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Synthesis of pseudobinary Cr-Al-N films with B1 structure by rf-assisted magnetron sputtering method
SURfACE
&CIIAlINIiS
ELSEVIER
Surface and Coatings Technology 98 (1998) 1008-1012
HGHNOLDGY
Synthesis of pseudobinary Cr-AI-N films with Bl structure by rf-assisted magnetron sputtering method Y. Makino *, K. Nogi Joining and We/ding Research Institute. Osaka University. 11-1. Mihogaoka. Ibaraki. Osaka 567. Japan
Abstract Pseudobinary Cr-AI-N films were synthesized by a new inductively combined rf-plasma assisted magnetron sputtering method.
It was found that phase transition from BI (NaCI) structure to B4 (wurtzite) structure occurs at an AIN content between 70 mol%
and 80 mol%, and the critical composition for the phase transition showed excellent agreement with the composition (77 mol% AIN) predicted by two band parameters. It was found that the aging effect is observed in the pseudobinary nitride films synthesized by the new magnetron sputtering method. No preferred orientation was observed in as-deposited pseudobinary nitride films with BI structure, while preferred orientation appeared in these films after aging at room temperature for six months. © 1998 Elsevier Science S.A.
1. Introduction Multicomponent nitride films based on titanium nit• ride have been widely produced for the various protec• tive coatings such as corrosion- and oxidation-barriers [1-4]. For example, it is believed that the AIN addition to TiN is effective for the improvement of the intrinsic properties of TiN by the formation of aluminum oxide [5,6]. However, further improvement of these films is not expected in higher temperature usages. Insufficient improvement of the intrinsic properties of TiN by AIN addition is probably related to the formation of coexist• ence of titanium dioxide [7] and/or aluminum titanate in which fairly fast diffusion of oxygen in these oxide films can not fully be suppressed. Comparing with these titanium oxides, more effective suppression for oxygen diffusion is expected by the formation of chromium sesquioxide and fortunately, according to our previous result [8], it is predicted that CrN shows the highest solubility for AIN among the transition nitrides with BI structure. Thus, Cr-AI-N film is one of the most promis• ing pseudobinary nitrides for the protective coatings on account of the formation of both aluminum and chro• mium sequioxides which are much more effective for the suppression of oxygen diffusion. In the present study, synthesis of a new pseudobinary Cr-AI-N film was tried by a new rf-assisted magnetron sputtering method, and the experimentally determined
* Corresponding author. 0257-8972/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PI! S0257-8972(97)00391_5
composition for the BI/B4 phase transition in the pseu• dobinary nitride was compared with the critical composi• tion for the BI/B4 transition predicted by the band parameters [8]. Further, the results in the present study were compared with those in the companion paper [9], in which the same Cr-AI-N films were synthesized using the planar-type magnetron sputtering method. 2. Experimental procedures Cr-AI-N films were synthesized in the mixed atmo• sphere of nitrogen and argon using the reactive sputter• ing method. An inductively combined rf-plasma assisted magnetron sputtering apparatus (MPS-200-HC3, ULVAC Co.) with dual targets was operated under a vacuum condition between 6 x 10 - 2 Pa and 1.5 x 10 -1 Pa. In the rf-assisted magnetron sputtering apparatus, both Al and Cr atoms can be simultaneously deposited on the substrate using the respective targets. The details of the experimental conditions are given in Table I. The compositions of the pseudobinary films were controlled by changing the ratio of rf-power for Cr cathode to that for Al cathode. The conditions of the rf-powers were determined from the experimental data on the same pseudobinary nitride films by the planar-type magnetron sputtering method in the com• panion paper [9], referring to the deposition rates for respective single nitrides by the rf-plasma assisted mag• netron sputtering method. The film composition was
Y. Makino. K. Nogi / Surface and Coatmgs Technology 98 ( 1998) 1008-1012 Table I Experimental conditions Apparatus Purities of targets Target size Substrate temperature Purities of gases RF power of cathode RF power of coil Gas pressure Gas flow Film thickness
MPS-2000-HC3 (ULVAC Japan Ltd) Cr 99.99% AI 99.99% 51mm Room temperature for unitary nitrides 573 K for pseudobinary nitrides Ar 99.9999% N 2 99.9999% Cr 8h:l50 W, AI 150~200 W Cr 50 W, AI 25 W 0.9 ~ 1.5 x 10- 3 Torr Ar 9~ 18 sccm, N 2 5 secm -150 nm
briefly varied from 60 mol% AIN to 80 mol% AIN only for the purpose of proving the validity of the critical composition for the phase transition from Bl type to B4 type, which was predicted by the structure map and the band parameters [8]. The impurity concentrations in the reactive gases were suppressed to be less than 10 ppb at the exit of the gas purifiers. Crystalline phases of the deposited films were iden• tified by X-ray diffraction method using Cu K~ radiation, which were measured with the 0-20 method at the operating conditions of 50 kV and 200 mAo Reflectance spectra of the deposited films were measured by the ATR method in the range of 400 cm - 1 and 1500 cm - 1 using a spectrometer (Nicolet, Magna 760) for detecting the characteristic vibration due to the AI-N bond in the deposited films.
