United States Patent [191
`Timlin et a1.
`
`llllllllllllllIllllllllllllllllllllllllllllllllIlllllllllllllllllllllllllll
`USOO5227656A
`Patent Number:
`5,227,656
`[11]
`Jul. 13, 1993
`[45] Date of Patent:
`
`[54]
`[75]
`
`[73]
`
`[21]
`[22]
`[5 1]
`[52]
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`[53]
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`[56]
`
`ELECTRO-OPTICAL DETECTOR ARRAY
`Inventors: Harold A. Timlin, Mason; Charles J.
`Martin, West Chester, both of Ohio
`Assignee: Cincinnati Electronics Corporation,
`Mason, Ohio
`Appl. No.: 609,678
`Filed:
`Nov. 6, 1990
`
`Int. Cl.5 .................... .. H01L 27/14; H01L 31/00
`US. Cl. .................................. .. 257/441; 257/443;
`257/459; 257/460
`Field of Search ............... .. 357/30 B, 30 H, 30 P,
`357/32, 16, 45, 61; 250/208.1, 211 J
`References Cited
`U.S. PATENT DOCUMENTS
`
`3,483,096 12/1969 Gri et a1. ............................. .. 204/15
`3,555,818 l/197l Lambert et a1.
`148/186
`.
`3,577,175 5/1971 Gri et a]. .... ..
`317/237
`3,808,435 4/1974 Bate et al. .............. ..
`250/332
`4,053,919 10/1977 Andrews, II et a1.
`357/30 B
`4,364,077 12/1982 Chiang ........................ .. 357/30 P
`4,646,120 2/1987 Hacskaylo et al. ..
`357/32 X
`4,783,594 11/1988 Schulte et a1. ..... ..
`.. 250/370.08
`
`. . . .. 357/30 H
`4,956,687 9/1990 de Bruin et a1. . . . . .
`4,975,567 12/1990 Bishop et a1. ......................... .. 357/4
`
`FOREIGN PATENT DOCUMENTS
`
`0116791 8/1984 European Pat. Off. .
`0350351 U 1990 European Pat. Off. .
`
`57-73984 5/1982 Japan .
`58-164261 9/1983 Japan .
`WO87/07083 11/1987 PCT Int’l App]. .
`Primary Examiner-Andrew J. James
`Assistant Examiner-—Sara W. Crane
`Attorney. Agent, or Firm-Lowe, Price, LeBlanc &
`Becker
`ABSTRACT
`[57]
`Each diode of an indium antimonide electro-optical
`detector array on a dielectric backing transparent to
`optical energy to be detected includes a junction that
`less than about a half micron from the diode surface on
`which the energy is initially incident. The optical en
`ergy is incident on a P-type doped region prior to being
`incident on a bulk N-type doped region. Both P- and
`N-type doped regions of adjacent diodes are spaced
`from each other. Metal electrically connects the P-type
`doped regions together without interfering substantially
`with the incident optical energy. A multiplexer inte
`grated circuit substrate extends parallel to the backing
`and includes an array of elements for selective readout
`of the electric property of the diodes. The elements and
`diodes have approximately the same topographical ar
`rangement so that corresponding ones of the elements
`and diodes are aligned. An array of indium columns or
`bumps connects the corresponding aligned elements
`and diodes.
`
`38 Claims, 3 Drawing Sheets
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`Raytheon2064-0001
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`Sony Corp. v. Raytheon Co.
`IPR2015-01201
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`

`
`US. Patent
`
`July 13,1993
`
`Sheet 1 (‘1r 3
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`5,227,656
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`(PRIOR ART)
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`(PRIOR ART)
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`Raytheon2064-0002
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`

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`U.S. Patent
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`July 13, 1993
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`Sheet 2 of 3
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`5,227,656
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`US. Patent
`
`July 13,1993
`
`Sheet 3 of 3
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`5,227,656
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`Raytheon2064-0004
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`

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`1
`
`ELECTRO-OPTICAL DETECTOR ARRAY
`
`FIELD OF THE INVENTION
`The present invention relates generally to electro-op
`tical detector arrays and more particularly to an electro
`optical detector array having front faces of semiconduc
`tor elements illuminated by the optical energy, and to a
`method of making same. The invention is also related to
`an electro-optical detector array including multiple
`semiconductor elements that are spaced from each
`other on a dielectric backing, and to a method of mak
`ing same.
