Evolution of texture and residual stresses with the thickness for aluminum nitride deposited
by dcMS on Si (100)
B. Riah1*, A. Ayad1, 2, J.Camus3, M.A. Djouadi3, N. Rouag1, F.Boukari4
1Laboratoire Microstructures et Défauts dans les Matériaux, Université des frères Mentouri Constantine 1, Route Ain El Bey, Constantine 25017, Algeria.
2Département de Pharmacie, Faculté de Médecine, Université Constantine 3, Nouvelle ville Ali Mendjeli, Algeria.
3Institut des Matériaux Jean Rouxel IMN UMR 6502, Université de Nantes, 2 rue de La Houssinière BP 32229, 44322 Nantes Cedex France.
4Département Génie Chimique Génie des Procédés (GCGP), 19 Allée des Vignes 78120 Rambouillet.
Abstract— This work presents a study of XRD measurements on the development of the fiber (0001) and residual stress with the film thickness. Aluminum nitride (AlN) films were deposited by dc magnetron sputtering (dcMS) on Si (100) substrates in Ar-N2 gaz mixture, at different thickness. The texture characterizations of the films were performed by X-ray pole figure technique. It was found that with increasing of the thickness the fiber (0001) becomes more marked. The (10-11) and (10-12) FDPs confirm the presence of reinforcements on the (0001) fiber. The angles between these reinforcements are about 60° and 120°. The observed asymmetry increases with thickness and could be connected to the angular differences between the AlN (0001) and Si (100) which lead to a full distortion. The residual stress decreases with the thickness increase.
Keywords: AlN thin films, DC-PVD, Fiber texture, Asymmetry.
I. INTRODUCTION
Texture describes the statistical distribution of crystal grain orientations in thin films. The distribution is an important characteristic of the microstructure in thin films, and it determines various electrical, magnetic, and mechanical properties. Three types of texture components are usually distinguished in thin films: random texture, when grains have no preferred orientations; fiber texture, for which one crystallographic axis of the film is parallel to the substrate normal, while there is a rotational degree of freedom around the fiber axis; and epitaxial alignment _or in-plane texture_ on single-crystal substrates,where an in-plane alignment fixes all three axes of the grain with respect to the substrate.Therefore, epitaxial growth is not generally observed in fiber texture [1, 2].
Aluminum nitride (AlN) is a material with remarkable properties, a large optical band gap of about 5.9–6.02 eV [3] , high hardness [4], chemical stability, large acoustic velocity Moreover, AlN is fully compatible with conventional silicon technology [4,5] and has a good thermal conductivity 320
W/mk [6]. AlN thin films are one of the most interesting materials in microelectronic and optoelectronic devices such as ultraviolet detector, light emitting diodes [7], thermal interface materials [8], dielectric layers in integrated circuits [9] and piezoelectric materials in surface acoustic wave devices [6]. The deposition of AlN films with controlled morphology and high crystalline quality is one of the key issues to be addressed in order to fabricate high performance AlN based devices. To date, various deposition techniques have been reported for AlN films including: dc magnetron sputtering and high power impulse magnetron sputtering (HiPIMS), CVD, MoCVD. The aim of this work we study the evolution of the texture and residual stresses with the thickness for aluminum nitride hexagonal deposited by dcMS on Si (100).
II. PROCEDURE EXPERIMENTAL
Aluminum nitride films, for different thickness, were deposited by dcMs on Si (100) substrates. Prior to deposition, the substrates were ultrasonically cleaned in acetone and ethanol, then dried under nitrogen gas flow. The sputtering target (aluminium) was 99.9999% in purity with 5 cm in diameter, held on a water-cooled magnetron cathode. The distance between the target and substrate holder was 3 cm.
The system was pumped to a base pressure of 5*10−3 Pa with a turbomolecular pump before introducing argon and nitrogen gases. The sputtering system employed an unbalanced magnetron powered by a 150 W dc power supply. Before deposition, the target was cleaned using argon gas discharge plasma for 15 min followed by a pre-sputtering step, using the same conditions as the subsequent film deposition with a shutter shielding the sample. The total gas flux rate during deposition by the two processes was maintained constant at 40 sccm while that of the reactive N2 gas was fixed at 35%. The sputtering pressure was fixed at 0.40 Pa. The texture characterizations of AlN films were performed by X-ray diffraction (XRD), using an X-ray diffractometer Panalytical Empyrean with (Cu Kα) radiation (λ = 0.154 nm).
III. RESULTS AND DISCUSSION
XRD diffraction patterns of AlN films deposited by dcMS at different thickness are shown in Fig. 1. All the films starting from a thickness of 640 nm, are found to have the hexagonal wurtzite structure. This evolution is significant due to an improvement in the crystalline quality of the films. This type of diagram provides us with partial information on the direction of crystallites in deposits. Indeed, only the planes {hkl} whose normal is parallel to the bisector formed by the incident beam and the diffracted beam are analyzed. In the case of recording in Bragg-Brentano geometry, there will, therefore, be only information on the diffracting planes parallel to the sample surface.
30 31 32 33 34 35 36 37 38 39 40
2000 4000 6000 8000 10000 12000 14000
Intensity(Cps)
2 thétha (°) 12 nm 640 nm 2200 nm
Fig.2 shows the rocking curve spectra of the AlN/Si (100) structure at different thicknesses. The full width at half maximum (FWHM) of the X-ray rocking curve of the AlN films decrease from 2.8° to 2.7°.