1009
domains of the compounds with Bl and B4 structures. Though the details are omitted here on account of the precise explanation for calculating the critical composi• tion (x) [8], the composition for the pseudobinary nitrides containing AIN can be calculated by the following equation:
x = [hnV(MN) (2. 78SMN - H MN )]/[!.nV(AIN) (HAIN - 2. 78SAIN) -!.nv(MN)(HMN -SMN)] where H MN , SMN andJ.nv(MN) are the hybrid fuction, gap reduction parameter and compositional factor of trans• ition metal nitride (MN), and H A1N , SAIN and finV(AIN) are those of AIN, respectively. The numerical value of 2.78 is the slope of the boundary line between Bl and B4 domains in the structural map [8]. The critical composition for the Bl/B4 phase transition in the Cr-AI-N psuedobinary system is calculated to be 77mol% AIN. X-ray diffraction patterns obtained from the Cr-AI-N films with various compositions are shown in Fig. I.
AIN/CrN=6/4
3. Results and discussion Before explaining the experimental results, we briefly explain the prediction method to calculate critical com• positions for Bl/B4 phase transition in the pseudobinary nitrides containing aluminum and transition metal. Detailed explanations were given in the companion paper [9] and elsewhere [8]. The critical composition for Bl/B4 phase transition for the above-described pseu• dobinary nitrides can be estimated by the two band parameters [hybrid function (H) and gap reduction parameter (S)] [10] and the crystal structure map for AB type compounds [II], which was constructed by these parameters and compositional factor (!.nv)' Roughly explaining, Hand S correspond to the ionic and covalent band gaps, respectively, which were defined by dielectric properties [12]. The compositional factor was defined on the basis of the regular solution model and valence electron numbers of constituent elements. Critical compositions for Bl/B4 phase transition in the pseudobinary nitrides formed from Bland B4 type nitrides are determined by the two band parameters of these single nitrides and the boundary line between the
AIN/CrN=8/2
20
40
60
80
100
120
28 (degree) Fig. I. X-ray diffraction patterns obtained from the as-<1eposited Cr-AI-N films synthesized by the inductively combined rf-plasma assisted magnetron sputtering method. [C:B I phase (NaCI), H:B4 phase (wurtzite»).
Y. Makino, K. Nogl! Surface and Coatings Technology 98 (1998) 1008-1012
1010
Atomic ratios between Cr and Al for deposited films were determined by the deposition rate of the respective atom. For the pseudobinary films deposited at the atomic ratio less than NA.lN cr = 7/3, the single phase with Bl structure was identified, while the single phase with B4 structure was detected for the pseudobinary nitride film at the atomic ratio of N All Ncr = 812. The lattice constants of the BI and B4 phases are shown in Fig. 2 together with the results obtained by the planar magnetron sputtering method [9]. The phase identifica• tion leads to the conclusion that the phase transition from Bl type to B4 type occurs at the composition of AIN between 70 mol% and 80 mol%. The conclusion shows quite good agreement with the prediction that Bl/B4 phase transition occurs at 77 mol% AIN in the pseudobinary nitride. Further, the conclusion also agrees with the experimental result by the planar-type magnet• ron sputtering method in the companion work [9], in which the phase transition occured between 67 mol% and 75 mol% AIN. Reflectance IR spectra of the deposited Cr-AI-N films are shown in Fig. 3. Three or four absorptions were observed near 950 cm -1, 770 cm -1, 560 cm - 1 and 665 cm -1, respectively. Comparing with the reflectance IR spectra obtained from substrate silica glass, the former three absorptions are assigned to the characteris• tic absorptions due to the Si-O bond in silica glass. The
j
i
/
~ AIN/CrN=8/2
!
