Modifikacija svojstava tankoslojnih TiN struktura na silicijumskoj podlozi bombardovanjem jonima
Modification of the properties of TiN thin structures onsilicon substrate by ion bombardement
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Istraživanja tankoslojnih struktura titan-nitrida (TiN) su od izuzetnog znacaja zbog
jedinstvene kombinacije fizickih i hemijskih svojstava koje ovaj materijal poseduje.
Titan-nitrid je materijal koji ima primenu u razlicitim oblastima tehnologije zahvaljujuci
svojstvima kao što su visoka tvrdoca, visoka tacka topljenja, dobar otpor na habanje i
koroziju, visoka elektricna provodnost, mali kontaktni otpor, itd. Svojstva deponovanih
TiN struktura je moguce kontrolisano menjati primenom jonske implantacije. To je
neravnotežni proces u kome je moguca precizna kontrola parametara kao što su vrsta,
energija i koncentracija ugradenih jona. Na taj nacin jonska implantacija može dovesti
do promene kristalne strukture materijala, amorfizacije, stvaranja nano-ukljucaka,
jedinjenja, promene morfologije površine, itd. Nabrojane strukturne promene mogu da
menjaju fizicka, hemijska, mehanicka, opticka i druga svojstva materijala.
U okviru ov...og rada tankoslojne strukture TiN debljine ~.240.nm dobijene su metodom
reaktivnog jonskog rasprašivanja. Kao podloge su korišcene monokristalne (100)
silicijumske plocice. Slojevi TiN su deponovani na sobnoj temperaturi podloge i na
temperaturi podloge od T.~150oC. Modifikacija deponovanih slojeva uradena je
tehnikom jonske implantacije. Uzorci su ozracivani gasovitim jonima argona energije
120.keV i 200.keV i metalnim jonima vanadijuma energije 80.keV. Jonske doze su u
slucaju jona argona bile u opsegu 5×1015 –.20×1015 jona/cm2, dok su za jone vanadijuma
doze bile 1×1017 jona/cm2 i 2×1017 jona/cm2. Osnovni cilj ovih eksperimentalnih
istraživanja je proucavanje uticaja i poredenje razlike uticaja inertnog i metalnog
upadnog jona na strukturna, elektricna i opticka svojstva TiN slojeva. Pored toga,
proucavan je i uticaj temperature podloge na strukturu deponovanih tankih slojeva TiN.
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Stehiometrija, homogenost i debljina tankih slojeva TiN pre i posle implantacije jonima
argona i vanadijuma analizirana je metodom Rutherford-ovog povratnog rasejanja
(RBS). Analiza pokazuje da joni argona nisu prouzrokovali promene stehiometrijskog
odnosa komponenata u TiN sloju cak ni posle najvece doze argona. U slucaju
implantacije jonima vanadijuma sloj pokazuje nestehiometrijske koncentracione profile
u oblasti gde se najveci broj jona vanadijuma zaustavio kao i u oblasti ispod
implantirane zone. Takode je zapaženo da joni vanadijuma dovode do porasta efektivne
debljine sloja.
Strukturna analiza tankih slojeva je uradena difrakcijom X zraka (XRD), transmisionom
elektronskom mikroskopijom u kombinaciji sa elektronskom difrakcijom na odabranoj
površini (TEM./.SAD) i visokorezolucionom elektronskom mikroskopijom uz analizu
pomocu Fourier-ove transformacije (HRTEM./.FFT). Ove metode su nam omogucile da
definišemo prisustvo faza u deponovanim i implantiranim strukturama. Uocili smo da
TiN slojevi rastu u vidu vrlo fine polikristalne stubicaste strukture. Nakon implantacije
jonima argona slojevi zadržavaju polikristalnu strukturu uz narušavanje stubicaste
strukture u oblasti oštecenja uzrokovanog implantacijom. XRD i FFT analiza je
pokazala da je prisutna samo površinski centrirana kubna TiN faza uz smanjenje
velicine zrna nakon implantacije jonima argona. Dakle, jonsko zracenje dovodi samo do
lokalnog atomskog preuredivanja unutar sloja. U slucaju jona vanadijuma TEM analiza
pokazuje prisustvo amorfnog sloja iznad implantirane oblasti. Implantirana oblast koja
ima polikristalnu strukturu sadrži veliku kolicinu defekata. XRD i FFT analize su
pokazale pored površinski centrirane kubne TiN faze prisustvo nove VN faze u oblasti
gde se najveci broj jona vanadijuma zaustavio. Može se zakljuciti da implantacija
jonima vanadijuma dovodi do formiranja nove faze usled hemijskih efekata. Takode je
primeceno da je dubina oštecenja znacajno veca od one predvidene SRIM2003
simulacijom.
