A Review of SiC Reactive Ion Etching in Fluorinated Plasmas

F rF ih et lFX e eview of ig etive son ithing in pluorinted lsms

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physF sttF solF @A PHPD THS @IWWUA ujet lssifitionX TIFVHFthY TVFQSFfsY UQFRHFxsY T

e eview of ig etive son ithing in pluorinted lsms

F rF ih @AD F xen @AD nd eF tF teklI @A

@A fell vortoriesD vuent ehnologiesD yrlndoD pv QPVIWD e

@A xnoeletronis vortoryD heprtment of iletril nd gomputer ingineeringG gomputer ieneD niversity of gininntiD gininntiD yr RSPPIEHHQHD e

@eeived tnury QID IWWUA

eserh nd development in semionduting silion ride @igA tehnology hs produed signifiE nt progress in the pst five yers in mny resX mteril @ulk nd thin filmA growthD devie fritionD nd pplitionsF e mjor ftor in this rpid growth hs een the development of ig ulk rystls nd the vilility of rystlline sustrtesF gurrent leding pplitions for ig deE vies inlude high power nd high temperture devies nd light emitting diodesF hue to the strong onding etween i nd g @i?g IXQR ? i?iAD wet hemil ething n only e performed t high tempertureF hereforeD plsmEsed @?dry?A ething plys the ruil role of ptterning ig for the frition of vrious eletroni deviesF sn the pst severl yersD retive ion ething @siA of ig polytypes @Qg nd TrA hs een investigted in fluorinted gses @primrily grpQD gfrpQD gpRD pTD nd xpQAD usully mixed with oxygen nd osionlly with other dditives or in mixE ture of fluorinted gsesF sn this pperD review of ig si is presentedF he primry emphsis is on ething of the Qg nd Tr polytypesD ut some results on si of the Rr polytype re inludedF he pper overs the si ething mehnismsD provides typil ething properties in seleted plsE m onditionsD disusses the effets of hnges in vrious ething prmetersD suh s plsm presE sureD density nd powerD ething timeD etF he ething of fetures of sizes vrying from suEmm to tens of mm9s is ddressedF pinllyD optimum ething onditions nd trdeEoffs re onsidered for vrious devie onfigurtionsF

IF sntrodution

sn the erly IWTH9sD t the eginning of modern silion ride @igA developmentD ig reserh ws onduted only on smll piees @`I mA produed y the eheson proess ID whih is urrently used for the snd pper industryF sn the reent yersD lrger re TrE nd RrEig sustrtes @rehing %S m dimeterA otined from oules grown y the modified vely sulimtion method hve eome ommerilly ville PF he vilility of these ig sustrtes hs led to gretly inresed reserh nd developE ment in ll spets of igF righEqulity ui nd hexgonl ig epitxil lyers hve een suessfully grown on the rystlline ig sustrtesF por useful ig devie produE tionD lrge re nd defetEfree Q sustrtes re requiredF et the sme timeD the growth of QgEig on i sustrtesD hs ontinued to improve R to UF his heteroepitxil pE proh hs the ultimte gol to provide truly lrge re nd low ost ig sustrte mterilsD s well s the potentil integrtion of ig high voltge tehnology with i

I he uthor to whom orrespondene on this pper should e ddressedF eEmilX FsteklduFedu

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F rF ihD F xenD nd eF tF tekl

miroeletronisF his generl mteril vilility hs opened the wy to signifint progress in the frition of vrious ig eletroni devies for pplitions requiring highEtempertureD highEspeedD nd highEpower opertion V to IQF romising eletril performne for wipi9s IRD ISD wypi9s ITD IUD thyristors IVD IWD nonEvoltile memory devies PHD PID heterojuntion ipolr trnsistors @rfA PP to PUD hrgeE oupled devies @gghA PVD nd high rekdown voltge hottky PW to RH nd p?n juntion diodes RI to RS hve een reportedF rious ething hrteristis re reE quired for the ptterning of these deviesF eviews RTD RU of higher power semionduE tor eletronis show ig s the est ndidte mteril for the ner future smrt power tehnologyF his is minly due to its outstnding mteril properties suh s high therE ml ondutivityD high eletri field rekdownD high eletron sturtion veloityD nd reltively etter developed devie frited proessesF