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`25
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`30
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`BACKGROUND ART
`15
`Semiconductor electro-optical detectors are either of
`the photovoltaic or photoresistive type. Different types
`of electro-optical detectors are employed for different
`wavelength regions from infrared through ultraviolet.
`For example, photovoltaic electro-optical detectors for
`the infrared wavelength range from approximately 8 to
`12 microns and l to 5.6 microns are frequently made of
`mercury cadmium telluride (I-IgCdTe) and indium anti
`monide (InSb), respectively. The speci?c construction
`of indium antimonide electro-optical detectors is de
`scribed, for example, in commonly assigned U.S. Pat.
`Nos. 3,483,096, 3,554,818 and 3,577,175. While the fol
`lowing description is made for InSb electro-optical
`detectors, the invention in many of its broadest aspects
`is not limited to this material.
`Single element devices, as disclosed in the aforemen
`tioned patents, typically include a P-N junction wherein
`an N-doped bulk substrate carries a P-doped region that
`is exposed to an optical energy source being detected
`Usually, the P-N junction is no greater than about 4
`microns from the surface of a P-type region on which
`the optical energy to be detected is incident. In other
`words, the P-type region exposed to the optical radia
`tion to be detected has a thickness of no greater than
`about 4 microns For. certain InSb devices, the P-N
`junction is closer than 0.5 microns to the surface of the
`P-type region exposed to the radiation. The P-type
`region is desirably positioned so that the optical radia
`tion is directly incident thereon to enable photo
`generated charge carriers formed in the P-type region
`to diffuse, somewhat uninterrupted, to the junction.
`Even in this con?guration, a signi?cant amount of opti
`cal energy penetrates through the P-type region into the
`P~N junction where some additional charge carriers are
`generated and on into the N-type region where still
`more charge carriers are generated. As long as this
`absorption in the n-type material does not occur too far
`away from the junction, the resulting charge carriers
`also diffuse back to the junction. In addition, this ar
`rangement enables optical energy that is not absorbed in
`the P-type region to reach the P-N junction directly.
`Thereby, efficiency in converting optical energy to
`electric energy is relatively high if the P~doped region
`of an indium antimonide detector is arranged such that
`the optical energy is incident on the P-type region.
`While these characteristics have long been known, to
`our knowledge, they have not been achieved when
`relatively large InSb electro-optical semiconductor
`detector arrays have been manufactured. In the large
`InSb array prior art of which we are aware, it has been
`the practice to illuminate the relatively thick N-type
`doped bulk substrate semiconductor material, i.e., the
`"back” face of the array has been illuminated. The
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`5,227,656
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`thickness of the illuminated N-type doped bulk sub
`strate is typically 10 microns which increases the proba
`bility that photogenerated charge carriers will interact
`with crystal defects or other charge carriers in the N
`type bulk substrate. This is particularly true of the
`shortest wavelength energy to which the optical detec
`tor is exposed because the shortest wavelength energy is
`absorbed closest to the back face, and the resulting
`photogenerated charge carriers must travel the greatest
`distance to the P-N junction. In addition, very little, if
`any, of the optical energy in the 1-4 micron region can
`propagate unimpeded to the P-N junction through the
`bulk material.
`The construction and manufacturing method of a
`typical prior art indium antimonide, photovoltaic detec
`tor array are illustrated in FIGS. 1 and 2. In this and
`other prior art arrangements, the optical energy to be
`detected is ?rst incident on the relatively thick (about
`10-20 microns) N—type bulk substrate. Hence, the dis
`tance between the P-N junction and the surface on
`which the optical radiation to be detected is first inci
`dent is approximately l0-2O microns. For the shortest
`wavelengths in the 1-5.6 micron band to be detected,
`i.e., between 1 and 3 microns, there is a relatively low
`quantum ef?ciency because photogenerated charge
`carriers created in the N-type bulk substrate in response
`to the incident optical energy do not proceed in an
`unimpeded manner to the N-type bulk substrate. In
`stead, the free charge carriers resulting from absorption
`of optical energy photons frequently interact with the
`InSb crystal lattice and crystal defects prior to reaching
`the P-N junction, causing the carriers to lose energy and
`recombine with other carriers of the opposite type and
`therefore go undetected In addition, very little of the
`shortest wavelength energy is able to reach the junction
`without being absorbed in the N-type material and cre
`ate photogenerated carriers therein.
