Modifikacija svojstava tankoslojnih TiN struktura na silicijumskoj podlozi bombardovanjem jonima

Abstract

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 ovog 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. ii 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 iii 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 titanium 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. v 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 vi defects after argon ion implantation and the formation of new phase after vanadium implantation.