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Annealing studies of TiN films deposited by plasma-assisted CVD
Surface and Coatings Technology 138 Ž2001. 237᎐241
Annealing studies of TiN films deposited by plasma-assisted CVD Zhao ChengU , Hong-rui Peng, Guang-wen Xie, Yu-long Shi Thin Films Laboratory, Qingdao Institute of Chemical Technology, 53 Zhengzhou Road, 266042 Qingdao, PR China Received 18 July 2000; received in revised form 27 October 2000; accepted 27 October 2000
Abstract Titanium nitride films prepared by plasma-assisted chemical vapor deposition ŽPACVD. on high speed steel were heated in the range of 1073᎐1373 K. The samples were analyzed by microhardness, XRD, EDX, SEM and XPS. It was found that the annealing temperatures had significant effects on the composition, microstructure and mechanical properties of the films. The chlorine content and lattice parameters of the films were reduced with the rise of the annealing temperature. The microhardness of the films had a minimal value at the annealing temperature of 1173 K. These results were interpreted in terms of the changes of microstructures of the PACVD TiN films. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Plasma-assisted CVD; TiN film; Annealing treatment
1. Introduction Hard films are widely used to improve the wear resistance of cutting tools and forming dies w1,2x. The mechanical properties of coated steels have a direct effect on the lifetime of cutting tools and dies, especially the hardness of the coated steel. Thus, it is necessary to maintain the high hardness of the coated steel after deposition in order to avoid the failure of the tool. The deposition temperature is an important parameter during film deposition. Each kind of vapor deposition technology has its minimal deposition temperature to ensure the film properties. However, for most hardened steels, the tempering temperature is below the minimal deposition temperature. The coated steel will soften if the deposition temperature is beyond the
U
Corresponding author. Tel.: q86-532-4022664; fax: q86-5324856613. E-mail address: [email protected] ŽZ. Cheng..
tempering temperature. Heat-treatment after deposition is another way to increase the hardness of the coated steel. Previous work has shown that the plasma assisted chemical vapor deposition ŽPACVD. TiN film did not peel off after heating at 1300 K and quenching in a vacuum heat-treatment furnace. It was found that the heat-treatment not only increased the hardness of coated steels, but also had significant effects on the microstructure of the film w3x. It was the aim of this work to study the effects of the annealing temperature on the microstructure, composition and mechanical properties of PACVD TiN films in order to improve the properties of both the coating and the underlying steel.
2. Experimental Fig. 1 is a schematic diagram of the DC-PACVD apparatus used for the experiments. The substrates used were high-speed M2 steel. The dimensions of the substrates were 15 = 10 = 3 mm. The deposition
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 1 3 8 - 5
Z. Cheng et al. r Surface and Coatings Technology 138 (2001) 237᎐241
238
3. Experimental results 3.1. Microhardness Fig. 2 shows the variation of the film microhardness with respect to the annealing temperature. It was found that there is a minimum value at the annealing temperature of 1173 K and a maximum value at the annealing temperature of 1313 K. 3.2. XRD analysis Fig. 1. Schematic diagram of the DC-PACVD apparatus.
parameters of the PACVD TiN films are listed in Table 1. Under these conditions the film thickness was 5 m. After deposition, the samples coated with the TiN film were put into a quartz tube with an auxiliary heater outside the tube. Before heating, the tube was alternately evacuated and flushed with high purity hydrogen several times. The annealing parameters were: hydrogen flow rate 80 mlrmin, the pressure 200 Pa, the annealing temperatures in the range of 1073᎐1373 K, keeping the temperature for 1 h and then cooling the substrates below 400 K under the hydrogen protection. After annealing treatments the color of the TiN films became pale purple because of the oxidation. However, the thickness of oxidation layer was only a few nanometers. Therefore, the annealing treatment of PACVDTiN films within the range of 1073᎐1373 K did not change the film thickness. The microhardness of the films was measured with a Vickers’ indentor at a load of 0.3 N. The crystalline structure was analyzed by X-ray diffraction ŽXRD. using Cu K ␣ radiation. The film’s composition was examined by energy-dispersive X-ray analysis ŽEDX.. The morphology and the cross-sectional structure of the films were investigated by scanning electron microscopy ŽSEM.. The chlorine state which remained in the films was determined by X-ray photoelectron spectroscopy ŽXPS.. Because of the contamination of the film surface after annealing treatments, the films were sputtered with 3 keV Arq for 5 min before XPS analysis.
