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On the formation of nonequilibrium A15 crystal structure chromium thin films by sputter deposition
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ELSEVIER
ThiI~ SolId l:illm, /,12 (IOt,l.8) 71',I 85
On the formation of nonequilibrium A I5 crystal structure chromium thin films by sputter deposition J.P. Chu ~", J.W. Chang ", P.Y. Lee ", J.K. Wu ;', J.Y. W a n g h I,':.~lit.lc . t ,~h,,'h';'i,~,,I,, I:t:k'i.,','ri.k'. ,~'~ll,z,mll "l'~ti'~ ,m q h ' c . . I r,~,'i~cr~itv. K,'rl.,'t~., 2#2, lhl'.'rm ~' ,~lr~lcrlrl/~ I¢c~r'~lrr h rl:ld Ihu cl~,l.llctll (','tIler, ("llltll ,~'h~lll Ill~lltlllc t~l .~d'l~IIt('l ' (ltlll "li'~'jlli~/(~L'~. I.l.tk'hl~, "1~.~ "nln .'~2.~, l ' t i u . n ,I
Receixed 14 Ap, il lt~-~7: ,IccepLed Ih .hils It~Y/
Abstrarl I:,.'mati~.~ o f nt-~equilil~riu,n ~S-AI~ ( ' r tim> tilim. Prelxlru'd I~y nptlller dep~njlioil tlan buen Mtldied. Altlq~l|~ I'~l'ocesnil|~ I'~aranleler.s e~ilinillet]. ~ . k i n ~ Ill'esslll'L ', tlel'.~sil,i~n l¢llll"~er';lllllt,, mid t i m e vv~,l-¢ IoUIId Io Pla> an jllll'~t~rlLlnl I'OI~." in al'i'eu'ljll~ Ihe fol'lll~.lljol'l o f c~-A 15
('r phu~,e. Su~,ceplihilil,y of ,%A I ~ Cr Iornnalitm It~ Ih¢ proeessin~ ¢~mditi~m ~,~ane,,senlkdlv ancl'il~ed Io its melu.~lable nalure. Sinue it Could irrevernibly ll'annlornl ilt/h~ Ihe equilibrium ~-B('(" (',' upon huali,]g. Ihe vmnequilil~riuln 6-AI~ ('r became ulffaw~ral~le I,o form under l,he i~locennil~ conditium, Ih~.ll led I,o .,,ignil'ical~l in¢l'e:lsen ill I'ilnl ntll't';~u'~.' IL'llll)u'ralttre MIL'h an len~lhy dep~.,,itions t>t' eleval,ed depo.,,il,ion I¢lllperillufe~s. I)til'illg Ih¢ IenL211~ytteposili~,L the tJlnl nllll:tce h.'nll~el';llure inevilal~l~ it~cl'ea~,u,das a n'entllt of o~lllilltlt)un eltergelic parli¢le t~otllbilldlllenfn. SuCh I'iln> .,,ul'l':~ce tenll~eral,Ul'¢ jtl¢l'e~' ',¢ ~:ts all:|lo~otls Io all ill silt| alllle~tljlt~ l,hal, was delrjlllu'fll;l] Io II1¢ t'orlnal,iol~ o1' Ihicker ~'LA 15 Cr Iitms. "1"o InilHnli/e Ihe in nilu anllealing effeu'l. Ihe ttept~nili~m wilh prohmL2ed inl,ernli~,siolls han .sho~ed very efle¢l,ively Io ,..:row Ille relali~elv thick ('r films Ihat Iliad Ih¢ mmequilil~lium ~S-,&I~ er>nlal nll'uq.:lur¢. ~" te)~)~ I:.l.,,evier SCience S.A. flr'~ ~,,,rd~: ('hr, q'nium: Sl'il.ilI,..'lii|,~: Tl'iin..,lilJ.,-.i,.ili electra,r1 micr{,,,c{q',',, ('l'l.2xl); X-i~,> dillr~,.:li~m
I. Intr, Murtion
('llr~lniltm w'il,h :.l non-B('(" cuysl,al slruclure ohl,:iirled by evaporalicm wa.,, I'irsl repol'led hy KilllOto el. al. [I]. Pre.,,el'~Ce o f l,his i'l(.)ll-l~CC chrc~rniun~, desi~,ned an ~'~-A15 C'r..,,ub.,,equenl,ly ha.,, heen c,.mfirrned I~y a ilul'nl~o" of nludies irl Ii,..ir,. spuuered l'iln'l.,, and fine evap,.>ral,ed i~arl,icle:,, [2-21)1. Similar I,o 6 - A I ~ Cr, A I 5 ¢'ry~taI strttcltll'e has h¢¢n found as welt in oilier B('(" refraclory lll¢lal fillns and I'~arl,i¢les such as Ilill~Me11. molyhdenllnl and niolfiuln [13.21-24]. F'r¢.sen¢'e o f the A I~ erysl,al .slruelure lhus :q'q~eat's Io he a u'otllnlovl Ieallll'e !(> Ihj.~ grOUp of t']C(" mel,aln. Ba.,,ed on all of l,he A 15 cr'yMal sl,rllL'l,lll'e inveMi~al,ion',, i~ in revealed l,hili A I~ phase,, are Inel,aslable and Irilllsl'orlnill,ion of A IS Jlllq) B ( ' C occurs duriI1g annealing. |;or il|MalK.'e, our leCelll .',,iudy nl1()w',~ l,he phase l,r~.lllSlOrlllillion o f 6-A 15 ('r inl~> lhe equilibrium B ( ' C Ur. de.,,igned a,, ¢~-BCC ('r. is a fir.,,l, order, irreversiMe, exolherlnic llall.sJl.ion, furl,her ¢onlirmil+g l,he i++el,a.sl,al+le iln,d altol,n~pic halure t>l+ 6-A 15 Cr phase [2()].
Similar exol,hermic, irreversible pll:Lse Iransforn|al,ion.s I'reqtlelll.ly lake phLee in ol,her lypes ol' nlel,asl,;|hle i'fl'la.,,e upon tl'kel'nla] Ilealin~. These illel,asl,al~le phases are ¢OIllnlonly i)roduu'ed via I.tllCOnvelil,it)ll~.Li (o1" so-called tloneqtlilihriurn) processirl,,..~ t'Ol.lle~', for eXalllple, inanv, alllOl'l)hotlS alloys prepared hy ineeharfieal alloyin~ or rapid solidifiu':llion show l,he irreversible, exol,herlniC ph,'lne tI'~.lnsl'('.rlll~.|lion at l,heir eryslallizalion l,elnperalures [25,26]. It js ~.[ltls inl,ere.,,l,il|~ for the pl'esetlL sl,lldy It) ce~ntiillte our previous work [20], all,¢tllpling I,o exanliile whel,her the & A iS Cr is a Pl'oduct. (>1 nonequilihl"ium processing, k'ormalion of ~% A I~ ('r filnls Brown tly spull,er deponilion has heen inve,,,l,i~al,ed, We synl.emal,ically varied deposil,i(m ¢olldil,iOlln ill order to deleHllille dolnJllanl, efl~.¢l.s on Ihe Iormal,iOli of fJlnls, l)eposiljon colldjlions exarllilled were WOl'kin~ pressure, deposilioll tenlpeI'ature and Ijllle.
2. Exi)erimenlul procedure Cr thin I'ilm deposil,ions
('lmrie-.ix~n,.lin ~ ~,|iIIil,,ll. Tel.: t ~Sh-2..lf1221',~2: lax: -I- 881,-2-41~25~24: k'.lll,ilJl: ~ . [ 1 1 ~ ~'IlIOLl'~l~l.ll[I.'ql..u'dLl.[~.. (X)4II-fl, II~'JI)/'L.I~/"'~I'U'~IXF ' I~)()X lil,,e,,io ~u'iell,,.'~' N.,.\. All ri~hl,, re,,er~,ed. PII SIHI4q'I.(H'IUII(U7 )(IIt5L).1 2
were
conducl,ed in an R,F,
II1~.1~11cl1"O11 spul,ler tlepo.,,iliol,i .'.,y.Mk?lll etluil)l~ed wit]l a II.lI'-
hoittq>leclllar
ptllnp
alld .'111 Lill¢()()letl I'(~l,aling nuhslrale
.Lit Ch. el .I. / lTfi. S . l i d I'dm~ 312 11t~,~,~J 7,~ ,~5
holder, The buse VtlClttlltl in the system was in the I0 7 Ton" I'm'~ge. Cr target with a purity > 99.q5+~ was used and ar~tln as tile wot'khlg ,~am was at leasl 99.995++ pure. Pritu" to deposition, the Cr larger was sputter-cleaned by h]sel'ting ;.~ shuUer betweell tile subxtrate and target. Working pre~:,ure was varied in the ran,~e of I - I 0 reTort while R,F. power was kept 50 W and I()0 W for 8-AI5 and ~-B(_?C Cr I'ill]] deposilions, respeelivelv. Except for hroatl-fi~ce transmission electron microscopy (TEM)observations, tile .~Iassslide was used as the .,;ub,~trate material. For the broad-fac'e microstructtH'~.fl e×anlillation, TEM hoIcy cat'hol~ suppor! I'ihn was uned for film deposition, To sludy Ihe deposiliun lelnper;flure etTecl, healing lanlpS on the I~ack of .~llhStrate were used and a tilerrnocouple wux placed us close as possible It} the ,~[IbMl';Ite tO IllOllJ|or tile del)t~sition tenlpel'attll'e. W h e l l tile stlhsti'ate was uillleated hy lamps, the temperature was hlvoluntarily elevated at --- (k3-().4°C/min during deposition while it cooled rather slowly at "-- O.OS-O.()6':'C/min after deposition. X-ray dil'fraethm ( X R I ) ) analysis ~}I" I'ilm.,, was ~.arried otlt tlsin~ a thin I'illl] dift'ractorne~er (SIEMENS DS()()()) with nlori~chroillalic('uK. radialion. "['l'~.lll,~llliX,~iOII elecIron n~iert~scopes (JE()l., JEM-2000 operated ;It 160 kV and J E M - 4 0 0 ( ) F X ;,it 4(10 k V ) were u,,,;ed to ex;,itnJile the hroildIl'aee :ltid cl'O.ss-~ecliOlla] I11icl'(~,strUCILIl'e,s of rilms. For cross-sectionalTEM examim, tions, l'ilms deposiled on the glass ,,ul'~strate were cut into slices anti sandwiched with all epoxy glue for holdiny. TEM disks were Ihen nlecllalfically polished to a thickness of --- I1)() p.nl, Ibllowed by tllimlin~ tt~ .--~0 ,u.m usin~ a dimpler. Final perf,)ration of the TEM disk wus accomplished hy un it,ll nlill (G~.lt~.tll 0(X) CTMT). Auger eleelron .speclrt~scopy (AES) o1" films was done with a I'erkin F.Inler PHi 670 Auger Nmloprobe. An argon-ion heron of 4 keV uver an area of approximately I.,~ x 1,5 nlnl ~ w;~s used for tile deplh prol'ilin~, with ].Ill etching r;Ite of ".- 11)() A / l l l i l l based Ol1 thai 'af the silicon dioxide.
