SEL EXHIBIT NO. 2015
`INNOLUX CORP. v. PATENT OF SEMICONDUCTOR ENERGY
`LABORATORY CO., LTD.
`
`IPR2013-00064
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`

`

`SIMPLE PROCESS FOR MAKING NEW SELF-ALIGNED TIT
`WITH IMPROVED ON-CURRENT.
`
`Joe-Beam Cboi, Hoo-Youna Lee, In-Woo Kim, Suna-Jun Boe,
`Oyu-Hyun Lee and Hoc-Sup Soh
`Raearch I Group, LCD Division, LO ElcclrOnics Inc.
`LO RctDCenter, m H~ ~u.
`Anyq-sbi, K)'Wl31d-do, 430-080, KOREA
`
`A oimplc process for maltina ocw oclf-alijncd a-Si:H thin film
`tnnsistor bu boon popoood in Ibis paper. In orcle: 1o pattern boCh ecdl
`otopper SiN, and tbannel a-Si:H simultaneously, only one photo and
`one rac:ti"' ion ecdllna (RIE) process were used. Second ..SI:H J.ya(cid:173)
`was deposiled prior 1o the deposition of n • a-Si:H lay<r. Compored to
`that of the TFT without oeeoncl ..Si:H laytt, !.,. of the TFT with
`occoncl a-Si:H lay<r incmoocs because of the increaoc of spece chorgc
`limlled curmtt throuah the looser overlop lenath- As a resul~ the .,.,.
`cuneot of the new self-elisned TFT is comparable 1o that of the
`oon..,.tional oclf-ellsned TFT. As the deposition power of occoncl ..
`Si:H inaeaocs, the thresllold •ol113<' dectcues and the roeld effect
`mobility iDcreases. At the hiah depositioo power, the damaa<d SiH
`bond, considered as a positive chorge-trapping ceotef, 11 the top of the
`pte illsulator in the overlop rqioo would be etched more effectively
`by the hiah encrsY hydrosen plasma. This decrease of positi"' chorge(cid:173)
`trapping call"' is c:oasistant with the lower thresllold voltaae-
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`INTRODUcnON
`
`Since the bydtoaenated amorpbo., silicon (a-Si:H) thin-film tnnsistor (11'1') has
`been considered u 1 good driving and switching device for the active matrix liquid
`crystal disploy(AMLCO) and other larsc 8lal electronics( I], the TIT-LCD industry has
`been srown up to tbe mass production era. So many roocar<hcs have been focused not
`only on the physics but also on the improvement of image quality of the Iorge an:
`AMLCD with low manufi>cturing cost and high production yield.
`
`T)'plc:ally, there are two kinds of structure in inverled-sla88ered TIT, bock channel
`cleb (BCE) type and etch stopper (E/S) type. Among the two stru<:luno, EIS type TIT is
`less photo sensitivity due to the thinner a-Si:H layer and less lcalcagc cumnt due to its
`lower top interfacial density of stAie3 than the Bell type TIT.(2]1lspccially, self-aligned
`TIT (SA·TFT) is considered as a prominent structure for better imoge quality because
`the uniform and SlDill capoocitance between BJ101drain overlap could be made all over
`the display arca.(3]. But, the process for making SA-TIT is more complicated than that
`for BCil TIT. Usually, in order to make EIS SiN, and channel a-Si:H, pbotolitbosJapby
`and ciCb steps arc used twice. These are wet ciCb process with buffered hydroOuoric
`(BHF) acid for EIS SiN., and dry ciCb for channel a-Si:H.
`
`In order to reduce the process steps, Kuo(4] reported a simple process with OM
`photo step and two ctdt. step~ to set EJS SiN. and channel ... si:H . But the on--current of
`the TIT prepared by that process is not ao high u that of the SA-TIT prepared by
`conventional method. Baides, the BHF was used to pattern the EIS SiN,. As the Keto
`et aJ rcported.{S], oomc porticlcs ...,h u (Nf4)JAIF• and (NH,)>Sif, would be procluccd
`from the intcnetion between the glass substlate and BHF solution. These porticlcs arc
`hardly mnovcd by conventional cleaning method. If these porticles would be auacbed to
`the glass suhstralc, these might causcaomc defects in TIT omoy.
