`US 6,791,119 B2
`(10) Patent No.:
`
`Slater, Jr. et al. Sep. 14, 2004 (45) Date of Patent:
`
`
`US006791119B2
`
`LIGHT EMITTING DIODES INCLUDING
`MODIFICATIONS FOR LIGHT
`5/1982
`0 051 172
`EP
`EXTRACTION
`
`EP 0 961 328 A2=12/1999
`Lip
`1 168 460 A2
`1/2002
`GB
`2 346 480 A
`8/2000
`JP
`56-131977
`10/1981
`
`(54)
`
`(75)
`
`Inventors: David B. Slater, Jr., Raleigh, NC (US);
`Robert C. Glass, Chapel Hill, NC
`(US); Charles M. Swoboda,
`Morrisville, NC (US); Bernd Keller,
`Golcta, CA (US); James Ibbetson,
`Goleta, CA (US); Brian Thibeault,
`Santa Barbara, CA (US); Eric J. Tarsa,
`Goleta, CA (US)
`
`Assignee:
`Notice:
`
`Cree, Inc., Durham, NC (US)
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`US.C. 154(b) by 0 days.
`
`Appl. No.:
`Tiled:
`
`10/057,821
`
`Jan. 25, 2002
`Prior Publication Data
`
`FOREIGN PATENT DOCUMENTS
`
`(List continucd on next page.)
`OTHER PUBLICATIONS
`
`OSRAM Enhances Brightness of Blue InGaN LEDs, Com-
`pound Semiconductor, vol. 7, No. 1, Feb. 2001, p. 7.
`Craford, Outlook for AllnGaP Technology, Presentation,
`Strategies in Light 2000.
`Krames et al., High-Power Truncated—Inverted—Pyramid
`(Al,Ga,_.)o,5lNp sP/GaP
`Light-Emitting
`Diodes
`Exhibiting > 55External QuantumEfficiency, Applied Phys-
`ics Letters, vol. 75, No. 16, Oct. 18, 1999, pp. 2365-2367.
`(List continued on next page.)
`Primary Examiner—Jerome Jackson
`(74) Attorney, Agent, or Firm—Myers Bigel Sibley &
`Sajovec
`(57)
`
`ABSTRACT
`
`US 2002/0123164 Al Sep. 5, 2002
`
`Related U.S. Application Data
`Provisional application No. 60/307,235, filed on Jul. 23,
`2001, and provisional application No. 60/265,707,filed on
`Feb. 1, 2001.
`
`Tint. C0? cee cccccscecsestenesteeees HOIL 33/00
`US. Ch. cece eee cetereneeee 257/99; 257/95; 257/98
`Field of Search ......0...0..ce 257/95, 98, 99
`References Cited
`
`Light emitting diodes include a substrate having first and
`second opposing faces and that is transparent to optical
`radiation in a predetermined wavelength range and that is
`patterned to define, in cross-scction, a plurality of pedestals
`hat extend into the substrate from the first face towards the
`second face. A diode region on the second face is configured
`o emit light in the predetermined wavelength range, into the
`substrate upon application of voltage across the diode
`region. A mounting support on the diode region, opposite the
`substrate is configured to support the diode region, suchthat
`he light
`that
`is emitted from the diode region into the
`substrate, is emitted from the first face upon application of
`4/1990 Fdmond ..............:0:000 357/17
`4,918,497
`voltage across the diode region. The first face of the sub-
`10/1990 Edmond.........
`.
`4,966,862
`
`strate may include therein a plurality of grooves that define
`4/1991 Matsuokaet al.
`5,006,908
`he plurality of triangular pedestals in the substrate. The
`6/1991 Edmond ......
`5,027,168
`grooves may include tapered sidewalls and/or a beveled
`2/1992 Haitz ...
`5,087,949
`
`floor. Thefirst face of the substrate also may include therein
`2/1993 Niina etal.
`5,187,547
`an array of via holes. The via holes may include tapered
`.
`5/1993 Carter, Jn...
`5,210,051
`
`sidewalls and/orafloor.
`5,237,182
`8/1993 Kitagawaet al. oo... 257/15
`
`
`
`
`104 Claims, 15 Drawing Sheets
`
`1730
`
`1724
`
`
`
`C
`
`1310b
`
`1320
`| /
`~~
`Ohmic
`reflector
`barrier
`i
`ponding
`
`
`
`
`
`1750.
`1738:
`1736
`bonding
`barrier
`1734,
`art
`1700
`adhesion
`Ohmic/reflector
`\ 1732
`1310a
`1310
`1722
`
`
`
`1726
`
`wal
`1744
`1746
`!
