- Email: [email protected]
Preparation and properties of nitrogen and titanium oxide incorporated diamond-like carbon films by plasma source ion implantation
Surface and Coatings Technology 136 Ž2001. 192᎐196
Preparation and properties of nitrogen and titanium oxide incorporated diamond-like carbon films by plasma source ion implantation Koumei BabaU , Ruriko Hatada Industrial Technology Center of Nagasaki, 2-1303-8 Ikeda, Omura, Nagasaki 856-0026, Japan
Abstract Nitrogen and titanium oxide incorporated diamond-like carbon ŽDLC. films were deposited by a plasma source ion implantation on silicon wafer and quartz glass. Pure acetylene gas was used as a working gas for plasma. Additional nitrogen and titanium tetraisopropoxide gases were fed into acetylene plasma to prepare nitrogen and titanium oxide incorporated DLC films. The plasma was generated by a radio frequency glow discharge. Ions were accelerated from the plasma by a high-voltage pulse Žy20 kV, 100 Hz, 50 s. applied directly to the substrates. The surface morphology was observed by a scanning electron microscope ŽSEM. and an atomic force microscope ŽAFM.. The compositional and structural characterization of the films was carried out using X-ray diffraction ŽXRD., X-ray photoelectron spectroscopy ŽXPS. and Raman spectroscopy. The hardness of the films was measured by an indentation method. The sheet resistivity of the films was measured by a four-point probe method. The results showed that all of the N incorporated and unincorporated films were amorphous and showed typical Raman spectra of DLC films. The XPS and the FT-IR spectra indicated the formation of C᎐N, C⫽N and C⬅N valence bonds. XPS measurement for titanium oxide incorporated films revealed the existence of Ti᎐C, Ti᎐O, C᎐C bonding in the DLC films. The hardness of the nitrogen and titanium oxide incorporated films decreased with the amount of incorporated species. The sheet resistivity of the films decreased abruptly with increasing nitrogen and titanium oxide contents in the films. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Plasma source ion implantation; Diamond-like carbon; Nitrogen; Titanium oxide; Resistivity; Hardness
1. Introduction Diamond-like carbon ŽDLC. films are a subject of considerable interest, due to their special properties such as high hardness, low friction, high wear resistance, and chemical inertness. Recently, there have been several attempts to improve the properties of DLC films by the addition of elements, such as silicon w1᎐3x, nitrogen w4᎐7x, fluorine w8᎐10x and various metals w11᎐14x. For example, an increase in water contact
U
Corresponding author. Tel.: q81-957-521133; fax: q81-957521136. E-mail address: [email protected] ŽK. Baba..
angle was observed for F and Si incorporated DLC films w8x. Nitrogen or metal element in DLC films has been shown to reduce the inner stress, electrical resistivity and friction coefficients w15,16x. Plasma source ion implantation ŽPSII. has attracted attention as an alternative ion implantation method w17᎐19x. This method has several advantages over conventional ion implantation, such as low cost, large area, multi-target and non-line-of-sight process. In this paper, we have reported some properties of nitrogen or titanium oxide incorporated DLC films prepared by PSII. In PSII, samples were placed in a gas mixture of acetylene and nitrogen or titanium tetraisopropoxide plasma created by radio frequency ŽRF. discharge, and a pulsed high negative bias voltage was
0257-8972r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 7 - 8 9 7 2 Ž 0 0 . 0 1 0 5 4 - 9
K. Baba, R. Hatada r Surface and Coatings Technology 136 (2001) 192᎐196
193
applied to the samples. All samples were subsequently characterized by scanning electron microscopy ŽSEM., atomic force microscopy ŽAFM., X-ray photoelectron spectroscopy ŽXPS. and Raman spectroscopy. Hardness and electrical resistivity were measured and related to the composition of the films.