`
`In this worlc, a new SA-TIT with improved O<KUrrcnl has been prepared by simple
`and clean process. Only one photo and etch step was used for the EIS and channel a-Si:H.
`In order to - the oo-cuncnt of the new SA-TIT, the sec:ond intrinsic a-Si:H layer
`was deposited a1 different deposition power. The role of the sec:ond a.Si:H layer and the
`effect of the deposition power of it on the TfT characteristics was investigated.
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`EXPEREMENTALPROCEDURES
`
`Figun: I shows the ~cal structure of the new SA-TFT with second a-Si:H Ioyer.
`
`P aaelvatlo
`
`P ixe l
`
`Gate lneulatol Gate
`
`\
`
`Fig. 1 . The ~cal view of new oelf-allsned TFT.
`Al-liloy of 2500 A wu depositN oo the &Ws subotrale (Coming 1737) by
`magnetron sputterlna system (Leybold, ZV6000), IUld ponemed as a gate bus line IUld
`then anodized. The gate inaualor SiN, (4000 A). channel a-Si:H (600 A) IUld 1!/S SiN,
`(2000 A) wae deposi!N oequenlially by plosma eDhalx:ed c:bomical vapor deposltioo
`system (PECVD, ADelva 9106) at 320 "C, 250 "C IUld 230 "C, rapectively. The bock
`side exposing method was used 10 fonn the 1!/S blend photo resist pott<m. The initili
`overlap length after developmelll was O.S ,._ Then reactive ion etchilla (RIE) process
`(PSC, DES-325EA) was applied 10 poaem both 1!/S SiN, IUld clwwl a-Si:H
`simultaneously in one vacuum chamber with the feedlns sases of CF, + He + 0, for SiNx
`IUld CF,+ C!,+O, fora-Si:H. Because the etch selectivity between thiek SIN, end thin a(cid:173)
`Si:H was very low, end point deu:ctor (EPD) aensor was used 10 minintW. the damaae on
`the sate insulator for 1!/S SiN, . Then n • a-Si:H Ioyer of 500 A IUld Cr of I SOO A wae
`deposited. After aoun:c/drain dectrod<o --. poUemod, n' a-SI:H was etched usins
`sowceldrain pattern as a maslc. Then the passivation SiN, of 3000 A was deposi!N IUld
`the ooJJiaet bole was patterned. Finlily, the ITO u a pixel electrode was deposl!N IUld
`then patterned 10 oomplete the new SA-TFT.
`Seoond a-Si:H layer of SOO A was deposi!N prior 10 the depositioo of n' a-Si:H
`Ioyer in order 10 lncreeoc the on-cumnL And seoond a-Si:H layer was deposited at
`diiTerutt power of 70 W, 100 Wand 200 Win order 10 invostlgate its effect on the V,..
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`The overlap length was meas!UM by lhc scanning electron microscope (SEM).
`Transftt curves and outpul c:urves ""'"' measut<d wilh HP414SB panmeler analyur.
`The leasl·squate melbod was wed lo extn1c1 porameoen such as V,. from 1< Ill vs V 4
`c:urv ... The deplh profilina was pttfonned by secondaly ion mass spectroooopy (SIMS)
`in order to dctaminc the composition profile at the interface between sooond a-5i:H and
`damaaed gsle insulslor SiN,.
`
`RESULTS AND DISCUSSION
`
`Figure I shows lhc lop view of lhc new SA·TFT with second a.Si:H layer. The
`oompleled overlap length is about 0.8 1.111 which means lhallhc undercut of EIS SiN, is
`about 0.3 uo below the EIS pholo r..isr pallcm. Because lhc RlE crchina melbod is an
`anisolropic process, il is much easitt 10 control lhc undercut length of lhc EIS SiN, by
`RlE melbod than by Wei etching method with BHF.