`In the prior art arrangement illustrated in FIGS. 1
`and 2, an indium antimonide N-type bulk substrate 23,
`having a thickness of approximately 15 mils with an
`array of P-type regions 24 formed thereon, is connected
`to multiplexer substrate 25 by indium columns 26,
`which can be grown on metal contact pads (not shown),
`typically of gold, nickel or chromium for the P-type
`regions or on the multiplexer substrate or on a combina
`tion of both. A P-N junction, forming a diode, exists at
`each location of P-type region 24 on N-type bulk sub
`strate 23. After the detector assembly including N-type
`bulk substrate 23 and an array of P-type regions 24,
`formed by gaseous diffusion or ionic bombardment, has
`been connected to multiplexer substrate 25, the bulk
`material substrate is mechanically and/or chemically
`thinned and polished to a thickness of approximately 10
`microns, as illustrated in FIG. 2. Multiplexer substrate
`25 includes electronic circuitry having switching ele
`ments with substantially the same topography as the
`topography of P-type regions 24. The electronic cir
`cuitry in multiplexer substrate 25 selectively reads out
`the signal from a selected diode of the electro-optical
`detector array through the indium bump to one or a few
`common signal leads on the multiplexer chip. This
`causes readout of the optical energy incident on a sur
`face of N-type bulk substrate 23 corresponding gener
`ally with the P-type region 24 connected to the indium
`column or bump 26 which is selected by the circuitry on
`multiplexer N-type bulk substrate 25.
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`To withstand the mechanical forces during and after
`thinning, an epoxy bonding agent is injected between
`the array including N-type bulk substrate 23 and P-type
`regions 24 and multiplexer 25. The bonding agent ?lls
`the space between indium columns or bumps 26.
`In use, the structure of FIG. 2 is arranged so that the
`optical energy is initially incident on N-type bulk sub
`strate 23. The optical energy creates free charge carri
`ers, an electron-hole pair for each photon absorbed, in
`bulk substrate 23. If the minority carrier, i.e., the hole in
`N-type indium antimonide N-type bulk substrate 23,
`recombines with a majority carrier, no current results
`and the optical energy is not detected. If, however, the
`minority carrier diffuses to and crosses the junction
`between N-type bulk substrate 23 and a particular P
`type region 24, current is produced in the P-type region.
`Whether a minority carrier diffuses across the junc
`tion is a function of (1) how far away from the junction
`the electron-hole pair is at the time it is created by the
`incident optical energy, (2) the diffusion length in bulk
`material 23, and (3) the density of the bulk material
`defects which act as recombination centers. These de
`fects can exist before processing is performed. How
`ever, other defects are created by several of the many
`processing steps, e.g., by ion implantation, thinning
`and/ or bump bonding. In general, detector efficiency in
`converting optical energy to electrical energy decreases
`as the distance between the junction and the surface on
`which the optical energy is initially incident increases.
`Thinning and polishing operations performed on N
`type bulk substrate 23 place severe stresses on the detec
`tor and often result in N-type bulk substrate cracking.
`Polishing compounds and mechanical abrasion used to
`thin N-type bulk substrate 23 result in microcrystalline
`damage on the surface of and into bulk material 23 on
`which the optical energy is initially incident. The mi
`crocrystalline damage has severe detrimental effects on
`the electrical characteristics of the array. The resulting
`degradation of the bulk material in N-type bulk sub
`strate 23 on which the optical energy is incident pro
`duces a high surface recombination rate in the N-type
`bulk substrate, lowering quantum efficiency dramati
`cally, particularly at the shortest wavelengths which
`are absorbed close to the surface of N-type bulk sub
`45
`strate 23.
