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Titanium carbide thin films obtained by reactive magnetron sputtering
Vacuum/volume 36/number Printed in Great Britain
0042-207X/86 $3.00+ .OO Pergamon Journals Ltd
1 O/pages 595 to 597/l 986
Titanium carbide thin films obtained magnetron sputtering
by reactive
G Georgiev, N Feschiev, D Popov and Z Uzunov, Department of Physics, Technical University ‘A Kanchev’, Russe 7004, Bulgaria
The deposition rate, composition and diffraction spectra of Tic thin films, obtained by magnetron sputtering in the CH,-pressure range from 0.5 x 10m2 to 9 x 10e2 Pa have been measured. Deposition rate measurements show that at low pressures (< 1.5x 10e2 Pa) the system operated under conditions such that pure Ti was sputtered. At pressures higher than 4 x 10 - 2 Pa a Tic layer covered the target (reactive conditions). In the intermediate case the target surface consisted of Ti and Tic. Study of the composition, diffraction spectra and crystal lattice constants of the films showed that continuous conversion occurred from pure Ti films to stoichiometric Tic films when the CH,-pressure was raised from 1.5 x lo- 2 to 4 x lo- 2 Pa.
Introduction
Titanium carbide coatings possess some unusual properties such as: thermal stability’, high hardness2, anticorrosion stability3 and good electrical and thermal conductivity. For deposition of such coatings two methods are mainly used: chemical vapour deposition4 (CVD) and physical vapour deposition5*6 (PVD). Each of these methods possess definite advantages and disadvantages. For CVD the main disadvantage is the high temperature at which the substrate is held when the coating is deposited. With PVD the effects of substrate surface shadowing render difficult the covering of a surface of complicated configuration. CVD has been known and used in practice for the longer time and it is better investigated. For PVD, especially reactive magnetron sputtering, the process is comparatively incompletely investigated. In this connection we present in this paper our investigation of the composition, structure and conditions of obtaining TiC coatings when prepared by reactive magnetron sputtering.
Experimental procedures
The coatings investigated were obtained by reactive magnetron sputtering of titanium in an Ar +CH, atmosphere. A watercooled circular planar magnetron with target diameter of 100 mm was used. The magnetic field was formed by two magnets (cylindrical and annular), placed coaxially on the ring-shaped magnetic conductor. The component of the magnetic induction parallel to the target plane has a maximum of 0.03 T at a distance about 20 mm from the centre of the magnetron. The sputtering zone was a ring with 10 mm inner diameter and 90 mm outer diameter. The average current density was about 13 mA cm-‘. The target to substrate distance was 150 mm for all experiments.
Before Ar and CH, gases were admitted the system was pumped down to a final pressure 6 x 10m3 Pa. The CH, partial pressure was adjusted in the interval from 5 x 10e3 to 9 x lo-’ Pa and other deposition parameters were not varied. Their values were as follows: working pressure of the Ar+CH, mixture6 x lo- 1 Pa; discharge current-800 mA; target voltage-500 V; substrate temperature-100°C. Substrate cleaning consisted of the following procedure: degreasing with tetrachloridemethane and alcohol; heating in vacuum for 10 min at temperature of about 500°C and after this setting the working temperature of the substrate at 100°C. The target was cleaned in a glow discharge for about 20 min in a pure Ar atmosphere and the substrate was masked before beginning sputtering under certain chosen conditions. The deposition rate was determined by weighing the substrate before and after deposition. Correction for the change of film density with increase in the carbide content of the coating has not been made. The results obtained by Sundgren et al’ and Shikama et al’ show that the density of the deposited TIC films changes about 20% when the ratio Ti/C varies from 0.2 to 1. As the deposition rate in our experiments changed about two times (Figure 1) the influence of the density change on the calculated deposition rate can be neglected in comparison with the changes due to the variation of the sputtering rate. The X-ray diffraction measurements were done using apparatus type URS-50 IM. The X-ray diffraction lines were obtained with Cu,. X-rays at a voltage of 40 kV, an anode current of 10 mA and with stationary pattern in respect to the plane of the coating. Changes of the composition of the coating were measured using a scanning electron microscope type JXA-733. All measurements have been made at an accelerating voltage of 25 kV. To determine changes in coating composition the following X-ray lines have been measured: K, for C, N, 0 and Kel for Ar and Ti. 595
G Georgiev ef al: Titanium carbide thin films
345681 x10-3
x10-2
X10-l
PcH4(Pa)
Figure 1. The deposition rate D vsCH, partial pressure for reactively sputtered Ti.
