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Composition and structure of titanium nitride films prepared by ion beam enhanced deposition
Nuclear Instruments and Methods in Physics Research B59/60 (1991) 272-275 North-Holland
272
Composition and structure of titanium nitride films prepared by ion beam enhanced deposition Wang Xi, Liu Xianghuai, Chen Youshan, Yang Genqing, Zhou Zuyao, Zheng Zhihong, Huang Wei and Zou Shichang Ion
Beam Laboratory, Shanghai Institute of Metallurgy, Academia Sink,
Shanghai 200050, China
Titanium nitride films have been prepared by simultaneous vacuum deposition of titanium and nitrogen ion beams with ion energy of 40 keV. The atomic arrival ratio of implanted ions to deposited atoms was varied from 0 to 0.5. The fihn composition and structure were analyzed by BBS, AES, TEM and XRD. The results show that nitrogen ion bombardment can clearly reduce the oxygen concentration in the film. The component ratio (N/Ti) in films prepared at low temperature was greater than that in the films prepared at high temperature. At the same atomic arrival ratio, the component ratio (N/Ti) in the fiis decreased with increasing titanium deposition rate. These results are considered to occur since the film composition is strongly affected by the adsorption of nitrogen, which depends sensitively on the substrate temperature, titanium deposition rate and pressure of nitrogen gas in the target chamber. The films were mainly TiN polycrystals, whereas only amorphous structures have been observed in films prepared under the same condition but without nitrogen ion bombardment. The preferred crystalline orientation of the film changed from (111) to (200) with an increase of the atomic arrival ratio (N/ Ti). Such a variation is due to the difference in energy deposition on each titanium atom from the nitrogen ion beam during the ion beam enhanced deposition (IBED) process.
1. Introduction Titanium nitride is one of the remarkable materials for wear-resistant coatings. The commonly used methods for preparing such films are still limited in application due to high-temperature processing, insufficient adhesion of film to substrate etc. Ion beam enhanced deposition (IBED), in which evaporation-deposition and ion implantation proceed simultaneously [l-2], has alleviated both problems [3-61. The present article reports the synthesis of titanium nitride films by electron beam evaporation of titanium accompanied with 40 keV nitrogen ions simultaneously bombarding the specimens. The films were analyzed for composition and structure by RBS, AES, TEM and X-ray diffraction. In particular, chemical adsorption effects in IBED are investigated in detail.
2. Experimental The synthesis of titanium nitride films was carried out using an Eaton Z-200 ion beam mixing and deposition system. Titanium vapor evaporated from an electron beam evaporator was deposited onto a substrate, to which a beam of 40 keV nitrogen ions was directed simultaneously. The normal of the substrate was commonly put at 45 o to both ion incidence and vapor flux. 0168-583X/91/$03.50
Films were prepared with various atomic arrival ratios of implanted nitrogen ions to deposited titanium atoms ranging from 0 to 0.5. The base pressure in the target chamber was lo-’ Torr and the typical working pressure was 5 x lop6 Torr because of a nitrogen gas leak from ion source. The films were prepared at two substrate temperatures, i.e. ambient (below 100” C) and 300°C. Silicon wafers and polished graphite were selected as substrates for RBS, AES, TEM and X-ray diffraction analysis.
3. Results and discussion Fig. 1 shows the RBS spectra of titanium nitride films deposited on graphite substrates both with ion bombardment at an atomic arrival ratio (N/Ti) of 0.4 and without ion bombardment. The deposition rate for Ti was 3 A/s for both cases. The component ratio of titanium, nitrogen and oxygen is 1 :0.9:0.18 for the IBED film and 1: 0.7: 0.6 for the non-ion-bombarded film, respectively. Oxygen was incorporated into the films due to high reactivity between titanium and oxygen-containing molecules present in the residual gas. The oxygen concentration of the non-ion-bombarded film was about 27 at.%, much more than that of the IBED film (about 9 at.%). This is consistent with Rant’s result that the oxygen concentration of IBED titanium
0 1991 - Elsevier Science Publishers B.V. (North-Holland)
213
Wtmg Xi et al. / TiN films prepared by ion beam enhanced deposition 4000 2 3000
MeV He+ * * + Implanted 0 0 0 0 0 &implanted l
t
l
_
G0.4 E g 0.2 8 0
0
CHANNEL Fig. 1. Rutherford back~tt~g spectra of an ~rnpl~t~ film and an IBED titanium nitride fii formed with the substrate at 70 o C.
