trashilov Bulgarian Journal of Physics 26 Nos I / 2 ( 1999) 65-70 e, but can be approximated using a f constituents. Novel experimental on/polymer composite are expected DIFFUSION BARRIER PROPERTIES OF CVD THIN TUNGSTEN AND TANTALUM FILMS, DEPOSITED ON WC/Co METALLOCERAMICS
ia (Nauka, Moscow 1989) (in Russian). 0. K. GESHEVA, D. GOGOVA, T. IVANOVA Central Laboratory for Solar Energy and New Energy Sources 1. Ferroelec. Freq. Con tr. 34 ( 1987) 8. Bulgarian Academy of Sciences (1982) 327. E Ultrasonics Symposium 505. 72 Tzarigradsko Chaussee Blvd, 1784 Sofia, Bulgaria s: Application au Traitement du Signal Received 5 May 1998
ty of America 1976) Ch. 3. m. 75 (1984) 1629. Abstract. Thin Tungsten (W) and Tantalum (Ta) films were deposited by py Trans.Ultrason. Ferroelec. Freq. Contr. rolysis from W(C0)6, WCl5 and TaC1 5 precursors on WC/Co metalloceramics substrates, containing 7- 8 % and 11 - 12 % Co. Their properties to preventing a Co diffusion from the substrate to the surface coating have been studied by X E Ultrasonics Symposium 403. ray microprobc analysis, Auger electron spectroscopy and Direct Layer by Layer Spectral Analyses in Hallow Cathode method.
PACS number: 72.15.Eb
1. Introduction
Tungsten is the most intensively studied transition metal as his good properties satisfy the high requirements of the IC technology [1-3]. The chemical vapor deposition (CVD) is now popular not only in thin films preparation for microelectronics, but for wear-resistant hard coatings [4]. Conventional hard metal coatings on WC/ Co metalloceramics are affected at el evated temperatures by cobalt diffusion. This could be prevented applying suitable barrier sublayer. Hard metal coatings as transition metal carbides and nitrides posses very good dif fusion barrier properties, i. e. they prevent the undesired diffusion from the substrate to the cutting tool [4 - 6]. Though Wand Ta do not perform the hardness their carbides and nitrides do, their diffusion barrier properties are good. The purpose of this study is to investigate the diffusion barrier properties of CVD-W and Ta coatings, obtained by carbonyl (using W(C0)6 ) and chloride (using WC1 6 , TaC15 ) processes.
2. Materials and Experimental Technique For the deposition of thin W and Ta films a CVD horizontal reactor with hot walls was used. A high-frequency generator (HFG) heated the susceptor and the temperature
© 1999 St. Kliment Ohridski University Press All rights reserved 65 66 K. Gesheva, D. Gogova, T Jvanova D(ff11si01
was controlled by a thermocouple connected to a thennoregulator, switching on and off diffraction pattern of W fil one of the three phases in the feed line of the generator. Two types of precursors were hows no evidence for textu used for W deposition - tungsten hexacarbonyl (W(C0)6) and tungsten hexacloride (2.28, 1.61, l.31 and 1.12 (WC16 ), heated at 100 °C and 140 °C, respectively. 1.11 A) ones [10], a pres The following reactions take place in the CVD-reactor. films are in good coinciden
W(C0)5(g) --> W(s) + 6CO(g) at 400 °C (1) Table 1. RHEED expected and WCl5(g) + H2(g) --> W(s) + 6HCl(g) at 750 °C (2) CVD-\V films TaCls(s) + H2(g)--> Ta(s) + HCl(g) at 750 °C (3) I The cutting tool substrates were cleaned before the deposition by immersing in a hot bath of alcohol for a few minutes. They were arranged on a graphite susceptor 2.28 heated by the HFG. 1.61 Reflection high-energy electron diffraction (RHEED) and Scanning electron mi 1.::11 1.12 croscopy (SEM) were used to study the microstructure of the films. X-ray microprobe analysis was applied for chemical composition analysis, Auger electron spectroscopy and direct layer by layer spectral analyses in hollow cathode method were applied for the depth profile of the chemical composition of the films. Film thickness was By scanning electron m· controlled by a TALYSTEP profilometer. The results presented refer metallocerarnics with 7- 8 o/c 3. Results and Discussions deposited at 400 °C and anne that the film deposited fr01 3.1. Phase Composition and Crystal Structure of the Films densely arranged and there The chemical and physical properties of a solid are mainly determined by its crystal and the existence of CO co structure, crystallographic orientation and morphology. In CVD, the crystal structure, and the grains are mall ( crystallographic orientation and morphology vary widely according to the deposition impurities - 0 2 and C (1 WCI;, . The higher depositi conditions [7). di tributed. well shaped big
Fig. I. RHEED electron diffraction pattern of W films, deposited from (a) tungsten hex acarbonyl and (b) tungsten hexacloride on Si(l 00) and (c) Ta film
As seen from Fig. la W films, obtained from hexacarbonyl have a well expressed textured structure. The lattice parameters for Si(lOO) is 5.431 A and for /3 -W - 5.036 A. There is 8 % lattice mismatch between j3 -W and Si. This makes the epitaxial relation highly unlikely. The reason for the observed texturing may be the nature of the carbonyl CVD process where different growth-rate in different crystallographic orientations is possible. Similar results for carbonyl Mo have been reported by [8], but the texturing is in different crystallographic directions. At the same time RHEED Iva nova Diffusion Barrier Properties of CVD Wand Ta 67
oregulator, switching on and off diffraction pattern of W film , prepared by hydrogen reduction of WC16 on Si(lOO) r. Two types of precursors were shows no evidence for texturing (as reported by Sivaram [9]). The observed d-spacings (C0)6) and tungsten hexacloride (2.28, l.61, l.31 and 1.12 A) coincide well with the expected (2.23, l.58, l.29 and I.I I A) ones [JO], as presented in Table l. The expected and observed data for Ta ct or. films are in good coincidence, as well.