3. Results In this sludy, when tile Wol'kin~ pressures were in the range of 5-7 niTtlrr deptlsitiwlS produced ++-A 15 Cu' I'ihl~,,, as evidenced hy tile presellCe tfl ~,.~. ('~.~lll and I"~l I pe~k,, in XRD pallel'ns. An example o1' XRI) p~llel'n I'~r i~-A I~ Cr is shown in lg~. la. in C'Ollll';Isl Io Ii~e i~-Ai5 ('r. ¢~-BC(7 Cr ill Fig. Ib exhibiled an ~vt~. peak a! -,- 44.S' of 2/t with the nl'~sence of illeaSlmfl'~le ++,,,,+ and ~,,, I'~eak.,,. Con]pared with lll;,il o1" t+~,, peak in Fig. Ih. relatively lar,ue width (l'ull-wMIh at hall'-nlaxinluni. F W t l M ) o f ~+,~,, peak in Fi,g. la is noticed. This might have heen re.suhed from a fine rihn KII'LICILIre or I.I po,~sihle prenellce of lllillOr ~-iICC Cr phase in the ~-AI~ Cr film, "I'EM bri~llt field (FtF) and dark i'ietd (I)1;) inlaBe,~ in l:i~, 2 shu~v tile 6-A 15 ('r film consisted o1' a number of 'clusters' Ibrmed by ',er', fine erystalliles, These ery.,,tallite~ ~,Vel'e estim;fled to be
7 c)
. . . . . . . .
I
I
I
[b) 1 mTorr
|
' 3S
I 37
'
1 39
'
I 4 t
'
i 43
~'
I 45
~
1 47
'
'~' 49
2() (deg,)
i:i.~. 1. XRI) p;lllern,, of ('r tihu', det~iled aL dittelcnL ~orkm~ ple~.~lll~...: (a) 7 mTorr arid (1~) I lllT,~rr. ,&pl'U~xhl~lle ,~.,,,,. ~'~;.,. "~..ll. ~md cl~ m pc~k p,.,ili~m., ar~ m~u'kcd, ahu~ ,,~.ilh ;t da,,ll liue dragon 1~; th~ IoL.'uliLm ~1 f'~,.~ peak I~ I'acililah: ~i,,ual c~mq~Lt'i~,~m.
- I11 nm in size. TIle diffraction pallel'n fro111 this fihll is shown in Fi,#. 2c. pmvidintz a direel e','idellce of i~-Ai5 Cr f{~rlnalion with IIll dele¢l;.lhl¢ plxtsenec of (~-BC(" Cr phase. For tile ~-BCC Cr film, TEM ob.,,ervations revealed dis. liilctl)' different I'ealtlres (a'~ sho~,vn in Fig. 3); that is tile relatively lartze er>'stallite size { -.- 21) ran) and dense film xtrl.letLIl'e,
i)epo.,,ilion temperature tlependence of &-AI~ Cr film I'ormation is depicled it] Xl,tl) resulls ~,f Fi~. 4. These I'ilm,~ were prepared at 5(1 W and 7 retort for 31) rain. I'a,,cm.~ble for ~'~-A15 Cr fornlali~m vd]en unheated, When tile dern~silion was done behlv, 15IF('. an im.'reasin~ der~silion lemperalure led Io irnprm,'emenl of ~-AI.~ Cr film erystallinil) as imlicated IL~'the appearance of ,~:.. arid i~,~ peak,,,. This t'ilm ery.,,tallinily improvemenl is pt'esumabl~; allrihuled Io an i~¢rease in udalom nlohilily for the film groxvlh resullin~ I'mm the temperature ele~alion I271. When the deposition tenq'~erattnx." v, a.,, further increased to 211(1'~(", ~l~e ~¢-!tCC el" t~eemlle a major phase and ,~-AI5 ('r m, a minor pllu~e. This high-tenli~erature induced the ~oB(,(" (,r I'~rlUation i,,, considered to he a i'e~ult of Ihe 6 ---,,,. pl]a,,,e mm,;l'~}rnlali~.rl occurred during Ihe del'~Osition. Similar temperature depel]dence for tile t'ormali~ul of 6-;\ 15 (.'r hax a l,,~} been rept}rled hv ulller earlier sludies I4, I ('~L .&llht~u~l'~ n~}t presenl IletV, we did m}t ot',,,er,,e the del',~,,iticul tellll'~lature dependence I'~r the ~.-B('C (.'r fihu I'urmatior~ I,..,~],
~ll
.I,P. ('tin ~'t .I, / 7"hi~ Sn/h/ I"ihns 312 t 199,'¢,~ 7,~-,~'5
Fig. 2. (a) 13righl field. (h) dark Iield Ti'.'M micr~=graphs, m=d (c) a .',elc¢led ;nrea diffracli~m pauern of a ~-A 15 Cr lilm. The rings in Ihe paUern are imtexeJ tnm) the .,,mallcst it~ Ihe lal'[Ze.,,t a,,, ,$,~.~, rS,=n, ;lll~.l ~q'-'t1'
The deposition time effcci on lh¢ phase forrnaliol|of Cr fihn is shown in FiBs. 5 and 6, hi I:"ig, 5. a series of XRD pa|lerns was ohl:|ined from Cr films grown under Ihe condition (50 W, 7 mTorr and no Ilealing) I'aw~rahle for tile ~-AI5 Cr with dil'ferenl deposition limes, Since these films had dil't~renl Ihicknes.'~e.,;and tile thicker t'ilms would naturally lead to more promiaent XRD peaks, peak intensilies of ~'~tH~;llld t~211 ill relative to that of u I t~,, rather than their absolute peak values, were a more meaningful indicator in determining the exi.stence of & A IS phase ill the film. "i'hus, as long as relative peak intensities for a given XRD pattern provided enough int't~rmalion, le~.~ prominent inlensities obtained from Ihinner films slill could he used for comparison with those fl'Oln lhicker films, For tile depositior= duration effect it! Fig. 5, with increasing deposition duration, tile crystal strtlcture of Cr films gradually changed from ~-AI5 Cr to t~-BCC Cr. When deposited for 20 rain, the ~'~-Cr fihn was s~ thin that XRD ,showed relatively small ~:~,~ peak (Fig, 5a). For depo.sition lime of 30 Illill.~$-AI5 filIllwill] ~,2..~. ~$:1,~ and ,I'~211 appeared (Fig. 5h). For 40 rain, h~lh ~S-AI5 Cr and t~-HCC Cr peaks co-existed in the fihll (Fig. 5c). Cr filnl gl'()Wll for 50 Ilfinl resulted in (~-BCC' ('r as a major phase will] no ob.servahle presence of ~$-A15 Cr plla,~e. FWHM o1" major
peak appeared to deerea,~e wilh the deposition time. 'l'his deposition lime dependence of i~-A 15 Cr fornlation implies lhe tran.~fornlathm of ~-AI5 Ct' into tr-BC'C Cr mi~hL have oeeurn'ed dun'ing Ihe deposition ~s a result af changing deposition condition, such as a stLhsU'ate heating from the COilthltli~tl,~ p;.u'tiele hot|lbardlllei11. Or1 the o t h e r hand, the depc~sili~m lime dependence ot" tt,-BC'C Cr was not observed, as shown in Fig. 6. XRD patlern~ ill Fig, 6 were obtained I'rom a .~eries o1" Cr film ~ample,~ deposiled under tile condition (i(}0 W, 4 mTorr and no healing) favorable for the t~-HC?C? Cr willl dilTerenl deposition limes. As indicaled, these I'ilms were predominantly tile tv-BCC? Cr Stl'tlCltll'e except for the II)-min I'ilm. The IO-min i'ilm ~howed t~-BCC was the nlajor phase with po.~sihle c~-AI5 C r ~,|,~a nlin~l', i!,~ reh.ilively ~mall ,~q,~ peak at ~ 39.2" of 20 appeared and FWHM of t~,,,, peak at '-.44,5 ° was rather large as compared with Ihose of other Ihree filtns, indicative t~l" the po,~.~ihle presence of mintlr &AI5 (?r l~ha,~e. 1"o further verify the ternperalure el'feels on tile formaLion of ~-AI5 Cr pha~e, cycle depositions with variou~ inlel'mis.~ions were era'tied otll Io examine tile l'ilm ,~url'ace temperature elTeel title to tile in silu healin~ t'rom t'~omhat'dmenlls of energetic .speeie~ during deposition. XRI) results
J.P. ('ira el ~d, / 7"hit~ .%~Ii,I l.Tht~s .H21199,~J ?,~1~,~15
~I
I:i~. 3, (,'z) Ilri~ht fiehl, (h) thzrk tield "I'I~M rnicroBl'~q~l'~s, mid (c) a ~elecled area difl'r~zcli~)l) p~dt~.'rn ~f :,z (z-lt(.'C Cr film. The: rinB.~ in the: pallors ~zz.~
in Fi B, 7 were ohlained fl'om Cr films deposited under tile condition (5() W, 3 mTorr mid no Ile~t~tirlg) in I'm,,or of the ~-AI5 Cr I'~rnmlion. For sinlplicitymid chuily, each filn~ was desi~m~ted acc~rtling to its depositi~m condilion. For i,lsta,lcc, 8 / 1 0 / 5 0 indicates tile I'ilm was dept~sited I'(~r 8 cycles and each cycle consisted of IO-min dcp~silion m~d 50-rain inlermission I~e~ween depositions. Fi~.. 7 rereads tile effects o1" dep~silion cycle nnd imcrmissiou on tile t'ormalion t~l' ~-AI3 Cr ph~tse. When tile l'ilm wits deposited I~)r 3 cycles with .'~O-Illin intel'nlissi~.q~ (3/10/30, Fig, 7h), tile ~-A 13 Cr crystal sti'UCtLire remained. With tile same intermission, incre~sin~ deposition cycles l'rom 3 to X (Fig, 7b-d) evet~ttmlly resulled in tl~e ~-BC.C Cr ~.s ~ donlimmt pirate, t::urthermore, with increasing imermission l'ronl ~0 Io 50 rain the ~-I]CC Cr dimini.shed, e.g., S / 1 0 / 5 0 (Fig. 7e). When tile in|termissitm was ftu'ther extended to 120 rain (6/1()/12(), Fig. 71"), the i~-AI3 Cr became the m~jor plmse, Simihu' el'fecl~ of i,~termission or del~l~iliot) cycle were not t)hserved it) the cases tile ~,-BCC C'r phase was formed when hmBer del'~Osition limes (sud~ ~ts 15 ~r 30 mia) were emr~loyed [21,I], Cross-section~.il '['I'~M exmuinati~ms indic;~ted I10 distinct
'kzyet'" structures, de~pite of the len~,thy intermis.~ion between deposition.s, Presemed in Fi~, 8a is a typicul cm.,~,ssectional "I"EM I'~riL~hl-fieldrrdcrograph t~ketz from a c~-Ai5 Cr film deposited at 120-min imermission ( 6 / I O/121)), The micm~ruph depicts tIle film had a well-dev¢loi~d ¢olumlmr B,';Ihl ,~|l'ucllil'~ ~J,lld tIle film thickness w~l,s ,,- 2~1 nm with no visible layer sIrLleILiI%', As indi¢~,ded by the difl'rtzcth~n pattern in Fig, 8, the film was of prcdL~nlinat,~ly iL ~-A 15 phtuse, ill a~tvement with the XRD r~sult .shl)wn in Fig. 7f. Spectroscopically, AES depth profile atmlyses I'urlher denu:mstrated Ihe Ii,mlogem~us tin,lure ~.~1"fihns, in l'ig. 9 in u rel'q'e.sentalive of AI-:S deplll profile L~bluined from a 3 / 1 0 / 3 0 Cr Film. The ndher slllt.~l~tll Cr mid O curves in the pml'ile indicate the I'ilm ~,,'as unil'~nn in o.mlp~siti~n m~d no layer-like COml~siticq~ was detected, I)resence t)l" impun'ities, O ~.lild C, is thought to he li~111 resithml ~ases in tile deposition chamber almost)here or from lhe speller hlr~et or the c,Ullbin~lion of h~th. In our ,~tudy, toted iml'~tu'ily co~lcenlr~lliozls it~ tile fihlls l~pie~d~y :~|ccotinled t~)t" 2()-3.~ ~.zl,~;~,~,lsme~isured by AES. Based on X-t';~) photoelectron Sl~eCtmsc~q~ystudies hy O' Keefe el ~d. [I 8] and Chu et al, [3~)], i'~q' both ~.-BCC a~d ~S-Al.~ ('r
82
.I.i'. ['h:+ ,'I .I./"
c;.'c,O
~'~,+111 ¢t1111 i]
:i . . . .
