Near edge x-ray absorption fine structure spectroscopy study of atomic nitrogen implanted in Al2O3 by low energy N2+ bombardment

Nea edge x- ay abso p ion ine s uc u e spec oscopy s udy o a omic ni ogen implan ed in Al2O3by low ene gy N2 ¿bomba dmen A. Ba anco, J. P. Holgado, F. Yube o, J. P. Espino ´s, A. Ma ı ´n, and A. R. Gonza ´lez-Elipea) Ins i u o de Ciencia de Ma e iales de Se illa (CSIC-Uni e sidad de Se illa) and Depa amen o de Quı ´mica Ino ga ´nica, c/Ame ´ ico Vespucio s/n E- 41092 Se illa, Spain 共Recei ed 27 Oc obe 2000; accep ed 22 Janua y 2001兲 N2 ⫹bomba dmen o Al2O3has been in es iga ed by nea edge x- ay abso p ion ine s uc u e spec oscopy. Two kinds o species we e de ec ed and we e a ibu ed o implan ed ni ogen a oms and ni ide species. These esul s a e discussed in ela ion o p e ious a ibu ions in he li e a u e o hese species o AlNO and AlN. © 2001 Ame ican Vacuum Socie y. 关DOI: 10.1116/1.1355762兴 I. INTRODUCTION Low ene gy ion implan a ion in me al oxides has been widely s udied because o i s undamen al and applied in e - es o he p epa a ion o hin ilms and o he echnological ma e ials.1Ni ogen 共i.e., N2 ⫹兲bomba dmen o me al oxides has been epo ed o p oduce changes in s oichiome y by subs i u ion o oxygen by ni ogen ions.2,3 Typically, he chemical s a e o his implan ed ni ogen has been ecog- nized as ni ide species. Choi e al.4,5 ha e ecen ly epo ed ha mo e han one ype o ni ogen species is o med when Al2O3is subjec ed o low ene gy (0.5⬍E⬍2 keV) ion bom- ba dmen . Based on he binding ene gy 共BE兲 alues o he x- ay pho oemission spec oscopy 共XPS兲peaks o hese spe- cies, Choi e al. assigned hem o AlON (N 1sBE 402.5 eV兲 and Al–N (N1sBE 396 eV兲. The i s ype o species is o med by low ene gy ion bomba dmen (E⬇0.5keV), while bo h o hem a e o med a E⭓1 keV. Besides, a badly de ined peak a 397.6 eV, which appea s a in e media e al- ues o bomba ding ene gy, is a ibu ed o Al–N. Ve y e- cen ly we ha e also epo ed hese N2 ⫹bomba dmen p o- cesses in Al2O3.6Basically his is a con inua ion o p e ious wo k by Be o i e al.7on he same subjec . In bo h cases we ha e ound by XPS a beha io simila o ha epo ed by Choi e al. Howe e , ou in e p e a ion o he highe binding ene gy peak subs an ially di e s om ha o hose au ho s. A e a ca e ul analysis o XPS and ion sca e ing spec os- copy 共ISS兲spec a in a simila ion implan a ion expe imen , in which peak posi ions, in ensi ies and he mal s abili y o hese species we e conside ed, we p oposed ha he peak should be a ibu ed o a omic ni ogen occupying la ice and/o acancy posi ions o an al e ed Al2O3ne wo k.6In he same pape he appea ance o a small O1speak a 537 eV upon O2 ⫹bomba dmen was a ibu ed o he o ma ion o simila ly apped species o a omic oxygen. Wi h he aim o adding mo e suppo o his assignmen we ha e ca ied ou expe imen s by x- ay abso p ion spec- oscopy 共XAS兲by eco ding he nea edge ine s uc u e 共NEXAFS兲spec um o ni ogen implan ed Al2O3samples. NEXAFS spec a o elemen al a omic species o ni ogen implan ed in solids a e ypically cha ac e ized by sha p eso- nance peaks.8–10 So, in p