`1748:
`™~
`
`2107
`
`U.S. PATENT DOCUMENTS
`
`AAAAAAAA
`
`(List continucd on next page.)
`
`1740
`
`Cree Ex. 1012
`
`Page 1
`
`Cree Ex. 1012
`
`Page 1
`
`
`
`US 6,791,119 B2
`
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`
`
`.
`
`
`
`$5,247,533 A
`9/1993 Okazaki et al. oo... 372/45
`
`5,338,994 A
`1+, 307/86
`8/1994. Lezan et al.
`....
`oes ‘ 4 joe manaal
`, oes
`5416342 A
`5/ 9005 Fdmond etal. _........ 257/76
`5,523,580 A
`6/1996 Edmondet al.
`577
`5,585,648 A
`12/1996 Tischler.......
`. 257/77
`5,604,135 A
`2/1997 Fdmondetal.
`. 437/22
`5,631,190 A
`5/1997 Negley ........
`. 438/33
`5,718,760 A
`2/1998 Carter et al.
`.
`. 117/84
`5,739,554 A
`4/1998 Edmondetal.
`-- 257/103
`5,760,479 A
`6/1998 Yanget al.
`
`» 257/749
`3.767.581 A
`6/1998 Nakamura et al.
`5,777,350 A
`7/1998 Nakamuraetal.
`. 257/96
`
`5.779.924 A
`7/1998 Kramesetal.
`16/24
`5,846,694 A * 12/1998 Strandetal.
`430321
`. 257/95
`5,912,477 A
`6/1999 Negley .....
`
`5,917,202 A
`6/1999 Haitz etal.
`, 257/98
`
`9/1999 Chen...........
`. 257/89
`5,952,681 A
`6,015,719 A
`1/2000. Kish, Jr. ct al.
`. 438/29
`
`wee 257/98
`2/2000 Taylor...
`6,031,243 A *
`
`....
`+ 257/98
`6,046,465 A
`4/2000 Wangelal.
`Cooroat “
`e300 ester a
`. solos
`
`.
`6,118,259 A
`9/2000 Bucks et al.
`323/312
`9/2000 Edmondetal.
`6,120,600 A
`- 117/89
`
`6,121,636 A
`9/2000 Morita et al.
`_ 257/99
`6,121,637 A
`9/2000.
`Isokawactal. .
`w. 257/99
`
`. 257/103
`6,133,589 A
`10/2000 _Kramesetal.
`6,139,166 A
`10/2000 Marshall et al
`362/231
`
`6,147,458 A
`11/2000 Bucksetal. ....
`325/225
`6,169,294 BL
`1/2001 Biing-Iye etal.
`» 257/79
`6,177,688 B1
`1/2001 Linthicum etal.
`. 257/77
`6,187,606 B1
`.
`2/2001 Edmond et al.
`. 438/46
`
`22001 Kern et al...
`6194742 BI
`"957/04
`
`6,201,264 BL
`3/2001 Khare etal.
`| 57/97
`
`....
`6,204,523 B1
`3/2001 Careyet al.
`_ 257/98
`4/2001 Carter-Comanet al.
`...... 257/98
`6,222,207 B1
`
`.
`we. 257/94
`6,229,160 Bl
`5/2001 Krameset al.
`6,455,878 BL
`9/2002 Bhatetal. ...
`. 257/99
`
`2003/0006418 Al
`1/2003 Emersonetal.
`» 257/79
`2003/0025212 AL
`2/2003 Bhatet al.
`FOREIGN PATENT DOCUMENTS
`61110476
`1-225377
`06-232510
`07-235729
`08-321660)
`9-82587
`09-223846
`10-163530
`10-233549
`10-256604
`11-150302 A
`11-191641
`11-220168 A
`2000-77713 A
`2000-195827
`
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`
`5/1986
`9/1989
`8/1994
`9/1995
`12/1996
`3/1997
`8/1997
`6/1998
`9/1998
`9/1998
`6/1999
`7/1999
`8/1999
`3/2000
`7/2000
`
`Wo
`WO
`
`WO 00/33365
`WO01/47039 Al
`
`6/2000
`6/2001
`
`
`
`OTHER PUBLICATIONS
`Lambrechtet al., Band Structure Interpretation of the Opti-
`cal Transitions Between Low-Lying Conduction Bands in
`n-Type Doped SiC Polytypes, Materials Science Forum,
`«Vols. 264-268, 1998, pp, 271-274.
`Craford, Overview of Device Issues in High-Brightness
`Light-Emitting Diodes, Chapter 2, High Brightness Light
`Emitting Diodes: Semiconductors and Semimetatis, vol. 48,
`Stringfellow et al. ed., Academic Press, 1997, pp. 47-63.