he prmount reson for using plsmEsed ething of i or sss? semiondutor mterils is to tke dvntge of the reltive nisotropy of plsm ething in order to preisely ontrol the lineEwidthF his eomes extremely importnt when the devie feE ture is t the suEmm sle `I mmAF por igD nother importnt reson to employ plsE m ething is the hemil stility of ig whih mkes ?wet? ething of devie struE ture very diffiultF sndeedD wet ething of ig hs to e done either t elevted temperture @bTHH gA in lkline solutions RV or with photoeletrohemil ething t room temperture RW to SIF st is importnt to note tht lineEwidth ontrol is very diffiult in the wet ething of ig proess under suh high temperture or photoEssisted hemil ethingF his explins why plsmEssisted @?dry?A ething plys ruil role in the frition of vrious of ig deviesD for oth lrge nd smll dimensionsF

etive ion ething @siA of ig in fluorinted plsms hs een developed to the point where it is now widely employed in oth the reserh nd development environE ment nd ommeril produt frition PF sn our reserh lortory t the niverE sity of gininntiD we hve worked for the pst ten yers on the si of ig for eletroE ni devie fritionF e hve investigted spets of ig si in fluorineEsed plsmsD leding to greter understnding of dry ething issues of ig mterilsF sn the erly stge of these investigtionsD morphous SP nd polyrystlline ig SQ were emE ployedF wore reentlyD QgED RrE nd TrEig si hve een reported in vriety of fluorinted gses @grpQD gfrpQD gpRD pTD nd xpQ usully in omintion with oxyE genF ig si in fluorinted plsms hs een shown to produe useful eth rtes @IHH to IHHH #eGminA nd high degree of ething nisotropy leding to the ptterning of suE mm feturesF yne diffiult spet of ig si hs een the formtion of residues @whih led to rougher surfeA fter longer term ething under mny onditionsF his is @in prtA euse the ommeril si systems re designed to ommodte multiple lrge i wfers rther thn the muh smller ig sustrtes urrently ville @thus the re of the eletrode is usully muh lrger thn tht of the ig smples eing ethedAF esiE due formtion n e serious prolem for susequent proessesD suh s metl ontt @ohmi or hottkyA formtionF everl tehniques whih hve now een suessfully developed to prevent residue formtion re reviewed in the ltter setion of this pperF ery limited informtion hs een reported SR on ig ething in hlorineEsed plsE msD whih hs the potentil for using nonEmetlli eth msk mterils @eFgF iyP nd otining residueEfree ethingF ig ething in fluorineEsed high density eletron yloE tron resonne @igA plsm ws reported reently SSD ST with promising results for high eth rteD nisotropi profileD nd residueEfree @smoothA surfe topogrphyF

e eview of ig etive son ithing in pluorinted lsms

THU

sn this pperD review of the urrent understnding nd prtie of retive ion ethE ing of ig is presentedF e onentrte on the fluorineEsed si of TrEigD the most widely used polytypeF roweverD some results in the plsmEssisted ething of Qg nd Rr polytypes re lso disussedF he topis inludeX A si plsm ething mehnisms in fluorintedEoxygen mixturesY A ething hreristis ?? eth rte @iAD eth spet rtio @ieAD eth rte rtio @i or seletivityA to iD iyP ?? nd their dependene on plsm prmeters @powerD pressureD nd densityAY A tehniques for otining smooth @residueEfreeA ethed surfesY dA tehniques for ething suEmm feturesY eA n introduE tion to vrious high density plsm souresY fA disussion of suggested ething ondiE tions nd trdeEoffs in light of vrious devie onfigurtionsF pinllyD we disuss the reent progress on high density plsm ething of igF