nitride fihn decreases with increasing atomic arrival ratio @I/ Ti) [3]. This phenomenon might be attributed to preferred rejection of oxygen from IBED fihn by the nitrogen ion beam. It is of interest to note that in the film without nitrogen ion bombardment the nitrogen concentration is as high as 30 at.%%.This could be accounted for by the adsorption of nitrogen, leaked from the ion source, onto the fresh surface of deposited tit~um. That is to say the nitrogen ~n~tration of the IBED titauium nitride fihns arises from two mechanisms: direct nitrogen implantation and adsorption of nitrogen. As to adsorption, the sticking coefficient of impinging nitrogen molecules on a freshly deposited titanium surface is dependent on the temperature of the sample. The higher the sample tem~rat~e, the less nitrogen is adsorbed. That is shown in fig. 2, where the component ratio (N/Ti) in the IBED film prepared at low temperature is greater than that prepared at higher temperature. Fig. 3 gives the relationship between the component ratio (N/Ti) in the film and the titanium deposition
10000
0.0
1 1,
I
I
4
,
,
,
I
I
,
I
I
I
I
,
1
I
I
I
0
15 ~~~*~~~~~~O~~~ (A/kc) Fig. 3. ~orn~~~t ratio N/Ti in films versus deposition rate. The atomic arrival ratio is 0.066.
rate. It is shown that the component ratio (N/Ti) decreases as the titanium deposition rate increases at a constant atomic arrival ratio of 0.07. This implies that the adsorption of nitrogen is not saturated during deposition in the present case, and perhaps repeatedly covers the as-deposited titanium layer. Of course, the atomic arrival ratio (N/Ti) still determines the composition of the IBED titanium nitride films. But when the titanium deposition rate is low, the component ratio (N/Ii) in the film is much larger compared to the atomic arrival ratio (N/TX). This suggests that when the titanium deposition rate is low, the adsorption effect dominates. The adsorption effect has been taken into account in computer simulation in an another paper 171. Component depth profiles of the films were obtained using AES combined with argon ion sputtering. The method used for determining the nitrogen-to-titanium ratio in the film has been described elsewhere [8]. Fig. 4 is the AES measured component depth profiles of an IBED titanium nitride fihn formed on an iron substrate.
I 2 MeV He+
0
CHANNEL Fig. 2. Rutherford backscattering spectra of titanium nitride fiis formed at different temperatures.
SPUTTERING TIME (rnin) Fig. 4. AES depth profiles of a titanium nitride film formed by IBED. III. ION-ENHANCED
DEPOSITION
274
Wang Xi
et al. /
~iN~~~
prepared
It is shown that the nitrogen and titanium distribute evenly inside the film. There is a transition region between the film and the substrate, and the thickness of the transition region is about 35 nm. It is this transition region that is of great benefit to the adhesion of the fihn to the substrate [9]. Transmission electron microscopy and X-ray diffraction were used to examine the structure of the IBED titanium nitride fihns. The electron diffraction patterns of a non-ion-bomb~d~ film and an IBED tithe nitride film are shown in figs. 5a and 5b, respectively. The diffuse rings of electron diffraction in fig. 5a indicate the non-ion-bombarded film is amorphous. For the IBED fii, its electron diffraction pattern shows three rings corresponding to (ill), (200) and (220) orientations in the TiN phase of NaCl-type structure. This demonstrates that a TiN polycrystalhne film has been formed. The structure difference between the two films might arise from thermal spikes, induced by injected nitrogen ions, which could make the film crystalline. Fig. 6 shows the variation of the intensity ratio of the (200) peak to the (111) peak of XRD spectra in
by ion beam enhanced depasition
o*“ov ATOMIC ARRIVAL RATIO (N/T Fig. 6. The preferred orientation of ~lyc~~e atomic arrivaI ratio N/Ti.
TiN versus
relationship with the atomic arrival ratio (N/Ti). According to the powder diffraction data, Z(2OO)/Z(lll) is 100/75 [lo], which is indicated by the dashed line in the figure. It can be seen that the (111) orientation is preferential at low atomic arrival ratio, but the (111) preferential orientation decreases with increasing atomic arrival ratio to an unoriented structure, then the (200) orientation has increased. We conclude Presley that such a variation in crystallization is due to the difference in energy deposition per titanium atom from the nitrogen ion beam.