`
`Fig. I . The vmical and lOp view of new self-aligned TFT.
`
`The Slacked l4ym atlhc overlap n:gion consist ofCf I n• •·Si:H I second ...Si:H I
`SiN1 • Therefon:, thtte is no increase oflhc contact r..isrance by the second a·Si:H layer
`compan:d 10 lhc conventional SA· TFT.
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`The ln.I>SfercurYeS of the new SA·TFT wilh a WI Lratio of24,./9 ,.are shown
`in Fig. 2. The aolld line is a result of the TFr wllh ocoond o-Si:H Ioyer ODd the duhcd
`line is a result of the TFr without scoond ..Si:H layer. 1,. i.....,.. in the TFr wllh lhc
`ocoond a-Si:H layer. Especially, the incmuc of the on-eumnt is teen more clarly in lhc
`sotutation resJon. The 1,. of the TFr wllhcut oecond a-Si:H Is as low as 0.3 IJ}.,II V1 •
`20 V ODd v, •10 V. This is not comparable to the penormanca ofSA·TFT prepoz<d by
`conventiooal method. In tbe case of the TFr wllh the second a-Si:H Ioyer, the 1,.
`incmues up to 3 .. 52 pA which is comparable to lhllofthe conventiooal SA-TFT.
`
`WIL • J41t (J ,. J
`V, • 11Y.Y,•JIV
`
`10 ..
`
`10 ..
`
`10 ..
`10"7
`
`< to ..
`_..,
`• 10''
`10·10
`
`10"11
`to"" ~---"'
`10"1,
`1 o· ,. ~:!-:'"-!:'~~"""!-~,....,'="'='
`·20·15·10 ·& 0 5 10 15 20
`Vg(V)
`
`Fis.2. The transfer cW"VCS of the new self·
`aligned TFr : Solid line is for the TFr
`wllh ocoond o-Si:H !eyer ODd the dulled
`line is for tbe TFr wllhout second ..Si:H
`Ioyer.
`
`V, • 11V,Y,•JOY
`
`' WIL • lllt2 (Jl fll)
`i
`( i
`I I
`.li 2
`~ • •
`I
`_..,
`) I IL•c
`
`0
`3
`2
`1
`0
`·1
`4
`4
`Gate/Source overlap (~m)
`
`Fig.J. The dRin cwn:nt dcpenderu on
`tbe pk/""""" overlop lenslh It V 1 • IS
`Vllld V,• IS V from ref.(S)
`
`Assumlns tbe toCa1 cumnt consists of the channel cumnl in the intrinsic TFr ODd the
`spoce cJwae limilcd cUITCIII ( SCLC ) Ullda- the contoc1 resJons, the TFr penormonce
`would be _.,ximllely IIIIDC as the 1011li-infinite oontoc1 wben the overlep .,..,.,.... duee
`timca oftbe chanootcriotie lenslh (A ,)[6].1n Ibis ranse. tbe on-eumnt is limited. by tbe
`channel mobility in tbe intrinsic TFT. Wbe:rus, if tbe overlep lenslh is less !han critical
`overlap lenslh ( I., ), tbe total current could be limited by lhe SCLC Wider tbe eontoc1
`resJon.(7) The I., would be the same meanins as 3 X A , • Tbe5C raults has bcc:n
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`proved experimentally with the SA· TFT structure. (8] A!J shown in Fig. 3, the 1,
`increaoes as the overlap length increaoes up 10 L,. but the !.,. keeps almost - t in the
`range of the oved.op length over L,..