Results and discussions The basic sputtering condition which was changed during the deposition of TiC was the partial pressure of the CH, in the gas mixture with Ar. When the CH,-pressure was changed in the interval from 5 x 10m3 to 9 x lo-'Pa the deposition rate varied in a way shown in Figure 1. One can see that the deposition rate decreases by half as the CH, partial pressure is raised from 5~10~~to9xlO~~Pa. For a CH, pressure up to 1.5 x lo-* Pa the sputtering was realized under so-called elemental conditions, there was no TIC on the target surface and in this case pure Ti was sputtered. In the interval from 1.5 x lo-’ to 4x lo-’ Pa the sputtering rate decreased because of increase of the TIC concentration on the target surface. At a partial pressure above 4 x lo-* Pa one observes nearly full covering of the target surface with a layer of TIC. In this case mainly TIC was sputtered at a rate much smaller than the sputtering rate of pure Ti. This type of sputtering is known as reactive sputtering. Figure 2 presents the CH, pressure dependence of the relative concentrations Ii/Z, of Ti, C and N in the deposited films. In the
ratio ZJZ,, Zi is the X-ray intensity for films sputtered at partial pressure Pi and I, is the same intensity obtained for films deposited under the elemental conditions. One can see in Figure 2 that with increase of the CH, partial pressure, the content of Ti decreases, but that of C increases. The changes of the relative concentration of Ti and C are in good correspondence with the deposition rate (D)as a function of PcH4 as shown by the curve in Figure 1 for which there is a decrease in the deposition rate as the CH, pressure increases. At partial pressures above 4 x lo- * Pa the sputtering rate and the relative content of Ti and C are nearly constant. In this case a TiC layer covers the target with sputtering of TIC and further increase in the CH, partial pressure does not change the composition of the deposit. Measurement of the content of 0, N and Ar using X-ray analysis shows that the concentration of these elements is constant and independent of the sputtering conditions. In Figure 2 only the relative concentration of N is shown. We believe that the existence of 0, N, and Ar in our films arose from gas in the residual atmosphere in the sputtering chamber. Figure 3 shows the position of X-ray diffraction maxima and their intensities in arbitrary units. The diffraction maxima of sintered TIC are also given as a comparison (Figure 3(a)). From this figure one can see the distinctive peculiarity of the NaCl type crystal lattice for which the X-ray diffraction maxima are considerably smaller for uneven indices than for even indices. The lines (200), (220) (222), (420) and (422) have the largest intensities. The comparison of Figure 3(b) and Figure 3(c) with Figure 3(a) shows that with the increase of the CH, partial pressure the coatings became nearly stoichiometric TIC. The number of X-ray diffraction maxima and their intensities increase and approach the diffraction characteristics of sintered Tic’.‘. Another aspect of our investigations is the dependence of the crystal lattice parameter on the CH, partial pressure (Figure 4). From this figure one can see the increase of the lattice parameter with increase of the partial pressure, which is in good agreement with the changes of the deposition rate (Figure 1). At a partial pressure of 3 x lo-* Pa the lattice parameter of the TiC deposit is equal to that of sintered TIC. Our results show good agreement with those obtained by Sundgren et al ’ and Shikama et al’.
-50
-4.0
3 -3.0
5 :-
(bl 3 -2.0
5 L-;
-I
051
’
5 x 10-3
I I x10-2
I 2
I
34
/
1
I
6
81
I
0
JO
x lo-’
&,(Pa) Figure 2. Relative change of the content of Ti (0), C (0) and N(a) vs CH, partial pressure. I, is the X-ray intensity at CH, pressure Pi and I, is the same intensity under elemental sputtering conditions.
596
Diffraction
angle 28
Figure 3. X-ray diffraction pattern for T&C, _-xdepositions (Cu K,,I =
1.54178 A): a-for sintered TIC; b-for TiC coating obtained at CH, pressure 3 x lo-’ Pa; c-for TIC coating obtained at CH, pressure 2 x lo-’ Pa.
G Georgiev
et a/c Titanium
carbide
thin films
deposition rate depends essentially on the sputtering conditions, because of the different sputtering yields of Ti and TIC. (2) The film composition depends essentially on the composition of the target surface, i.e. on the sputtering conditions. The film composition measured by X-ray fluorescence varies from pure Ti at low CH, pressure to stoichiometric TiC at high pressure. Comparison of the X-ray diffraction spectra of the deposited film and that of sintered TIC also show continuous conversion from pure Ti to stoichiometric TiC when the CH, pressure varies from 1.5 x lo-’ to 4 x 10m2 Pa.
