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Nitride film formation by ion and vapour deposition
910
Nuclear Instruments and Methods in Physics Research B7/8 (1985) 910-914 North-Holland, Amsterdam
NITRIDE FILM FOBMATION
BY ION AND VAPOUR DEPOSITION
M. SATOU Government Industrial Research Institute. Osaka, Ikeda, Osaka 563, Japan
K. YAMAGUCHI Kyocera Corporation, Central Research Laboratory, Kagoshima 899 - 43, Japan Y. ANDOH,
Y. SUZUKI
and K. MATSUDA
Ntssin Electric Co., Ltd, Kyoto 615, Japan
F. FUJIMOTO College of General Edttcatron, University of Tokyo, Tokyo 133, Japan
Boron nitride coating films were produced using ion beams of nitrogen molecules with energies 25-40 keV and simultaneous evaporation of boron (IVD method) and were analysed by infrared absorption spectra, X-ray diffraction and electron microscopy. Films with the composition ratio B/N larger than about 0.9 have structures of cubic BN or close to this. Those with smaller B/N than about 0.9 consist of hexagonal (layered) boron nitride or close to this. Dn some films, well oriented wurtzite type crystal was observed. A depth analysis for a titanium nitride film deposited on stainless steel prepared by IVD indicates the presence of a thick mixed layer of film and substrate.
1. Introdwtion Ion implantation is one of the most useful techniques for the surface modification of materials such as reduction of wear and corrosion. Method of surface modification is the plating of different materials by, for example, electrochemical or vapour deposition. The former technique may give difficulties in making thick coating layers of material different from the substrate and the latter one has the fault that the adhesion of the coating to the substrate is not strong. In order to overcome these problems, various deposition methods using ion beams, such as ion beam sputtering, ion plating and cluster ion depositions, are being used. For these methods, the kinetic energy of ions and atoms is from a few to several hundred eV, and some of them enter the substrate. However, the thickness of the mixed layer between the substrate and deposited film may not be enough to provide strong adhesion. The present authors (M.S., K.M. and F.F.) have developed a new deposition method utilizing ion implantation and vapour deposition (IVD) and formed coating films such as aluminum, boron and titanium nitrides which have very strong adhesion [l-3]. It is well known that stoichiometric boron nitride has three kinds of structure. These are, cubic (c-BN), wurt0168-583X/85/$03.30 @ Elsevier Science Publishers B.V. (North-Holland physics Publishing Division)
zite (w-BN) and hexagonal (layered) (h-BN). Their lattice constances are u = 3.62 A for oBN, u = 2.55 A and c = 4.20 A for w-BN and a = 2.50 A and c = 6.66 A for h-BN. The c-BN has almost the same hardness as diamond and is very stable thermally. Concerning the formation of c-BN, Weissmantel has reported evidence for its presence in films produced by ion beam depositions [4] and Shanfield and Wolfson have synthesized c-BN coating film using an ion beam extracted from a borozine plasma [S]. In the present paper, we report in detail on the film productions of boron nitride under various conditions by the IVD method and present results of infra-red absorption, X-ray and electron microscopic analyses of the deposited films. Furthermore, we show the variation of composition with film depth on titanium nitride.
2. Experimental A schematic diagram of the film deposition apparatus for boron nitride is shown in fig. 1. NC ions from a PIG ion source (1) were accelerated to 25-40 keV and analyzed by a magnet (2). After passing through a lens system and a suppressor (4), the ions bombarded substrates mounted on a stage (6), where the bombarded area was 10 cm’. The bomb~dment rate of nitrogen
911
M. Sarou et al. / Nitride film formation
.6 _
.4 _
.2 _
.Oi Fig. 1. Schematic diagram of IVD apparatus. 1. PIG ion source and accelerating tube, 2. analyzing magnet, 3. gate value, 4. lens system, 5. electron beam evaporator, 6. substrate holder, 7. thickness monitor, 8. current monitor, 9. TM pump.