`The increase of!.,. in the new SA·TFT could be explained like followinas ; If the
`oceond a-Si:H layer is not deposited, the overlap length is only 0.06 ja of the side Will
`of the channel..Si:H layer. Because this overtop length is much smaller than the L,., the
`on-cumnt is limited by the SCLC under the contad region. If the second a-Si:H layer is
`deposited prior to the dcpcsition ofn' a-Si:H layer, the ovcrlop length i~ up 10 0.8
`sa In this ovcrlop length, the total cumnt is limited by the channel mobility. Because the
`interface bctw<cn the gate insula10< ood the channel ..Si:H layer would keep in low
`density of stela, the clwlllcl mobility could be as 111111e as tlllt of the conventional SA·
`TFT. lbercfORI, the on-curmrt in the new SA·TFT with second ..Si:H layer could be
`improved 10 the value comparable to that of the conventional SA-TFT.
`
`Fig= 4 shows the effect of deposition power of occood a·Si:H layer on the threshold
`voltage. The second a·Si:H layer was deposited 11 70 W, roo W ood 200 W. As the
`deposition power incruscs, the V • decreases. Abo as shown in Fig. S, the mobility
`in<m~SCS as the deposition power i~.
`
`2.1110''
`
`2.0x104
`
`--200W
`•••••• IOOW
`.......... 70W
`
`7.0
`
`•••
`
`1.0 •
`- 1.1
`!
`
`>
`>Iii
`
`1.0
`
`4.1
`
`~ 1.1x10'1
`;
`
`1.0x104
`
`I.Ox10-4
`
`_ w I
`
`4 .0 10
`uo
`tOO
`200
`D•po•lllon Power ( W I
`
`0.0
`0
`
`' •'
`l •
`•'
`•
`
`·' • ·' < ·' ;'
`
`/
`.•
`' < ,.
`·'
`I
`
`10
`V01VI
`
`u
`
`20
`
`Fia. 4. The dcpcndcncc ofV • oo
`deposition power of second a·Si:H layer.
`
`Flg. S. The output curves foe the TFTs
`with dilf<:mll second ..Si:H layer
`deposition power.
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`Genenlily, if the density of states at inlcrface between the ~ inrulalOr and the a(cid:173)
`Si:H is low, the v. incn:ues u the deposition power of a-Si:H layer iDcreues bccauoe
`the surface of the~ insulator would be clamaBed by the blah enersy plasma durins the
`deposition process.[9]
`But in this new SA-TFT, the -race of the ~ insulator at the o><:rlap rogion might
`be clamaBed during the previous dry etclt process for EIS SiN, and channel a-SI:H laya-.
`l!speeially, the cJamaae would be more oerious lo the Si-H bond lhan lO the N-H bond in
`the gale insulator SiN, bocauoe the bondina enersy of the Si-H is 3.9 eV and that of the
`N-H bond is 9.8 eV. As a resull, the Si danglina bonds might ir1aase and the bond
`slrenith of Si-H would be wealcmed after dry etch process. Besides, the SiH I NH ratio at
`the lop of the ~ insulaiOr is nne of the faeiOrs wnlch would affect the lhrosbold wlla8e
`bccauoe SiH in the nilride is lobo u the positive cbar&o-4lapplog cenler and NH in the
`nilride is lobo u the negative cJwse-ttappina center.
`
`-
`
`a l
`
`f
`
`_., ": • .. • • •
`H
`~· · ·•·('•'
`. ,.
`-},,.[
`
`--
`
`a 1
`-- - --~-
`• • • • • • • • • • • • • • • • • •
`H
`200W
`
`.. -c:
`
`" 0
`
`0
`
`a 1
`-----------~
`H
`"' • • • • • • • • • • • • • • • • .. • •
`~ •• •• • .. • •• • • • .. /1 • •
`H
`• N
`,
`1 0 0 w
`
`I
`
`~ a 1
`~
`r,, -,-, .. 411' .... """
`~ a 1
`a 1
`1/_
`-- - ------~
`.,.. -=--· • • .... • • • .. .... • • .. • • •
`H
`H
`.... • • ...... • .. .. .. • .. , ...
`·.,• N
`I
`r; ...... ,-.. -' -1\.._ ..... ,.....