il
+ +,++
/
J~A
(a) Unhealed
i
37
.+i+,li+l l"ilm'+
4"~"T,I 1-----]
.++0+
35
17m+
'
I
39
'
I
41
'
I
43
'
i
45
+
I
47
'
I
49
2tl (deg.~
.+12
f lU<~,~+l
7A' ,~'.+
atzrce.', willl other +tlrlier results, in which the exisl, in a very tllin I'ilrrts (al, most IL, w I l n l ) alld elevated lCIllperilturest>1"l~rtflo+Itzeddeposition unI'avtlred fm'nmthln or +S-A 15 ('r I+ilnls.The ,+usccptihiIity I,o tile proces,,+in# ctmdilhm.,, Fur l,he evaporuted or sputtered Cr alonls, the suhstrule t, tld deposited I'ilnl..surt'ace are st+ cool that it provide.,+ as a heat sink when l,hes¢ Cr art>his dept~sit. The time required For un arriving, attml Io enert.tetie+,lly e<.luilil'+ral¢ with the suhslral,e surfac'e is e,+timated to he oil, the order or !() ~: s. t,'or the utmll with ().1 eV enert.zy, which is equivalent to ~l tenll~erature ol" I()()()<~C`, thu" dcpt~,,,iiit,i~of alt+nl in a+.:llieved ,Ail,h +.it+ el'l~'ctive <.lUenu'hintzrate aPI+rtmchin ~ I()~"C/~, [27]. In tile cuse t~I' spUll,el" deposititm, tile qUellcllin~ rates are exceedin#ly
llundrcd
l'i~. 4. X R I ) p:~tteit],, u l ,S-,,\15 ( ' i fihn],, del+,~,,iled al dilTerenl lu'mpera. Imp.',,: la) tmli~..a|u.d. Ill) Ii)+.) ('. (~..) I~<) (" ~,nd (d) 201r ('. "l'he,,e rilm,, ,,,,+.'re d,:l~,,il~.,d al 5II ~,~,' aml 7 nFl'orr I~+r .'~<} ram. la~rul'+le fl~r r"i.Al.~ ('r l'orliltlliOll sAh~.,n ullhu, illed
tG;>00 t
~'~ tl) ext 10 °:+
~'~lt
i+
I
. . . .
"i
I I
l'ilIllS, tile C'r v+'m, predonlinantly in an elei11enl,ttl or unl'~oulld state. St+. c'ai'l'~t+ll and +.+x)'~ell v , , e l e i'elallvcly nlint~r
and present in tile l'ortllSof carbides und oxides It X,21)].
4. l)i.,+cu+,+sion
In this study. ('r Films with both types uf eryslat sl,rl.l~:lure. <:I,-BCC [illd +S-AIS. huve been obtuined. According to tmr X R D and TI:M rcsulls ill h#n. I and 2, the +,:alcl, hlted lattiu'e parameter is 2.~I,I ,g for ~-B(7( "+ Cr and 4.:+,9 ;~ For ,~-AI5 Cr. consistent with previoL, s dula [2.16. It~]. In ¢OIltr;Ist to tile n,-H('C ('r. lhe ftmnaliun oI' +S-AI.+;i ('r i'ilms was l'mmd to he very seilsiti,¢e tt~ l,he proeessirl# c,tmdititms. O'Keefe el ul. (ll'l] sllt~,,,ed l,llal ,5-A15 ('r l'oniled under ~, certain ra,+~e (15-30 al,.+/+) oi" l,oltd impurity contenl, and. tllereI'ore, proposed the <~-AI5 ('r phase is an iillptsrily-lt+cked, melusltd~,le plla.,,e. ()ur l'ilms typically had It+lld impurity u'~Hllenl,s ill 20-35 al.'+, hut si'~{+v~'ed two distinct c','ystal StlJU+,.'tures. Tlle inlpurity efl'e~.'l lllu.S .seemed unlikely It~ play an iml'~t+rlant r~le: instead, l,ile del'+t~,~ition teml'~eratt;re appeared d
"L~'a,,,..u.wd ~
35
37
39
41
43
.15
+17
49
21~ (d(,'[l,)
I'i~+ +~. Xl,tl) l+,h11L:In,, ll~ml ('n lihns tl~.'l+~l',ilL'tl tinder the ~.'imdilkm (511 W. '7 llt'l't+iT and II++ h+.'athi[2) l~i~,,++'~lhl~.' hlr the ,'i. AI5 ('I ~AiLII +.Iill~.'lt_'l|l dcp4,,,ilh,t+ irate,,: (,i] 213 IIIHI, II~) 3() trim. (~.) 4(+ ram+ itlld ((I) 54) 11|J11.
.I.1'. ('/m ,'t a/. ,17'1,..~li,I (~;?(],) l
~'J~0,
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....
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I
fo,2o t'--
(C)
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37
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I.ilm~ 312 1 Iq',~,~) 7i~'--,~"~
~.~
rS ~ ~ transformation is not possible ~o achieve under lhe equilibrium condition taxi thus it has demonstrated th,: nonequilihrium properly of ~$-AI5 Cr pha,se. As lhe f'~-A15 Cr i,,, a mmequilibrium phase, a Ihenllal heating gmleraled dul'ing deposition could induce the in'cvelsihle phase tlan.sformation. Although the t'ilnl surl'acetemperature was virtually impo,ssible to measure in this study, the uncooled suhslrat¢ may have reached as high as 5()()°C [27] mid lhe film surfilee could be at lemperalu[cs well above the lran.sfornmthwl lemperature. It is thus teadiiy under.smc.d that an increase irl deposition lemperalure fav,a.ed tile Iommtion of equilibrium t~-BCC Cr, as shown in Fig. 4. In addition, during onheated len~lhy depo,silion, an involumary l'ilm surt'ace-temperalure increase from lhe energetic particle I'~omb~rdments could lead to significm~t healing and, Illerefore, !gave rise to the (~-BCC Cr formalion. As a result, diffcr1:nt exlcllts o1" in situ anne~flin~ have II.|kell plm.'e during deposilion, This in ,silu annealing in ii, lrri WIIS lllllih)gOtl,~ IO the post-deposition ex silu allll¢;.iling. The posl-depositi,m armealirlg could cause the ln.msrormaliun of ~S--, ~ [20], while lhe in silu amlealing el'reclively iml)roved l'ihn cryslallinily, a:,; ilhistrated in Fig. 4. and ever~tually induced occurrence of the irreversible phase m, nsformation m Hg. 5. Accordingly, to minimize
20 (deg.) Fig. h, XI, I) l~aLl~.'l'nnII'~,111('I filnP, dep,~,,iled |llRh.'rthe ~.~mdidun (1(}~) %,V, 4 mTol'1 ,llld il~, he.'llin~) lax,,rai*le l,,r lhe ,|..IR'(' ('i' with Llil1~'i'enl del~o,,ili{v~ liln~."-,: (;.i) Ill nlill, Ih) 21) illin, (~.') .~.i| Inin. ;.ind Id) 40 lllil|.