was obtained by measuring the ion beam current (8). Boron was simultaneously evaporated from a source with an electron gun (5). Its deposition rate was obtained by a thickness monitor (7) placed separately. The preparation chamber was evacuated by a 650 l/s turbo molecular pump. The residual pressure was 3 X lo-’ Pa and the operating pressure was 1 X lo-’ Pa. The film formation of titanium nitride was carried out by a new apparatus which has a bucket type ion source emitting 100 mA and a deposition area of 4 x 10 cm2. Details of this apparatus are reported elsewhere [6]. Silicon wafer and cleaved rocksalt substrates were mounted on the stage. The temperature of the substrate was not controlled. A separate measurement of the temperature showed about 200°C on the silicon wafer during ion bombardment. The ion beam current of NC which indicates the dose rate was measured without the suppressor, in order to prepare films with area as large as 10 cm2. Therefore the measured current intensity is considered to be about one third lower than that due to the exact ion current, from a measurement with the suppressor for ion bombardment over a small area. The ion current was kept as constant as possible and the deposition rate of boron was varied. The growth rate of films was l-5 nm/min. The thickness of the films was 100-500 nm. The composition of the films was obtained by the following method: Fig. 2 shows a backscattering spectrum of 2.0 MeV proton beam from a polycrystalline target of h-BN where the composition ratio of boron and nitrogen B/N is unity. We prepared films with various B/N ratios and with a thickness of about 1 gm on aluminum foils of thickness 0.7 pm. A backscattering spectrum from a sample is shown in fig. 3. As seen in fig. 2, the scattering cross sections are non-Ruther-
0
50
100
150
200
2! 1
CHANNEL NUMBER Fig. 2. Backscattering spectrum of 2.0 MeV protons from polycrystalline h-BN.
ford. However, we can obtain the ratio of the B and N scattering cross sections from the ratio of the “B +“B and 14N step height in fig. 2. Using this information in conjunction with the “B+i’B and 14N peak areas in fig. 3 provides the B/N ratio in the film. For the sample shown in fig. 3, the atomic number ratio B/N obtained from the current intensity without the suppressor is 4.1 and the estimated number ratio between deposited boron atoms and bombarded ions is about 1.4 which is obtained by multiplying l/3 by the former value. The composition ratio B/N in the film measured from the two spectra shown in figs. 2 and 3 is 0.75. Samples prepared on silicon wafers were used to observe the infrared absorption spectra and X-ray diffraction (Cu-K,). Those on cleaved rocksalts were 1. 0
.,._ ,.‘.‘,“-‘,-‘.-.I
6.
-2 . 4. n ii
‘LN
BN
Al I ‘OB
7
CHANNEL NUMBER Fig. 3. Backscattering spectrum of 2.0 MeV protons from a BN sample on a 0.7 firn aluminum foil. XI. FINE LINE STR./DEPGSITION/ADHESION
M. Saw
912
et aL / Nrtrrde &Im formation
floated off on water and observed by a 200 kV electron microscope at 150 kV.
3. Experimental
results
The composition ratio B/N obtained from backscattering spectra of 2.0 MeV protons shown in figs. 2 and 3 is about half of the number ratio between two element atoms deposited on a substrate. This means that the sputtering of boron takes place during nitrogen ion bomb~dment and its yield is estimated to be unity. This value is quite reasonable in the case of boron target and nitrogen incident [7]. In the following we indicate the composition ratio B/N calibrated by the former method. A series of infrared absorption spectra from samples manufactured at 35 keV is shown in fig. 4 together with those of boron, h-BN and c- and w-BN. Spectra of cand w-BN are essentially the same and have a large peak at 1080 cm-‘. The spectrum of h-BN shows two peaks at 1370 and 780 cm-’ which are caused by the vibration modes in-plane and out-of plane, respectively PI. Spectra obtained from films with values of B/N lower than 0.4 did not show any dominant absorption peak and have only a small hump at 800 cm-‘. When
BIN 0.20
the value of B/N increases, two peaks appear at 1330 and 780 cm-’ and increase. These peaks are considered to correspond to those of h-BN. However, the larger peak at 1330 cm-’ shifts to the lower wavenumber side and becomes broader than the peak at 1370 cm-t of h-BN and the peak at 780 cm-’ is not so clear as that of h-BN. For B/N values larger than 0.85, the peak at 1330 cm-’ becomes roundish and shifts to about 1250 cm-’ and the peak at 780 cm-’ disappears. For films with large values of B/N, the main peak shifts further to the lower wavenumber side and becomes smaller. In the X-ray diffraction m~surements, only a broad peak can be observed in the vicinity of 44O, and strong peaks due to the (n, n, n) reflections of silicon shown in fig. 5. This broad peak corresponds to the (111) reflection of c-BN (43.39, the (0002) and (IOil) ones of w-BN (42.8”, 46.3O). It seems that the position of the peak maximum is near to that of c-BN for samples produced under conditions of high B/N value and NT ion beam with low energy and 44* for those with low energy and 44’ for those with low B/N value and high energy. it should be noted that no peak near to 26.8”, which is the position of the (0002) reflection of h-BN, appears. Mo~hological and structure studies on films have been made with a transmission electron microscope, We can classify the films morphologically into three groups as shown in fig. 6. Films belonging to group A shown in fig. 6a are usually smooth and some of them are very uniform. The atomic distances corresponding to the first, second and third rings in the diffraction patterns are 4.0, 2.4 and 14 A, respectively. These values suggest that films of this group have a structure close to c-BN w-BN (10 Il)?