4. Conclusions
Fig. 5. Electron diffraction patterns from (a) a non-ionbombarded film; and (b) an IBED titanium nitride film.
The titanium nitride films formed by IBED have less oxygen content wmpared with those formed without ion ~rnb~~ent. The wmpon~t ratio (N/Ti) in the films decreases with increasing sample temperatures or titanium deposition rate at constant atomic arrival ratio. This arises from nitrogen adsorption. Between the uniform film and the substrate there is a transition region. The IBED films are mainly composed of polycrystal TiN whereas films without ion beam bombardment have an amorphous structure. The preferred crystalline orientation of the films changes from (111) to (200) with increasing atomic arrival ratio (N/Ti). Such a variation in crystalline orientation may be due to the difference in the energy deposition per titanium atom from the nitrogen ion beam.
Wang Xi et al. / TiN film prepared by ion beam enhanced deposition
References [l] SM. Rossnagel and J.J. Cuomo, MRS Bull. 16 (1987) 40. [2] J.M.E. Harper, J.J. Cuomo, R.J. Gambino and H.R. Kaufman, Nucl. Instr. and Meth. B7/8 (1985) 886. [3] R.A. Kant, B.D. SartweIl, I.L. Singer and R.G. Vardiian, Nucl. Instr. and Metb. B7/8 (1985) 915. [4] M. Kiuchi, M. Tom&a, K. Fujii, M. Satou and R. Shimizu, Jpn. J. Appl. Phys. 26 (1987) 98. [5] M. Satou, Y. Andoh, K. Ogata, Y. Suzuki, K. Matsuda and F. Fujimoto, Jpn. J. Appl. Phys. 24 (1985) 656.
215
[6] Zhou Jiankun, Liu Xianghuai, Chen Youshan, Zheng &hong, Huang Wei, Zhou Zuyao and Zou Shichang, Chin. J. Semiconductors 10 (1989) 440. [7] Wang Xi, Zhou Jiankhn, Chen Youshan, Liu Xianghuai and Zou Shichang, Acta Metall. Sinica 27 (1991) B203. (81 P.T. Dawson and K.K. Tzatzov, Surf. Sci. 149 (1985) 105. (91 Wang Xi, Liu Xianghuai and Zou Shichang, Thin Solid Films, to be published. [lo] Power diffraction data: JCPDS card 6-642.
272
Composition and structure of titanium nitride films prepared by ion beam enhanced deposition Wang Xi, Liu Xianghuai, Chen Youshan, Yang Genqing, Zhou Zuyao, Zheng Zhihong, Huang Wei and Zou Shichang Ion
Beam Laboratory, Shanghai Institute of Metallurgy, Academia Sink,
Shanghai 200050, China
Titanium nitride films have been prepared by simultaneous vacuum deposition of titanium and nitrogen ion beams with ion energy of 40 keV. The atomic arrival ratio of implanted ions to deposited atoms was varied from 0 to 0.5. The fihn composition and structure were analyzed by BBS, AES, TEM and XRD. The results show that nitrogen ion bombardment can clearly reduce the oxygen concentration in the film. The component ratio (N/Ti) in films prepared at low temperature was greater than that in the films prepared at high temperature. At the same atomic arrival ratio, the component ratio (N/Ti) in the fiis decreased with increasing titanium deposition rate. These results are considered to occur since the film composition is strongly affected by the adsorption of nitrogen, which depends sensitively on the substrate temperature, titanium deposition rate and pressure of nitrogen gas in the target chamber. The films were mainly TiN polycrystals, whereas only amorphous structures have been observed in films prepared under the same condition but without nitrogen ion bombardment. The preferred crystalline orientation of the film changed from (111) to (200) with an increase of the atomic arrival ratio (N/ Ti). Such a variation is due to the difference in energy deposition on each titanium atom from the nitrogen ion beam during the ion beam enhanced deposition (IBED) process.
1. Introduction Titanium nitride is one of the remarkable materials for wear-resistant coatings. The commonly used methods for preparing such films are still limited in application due to high-temperature processing, insufficient adhesion of film to substrate etc. Ion beam enhanced deposition (IBED), in which evaporation-deposition and ion implantation proceed simultaneously [l-2], has alleviated both problems [3-61. The present article reports the synthesis of titanium nitride films by electron beam evaporation of titanium accompanied with 40 keV nitrogen ions simultaneously bombarding the specimens. The films were analyzed for composition and structure by RBS, AES, TEM and X-ray diffraction. In particular, chemical adsorption effects in IBED are investigated in detail.