2. Experimental 2.1. Film deposition The plasma source ion implantation apparatus used in this study is described in detail elsewhere w20x. Fused silica glass plates and silicon wafers Ž100. were used as substrates. The substrates were mounted on a holder and placed in the PSII chamber. Acetylene gas was introduced into the chamber at a constant flow rate to deposit DLC films. Nitrogen gas was introduced into the chamber to deposit nitrogen incorporated DLC films. Titanium tetraisopropoxide ŽTTIP. was vaporized by heating and introduced into the chamber without carrier gas at a pressure of 0.8᎐1.3 Pa. Through a matching network, 50 W r.f. power was supplied to the antenna at 13.56 MHz. A negative voltage pulse of 20 kV was applied to the sample holder at pulse duration of 50 s with a pulse repetition rate of 100 Hz. 2.2. Characterization of films The surface morphology was observed by using field emission scanning electron microscopy ŽSEM. and atomic force microscopy ŽAFM.. The chemical composition and chemical state of the films were evaluated using X-ray photoelectron spectroscopy ŽXPS.. Structural information of the films was obtained by a microRaman spectrometer at an excitation wavelength of 514 nm. The film thickness was estimated by a crosssectional SEM observation. The hardness measurements of the films were performed using an indentation method ŽHysitron Picoindenter TM . with the maximum force of 100 N. Measurement of the electrical resistivity of the films deposited on glass plate substrates was performed using a four-point probe station Ž1.0 mm probe spacing, 1.96 N load and 40 m radius tip..
Fig. 1. Dependence of deposition rate of the films and actual nitrogen concentration in the films on nitrogen fraction in the feed gas mixture during deposition.
the nitrogen gas fraction in the feed gas mixture. The deposition rate decreased with increasing nitrogen gas fraction. This decrease in the deposition rate seems to be the direct result of dilution of the hydrocarbon vapor in the reactant gas mixture. The composition of the films was measured by XPS and shown in Fig. 1 as a function of the nitrogen fraction. The nitrogen content incorporated in the films increased with N2 fraction in the feed gas, but it seems to reach maximum value at approximately 10 at.%. The XPS N1s and C1s spectra of 5.5 at.% nitrogen incorporated film are shown in Fig. 2. The N1s spectrum can be deconvoluted into three peaks at 398.6, 400.2 and 402.9 eV. The first and second peaks of N1s can be attributed to N᎐C, N⬅C and N⫽C bonds, respectively w4x. And the peak at 402.9 eV can be assigned to N᎐O or N᎐N bonds w21x. Similarly the C1s spectrum can be deconvoluted into three peaks at 284.5, 285.9 and 288.0 eV. The first peak at 284.5 eV can be attributed to graphitic or hydrogenated C᎐C bonding. The second peak at 285.9 eV is consistent with two binding states of C⫽N Ž285.3 eV. and C⬅N Ž286.7 eV. bonds. And the third peak at 288.0 eV is assigned to the C᎐N bond w4x. A Raman spectrum obtained from a 5.5-at.% nitrogen incorporated film is shown in Fig. 3. A broad peak between 1000 cmy1 and 1800 cmy1 indicates that the
3. Results and discussion 3.1. C᎐N films X-Ray diffraction measurements showed that all the films have an amorphous structure. The deposited films were black in color. The film deposition rate of C᎐N films estimated from cross-sectional SEM observation and deposition time is shown in Fig. 1 as a function of
Fig. 2. C1s and N1s XPS spectra of 5.5 at.% nitrogen incorporated film.
194
K. Baba, R. Hatada r Surface and Coatings Technology 136 (2001) 192᎐196
Fig. 3. Raman spectrum of 5.5 at.% nitrogen incorporated DLC film. The spectrum includes the G- and D-line Gaussian fits for the major 1561 cmy1 shift and the minor 1387 cmy1 shift, respectively.