4ooo
2ow
l600
1200
800
*
1
WAVENUFBER I an-’
Fig. 4. A series of infrared absorption spectra of BN films with various compositions on silicon wafers, together with those of boron h-BN, c- and w-BN.
SCATTER
t
NGANGLE I 2B
Fig. 5. X-ray diffractometer scans of BN films coated on siiicon wafers. (a) B/N = 1.0 (b) and (c) B/N = 1.5.
M. Sarou et al. / Nirnde firm /ormatron
913
pattern, as seen in figs. la and b. However, the cubic structure of fig. 7c is not identified. Films belonging to this group were mainly prepared under conditions of B/N ,( 1 and ion energy 2 28 keV. Films of group C shown in fig. 6c are bumpy and their diffraction patterns are quite diffuse. Atomic distances calculated from diffraction rings are 3.2, 2.0 and 1.13 A. From this result, we can consider that these films have a structure close to h-BN. The films belonging to this group can be found in the region of almost the same preparation conditions as the B-group.
Fig. 6. Electron micrographs and their diffraction patterns. Composition ratios and ion beam energies are, (a) B/N = 1.1, 35 keV, (b) B/N = 0.95, 35 keV and (c) B/N = 0.95, 30 keV. The scale marker shown in the lowest micrograph = 2 pm.
and the plane corresponding to (111) of c-BN is parallel to the film surface. This group was observed on samples prepared with B/N value > 0.9 or, small B/N and using an ion beam of energy as low as 25 keV. Films of group B have a granular structure and their diffraction rings are sharp, as seen in fig. 6b. The atomic distances estimated from three strong rings are 3.4, 2.2 and 1.24 A. This result suggests that the crystal structure of these films is h-BN. A sample with B/N - 0.5 and produced by 35 keV ion beam showed diffraction patterns due to crystal of w-BN together with the ring
Fig. 7. Electron micrographs and their diffraction patterns of samples with B/N = 0.50 and prepared at 30 kV. (a) and (b) w-BN and (c) cubic. The s&e marker shown in the lowest micrograph = 2 pm. XI. FINE LINE ~R./DE~SITION/ADH~ION
M. ‘Satou et al. / Nitride film jormation
was not observed for a titanium film prepared on stainless steel by evaporation only. Its thickness is about 500 A. It is also noteworthy that the distribution of nitrogen shifts to the deeper side than that of titanium and the magnitude of the shift is roughly 150 A which is nearly equal to the range of nitrogen ion in titanium. Detail of this study will be reported separately.
4. Conclusions
Fig. 8. Electron micrograph and its diffraction pattern of a sample with B/N = 1.0 and prepared at 30 kV. (Scale marker = 2 pm.) Diffraction pattern shows that of c-BN.
1 SURFACE
We have produced boron nitride coating films using molecular nitrogen ion beams of energy 25-40 keV and simultaneous evaporation of boron (the IVD method). The structure of films with B/N values larger than about 0.9 was c-BN or close to this. On films formed by low energy ions (25 keV), structures close to c-NB were also observed even for B/N values lower than 0.9. Films with B/N values smaller than unity and prepared by ions with energy higher than 28 keV have the h-BN structure or a h-BN like one. Some of these showed diffraction patterns due to well oriented w-BN crystal.