`Yoo ct al., Bulk Crystal Growth of 6H-SiC on Polytype—
`Controlled Substrates Through Vapor Phase and Charac-
`on
`'
`terization, Journal of Crystal Growth, vol. 115, vol. 1991,
`pp. 733-739.
`.
`.
`o,
`Biederman, The OpticalAbsorption Bands and TheirAnisot-
`ropy in the Various Modifications of SiC, Solid State Com-
`munications, vol. 3, 1965, pp. 343-346.
`U.S. application Ser. No. 09/154,363, entitled Vertical
`Geometry InGaN LED.
`U.S. application Ser. No. 60,411,980,filed Sep. 19, 2002,
`Phosphor—Coated Light Emitting Diodes Including Tapered
`‘Sidewalls, and Fabrication Methods.
`US. application Ser. No. 10/003,331, filed Oct. 31, 2001,
`Low Temperature Formation of Backside Ohmic Contacts
`for Vertical Devices.
`U.S. application Ser. No. 60/294,445, filed May 30, 2001,
`Multi-Quantum Well Light Emitting Diode Structure.
`USS. application Ser. No. 60/294,378, filed May 30, 2001,
`Light Emitting Diode Structure With Multi-Quantum Weil
`and Superlattice Structure.
`+
`or
`.
`”
`US. application Ser. No. 60/294,308,filed May 30, 2001,
`Light Emitting Diode Structure With Superlattice Structure.
`USS. application Ser. No. 09/787,189, filed Mar. 15, 2001,
`Low Temperature Formation of Backside Ohmic Contacts
`for Vertical Devices.
`Invitation to Pay Additional Fecs, Annex to Form PCT/ISA/
`206, Communication Relating to the Results of the Partial
`International Search, PC'1/US02/02849, Aug. 26, 2002.
`International Search Report, PCT/US02/02849, Dec. 2,
`2002.
`
`
`
`Mensz et al., In,GA,_.N/AL.GA,_,N Violet Light Emitting
`Diodes with Reflective p—Contacts for High Single Sided
`Light Extraction, Llectronics Letters, vol. 33, No. 24, Nov.
`20, 1997, pp. 2066-2068.
`Honmaet al., Evaluation ofBarrier Metals ofSolder Bumps
`for Flip-Chip Interconnection, Electronic Manufacturing
`Technology Symposium, 1995, Proceedings of 1995 Japan
`International, 18° TEEE/CPMT, Nec.4, 1995, pp. 113-116.
`Lecct al., Bonding ofInP Laser Diodes byAu—Sn Solder and
`Tungsten—Based Barrier Metallization Schemes, Semicon-
`ductor Science and ‘Technology, vol. 9, No. 4, Apr. 1994,pp.
`379-386.
`
`* cited by examiner
`
`Cree Ex. 1012
`
`Page 2
`
`Cree Ex. 1012
`
`Page 2
`
`
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 1 of 15
`
`US 6,791,119 B2
`
`100 \
`
`160
`
`FIG. 1
`
`PF 140
`130
`
`5170
`
`150
`oe|-
`
`
`,
`|S
`llob
`
`A
`110a
`
`110
`
`
`
`Cree Ex. 1012
`
`Page 3
`
`Cree Ex. 1012
`
`Page 3
`
`
`
`Sep. 14, 2004
`
`Sheet 2 of 15
`
`U.S. Patent
`
`US 6,791,119 B2
`
`Cree Ex. 1012
`
`Page 4
`
`Cree Ex. 1012
`
`Page 4
`
`
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 3 of 15
`
`US 6,791,119 B2
`
`400
`
`FIG. 4
`
`210
`0c
`
`o\,
`
`FIG. 5
`
`Cree Ex. 1012
`
`Page 5
`
`Cree Ex. 1012
`
`Page 5
`
`
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 4 of 15
`
`US 6,791,119 B2
`
`9Ol4
`
`eT,
`
`OSS00SOS?0OvOSE
`
`c0
`
`00
`
`
`
`(Wu)UuUasAeAA
`
`uoijduosqy
`
`a)
`
`Cree Ex. 1012
`
`Page 6
`
`Cree Ex. 1012
`
`Page 6
`
`
`
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 5 of 15
`
`US 6,791,119 B2
`
`FIG. 7A
`
`\ 722
`\/
`
`710a
`
`7B
`
`-——>
`
`ap
`
`ct
`
`700
`
`710a
`
`720
`
`FIG. 7B
`
`/
`
`Cree Ex. 1012
`
`Page 7
`
`Cree Ex. 1012
`
`Page 7
`
`
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 6 of 15
`
`US 6,791,119 B2
`
`FIG. 7C
`
`720
`
`710a'
`
`a \
`
`re
`
`724'
`
`722!