\ \,
"• Deposition temprature, 573K As-deposited
1200
1000
800
600
400
r.=============::::;------, •
• 0.5
81 ph_(RF)
------ ... ------------.
B4 ph_(a axl.. RF)
i--_composition : .. -_ .. - .... ------ ... -.
I
B4 ph_I. axl.. RF)
" 0
8Iph_(MG)
CJ
B4 ph_(a axi.. MG)
A
84ph_(. axl.. MG)
: Predl.ted .rltI.al ~
I I
,l I I I
llit.~
"
81 typeAIN
8
0.4
I...-_ _........_ _---L
o
0.2
0.4
Fig. 3. Reflectance IR spectra of as-deposited Cr-AI-N films synthe• sized by the inductively combined rf-plasma assisted magnetron sput• tering method.
:
A
•
0.3
(\
!
1400 0.6
I
1~~
.L--_----"-'-_ _--'
0.6
0.8
Ratio of Al to total cations, RAJ
Fig. 2. Dependence of the lattice constants of BI and B4 phases in the as-deposited Cr-AI-N films upon the ratio of AI to total cations [RAJ· The data on the lattice constants are plotted in this figure together with the lattice constants obtained from the Cr-AI-N films which were produced by the planar-type magnetron sputtering method [9].
last IR absorption was only observed in the Cr-AI-N film with the atomic ratio of NA.lN cr = 8/2, correspond• ing to the AIN content of about 80 mol%. Because the characteristic absorption near 700 cm - 1 was also observed in the pure AIN film [13], it may be concluded that the absorption is attributed to the AI-N bond of wurtzite-type AIN. On the other hand, no characteristic IR absorption was observed from the deposited films with B1 structure. Thus, aluminum atoms in the B4 type pseudobinary nitride film are in a similar chemical state to those of wurtzite-type AIN as far as the crystalline state of the film is preserved to be in the wurztite (B4) structure irrespective of dissolution of CrN. By measuring XRD patterns and IR spectra of these films after six months, the aging effect at room temper• ature was found in the pseudobinary Cr-AI-N films. These results are shown in Figs. 4 and 5. Comparing with the XRD patterns obtained from the as-deposited films, strong preferred orientations in every aged film with Bl or 84 structure were observed, and their peak widths remarkably decreased in these films. The charac-
Y. Makino, K Nogi 1Surface and Coatings Technology 98 ( 1998) /008-/OI:Z
IOJl
After aged for six months
2
3 4
5 40
30
60
50
70
80
90
26 (degree) Fig, 4. X-ray diffraction patterns of the Cr-AI-N films which were aged for six months after being synthesized by the inductively combined rf-plasma assisted magnetron sputtering method. [CB I phase (NaCl). H:B4 phase (wurtzite). I:AIN. 2:AIN/CrN = 8/2. 3:AIN/CrN = 7/3. 4:AIN/CrN =6/4. 5:CrN].
Deposition temprature, 573K After aged
/
.........
/
I
'J
"
L
J AIN/CrN=6/4 After aged
-------'
/~
; /-----~
, /
/ \~/,/
, -./
AIN/CrN=7/3 After aged / _/
(
AIN/CrN=8/2 After aged
I--~/I /~ AtN/CrN=8/2 As-deposited
~
/ ;
\
J
/~A~ /~
V
;' /
4. Summary
"
i ':
I----~
\~
1400
1200
1000
800
600
teristic absorption observed near 660 cm -1 in the as-deposited film with AIN/CrN = 8/2 shifted to a lower wavenumber of about 620 cm -1 and a similar shift was also observed in the aged AIN film. Because the IR absorption spectrum of the as-deposited AIN film was unfortunately not measured in this study, the position of the characteristic absorption for the as-deposited AIN film is unclear. However, the satellite peak near 660 cm - 1 in the aged AIN film is probably attributed to the AIN lattice without any influence of aging effect and the position of the satellite peak agrees with the position of the as-deposited film with AIN/CrN = 8/2. Accordingly, it is suggested from IR absorption spectra that some amount of tetrahedrally-coordinated alumi• num with no influence of aging effect at room temper• ature still exists in both the AIN and AI-Cr-N films with B4 structure.
400
Wavenumber (em") Fig. 5. Reflectance IR spectra of the Cr-AI-N films after being aged for six months.