References
PI M. Satou, F. Fukui and F. Fujimoto, Proc. Int. Workshop
ETCHING
TIME
( MIN.)
Fig. 9. Depth distribution of the constituent elements of a TiN coating Blm prepared by IVD method on stainless steel.
A micrograph of a cubic structure which is considered to be c-BN is shown in fig. 8. The B/N value of this film was unity and the energy of ion beam was 30 keV. As an example of the study on the interface structure between the coating film and the substrate, we measured the concentration profiles of film and substrate elements by the sputtering by 5 keV Ar+ ions and ESCA on a TiN coating film produced by using 30 keV ions on stainless steel. The result is shown in fig. 9, where 77 min etching approximately corresponds to 1000 A. We can see very clearly a mixed layer which
by Professional Groups on Ion-based Techniques for Film Formation (Ion& Corp. Ltd., Tokyo, 1981) p, 349. PI M. Satou, K. Matsuda and F. Fujimoto, Proc. 6th Symp. Ion Sources & Ion-Assisted Technology (Tokyo, 1982) p, 425. 131 M. Satou and F. Fujimoto, Jpn. J. Appl. Phys. 22 (1983) L171. I41 C. Weissmantel, K. Bewilogua, D. Dietrich, H.-J. Erler, H.-J. Himerberg. S. Klose, W. Nowick and G. Reisse, Thin Solid Films 72 (1980) 19. C. Weissmantel, J. Vat. Technol. 18 (1981) 179. 151 S. Shanfield and R. Wolfson, J. Vat. Sci. Technol. Al (1983) 323. WI Y. Andoh, Y. Suzuki, M. Matsuda. M. Satou and F. Fujimoto, Proc. 5th Int. Conf. on Ion Implantation Equipment and Techniques, Nucl. Instr. and Meth. B6 (1985) 111. 171 Y. Yamamura, N. Matsunami and N. Itoh, Radiat. Effects 71 (1983) 65. 181 R. Geick, C.H. Perry and G. Rupprecht, Phys. Rev. 146 (1966) 543.
Nuclear Instruments and Methods in Physics Research B7/8 (1985) 910-914 North-Holland, Amsterdam
NITRIDE FILM FOBMATION
BY ION AND VAPOUR DEPOSITION
M. SATOU Government Industrial Research Institute. Osaka, Ikeda, Osaka 563, Japan
K. YAMAGUCHI Kyocera Corporation, Central Research Laboratory, Kagoshima 899 - 43, Japan Y. ANDOH,
Y. SUZUKI
and K. MATSUDA
Ntssin Electric Co., Ltd, Kyoto 615, Japan
F. FUJIMOTO College of General Edttcatron, University of Tokyo, Tokyo 133, Japan
Boron nitride coating films were produced using ion beams of nitrogen molecules with energies 25-40 keV and simultaneous evaporation of boron (IVD method) and were analysed by infrared absorption spectra, X-ray diffraction and electron microscopy. Films with the composition ratio B/N larger than about 0.9 have structures of cubic BN or close to this. Those with smaller B/N than about 0.9 consist of hexagonal (layered) boron nitride or close to this. Dn some films, well oriented wurtzite type crystal was observed. A depth analysis for a titanium nitride film deposited on stainless steel prepared by IVD indicates the presence of a thick mixed layer of film and substrate.