`The-detector arrays are usually operated at cryogenic
`temperatures, in the liquid helium or liquid nitrogen
`range. While lower quantum efficiencies at short wave
`lengths may not occur in InSb arrays at liquid nitrogen
`temperatures, the diffusion length (mentioned above)
`decreases dramatically as temperature is lowered fur
`ther such that at liquid helium temperature ranges (of
`interest to astronomers), the performance of the prior
`art devices is degraded. Also, operation at liquid nitro
`gen temperatures causes the arrays to undergo severe
`mechanical strain due to thermal expansion mismatch
`between the bulk material of N-type bulk substrate 23
`and multiplexer substrate 25. The very thin bulk mate
`rial of N-type bulk substrate 23 cannot always accom
`modate the induced strain and is subject to breakage or
`may become deformed to cause bonds between indium
`columns 26 and N-type bulk substrate 23 or the pads
`thereon to fail.
`An additional disadvantage of the prior art methods is
`that the thinning process is performed after sawing the
`detector wafer into individual chips and after bump
`bonding occurs. Hence, e.g., if there are ten arrays on a
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`5,227,656
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`wafer, the thinning process is performed ten different
`times, resulting in an expensive processing technique.
`It is, accordingly, an object of the present invention
`to provide a new and improved electro-optical detector
`array and to a method of making same.
`Another object of the invention is to provide a new
`and improved electro-optical detector array having
`P-N junctions in very close proximity to a surface on
`which optical energy is initially incident, and to a
`method of making same.
`An added object of the invention is to provide a new
`and improved electro»optical detector for infrared en
`ergy in the 1-5.6 micron wavelength band, which de
`tector has relatively high quantum efficiency for wave
`lengths throughout the aforementioned spectrum, and
`to a method of making same.
`A further object of the invention is to provide a new
`and improved electro-optical detector adapted to be
`used in cryogenic temperature environments, but which
`has stable mechanical and electrical properties even
`though the array is subject to temperature cycle ex
`tremes, and to a method of making same.
`Still another object of the invention is to provide a
`new and improved electro-optical detector array
`wherein all detector processing is performed prior to
`.connecting the wafer to external control circuitry, e.g.,
`a multiplexer N-type bulk substrate.
`An additional object of the invention is to provide a
`new and improved indium antimonide detector array
`having relatively high quantum ef?ciency over the
`entire spectrum of use for such arrays, wherein the
`array has stable mechanical and electrical properties,
`even though it is operated at cryogenic temperatures
`and is subject to cycling between those temperatures
`and ambient temperatures, and to a method of making
`same.
`Still another .object of the present invention is to
`provide a new and improved indium antimonide detec
`tor array wherein P-type material in the indium anti
`monide is positioned so that infrared optical energy to
`be detected is initially incident on the P-type material,
`instead of on the N-type material of the detector, and to
`a method of making same.
`
`30
`
`THE INVENTION
`In accordance with one aspect of the present inven
`tion an electro-optical detector comprises a non-metal
`lic mechanical support backing transparent to optical
`energy to be detected, in combination with an array of
`semiconductor diodes on the backing, which diodes
`have an electrical property affected by optical energy
`incident thereon and include a' junction separating ?rst
`and second differently doped regions, wherein the first
`and second regions are positioned on the backing and
`are arranged so that the optical energy to be detected
`and propagating through the backing is incident on the
`?rst region prior to being incident on the second region.
`The first regions are made of a material and have a
`thickness that is a function of the lifetime of carriers
`produced in the first regions in response to photons of
`the optical energy and the capture cross section of the
`optical energy photons by the lattice such that the carri
`ers reach the junction without interacting with other
`possible carriers in the first regions or the photons tra
`verse the ?rst regions without being absorbed; for InSb,
`this thickness is less than one-half micron.
`In accordance with another aspect of the invention an
`electro-optical detector comprises a non-metallic me
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`5,227,656
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`semiconductor. The junctions are between the ?rst
`chanical support backing transparent to optical energy
`conductivity type bulk semiconductor and semiconduc
`to be detected, in combination with an array of indium
`tor regions of a second conductivity type (P-type mate
`antimonide semiconductor diodes on the backing,
`rial for an InSb array). A portion of the semiconductor
`which diodes include a junction separating P-type and
`regions is metallized. The semiconductor regions are
`N-type doped regions that are positioned on the backing
`bonded to a transparent mechanical support backing so
`and arranged so that the optical energy to be detected
`that an optical path subsists through the backing to at
`and propagated through the backing is incident on the
`least a segment of the semiconductor regions. The
`P-type doped region prior to being incident on the N
`thickness of the N-type bulk substrate is reduced while
`type doped region.