~'~210 tZ110 ....... ~"
~21 I
II
II
(t) 6q0/120
raster a,~ the s[}utlei'ed a t o m s have Oll~ ll.l tWO
orders o f
i1111[zililtt+l,, ' ,re'eateraverage energie,,, than the evaporation. Prior studies have slmwn that such high quenchinB rate.,, rrequenlly allow nonetluilil~rium atomic I.irl'i.lltgetlletllx IO he readily quenched-in, producing film.,, with ~.'omlx~sitions Or ,',ill'll¢lLll'kL~ which normally would 11oIhe allowed accordint-z m hulk lhern|odyllallliC C(lll,%tl'ainls [29-33], The pseudo-alhtv film,,,, l'or insmm.'e, can be furmed using co-spullerintz under ihi,~ nonequilihrium proce,,,sing condilion hy forced combimilions or the eh.,menls which have essentially zero I1]utual solid or liquid solubilities. Mo-('u [.~t2] illld ("tl-C []i.'~] systems ill'e exanll'~les of these yscmh~-~dho" films. As i','Ol'x~sed hy many in~.e.,,ligator,~[8,15,2(I], the ~'~-A15 ('r is a high-temperalure allotropic chromium i'~hase m,.! f(~rms under :~oneqLiilir,'ium condilions, beCOlllin~ a mela'dql~le phane al r o o m i e m p e r a l u r e , I)l, le io iln m¢iastal'~le nalure, the 6-AI5 (,r pha.ne eventually Iran.sl'c,'ms into lhe equilibrium ~-I}(,C ('r ulmn therlnal almealin~ al -- 42"7"(' [2()]. As the ¢I-A15 ('r is rormed under Sl'~ecifi~:i~oneguilibriul|| c o n d i l i o l l n ,
the ~'~ -~ ~ Illlax¢ trannl'orlllalion
I~¢collles
irreversible [20]. ()ur view on Iilin nonequilibrium producl in furlhcr stlPl~orled I~.Va la,,,cr-irradiated 6-AI5 ('r stud), of B]~iega and Pot~encu-Pogrion 115]. They showed Ihe ~'~--, ¢~" |r;.lll.q'OrllIilliOll lle¢;.|llle l'e,~,el',ql'~lewhell llle ('r was irradialed wilh a 6(l-n,,, pulse-laser, This pul,~e la,~er-indu~.'ed
(e) 8/10/50
(d) 8'10/30
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(b) t.10:30
tal I;I0.0
I
35
37
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i
39
'
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41
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I
43
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I
45
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47
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2o (deg) I'l~ T. XR[) I~alK'|tt ,, |lore ['| him,, depL~,,ited tmdel" the di|ielVnt ¢~'1¢ u'on~.ii|lOli',,(.~4) ~,~'..~ mr,~il mid itt~ he,illl1:21in i,l~.of ol lhe ,S-,,\IS t'l lorillaUOil: Ial I ' Ill. II. (b) ~ lli.llI, (~.')h .'ill.,-If). Id! ~ 'If).'.It).l.e! :4 l(I 5U and IIl I~,.Ill 121) N¢~.'lq\I I,~i dClall',t~l film i.~',,i.+,:,ii,,itiOtl.
84
J.l'. C/m t.t .I. / 71d. Solid l"ilm,~ 312 ¢ IW),S'i 78 ,~5
"r;ihlc 1 Averli~¢ deposition I'itli.'~, of ('r fillil~ lind their crystal .~lruclurc.~ I.ilnl"
Axerllge tlel+O~ititlii rate (nnl I iliiili
(.'r)',~laf slrtlcturc I'
1/10/0 3/lll/3l) h/1t1/311
8/I(tl31l 8/I0/4(i gi' 1111511
~ 4.5 -- 4.4 .,- 4,14 - 5.4 - 5.1) - 4.5
5-AI5 f-AI5 m l l C U < . ~-A t5 rr-IlCC r e l i C ( '< , fi-A 15 ~ r - I t ( ' l " , fi-A 15
3 1 1()1121i 6t 1l)/12(i
- J,(t - 4,3
fi-AI5 &AI5
aSItit h.'Xl for delail~ td' l'iiln designation, i~('l'),~litl ,Mrii~'tUl¢s wert" delerlllJned by XRIJ :ind T i i M .
' Maj,r pttasc.
Fig, 8. A cro.,,.,.-secii~mal Ti'M bright-field micrngraph with the selected ar,,ta diffraction pattern (inset)ilhlained t'rt~lll a (if 10/120 Cr tihn.
the in situ annealing effect, we deposited the ~-AI5 Cr fihns wilh the prolonged internlissions to prevent the filnl surface from overheating, As shown by XRD results in Fig. 7 and TEM observations in Fig. 8, the longer was the intermission the more sati.,,factt~ry to prnduce the ,,5-A15 Cr film. Therelore, with this prolonged intermission deposition approach, much thicker Cr films thai have the ~-Ai5 crystal structure would be able to grow. To further examine the in situ annealing effect on the
forrnation of g-AI5 Cr I'ilm. deposition rates measured from films grown under various condiiilms are considered, as listed in Table i. It appears that the 8-AI5 Cr film was likely to forni tit low dcposition rates, whereas, the tr-BCC Cr forrned otherwise. This phenomerton can he qualitatively explained well when taking into account tile in situ annealing effect, tks nlerltioned above, the high-ternperature, nonequilibrium ti-Ai5 Cr was quenched-in during the deposition. When the deposition rate was relatively low, the cooling rate effects were significant because of the film surface not being heated-up. Thus, the in situ annealing was trivial and tile high-iemper:lture ,,5-AI5 Cr phase lbrmed favorably. Conversely, the equilibrium ce-BCC Cr phase litw~rably formed when the film grew faster becau,sc the in situ annealing of filiu became increasingly inllueniial as a result of niany nlor¢ high-i¢inperatLirl2 sputtered aloni.~ arrived. Variations in the cry.~iallit¢ size for each phase observed ill TL:M niierilgl'aphs ill" l=igs. 2 and 3. thus. can be recognized in ¢llnsetluence ill' differences in the deposition i'i.il¢. This similar hi siiu annealirtg el'feet on the high-tenlr)erature phase fornialioil has also 110011 dellionsiraled by Cllu el al. 134] in sputter-deposited ililignesiuill iungsiaie (MgW()~) thin filnl phosphor.
iO0
5, Conclusions /~ o=
E r~ .u E
Cr
80-
60 40-
O
o
2o-
o
c 0-.
0
i
i
5
10
i
c i
15 2o Sputter Time (rain)
I
25
30
l:ig. q. An AES tlcplll pmlilc i~i' .3 3/11)/311 (.*I" lihn sh1~,,~,ing ra(her Mlllli;lh ('r, (), arld (." ctlrv¢.,., lhl'lill~h the film anMy/cd.
Formation of nonequilihlium ~-AI5 Cr dlin films by ~putter deposition has been examined. The 6-A 15 Cr phase was found to form under specific i~rouessing conditions. Susceptibility tit" ~':J-AI5 Cr forrrultilm to the processing condition was primarily attributed to its rnetastable nature. As it could irreversibly trarhsfon'n into the eqt, ilibriun~ ~I'-BCC Cr upon heating, the mlnequilihrium ~'~-AI5 Cr hecanle unl'avi)rahle to l't)rerk under tile processing cotlditions that caused a raise it} the I'ilm surfaee-temperatu,'e, such as lengthy depositions or del)ositi(wi temperature being elevated. During the lengthy deposititm, an involtilltary film surt'aceitemperature increase, resulting from colltilltl-
.I.P. ("/tit et , I . / 77ti, Solid bilm~ 312 119~,S'J 7,~--,'~5
otis I'toMbartlMellts o1' energetic species, is considered as
the in situ annealing th,'~t was delrimental to the formation o1' ¢i-Ai5 Cr films. To effectively minimize the in .,,itu annealing effect and L.zrow |'clativcly thick ~-A 15 Cr films. the deposition with p|'olonged intermissions has been shown ,~'u'y satisfactory.
Acknowledgements Autl'lors thank Mr. 3,L. Hong and Mr. T,N. Lin for their help in conducting this research program. Mr. C.C. Hsu of Materials Research and Development Center at CI1L||I Shah Institute ot' Science and Techut)logy is also thanked for his help in TEM sample pt'cparations, This study was supported by the National Science Council of the Republic of C h i | | a u n d e r C o t l l r a c t N o . N S C 85-2216-1-:,-019-1}114, w h i c h was gratefully ackrtowlctlged.
References [1] K. Kimolo, Y. Kanfya. M. N~qmy;m~a. R, Ityctk~, Jpn. J. AppI. Ph.vs. 2 (lt)('~3) 7{12. ~2] K, Kimball;. !. Ni',hida. J. Ph3",. S~¢, Jpu. 22 (1q67) 744, {3] J. For~,nu,ll.B. Persstm. J. Phys. Stw..Ipn. 27 (l~,~(~t)) 13(~S. 141 .I. I:tu'ssell, I:1. I)ers,,on, .I. Phy,,. Sure..ll)n. 2~,)(lqT()) 15.'42. t51 l. Nishi:t. T, Sitha.,,hi. K. Kimot~. 'rhii; S(~hl I:ihu~, I1) (1~172) 265. 16] K. Kimolo. I. Ni,,hida, Thin Solid Films 17 (1~)73) 4~,L 171 I. NishJtkl. K. Kill|Otto. Thin Solid i:ilnls 23 (It,~74) 17~,1, 18] R. I;vctl~. J. ('r.s,,t. (in~vth 24/25 {Iq74) 6~,t. It') 1 ('.{i. (~l';I.IItlViM, (;.J. Milillt~w,',ki. R.A, lluhrlllatl. I~hy~,. I.cll. A 54 (1974) 245. [11)] ('..I. I)ol~¢l'lt.. J.M. f ' ~ t ¢ , R..I.H. \"~orht~ex¢..I. ,.\i3~1. Ph',n. 48 ( It)77J 2{150.