1. Introdwtion Ion implantation is one of the most useful techniques for the surface modification of materials such as reduction of wear and corrosion. Method of surface modification is the plating of different materials by, for example, electrochemical or vapour deposition. The former technique may give difficulties in making thick coating layers of material different from the substrate and the latter one has the fault that the adhesion of the coating to the substrate is not strong. In order to overcome these problems, various deposition methods using ion beams, such as ion beam sputtering, ion plating and cluster ion depositions, are being used. For these methods, the kinetic energy of ions and atoms is from a few to several hundred eV, and some of them enter the substrate. However, the thickness of the mixed layer between the substrate and deposited film may not be enough to provide strong adhesion. The present authors (M.S., K.M. and F.F.) have developed a new deposition method utilizing ion implantation and vapour deposition (IVD) and formed coating films such as aluminum, boron and titanium nitrides which have very strong adhesion [l-3]. It is well known that stoichiometric boron nitride has three kinds of structure. These are, cubic (c-BN), wurt0168-583X/85/$03.30 @ Elsevier Science Publishers B.V. (North-Holland physics Publishing Division)
zite (w-BN) and hexagonal (layered) (h-BN). Their lattice constances are u = 3.62 A for oBN, u = 2.55 A and c = 4.20 A for w-BN and a = 2.50 A and c = 6.66 A for h-BN. The c-BN has almost the same hardness as diamond and is very stable thermally. Concerning the formation of c-BN, Weissmantel has reported evidence for its presence in films produced by ion beam depositions [4] and Shanfield and Wolfson have synthesized c-BN coating film using an ion beam extracted from a borozine plasma [S]. In the present paper, we report in detail on the film productions of boron nitride under various conditions by the IVD method and present results of infra-red absorption, X-ray and electron microscopic analyses of the deposited films. Furthermore, we show the variation of composition with film depth on titanium nitride.
2. Experimental A schematic diagram of the film deposition apparatus for boron nitride is shown in fig. 1. NC ions from a PIG ion source (1) were accelerated to 25-40 keV and analyzed by a magnet (2). After passing through a lens system and a suppressor (4), the ions bombarded substrates mounted on a stage (6), where the bombarded area was 10 cm’. The bomb~dment rate of nitrogen
911
M. Sarou et al. / Nitride film formation
.6 _
.4 _
.2 _
.Oi Fig. 1. Schematic diagram of IVD apparatus. 1. PIG ion source and accelerating tube, 2. analyzing magnet, 3. gate value, 4. lens system, 5. electron beam evaporator, 6. substrate holder, 7. thickness monitor, 8. current monitor, 9. TM pump.
was obtained by measuring the ion beam current (8). Boron was simultaneously evaporated from a source with an electron gun (5). Its deposition rate was obtained by a thickness monitor (7) placed separately. The preparation chamber was evacuated by a 650 l/s turbo molecular pump. The residual pressure was 3 X lo-’ Pa and the operating pressure was 1 X lo-’ Pa. The film formation of titanium nitride was carried out by a new apparatus which has a bucket type ion source emitting 100 mA and a deposition area of 4 x 10 cm2. Details of this apparatus are reported elsewhere [6]. Silicon wafer and cleaved rocksalt substrates were mounted on the stage. The temperature of the substrate was not controlled. A separate measurement of the temperature showed about 200°C on the silicon wafer during ion bombardment. The ion beam current of NC which indicates the dose rate was measured without the suppressor, in order to prepare films with area as large as 10 cm2. Therefore the measured current intensity is considered to be about one third lower than that due to the exact ion current, from a measurement with the suppressor for ion bombardment over a small area. The ion current was kept as constant as possible and the deposition rate of boron was varied. The growth rate of films was l-5 nm/min. The thickness of the films was 100-500 nm. The composition of the films was obtained by the following method: Fig. 2 shows a backscattering spectrum of 2.0 MeV proton beam from a polycrystalline target of h-BN where the composition ratio of boron and nitrogen B/N is unity. We prepared films with various B/N ratios and with a thickness of about 1 gm on aluminum foils of thickness 0.7 pm. A backscattering spectrum from a sample is shown in fig. 3. As seen in fig. 2, the scattering cross sections are non-Ruther-
0
50
100
150
200
2! 1
CHANNEL NUMBER Fig. 2. Backscattering spectrum of 2.0 MeV protons from polycrystalline h-BN.
ford. However, we can obtain the ratio of the B and N scattering cross sections from the ratio of the “B +“B and 14N step height in fig. 2. Using this information in conjunction with the “B+i’B and 14N peak areas in fig. 3 provides the B/N ratio in the film. For the sample shown in fig. 3, the atomic number ratio B/N obtained from the current intensity without the suppressor is 4.1 and the estimated number ratio between deposited boron atoms and bombarded ions is about 1.4 which is obtained by multiplying l/3 by the former value. The composition ratio B/N in the film measured from the two spectra shown in figs. 2 and 3 is 0.75. Samples prepared on silicon wafers were used to observe the infrared absorption spectra and X-ray diffraction (Cu-K,). Those on cleaved rocksalts were 1. 0
.,._ ,.‘.‘,“-‘,-‘.-.I
6.