4.32-
4.30-
oq b
4.26-
4.26-
4.221 5 X10-3
I I x10-2
, 2
, 3
I 4
,,,I 5661
References x10_'
Pa
Figure 4. Crystal lattice constant of Ti,C, _x vs CH, partial pressure. The value of the lattice parameter of sintered TiC is shown by @I.
Conclusion From the results presented in this paper the following conclusions can be made. (1) At constant glow discharge current the CH, pressure defines the composition of the target surface. At low pressures (< 1.5 x 10 -’ Pa) the system operates under elemental Ti conditions and
pure Ti is sputtered. At partial pressures above 4 x lo-’ Pa (reactive conditions) a TiC layer covers the target surface. In the intermediate case the target surface consists of Ti and Tic. The
1T Shikama, M Fukutomi, M Fujitsuki and M Okada, JNucl Materials, 122/123, 1281 (1984). ’ J E Sundgren, B 0 Johansson, S E Karlsson and H T J Hentzell, Thin Solid Films, 105, 367 (1983). 3 G Georgiev, I Entchev, N Kolev, Z Uzunov and P Hovsepjan, Scientific session of Technical University ‘A. Kanchev’, Russe (1984). 4 M Okada, M Fukutomi, M Kitajima, H Shinno, T Shikama and M Fujitasuka, International Atomic Energy Agency, Vienna, p 403 (1984). ’ M Fukutomi, M Fujitsuka and M Okada, Thin Solid Films, 120, 283 (1984). ’ A K Dua, V C George and R P Agarvala, Thin Solid Films, 121, 35 (1984). ’ T Shikama, H Araki, M Fujitsuka, M Fukutomi, H Shinno and M Okada, Thin Solid Films, 106, 185 (1983). s J E Sundgren, B 0 Johansson and S E Karlsson, Thin Solid Films, Ml,77 (1981). 9 T Shikama, H Shinno, M Fukutomi, M Fukitsuka, M Kitjima and M Okada, Thin Solid Films, 101, 233 (1983).
597
0042-207X/86 $3.00+ .OO Pergamon Journals Ltd
1 O/pages 595 to 597/l 986
Titanium carbide thin films obtained magnetron sputtering
by reactive
G Georgiev, N Feschiev, D Popov and Z Uzunov, Department of Physics, Technical University ‘A Kanchev’, Russe 7004, Bulgaria
The deposition rate, composition and diffraction spectra of Tic thin films, obtained by magnetron sputtering in the CH,-pressure range from 0.5 x 10m2 to 9 x 10e2 Pa have been measured. Deposition rate measurements show that at low pressures (< 1.5x 10e2 Pa) the system operated under conditions such that pure Ti was sputtered. At pressures higher than 4 x 10 - 2 Pa a Tic layer covered the target (reactive conditions). In the intermediate case the target surface consisted of Ti and Tic. Study of the composition, diffraction spectra and crystal lattice constants of the films showed that continuous conversion occurred from pure Ti films to stoichiometric Tic films when the CH,-pressure was raised from 1.5 x lo- 2 to 4 x lo- 2 Pa.
Introduction
Titanium carbide coatings possess some unusual properties such as: thermal stability’, high hardness2, anticorrosion stability3 and good electrical and thermal conductivity. For deposition of such coatings two methods are mainly used: chemical vapour deposition4 (CVD) and physical vapour deposition5*6 (PVD). Each of these methods possess definite advantages and disadvantages. For CVD the main disadvantage is the high temperature at which the substrate is held when the coating is deposited. With PVD the effects of substrate surface shadowing render difficult the covering of a surface of complicated configuration. CVD has been known and used in practice for the longer time and it is better investigated. For PVD, especially reactive magnetron sputtering, the process is comparatively incompletely investigated. In this connection we present in this paper our investigation of the composition, structure and conditions of obtaining TiC coatings when prepared by reactive magnetron sputtering.