PF fsi lsm ithing wehnisms

sn this setion rief overview is given of the si mehnisms t work during retive ion ething @siA of ig t room tempertureF foth physil nd hemil proesses prtiipte in the overll removl of i nd g toms of igF fsillyD ll hemil ethE ing proesses proly onsist of three sequentil steps SUD SVX IF dsorption of the ething speiesY PF produt formtionY QF produt desorptionF huring plsm dishrge vriety of speies re produed SWX hrged prtiles @ions nd eletronsAD photonsD nd neutrls @rdilsAF lsm ething of mterils n proeed vi omintion of physil nd hemil mehnismsF he dominnt mehnism is determined y the volE tility of the retion yEproduts nd the energy of the ionized speiesF sn prtieD this trnsltes into hoies regrding the feed gs @inert or retiveAD the plsm pressure nd the hoie of onneting the smple ising eletrode to the p power or to groundF hese onditions result in plsm ething proesses whih n e grouped into four teE goriesX A sputtering ?? purely physil removl of the mteril y energeti ions of the gs moleulesY A hemil plsm ething ? neutrl rdils formed in the plsm ret with the sustrte mteril to produe voltile speies Y A ionEenhned hemil ethE ing ? energeti ions dmge the eth surfeD enhning its retivityY dA inhiitorEonE trolled hemil ething ? ion omrdment removes inhiitor lyers from surfes orthogonl to the ion fluxD llowing hemil ething to proeedF etive ion ethingD whih enompsses the lst two tegoriesD opertes t reltively low pressures @from few morr to hundreds of morrA with the smple pled on the thodeD thus resulting in the prodution of firly energeti ions long with the formtion of retive rdilsF lsmEsed ething in the si mode generlly llows for the most useful trdeEoffs etween eth rtes nd nisotropyF

he overll eth rte is given y the omintion for the mteril removing mehE nisms outlined oveX

i xi six sgx Y

I

where i is the ion sputterEremovl rteD xi is the hemil ething perE formed y neutrl rdilsD six is the ionEenhned neutrl hemil ethingD nd sgx is the inhiitorEontrolled neutrl ethingF o understnd the effet of the rrivl rte of

ions nd neutrls on the overll eth rteD iqF @IA n e expnded TH to TP s followsX

psj pxI ? a ? b jx pxajBx pxbjBxB Y

P

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F rF ihD F xenD nd eF tF tekl

where ps is the ion flux @ionsGmP sAD px is the flux of neutrl prtilesD j is the sputE tering effiieny @mQGionAD jx is the hemil eth rte effiieny of neutrl speies @mQGneutrlAD jBx nd jBxB re the hemil eth rte effiienies of neutrl speies on the frtion a of the surfe whih hs een ion omrded @?sensitized?A nd on the surfe frtion b overed y n eth inhiitorF he sensitized surfe frtion oE viously inreses with the ion fluxF he ion flux lso @negtivelyA ffets the inhiitor overed frtionD thus enhning the hemil @neutrlA eth rteF fsillyD this model simply explins the reltionship etween the two mjor plsm speies @neutrl rdils nd ionsA involved in the plsmEssisted @?dry?A ething proessF

por ig ething in mixtures of fluorinted gses nd oxygenD the most likely hemil retions ssoited with the removl of i nd g toms re given in iqF @QA to @SA SQD leding to the omined hemil retion shown in iqF @TA for the removl of ig moleE ulesF roweverD it is ssumed tht tul moleulr removl is unlikelyF o some extentD we do not onsider the other retion ompoundsD suh s gypPD in the following disussionX

i mp 3 ipm m I to R Y

Q

g mp 3 gpm Y

R

g ny 3 gyn n I to P Y

S

ig mp ny 3 ipm gyn gpm X

T

sn silion siD the presene of oxygen in fluorinted plsm produes importnt efE fetsD due to severl mehnisms TQF pirstD y toms ret with unsturted fluoride speies generting retive p tomsD while simultneously depleting these polymerEformE ing speiesF eondD when inresing yP is dded to the feed gsD suffiient y hemiE sors on the silion surfe mking it more ?oxideElike?D thus reduing the ville i sites for ethingF hirdD if the oxygen dditive is introdued s replement for the fluorinted gs in order to keep the totl flow rte onstntD dilution effets redue the eth rteF he effet of oxygen dditive n e redily seen in the ething of i in gfrpQGyPD gpRGyPD nd pTGyP gs mixtures SQF he highest eth rte is otined when reltively low oxygen @%S to PH7A perentge is dded to the fluorinted gs to enhne the genertion of ethnt speies nd to deplete polymer speiesF feyond this pointD s the oxygen perentge ontinues to inreseD the eth rte monotonilly deE resesF e model ws proposed for the ething of i TRD TSF hen i is exposed to p tomsD it quires fluorinted skin @fluorine tom dsorptionA whih extends few monolyers elow the surfeF hile most p toms involved in the ething proess ret with the surfeD smll frtion ttk underlying i?i onds @QFQV eAD liertE ing ipm moleulesF sn i ethingD the pGg rtioD where g origintes in the gs phse @ethntAD ws proposed SV s determinnt of the ething dependene on the proess pressureD input powerD nd dditivesF e high pGg rtio in the gs produes high eth rteD while t suffiiently low pGg rtio polymer film ould e deposited on the surfe during the proessD resulting in negtive eth rte or tper @width of top ` otE tomA ething profileF olymer formtion ould e even more severe when rP is present in the plsmF his is typil exmple of ompetition etween ething nd deposition tht determines the ething profile TTF