`
`730!
`
`730
`
`722!
`
`710'
`
`740
`
`FIG. 8C
`
`810a'
`
`820
`
`/
`
`840
`
`800'
`
`810
`
`Cree Ex. 1012
`
`Page 8
`
`Cree Ex. 1012
`
`Page 8
`
`
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 7 of 15
`
`US 6,791,119 B2
`
`FIG. 8B
`
`800
`800
`
`810a
`
`820
`
`Cree Ex. 1012
`
`Page 9
`
`Cree Ex. 1012
`
`Page 9
`
`
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 8 of 15
`
`US 6,791,119 B2
`
`FIG. 9
`
`720
`
`710a'
`
`900
`
`
`Cree Ex. 1012
`
`Page 10
`
`Cree Ex. 1012
`
`Page 10
`
`
`
`710
`
`740
`
`412
`
`414
`
`155
`
`810a
`
`820
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 9 of 15
`
`US 6,791,119 B2
`
`FIG. 11
`
`710a
`
`720
`
`220
`1200
`
`Cree Ex. 1012
`
`Page 11
`
`Cree Ex. 1012
`
`Page 11
`
`
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 10 of 15
`
`US 6,791,119 B2
`
`710a
`
`720
`
`FIG. 14A
`
`
`
`
`1410
`
`143q 1410
`
`FIG. 14B
`
`Cree Ex. 1012
`
`Page 12
`
`Cree Ex. 1012
`
`Page 12
`
`
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 11 of 15
`
`US 6,791,119 B2
`
`FIG. 15A
`
`810a
`
`820
`
`Cree Ex. 1012
`
`Page 13
`
`Cree Ex. 1012
`
`Page 13
`
`
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 12 of 15
`
`US 6,791,119 B2
`
`FIG. 16
`
`{/
`79 J130_//
`a[Genn-GaN
`
`280
`
`bonding
`
`1620
`
`sic
`
`reflector
`
`barrier
`
`Cree Ex. 1012
`
`Page 14
`
`Cree Ex. 1012
`
`Page 14
`
`
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 13 of 15
`
`US 6,791,119 B2
`
`FIG. 17B
`
`1750
`
`:
`
`1738
`
`1734
`
`\, 1732
`
`
`
`
`
`
`
`
`FIG. 17A
`
`1730
`
`
`
`
`
`1724
`
`1730a
`Ohmic/reflector
`
`1740
`
`reflector
`
`
`barrier
`
`Cree Ex. 1012
`
`Page 15
`
`Cree Ex. 1012
`
`Page 15
`
`
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 14 of 15
`
`US 6,791,119 B2
`
`FIG. 18
`
`1800
`
`1822
`
`1824
`
`1826
`
`1828
`
`1830
`
`
`
`
`
`reflector
`
`
`
`
`
`
`
`1820
`
`
`
`
`
`barrier
`
`1810
`
`Cree Ex. 1012
`
`Page 16
`
`Cree Ex. 1012
`
`Page 16
`
`
`
`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 15 of 15
`
`US 6,791,119 B2
`
`FIG. 19
`
`LED Manufacturing
`
`
`
`Fabricate diode region on
`silicon carbide substrate
`
`Form grooves and/or
`via holes
`
`
`
`Form semi-transparent
`electrode and/or reflector
`
`Dice
`
`
`Join
`
`
`1910
`
`1920
`
`1930
`
`1940
`
`1950
`
`1960
`
`End
`
`Cree Ex. 1012
`
`Cree Ex. 1012
`
`Page 17
`
`
`
`US 6,791,119 B2
`
`1
`LIGHT EMITTING DIODES INCLUDING
`MODIFICATIONS FOR LIGHT
`EXTRACTION
`
`CROSS-REFERENCE TO PROVISIONAL
`APPLICATIONS
`
`This application claims the benefit of Provisional Appli-
`cation Serial No. 60/265,707, filed Feb. 1, 2001 entitled
`Light Emitting Diode With Optically Transparent Silicon
`Carbide Substrate, and Provisional Application Serial No.
`60/307,235,
`filed Jul. 23, 2001, cntitled Light Emitting
`Diodes Including Modifications for Light Extraction and
`Manufacturing Methods Therefor, the disclosures of both of
`which are hereby incorporated herein byreference in their
`entirety as if set forth fully herein.
`STATEMENT OF FEDERAL SUPPORT
`
`This invention was made possible with government sup-
`port under grant numbcr 7ONANB8H4022 from the
`National Institute of Standards and Technology (Advanced
`‘lechnology Program). ‘The United States government has
`certain rights to this invention.