115
111] Y. Saito, S. Yat,,u)~h, K, Mihama, R. tl}cda, J. ('r),,u (;r~vdht 45 { 1~711) 5{tl. [12] M.I. I'l~t;icga, N. I~pcscu-Pogrion, (', S~u'hu, V. Top:u Thin Solid Fil,n~, 5~ ( 197t.II 217. [13] Y. S~fil~. K. Mih:un~i, R. Uycd;u Jl'm, ,I. Appl, I~hy.,,. iq UltimO) 1603. II--I[ M. (ia~,glfit,|', I., N~,ol, Phy,,, Staltts ,"i~lidi A f~6 {It.lb;I) 525. [15] M.I. Bh~iu'ga. N. I'tq~.'seu-I'c~pri~m. "l'hitl Solid I:itms 191 (l~)Sq) 33. [11~] It. Niircnbcrg. II.-G, Neum;mn, Thin Solid I:ihns It)bl ( It)t;l ) "4t. [17j M.J. ()'Kcelc. S. Iloriuchi. J,P. ('hu, J.M, Rig~hu,¢, Mater, Ru,n. Sty'. Przw, 311 (Iqt)3) 3{)1. [IN] M.J. ()'Kcclc, ,S, thwiuehi. J,M. Rigshcc, J,P, ('hu, Thin Solid Filmn 247 ( Iqq4) 16tL (Iql II. Inhihashi, M. Arila, I. Nishida, A. Yana',~'. K. Nakahiga,,hi, J. lqlyxl ('~uldc|l~. Muller 6 (!9()4) N(~8I. [20] J,P. ('hu, J.W. ('h;mu, P.Y.I.cc, Malc~ials ('hcmistry mid Physius 50 (ItJ(J7) 31. [21] (i. Ilii ug. N. Schiinheru. A¢la ('r3,,talhlur, 7 ( Iq541 351. 122] P.M. I~elrolf. W.A. Recd. Thin So|id Film~, 21 (It174) 73. 1231 M. Arila, 1. Ni,,hida. Jpn. J. Appl, Phi,,. 32 (It)t)3) 175t), [241 M.J. (YKeele, J.T. (itanl. J. Appl, Phy,,, 79 (tq~)l~) ~J134, 1251 M.S. I:.l-I.~skantlat~.n~, K. A~ki, K, Su/ul.,i, Appl. I)h.s~,. I,eu. 1'~1) (lq~)2) 1562. 126] M.S. lil-l'skm~tku'au 3, K. A~ki. K. Su,,uki, J. Appl, Ph},,. 72 11~)~)2) 261~5. [27] LM, Ri~,,Ix, e. Ph~.,,ieal Vapt~r I)Cl~O,,ilion, ill: R. Kos.',~a.,,k3..~lll'l'{I,.,.'~2 M~Milicati~m I.in~inecrm~, Vol. I, ('R(' Pre,,,,. ih~.'a Ra0.~ll, FI., USA, tqn*~, pp. 23t .°255. [2,"¢.] J.P, ('hit, J,W. ('haiku, *I.N, l.in, J,l,, |ltqlg, unl~lll'tlishe,,i at~l'k, [2~.1] II, ('allt~r. R.W. ('ahn..-\¢la Mclall. 2-~ (ltl7t~) H,.15. [30] S.M..";bin. M.A. Ra~,. J.M. Rig.,,bee, ].F.. (;reene, AppI. Phi,,. I.elt. 43 1,~) { tq83) 2-1q. [31] N. Si~ul~tler,,. A,|~, ,Miodo~,~-tfik. J. n;ilt'l. Sfi. 22 11~1117)(~26. {32] (;, Riuultnaih, II,Z, Xiat~, I..C. Yang, A. R~¢kell, I..11, Allen, J, AppI. Ph.~~,. 78 i lilt.|5) 2435. 1331 ,I,1'. ('hu, ('.S, ('hung, P,Y, I.ec, J.M. Rig,,l&'e, M¢I. Mitt. Tran.,,.. ;.icek'plu'd liq publik'atioll. 1341 J.l', Chu. l.J. II,,ich, J/l'. ('hen. M,S, I:enB, ,,ubvltillcd It; Malt'r, ('hem. Ph3,,~, Iq~)7.
%
.... ~
•
ELSEVIER
ThiI~ SolId l:illm, /,12 (IOt,l.8) 71',I 85
On the formation of nonequilibrium A I5 crystal structure chromium thin films by sputter deposition J.P. Chu ~", J.W. Chang ", P.Y. Lee ", J.K. Wu ;', J.Y. W a n g h I,':.~lit.lc . t ,~h,,'h';'i,~,,I,, I:t:k'i.,','ri.k'. ,~'~ll,z,mll "l'~ti'~ ,m q h ' c . . I r,~,'i~cr~itv. K,'rl.,'t~., 2#2, lhl'.'rm ~' ,~lr~lcrlrl/~ I¢c~r'~lrr h rl:ld Ihu cl~,l.llctll (','tIler, ("llltll ,~'h~lll Ill~lltlllc t~l .~d'l~IIt('l ' (ltlll "li'~'jlli~/(~L'~. I.l.tk'hl~, "1~.~ "nln .'~2.~, l ' t i u . n ,I
Receixed 14 Ap, il lt~-~7: ,IccepLed Ih .hils It~Y/
Abstrarl I:,.'mati~.~ o f nt-~equilil~riu,n ~S-AI~ ( ' r tim> tilim. Prelxlru'd I~y nptlller dep~njlioil tlan buen Mtldied. Altlq~l|~ I'~l'ocesnil|~ I'~aranleler.s e~ilinillet]. ~ . k i n ~ Ill'esslll'L ', tlel'.~sil,i~n l¢llll"~er';lllllt,, mid t i m e vv~,l-¢ IoUIId Io Pla> an jllll'~t~rlLlnl I'OI~." in al'i'eu'ljll~ Ihe fol'lll~.lljol'l o f c~-A 15
('r phu~,e. Su~,ceplihilil,y of ,%A I ~ Cr Iornnalitm It~ Ih¢ proeessin~ ¢~mditi~m ~,~ane,,senlkdlv ancl'il~ed Io its melu.~lable nalure. Sinue it Could irrevernibly ll'annlornl ilt/h~ Ihe equilibrium ~-B('(" (',' upon huali,]g. Ihe vmnequilil~riuln 6-AI~ ('r became ulffaw~ral~le I,o form under l,he i~locennil~ conditium, Ih~.ll led I,o .,,ignil'ical~l in¢l'e:lsen ill I'ilnl ntll't';~u'~.' IL'llll)u'ralttre MIL'h an len~lhy dep~.,,itions t>t' eleval,ed depo.,,il,ion I¢lllperillufe~s. I)til'illg Ih¢ IenL211~ytteposili~,L the tJlnl nllll:tce h.'nll~el';llure inevilal~l~ it~cl'ea~,u,das a n'entllt of o~lllilltlt)un eltergelic parli¢le t~otllbilldlllenfn. SuCh I'iln> .,,ul'l':~ce tenll~eral,Ul'¢ jtl¢l'e~' ',¢ ~:ts all:|lo~otls Io all ill silt| alllle~tljlt~ l,hal, was delrjlllu'fll;l] Io II1¢ t'orlnal,iol~ o1' Ihicker ~'LA 15 Cr Iitms. "1"o InilHnli/e Ihe in nilu anllealing effeu'l. Ihe ttept~nili~m wilh prohmL2ed inl,ernli~,siolls han .sho~ed very efle¢l,ively Io ,..:row Ille relali~elv thick ('r films Ihat Iliad Ih¢ mmequilil~lium ~S-,&I~ er>nlal nll'uq.:lur¢. ~" te)~)~ I:.l.,,evier SCience S.A. flr'~ ~,,,rd~: ('hr, q'nium: Sl'il.ilI,..'lii|,~: Tl'iin..,lilJ.,-.i,.ili electra,r1 micr{,,,c{q',',, ('l'l.2xl); X-i~,> dillr~,.:li~m
I. Intr, Murtion
('llr~lniltm w'il,h :.l non-B('(" cuysl,al slruclure ohl,:iirled by evaporalicm wa.,, I'irsl repol'led hy KilllOto el. al. [I]. Pre.,,el'~Ce o f l,his i'l(.)ll-l~CC chrc~rniun~, desi~,ned an ~'~-A15 C'r..,,ub.,,equenl,ly ha.,, heen c,.mfirrned I~y a ilul'nl~o" of nludies irl Ii,..ir,. spuuered l'iln'l.,, and fine evap,.>ral,ed i~arl,icle:,, [2-21)1. Similar I,o 6 - A I ~ Cr, A I 5 ¢'ry~taI strttcltll'e has h¢¢n found as welt in oilier B('(" refraclory lll¢lal fillns and I'~arl,i¢les such as Ilill~Me11. molyhdenllnl and niolfiuln [13.21-24]. F'r¢.sen¢'e o f the A I~ erysl,al .slruelure lhus :q'q~eat's Io he a u'otllnlovl Ieallll'e !(> Ihj.~ grOUp of t']C(" mel,aln. Ba.,,ed on all of l,he A 15 cr'yMal sl,rllL'l,lll'e inveMi~al,ion',, i~ in revealed l,hili A I~ phase,, are Inel,aslable and Irilllsl'orlnill,ion of A IS Jlllq) B ( ' C occurs duriI1g annealing. |;or il|MalK.'e, our leCelll .',,iudy nl1()w',~ l,he phase l,r~.lllSlOrlllillion o f 6-A 15 ('r inl~> lhe equilibrium B ( ' C Ur. de.,,igned a,, ¢~-BCC ('r. is a fir.,,l, order, irreversiMe, exolherlnic llall.sJl.ion, furl,her ¢onlirmil+g l,he i++el,a.sl,al+le iln,d altol,n~pic halure t>l+ 6-A 15 Cr phase [2()].
Similar exol,hermic, irreversible pll:Lse Iransforn|al,ion.s I'reqtlelll.ly lake phLee in ol,her lypes ol' nlel,asl,;|hle i'fl'la.,,e upon tl'kel'nla] Ilealin~. These illel,asl,al~le phases are ¢OIllnlonly i)roduu'ed via I.tllCOnvelil,it)ll~.Li (o1" so-called tloneqtlilihriurn) processirl,,..~ t'Ol.lle~', for eXalllple, inanv, alllOl'l)hotlS alloys prepared hy ineeharfieal alloyin~ or rapid solidifiu':llion show l,he irreversible, exol,herlniC ph,'lne tI'~.lnsl'('.rlll~.|lion at l,heir eryslallizalion l,elnperalures [25,26]. It js ~.[ltls inl,ere.,,l,il|~ for the pl'esetlL sl,lldy It) ce~ntiillte our previous work [20], all,¢tllpling I,o exanliile whel,her the & A iS Cr is a Pl'oduct. (>1 nonequilihl"ium processing, k'ormalion of ~% A I~ ('r filnls Brown tly spull,er deponilion has heen inve,,,l,i~al,ed, We synl.emal,ically varied deposil,i(m ¢olldil,iOlln ill order to deleHllille dolnJllanl, efl~.¢l.s on Ihe Iormal,iOli of fJlnls, l)eposiljon colldjlions exarllilled were WOl'kin~ pressure, deposilioll tenlpeI'ature and Ijllle.