film structure is amorphous. The broad peak in Fig. 3 can be resolved into two Gaussian profiles centered at 1387 cmy1 corresponding to the D-line assigned to disordered structure, and at 1561 cmy1 , corresponding to the G-line assigned to graphite structure w22,23x. The integrated intensity ratio Ž I D rIG . of each profile has been correlated with sp 3rsp 2 bonding ratio and the graphitic particle size w24,25x. Fig. 4 shows the I D rIG ratio changes with nitrogen content in the films. It is clearly seen that I D rIG ratios increase with nitrogen content. This result indicates that the graphite structure is destroyed or that the graphite particle size decreases with the increase in nitrogen content in the films. These structural changes are explained as the substitution of nitrogen atoms for carbon or hydrogen atoms and the bombardment by nitrogen ions which destroy the graphitic crystal structure in the film at high nitrogen fraction. There was no dependence of the position of D-line and G-line on nitrogen content. Fig. 5 shows the hardness of the films measured by a nano-indentation method. The highest hardness was derived for the nitrogen free film, and decreased gradually when increasing nitrogen content. This result is explained by the increase in the number of C⬅N bonds which terminate the carbon backbone leading to less tightly bound C atoms. Electrical resistivity of the films is shown in Fig. 5 as a function of nitrogen content in the films. The resistiv-
Fig. 4. The ratio of the integrated areas of the Raman D- and G-lines Ž I D rIG . as a function of nitrogen content in the films.
Fig. 5. Dependence of hardness of the films and resistivity of the films on the nitrogen content in the films.
ity of 8 at.% nitrogen incorporated film was out of the range of the instrument. It was found that nitrogen incorporation into the DLC films is effective for the reduction in the resistivity, and, at 5.5 at.% nitrogen, the resistivity is decreased by a factor of 30 as compared to the nitrogen-free film. SEM observation showed that the surface of all the films were smooth and featureless. Fig. 6 presents an AFM image obtained from 5.5 at.% nitrogen incorporated DLC film as an example. The average roughness ŽR a . 0.23 nm values were calculated from 1 = 1 m2 scan. This R a value is a little higher than the nitrogen free film whose value was 0.17 nm. 3.2. C᎐Ti᎐O films Titanium and oxygen incorporated DLC films were prepared by use of several mixtures of acetylene and TTIP gases for a plasma. The composition and chemical states of the films were estimated by XPS. Fig. 7 shows the XPS C1s, O1s and Ti2p spectra of the film deposited at a TTIP partial pressure of 65%. The C1s spectrum can be deconvoluted into two peaks at 282.1 and 284.2 eV. The first peak and the second one are attributed to Ti᎐C and C᎐C bonds, respectively. The
Fig. 6. AFM micrograph of 5.5 at.% nitrogen incorporated DLC film. The average roughness ŽR a . is 0.23 nm.
K. Baba, R. Hatada r Surface and Coatings Technology 136 (2001) 192᎐196
195
Fig. 7. O1s and Ti2p XPS spectra of the titanium oxide incorporated film deposited at partial pressure of 65%.
O1s peak position is 530.8 eV and can be assigned to Ti᎐O bond. A very broad peak was observed for the Ti2p spectrum and assigned to Ti᎐C Ž454.4 eV., Ti᎐O Ž455.1 eV., Ti 2 O 3 Ž457.8 eV. and TiO 2 Ž458.8 eV. w26x. The film composition, the hardness and the resistivity are summarized in Table 1 as a function of the TTIP partial pressure in the reactive plasma. The titanium and oxygen contents increased similarly with increasing TTIP partial pressure, and the composition of the film deposited in a pure TTIP atmosphere was CrTirOs 25:35:40 at.%. It is clearly found that the hardness and the resistivity were influenced significantly by TTIP partial pressure. The electrical resistivity of the film deposited at the TTIP partial pressure of 65% is very low, but the hardness decreased by approximately onethird compared to the undoped DLC film.
3. the nitrogen incorporated in the films was predominantly C⬅N and C⫽N bonding states; 4. the integrated intensity ratio I D rIG of Gaussian profiles increased with the nitrogen content; 5. the hardness of the films decreased gradually with increasing the nitrogen content ᎏ the electrical resistivity of the films decreased significantly with increasing the nitrogen content; and 6. the hardness of the films prepared from acetylene and TTIP mixture decreased with increasing the titanium and oxygen contents.
Acknowledgements The authors would like to thank Mr K. Okamura and Mr O. Nakano from Nippon Tungsten Co. Ltd. for the electrical resistivity measurement.