`TIELD OF THE INVENTION
`
`This invention relates to microelectronic devices and
`fabrication methods therefor, and more particularly to light
`emitting diodes (I.EDs) and manufacturing methods there-
`for.
`
`BACKGROUND OF THE INVENTION
`
`
`
` ficiency of LEDsis the cost per lumen.
`
`Light emitting diodes are widely uscd in consumer and
`commercial applications. As is well known to those having
`skill in the art, a light emitting diode generally includes a
`diode region on a microelectronic substrate. The microelec-
`tronic substrate may comprise,
`for example, gallium
`arsenide, gallium phosphide,alloys thereof, silicon carbide
`
`
`and/or sapphire. Continued developments in TLLEDs have
`
`
`resulted in highly efficient and mechanically robust light
`sources that can cover the visible spectrum and beyond.
`These attributes, coupled with the potentially long service
`life of solid state devices, may enable a variety of new
`display applications, and may place LEDsin a position to
`compete with the well entrenched incandescent and fluores-
`cent lamps.
`One measure of €
`The cost per lumen for an LED may be a function of the
`manufacturing cost per LED chip,
`the internal quantum
`efficiency of the LED material and the ability to couple or
`extract the generated light out of the device. An overview of
`light extraction issues may be found in the textbook entitled
`High Brighiness Light Emitting Diodesto Stringfellow etal.,
`Academic Press, 1997, and particularly Chapter 2, entitled
`Overview of Device Issues in High-Brightness Light Emit-
`ting Diodes, to Craford, at pp. 47-63.
`Light extraction has been accomplished in many ways,
`depending, for example, on the materials that are used to
`fabricate the diode region and the substrate. For example, in
`gallium arsenide and gallium phosphide material systems, a
`thick, p-type, topside window layer may be used for light
`extraction. The p-type window layer may be grown because
`high epitaxial growth rates may be possible in the gallium
`arsenide/gallium phosphide material systems using liquid
`and/or vapor phase epitaxy. Moreover, current spreading
`may be achieved due to the conductivity of the p-type
`topside window layer. Chemical etching with high etch rates
`
`10
`
`is
`
`rya
`
`30
`
`35
`
`40
`
`50
`
`55
`
`60
`
`65
`
`
`
`2
`and high etch selectivity also may be used to allow the
`removal of at least some of the substrate if it is optically
`absorbent. Distributed Bragg reflectors also have been
`grown between an absorbing substrate and the diade region
`o decouple the emitting and absorbing regions.
`Other approaches for
`lhght extraction may involve
`mechanical shaping or texturing of the diode region and/or
`he substrate. However, it may be desirable to provide other
`
`ight extraction techniques that can allow further improve-
`
`
`
`ments in extraction efficiency. Moreover, it maybe desirable
`© increase the area of an LED chip [rom about 0.1 mm? to
`
`
`arger areas, to thereby provide larger LEDs. Unfortunately,
`
`he effectiveness of these shaping techniques may not be
`maintained as the chip dimensionsare scaled up for higher
`power/intensity and/or other applications.
`Much development
`interest and commercial activity
`recently has focused on ILEDs that are fabricated in or on
`silicon carbide, because these LEDscan cmit radiation in the
`blue/green portions of the visible spectrum. See,
`for
`example, U.S. Pat. No. 5,416,342 to Edmondetal., entitled
`Blue Light-Emitting Diode With High External Quantum
`Efficiency, assigned to the assignee of the present
`application, the disclosure of which is hereby incorporated
`herein byreferencein its cntircty as if sct forth fully hercin.
`There also has been much interest in LEDs that include
`gallium nitride-based diode regions on silicon carbide
`substrates, because these devices also may emit light with
`high efficiency. See, for example, U.S. Pat. No. 6,177,688 to
`Linthicum et al., entitled Pendeoepitaxial Gallium Nitride
`Semiconductor Layers On Silicon Carbide Substrates, the
`disclosure of which is hereby incorporated herein by refer-
`ence in its entirety as if set forth fully herein.
`In such silicon carbide LEDsor gallium nitride LEDs on
`silicon carbide,
`it may be difficult
`to use conventional
`
`techniques for light extraction. or example,
`it may be
`
`
`difficult to use thick p-type window layers because of the
`relatively low growthrate of galliumnitride. Also, although
`
`
`such LEDs may benefit from the use of Bragg reflectors
`
`
`and/or substrate removal techniques, it may be difficult to
`fabricate a reflector between the substrate and the gallium
`nitride diode region and/or to etch awayat least part of the
`silicon carbide substrate.