2. Exi)erimenlul procedure Cr thin I'ilm deposil,ions
('lmrie-.ix~n,.lin ~ ~,|iIIil,,ll. Tel.: t ~Sh-2..lf1221',~2: lax: -I- 881,-2-41~25~24: k'.lll,ilJl: ~ . [ 1 1 ~ ~'IlIOLl'~l~l.ll[I.'ql..u'dLl.[~.. (X)4II-fl, II~'JI)/'L.I~/"'~I'U'~IXF ' I~)()X lil,,e,,io ~u'iell,,.'~' N.,.\. All ri~hl,, re,,er~,ed. PII SIHI4q'I.(H'IUII(U7 )(IIt5L).1 2
were
conducl,ed in an R,F,
II1~.1~11cl1"O11 spul,ler tlepo.,,iliol,i .'.,y.Mk?lll etluil)l~ed wit]l a II.lI'-
hoittq>leclllar
ptllnp
alld .'111 Lill¢()()letl I'(~l,aling nuhslrale
.Lit Ch. el .I. / lTfi. S . l i d I'dm~ 312 11t~,~,~J 7,~ ,~5
holder, The buse VtlClttlltl in the system was in the I0 7 Ton" I'm'~ge. Cr target with a purity > 99.q5+~ was used and ar~tln as tile wot'khlg ,~am was at leasl 99.995++ pure. Pritu" to deposition, the Cr larger was sputter-cleaned by h]sel'ting ;.~ shuUer betweell tile subxtrate and target. Working pre~:,ure was varied in the ran,~e of I - I 0 reTort while R,F. power was kept 50 W and I()0 W for 8-AI5 and ~-B(_?C Cr I'ill]] deposilions, respeelivelv. Except for hroatl-fi~ce transmission electron microscopy (TEM)observations, tile .~Iassslide was used as the .,;ub,~trate material. For the broad-fac'e microstructtH'~.fl e×anlillation, TEM hoIcy cat'hol~ suppor! I'ihn was uned for film deposition, To sludy Ihe deposiliun lelnper;flure etTecl, healing lanlpS on the I~ack of .~llhStrate were used and a tilerrnocouple wux placed us close as possible It} the ,~[IbMl';Ite tO IllOllJ|or tile del)t~sition tenlpel'attll'e. W h e l l tile stlhsti'ate was uillleated hy lamps, the temperature was hlvoluntarily elevated at --- (k3-().4°C/min during deposition while it cooled rather slowly at "-- O.OS-O.()6':'C/min after deposition. X-ray dil'fraethm ( X R I ) ) analysis ~}I" I'ilm.,, was ~.arried otlt tlsin~ a thin I'illl] dift'ractorne~er (SIEMENS DS()()()) with nlori~chroillalic('uK. radialion. "['l'~.lll,~llliX,~iOII elecIron n~iert~scopes (JE()l., JEM-2000 operated ;It 160 kV and J E M - 4 0 0 ( ) F X ;,it 4(10 k V ) were u,,,;ed to ex;,itnJile the hroildIl'aee :ltid cl'O.ss-~ecliOlla] I11icl'(~,strUCILIl'e,s of rilms. For cross-sectionalTEM examim, tions, l'ilms deposiled on the glass ,,ul'~strate were cut into slices anti sandwiched with all epoxy glue for holdiny. TEM disks were Ihen nlecllalfically polished to a thickness of --- I1)() p.nl, Ibllowed by tllimlin~ tt~ .--~0 ,u.m usin~ a dimpler. Final perf,)ration of the TEM disk wus accomplished hy un it,ll nlill (G~.lt~.tll 0(X) CTMT). Auger eleelron .speclrt~scopy (AES) o1" films was done with a I'erkin F.Inler PHi 670 Auger Nmloprobe. An argon-ion heron of 4 keV uver an area of approximately I.,~ x 1,5 nlnl ~ w;~s used for tile deplh prol'ilin~, with ].Ill etching r;Ite of ".- 11)() A / l l l i l l based Ol1 thai 'af the silicon dioxide.
3. Results In this sludy, when tile Wol'kin~ pressures were in the range of 5-7 niTtlrr deptlsitiwlS produced ++-A 15 Cu' I'ihl~,,, as evidenced hy tile presellCe tfl ~,.~. ('~.~lll and I"~l I pe~k,, in XRD pallel'ns. An example o1' XRI) p~llel'n I'~r i~-A I~ Cr is shown in lg~. la. in C'Ollll';Isl Io Ii~e i~-Ai5 ('r. ¢~-BC(7 Cr ill Fig. Ib exhibiled an ~vt~. peak a! -,- 44.S' of 2/t with the nl'~sence of illeaSlmfl'~le ++,,,,+ and ~,,, I'~eak.,,. Con]pared with lll;,il o1" t+~,, peak in Fig. Ih. relatively lar,ue width (l'ull-wMIh at hall'-nlaxinluni. F W t l M ) o f ~+,~,, peak in Fi,g. la is noticed. This might have heen re.suhed from a fine rihn KII'LICILIre or I.I po,~sihle prenellce of lllillOr ~-iICC Cr phase in the ~-AI~ Cr film, "I'EM bri~llt field (FtF) and dark i'ietd (I)1;) inlaBe,~ in l:i~, 2 shu~v tile 6-A 15 ('r film consisted o1' a number of 'clusters' Ibrmed by ',er', fine erystalliles, These ery.,,tallite~ ~,Vel'e estim;fled to be
7 c)
. . . . . . . .
I
I
I
[b) 1 mTorr
|
' 3S
I 37
'
1 39
'
I 4 t
'
i 43
~'
I 45
~
1 47
'
'~' 49
2() (deg,)
i:i.~. 1. XRI) p;lllern,, of ('r tihu', det~iled aL dittelcnL ~orkm~ ple~.~lll~...: (a) 7 mTorr arid (1~) I lllT,~rr. ,&pl'U~xhl~lle ,~.,,,,. ~'~;.,. "~..ll. ~md cl~ m pc~k p,.,ili~m., ar~ m~u'kcd, ahu~ ,,~.ilh ;t da,,ll liue dragon 1~; th~ IoL.'uliLm ~1 f'~,.~ peak I~ I'acililah: ~i,,ual c~mq~Lt'i~,~m.
- I11 nm in size. TIle diffraction pallel'n fro111 this fihll is shown in Fi,#. 2c. pmvidintz a direel e','idellce of i~-Ai5 Cr f{~rlnalion with IIll dele¢l;.lhl¢ plxtsenec of (~-BC(" Cr phase. For tile ~-BCC Cr film, TEM ob.,,ervations revealed dis. liilctl)' different I'ealtlres (a'~ sho~,vn in Fig. 3); that is tile relatively lartze er>'stallite size { -.- 21) ran) and dense film xtrl.letLIl'e,
i)epo.,,ilion temperature tlependence of &-AI~ Cr film I'ormation is depicled it] Xl,tl) resulls ~,f Fi~. 4. These I'ilm,~ were prepared at 5(1 W and 7 retort for 31) rain. I'a,,cm.~ble for ~'~-A15 Cr fornlali~m vd]en unheated, When tile dern~silion was done behlv, 15IF('. an im.'reasin~ der~silion lemperalure led Io irnprm,'emenl of ~-AI.~ Cr film erystallinil) as imlicated IL~'the appearance of ,~:.. arid i~,~ peak,,,. This t'ilm ery.,,tallinily improvemenl is pt'esumabl~; allrihuled Io an i~¢rease in udalom nlohilily for the film groxvlh resullin~ I'mm the temperature ele~alion I271. When the deposition tenq'~erattnx." v, a.,, further increased to 211(1'~(", ~l~e ~¢-!tCC el" t~eemlle a major phase and ,~-AI5 ('r m, a minor pllu~e. This high-tenli~erature induced the ~oB(,(" (,r I'~rlUation i,,, considered to he a i'e~ult of Ihe 6 ---,,,. pl]a,,,e mm,;l'~}rnlali~.rl occurred during Ihe del'~Osition. Similar temperature depel]dence for tile t'ormali~ul of 6-;\ 15 (.'r hax a l,,~} been rept}rled hv ulller earlier sludies I4, I ('~L .&llht~u~l'~ n~}t presenl IletV, we did m}t ot',,,er,,e the del',~,,iticul tellll'~lature dependence I'~r the ~.-B('C (.'r fihu I'urmatior~ I,..,~],
~ll
.I,P. ('tin ~'t .I, / 7"hi~ Sn/h/ I"ihns 312 t 199,'¢,~ 7,~-,~'5
Fig. 2. (a) 13righl field. (h) dark Iield Ti'.'M micr~=graphs, m=d (c) a .',elc¢led ;nrea diffracli~m pauern of a ~-A 15 Cr lilm. The rings in Ihe paUern are imtexeJ tnm) the .,,mallcst it~ Ihe lal'[Ze.,,t a,,, ,$,~.~, rS,=n, ;lll~.l ~q'-'t1'
The deposition time effcci on lh¢ phase forrnaliol|of Cr fihn is shown in FiBs. 5 and 6, hi I:"ig, 5. a series of XRD pa|lerns was ohl:|ined from Cr films grown under Ihe condition (50 W, 7 mTorr and no Ilealing) I'aw~rahle for tile ~-AI5 Cr with dil'ferenl deposition limes, Since these films had dil't~renl Ihicknes.'~e.,;and tile thicker t'ilms would naturally lead to more promiaent XRD peaks, peak intensilies of ~'~tH~;llld t~211 ill relative to that of u I t~,, rather than their absolute peak values, were a more meaningful indicator in determining the exi.stence of & A IS phase ill the film. "i'hus, as long as relative peak intensities for a given XRD pattern provided enough int't~rmalion, le~.~ prominent inlensities obtained from Ihinner films slill could he used for comparison with those fl'Oln lhicker films, For tile depositior= duration effect it! Fig. 5, with increasing deposition duration, tile crystal strtlcture of Cr films gradually changed from ~-AI5 Cr to t~-BCC Cr. When deposited for 20 rain, the ~'~-Cr fihn was s~ thin that XRD ,showed relatively small ~:~,~ peak (Fig, 5a). For depo.sition lime of 30 Illill.~$-AI5 filIllwill] ~,2..~. ~$:1,~ and ,I'~211 appeared (Fig. 5h). For 40 rain, h~lh ~S-AI5 Cr and t~-HCC Cr peaks co-existed in the fihll (Fig. 5c). Cr filnl gl'()Wll for 50 Ilfinl resulted in (~-BCC' ('r as a major phase will] no ob.servahle presence of ~$-A15 Cr plla,~e. FWHM o1" major