inciple, hei iden i ica ion should be easy since he spec a a e cha ac e ized by na ow sha p peaks, in con as wi h he b oade s uc u e o ypical ni ide species. II. EXPERIMENT The XPS spec a o ni ogen implan ed in Al2O3we e eco ded on a Leybold–He aeus LHS-10 spec ome e wo k- ing in he pass ene gy mode a a alue o 50 eV. The MgK ␣ line (h ⫽1253.6eV) was used as he exci a ion sou ce. A e e ence o he BE scale o he spec a was aken a 284.6 eV o he C1speak o he ca bon con amina ing he sample. N2 ⫹bomba dmen in he ene gy ange o 0.5⬍E ⬍2 keV was ca ied wi h a Leybold–He aeus hollow ca h- ode ion gun 共IQP-10兲. Bomba dmen was ca ied ou o 30 min 共 o al dose o 0.9 and 5.8⫻1016 ionscm⫺2 o 0.5 and 2 keV, espec i ely兲up o sa u a ion o he N1ssignals. A ho ough XPS in es iga ion o his N2 ⫹bomba dmen p ocess can be ound in a p e ious pape .6A e p epa a ion he samples we e exposed o ai and s o ed wi hou any special p ecau ion. Apa om an inc ease in he in ensi y o he C1ssignal, no change in he shape o N1ssignals o in he ela i e in ensi y o spec um componen s was de ec ed by XPS a e se e al weeks o exposu e o ai . Howe e some a enua ion o he Al2p,O1s, and N1ssignals was ob- se ed, as expec ed om his su ace con amina ion by ca - bon. These samples we e in es iga ed by NEXAFS oge he wi h o he un ea ed Al2O3samples ha we e bomba ded in si u in he ul ahigh acuum 共UHV兲chambe used o he NEXAFS expe imen . No no iceable di e ences in he shape o he spec a we e de ec ed o he ex si u o in si u samples subjec ed o ni ogen bomba dmen a he same ene gies, al- hough he in ensi y o he signals was sligh ly smalle in he o me case p obably due o con amina ion o he su ace. NEXAFS spec a a he N Kedge we e eco ded a he PM-1 beam line a he BESSY II synch o on in Be lin 共Ge - many兲. The pho on ene gy was selec ed wi h a SX-700 plane g a ing monoch oma o and he spec a we e eco ded by a兲Elec onic mail: [email p o ec ed] 1024 1024J. Vac. Sci. Technol. A 19„3…, MayÕJun 2001 0734-2101Õ2001Õ19„3…Õ1024Õ3Õ$18.00 ©2001 Ame ican Vacuum Socie y o al elec on yield 共TEY兲by measu emen o he d ain cu - en h ough he sample o by channel on de ec ion. Excep o he backg ound line, simila shapes we e eco ded o he spec a by hese wo me hods o de ec ion. De e mina ion o pho on in ensi y a each ene gy 共i.e., I0measu emen 兲was done by measu ing he cu en wi h a gold g id placed in on o he samples. Spec a a e ep esen ed a e di iding he sample signal by his e e ence signal. Fo NEXAFS analysis, he Al2O3samples consis ed o hin ilms 共 hickness ⬃0.5 ␮ m兲o his ma e ial deposi ed on o a me al subs a e by plasma enhanced chemical apo deposi ion 共CVD兲. By XPS analysis ei he hese hin ilm samples o ␣ -Al2O3single c ys als we e used. In bo h cases he XPS esul s ob ained we e qui e simila . Thin ilm samples we e p e e ed o XAS s udies because hey p e- sen ed enough conduc i i y so o a oid undesi ed cha ging e ec s and o enable d ain cu en eco ding o he spec a. III. RESULTS AND DISCUSSION Figu e 1 shows N1spho oelec on spec a o ni ogen implan ed a 0.5 and 2 keV on Al2O3 hin ilms. These spec- a a e equi alen o hose p