4. Conclusions The nitrogen and titanium oxide incorporated DLC films were prepared from mixture of acetylene and nitrogen gases or TTIP gases using PSII. The surface morphology and film thickness were observed by SEM and AFM. The most important results can be summarized as follows: 1. the deposition rate decreased when increasing the nitrogen fraction in the feed gas mixture; 2. very smooth surface was obtained for the nitrogen incorporated DLC films; Table 1 Composition, hardness and resistivity of the Ti and O incorporated DLC films TTIP partial pressure Ž%.
Composition ŽCrTirO, at.%.
Hardness ŽGPa.
Resistivity Ž ⍀ cm.
0 10 49 65 100
100:0:0 95:2:3 84:8:8 39:28:33 25:35:40
17.3 15.0 12.7 6.2 4.8
1.81= 103 2.01= 103 7.52= 103 5.72 2.32
References w1x A.A. Ogwu, R.W. Lamberton, S. Morley, P. Maguire, J. McLaughlin, Physica B 269 Ž1999. 335. w2x S.S. Camargo Jr., R.A. Santos, A.L. Baia Neto, R. Carius, F. Finger, Thin Solid Films 332 Ž1998. 130. w3x K.R. Lee, M.G. Kim, S.J. Cho, K.Y. Eun, T.Y. Seong, Thin Solid Films 308-309 Ž1997. 263. w4x S. Bhattacharyya, C. Cardinaud, G. Turban, J. Appl. Phys. 83 Ž1998. 4491. w5x F.L. Freire Jr., D.F. Franceschini, Thin Solid Films. 293 Ž1997. 236. w6x A. Bousetta, M. Lu, A. Bensaoula, J. Vac. Sci. Technol. A13 Ž1995. 1639. w7x J. Schwan, V. Batori, S. Ulrich, H. Ehrhardt, S.R.P. Silva, J. Appl. Phys. 84 Ž1998. 2071. w8x S. Miyake, R. Kaneko, Y. Kikuya, I. Sugimoto, J. Tribol. 113 Ž1991. 384. w9x J. Seth, S.V. Babu, Thin Solid Films 230 Ž1993. 90. w10x T.W. Mountsier, J.A. Samuels, Thin Solid Films 332 Ž1998. 362. w11x C.P. Klages, R. Memming, Mater. Sci. Forum 52-53 Ž1989. 609. w12x M. Wang, K. Schmidt, K. Reichelt, H. Dimigen, Hubsch, J. Mater. Res. 7 Ž1992. 667. w13x M. Grischke, K. Bewilogua, H. Dimigen, Mater. Manuf. Processes 8 Ž1993. 407. w14x W.J. Meng, B.A. Gillispie, J. Appl. Phys. 84 Ž1998. 4314.
196
K. Baba, R. Hatada r Surface and Coatings Technology 136 (2001) 192᎐196
w15x H. Dimigen, C.P. Klages, Surf. Coat. Technol. 49 Ž1991. 543. w16x D.P. Monaghan, D.G. Teer, P.A. Logan, I. Efeoglu, R.D. Arnell, Surf. Coat. Technol. 60 Ž1993. 525. w17x J.R. Conrad, T. Castagna, Bull. Am. Phys. Soc. 31 Ž1986. 1479. w18x J.R. Conrad, J. Appl. Phys. 62 Ž1987. 777. w19x J.R. Conrad, J.L. Radtke, R.A. Dodd, F.J. Worzala, N.C. Tran, J. Appl. Phys. 62 Ž1987. 4591. w20x K. Baba, R. Hatada, Surf. Coat. Technol. 103r104 Ž1998. 235. w21x S. Kobayashi, K. Miyazaki, S. Nozaki, H. Morisaki, S. Fukui, S. Masaki, J. Vac. Sci. Technol. A14 Ž1996. 777.
w22x R.O. Dillon, J.A. Woollam, V. Katkanant, Phys. Rev. B29 Ž1984. 3482. w23x M. Ramsteiner, J. Wanger, Appl. Phys. Lett. 51 Ž1987. 1355. w24x D. Beeman, J. Silvermann, R. Lynds, M.R. Anderson, Phys. Rev. B 30 Ž1984. 87. w25x F. Tuinstra, J.L. Koenig, J. Chem. Phys. 53 Ž1940. 1126. w26x JEOL, Handbook of X-Ray Photoelectron Spectroscopy, Japan, 1991.