The PACVD TiN films had a strong Ž200. preferred orientation w4x. After annealing, the Ž200. preferred orientation of the films became even more pronounced ŽFig. 3.. Fig. 3 also shows that the diffraction peak of Ž110.␣ -Fe is decreased after annealing, although the thickness of the films after annealing was the same as the as-deposited film. Fig. 4 shows the ratio of I Ž200. TiNrI Ž110.␣ -Fe of the films and the TiNŽ200. FWHM Žfull width of half maximum intensity . at different annealing temperatures. The results of XRD analyses indicated that the lattice parameters of the films decreased from 0.426 to 0.424 nm with increasing annealing temperature; the latter is the standard value for TiN from the ASTM Žthe American Society for Test Materials . card ŽFig. 5.. At the same time, the half-width of the Ž200. diffraction peaks also decreased with increasing annealing temperature Žsee Fig. 4.. 3.3. EDX analysis Fig. 6 shows the atomic ratio of Cl to Ti in the films at different annealing temperatures. It can be seen that the ratio decreased with increasing annealing temperature. Above 1173 K, the chlorine content in the annealed films was much lower than that of TiN films in the as-deposited state w4,5x. 3.4. SEM obser¨ ation Fig. 7 shows SEM fracture cross-sections of the films, both as-deposited and annealed at 1373 K. Comparing
Table 1 Deposition parameters Reactive gases Žpurity. Ratio of the feeding gases Discharge voltage Gas pressure Deposition temperature Deposition time
Hydrogen Ž99.999%., Nitrogen Ž99.999%., TiCl4 Ž99.9%. H2 rN2rTiCl4 s 2:1:0.4 1000 V ; 133 Pa 873 K 25 min
Z. Cheng et al. r Surface and Coatings Technology 138 (2001) 237᎐241
Fig. 2. Microhardness of PACVD TiN films vs. annealing temperature.
239
Fig. 4. The TiNŽ200.FWHM and the ratio of I Ž200. TiN rI Ž110.a-Fe at different annealing temperatures.
the micrographs, we found that the toughness and the adhesion strength of the PACVD TiN film could be
Fig. 5. The lattice parameters of PACVD TiN films vs. the annealing temperature.
improved after annealing. Some cracks in the film and on the interface between film and steel can also been seen from the cross-sectional scanning electron micrograph of TiN film before annealing ŽFig. 7a..
Fig. 3. XRD patterns of PACVD TiN films. Ža.: as-deposited; and Žb.: annealed at 1373 K.
Fig. 6. The ratio of Cl to Ti in PACVD TiN films vs. the annealing temperature.
Z. Cheng et al. r Surface and Coatings Technology 138 (2001) 237᎐241
240
Fig. 7. The SEM cross-section fracture of TiN films before and after annealing. Ža.: as-deposited; and Žb.: annealed at 1373 K.
3.5. XPS analysis
4.2. Chemical composition
The PACVD TiN films before and after annealing were analyzed by XPS in order to determine the state of chlorine atoms in the films. Table 2 indicates the binding energies of Cl 2p in TiN films, Cl and TiCl 4 .