e iously epo ed by Choi e al.4,5 and by ou sel es6 o a simila bomba dmen expe i- men on ␣ -Al2O3single c ys als. By low ene gy bomba d- men a N1speak a 403.4 eV is he majo i y species de- ec ed. Besides, a badly de ined s uc u e appea s a lowe BE. Meanwhile, by bomba dmen a he high ene gy, wo peaks a 403.4 and 396.4 eV a e clea ly de ec ed. In his second case he asymme y on he high BE side o he 396.4 eV peak s ill sugges s he p esence o mino i y species wi h an in e media e alue o BE. These wo samples we e hen examined by NEXAFS spec oscopy and hei co esponding spec a a e shown in Fig. 2. In he sample bomba ded wi h 0.5 keV ions a sha p peak a 398 eV wi h a ull wid h a hal maximum 共FWHM兲o ⬃1 eV is he mos no iceable ea u e obse able in he spec um. This signal mus ha e o igina ed om he same ni ogen species as ha p oducing he N1s pho oelec on band a 403.4 eV. Meanwhile, in he XAS spec um o he sample bomba ded wi h 2 keV ions his sha p peak, oge he wi h a much b oade signal, is de ec ed. This second signal is cha ac e ized by main maxima a a ound 404 and 411 eV and is simila o he N1sNEXAFS spec a o ni ide species epo ed in many me al ni ide sys ems11 共No e ha hese ene gy alues e e o he app oxi- ma e posi ion o he maxima and no o he ene gies o he abso p ion h esholds and ha , he e o e, hey canno be di- ec ly compa ed wi h BEs o pho oemission peaks兲. Some hin s o a simila species can be also seen in he 0.5 keV spec um. A small concen a ion o a species o ha kind would ag ee wi h he appea ance o a badly de ined s uc u e be ween 400 and 396 eV in he pho oelec on spec um o he 0.5 keV sample 共c . Fig. 1兲. Howe e , addi ional in es- iga ions a e s ill necessa y o p ope ly accoun o hese small ea u es. Sha p esonance peaks o 1 eV wid h a he N Kedge abso p ion spec a a e no compa ible wi h N–O species. Spec a o abso bed NO on me al su aces a e cha ac e ized by ␲ *and ␴ * esonances a ⬃400 and 412 eV.12 In nono i- en ed samples an a e age weigh ed in ensi y should be ex- pec ed o hese wo esonances, a si ua ion ha is no ound in ou expe imen wi h 0.5 keV. N Kedge spec a o mo- lecula ni ogen adso bed on me als ha e also been epo ed.13,14 Two ea u es a 401, sha p and in ense, and a 418 eV, b oad and lesse in heigh , cha ac e ize his ype o elemen al ni ogen. The absence o any hin o his second ea u e a 418 eV in he spec um o he 0.5 keV ion bom- ba dmen sample elimina es any sugges ion ha molecula ni ogen can be he species ha cause he sha p ea u e a 398 eV. S e ic hind ance o he inco po a ion o such mo- lecula species wi hin he aluminum oxide la ice is ano he eason o dis ega d i as esponsible o he signal eco ded. Thus, we a ibu e he sha p esonance line o a omic ni o- gen species loca ed in emp y posi ions o he la ice. A simi- la sha p esonance has been epo ed by So iano e al. o FIG. 1. XPS spec a o Al2O3su aces modi ied by N2 ⫹ion bomba dmen . FIG. 2. NEXAFS spec a co esponding o he wo samples in Fig. 1. 