`the semiconductor regions are bonded to the backing.
`In accordance with an additional aspect of the inven
`The reduced thickness N-type bulk substrate is etched
`tion, an electro-optical detector comprises a dielectric
`to form an array of diode islands. Each of the different
`backing transparent to optical energy to be detected in
`diode islands includes a corresponding region of the
`combination with an array of semiconductor diodes on
`bulk semiconductor, a junction, and the second conduc
`the backing, which diodes have an electrical property
`tivity type semiconductor. Electrodes are attached to
`affected by optical energy incident thereon and include
`the ?rst conductivity type regions of the islands.
`a junction separating the ?rst and second differently
`The above and still further objects, features and ad
`doped regions, wherein the ?rst and second regions are
`vantages of the present invention will become apparent
`positioned on the backing and arranged so that the
`upon consideration of the following detailed description
`optical energy to be detected and propagating through
`of several speci?c embodiments thereof, especially
`the backing is incident on the ?rst region prior to being
`when taken in conjunction with the accompanying
`incident on the second region. Both regions of adjacent
`drawings.
`ones of the diodes are spaced from each other, to basi
`cally form islands in the backing.
`BRIEF DESCRIPTION OF DRAWING
`The second regions are thinned bulk semiconductor
`FIGS. 1 and 2, described supra, are illustrations of a
`material while the ?rst regions are layers of the semi
`prior art indium antimonide infrared detector array;
`conductor material formed on the thinned bulk semi
`FIG. 3 is a side view of one preferred embodiment of
`conductor material.
`an indium antimonide detector array in accordance
`In accordance with a further aspect of the invention
`with the present invention;
`an electro-optical detector comprises a non-metallic
`FIGS. 4-7 are illustrations of intermediate structures
`mechanical support backing transparent to optical en
`used to form the indium antimonide detector array of
`ergy to be detected in combination with an array of
`FIG. 3;
`semiconductor diodes on the backing, which diodes
`FIG. 8 is a side sectional view of a further embodi
`have an electrical property affected by optical energy
`ment of the present invention; and
`incident thereon and include a junction separating ?rst
`FIG. 9 is a plan sectional view through lines 9-—9,
`and second differently doped regions, wherein the ?rst
`FIG. 8.
`regions are positioned on the backing and are arranged
`so that the optical energy to be detected and propagat
`ing through the backing is incident on the ?rst region
`prior to being incident on the second region. The sec
`ond regions are formed of bulk material, while the ?rst
`40
`regions are layers formed by diffusing a dopant into the,
`bulk material, or by implanting ions into the bulk mate
`rial.
`In a preferred embodiment, metal on the non-metallic
`mechanical support backing electrically connects the
`?rst regions together without interfering substantially
`with the optical energy incident on the ?rst region, i.e.,
`on the P-type region of the indium antimonide detector
`In one embodiment, the metal is arranged as a grid of
`intersecting strips extending in mutually perpendicular
`directions. In a second embodiment, the metal is ar
`ranged as a ?lm having windows for enabling the opti
`cal energy to be detected to be incident on the ?rst
`regions.
`'
`A multiplexer integrated circuit substrate extends
`parallel to the backing and includes an array of elements
`for selective readout of the electric property of the
`diodes. The readout elements and diodes have approxi
`mately the same topography so that corresponding ones
`of the elements and diodes are aligned. An array of
`60
`metal (preferably indium) bumps or columns connects
`the corresponding adjacent elements and diodes.
`In accordance with still a further aspect of the inven
`tion, a method of making a semiconductor optical de
`tector array comprises the steps of forming an array of
`65
`P-N junctions on a bulk semiconductor of a ?rst con
`ductivity type (N-type material for InSb bulk material),
`such that the junctions are close to a surface of the bulk
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`Reference is now made to FIG. 3 wherein photovol
`taic indium antimonide infrared detector diode array 52
`for radiation in the wavelength region from 1 to 5.6
`microns is illustrated as being mounted on optically
`transparent backing 51. Multiplexer integrated circuit
`substrate 53, that extends parallel to backing 51, is elec
`trically connected to the diodes of the array by indium
`columns 54.