4. Discussion 4.1. Microstructure The microstructure of PACVD TiN films undergoes some changes during annealing, which develop in a direction favorable to the improvement of the properties of PACVD films. The changes are briefly described below: 1. An improvement in the crystallinity of the film was observed with the rise of the annealing temperature. This was confirmed by the increase of the ratio of I Ž200. TiNrI Ž110.␣ -Fe and the decrease in the half-width of the Ž200. TiN of XRD peaks. The lattice perfection has a favorable effect on the wear resistance and corrosion resistance of PACVD films. 2. During annealing, the diffusion of atoms between the film and the substrate increased the adhesive strength and a layer of metallurgical combination could be formed on the interface, which can be found in CVD films.
Metal chlorides are often used as precursors in the PACVD process. A little amount of chlorine always remains in the films. The chlorine content in PACVD films depends on the deposition temperature w6x. In our previous work w7x, we found that the chlorine content in the PACVD TiN films decreased to a low level when the deposition temperature was beyond a critical temperature Žapprox. 873 K.. The chlorine content was almost unaffected by deposition temperatures below 1173 K, which is close to the deposition temperature of the CVD process. It is difficult to understand the state of chlorine in the film because the chlorine contents are very low. According to the analyses of XRD and XPS, we can infer that the chlorine atoms are incorporated in the TiN crystal lattice. The structure of TiN is NaCl-type. The ion radii of nitrogen and chlorine are 0.171 and 0.182 nm, respectively. If chlorine atoms are substituted for nitrogen atoms in the TiN crystal lattice, the interstitial incorporation of chlorine in the lattice in tetrahedral positions should result in an expansion of the lattice. Therefore, the lattice parameter of PACVD TiN films were larger than that of the CVD-TiN or PVD-TiN films w4x. The changes of the TiN lattice cause crystal distortion and, thus, an increase in distortion energy. The additional energy makes the TiN crystal lattice exist in a metastable state. When the PACVD TiN film is heated and the temperature is beyond a critical temperature, the chlorine atoms may be moved out of
Table 2 Binding energies of Cl 2p Peak ŽeV.
TiN As deposited
TiN Annealing at 1373 K
Cl Standard peak
TiCl4 Standard peak
Cl2p
199.2
199.42
199.9
198.2
Z. Cheng et al. r Surface and Coatings Technology 138 (2001) 237᎐241
their original position and be replaced by nitrogen atoms. The process reduces the distortion energy of the TiN crystal lattice. The lattice constant of the PACVD TiN film then reaches the ASTM standard value of TiN Ž0.424 nm.. Experimental results showed that the transformation temperature is approximately 1273 K. 4.3. Microhardness Internal stresses generated by thermal stress and the high density of defects, such as dislocations and vacancies, are generally found in films deposited from the vapor phase under the non-equilibrium condition of low temperature w8x. Thus, the hardness of these films is significantly influenced by the particular microstructure obtained during their growth. If the film is heated, the stresses in the film decrease and the hardness of the film changes simultaneously. Sanders and Verspui w9x investigated the effect of annealing temperatures on the microhardness of PVD-TiN films in the range of 773᎐1173 K. He found that the microhardness of the films decreased with the rising annealing temperature because of the decrease of the stress and strain in the films. A similar phenomenon also occurred in the PACVD TiN films if the annealing temperature was below 1173 K, because the films also grew under the non-equilibrium conditions of low deposition temperature. Compressive stresses of approximately 6 GPa were found in the film w10x. However, if the annealing temperature was beyond 1173 K, the film microhardness began to increase with the rising annealing temperatures until approximately 1313 K, which is as high as the deposition temperature of CVD-TiN films. At this temperature, the microhardness of PACVD TiN films can be close to the microhardness of CVD-TiN film w11x, which is prepared under the equilibrium conditions of high deposition temperature. In other words, when PACVD TiN films are heated, the microstructure of the films would change from the microstructure like that of the PVD-TiN films to the microstructure like that of the CVD-TiN films. In the changing process, there is a minimal microhardness of the PACVD TiN films at 1173 K.