Preparation and properties of nitrogen and titanium oxide incorporated diamond-like carbon films by plasma source ion implantation Koumei BabaU , Ruriko Hatada Industrial Technology Center of Nagasaki, 2-1303-8 Ikeda, Omura, Nagasaki 856-0026, Japan
Abstract Nitrogen and titanium oxide incorporated diamond-like carbon ŽDLC. films were deposited by a plasma source ion implantation on silicon wafer and quartz glass. Pure acetylene gas was used as a working gas for plasma. Additional nitrogen and titanium tetraisopropoxide gases were fed into acetylene plasma to prepare nitrogen and titanium oxide incorporated DLC films. The plasma was generated by a radio frequency glow discharge. Ions were accelerated from the plasma by a high-voltage pulse Žy20 kV, 100 Hz, 50 s. applied directly to the substrates. The surface morphology was observed by a scanning electron microscope ŽSEM. and an atomic force microscope ŽAFM.. The compositional and structural characterization of the films was carried out using X-ray diffraction ŽXRD., X-ray photoelectron spectroscopy ŽXPS. and Raman spectroscopy. The hardness of the films was measured by an indentation method. The sheet resistivity of the films was measured by a four-point probe method. The results showed that all of the N incorporated and unincorporated films were amorphous and showed typical Raman spectra of DLC films. The XPS and the FT-IR spectra indicated the formation of C᎐N, C⫽N and C⬅N valence bonds. XPS measurement for titanium oxide incorporated films revealed the existence of Ti᎐C, Ti᎐O, C᎐C bonding in the DLC films. The hardness of the nitrogen and titanium oxide incorporated films decreased with the amount of incorporated species. The sheet resistivity of the films decreased abruptly with increasing nitrogen and titanium oxide contents in the films. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Plasma source ion implantation; Diamond-like carbon; Nitrogen; Titanium oxide; Resistivity; Hardness
1. Introduction Diamond-like carbon ŽDLC. films are a subject of considerable interest, due to their special properties such as high hardness, low friction, high wear resistance, and chemical inertness. Recently, there have been several attempts to improve the properties of DLC films by the addition of elements, such as silicon w1᎐3x, nitrogen w4᎐7x, fluorine w8᎐10x and various metals w11᎐14x. For example, an increase in water contact
U
Corresponding author. Tel.: q81-957-521133; fax: q81-957521136. E-mail address: [email protected] ŽK. Baba..
angle was observed for F and Si incorporated DLC films w8x. Nitrogen or metal element in DLC films has been shown to reduce the inner stress, electrical resistivity and friction coefficients w15,16x. Plasma source ion implantation ŽPSII. has attracted attention as an alternative ion implantation method w17᎐19x. This method has several advantages over conventional ion implantation, such as low cost, large area, multi-target and non-line-of-sight process. In this paper, we have reported some properties of nitrogen or titanium oxide incorporated DLC films prepared by PSII. In PSII, samples were placed in a gas mixture of acetylene and nitrogen or titanium tetraisopropoxide plasma created by radio frequency ŽRF. discharge, and a pulsed high negative bias voltage was
0257-8972r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 7 - 8 9 7 2 Ž 0 0 . 0 1 0 5 4 - 9
K. Baba, R. Hatada r Surface and Coatings Technology 136 (2001) 192᎐196
193
applied to the samples. All samples were subsequently characterized by scanning electron microscopy ŽSEM., atomic force microscopy ŽAFM., X-ray photoelectron spectroscopy ŽXPS. and Raman spectroscopy. Hardness and electrical resistivity were measured and related to the composition of the films.