-2 . 4. n ii
‘LN
BN
Al I ‘OB
7
CHANNEL NUMBER Fig. 3. Backscattering spectrum of 2.0 MeV protons from a BN sample on a 0.7 firn aluminum foil. XI. FINE LINE STR./DEPGSITION/ADHESION
M. Saw
912
et aL / Nrtrrde &Im formation
floated off on water and observed by a 200 kV electron microscope at 150 kV.
3. Experimental
results
The composition ratio B/N obtained from backscattering spectra of 2.0 MeV protons shown in figs. 2 and 3 is about half of the number ratio between two element atoms deposited on a substrate. This means that the sputtering of boron takes place during nitrogen ion bomb~dment and its yield is estimated to be unity. This value is quite reasonable in the case of boron target and nitrogen incident [7]. In the following we indicate the composition ratio B/N calibrated by the former method. A series of infrared absorption spectra from samples manufactured at 35 keV is shown in fig. 4 together with those of boron, h-BN and c- and w-BN. Spectra of cand w-BN are essentially the same and have a large peak at 1080 cm-‘. The spectrum of h-BN shows two peaks at 1370 and 780 cm-’ which are caused by the vibration modes in-plane and out-of plane, respectively PI. Spectra obtained from films with values of B/N lower than 0.4 did not show any dominant absorption peak and have only a small hump at 800 cm-‘. When
BIN 0.20
the value of B/N increases, two peaks appear at 1330 and 780 cm-’ and increase. These peaks are considered to correspond to those of h-BN. However, the larger peak at 1330 cm-’ shifts to the lower wavenumber side and becomes broader than the peak at 1370 cm-t of h-BN and the peak at 780 cm-’ is not so clear as that of h-BN. For B/N values larger than 0.85, the peak at 1330 cm-’ becomes roundish and shifts to about 1250 cm-’ and the peak at 780 cm-’ disappears. For films with large values of B/N, the main peak shifts further to the lower wavenumber side and becomes smaller. In the X-ray diffraction m~surements, only a broad peak can be observed in the vicinity of 44O, and strong peaks due to the (n, n, n) reflections of silicon shown in fig. 5. This broad peak corresponds to the (111) reflection of c-BN (43.39, the (0002) and (IOil) ones of w-BN (42.8”, 46.3O). It seems that the position of the peak maximum is near to that of c-BN for samples produced under conditions of high B/N value and NT ion beam with low energy and 44* for those with low energy and 44’ for those with low B/N value and high energy. it should be noted that no peak near to 26.8”, which is the position of the (0002) reflection of h-BN, appears. Mo~hological and structure studies on films have been made with a transmission electron microscope, We can classify the films morphologically into three groups as shown in fig. 6. Films belonging to group A shown in fig. 6a are usually smooth and some of them are very uniform. The atomic distances corresponding to the first, second and third rings in the diffraction patterns are 4.0, 2.4 and 14 A, respectively. These values suggest that films of this group have a structure close to c-BN w-BN (10 Il)?
4ooo
2ow
l600
1200
800
*
1
WAVENUFBER I an-’
Fig. 4. A series of infrared absorption spectra of BN films with various compositions on silicon wafers, together with those of boron h-BN, c- and w-BN.
SCATTER
t
NGANGLE I 2B
Fig. 5. X-ray diffractometer scans of BN films coated on siiicon wafers. (a) B/N = 1.0 (b) and (c) B/N = 1.5.
M. Sarou et al. / Nirnde firm /ormatron
913
pattern, as seen in figs. la and b. However, the cubic structure of fig. 7c is not identified. Films belonging to this group were mainly prepared under conditions of B/N ,( 1 and ion energy 2 28 keV. Films of group C shown in fig. 6c are bumpy and their diffraction patterns are quite diffuse. Atomic distances calculated from diffraction rings are 3.2, 2.0 and 1.13 A. From this result, we can consider that these films have a structure close to h-BN. The films belonging to this group can be found in the region of almost the same preparation conditions as the B-group.