peak appeared to deerea,~e wilh the deposition time. 'l'his deposition lime dependence of i~-A 15 Cr fornlation implies lhe tran.~fornlathm of ~-AI5 Ct' into tr-BC'C Cr mi~hL have oeeurn'ed dun'ing Ihe deposition ~s a result af changing deposition condition, such as a stLhsU'ate heating from the COilthltli~tl,~ p;.u'tiele hot|lbardlllei11. Or1 the o t h e r hand, the depc~sili~m lime dependence ot" tt,-BC'C Cr was not observed, as shown in Fig. 6. XRD patlern~ ill Fig, 6 were obtained I'rom a .~eries o1" Cr film ~ample,~ deposiled under tile condition (i(}0 W, 4 mTorr and no healing) favorable for the t~-HC?C? Cr willl dilTerenl deposition limes. As indicaled, these I'ilms were predominantly tile tv-BCC? Cr Stl'tlCltll'e except for the II)-min I'ilm. The IO-min i'ilm ~howed t~-BCC was the nlajor phase with po.~sihle c~-AI5 C r ~,|,~a nlin~l', i!,~ reh.ilively ~mall ,~q,~ peak at ~ 39.2" of 20 appeared and FWHM of t~,,,, peak at '-.44,5 ° was rather large as compared with Ihose of other Ihree filtns, indicative t~l" the po,~.~ihle presence of mintlr &AI5 (?r l~ha,~e. 1"o further verify the ternperalure el'feels on tile formaLion of ~-AI5 Cr pha~e, cycle depositions with variou~ inlel'mis.~ions were era'tied otll Io examine tile l'ilm ,~url'ace temperature elTeel title to tile in silu healin~ t'rom t'~omhat'dmenlls of energetic .speeie~ during deposition. XRI) results
J.P. ('ira el ~d, / 7"hit~ .%~Ii,I l.Tht~s .H21199,~J ?,~1~,~15
~I
I:i~. 3, (,'z) Ilri~ht fiehl, (h) thzrk tield "I'I~M rnicroBl'~q~l'~s, mid (c) a ~elecled area difl'r~zcli~)l) p~dt~.'rn ~f :,z (z-lt(.'C Cr film. The: rinB.~ in the: pallors ~zz.~
in Fi B, 7 were ohlained fl'om Cr films deposited under tile condition (5() W, 3 mTorr mid no Ile~t~tirlg) in I'm,,or of the ~-AI5 Cr I'~rnmlion. For sinlplicitymid chuily, each filn~ was desi~m~ted acc~rtling to its depositi~m condilion. For i,lsta,lcc, 8 / 1 0 / 5 0 indicates tile I'ilm was dept~sited I'(~r 8 cycles and each cycle consisted of IO-min dcp~silion m~d 50-rain inlermission I~e~ween depositions. Fi~.. 7 rereads tile effects o1" dep~silion cycle nnd imcrmissiou on tile t'ormalion t~l' ~-AI3 Cr ph~tse. When tile l'ilm wits deposited I~)r 3 cycles with .'~O-Illin intel'nlissi~.q~ (3/10/30, Fig, 7h), tile ~-A 13 Cr crystal sti'UCtLire remained. With tile same intermission, incre~sin~ deposition cycles l'rom 3 to X (Fig, 7b-d) evet~ttmlly resulled in tl~e ~-BC.C Cr ~.s ~ donlimmt pirate, t::urthermore, with increasing imermission l'ronl ~0 Io 50 rain the ~-I]CC Cr dimini.shed, e.g., S / 1 0 / 5 0 (Fig. 7e). When tile in|termissitm was ftu'ther extended to 120 rain (6/1()/12(), Fig. 71"), the i~-AI3 Cr became the m~jor plmse, Simihu' el'fecl~ of i,~termission or del~l~iliot) cycle were not t)hserved it) the cases tile ~,-BCC C'r phase was formed when hmBer del'~Osition limes (sud~ ~ts 15 ~r 30 mia) were emr~loyed [21,I], Cross-section~.il '['I'~M exmuinati~ms indic;~ted I10 distinct
'kzyet'" structures, de~pite of the len~,thy intermis.~ion between deposition.s, Presemed in Fi~, 8a is a typicul cm.,~,ssectional "I"EM I'~riL~hl-fieldrrdcrograph t~ketz from a c~-Ai5 Cr film deposited at 120-min imermission ( 6 / I O/121)), The micm~ruph depicts tIle film had a well-dev¢loi~d ¢olumlmr B,';Ihl ,~|l'ucllil'~ ~J,lld tIle film thickness w~l,s ,,- 2~1 nm with no visible layer sIrLleILiI%', As indi¢~,ded by the difl'rtzcth~n pattern in Fig, 8, the film was of prcdL~nlinat,~ly iL ~-A 15 phtuse, ill a~tvement with the XRD r~sult .shl)wn in Fig. 7f. Spectroscopically, AES depth profile atmlyses I'urlher denu:mstrated Ihe Ii,mlogem~us tin,lure ~.~1"fihns, in l'ig. 9 in u rel'q'e.sentalive of AI-:S deplll profile L~bluined from a 3 / 1 0 / 3 0 Cr Film. The ndher slllt.~l~tll Cr mid O curves in the pml'ile indicate the I'ilm ~,,'as unil'~nn in o.mlp~siti~n m~d no layer-like COml~siticq~ was detected, I)resence t)l" impun'ities, O ~.lild C, is thought to he li~111 resithml ~ases in tile deposition chamber almost)here or from lhe speller hlr~et or the c,Ullbin~lion of h~th. In our ,~tudy, toted iml'~tu'ily co~lcenlr~lliozls it~ tile fihlls l~pie~d~y :~|ccotinled t~)t" 2()-3.~ ~.zl,~;~,~,lsme~isured by AES. Based on X-t';~) photoelectron Sl~eCtmsc~q~ystudies hy O' Keefe el ~d. [I 8] and Chu et al, [3~)], i'~q' both ~.-BCC a~d ~S-Al.~ ('r
82
.I.i'. ['h:+ ,'I .I./"
c;.'c,O
~'~,+111 ¢t1111 i]
:i . . . .
il
+ +,++
/
J~A
(a) Unhealed
i
37
.+i+,li+l l"ilm'+
4"~"T,I 1-----]
.++0+
35
17m+
'
I
39
'
I
41
'
I
43
'
i
45
+
I
47
'
I
49
2tl (deg.~
.+12
f lU<~,~+l
7A' ,~'.+
atzrce.', willl other +tlrlier results, in which the
llundrcd
l'i~. 4. X R I ) p:~tteit],, u l ,S-,,\15 ( ' i fihn],, del+,~,,iled al dilTerenl lu'mpera. Imp.',,: la) tmli~..a|u.d. Ill) Ii)+.) ('. (~..) I~<) (" ~,nd (d) 201r ('. "l'he,,e rilm,, ,,,,+.'re d,:l~,,il~.,d al 5II ~,~,' aml 7 nFl'orr I~+r .'~<} ram. la~rul'+le fl~r r"i.Al.~ ('r l'orliltlliOll sAh~.,n ullhu, illed
tG;>00 t
~'~ tl) ext 10 °:+
~'~lt
i+
I
. . . .
"i
I I
l'ilIllS, tile C'r v+'m, predonlinantly in an elei11enl,ttl or unl'~oulld state. St+. c'ai'l'~t+ll and +.+x)'~ell v , , e l e i'elallvcly nlint~r
and present in tile l'ortllSof carbides und oxides It X,21)].
4. l)i.,+cu+,+sion
In this study. ('r Films with both types uf eryslat sl,rl.l~:lure. <:I,-BCC [illd +S-AIS. huve been obtuined. According to tmr X R D and TI:M rcsulls ill h#n. I and 2, the +,:alcl, hlted lattiu'e parameter is 2.~I,I ,g for ~-B(7( "+ Cr and 4.:+,9 ;~ For ,~-AI5 Cr. consistent with previoL, s dula [2.16. It~]. In ¢OIltr;Ist to tile n,-H('C ('r. lhe ftmnaliun oI' +S-AI.+;i ('r i'ilms was l'mmd to he very seilsiti,¢e tt~ l,he proeessirl# c,tmdititms. O'Keefe el ul. (ll'l] sllt~,,,ed l,llal ,5-A15 ('r l'oniled under ~, certain ra,+~e (15-30 al,.+/+) oi" l,oltd impurity contenl, and. tllereI'ore, proposed the <~-AI5 ('r phase is an iillptsrily-lt+cked, melusltd~,le plla.,,e. ()ur l'ilms typically had It+lld impurity u'~Hllenl,s ill 20-35 al.'+, hut si'~{+v~'ed two distinct c','ystal StlJU+,.'tures. Tlle inlpurity efl'e~.'l lllu.S .seemed unlikely It~ play an iml'~t+rlant r~le: instead, l,ile del'+t~,~ition teml'~eratt;re appeared d
"L~'a,,,..u.wd ~
35
37
39
41
43
.15
+17
49
21~ (d(,'[l,)
I'i~+ +~. Xl,tl) l+,h11L:In,, ll~ml ('n lihns tl~.'l+~l',ilL'tl tinder the ~.'imdilkm (511 W. '7 llt'l't+iT and II++ h+.'athi[2) l~i~,,++'~lhl~.' hlr the ,'i. AI5 ('I ~AiLII +.Iill~.'lt_'l|l dcp4,,,ilh,t+ irate,,: (,i] 213 IIIHI, II~) 3() trim. (~.) 4(+ ram+ itlld ((I) 54) 11|J11.
.I.1'. ('/m ,'t a/. ,17'1,..~li,I (~;?(],) l
~'J~0,
I[1 ]0 =i]
....