Pseudobinary Cr-AI-N films were synthesized by a new inductively combined rf-plasma assisted magnetron sputtering method in order to prove the critical composi• tion for the phase transition from BI structure to B4 structure in the Cr-AI-N pseudobinary system, which is predicted by two band parameters. The phase trans• ition for the synthesized pseudobinary nitride films was observed at the AIN content between 70 mol% and 80 mol%, and the result agrees with the predicted critical composition of 77 mol% AIN. The as-deposited pseu• dobinary nitride films with BI structure showed no preferred orientation. while preferred orientation was observed in these films aged for six months at room
1012
Y. Makino. K. Nogi / Surface and Coatings Technology 98 (1998) 1008-1012
temperature. In the pseudobinary and AIN films with B4 structure, the character of preferred orientation was unchanged, but some increase of their crystallinity and delicate change of local structure of AI-N bond were detected.
Acknowledgement The present research was partly supported by the joint research project 'R&D of Environment Conscious Innovative Materials Processing Systems with Advanced Energies (ECOMAP)' promoted by Joining and Welding Research Institute, Osaka Univerisity and Institute of Advanced Energy, Kyoto University. The authors thank Mr T. Morita and Dr M. Matsuura (ULVAC JAPAN Ltd.) for preparing the nitride films. We also thank Mr T. Kubo (Rigaku Corporation) for the assistance with XRD measurement, and Mr A. Nara (Nicolet Japan Co.) for reflectance IR measurement, respectively.
References [I] O. Knotek, M. Bohmer, T. Leyendecker, F. Jungblut, Mater. Sci. Eng. A 105106 (1988) 481. [2] J.R. Roos, J.P. Celis, E. Vancoille, H. Veltrop, S. Boelens, F. Jungblut, J. Ebberink, H. Homberg, Thin Solid Films 193194 (1990) 547. [3] O. Knotek, A. Barimani, Bosserholf, Loffler, Thin Solid Films 193/194 (1990) 557. [4] H. Randhara, P.e. Johnson, R. Cunnigham, J. Vac. Sci. Techno\. A 6 (1988) 2136. [5] T. Ikeda, H. Satoh, Thin Solid Films 195 (1991) 99. [6] H. Ichimura, A. Kawana, J. Mater. Res. 8 (1993) 1093. [7] D. Mcintyre, J.E. Greene, G. Hakansson, J.-E. Sundgren, W.-D. Miinz, J. Appl. Phys. 67 (1990) 1542. [8] Y. Makino, Y. Setsuhara, S. Miyake, Proc. 9th IntI. Conf. on Ion Beam Modification of Materials, Canberra, Australia, Feb. 1995, p. 735. [9) A. Sugishima, H. Kajioka, Y. Makino, Surf. Coat. Technol. 97 (1997) 59\. [10] Y. Makino, Intermetallics 2 (1994) 55. [II] Y. Makino, Mater. Sci. Eng. A 179180 (1994) 238. [12] J.e. Phillips, Rev. Mod. Phys. 42 (\970) 317. [13] N. Quang Danh, K.H. Monz, H.K. Pulker, Thin Solid Films 257 (1995) 116.
&CIIAlINIiS
ELSEVIER
Surface and Coatings Technology 98 (1998) 1008-1012
HGHNOLDGY
Synthesis of pseudobinary Cr-AI-N films with Bl structure by rf-assisted magnetron sputtering method Y. Makino *, K. Nogi Joining and We/ding Research Institute. Osaka University. 11-1. Mihogaoka. Ibaraki. Osaka 567. Japan
Abstract Pseudobinary Cr-AI-N films were synthesized by a new inductively combined rf-plasma assisted magnetron sputtering method.
It was found that phase transition from BI (NaCI) structure to B4 (wurtzite) structure occurs at an AIN content between 70 mol%
and 80 mol%, and the critical composition for the phase transition showed excellent agreement with the composition (77 mol% AIN) predicted by two band parameters. It was found that the aging effect is observed in the pseudobinary nitride films synthesized by the new magnetron sputtering method. No preferred orientation was observed in as-deposited pseudobinary nitride films with BI structure, while preferred orientation appeared in these films after aging at room temperature for six months. © 1998 Elsevier Science S.A.
