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PROPERTIES OF ALN FILMS DEPOSITED TO SILICON SUBSTRATES USING MAGNETRON METHOD

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AlN coatings were deposited to silicon substrates by a magnetron method. Scanning ion-electron microscopy demonstrated that the aluminium nitride coatings had fibrous structures. An SPM method demonstrated that AlN surface was polycrystalline with a
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  ( Manuscript No: I12725-05)June 12, 2012    /  Accepted: June 20, 2012 1 PROPERTIES OF ALN FILMS DEPOSITEDTO SILICON SUBSTRATES USINGMAGNETRON METHOD A.D. Pogrebnjak * Ukraine Sumy Institute for Surface ModificationP.O.Box 163, 40030Sumy, Ukraine(Email: apogrebnjak@simp.sumy.ua) А. K. М. Muhammed Sumy State University,St.R-Korsakov 2, 40007Sumy, ukraine(Email: kareem19592003@yahoo.co.uk) Abstract - AlN coatings were deposited to silicon substrates by a magnetron method. Scanning ion-electronmicroscopy demonstrated that the aluminium nitride coatings had fibrous structures. An SPM methoddemonstrated that AlN surface was polycrystalline with a grain size of about 50-100 nm. A Nano spike heightreached 8 nm and roughness degree was 1.3 nm. It was found that the dielectric permeability of AlN filmsdecreased from 11.5 to 2.94 as far as frequency increased from 50 Hz to 1 MHz. A tangent peak of dielectricloss angle was observed at 10 kHz and reached 0.39. Keywords: AlN , Energy gap , HF- Magnetron , LEDS , Silicon substrate , Surface morphology  Introduction Aluminium nitride is a wide band gap material and can crystallize in both wurzite and zinc  –  blend structureshexagonal wurtzite structured AlN has direct room temperature band gap of 6.2 eV cubic zinc  –  blend structuredAlN has an indirect band gap .The wurtzitic AlN is the stable crystal structure at ambient temperature with thelattice constants, a= 3.111 Å and c=4.978 Å ,while the theoretical estimate of the lattice parameter of zinc  –   blend structured AlN is a=4.38 Å [1,2].The goal of this work was to study a surface morphology, dielectric properties, and mechanical properties of AlN coatings on silicon substrates deposited using the magnetron method.  Materials and Equipment AlN coatings were deposited to surfaces of single-crystalline silicon KEF 4,5 having (100) plane orientationusing unfiltered vacuum-arc source of the upgraded device Bulat-3T. Samples were heated to 700oCtemperature in vacuum at P= 3×10-3 Pa prior to deposition. Thereafter, heating of the substrate with the sampleswas switched off. Then, sample surfaces were cleaned using RF - discharge in nitrogen at UHF =1000 V, РN =2×10-1 Pa. Cleaning time was 10 min. A surface morphology was studied using scanning probe microscopeNTEGRA Aura. Dielectric properties were measured by the LCR-meter, the BR-2876. The sample surface wasembedded by silver contacts. To determine the micro hardness, we employed DM-8 device.  RESULTS AND DISCUSSION   International Journal Of Structronics & Mechatronics2The image shows that the coating has a fibrous structure [2].Fig 1 shows scans of aluminium nitride coatingsurface deposited to a silicon substrate.( a, b) Figure 1: The scans of aluminium nitride coating surface on silicon (a) in the contrast mode (phase composition); b) a topography of thesurface, which was obtained using the scanning probe microscope NTEGRA Aura. The surface morphology of aluminium nitride coatings demonstrates a Nano crystallize surface with about 50-100 nm grain size; a height of Nano spikes reaches 8 nm (fig 1), the degree of roughness is 1.3 nm. Figure 2: The surface topography of aluminium nitride coating on silicon, which was taken using the scanning probe microscope NTEGRAAura in 3D format (a), Dependence of AlN film capacitance (C) on frequency (f) (b). The dependence of AlN film capacity on frequency (f) was studied (fig.2 b).Dielectric permeability was calculated according to the formula (1).1.   hS C  r     0    where C is the capacity in F, є ₀ =is the dielectric constant, which is equal to ( 8 .8 ×10‾  22   F/m , є r = is a relativedielectric permeability, S= is an electrode area in m 2 , h = is a thickness of the dielectric in m.Results on the dielectric permeability of AlN and an angle tangent of dielectric losses are shown in Fig. 3 (a)  A.D. Pogrebnjak, А.K.М. Muhammed  3 Figure 4: Dependence of the dielectric constant and the dielectric loss tangent of AlN on frequency (a), . Indentation tests of silicon microhardness without coating and with AlN coating (b). The results show that the dielectric permeability reduced from 11.5 to 2.94 as far as frequency increased from50 Hz to 1 MHz, which seems to be related to the dipole oriented polarization in AlN [1]. A peak of the angletangent of dielectric losses angle was observed at 10 kHz and reached 0,39, which also indicates the existence of dipole oriented polarization [1].An action of AlN films on silicon micro hardness are presented in Fig. 3 (b). Analysis of the obtained resultsallows us to make a conclusion that AlN films hardened the silicon surface and this seems to be related to a highdegree of atomic packing arising in crystal lattices of AlN films [3] Conclusion It has been shown that aluminium nitride coatings had a fibrous structures., and then SPM method demonstratedthat AlNx had a nanocrystalline surface with about 50- 100 nm grain size, nano-spike height reached 8 nm, thedegree of roughness was 1.3 nm It was found that the dielectric permeability of AlNx coating reduced from 11.5to 2.94 as far as frequency increased from 50 Hz to 1 MHz. The peak of angle tangent of the dielectric loss wasobserved at 10 kHz and reached 0,39. Deposition of aluminium nitride coating leads to hardening of single-crystalline silicon.  References 1. Z.X.Bi, Y.D. Zheng, R. Zhang. Dielectric properties of AlN film on Si substrate. - Journal of MaterialsScience: Materials in electronics 15, 2004, 317-320 p.2. A. Stafiniak, D. Muszynska, A. Szyszka. Properties of AlNx thin films prepared by DC reactive magnetronsputtering. - Optica Applicata, 39, N4, 2009, 717-722 p.3. A.F. Belyanen , M.I, Samoelovich , V. D, Zhitkovsky. Impact-resistant protective film coatings based on AlNin electronic engineering. - Technology and design of electronic equipment. N5, 2005, 35- 41 p.4. S.N. Mohammad, A.A. Solvador, H.M. Morkoc. Emerging gallium nitride based devices. - Proceedings of theIEEE, 83, 1995, 1306-1355 p.5. A.D.Pogrebnyak, G. A-K. M. Muhammed, N. Y. Jamil. Effects of Al dopant on structural and opticalproperties of ZnO thin films prepared by sol-gel.  –  Przeglad Electrotechniczny, 03b,2012,106-111 p.
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