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
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1026 Ba anco
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: NEXAFS s udy o a omic ni ogen implan ed in Al2O31026
J. Vac. Sci. Technol. A, Vol. 19, No. 3, MayÕJun 2001