1. Introduction Multicomponent nitride films based on titanium nit• ride have been widely produced for the various protec• tive coatings such as corrosion- and oxidation-barriers [1-4]. For example, it is believed that the AIN addition to TiN is effective for the improvement of the intrinsic properties of TiN by the formation of aluminum oxide [5,6]. However, further improvement of these films is not expected in higher temperature usages. Insufficient improvement of the intrinsic properties of TiN by AIN addition is probably related to the formation of coexist• ence of titanium dioxide [7] and/or aluminum titanate in which fairly fast diffusion of oxygen in these oxide films can not fully be suppressed. Comparing with these titanium oxides, more effective suppression for oxygen diffusion is expected by the formation of chromium sesquioxide and fortunately, according to our previous result [8], it is predicted that CrN shows the highest solubility for AIN among the transition nitrides with BI structure. Thus, Cr-AI-N film is one of the most promis• ing pseudobinary nitrides for the protective coatings on account of the formation of both aluminum and chro• mium sequioxides which are much more effective for the suppression of oxygen diffusion. In the present study, synthesis of a new pseudobinary Cr-AI-N film was tried by a new rf-assisted magnetron sputtering method, and the experimentally determined
* Corresponding author. 0257-8972/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PI! S0257-8972(97)00391_5
composition for the BI/B4 phase transition in the pseu• dobinary nitride was compared with the critical composi• tion for the BI/B4 transition predicted by the band parameters [8]. Further, the results in the present study were compared with those in the companion paper [9], in which the same Cr-AI-N films were synthesized using the planar-type magnetron sputtering method. 2. Experimental procedures Cr-AI-N films were synthesized in the mixed atmo• sphere of nitrogen and argon using the reactive sputter• ing method. An inductively combined rf-plasma assisted magnetron sputtering apparatus (MPS-200-HC3, ULVAC Co.) with dual targets was operated under a vacuum condition between 6 x 10 - 2 Pa and 1.5 x 10 -1 Pa. In the rf-assisted magnetron sputtering apparatus, both Al and Cr atoms can be simultaneously deposited on the substrate using the respective targets. The details of the experimental conditions are given in Table I. The compositions of the pseudobinary films were controlled by changing the ratio of rf-power for Cr cathode to that for Al cathode. The conditions of the rf-powers were determined from the experimental data on the same pseudobinary nitride films by the planar-type magnetron sputtering method in the com• panion paper [9], referring to the deposition rates for respective single nitrides by the rf-plasma assisted mag• netron sputtering method. The film composition was
Y. Makino. K. Nogi / Surface and Coatmgs Technology 98 ( 1998) 1008-1012 Table I Experimental conditions Apparatus Purities of targets Target size Substrate temperature Purities of gases RF power of cathode RF power of coil Gas pressure Gas flow Film thickness
MPS-2000-HC3 (ULVAC Japan Ltd) Cr 99.99% AI 99.99% 51mm Room temperature for unitary nitrides 573 K for pseudobinary nitrides Ar 99.9999% N 2 99.9999% Cr 8h:l50 W, AI 150~200 W Cr 50 W, AI 25 W 0.9 ~ 1.5 x 10- 3 Torr Ar 9~ 18 sccm, N 2 5 secm -150 nm
briefly varied from 60 mol% AIN to 80 mol% AIN only for the purpose of proving the validity of the critical composition for the phase transition from Bl type to B4 type, which was predicted by the structure map and the band parameters [8]. The impurity concentrations in the reactive gases were suppressed to be less than 10 ppb at the exit of the gas purifiers. Crystalline phases of the deposited films were iden• tified by X-ray diffraction method using Cu K~ radiation, which were measured with the 0-20 method at the operating conditions of 50 kV and 200 mAo Reflectance spectra of the deposited films were measured by the ATR method in the range of 400 cm - 1 and 1500 cm - 1 using a spectrometer (Nicolet, Magna 760) for detecting the characteristic vibration due to the AI-N bond in the deposited films.
1009
domains of the compounds with Bl and B4 structures. Though the details are omitted here on account of the precise explanation for calculating the critical composi• tion (x) [8], the composition for the pseudobinary nitrides containing AIN can be calculated by the following equation:
x = [hnV(MN) (2. 78SMN - H MN )]/[!.nV(AIN) (HAIN - 2. 78SAIN) -!.nv(MN)(HMN -SMN)] where H MN , SMN andJ.nv(MN) are the hybrid fuction, gap reduction parameter and compositional factor of trans• ition metal nitride (MN), and H A1N , SAIN and finV(AIN) are those of AIN, respectively. The numerical value of 2.78 is the slope of the boundary line between Bl and B4 domains in the structural map [8]. The critical composition for the Bl/B4 phase transition in the Cr-AI-N psuedobinary system is calculated to be 77mol% AIN. X-ray diffraction patterns obtained from the Cr-AI-N films with various compositions are shown in Fig. I.