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5. Conclusion When PACVD TiN films were heated and then cooled in hydrogen, the following changes of the film were observed: 1. The microstructure of PACVD TiN films undergoes some significant changes during annealing treatment and these changes are favorable for the improvement of properties, such as wear resistance, corrosion resistance and adhesive strength of the films. 2. The chlorine content in PACVD TiN films can be reduced to a very low level when the annealing temperature is beyond 1273 K. At the same time, the lattice constant of the PACVD TiN films can be reinstated to the ASTM standard value of TiN. 3. There was a minimal microhardness of the PACVD TiN films annealed at approximately 1173 K due to the changes of residual stress, strain and microstructure in the films. Beyond 1173 K, the film microhardness increased with the rising of the annealing temperatures until the microhardness was close to the microhardness of the CVD-TiN film. The increase in microhardness was caused mainly by an improvement of crystallinity in the films.
References w1x J.-E. Sundgren, Thin Solid Films 128 Ž1985. 21. w2x S. Li, Z. Cheng, X. Xu et al., Surf. Coat. Technol. 43r44 Ž1990. 1007. w3x Z. Cheng, to be published w4x S. Li, W. Huang, H. Yang, Z. Wang, Plasma Chem. Plasma Process 4 Ž1984. 148. w5x K.S. Mogensen, N.B. Thomsen, S.S. Eskildsen, C. Mathiasen, J. Bottiger, Surf. Coat. Technol. 99 Ž1998. 140. w6x T. Arai, H. Fujita, K. Orguri, Thin Solid Films 165 Ž1988. 139. w7x Z. Cheng, H. Peng, Y. Xie, S. Li, Heat Treatment ŽTaiwan. 55 Ž1997. 55 in Chinese. w8x D.S. Rickerby, J. Vac. Technol. A4 Ž6. Ž1986. 2809. w9x F.H.M. Sanders, G. Verspui, Thin Solid Films 161 Ž1988. L87. w10x J. Chen, K. Xu, R. Gao, J. He, Z. Cheng, S. Li, Vacuum Sci. Technol. 4 Ž12. Ž1992. 309 Žin Chinese.. w11x F.V. Bernus, H. Freller, K.G. Gunther, Thin Solid Films 50 Ž1978. 39.
Annealing studies of TiN films deposited by plasma-assisted CVD Zhao ChengU , Hong-rui Peng, Guang-wen Xie, Yu-long Shi Thin Films Laboratory, Qingdao Institute of Chemical Technology, 53 Zhengzhou Road, 266042 Qingdao, PR China Received 18 July 2000; received in revised form 27 October 2000; accepted 27 October 2000
Abstract Titanium nitride films prepared by plasma-assisted chemical vapor deposition ŽPACVD. on high speed steel were heated in the range of 1073᎐1373 K. The samples were analyzed by microhardness, XRD, EDX, SEM and XPS. It was found that the annealing temperatures had significant effects on the composition, microstructure and mechanical properties of the films. The chlorine content and lattice parameters of the films were reduced with the rise of the annealing temperature. The microhardness of the films had a minimal value at the annealing temperature of 1173 K. These results were interpreted in terms of the changes of microstructures of the PACVD TiN films. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Plasma-assisted CVD; TiN film; Annealing treatment
1. Introduction Hard films are widely used to improve the wear resistance of cutting tools and forming dies w1,2x. The mechanical properties of coated steels have a direct effect on the lifetime of cutting tools and dies, especially the hardness of the coated steel. Thus, it is necessary to maintain the high hardness of the coated steel after deposition in order to avoid the failure of the tool. The deposition temperature is an important parameter during film deposition. Each kind of vapor deposition technology has its minimal deposition temperature to ensure the film properties. However, for most hardened steels, the tempering temperature is below the minimal deposition temperature. The coated steel will soften if the deposition temperature is beyond the
U
Corresponding author. Tel.: q86-532-4022664; fax: q86-5324856613. E-mail address: [email protected] ŽZ. Cheng..
tempering temperature. Heat-treatment after deposition is another way to increase the hardness of the coated steel. Previous work has shown that the plasma assisted chemical vapor deposition ŽPACVD. TiN film did not peel off after heating at 1300 K and quenching in a vacuum heat-treatment furnace. It was found that the heat-treatment not only increased the hardness of coated steels, but also had significant effects on the microstructure of the film w3x. It was the aim of this work to study the effects of the annealing temperature on the microstructure, composition and mechanical properties of PACVD TiN films in order to improve the properties of both the coating and the underlying steel.