2. Experimental 2.1. Film deposition The plasma source ion implantation apparatus used in this study is described in detail elsewhere w20x. Fused silica glass plates and silicon wafers Ž100. were used as substrates. The substrates were mounted on a holder and placed in the PSII chamber. Acetylene gas was introduced into the chamber at a constant flow rate to deposit DLC films. Nitrogen gas was introduced into the chamber to deposit nitrogen incorporated DLC films. Titanium tetraisopropoxide ŽTTIP. was vaporized by heating and introduced into the chamber without carrier gas at a pressure of 0.8᎐1.3 Pa. Through a matching network, 50 W r.f. power was supplied to the antenna at 13.56 MHz. A negative voltage pulse of 20 kV was applied to the sample holder at pulse duration of 50 s with a pulse repetition rate of 100 Hz. 2.2. Characterization of films The surface morphology was observed by using field emission scanning electron microscopy ŽSEM. and atomic force microscopy ŽAFM.. The chemical composition and chemical state of the films were evaluated using X-ray photoelectron spectroscopy ŽXPS.. Structural information of the films was obtained by a microRaman spectrometer at an excitation wavelength of 514 nm. The film thickness was estimated by a crosssectional SEM observation. The hardness measurements of the films were performed using an indentation method ŽHysitron Picoindenter TM . with the maximum force of 100 N. Measurement of the electrical resistivity of the films deposited on glass plate substrates was performed using a four-point probe station Ž1.0 mm probe spacing, 1.96 N load and 40 m radius tip..
Fig. 1. Dependence of deposition rate of the films and actual nitrogen concentration in the films on nitrogen fraction in the feed gas mixture during deposition.
the nitrogen gas fraction in the feed gas mixture. The deposition rate decreased with increasing nitrogen gas fraction. This decrease in the deposition rate seems to be the direct result of dilution of the hydrocarbon vapor in the reactant gas mixture. The composition of the films was measured by XPS and shown in Fig. 1 as a function of the nitrogen fraction. The nitrogen content incorporated in the films increased with N2 fraction in the feed gas, but it seems to reach maximum value at approximately 10 at.%. The XPS N1s and C1s spectra of 5.5 at.% nitrogen incorporated film are shown in Fig. 2. The N1s spectrum can be deconvoluted into three peaks at 398.6, 400.2 and 402.9 eV. The first and second peaks of N1s can be attributed to N᎐C, N⬅C and N⫽C bonds, respectively w4x. And the peak at 402.9 eV can be assigned to N᎐O or N᎐N bonds w21x. Similarly the C1s spectrum can be deconvoluted into three peaks at 284.5, 285.9 and 288.0 eV. The first peak at 284.5 eV can be attributed to graphitic or hydrogenated C᎐C bonding. The second peak at 285.9 eV is consistent with two binding states of C⫽N Ž285.3 eV. and C⬅N Ž286.7 eV. bonds. And the third peak at 288.0 eV is assigned to the C᎐N bond w4x. A Raman spectrum obtained from a 5.5-at.% nitrogen incorporated film is shown in Fig. 3. A broad peak between 1000 cmy1 and 1800 cmy1 indicates that the
3. Results and discussion 3.1. C᎐N films X-Ray diffraction measurements showed that all the films have an amorphous structure. The deposited films were black in color. The film deposition rate of C᎐N films estimated from cross-sectional SEM observation and deposition time is shown in Fig. 1 as a function of
Fig. 2. C1s and N1s XPS spectra of 5.5 at.% nitrogen incorporated film.
194
K. Baba, R. Hatada r Surface and Coatings Technology 136 (2001) 192᎐196
Fig. 3. Raman spectrum of 5.5 at.% nitrogen incorporated DLC film. The spectrum includes the G- and D-line Gaussian fits for the major 1561 cmy1 shift and the minor 1387 cmy1 shift, respectively.