AIN/CrN=6/4
3. Results and discussion Before explaining the experimental results, we briefly explain the prediction method to calculate critical com• positions for Bl/B4 phase transition in the pseudobinary nitrides containing aluminum and transition metal. Detailed explanations were given in the companion paper [9] and elsewhere [8]. The critical composition for Bl/B4 phase transition for the above-described pseu• dobinary nitrides can be estimated by the two band parameters [hybrid function (H) and gap reduction parameter (S)] [10] and the crystal structure map for AB type compounds [II], which was constructed by these parameters and compositional factor (!.nv)' Roughly explaining, Hand S correspond to the ionic and covalent band gaps, respectively, which were defined by dielectric properties [12]. The compositional factor was defined on the basis of the regular solution model and valence electron numbers of constituent elements. Critical compositions for Bl/B4 phase transition in the pseudobinary nitrides formed from Bland B4 type nitrides are determined by the two band parameters of these single nitrides and the boundary line between the
AIN/CrN=8/2
20
40
60
80
100
120
28 (degree) Fig. I. X-ray diffraction patterns obtained from the as-<1eposited Cr-AI-N films synthesized by the inductively combined rf-plasma assisted magnetron sputtering method. [C:B I phase (NaCI), H:B4 phase (wurtzite»).
Y. Makino, K. Nogl! Surface and Coatings Technology 98 (1998) 1008-1012
1010
Atomic ratios between Cr and Al for deposited films were determined by the deposition rate of the respective atom. For the pseudobinary films deposited at the atomic ratio less than NA.lN cr = 7/3, the single phase with Bl structure was identified, while the single phase with B4 structure was detected for the pseudobinary nitride film at the atomic ratio of N All Ncr = 812. The lattice constants of the BI and B4 phases are shown in Fig. 2 together with the results obtained by the planar magnetron sputtering method [9]. The phase identifica• tion leads to the conclusion that the phase transition from Bl type to B4 type occurs at the composition of AIN between 70 mol% and 80 mol%. The conclusion shows quite good agreement with the prediction that Bl/B4 phase transition occurs at 77 mol% AIN in the pseudobinary nitride. Further, the conclusion also agrees with the experimental result by the planar-type magnet• ron sputtering method in the companion work [9], in which the phase transition occured between 67 mol% and 75 mol% AIN. Reflectance IR spectra of the deposited Cr-AI-N films are shown in Fig. 3. Three or four absorptions were observed near 950 cm -1, 770 cm -1, 560 cm - 1 and 665 cm -1, respectively. Comparing with the reflectance IR spectra obtained from substrate silica glass, the former three absorptions are assigned to the characteris• tic absorptions due to the Si-O bond in silica glass. The
j
i
/
~ AIN/CrN=8/2
!
\ \,
"• Deposition temprature, 573K As-deposited
1200
1000
800
600
400
r.=============::::;------, •
• 0.5
81 ph_(RF)
------ ... ------------.
B4 ph_(a axl.. RF)
i--_composition : .. -_ .. - .... ------ ... -.
I
B4 ph_I. axl.. RF)
" 0
8Iph_(MG)
CJ
B4 ph_(a axi.. MG)
A
84ph_(. axl.. MG)
: Predl.ted .rltI.al ~
I I
,l I I I
llit.~
"
81 typeAIN
8
0.4
I...-_ _........_ _---L
o
0.2
0.4
Fig. 3. Reflectance IR spectra of as-deposited Cr-AI-N films synthe• sized by the inductively combined rf-plasma assisted magnetron sput• tering method.
:
A
•
0.3
(\
!
