Hence, when a plug exemplified by 311, 312 is attached to a
 socket of the invention, it is automatically aligned to both the
 optoelectronic devices 12 of said socket and to the underlying circuitry
 in integrated circuit die 51. Therefore, a connection such as depicted in
 FIG. 4 can be organized between several sockets of the invention on an
 electrically and optically interconnected integrated circuit 51, creating
 intra-chip optical interconnects. Also, such connection can be established
 between sockets of the invention on different electrically and optically
 interconnected integrated circuits 51, creating inter-chip optical
 interconnects between said chips.
 By using a socket structure of the invention on an integrated circuit die
 51 to create electrically and optically interconnected integrated circuit
 51, the total area of optoelectronic semiconductor material consumed is
 small as compared to the area of the silicon integrated circuit. This is
 favorable, because the price of optoelectronic semiconductor material per
 unit area is normally much larger than the price of silicon integrated
 circuits per unit area. Therefore, the proposed method for fabricating an
 electrically and optically interconnected integrated circuit 51 is
 economically more competitive than methods including bonding of an
 optoelectronic semiconductor wafer to a silicon wafer.
 According to another aspect of the invention, the use of a socket structure
 including a fiber optic face plate for providing optical connection to an
 integrated circuit is extended to the case where the optoelectronic
 devices are integrated in the integrated circuit rather than on a
 thin-film semiconductor. A fiber optic face plate with features is aligned
 to circuitry including optoelectronic devices in a carrier, which, in a
 preferred embodiment, is an integrated circuit die. The attachment means
 of the fiber optic face plate to carrier is transparent, and includes the
 use epoxy, cyanoacrilate glue and polyimide. In a preferred embodiment,
 said optoelectronic devices include detectors integrated in silicon
 circuitry.
 A preferred method for fabricating structures according to the present
 invention is disclosed in FIG. 6A to FIG. 6F. Shown in FIG. 6A are
 epitaxial layers (surface layers) 611, 612 grown on a substrate 62, which
 can be a semiconductor, typically selected from group IV, group III-V or
 group II-VI, or a dielectric material, such as sapphire. The epitaxial
 layers include layers 612 for selectively stopping a chemical etch and
 layers 611, that include a junction between two semiconductor materials of
 opposite doping type. Henceforth, the combination of epitaxial layers 611,
 612 with substrate 62 is called the semiconductor structure 63. After the
 growth, partial processing of semiconductor devices can be started, as
 shown in FIG. 6B. This partial processing is henceforth called "rear side
 Processing" 641, because it will ultimately be located at the rear side of
 the optoelectronic devices. Rear side processing 641 can typically be the
 deposition of a metal grid 6411 on top of the epitaxial layers 611, 612.
 It can also consist of a roughening 6412 of the surface of the epitaxial
 layers, using a process such as lithography. Shown in FIG. 6C, the
 semiconductor structure 63 is then flipped over, and epitaxial layers 611
 are attached to a fiber optic face plate 13. Said face plate can have
 preformed markers 211. Preferred means 16 for attachment of the epitaxial
 layers 611 to the fiber optic face plate 13 is a transparent,
 low-shrinkage, temperature resistant epoxy or polyimide. If rear side
 processing 641 is used to process structures in the epitaxial layers 611,
 and if the fiber optic face plate 13 contains markers 211, then alignment
 of said processed structures to said markers 211 is necessary during the
 attachment of the epitaxial layers 61 to the fiber optic face plate 13.
 The next step, illustrated in FIG. 6D, is the removal of substrate 62.
 Mechanical grinding and polishing, as well as chemical etching can be used
 to this end. This removal process stops in one of the epitaxial layers
 612, such that at least layers 611 remain intact. An example of an
 adequate substrate removal technique is given in U.S. Pat. No. 5,578,162.
 After this substrate removal, processing of optoelectronic devices 12 is
 continued, as shown in FIG. 6E. It is called "front side" processing 642.