Experimental procedures
The coatings investigated were obtained by reactive magnetron sputtering of titanium in an Ar +CH, atmosphere. A watercooled circular planar magnetron with target diameter of 100 mm was used. The magnetic field was formed by two magnets (cylindrical and annular), placed coaxially on the ring-shaped magnetic conductor. The component of the magnetic induction parallel to the target plane has a maximum of 0.03 T at a distance about 20 mm from the centre of the magnetron. The sputtering zone was a ring with 10 mm inner diameter and 90 mm outer diameter. The average current density was about 13 mA cm-‘. The target to substrate distance was 150 mm for all experiments.
Before Ar and CH, gases were admitted the system was pumped down to a final pressure 6 x 10m3 Pa. The CH, partial pressure was adjusted in the interval from 5 x 10e3 to 9 x lo-’ Pa and other deposition parameters were not varied. Their values were as follows: working pressure of the Ar+CH, mixture6 x lo- 1 Pa; discharge current-800 mA; target voltage-500 V; substrate temperature-100°C. Substrate cleaning consisted of the following procedure: degreasing with tetrachloridemethane and alcohol; heating in vacuum for 10 min at temperature of about 500°C and after this setting the working temperature of the substrate at 100°C. The target was cleaned in a glow discharge for about 20 min in a pure Ar atmosphere and the substrate was masked before beginning sputtering under certain chosen conditions. The deposition rate was determined by weighing the substrate before and after deposition. Correction for the change of film density with increase in the carbide content of the coating has not been made. The results obtained by Sundgren et al’ and Shikama et al’ show that the density of the deposited TIC films changes about 20% when the ratio Ti/C varies from 0.2 to 1. As the deposition rate in our experiments changed about two times (Figure 1) the influence of the density change on the calculated deposition rate can be neglected in comparison with the changes due to the variation of the sputtering rate. The X-ray diffraction measurements were done using apparatus type URS-50 IM. The X-ray diffraction lines were obtained with Cu,. X-rays at a voltage of 40 kV, an anode current of 10 mA and with stationary pattern in respect to the plane of the coating. Changes of the composition of the coating were measured using a scanning electron microscope type JXA-733. All measurements have been made at an accelerating voltage of 25 kV. To determine changes in coating composition the following X-ray lines have been measured: K, for C, N, 0 and Kel for Ar and Ti. 595
G Georgiev ef al: Titanium carbide thin films
345681 x10-3
x10-2
X10-l
PcH4(Pa)
Figure 1. The deposition rate D vsCH, partial pressure for reactively sputtered Ti.
Results and discussions The basic sputtering condition which was changed during the deposition of TiC was the partial pressure of the CH, in the gas mixture with Ar. When the CH,-pressure was changed in the interval from 5 x 10m3 to 9 x lo-'Pa the deposition rate varied in a way shown in Figure 1. One can see that the deposition rate decreases by half as the CH, partial pressure is raised from 5~10~~to9xlO~~Pa. For a CH, pressure up to 1.5 x lo-* Pa the sputtering was realized under so-called elemental conditions, there was no TIC on the target surface and in this case pure Ti was sputtered. In the interval from 1.5 x lo-’ to 4x lo-’ Pa the sputtering rate decreased because of increase of the TIC concentration on the target surface. At a partial pressure above 4 x lo-* Pa one observes nearly full covering of the target surface with a layer of TIC. In this case mainly TIC was sputtered at a rate much smaller than the sputtering rate of pure Ti. This type of sputtering is known as reactive sputtering. Figure 2 presents the CH, pressure dependence of the relative concentrations Ii/Z, of Ti, C and N in the deposited films. In the
ratio ZJZ,, Zi is the X-ray intensity for films sputtered at partial pressure Pi and I, is the same intensity obtained for films deposited under the elemental conditions. One can see in Figure 2 that with increase of the CH, partial pressure, the content of Ti decreases, but that of C increases. The changes of the relative concentration of Ti and C are in good correspondence with the deposition rate (D)as a function of PcH4 as shown by the curve in Figure 1 for which there is a decrease in the deposition rate as the CH, pressure increases. At partial pressures above 4 x lo- * Pa the sputtering rate and the relative content of Ti and C are nearly constant. In this case a TiC layer covers the target with sputtering of TIC and further increase in the CH, partial pressure does not change the composition of the deposit. Measurement of the content of 0, N and Ar using X-ray analysis shows that the concentration of these elements is constant and independent of the sputtering conditions. In Figure 2 only the relative concentration of N is shown. We believe that the existence of 0, N, and Ar in our films arose from gas in the residual atmosphere in the sputtering chamber. Figure 3 shows the position of X-ray diffraction maxima and their intensities in arbitrary units. The diffraction maxima of sintered TIC are also given as a comparison (Figure 3(a)). From this figure one can see the distinctive peculiarity of the NaCl type crystal lattice for which the X-ray diffraction maxima are considerably smaller for uneven indices than for even indices. The lines (200), (220) (222), (420) and (422) have the largest intensities. The comparison of Figure 3(b) and Figure 3(c) with Figure 3(a) shows that with the increase of the CH, partial pressure the coatings became nearly stoichiometric TIC. The number of X-ray diffraction maxima and their intensities increase and approach the diffraction characteristics of sintered Tic’.‘. Another aspect of our investigations is the dependence of the crystal lattice parameter on the CH, partial pressure (Figure 4). From this figure one can see the increase of the lattice parameter with increase of the partial pressure, which is in good agreement with the changes of the deposition rate (Figure 1). At a partial pressure of 3 x lo-* Pa the lattice parameter of the TiC deposit is equal to that of sintered TIC. Our results show good agreement with those obtained by Sundgren et al ’ and Shikama et al’.