2. Experimental Fig. 1 is a schematic diagram of the DC-PACVD apparatus used for the experiments. The substrates used were high-speed M2 steel. The dimensions of the substrates were 15 = 10 = 3 mm. The deposition
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 1 3 8 - 5
Z. Cheng et al. r Surface and Coatings Technology 138 (2001) 237᎐241
238
3. Experimental results 3.1. Microhardness Fig. 2 shows the variation of the film microhardness with respect to the annealing temperature. It was found that there is a minimum value at the annealing temperature of 1173 K and a maximum value at the annealing temperature of 1313 K. 3.2. XRD analysis Fig. 1. Schematic diagram of the DC-PACVD apparatus.
parameters of the PACVD TiN films are listed in Table 1. Under these conditions the film thickness was 5 m. After deposition, the samples coated with the TiN film were put into a quartz tube with an auxiliary heater outside the tube. Before heating, the tube was alternately evacuated and flushed with high purity hydrogen several times. The annealing parameters were: hydrogen flow rate 80 mlrmin, the pressure 200 Pa, the annealing temperatures in the range of 1073᎐1373 K, keeping the temperature for 1 h and then cooling the substrates below 400 K under the hydrogen protection. After annealing treatments the color of the TiN films became pale purple because of the oxidation. However, the thickness of oxidation layer was only a few nanometers. Therefore, the annealing treatment of PACVDTiN films within the range of 1073᎐1373 K did not change the film thickness. The microhardness of the films was measured with a Vickers’ indentor at a load of 0.3 N. The crystalline structure was analyzed by X-ray diffraction ŽXRD. using Cu K ␣ radiation. The film’s composition was examined by energy-dispersive X-ray analysis ŽEDX.. The morphology and the cross-sectional structure of the films were investigated by scanning electron microscopy ŽSEM.. The chlorine state which remained in the films was determined by X-ray photoelectron spectroscopy ŽXPS.. Because of the contamination of the film surface after annealing treatments, the films were sputtered with 3 keV Arq for 5 min before XPS analysis.
The PACVD TiN films had a strong Ž200. preferred orientation w4x. After annealing, the Ž200. preferred orientation of the films became even more pronounced ŽFig. 3.. Fig. 3 also shows that the diffraction peak of Ž110.␣ -Fe is decreased after annealing, although the thickness of the films after annealing was the same as the as-deposited film. Fig. 4 shows the ratio of I Ž200. TiNrI Ž110.␣ -Fe of the films and the TiNŽ200. FWHM Žfull width of half maximum intensity . at different annealing temperatures. The results of XRD analyses indicated that the lattice parameters of the films decreased from 0.426 to 0.424 nm with increasing annealing temperature; the latter is the standard value for TiN from the ASTM Žthe American Society for Test Materials . card ŽFig. 5.. At the same time, the half-width of the Ž200. diffraction peaks also decreased with increasing annealing temperature Žsee Fig. 4.. 3.3. EDX analysis Fig. 6 shows the atomic ratio of Cl to Ti in the films at different annealing temperatures. It can be seen that the ratio decreased with increasing annealing temperature. Above 1173 K, the chlorine content in the annealed films was much lower than that of TiN films in the as-deposited state w4,5x. 3.4. SEM obser¨ ation Fig. 7 shows SEM fracture cross-sections of the films, both as-deposited and annealed at 1373 K. Comparing
Table 1 Deposition parameters Reactive gases Žpurity. Ratio of the feeding gases Discharge voltage Gas pressure Deposition temperature Deposition time
Hydrogen Ž99.999%., Nitrogen Ž99.999%., TiCl4 Ž99.9%. H2 rN2rTiCl4 s 2:1:0.4 1000 V ; 133 Pa 873 K 25 min
Z. Cheng et al. r Surface and Coatings Technology 138 (2001) 237᎐241
Fig. 2. Microhardness of PACVD TiN films vs. annealing temperature.