Metoda „cetiri tacke” pokazuje da specificna otpornost raste sa porastom jonske doze.
Opticka merenja IR metodom su pokazala da opticka otpornost prati promenu
specificne otpornosti. Efekat promene specificne i opticke otpornosti je objašnjen
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akumulacijom defekata implantacijom jona argona i formiranjem nove faze u slucaju
jona vanadijuma.
Titanium-nitride (TiN) thin film structures research is of great importance because of
the unique combination of physical and chemical properties of this material. TiN is a
material commonly used in various fields of technology due to the properties such as
high hardness, high melting point, good corrosion and abrasion resistance, high
electrical conductivity, low contact resistance, etc. The process of ion implantation can
be used to change the properties of deposited TiN structures. It is a non-equilibrium
process by precise control of parameters such as type, concentration and energy of
implanted ions. In this way ion implantation can produce changes in crystal structure of
materials, produce of amorphization, creation of nano-inclusions, compounds, changes
in surface morphology, etc. These changes can alter physical, chemical, mechanical,
optical and other properties of materials.
In this work titaniu...m nitride thin films with 240.nm thickness were obtained using
reactive sputtering. The substrates used were monocrystalline (100).Si wafers. During
deposition the substrates were held at room temperature or at 150oC. Modification of the
deposited layers was performed using the ion implantation technique. The samples were
irradiated with 120.keV and 200.keV gaseous argon ions and 80.keV metal vanadium
ions. In the case of argon ions the fluences were in the range of 5×1015.–.20×1015
ions/cm2, whereas for the vanadium ions the fluences were 1×1017 ions/cm2 and 2×1017
ions/cm2. The main objective of this experimental research is to study the influence and
to compare the differences of incident inert and metal ions on the structural, electrical
and optical properties of titanium nitride layers. The influence of the substrate
temperature on the structure of as deposited thin films was also examined.
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Stoichiometry, homogeneity and thickness of TiN thin layers before and after
implantation of argon and vanadium ions was analyzed using Rutherford backscattering
spectrometry (RBS). This analysis showed that the implantation of argon ions did not
caused any changes in stoichiometric ratio of components in TiN layers even after
highest ion fluences. In the case of vanadium implantation the layer exhibit nonstoichiometric
concentration profiles in the region where the mostly vanadium ions are
stopped as well as in the region beneath of the implanted zone. It was also found that the
vanadium ions induced the increase of the effective thickness of the films.
Structural analysis of thin layers was done by means of X-ray diffraction (XRD),
transmission electron microscopy in combination with selected area electron diffraction
(TEM./.SAD) and high resolution TEM combined with fast Fourier transforms
(HRTEM./.FFT). These methods enabled us to identify phases present in the deposited
and implanted structures. We found that the TiN layers grow in the form of a very fine
polycrystalline columnar structure. After argon ion irradiation the layers retain their
polycrystalline structure, but the columnar grains were disconnected. XRD and FFT
analysis have shown only the presence of face-centered cubic TiN phase with a decrease
of grains after argon ion implantation. Hence, ion implantation induced only local
atomic rearrangements within the films. In the case of vanadium ions TEM analysis
showed the presence of amorphous layer above the implanted region. Implanted region
with a polycrystalline structure contains a large amount of defects. In the area where the
most of the vanadium ions stopped, XRD and FFT analysis showed the presence of
face-centered cubic TiN phase as well as the presence of a new VN phase. It can be
concluded that the implantation of vanadium ions leads to the formation of new phase
due to chemical effects. It was also observed that the depth of damage was significantly
greater than those provided with SRIM2003 simulation.
Four-point probe method showed that the resistivity increases with increasing ion
fluence. Optical measurements obtained by IR analysis have shown that the changes in
optical resistivites have the same trend as the changes in specific resistivites. The
variations of specific and optical resistivites are due to the accumulation of
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defects after argon ion implantation and the formation of new phase after vanadium
implantation.