12 14 16 18 20 22 24
0 500 1000 1500 2000 2500 3000 3500 4000
640 nm 2200 nm
Intensity (cps)
Angle (°)
nm
2200nm
Fig.3 shows the experimental pole figures (10-11) of AlN films for different thicknesses. The microstructure is a strong (0001) fiber texture from 640 nm. The fiber (0001) becomes more marked with increasing of the thickness. The observed
asymmetry increase with and could be connected to the existence of a transition layer. This layer could be composed of few layers of facetted cubic aluminum nitride [10]. The {10-11} pole figures confirm the apparition of reinforcements on the (0001) fiber. The angles between these reinforcements are about 60° and 120°. We think that the AlN thin layer begins to transform to a pseudo-cubic monocrystal which can leads and explain the presence of reinforcement on the fiber (0001).
Fig.4 represents the residual stress of AlN films deposited by dcMS at different thickness. It should be noted that the films of AlN suffer from compressive stress whatever is the thickness of the films. By decreasing the thickness, the residual stresses are more compressive which is probably caused by the presence of defects such as interstitials, Al or N vacancies, dislocations, etc. These can be formed in the films
3
1160 3
119
234
350
466
582
697
813
929
1044
1160 Phi=0 Phi=45 Phi=90
Reflection: 1 0 1
5
977 5
102
199
297
394
491
588
685
783
880
977 Phi=0 Phi=45 Phi=90
Reflection: 1 0 1
Fig.1. XRD patterns of AlN films deposited by dcMS at different thicknesses.
Fig.2. Rocking curves of AlN/Si(100) structure at different thickness
Fig.3. Experimental Pole figures (10-11) of AlN_H on Si (100) at different thickness at
2θ=37.78°
12 nm
640 nm
2200 nm
during the growth process. The residual stress can reach a value of -4.3Pa at a 12 nm thickness. and they probably disperses the fiber (0001) .
IV.CONCLUSION
In this paper, we see the evolution texture and residual stress with thickness for aluminum nitride on Si(100), it was found that with increasing of the thickness the fiber (0001) becomes more marked. The (10-11) and (10-12) pole figures confirm the presence of reinforcement on the (0001) fiber. The residual stress increase with the thickness increase and they probably disperses the fiber (0001) .
REFERECES
[1] C. Detavernier, A. S. Özcan, J. Jordan-Sweet, E. A. Stach, J. Tersoff, F. M. Ross & C. Lavoie,”An off-normal fibre-like texture in thin films on single-crystal substrates”, Nature 426, Letters to Nature, 641-645 (11 December 2003)
[2] Toshihiro Kamohara, Morito Akiyama, Naohiro Ueno, Kazuhiro Nonaka, and Noriyuki Kuwano, “Local epitaxial growth of aluminum nitride and molybdenum thin films in fiber texture using aluminum nitride interlayer”, Applied Physics Letters 89, 071919 (2006);
[3]. A. Shah, A. Mahmood, Phys. B Condens, “Effect of Cr implantation on structural and optical properties of AlN thin films,” Matter, 407 (2012), 3991.
[4]. C. Caliendo, P. Imperatori, and G. Scavia, “Quasi- epitaxial growth of crystalline wurtzite AlN thin films on Si(001) by RF magnetron sputtering,” (Proc. IEEE Ultrason Symp. 2009),1614.
[5]. T. Aubert, M. B. Assouar, O. Legrani, O. Elmazria, C.
Tiusan, and S. Robert, “Highly textured growth of AlN films on sapphire by magnetron sputtering for high temperature surface acoustic wave applications,” Journal of Vacuum Science & Technology A, 29 (021010) (2011).
[6]. K. Ait Aissa, A. Achour , J. Camus, L. Le Brizoual, P.-Y.
Jouan, M.-A. Djouadi, “Comparison of the structural properties and residual stress of AlN films deposited by dc magnetron sputtering and high power impulse magnetron sputtering at different working pressures,” Thin Solide Films, 550 (2014), 264-267
[7]. S. Joblot, E. Feltin, E. Beraudo, P. Vennéguès, M. Leroux, F. Omnès, M. Laügt, Y.Cordier, “Hexagonal c-axis GaN layers grown by metallorganic vapor-phase epitaxy on Si (001),” J. Cryst. Growth, 280 (2005), 53.
[8]. C. Duquenne, M.P. Besland, P.Y. Tessier, E. Gautron, Y.
Scudeller, D. Averty, “Thermal conductivity of aluminium nitride thin films prepared by reactive magnetron sputtering,”
J. Phys. D. Appl. Phys., 45 (2012), 015301.
[9]. Toshihiro Kamohara, Morito Akiyama, Naohiro Ueno, Kazuhiro Nonaka, and Noriyuki Kuwano, “Local epitaxial growth of aluminum nitride and molybdenum thin films in fiber texture using aluminum nitride interlayer,” Applied Physics Letters, 89 (071919) (2006).
[10] B. Riah, A. Ayad , J. Camus,L.Chekour, M. A. Djouadi, N. Rouag ,” Texture charaterization of AlN films. Formation and influence of facetted cubic AlN layer on the growth of AlN hexagonal phase”, 2nd Workshop on Multifunctional Coatings that will occur in Nantes, France at the Institute of Materials Jean Rouxel.
0 500 1000 1500 2000 2500
0 1 2 3 4 5
Residual stress (-GPa)
Thickness (nm) AlN/Si(100)
Fig4. Residual stress of AlN films at different thickness.