`
`
`
`
`
`USS. Pat. No. 4,966,862 to Edmond, entitled Method of
`Production of Light Emitting Diodes, assigned to the
`assignee of the present application, the disclosure of which
`is hereby incorporated herein by reference in its entirety as
`if set forth fully herein, describes a method for preparing a
`plurality of light emitting diodes on a single substrate of a
`semiconductor material. The method is used for structures
`where the substrate includes an epitaxial layer of the same
`semiconductor material
`that
`in turn comprises layers of
`p-type and n-type material that define a p-n junction ther-
`ebetween. The epitaxial layer and the substrate are etched in
`a predetermined pattern to define individual diode
`precursors, and deeply enough to form mesasin the epitaxial
`ayerthat delineate the p-n junctions in each diode precursor
`rom one another. The substrate is then grooved from the
`side of the epitaxial layer and between the mesas to a
`predetermined depth to define side portions of diode pre-
`cursors in the substrate while retaming enough of the
`substrate beneath the grooves to maintain its mechanical
`stability. Ohmic contacts are added to the epitaxial layer and
`o the substrate and a layer of insulating material is formed
`on the diode precursor. The insulating layer covers the
`portions of the epitaxial layer that are not covered by the
`ohmic contact, any portions of the one surface of the
`substrate adjacent the mesas, and the side portions of the
`
`
`
`Cree Ex. 1012
`
`Page 18
`
`Cree Ex. 1012
`
`Page 18
`
`
`
`US 6,791,119 B2
`
`3
`substrate. As a result, the junction and the side portions of
`the substrate of each diode are insulated fromelectrical
`contact other than through the ohmic contacts. When the
`diodes are separated they can be conventionally mounted
`with the junction side down in a conductive epoxy without
`concern that the epoxywill short circuit the resulting diode.
`See the abstract of U.S. Pat. No. 4,966,862.
`US. Pat. No. 5,210,051 to Carter, Jr., entitled High
`Efficiency Light Emitting Diodes From Bipolar Gallium
`Nitride, assigned to the assignee of the present application,
`the disclosure of which is hereby incorporated herein by
`reference in its entirely as if set forth fully herein, describes
`a method of growingintrinsic, substantially undoped single
`crystal gallium nitride with a donor concentration of 7x10"7
`cm?or Icss. The method comprises introducing a source of
`nitrogen into a reaction chambercontaining a growth surface
`while introducing a source of galliuminto the same reaction
`chamber and while directing nitrogen atoms and gallium
`atoms to a growth surface upon which gallium nitride will
`grow. The method further comprises concurrently maintain-
`ing the growth surface at a temperature high cnough to
`provide sufficient surface mobility to the gallium and nitro-
`gen atomsthat strike the growth surface to reach and move
`into proper lattice sites,
`thereby establishing good
`crystallinity,
`to establish an effective sticking coefficient,
`and to thereby growan epitaxial layer of gallium nitride on
`the growth surface, but low enough for the partial pressure
`of nitrogen species in the reaction chamber to approach the
`equilibrium vapor pressure of those nitrogen species over
`gallium nitride under the other ambient conditions of the
`chamber to thereby minimize the loss of nitrogen from the
`gallium nitride and the nitrogen vacancies in the resulting
`epitaxial layer. See the abstract of U.S. Pat. No. 5,210,051.
`Io view of the above discussion, improved light extraction
`techniques maybe desirable for LEDs, especially LEDsthat
`are fabricated from silicon carbide, that are fabricated from
`gallium nitride on silicon carbide and/or that have a rela-
`tively large arca.
`SUMMARYOF TIIE INVENTION
`
`Woin
`
`30
`
`40
`
`Light emitting diodes according to some embodiments of
`the invention include a substrate having first and second
`opposing faces that is transparent to optical radiation in a
`predetermined wavelength range and that
`is patterncd to
`define, in cross-section, a plurality of pedestals that extend
`into the substrate fromthe first face towards the secondface.
`As used herein, the term “transparent” refers to an element,
`such as a substrate, layer or region that allows someorall
`optical radiation in a predetermined wavelength range to
`wnDp
`pass therethrough, i.e., not opaque. A diode region on the 56
`second face is configured to emit light in the predetermined
`wavelength range, into the substrate upon application of
`voltage across the diode region. In other embodiments, a
`mounting support on the diode region, opposite the substrate
`is configured to support the diode region, such that the light
`that is emitted from the diode region into the substrate, is
`emitted from the first facc upon application of voltage across
`the diode region. In some embodiments, the light emitting
`diode on a transparent substrate with pedestals is flip-
`mounted on a mounting support, with the diode region
`adjacent to the mounting support and a substrate opposite
`the mounting support, for light emission through the sub-
`strate. In other embodiments, the light emitting diode on a
`transparent substrate with pedestals is mounted on a mount-
`ing support, with the substrate adjacent to the mounting
`support and the diode region opposite the mounting support.