1400 0.6
I
1~~
.L--_----"-'-_ _--'
0.6
0.8
Ratio of Al to total cations, RAJ
Fig. 2. Dependence of the lattice constants of BI and B4 phases in the as-deposited Cr-AI-N films upon the ratio of AI to total cations [RAJ· The data on the lattice constants are plotted in this figure together with the lattice constants obtained from the Cr-AI-N films which were produced by the planar-type magnetron sputtering method [9].
last IR absorption was only observed in the Cr-AI-N film with the atomic ratio of NA.lN cr = 8/2, correspond• ing to the AIN content of about 80 mol%. Because the characteristic absorption near 700 cm - 1 was also observed in the pure AIN film [13], it may be concluded that the absorption is attributed to the AI-N bond of wurtzite-type AIN. On the other hand, no characteristic IR absorption was observed from the deposited films with B1 structure. Thus, aluminum atoms in the B4 type pseudobinary nitride film are in a similar chemical state to those of wurtzite-type AIN as far as the crystalline state of the film is preserved to be in the wurztite (B4) structure irrespective of dissolution of CrN. By measuring XRD patterns and IR spectra of these films after six months, the aging effect at room temper• ature was found in the pseudobinary Cr-AI-N films. These results are shown in Figs. 4 and 5. Comparing with the XRD patterns obtained from the as-deposited films, strong preferred orientations in every aged film with Bl or 84 structure were observed, and their peak widths remarkably decreased in these films. The charac-
Y. Makino, K Nogi 1Surface and Coatings Technology 98 ( 1998) /008-/OI:Z
IOJl
After aged for six months
2
3 4
5 40
30
60
50
70
80
90
26 (degree) Fig, 4. X-ray diffraction patterns of the Cr-AI-N films which were aged for six months after being synthesized by the inductively combined rf-plasma assisted magnetron sputtering method. [CB I phase (NaCl). H:B4 phase (wurtzite). I:AIN. 2:AIN/CrN = 8/2. 3:AIN/CrN = 7/3. 4:AIN/CrN =6/4. 5:CrN].
Deposition temprature, 573K After aged
/
.........
/
I
'J
"
L
J AIN/CrN=6/4 After aged
-------'
/~
; /-----~
, /
/ \~/,/
, -./
AIN/CrN=7/3 After aged / _/
(
AIN/CrN=8/2 After aged
I--~/I /~ AtN/CrN=8/2 As-deposited
~
/ ;
\
J
/~A~ /~
V
;' /
4. Summary
"
i ':
I----~
\~
1400
1200
1000
800
600
teristic absorption observed near 660 cm -1 in the as-deposited film with AIN/CrN = 8/2 shifted to a lower wavenumber of about 620 cm -1 and a similar shift was also observed in the aged AIN film. Because the IR absorption spectrum of the as-deposited AIN film was unfortunately not measured in this study, the position of the characteristic absorption for the as-deposited AIN film is unclear. However, the satellite peak near 660 cm - 1 in the aged AIN film is probably attributed to the AIN lattice without any influence of aging effect and the position of the satellite peak agrees with the position of the as-deposited film with AIN/CrN = 8/2. Accordingly, it is suggested from IR absorption spectra that some amount of tetrahedrally-coordinated alumi• num with no influence of aging effect at room temper• ature still exists in both the AIN and AI-Cr-N films with B4 structure.
400
Wavenumber (em") Fig. 5. Reflectance IR spectra of the Cr-AI-N films after being aged for six months.
Pseudobinary Cr-AI-N films were synthesized by a new inductively combined rf-plasma assisted magnetron sputtering method in order to prove the critical composi• tion for the phase transition from BI structure to B4 structure in the Cr-AI-N pseudobinary system, which is predicted by two band parameters. The phase trans• ition for the synthesized pseudobinary nitride films was observed at the AIN content between 70 mol% and 80 mol%, and the result agrees with the predicted critical composition of 77 mol% AIN. The as-deposited pseu• dobinary nitride films with BI structure showed no preferred orientation. while preferred orientation was observed in these films aged for six months at room
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temperature. In the pseudobinary and AIN films with B4 structure, the character of preferred orientation was unchanged, but some increase of their crystallinity and delicate change of local structure of AI-N bond were detected.
Acknowledgement The present research was partly supported by the joint research project 'R&D of Environment Conscious Innovative Materials Processing Systems with Advanced Energies (ECOMAP)' promoted by Joining and Welding Research Institute, Osaka Univerisity and Institute of Advanced Energy, Kyoto University. The authors thank Mr T. Morita and Dr M. Matsuura (ULVAC JAPAN Ltd.) for preparing the nitride films. We also thank Mr T. Kubo (Rigaku Corporation) for the assistance with XRD measurement, and Mr A. Nara (Nicolet Japan Co.) for reflectance IR measurement, respectively.
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