 If fiber optic face plate 13 contains markers 211, then the front side
 processing requires alignment to the markers 211. This is straightforward
 to achieve with reasonable precision, because markers 211 are imaged by
 the fiber optic face plate to the interface between fiber optic face plate
 13 and epitaxial layers 611, and are visible there through the thin-film
 semiconductor. After front side processing of optoelectronic devices,
 means for electrically conductive bonding 14 are provided to contact the
 optoelectronic devices 12, as shown in FIG. 6F. A preferred means for
 electrically conductive bonding are solder balls. The structure generally
 depicted in FIG. 6F will further be referred to as structure 68.
 The fabrication method disclosed so far can be applied to wafer level. This
 is advantageous for mass production and low-cost manufacturing. The
 above-disclosed fabrication technique allows optoelectronic devices 12 to
 be aligned both to the backside processing 641 and to markers 211
 preformed in the fiber optic face plate 13 over the complete wafer. This
 alignment can be achieved using conventional alignment tools and
 techniques. The alignment of the different parts of the socket of the
 invention in fact is provided by way of the fabrication method.
 Fabrication of a structure according to the invention is terminated by
 separating an individual die 69 from structure 68, as shown in FIG. 6G,
 and bonding it to a carrier 15. In case the means for electrically
 conductive bonding 14 are solder balls, the bonding technique is flip-chip
 joining, eventually followed by filling of the space between carrier 15
 and epitaxial layers 611 using, for example, an underfill, glue, epoxy,
 resist, or equivalent.
 In an alternative fabrication method of the structure according to the
 present invention, the means for electrically conductive bonding 14 is
 applied to a carrier 15 rather than to structure 68. The process sequence
 as described above can also be applied for a face plate which does not
 contain markers. This is shown in FIGS. 7A-7F. FIG. 7G shows a piece 72
 including markers can be attached to the face plate using for instance
 glue 24. This can occur on wafer level before cleavage of the individual
 sockets 78. In an alternative process sequence, the markers can be
 attached after cleavage of the sockets 78. For both alternatives the
 markers can be aligned to the optoelectronic devices.
 Another method for fabricating the structure according to the invention, is
 described in FIG. 8. The thin-film semiconductor containing epitaxial
 layers that include a p-n junction are separated from the original
 substrate by epitaxial lift-off. Devices can be processed before or after
 transfer of said thin-film semiconductor to the fiber optic face plate. In
 the preferred embodiment, the processing is done after film transfer. FIG.
 8A depicts transferred epitaxial films 82, containing a p-n junction,
 attached to a fiber optic face plate 13. As shown in FIG. 8A, several
 epitaxial films 821, 822, . . . can be juxtaposed. This is useful, because
 it is notoriously difficult to lift-off an epitaxial film having the size
 of a wafer, and therefore it is desired to lift-off smaller pieces. The
 processing of the optoelectronic devices can proceed analogously as in the
 case explained in FIG. 6E to FIG. 6F. The structure obtained after
 processing is shown in FIG. 8B, and is referred to as structure 81. An
 alignment of optoelectronic devices 12 to markers 211 in the fiber optic
 face plate 13 is obtained during device processing, analogously as in the
 previously-described method. The application of the means for electrically
 conductive bonding is also analogous the said application in the
 above-described processing method.
 In FIG. 9 is shown an embodiment of the processing of the fiber optic face
 plate to create the markers for use in the fabrication methods of FIG. 6.
 FIG. 9A shows the top side of the face plate, perpendicular to the fibers
 in the plate. FIG. 9B shows the cross-section, with the fibers running
 vertically. The grooves 92 are sawn into the fiber optic face plate 91,
 for instance in a square pattern. The bottom of the groves has a shape
 suited for controlled cleaving of the fiber optic face plate after
 completion of the processing, as shown in FIG. 6G. Grooves 92 extend from
 one side to the other of the fiber optic face plate. Laser machining or
 milling can be used to create a notch 94 at both sides of the groves 92.
 Together with the groove 92, this notch will turn into the receptacle 2112
 for the plug feature 3112 after cleavage of one chip, exemplified as 69,
 from fiber optic face plate 91. Features 2111, that guide alignment pins
 311 of plug 311, can be made in the surface of the fiber optic face plate
 by precision drilling or laser machining. Features 2111 can consist of a
 circular hole 95 with a tapered end 96 for easy insertion of the alignment
 pins 3111.