at 400°C (1) Table 1. RHEED expected and observed d-spacing for CVD-W and Ta films (g) at 750 °C (2) CVO-W lilms g) at 750 °C (3) CVO-Ta films expect~d observed expected observed e deposition by immersing in a u(Al d(A) d arbonyl have a well expressed ) is 5.431 A and for /3-W - d Si. This makes the epitaxial texturing may be the nature te in different crystallographic Fig. 2. SEM micrograph of the surface morphology of (a) W film deposited by CYD of W(C0)6 lo have been reported by [8], at 400 °C on WC/ Co metalloceramics and annealed at 740 °C in H2 and (b) from WCls at 750 °C ons. At the same time RHEED 68 K. Gesheva, D. Gogova, T Ivanova Diffusion 3.2. Diffusion Barrier Test of W and Ta Coatings 25 Thin W and Ta films with thickness of about 1-2 µm on cutting tools were investigated. They undergo annealing at 1100 cc for 15 min, which is close to the working regime of the machining tools. The layers were tested for possible Co diffusion to the coating 20 surface. ,....., Auger spectroscopy has been performed as a basic analytical method. The results .~ § 15 obtained show that this method is not suitable for this study, because the detected Co c quantity is lower than the natural Auger spectrometer noise background. Therefore the b"' ii Direct layer by Layers spectral analyses in a Hollow cathode investigation [12, 13) was ~ 10 carried out to detennine the coating components depth profile...... The advantages of this method are: (a) intensive and narrow spectral lines (bands) are generated by the atoms and ions 5 of the various elements; (b) the excitation and atomization of the studied compounds proceed simultaneously 0 in the hollow cathode plasma, resulting in analytic signal generation; 0 ( c) high sensitivity exhibited, which allows a small step in the Direct layer by Layer spectral analyses in a Hollow cathode. The hollow cathode is an Al cylinder of 4 mm inner diameter and 12 mm length. Fig. 4. Chemical composition a Studies have been carried out at pressure PAr = 0.7 torr and current I = 30 mA. A 15 min by rapid thennal anneal STE-I spectrograph registers the intensity of the irradiated spectral lines. To obtain the depth distribution profile of the studied components the I = f (t) The numbers shown in ti dependence was plotted, where t is the sputtering time. In Fig. 3 the depth profile lights. The observed minim of the chemical composition of an as-deposited W coating on WC/ Co substrate is of the interface. It is well presented and in Fig. 4 - the same for a CVD-W coating on WC/Co heated by rapid crystal structure is sputtered thermal annealing (RTA) in vacuum at 1100 cc for 15 min. The obtained lines in Fig. 3 observed minimum. The C1 and 4 are the dependencies of intensity of the emitted spectral light of the elements direction towards the W fil under consideration - Co and W. The diffusion barrier pro X-ray microprobe analysis a 20 seen from Table 2 and 3, o which is an evidence for goc 1-2 µm. w 4294 A Table 2. W on WC/ Co metallo \ \ W~OOA Element Line w K \,_~~02A Co L I I I I 0 Table 3. Ta film with thicknes 0 50 100 150 200 250 Element Line t (min) Co K Fig. 3. Chemical composition analysis of CVD-W coating on WC/Co cutting tool w L van ova Diffusion Barrier Properties of CVD Wand Ta 69 25 n cutting tools were investigated. is close to the working regime w 4008 A sible Co diffusion to the coating 20 '"""~ \ analytical method. The results ·2 \ ::l 15 s study, because the detected Co \ w 4294A c \ noise background. Therefore the b"' \ ,,. :.0 \ .·· I thode investigation [ 12, 13] was .... 