`7 0 w
`0
`10 100 1 1 0 200 210 JO O J IO 4 00 41 0
`Sputte r ing Time (tee)
`Fis. 6. Tbe SIMS depth profile fiom the lop of aeeond a-SI:H 10 the middle
`of the~ Insulator SiN,.
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`Figun: 6 shows the SIMS depth profile from the top of sccond ..Si:H layer to the
`middle of gate insulator. As the deposition power of second ..Si:H layer increases, the
`SI·H bond II the interfK< u recluccd but the N-H bond k-
`eonstanl Thit would imply
`that the etchiJ18 of the daJDa&cd Si-H bond or daJ18lins bonded Si would be promoted by
`the hydrogen plasma with higber energy as the deposition power incraocs. Thlt
`cleerease of the SiHINH ratio II the interfoc:e eorrosponds to the deerease of density of
`positive c:harge>-trapping center wbich ls oonslstent with the lower tlue$hold voltage.
`This =Ut would sussest that the 1FT performance of the new SA·lFT could be
`improved by the surfoa: treatmcnt prior to the second a-Si:H layer on the gale insulator.
`
`CONCLUSION
`
`Simple process for maldns new self-aligned 1FT has been propoxd in lhU paper.
`The second a-Si:H layer has been deposited prior to lhe n'laycr. Without the sccond
`a.Si:H layer, the otKWtCDt is limited by the SCLC under the contact ~ns bccauoc the
`overlap length is too short. But in the case of the TFT with second ..Si:H layer, the
`overlap ICJ181h lnaascs ncar the critical overlap length. So 1.,. would be limited by the
`channel mobility which is comparable to that of the conventionaloelf-aligned lFT. The
`1.,. of3.S2 s.o1 with w 1 L• 24/9 could be obtained 11 v, - 20 v and v,-10 v .
`As the deposition power of secood a.Si:H layer increoses. the V o. decteascs due to the
`decrease of the positive chargo-llappins center of Si-H bond and the hydrogen would
`passivate the daJ18lina bond ofSi at lhe interface of the daJDaacd gale insulllor.
`Only one-step etch process. RIE. is used to form both EJS SiN, and channel a-Si:H
`layer simultaneously. Tbc: glus substrate could be pro ccueiJ under the clean condition
`bccauoc the reaction of glass and BHF is avoided. The whole self-aligned TFT array
`includiJ18 the pad area of the TFT array could be prepared by S mask steps.
`
`AC KNOWLEDGMENTS
`
`!appreciate the manasina director, Mr. C. R. Lee, for his encouraaement on lhe RAD
`activities and the member& of research I group for their helpful discussion on lhU report.
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`REFERENCES
`
`I I I See the pmceedinp or the Society £or Information Display (SID), 1996
`[2) M. J. Powell, IEEE Trans. Elrt:tron DCllicr1, 36, 2753, (1989)
`[3) N. lbmki,Jopa~~L>Uplay '92 DiBUI, 20S, (1992)
`(4) Y.Kuo,J. Eltctrocloem.Soc., l43,1469,(1996)
`(5) Yoshilllri Kato, Sbinlti<hi Miwo, and Sbiger Yunamolo, 1996 L>Uplay
`Monufactoulng Ttchnology Conf•nncr Digtll, 33 (1996)
`[6) R. R. Troutman and A. KOiwal,IEEETrans. EJoctron Dtvlcr~, 36, 291S (1989)
`(7) G. E. Possin, D. E. Castlc:bcrry, W. W. Piper, and H. G. Pllb, Prot. of the SID
`26, 183 (198S)
`(8) Shulcbi Ucbilc.op, Muabiko Akiyama, Talwbi Kolzumi, Mltsusbilkoda and
`Kouji SUluici, MDL Ru. Soc. Symp. Proc.l58, 1025,1992
`[9) Y. Kuo, The: ~ical Society Proceedings Vol 94-35, Tloin Film
`Trntulltor Ttchnologyll, 174, 1995
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