film structure is amorphous. The broad peak in Fig. 3 can be resolved into two Gaussian profiles centered at 1387 cmy1 corresponding to the D-line assigned to disordered structure, and at 1561 cmy1 , corresponding to the G-line assigned to graphite structure w22,23x. The integrated intensity ratio Ž I D rIG . of each profile has been correlated with sp 3rsp 2 bonding ratio and the graphitic particle size w24,25x. Fig. 4 shows the I D rIG ratio changes with nitrogen content in the films. It is clearly seen that I D rIG ratios increase with nitrogen content. This result indicates that the graphite structure is destroyed or that the graphite particle size decreases with the increase in nitrogen content in the films. These structural changes are explained as the substitution of nitrogen atoms for carbon or hydrogen atoms and the bombardment by nitrogen ions which destroy the graphitic crystal structure in the film at high nitrogen fraction. There was no dependence of the position of D-line and G-line on nitrogen content. Fig. 5 shows the hardness of the films measured by a nano-indentation method. The highest hardness was derived for the nitrogen free film, and decreased gradually when increasing nitrogen content. This result is explained by the increase in the number of C⬅N bonds which terminate the carbon backbone leading to less tightly bound C atoms. Electrical resistivity of the films is shown in Fig. 5 as a function of nitrogen content in the films. The resistiv-
Fig. 4. The ratio of the integrated areas of the Raman D- and G-lines Ž I D rIG . as a function of nitrogen content in the films.
Fig. 5. Dependence of hardness of the films and resistivity of the films on the nitrogen content in the films.
ity of 8 at.% nitrogen incorporated film was out of the range of the instrument. It was found that nitrogen incorporation into the DLC films is effective for the reduction in the resistivity, and, at 5.5 at.% nitrogen, the resistivity is decreased by a factor of 30 as compared to the nitrogen-free film. SEM observation showed that the surface of all the films were smooth and featureless. Fig. 6 presents an AFM image obtained from 5.5 at.% nitrogen incorporated DLC film as an example. The average roughness ŽR a . 0.23 nm values were calculated from 1 = 1 m2 scan. This R a value is a little higher than the nitrogen free film whose value was 0.17 nm. 3.2. C᎐Ti᎐O films Titanium and oxygen incorporated DLC films were prepared by use of several mixtures of acetylene and TTIP gases for a plasma. The composition and chemical states of the films were estimated by XPS. Fig. 7 shows the XPS C1s, O1s and Ti2p spectra of the film deposited at a TTIP partial pressure of 65%. The C1s spectrum can be deconvoluted into two peaks at 282.1 and 284.2 eV. The first peak and the second one are attributed to Ti᎐C and C᎐C bonds, respectively. The
Fig. 6. AFM micrograph of 5.5 at.% nitrogen incorporated DLC film. The average roughness ŽR a . is 0.23 nm.
K. Baba, R. Hatada r Surface and Coatings Technology 136 (2001) 192᎐196
195
Fig. 7. O1s and Ti2p XPS spectra of the titanium oxide incorporated film deposited at partial pressure of 65%.
O1s peak position is 530.8 eV and can be assigned to Ti᎐O bond. A very broad peak was observed for the Ti2p spectrum and assigned to Ti᎐C Ž454.4 eV., Ti᎐O Ž455.1 eV., Ti 2 O 3 Ž457.8 eV. and TiO 2 Ž458.8 eV. w26x. The film composition, the hardness and the resistivity are summarized in Table 1 as a function of the TTIP partial pressure in the reactive plasma. The titanium and oxygen contents increased similarly with increasing TTIP partial pressure, and the composition of the film deposited in a pure TTIP atmosphere was CrTirOs 25:35:40 at.%. It is clearly found that the hardness and the resistivity were influenced significantly by TTIP partial pressure. The electrical resistivity of the film deposited at the TTIP partial pressure of 65% is very low, but the hardness decreased by approximately onethird compared to the undoped DLC film.
3. the nitrogen incorporated in the films was predominantly C⬅N and C⫽N bonding states; 4. the integrated intensity ratio I D rIG of Gaussian profiles increased with the nitrogen content; 5. the hardness of the films decreased gradually with increasing the nitrogen content ᎏ the electrical resistivity of the films decreased significantly with increasing the nitrogen content; and 6. the hardness of the films prepared from acetylene and TTIP mixture decreased with increasing the titanium and oxygen contents.
Acknowledgements The authors would like to thank Mr K. Okamura and Mr O. Nakano from Nippon Tungsten Co. Ltd. for the electrical resistivity measurement.
4. Conclusions The nitrogen and titanium oxide incorporated DLC films were prepared from mixture of acetylene and nitrogen gases or TTIP gases using PSII. The surface morphology and film thickness were observed by SEM and AFM. The most important results can be summarized as follows: 1. the deposition rate decreased when increasing the nitrogen fraction in the feed gas mixture; 2. very smooth surface was obtained for the nitrogen incorporated DLC films; Table 1 Composition, hardness and resistivity of the Ti and O incorporated DLC films TTIP partial pressure Ž%.