1025 Ba anco e al. : NEXAFS s udy o a omic ni ogen implan ed in Al2O31025 JVST A - Vacuum, Su aces, and Films N2 ⫹bomba ded Z and H o o TiN hea ed in O2a high empe a u es.8,9 A ew yea s ago, Jime ´nez e al. a ibu ed he appea ance o a sha p peak a 398 eV o ni ogen a oms in in e s i ial posi ions o sp3BN,10 whe e only by ou gas- sing a T⬎1000K did emo al o hese species occu . Thus, he p esen NEXAFS esul s suppo ou p e ious assignmen o he wo XPS peaks a 403.4 and 396.4 eV o a omic 共i.e., N兲and ni ide species o ni ogen implan ed in Al2O3. I seems ha a low ene gy 共i.e., E⬃0.5keV), ni o- gen ions a e no able o p e e en ially emo e oxide ions om he Al2O3la ice. Howe e some ni ogen a oms may become inco po a ed wi hin he e y igid Al2O3ne wo k, likely a in e s i ial o acancy posi ions. A a highe ene gy 共i.e., E⬃2 keV) p e e en ial emo al o oxygen mus occu , and hei la ice posi ions become occupied by ni ogen in he o m o ni ide species 共i.e., Al–N bonds兲. This la e e ec occu s wi hou p ecluding he occupancy o some in- e s i ial si es by a omic ni ogen as indica ed by he appea - ance o he wo peaks in he pho oelec on spec um. I is also in e es ing ha due o he high s abili y o hese im- plan ed species o ni ogen u he ex si u he mal and en i- onmen al cha ac e iza ion would be possible wi h ega d o o he p ope ies such as op ical, magne ic, e c. P og ess is being made in ou labo a o y in ha di ec ion. ACKNOWLEDGMENTS The au ho s hank he CICYT 共P ojec No. MAT97-0689兲 o inancial suppo and he HCM p og am o he Eu opean Union o p o iding access o he synch o on ligh sou ce. 1J. C. Sa ´nchez-Lo ´pez, L. Con e as, A. Fe na ´ndez, A. R. Gonza ´lez-Elipe, J. M. Ma ı ´n, and B. Vache , Thin Solid Films 317, 100 共1998兲. 2J. Taylo and J. W. Rabalais, J. Chem. Phys. 75, 1735 共1981兲. 3I. Be o ´ i, R. Kelly, M. Mohai, and A. To ´ h, Nucl. Ins um. Me hods Phys. Res. B 80Õ81, 1219 共1993兲. 4W.-K. Choi, S.-C. Choi, H.-J. Jung, S.-K. Koh, D. Byun, and D.-W. Kum, J. Vac. Sci. Technol. A 16, 3311 共1998兲. 5W.-K. Choi, S.-K. Koh, and H.-J. Jung, J. Vac. Sci. Technol. A 17, 3362 共1999兲. 6J. P. Espino ´s, A. R. Gonza ´lez-Elipe, M. Mohai, and I. Be o i, Su . In e ace. Anal. 共in p ess兲. 7I. Be o i, R. Kelly, M. Mohai, and A. To ´ h, Su . In e ace Anal. 19,291 共1992兲. 8L. So iano, M. Abba e, J. C. Fuggle, C. Jime ´nez, J. M. Sanz, L. Gala ´n, C. My hen, and H. A. Padmo e, Su . Sci. 281, 120 共1993兲. 9L. So iano, M. Abba e, J. C. Fuggle, P. P ie o, C. Jime ´nez, J. M. Sanz, L. Gala ´n, and S. Ho mann, J. Vac. Sci. Technol. A 11,47共1993兲. 10I. Jime ´nez, A. F. Jankowski, L. J. Te minello, D. G. J. Su he land, J. A. Ca lisle, G. L. Doll, W. M. Tong, D. K. Shuh, and F. J. Himpsel, Phys. Re . B 55, 12025 共1997兲. 11J. G. Chen, Su . Sci. Rep. 30,1共1997兲. 12J. S o ¨h , K. Babe schke, R. Jaege , T. T eichle , and S. B ennan, Phys. Re . Le . 47, 381 共1981兲. 13L. Wenzel, D. A ani is, R. Schlo ¨gl, M. Muhle , D. No man, K. Babe - schke, and G. E l, Phys. Re . B 40, 6409 共1989兲. 14L. Wenzel, D. A ani is, R. Schlo ¨gl, M. Muhle , D. No man, K. Babe - schke, and G. E l, Phys. Sc . 41,1028共1990兲. 1026 Ba anco e al. : NEXAFS s udy o a omic ni ogen implan ed in Al2O31026 J. Vac. Sci. Technol. A, Vol. 19, No. 3, MayÕJun 2001