239
Fig. 4. The TiNŽ200.FWHM and the ratio of I Ž200. TiN rI Ž110.a-Fe at different annealing temperatures.
the micrographs, we found that the toughness and the adhesion strength of the PACVD TiN film could be
Fig. 5. The lattice parameters of PACVD TiN films vs. the annealing temperature.
improved after annealing. Some cracks in the film and on the interface between film and steel can also been seen from the cross-sectional scanning electron micrograph of TiN film before annealing ŽFig. 7a..
Fig. 3. XRD patterns of PACVD TiN films. Ža.: as-deposited; and Žb.: annealed at 1373 K.
Fig. 6. The ratio of Cl to Ti in PACVD TiN films vs. the annealing temperature.
Z. Cheng et al. r Surface and Coatings Technology 138 (2001) 237᎐241
240
Fig. 7. The SEM cross-section fracture of TiN films before and after annealing. Ža.: as-deposited; and Žb.: annealed at 1373 K.
3.5. XPS analysis
4.2. Chemical composition
The PACVD TiN films before and after annealing were analyzed by XPS in order to determine the state of chlorine atoms in the films. Table 2 indicates the binding energies of Cl 2p in TiN films, Cl and TiCl 4 .
4. Discussion 4.1. Microstructure The microstructure of PACVD TiN films undergoes some changes during annealing, which develop in a direction favorable to the improvement of the properties of PACVD films. The changes are briefly described below: 1. An improvement in the crystallinity of the film was observed with the rise of the annealing temperature. This was confirmed by the increase of the ratio of I Ž200. TiNrI Ž110.␣ -Fe and the decrease in the half-width of the Ž200. TiN of XRD peaks. The lattice perfection has a favorable effect on the wear resistance and corrosion resistance of PACVD films. 2. During annealing, the diffusion of atoms between the film and the substrate increased the adhesive strength and a layer of metallurgical combination could be formed on the interface, which can be found in CVD films.
Metal chlorides are often used as precursors in the PACVD process. A little amount of chlorine always remains in the films. The chlorine content in PACVD films depends on the deposition temperature w6x. In our previous work w7x, we found that the chlorine content in the PACVD TiN films decreased to a low level when the deposition temperature was beyond a critical temperature Žapprox. 873 K.. The chlorine content was almost unaffected by deposition temperatures below 1173 K, which is close to the deposition temperature of the CVD process. It is difficult to understand the state of chlorine in the film because the chlorine contents are very low. According to the analyses of XRD and XPS, we can infer that the chlorine atoms are incorporated in the TiN crystal lattice. The structure of TiN is NaCl-type. The ion radii of nitrogen and chlorine are 0.171 and 0.182 nm, respectively. If chlorine atoms are substituted for nitrogen atoms in the TiN crystal lattice, the interstitial incorporation of chlorine in the lattice in tetrahedral positions should result in an expansion of the lattice. Therefore, the lattice parameter of PACVD TiN films were larger than that of the CVD-TiN or PVD-TiN films w4x. The changes of the TiN lattice cause crystal distortion and, thus, an increase in distortion energy. The additional energy makes the TiN crystal lattice exist in a metastable state. When the PACVD TiN film is heated and the temperature is beyond a critical temperature, the chlorine atoms may be moved out of
Table 2 Binding energies of Cl 2p Peak ŽeV.