Composition ŽCrTirO, at.%.
Hardness ŽGPa.
Resistivity Ž ⍀ cm.
0 10 49 65 100
100:0:0 95:2:3 84:8:8 39:28:33 25:35:40
17.3 15.0 12.7 6.2 4.8
1.81= 103 2.01= 103 7.52= 103 5.72 2.32
References w1x A.A. Ogwu, R.W. Lamberton, S. Morley, P. Maguire, J. McLaughlin, Physica B 269 Ž1999. 335. w2x S.S. Camargo Jr., R.A. Santos, A.L. Baia Neto, R. Carius, F. Finger, Thin Solid Films 332 Ž1998. 130. w3x K.R. Lee, M.G. Kim, S.J. Cho, K.Y. Eun, T.Y. Seong, Thin Solid Films 308-309 Ž1997. 263. w4x S. Bhattacharyya, C. Cardinaud, G. Turban, J. Appl. Phys. 83 Ž1998. 4491. w5x F.L. Freire Jr., D.F. Franceschini, Thin Solid Films. 293 Ž1997. 236. w6x A. Bousetta, M. Lu, A. Bensaoula, J. Vac. Sci. Technol. A13 Ž1995. 1639. w7x J. Schwan, V. Batori, S. Ulrich, H. Ehrhardt, S.R.P. Silva, J. Appl. Phys. 84 Ž1998. 2071. w8x S. Miyake, R. Kaneko, Y. Kikuya, I. Sugimoto, J. Tribol. 113 Ž1991. 384. w9x J. Seth, S.V. Babu, Thin Solid Films 230 Ž1993. 90. w10x T.W. Mountsier, J.A. Samuels, Thin Solid Films 332 Ž1998. 362. w11x C.P. Klages, R. Memming, Mater. Sci. Forum 52-53 Ž1989. 609. w12x M. Wang, K. Schmidt, K. Reichelt, H. Dimigen, Hubsch, J. Mater. Res. 7 Ž1992. 667. w13x M. Grischke, K. Bewilogua, H. Dimigen, Mater. Manuf. Processes 8 Ž1993. 407. w14x W.J. Meng, B.A. Gillispie, J. Appl. Phys. 84 Ž1998. 4314.
196
K. Baba, R. Hatada r Surface and Coatings Technology 136 (2001) 192᎐196
w15x H. Dimigen, C.P. Klages, Surf. Coat. Technol. 49 Ž1991. 543. w16x D.P. Monaghan, D.G. Teer, P.A. Logan, I. Efeoglu, R.D. Arnell, Surf. Coat. Technol. 60 Ž1993. 525. w17x J.R. Conrad, T. Castagna, Bull. Am. Phys. Soc. 31 Ž1986. 1479. w18x J.R. Conrad, J. Appl. Phys. 62 Ž1987. 777. w19x J.R. Conrad, J.L. Radtke, R.A. Dodd, F.J. Worzala, N.C. Tran, J. Appl. Phys. 62 Ž1987. 4591. w20x K. Baba, R. Hatada, Surf. Coat. Technol. 103r104 Ž1998. 235. w21x S. Kobayashi, K. Miyazaki, S. Nozaki, H. Morisaki, S. Fukui, S. Masaki, J. Vac. Sci. Technol. A14 Ž1996. 777.
w22x R.O. Dillon, J.A. Woollam, V. Katkanant, Phys. Rev. B29 Ž1984. 3482. w23x M. Ramsteiner, J. Wanger, Appl. Phys. Lett. 51 Ž1987. 1355. w24x D. Beeman, J. Silvermann, R. Lynds, M.R. Anderson, Phys. Rev. B 30 Ž1984. 87. w25x F. Tuinstra, J.L. Koenig, J. Chem. Phys. 53 Ž1940. 1126. w26x JEOL, Handbook of X-Ray Photoelectron Spectroscopy, Japan, 1991.