-50
-4.0
3 -3.0
5 :-
(bl 3 -2.0
5 L-;
-I
051
’
5 x 10-3
I I x10-2
I 2
I
34
/
1
I
6
81
I
0
JO
x lo-’
&,(Pa) Figure 2. Relative change of the content of Ti (0), C (0) and N(a) vs CH, partial pressure. I, is the X-ray intensity at CH, pressure Pi and I, is the same intensity under elemental sputtering conditions.
596
Diffraction
angle 28
Figure 3. X-ray diffraction pattern for T&C, _-xdepositions (Cu K,,I =
1.54178 A): a-for sintered TIC; b-for TiC coating obtained at CH, pressure 3 x lo-’ Pa; c-for TIC coating obtained at CH, pressure 2 x lo-’ Pa.
G Georgiev
et a/c Titanium
carbide
thin films
deposition rate depends essentially on the sputtering conditions, because of the different sputtering yields of Ti and TIC. (2) The film composition depends essentially on the composition of the target surface, i.e. on the sputtering conditions. The film composition measured by X-ray fluorescence varies from pure Ti at low CH, pressure to stoichiometric TiC at high pressure. Comparison of the X-ray diffraction spectra of the deposited film and that of sintered TIC also show continuous conversion from pure Ti to stoichiometric TiC when the CH, pressure varies from 1.5 x lo-’ to 4 x 10m2 Pa.
4.32-
4.30-
oq b
4.26-
4.26-
4.221 5 X10-3
I I x10-2
, 2
, 3
I 4
,,,I 5661
References x10_'
Pa
Figure 4. Crystal lattice constant of Ti,C, _x vs CH, partial pressure. The value of the lattice parameter of sintered TiC is shown by @I.
Conclusion From the results presented in this paper the following conclusions can be made. (1) At constant glow discharge current the CH, pressure defines the composition of the target surface. At low pressures (< 1.5 x 10 -’ Pa) the system operates under elemental Ti conditions and
pure Ti is sputtered. At partial pressures above 4 x lo-’ Pa (reactive conditions) a TiC layer covers the target surface. In the intermediate case the target surface consists of Ti and Tic. The
1T Shikama, M Fukutomi, M Fujitsuki and M Okada, JNucl Materials, 122/123, 1281 (1984). ’ J E Sundgren, B 0 Johansson, S E Karlsson and H T J Hentzell, Thin Solid Films, 105, 367 (1983). 3 G Georgiev, I Entchev, N Kolev, Z Uzunov and P Hovsepjan, Scientific session of Technical University ‘A. Kanchev’, Russe (1984). 4 M Okada, M Fukutomi, M Kitajima, H Shinno, T Shikama and M Fujitasuka, International Atomic Energy Agency, Vienna, p 403 (1984). ’ M Fukutomi, M Fujitsuka and M Okada, Thin Solid Films, 120, 283 (1984). ’ A K Dua, V C George and R P Agarvala, Thin Solid Films, 121, 35 (1984). ’ T Shikama, H Araki, M Fujitsuka, M Fukutomi, H Shinno and M Okada, Thin Solid Films, 106, 185 (1983). s J E Sundgren, B 0 Johansson and S E Karlsson, Thin Solid Films, Ml,77 (1981). 9 T Shikama, H Shinno, M Fukutomi, M Fukitsuka, M Kitjima and M Okada, Thin Solid Films, 101, 233 (1983).
597