Fig. 6. Electron micrographs and their diffraction patterns. Composition ratios and ion beam energies are, (a) B/N = 1.1, 35 keV, (b) B/N = 0.95, 35 keV and (c) B/N = 0.95, 30 keV. The scale marker shown in the lowest micrograph = 2 pm.
and the plane corresponding to (111) of c-BN is parallel to the film surface. This group was observed on samples prepared with B/N value > 0.9 or, small B/N and using an ion beam of energy as low as 25 keV. Films of group B have a granular structure and their diffraction rings are sharp, as seen in fig. 6b. The atomic distances estimated from three strong rings are 3.4, 2.2 and 1.24 A. This result suggests that the crystal structure of these films is h-BN. A sample with B/N - 0.5 and produced by 35 keV ion beam showed diffraction patterns due to crystal of w-BN together with the ring
Fig. 7. Electron micrographs and their diffraction patterns of samples with B/N = 0.50 and prepared at 30 kV. (a) and (b) w-BN and (c) cubic. The s&e marker shown in the lowest micrograph = 2 pm. XI. FINE LINE ~R./DE~SITION/ADH~ION
M. ‘Satou et al. / Nitride film jormation
was not observed for a titanium film prepared on stainless steel by evaporation only. Its thickness is about 500 A. It is also noteworthy that the distribution of nitrogen shifts to the deeper side than that of titanium and the magnitude of the shift is roughly 150 A which is nearly equal to the range of nitrogen ion in titanium. Detail of this study will be reported separately.
4. Conclusions
Fig. 8. Electron micrograph and its diffraction pattern of a sample with B/N = 1.0 and prepared at 30 kV. (Scale marker = 2 pm.) Diffraction pattern shows that of c-BN.
1 SURFACE
We have produced boron nitride coating films using molecular nitrogen ion beams of energy 25-40 keV and simultaneous evaporation of boron (the IVD method). The structure of films with B/N values larger than about 0.9 was c-BN or close to this. On films formed by low energy ions (25 keV), structures close to c-NB were also observed even for B/N values lower than 0.9. Films with B/N values smaller than unity and prepared by ions with energy higher than 28 keV have the h-BN structure or a h-BN like one. Some of these showed diffraction patterns due to well oriented w-BN crystal.
References
PI M. Satou, F. Fukui and F. Fujimoto, Proc. Int. Workshop
ETCHING
TIME
( MIN.)
Fig. 9. Depth distribution of the constituent elements of a TiN coating Blm prepared by IVD method on stainless steel.
A micrograph of a cubic structure which is considered to be c-BN is shown in fig. 8. The B/N value of this film was unity and the energy of ion beam was 30 keV. As an example of the study on the interface structure between the coating film and the substrate, we measured the concentration profiles of film and substrate elements by the sputtering by 5 keV Ar+ ions and ESCA on a TiN coating film produced by using 30 keV ions on stainless steel. The result is shown in fig. 9, where 77 min etching approximately corresponds to 1000 A. We can see very clearly a mixed layer which
by Professional Groups on Ion-based Techniques for Film Formation (Ion& Corp. Ltd., Tokyo, 1981) p, 349. PI M. Satou, K. Matsuda and F. Fujimoto, Proc. 6th Symp. Ion Sources & Ion-Assisted Technology (Tokyo, 1982) p, 425. 131 M. Satou and F. Fujimoto, Jpn. J. Appl. Phys. 22 (1983) L171. I41 C. Weissmantel, K. Bewilogua, D. Dietrich, H.-J. Erler, H.-J. Himerberg. S. Klose, W. Nowick and G. Reisse, Thin Solid Films 72 (1980) 19. C. Weissmantel, J. Vat. Technol. 18 (1981) 179. 151 S. Shanfield and R. Wolfson, J. Vat. Sci. Technol. Al (1983) 323. WI Y. Andoh, Y. Suzuki, M. Matsuda. M. Satou and F. Fujimoto, Proc. 5th Int. Conf. on Ion Implantation Equipment and Techniques, Nucl. Instr. and Meth. B6 (1985) 111. 171 Y. Yamamura, N. Matsunami and N. Itoh, Radiat. Effects 71 (1983) 65. 181 R. Geick, C.H. Perry and G. Rupprecht, Phys. Rev. 146 (1966) 543.