TiN As deposited
TiN Annealing at 1373 K
Cl Standard peak
TiCl4 Standard peak
Cl2p
199.2
199.42
199.9
198.2
Z. Cheng et al. r Surface and Coatings Technology 138 (2001) 237᎐241
their original position and be replaced by nitrogen atoms. The process reduces the distortion energy of the TiN crystal lattice. The lattice constant of the PACVD TiN film then reaches the ASTM standard value of TiN Ž0.424 nm.. Experimental results showed that the transformation temperature is approximately 1273 K. 4.3. Microhardness Internal stresses generated by thermal stress and the high density of defects, such as dislocations and vacancies, are generally found in films deposited from the vapor phase under the non-equilibrium condition of low temperature w8x. Thus, the hardness of these films is significantly influenced by the particular microstructure obtained during their growth. If the film is heated, the stresses in the film decrease and the hardness of the film changes simultaneously. Sanders and Verspui w9x investigated the effect of annealing temperatures on the microhardness of PVD-TiN films in the range of 773᎐1173 K. He found that the microhardness of the films decreased with the rising annealing temperature because of the decrease of the stress and strain in the films. A similar phenomenon also occurred in the PACVD TiN films if the annealing temperature was below 1173 K, because the films also grew under the non-equilibrium conditions of low deposition temperature. Compressive stresses of approximately 6 GPa were found in the film w10x. However, if the annealing temperature was beyond 1173 K, the film microhardness began to increase with the rising annealing temperatures until approximately 1313 K, which is as high as the deposition temperature of CVD-TiN films. At this temperature, the microhardness of PACVD TiN films can be close to the microhardness of CVD-TiN film w11x, which is prepared under the equilibrium conditions of high deposition temperature. In other words, when PACVD TiN films are heated, the microstructure of the films would change from the microstructure like that of the PVD-TiN films to the microstructure like that of the CVD-TiN films. In the changing process, there is a minimal microhardness of the PACVD TiN films at 1173 K.
241
5. Conclusion When PACVD TiN films were heated and then cooled in hydrogen, the following changes of the film were observed: 1. The microstructure of PACVD TiN films undergoes some significant changes during annealing treatment and these changes are favorable for the improvement of properties, such as wear resistance, corrosion resistance and adhesive strength of the films. 2. The chlorine content in PACVD TiN films can be reduced to a very low level when the annealing temperature is beyond 1273 K. At the same time, the lattice constant of the PACVD TiN films can be reinstated to the ASTM standard value of TiN. 3. There was a minimal microhardness of the PACVD TiN films annealed at approximately 1173 K due to the changes of residual stress, strain and microstructure in the films. Beyond 1173 K, the film microhardness increased with the rising of the annealing temperatures until the microhardness was close to the microhardness of the CVD-TiN film. The increase in microhardness was caused mainly by an improvement of crystallinity in the films.
References w1x J.-E. Sundgren, Thin Solid Films 128 Ž1985. 21. w2x S. Li, Z. Cheng, X. Xu et al., Surf. Coat. Technol. 43r44 Ž1990. 1007. w3x Z. Cheng, to be published w4x S. Li, W. Huang, H. Yang, Z. Wang, Plasma Chem. Plasma Process 4 Ž1984. 148. w5x K.S. Mogensen, N.B. Thomsen, S.S. Eskildsen, C. Mathiasen, J. Bottiger, Surf. Coat. Technol. 99 Ž1998. 140. w6x T. Arai, H. Fujita, K. Orguri, Thin Solid Films 165 Ž1988. 139. w7x Z. Cheng, H. Peng, Y. Xie, S. Li, Heat Treatment ŽTaiwan. 55 Ž1997. 55 in Chinese. w8x D.S. Rickerby, J. Vac. Technol. A4 Ž6. Ž1986. 2809. w9x F.H.M. Sanders, G. Verspui, Thin Solid Films 161 Ž1988. L87. w10x J. Chen, K. Xu, R. Gao, J. He, Z. Cheng, S. Li, Vacuum Sci. Technol. 4 Ž12. Ž1992. 309 Žin Chinese.. w11x F.V. Bernus, H. Freller, K.G. Gunther, Thin Solid Films 50 Ž1978. 39.