10 \ I ~ \ .. I profile...... \ I \ I 5 \ I ' \...... / -- Co 3502 A pounds proceed simultaneously 0 ic signal generation; 0 50 JOO 150 200 250 step in the Direct layer by Layer t (min) er diameter and 12 mm length. Fig. 4. Chemical composition analysis of W coating on WC/Co substrate heated at 1100 °C for torr and current I = 30 mA. A 15 min by rapid thermal annealing in vacuum ·ated spectral lines. died components the I = f (t) The numbers shown in the figure refer to the wavelengths of the emitted spectral e. In Fig. 3 the depth profile lights. The observed minimum of the intensities profile is connected with the position coating on WC/Co substrate is of the interface. It is well known that the interface being a diffusion area with different ing on WC/Co heated by rapid crystal structure is sputtered with smaller coefficient of sputtering, which leads to the in. The obtained lines in Fig. 3 observed minimum. The Co profile shows decreasing of the Co concentration in the spectral light of the elements direction towards the W film and no Co was observed in the film. The diffusion barrier properties of CVD W and Ta coatings were also studied by X-ray microprobe analysis carried out on the Super probe-733 equipment. As it can be seen from Table 2 and 3, only 0.62 wt. % of Co are registered on the coating surface, which is an evidence for good diffusion barrier properties of W coatings with thickness l -2µm. w4294 A Table 2. W on WC/Co metalloceramics with about 8 3 Co Element Line wt.% at.% Net intensity w K 0.62 1.90 1.68 Co L 99.38 98.10 59.43 Table 3. Ta film with thickness I µm on WC/Co metalloceramics with about 11 - 12 3 Co 250 Element Line wt.% at.% Net intensity Co K 5.64 15.50 14.43 ·ng on WC/Co cutting tool w L 94.36 84.50 60.24 70 K. Gesheva, D. Gogova, T. Ivanova Bulgarian Journal of Physics For Ta coatings, obviously the cobalt is much less than in the volume but since the coating thickness is only around 1 µm some Co reaches the surface. If the thickness is made bigger (1.5-2 µm), then Ta coating may serve as a good diffusion barrier for SUP ERO Co. PHASE 4. Conclusion N.BALC The applied thin W and Ta films on WC/Co metalloceramics proved to be good Institute of diffusion barriers for the Co contained in the cutting tool substrates W(C0) -CVD 6 1784 Sofia, process used for deposition ofW films and CVD-TaC15 process for Ta films are suitable technological processes for fabrication of barrier diffusion coatings for cutting tools. J. THOMA References Institut fur 01171 Dres I. S. M. Sze, VLSI Technology, 2nd ed. (Mc Graw-Hill, New York 1988). 2. J. Ammerlaan. Ph. D. Thesis, Delft University Press, The Netherlands, 1994. K. KONST 3. E. H. A. Granneman. Thin Solid Films 228 (1993) I. Institute of 4. I. J. Konyashin. Thin Solid Films 249 ( 1994) 174. Sciences 5. C.-1. Li, A. Ohmori, Y. Harada. J. Mat. Sci. 31 (1996) 785. lll3 Sofia, 6. R. Porat. J. de Phys. JV, suppl. II, I (1991) C2-549. 7. C.-S. Park, J.-G. Kim, J. S. Chun. J. Electrochem. Soc. 130 ( l083) 1607. 8. B. E. Ivanov, E. P. Nechiporebko,V. M.Krivorushko, V.Y.Sagalovich,V.P.Podtikan,N. B.KUNEV S.Poltavtzev. Nonorganic Materials III 11 ( 1967). Institute of 9. S. Sivaram, M. L. Dass, C. S. Wei, B. Tracy, R. Shukla. J. Vac. Sci. Techn. All(!) (1993) 87. 1113 Sofia, I 0. L. I. Mirkin. XRD analysis handbook of crystals, (Ed. Umalskii Moscow 1961 ). 11. K. Gesheva, Y. Abrosimova, G. Beshkov. J. de Phys. IV.I (1991) 865. Received 20 12. R. Djulgerova, Y. Mihailov. Spectroscopy Lett. 26(2) (1992) 347. 13. R. Djulgerova, V. Mihailov. Appl. Phys. B56 (1993) 301. Abstract. A Cdo.sBa2 (Y The obtaine 123. It was fonnation. the distributi elements ent Cd-Ba-Y-C PACS numti 1. Introduction Since the discovery of the conducting copper oxide c is an appropriate candidat divalent element with an Ca2+ (1.14 A). For the l © 1999 St. Kliment Ohridski