`_
`The diodes of array 52 are arranged on backing 51,
`transparent to the optical energy to be detected, so that
`P-type doped regions 62 of the diodes have the optical
`energy to be detected incident on them prior to the
`energy being incident on N-type bulk substrate regions
`63 of the diodes in the array. The diodes of the array are
`formed as islands, such that adjacent diodes are spaced
`from each other by dielectric. P-N junctions of the
`diodes of array 52 between P-type and N-type regions
`62 and 63 are no more than approximately four microns _
`(and are typically less than about a half micron) from
`the surface of each diode on which the optical energy to
`be detected is initially incident. Because of the close
`distance of the individual junctions to the surface on
`which the optical energy is initially incident, charge
`carriers formed in P-type regions 62 diffuse directly to
`the junction to cause ef?cient transfer of optical energy
`into electrical energy by the semiconductor diodes of
`array 52, throughout the wavelength region of interest,
`including the short wavelength end of the spectrum.
`Current ?owing in the N-type regions of the diodes of
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`deposited in sequence on the exposed, upper face of
`array 52 as a result of the incident optical energy is
`N-type bulk substrate 71 and P-type regions 62 to form
`transferred to elements in multiplexer 53 by way of
`the structure, somewhat as illustrated in FIG. 5. (FIG.
`metal contact pads 55 on N-type regions 63, and the
`5 is a schematic representation of metal grid layer 59, as
`connections of the metal pads to the multiplexer ele
`well as the top surfaces of P-type regions 62 and N-type
`ments by way of indium columns 54.
`bulk substrate 71; oxide layer 61 is not illustrated, for
`Dielectric backing 51, transparent to the optical en
`clarity.) Thereby,_there is formed a matrix of square
`ergy to be detected, includes dielectric plate 57 (e.g., of
`mutually spaced P-type regions 62 which overlay the
`sapphire or gallium arsenide) which serves as a window
`top face of N-type bulk substrate 71, leaving a row and
`and has a backface covered with epoxy glue layer 58,
`column matrix arrangement of the N-type bulk sub
`which overlays metal grid layer 59, typically formed of
`intersecting gold strips extending in mutually perpen
`strate that is not covered by the P-type regions. Metal
`grid 59 overlays a portion of illustrated faces of P-type
`dicular directions. Metal grid layer 59 connects each of
`region 62 and N-type bulk substrate 71.
`P-type regions 62 to a reference potential level, such as
`Plate, i.e. window, 57 is bonded to the exposed sur
`ground. The vast majority of metal grid 59 extends over
`faces of metal grid 59 and oxide layer 61 by epoxy glue
`oxide layer 61, preferably silicon monoxide or silicon
`layer 58 to form the structure illustrated in FIG. 4.
`dioxide, which overlays the vast majority of each of
`Typically, anti-reflective coatings are provided for the
`P-type regions 62 of the indium antimonide diodes of
`indium antimonide face exposed to the optical energy,
`array 52 and is transparent to the optical energy to be
`in a manner well known to those skilled in the art. For
`detected, as is plate 57. Metal pads 55 are deposited on
`clarity purposes, the anti-re?ective coatings are not
`the faces of N-type regions 63 remote from the faces of
`20
`illustrated.
`P-type regions 62 on which the optical energy to be
`After the structure illustrated in FIG. 4 has been
`detected is initially incident.
`fabricated, the thickness of N-type bulk substrate 71 is
`Metal grid 59 extends through a portion of oxide
`reduced, to about 10 to 20 microns, as illustrated in
`layer 61 to establish contact with the front face of each
`FIG. 6. The thickness of N-type bulk substrate 71 is
`of P-type regions 62. The percentage of the area of each
`reduced, i.e., the N-type bulk substrate is thinned, by
`front face of region 62 covered by metal grid 59 is rela
`conventional mechanical and/or chemical means. An
`tively small so that the metal grid does not shadow a
`etchant mask is then formed on the exposed regions of
`substantial portion of the otherwise exposed front face
`bulk substrate layer 71 corresponding generally to the
`of P-type regions 62. The diodes of array 52 and metal
`oxide layer regions that contact N-type bulk substrate
`grid 59 are preferably arranged in a square matrix, al
`71, FIG. 6. An indium antimonide wet chemical etchant
`though this is not necessarily the case; e.g., the diodes of
`is then applied to the etchant mask and the exposed face
`array 52 can be arranged in a linear array, a rectangular
`of N-type bulk substrate 71, to cause trenches to be
`array or even in a circular array. Usually at least l6
`formed between the N-type regions 63, as illustrated in
`diodes comprise an array of interest for the present
`FIG. 7. Dry, i.e., plasma, etching or ion beam milling
`invention.