urning now to ig si in fluorinted plsmsD the ething proess ontins oth similrities nd differenes from the i seF por exmpleD highly nisotropi ething profiles re otined @bIH X I during the residueEfree ething proess whih employs

e eview of ig etive son ithing in pluorinted lsms

THW

grphite sheet overing the powered eletrode TUF sn this seD n pGg rtio muh smller thn unity is expetedD sine opious levels of g re produed from severl souresX the ig itselfD the ethnt gs @in the se of fluororonsAD nd most imporE tntly from the grphite sheetF his indites tht the pGg rtio model used suessE fully for i ething must e modified for ig ethingF por exmpleD n nisotropi ethE ing profile ws otined for ig in pTGyP mixturesD whih is not the se of normlly underut ething profile for i TVD TWF he reson is due to ig itself providing ronD whih enhnes the polymer formtionD preventing the side wll from eing ethedF rowE everD there were no fluorinted gses we hve investigted whih produed n underut profile during ig ethingF

sn ddition to the indiret roles of oxygen in the gs phse retionD oxygen lso prtiE iptes y diretly removing g toms in ig through the retion given in iqF @SAF gron n e ethed in either pure fluorineEontining plsm @iqF @RAA or pure yP @iqF @SAA plsmF es reported y severl reserh groups SPD SQD TUD UHD thin ronE rih lyer is formed on the ethed surfeF his indites tht g is not removed suffiE iently fst from the ethed surfe through the retion of either ron?fluorine g?p or ron?oxygen g?y retionsF et low @or zeroA 7 yPD it hs een suggested UH tht ron is preferentilly removed through the formtion of gpm @iqF @RAA rther thn g?yn @iqF @SAAD wheres t high yP7 removl of ron is dominted y the g?y retionF roweverD generlly the ig eth rte dereses s the yP perentge inresesF his indites tht the g?y retion through iqF @SA my not e s effiient s the g?p retion through iqF @RAF his explins why one otins the highest QgEig eth rte under low oxygen perentge onditionsD whih produe high fluorine intensity in gpRayPD xpQGyPD nd pTGyP mixtures @pigF I to QAD nd for higher oxygen perentge @TH to VH7A in grpQGyPF

elong with the purely hemil plsm ething proessD the effet of the energeti ion flux needs to e onsideredF his primrily onsists of dmge or reking of the surfe i?g ond @RFSP eAD whih enhnes the hemil retion effiienyD nd removl of nonEvoltile surfe speiesD whih enles the hemil retion to proeedF he ltter inludes providing suffiient energy to rek the strong g?g onding @TFPU eA tht ould exist in the gErih lyerF his omintion of effets hve led to two regime model for the effet of d is on the eth rte of polyrystlline ig SQX A t low d is onditionsD the low energy @nd effetivenessA of the ion flux is the dominnt meE hnismY A t suffiiently high vlues of the d isD the ion energy is high enough to no longer limit the proess nd the eth rte is determined y the removl effiieny of the hemil retionF

QF ixperimentl gonditions

sn order to drw meningful onlusions regrding effets of vrious ething prmeters we hve mostly utilized ommon set of ething onditions in ll experimentsF his onsists of n rf power of PHH @HFR GmPAD pressure of PH morrD totl flow rte of PH smD nd eth times of SD PHD ndGor QH minF sn the following setionsD we refer to these experimentl vlues s the ?stndrd? ething onditionF e few exeptions to the stndrd ondition re mdeX A for the use of low flow rte @S smA rP dditive in whih se the plsm pressure ws inresed y S morr to minimize the retntElimE ited effetY A for evluting mixtures of xpQGpT where flow rte s high s QS sm ws utilizedF everl other reserh groups lso reported on the si ething of ig in

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