`Thus, non-flip-chip mounting also may be provided.
`
`55
`
`aa
`
`4
`In yet other embodiments of the invention,a reflector also
`is provided between the mounting support and the diode
`region or the substrate. The reflector may be configured to
`reflect
`light
`that
`is cmitted from the diode region back
`through the diode region, through the substrate and from the
`pedestals, upon application of voltage across the diode
`region. In other embodiments, a transparent electrode also
`may be provided between the diode region and thereflector.
`In still other embodiments, a solder preform and/or other
`bonding region may he provided between the reflector and
`the mounting support and/or an optical element such as a
`windowor lens may be provided adjacent the first face
`opposite the diode region. In yet other embodiments, the
`diode region includes a peripheral portion and at least one
`central portion that is enclosed by the peripheral portion, and
`the light emitting diode further comprises at
`least one
`electrode on the diode region, that is confined to within the
`at least one central portion and does not extend onto the
`peripheral portion. It will be understood that the central
`portion need not be centered on the diode region.
`In other embodiments of the invention, a contact structure
`for the substrate and/or the diode region of an LED includes
`a transparent ohmic region, a reflector, a barrier region and
`a bonding region. The transparent ohmic region provides
`electrical contact and/or current spreading. The reflector
`reflects at least some incident radiation and also may provide
`current spreading. The barricr region protects the reficctor
`and/or the ohmic region. The bonding region bonds the LED
`package to a mounting support. In some embodiments, the
`unctionalily of the transparent ohmic region and the reflec-
`or can be combined in a single ohmic andreflector region.
`Contact structures according to these embodiments of the
`invention also may be used with conventional silicon car-
`bide LEDs, gallium nitride on silicon carbide LEDs and/or
`other LEDs.
`
`In still other embodiments of the present invention, the
`first face of the substrate may include thercin at least onc
`groove that defines a plurality of pedestals, such as trian-
`gular pedestals, in the substrate. ‘The grooves may include
`apered sidewalls and/or a beveled floor. Thefirst and second
`aces of the substrate may have square perimeters, and/or the
`first face of the substrate may be textured. The light emitting
`diode may further include a plurality of cmission regions
`and/or electrodes on the diode region, a respective one of
`whichis confined to within a respective one of the pedestals
`and does not extend beyond the respective one of the
`pedestals.
`In yet other embodiments of the present invention, the
`first face of the substrate includes therein an array of via
`holes. The via holes may include tapered sidewalls and/or a
`floor. The via holes preferably extend only part way through
`the substrate, but in other embodiments they can extend all
`the way through the substrate. Thefirst and second substrate
`faces may have square perimeters, and/orthe first face may
`be textured. The light emitting diodes may further includeat
`least one electrode on the diode region that does not overlap
`the array of via holes.
`The pedestals and/or array of via holes also may be used
`with light emitting diodes that include silicon carbide or
`non-silicon carbide substrates,
`to allow improved light
`extraction therefrom. Moreover, electrodes as described
`above also may be used with light emitting diodes that
`include a non-silicon carbide substrate. For example, when
`the first face of the substrate has smaller surface area than
`the second face, and the diode regionis on the second face,
`an emission region may be provided on the diode region that
`is confined to within the smaller surface area of thefirst face.
`
`
`
`Cree Ex. 1012
`
`Page 19
`
`Cree Ex. 1012
`
`Page 19
`
`
`
`US 6,791,119 B2
`
`5
`light
`invention,
`In other embodiments of the present
`emitting diodes include a compensated, colorless silicon
`carbide substrate having first and second opposing faces and
`a gallium nitride-based diode region on the second face that
`is configured to cmit light into the substrate upon application
`of voltage across the diode region. Mounting supports,
`reflectors, contact structures, grooves, pedestals, texturing
`and/or confined emission areas/electrodes may be provided
`according to any of the embodiments that were described
`above.
`
`be a
`
`Accordingly, many of the above-described embodiments
`comprise embodiments of means for extracting from the
`substrate at least some of the light that is emitted into the
`substrate by the diode region. Examples of these means for
`extracting include compensating dopants in the silicon car-
`bide substrate to provide a colorless silicon carbide
`substrate, patterning the substrate to define, in cross-section,
`a plurality of pedestals that extend into the substrate from the
`first face toward the second face and/or many of the other
`2 a
`embodiments that were described above, including mount- ,
`ing supports,
`reflectors, contact structures, grooves,
`pedestals,
`texturing and/or confined emission areas/
`electrodes.
`
`Light emitting diades may be manufactured, according to
`some embodiments of the invention, by forming a diode
`region that is configured to emit light in a predetermined
`wavelength range on a secondface of a substrate havingfirst
`and second opposing faces, and that is transparent to the
`optical radiation in the predetermined wavelength range.