`P~type region 62, N-type region 63 and the associated
`can also be used to form trenches in the detector mate
`rial; the trenches isolate individual islands of the detec
`junction of each indium antimonide diode of array 52
`tor material to form isolated detector diodes. Thereby,
`are arranged so that almost all of the 1-2 micron radia
`multiple spaced diodes, each including P-type region 62
`tion to be detected is either absorbed in the P-type re
`and N-type region 63, are formed. The N-type regions
`gion or the junction, while some of the 2 micron and
`of all the diodes are mechanically and electrically
`longer wavelength radiation penetrates through the
`spaced from each other; the P-type regions of the diodes
`P-type region and the junction to the N-type region. To
`are all mechanically spaced from each other, but are
`this end, the distance to the electrical P-N junction
`electrically connected to each other by metal grid 59.
`between regions 62 and 63 from the face of P-type re
`After the structure illustrated in FIG. 7 has been
`gion 62 contacting oxide layer 61 is no more than 4
`45
`manufactured, metal ohmic contact pads 55 (FIG. 3) are
`microns and is likely to be 0.5 micron or less, while the
`deposited on N-type regions 63 and columns or bumps
`thickness of N-type region 63 is between 5 and 20 mi
`54 are grown on the metal pads. In particular, multi
`crons. This construction enables a signi?cant number of
`plexer substrate 53 is connected to the diodes of array
`photons to be absorbed in or near the junction such that
`charge carriers resulting from the incident optical radia
`52 by growing indium columns or bumps 54 on the
`metal pads and/or regions of the multiplexer corre
`tion diffuse to the junction without recombining.
`sponding with and topographically aligned with the
`Thereby, there is improved quantum efficiency in trans
`ferring optical energy to electrical energy, particularly
`diodes of array 52. Then the wafer is sawed into individ
`ual arrays that are bump-bonded to multiplexer read
`in the short wavelength 1 to 2 micron region.
`Oxide layer 61 engages upper and side surfaces of
`outs.
`In contrast to previous structures, which were P-type
`P-type regions 62, as well as side surfaces of N-type
`regions 63, to provide an electrical insulating layer for
`indium antimonide “islands” with a common N-type ,
`indium antimonide N-type bulk substrate (commonly
`the P-N junctions. In addition, oxide layer 61 prevents
`etchants used to isolate the indium antimonide diodes of
`referred to as a “P on N” structre), the structure of the
`present invention consists of islands each having an
`array 52 into islands, as described infra, from attacking
`60
`metal grid layer 59.
`N~type region on a P-type region to form a separate
`diode having a P-N junction. In the prior art, the opti
`A preferred method of forming the structure illus
`cally produced carriers must traverse many microns of
`trated in FIG. 3 is illustrated in FIGS. 4-7. Initially, as
`N-type indium antimonide to reach a carrier collection
`illustrated in FIG. 4, bulk N-type indium antimonide
`region. In the InSb embodiment of the present inven
`substrate 71, having a thickness of approximately 10
`tion, the optically produced carriers only must traverse
`mils, for example, has P-type regions 62 formed thereon
`0.5 microns (or less) of P-type region 62 to reach the
`by using a gaseous deposition process or by ion bom
`carrier collection region. In the present invention, the
`bardment. Oxide layer 61 and metal grid 59 are then
`
`40
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`65
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`Raytheon2064-0008
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`20
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`5,227,656
`10
`9
`The edge of the P-N junction of each diode is exposed
`P-type material in the islands is electrically connected
`on the side walls of each mesa. Oxide and metal patterns
`by metal grid pattern 59 and all of the diode islands are
`mechanically spaced from each other by etching the
`are then deposited on this surface just prior to attach
`ment to the transparent backing. Subsequent backside
`material between the P-type layers. Because of these
`thinning and etching are performed in accordance with
`factors, the present invention is considered as an “N on
`the present invention, as previously described in con
`P” device.
`nection with FIGS. 3-7.
`The only reason, in the present invention, for thin