2. Experimental The synthesis of titanium nitride films was carried out using an Eaton Z-200 ion beam mixing and deposition system. Titanium vapor evaporated from an electron beam evaporator was deposited onto a substrate, to which a beam of 40 keV nitrogen ions was directed simultaneously. The normal of the substrate was commonly put at 45 o to both ion incidence and vapor flux. 0168-583X/91/$03.50
Films were prepared with various atomic arrival ratios of implanted nitrogen ions to deposited titanium atoms ranging from 0 to 0.5. The base pressure in the target chamber was lo-’ Torr and the typical working pressure was 5 x lop6 Torr because of a nitrogen gas leak from ion source. The films were prepared at two substrate temperatures, i.e. ambient (below 100” C) and 300°C. Silicon wafers and polished graphite were selected as substrates for RBS, AES, TEM and X-ray diffraction analysis.
3. Results and discussion Fig. 1 shows the RBS spectra of titanium nitride films deposited on graphite substrates both with ion bombardment at an atomic arrival ratio (N/Ti) of 0.4 and without ion bombardment. The deposition rate for Ti was 3 A/s for both cases. The component ratio of titanium, nitrogen and oxygen is 1 :0.9:0.18 for the IBED film and 1: 0.7: 0.6 for the non-ion-bombarded film, respectively. Oxygen was incorporated into the films due to high reactivity between titanium and oxygen-containing molecules present in the residual gas. The oxygen concentration of the non-ion-bombarded film was about 27 at.%, much more than that of the IBED film (about 9 at.%). This is consistent with Rant’s result that the oxygen concentration of IBED titanium
0 1991 - Elsevier Science Publishers B.V. (North-Holland)
213
Wtmg Xi et al. / TiN films prepared by ion beam enhanced deposition 4000 2 3000
MeV He+ * * + Implanted 0 0 0 0 0 &implanted l
t
l
_
G0.4 E g 0.2 8 0
0
CHANNEL Fig. 1. Rutherford back~tt~g spectra of an ~rnpl~t~ film and an IBED titanium nitride fii formed with the substrate at 70 o C.
nitride fihn decreases with increasing atomic arrival ratio @I/ Ti) [3]. This phenomenon might be attributed to preferred rejection of oxygen from IBED fihn by the nitrogen ion beam. It is of interest to note that in the film without nitrogen ion bombardment the nitrogen concentration is as high as 30 at.%%.This could be accounted for by the adsorption of nitrogen, leaked from the ion source, onto the fresh surface of deposited tit~um. That is to say the nitrogen ~n~tration of the IBED titauium nitride fihns arises from two mechanisms: direct nitrogen implantation and adsorption of nitrogen. As to adsorption, the sticking coefficient of impinging nitrogen molecules on a freshly deposited titanium surface is dependent on the temperature of the sample. The higher the sample tem~rat~e, the less nitrogen is adsorbed. That is shown in fig. 2, where the component ratio (N/Ti) in the IBED film prepared at low temperature is greater than that prepared at higher temperature. Fig. 3 gives the relationship between the component ratio (N/Ti) in the film and the titanium deposition
10000
0.0
1 1,
I
I
4
,
,
,
I
I
,
I
I
I
I
,
1
I
I
I
0
15 ~~~*~~~~~~O~~~ (A/kc) Fig. 3. ~orn~~~t ratio N/Ti in films versus deposition rate. The atomic arrival ratio is 0.066.
rate. It is shown that the component ratio (N/Ti) decreases as the titanium deposition rate increases at a constant atomic arrival ratio of 0.07. This implies that the adsorption of nitrogen is not saturated during deposition in the present case, and perhaps repeatedly covers the as-deposited titanium layer. Of course, the atomic arrival ratio (N/Ti) still determines the composition of the IBED titanium nitride films. But when the titanium deposition rate is low, the component ratio (N/Ii) in the film is much larger compared to the atomic arrival ratio (N/TX). This suggests that when the titanium deposition rate is low, the adsorption effect dominates. The adsorption effect has been taken into account in computer simulation in an another paper 171. Component depth profiles of the films were obtained using AES combined with argon ion sputtering. The method used for determining the nitrogen-to-titanium ratio in the film has been described elsewhere [8]. Fig. 4 is the AES measured component depth profiles of an IBED titanium nitride fihn formed on an iron substrate.