I~.'] I
I
fo,2o t'--
(C)
30 r'1~h'~
/
/
a)
g
=i
35
[
37
,
I
39
'
I
41
'
I
43
'
I
45
'
"'I
47
"
I
49
I.ilm~ 312 1 Iq',~,~) 7i~'--,~"~
~.~
rS ~ ~ transformation is not possible ~o achieve under lhe equilibrium condition taxi thus it has demonstrated th,: nonequilihrium properly of ~$-AI5 Cr pha,se. As lhe f'~-A15 Cr i,,, a mmequilibrium phase, a Ihenllal heating gmleraled dul'ing deposition could induce the in'cvelsihle phase tlan.sformation. Although the t'ilnl surl'acetemperature was virtually impo,ssible to measure in this study, the uncooled suhslrat¢ may have reached as high as 5()()°C [27] mid lhe film surfilee could be at lemperalu[cs well above the lran.sfornmthwl lemperature. It is thus teadiiy under.smc.d that an increase irl deposition lemperalure fav,a.ed tile Iommtion of equilibrium t~-BCC Cr, as shown in Fig. 4. In addition, during onheated len~lhy depo,silion, an involumary l'ilm surt'ace-temperalure increase from lhe energetic particle I'~omb~rdments could lead to significm~t healing and, Illerefore, !gave rise to the (~-BCC Cr formalion. As a result, diffcr1:nt exlcllts o1" in situ anne~flin~ have II.|kell plm.'e during deposilion, This in ,silu annealing in ii, lrri WIIS lllllih)gOtl,~ IO the post-deposition ex silu allll¢;.iling. The posl-depositi,m armealirlg could cause the ln.msrormaliun of ~S--, ~ [20], while lhe in silu amlealing el'reclively iml)roved l'ihn cryslallinily, a:,; ilhistrated in Fig. 4. and ever~tually induced occurrence of the irreversible phase m, nsformation m Hg. 5. Accordingly, to minimize
20 (deg.) Fig. h, XI, I) l~aLl~.'l'nnII'~,111('I filnP, dep,~,,iled |llRh.'rthe ~.~mdidun (1(}~) %,V, 4 mTol'1 ,llld il~, he.'llin~) lax,,rai*le l,,r lhe ,|..IR'(' ('i' with Llil1~'i'enl del~o,,ili{v~ liln~."-,: (;.i) Ill nlill, Ih) 21) illin, (~.') .~.i| Inin. ;.ind Id) 40 lllil|.
~'~210 tZ110 ....... ~"
~21 I
II
II
(t) 6q0/120
raster a,~ the s[}utlei'ed a t o m s have Oll~ ll.l tWO
orders o f
i1111[zililtt+l,, ' ,re'eateraverage energie,,, than the evaporation. Prior studies have slmwn that such high quenchinB rate.,, rrequenlly allow nonetluilil~rium atomic I.irl'i.lltgetlletllx IO he readily quenched-in, producing film.,, with ~.'omlx~sitions Or ,',ill'll¢lLll'kL~ which normally would 11oIhe allowed accordint-z m hulk lhern|odyllallliC C(lll,%tl'ainls [29-33], The pseudo-alhtv film,,,, l'or insmm.'e, can be furmed using co-spullerintz under ihi,~ nonequilihrium proce,,,sing condilion hy forced combimilions or the eh.,menls which have essentially zero I1]utual solid or liquid solubilities. Mo-('u [.~t2] illld ("tl-C []i.'~] systems ill'e exanll'~les of these yscmh~-~dho" films. As i','Ol'x~sed hy many in~.e.,,ligator,~[8,15,2(I], the ~'~-A15 ('r is a high-temperalure allotropic chromium i'~hase m,.! f(~rms under :~oneqLiilir,'ium condilions, beCOlllin~ a mela'dql~le phane al r o o m i e m p e r a l u r e , I)l, le io iln m¢iastal'~le nalure, the 6-AI5 (,r pha.ne eventually Iran.sl'c,'ms into lhe equilibrium ~-I}(,C ('r ulmn therlnal almealin~ al -- 42"7"(' [2()]. As the ¢I-A15 ('r is rormed under Sl'~ecifi~:i~oneguilibriul|| c o n d i l i o l l n ,
the ~'~ -~ ~ Illlax¢ trannl'orlllalion
I~¢collles
irreversible [20]. ()ur view on Iilin nonequilibrium producl in furlhcr stlPl~orled I~.Va la,,,cr-irradiated 6-AI5 ('r stud), of B]~iega and Pot~encu-Pogrion 115]. They showed Ihe ~'~--, ¢~" |r;.lll.q'OrllIilliOll lle¢;.|llle l'e,~,el',ql'~lewhell llle ('r was irradialed wilh a 6(l-n,,, pulse-laser, This pul,~e la,~er-indu~.'ed
(e) 8/10/50
(d) 8'10/30
(c) (;' 10:30
(b) t.10:30
tal I;I0.0
I
35
37
~
i
39
'
/
41
g
I
43
'
I
45
'
I
47
'
I
49
2o (deg) I'l~ T. XR[) I~alK'|tt ,, |lore ['| him,, depL~,,ited tmdel" the di|ielVnt ¢~'1¢ u'on~.ii|lOli',,(.~4) ~,~'..~ mr,~il mid itt~ he,illl1:21in i,l~.of ol lhe ,S-,,\IS t'l lorillaUOil: Ial I ' Ill. II. (b) ~ lli.llI, (~.')h .'ill.,-If). Id! ~ 'If).'.It).l.e! :4 l(I 5U and IIl I~,.Ill 121) N¢~.'lq\I I,~i dClall',t~l film i.~',,i.+,:,ii,,itiOtl.
84
J.l'. C/m t.t .I. / 71d. Solid l"ilm,~ 312 ¢ IW),S'i 78 ,~5
"r;ihlc 1 Averli~¢ deposition I'itli.'~, of ('r fillil~ lind their crystal .~lruclurc.~ I.ilnl"
Axerllge tlel+O~ititlii rate (nnl I iliiili
(.'r)',~laf slrtlcturc I'
1/10/0 3/lll/3l) h/1t1/311
8/I(tl31l 8/I0/4(i gi' 1111511
~ 4.5 -- 4.4 .,- 4,14 - 5.4 - 5.1) - 4.5
5-AI5 f-AI5 m l l C U < . ~-A t5 rr-IlCC r e l i C ( '< , fi-A 15 ~ r - I t ( ' l " , fi-A 15
3 1 1()1121i 6t 1l)/12(i
- J,(t - 4,3
fi-AI5 &AI5
aSItit h.'Xl for delail~ td' l'iiln designation, i~('l'),~litl ,Mrii~'tUl¢s wert" delerlllJned by XRIJ :ind T i i M .
' Maj,r pttasc.
Fig, 8. A cro.,,.,.-secii~mal Ti'M bright-field micrngraph with the selected ar,,ta diffraction pattern (inset)ilhlained t'rt~lll a (if 10/120 Cr tihn.
the in situ annealing effect, we deposited the ~-AI5 Cr fihns wilh the prolonged internlissions to prevent the filnl surface from overheating, As shown by XRD results in Fig. 7 and TEM observations in Fig. 8, the longer was the intermission the more sati.,,factt~ry to prnduce the ,,5-A15 Cr film. Therelore, with this prolonged intermission deposition approach, much thicker Cr films thai have the ~-Ai5 crystal structure would be able to grow. To further examine the in situ annealing effect on the
forrnation of g-AI5 Cr I'ilm. deposition rates measured from films grown under various condiiilms are considered, as listed in Table i. It appears that the 8-AI5 Cr film was likely to forni tit low dcposition rates, whereas, the tr-BCC Cr forrned otherwise. This phenomerton can he qualitatively explained well when taking into account tile in situ annealing effect, tks nlerltioned above, the high-ternperature, nonequilibrium ti-Ai5 Cr was quenched-in during the deposition. When the deposition rate was relatively low, the cooling rate effects were significant because of the film surface not being heated-up. Thus, the in situ annealing was trivial and tile high-iemper:lture ,,5-AI5 Cr phase lbrmed favorably. Conversely, the equilibrium ce-BCC Cr phase litw~rably formed when the film grew faster becau,sc the in situ annealing of filiu became increasingly inllueniial as a result of niany nlor¢ high-i¢inperatLirl2 sputtered aloni.~ arrived. Variations in the cry.~iallit¢ size for each phase observed ill TL:M niierilgl'aphs ill" l=igs. 2 and 3. thus. can be recognized in ¢llnsetluence ill' differences in the deposition i'i.il¢. This similar hi siiu annealirtg el'feet on the high-tenlr)erature phase fornialioil has also 110011 dellionsiraled by Cllu el al. 134] in sputter-deposited ililignesiuill iungsiaie (MgW()~) thin filnl phosphor.
iO0
5, Conclusions /~ o=
E r~ .u E
Cr
80-
60 40-
O
o
2o-
o
c 0-.
0
i
i
5
10
i
c i
15 2o Sputter Time (rain)
I
25
30
l:ig. q. An AES tlcplll pmlilc i~i' .3 3/11)/311 (.*I" lihn sh1~,,~,ing ra(her Mlllli;lh ('r, (), arld (." ctlrv¢.,., lhl'lill~h the film anMy/cd.
Formation of nonequilihlium ~-AI5 Cr dlin films by ~putter deposition has been examined. The 6-A 15 Cr phase was found to form under specific i~rouessing conditions. Susceptibility tit" ~':J-AI5 Cr forrrultilm to the processing condition was primarily attributed to its rnetastable nature. As it could irreversibly trarhsfon'n into the eqt, ilibriun~ ~I'-BCC Cr upon heating, the mlnequilihrium ~'~-AI5 Cr hecanle unl'avi)rahle to l't)rerk under tile processing cotlditions that caused a raise it} the I'ilm surfaee-temperatu,'e, such as lengthy depositions or del)ositi(wi temperature being elevated. During the lengthy deposititm, an involtilltary film surt'aceitemperature increase, resulting from colltilltl-
.I.P. ("/tit et , I . / 77ti, Solid bilm~ 312 119~,S'J 7,~--,'~5
otis I'toMbartlMellts o1' energetic species, is considered as
the in situ annealing th,'~t was delrimental to the formation o1' ¢i-Ai5 Cr films. To effectively minimize the in .,,itu annealing effect and L.zrow |'clativcly thick ~-A 15 Cr films. the deposition with p|'olonged intermissions has been shown ,~'u'y satisfactory.
Acknowledgements Autl'lors thank Mr. 3,L. Hong and Mr. T,N. Lin for their help in conducting this research program. Mr. C.C. Hsu of Materials Research and Development Center at CI1L||I Shah Institute ot' Science and Techut)logy is also thanked for his help in TEM sample pt'cparations, This study was supported by the National Science Council of the Republic of C h i | | a u n d e r C o t l l r a c t N o . N S C 85-2216-1-:,-019-1}114, w h i c h was gratefully ackrtowlctlged.
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115
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