`The substrate is patterned before, during and/or after form-
`ing the diode region to define, in cross-section, a plurality of
`pedestals that extend into the substrate from the first face
`towards the second face. In other embodiments, the diode
`region is mounted onto a mounting substrate thal is config-
`ured to support the diode region such that the light that is
`emitted from the diode region into the substrate is emitted
`from the first face upon application of voltage across the
`diode region. The mounting may be preceded by forming a
`reflector on the diode region such that
`the reflector is
`configured to reflect light thal is emitted from the diode
`region back into the diode region through the substrate and
`from the first face, upon application of voltage across the
`diode region. Prior to forming the reflector, a transparent
`ohmic electrode also may be formed on the diode region
`opposite the substrate. A barrier region and/or an adhesion
`region also may be formed after forming the reflector. In
`other embodiments, a mounting support is placed adjacent
`the reflector with the barrier region and/or the adhesion
`region therebetween, and the TED is joined to the mounting
`support. In still other embodiments, an electrode is formed 5,
`on the diode region that is confined to within the central
`portion thereof and does not extend onto the peripheral
`portion thereof.
`Other method embodiments include forming a plurality of
`intersecting grooves into the first face of the substrate to
`define the plurality of pedestals, suchas triangular pedestals,
`in the substrate. The grooves may include tapered sidewalls
`and/or a beveled floor. The first face of the substrate also
`may be textured. A plurality of electrodes also may be
`formed onthe diode region. In some embodiments,a respec-
`tive one of the electrodes is confined to within a respective
`one of the pedestals and does not extend beyond the respec-
`tive one of the pedestals.
`Still other method embodiments according to the present
`invention include reactive ion etching an array of via holes
`in the first face of the substrate. The via holes may include
`tapered sidewalls and/or a floor. The first face also may be
`
`aa
`
`6
`textured. An electrode may be formed on the diode region
`that does not overlap the array of via holes.
`Sawinga plurality of intersecting grooves and/orreactive
`etching an array of via holes into the first face may be used
`for light emitting diodes that include a silicon carbide or
`non-silicon carbide substrate to allow improvedlight extrac-
`tion therefrom. Morcover,
`the formation of an cmission
`region on the diode region that is confined to within the
`smaller surface area of the first face also may be used for
`other conventional light emitting diodes, to allow improved
`light extraction therefrom.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`TIGS. 1-5 are cross-sectional views of light emitting
`diodes according to embodiments of the present invention.
`FIG. 6 graphically illustrates absorption of light versus
`wavelength for silicon carbide at various doping levels.
`FIG. 7A is a top view and FIGS. 7B and 7C are cross-
`sectional views along the line 7B—7B' of FIG. 7A,oflight
`emitting diodes according to other embodiments of the
`present invention.
`FIG. 8A is a top view and FIGS. 8B and 8C are cross-
`sectional views along the line 8B-8B' of TIG. 8A,oflight
`emitting diodes according to other embodiments of the
`present invention.
`FIGS. 9-13 are cross-sectional views of light emitting
`diodes according to yet other embodiments of the present
`invention.
`
`FIG. 14A a cross-sectional view taken along the lines
`14A-14A' of FIG. 14B, which is a bottom view oflight
`emitting diodcs accordingto still other embodiments of
`the
`present invention.
`
`
`
`
`
`TIG. 15A a cross-sectional view taken along the lines
`15A-15A' of FIG. 15B, which is a bottom view of
`light
`emitting diodes according to yet other embodiments of the
`present invention.
`FIGS. 16, 17A and 18 are cross-sectional views of
`emitting diodes accordingto still other embodiments o
`present invention.
`
`ight
`the
`
`FIG. 17B is a top view of FIG. 17A according to embodi-
`ments of the present invention.
`FIG. 19 is a flowchartillustrating manufacturing methods
`or light emitting diodes according to embodiments of the
`present invention.
`
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`The present invention now will be described more fully
`hereinafter with reference to the accompanying drawings, in
`whichpreferred embodiments of the invention are shown.
`This invention may, however, be embodied in manydifferent
`forms and should not be construed as limited to the embodi-
`ments set forth herein. Rather, these embodiments are pro-
`vided so that this disclosure will be thorough and complete,
`and will fully convey the scope of the invention to those
`skilled in the art. In the drawings, the thickness of layers and
`regions are exaggerated for clarity. Like numbers refer to
`like elements throughout. It will be understood that when an
`element such as a layer, region or substrate is referred to as
`being “on” or extending “onto” another element, it can be
`directly on or extend directly onto the other element or
`intervening elements may also be present. In contrast, when
`an elementis referred to