I 2 MeV He+
0
CHANNEL Fig. 2. Rutherford backscattering spectra of titanium nitride fiis formed at different temperatures.
SPUTTERING TIME (rnin) Fig. 4. AES depth profiles of a titanium nitride film formed by IBED. III. ION-ENHANCED
DEPOSITION
274
Wang Xi
et al. /
~iN~~~
prepared
It is shown that the nitrogen and titanium distribute evenly inside the film. There is a transition region between the film and the substrate, and the thickness of the transition region is about 35 nm. It is this transition region that is of great benefit to the adhesion of the fihn to the substrate [9]. Transmission electron microscopy and X-ray diffraction were used to examine the structure of the IBED titanium nitride fihns. The electron diffraction patterns of a non-ion-bomb~d~ film and an IBED tithe nitride film are shown in figs. 5a and 5b, respectively. The diffuse rings of electron diffraction in fig. 5a indicate the non-ion-bombarded film is amorphous. For the IBED fii, its electron diffraction pattern shows three rings corresponding to (ill), (200) and (220) orientations in the TiN phase of NaCl-type structure. This demonstrates that a TiN polycrystalhne film has been formed. The structure difference between the two films might arise from thermal spikes, induced by injected nitrogen ions, which could make the film crystalline. Fig. 6 shows the variation of the intensity ratio of the (200) peak to the (111) peak of XRD spectra in
by ion beam enhanced depasition
o*“ov ATOMIC ARRIVAL RATIO (N/T Fig. 6. The preferred orientation of ~lyc~~e atomic arrivaI ratio N/Ti.
TiN versus
relationship with the atomic arrival ratio (N/Ti). According to the powder diffraction data, Z(2OO)/Z(lll) is 100/75 [lo], which is indicated by the dashed line in the figure. It can be seen that the (111) orientation is preferential at low atomic arrival ratio, but the (111) preferential orientation decreases with increasing atomic arrival ratio to an unoriented structure, then the (200) orientation has increased. We conclude Presley that such a variation in crystallization is due to the difference in energy deposition per titanium atom from the nitrogen ion beam.
4. Conclusions
Fig. 5. Electron diffraction patterns from (a) a non-ionbombarded film; and (b) an IBED titanium nitride film.
The titanium nitride films formed by IBED have less oxygen content wmpared with those formed without ion ~rnb~~ent. The wmpon~t ratio (N/Ti) in the films decreases with increasing sample temperatures or titanium deposition rate at constant atomic arrival ratio. This arises from nitrogen adsorption. Between the uniform film and the substrate there is a transition region. The IBED films are mainly composed of polycrystal TiN whereas films without ion beam bombardment have an amorphous structure. The preferred crystalline orientation of the films changes from (111) to (200) with increasing atomic arrival ratio (N/Ti). Such a variation in crystalline orientation may be due to the difference in the energy deposition per titanium atom from the nitrogen ion beam.
Wang Xi et al. / TiN film prepared by ion beam enhanced deposition
References [l] SM. Rossnagel and J.J. Cuomo, MRS Bull. 16 (1987) 40. [2] J.M.E. Harper, J.J. Cuomo, R.J. Gambino and H.R. Kaufman, Nucl. Instr. and Meth. B7/8 (1985) 886. [3] R.A. Kant, B.D. SartweIl, I.L. Singer and R.G. Vardiian, Nucl. Instr. and Metb. B7/8 (1985) 915. [4] M. Kiuchi, M. Tom&a, K. Fujii, M. Satou and R. Shimizu, Jpn. J. Appl. Phys. 26 (1987) 98. [5] M. Satou, Y. Andoh, K. Ogata, Y. Suzuki, K. Matsuda and F. Fujimoto, Jpn. J. Appl. Phys. 24 (1985) 656.
215
[6] Zhou Jiankun, Liu Xianghuai, Chen Youshan, Zheng &hong, Huang Wei, Zhou Zuyao and Zou Shichang, Chin. J. Semiconductors 10 (1989) 440. [7] Wang Xi, Zhou Jiankhn, Chen Youshan, Liu Xianghuai and Zou Shichang, Acta Metall. Sinica 27 (1991) B203. (81 P.T. Dawson and K.K. Tzatzov, Surf. Sci. 149 (1985) 105. (91 Wang Xi, Liu Xianghuai and Zou Shichang, Thin Solid Films, to be published. [lo] Power diffraction data: JCPDS card 6-642.