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The mechanical properties of hydrogenated hard carbon films
The mechanical properties of hydrogenated Nobuki
Mutsukura,
Departmenr
of Electronic
(Received
October
Shotare
Engineering,
2. 1991; accepted
Tomita
and Yoshie
Faculty of’ Enginerring. January
Tokyo
hard carbon films
Mizuma
Denki Unicersiiy,
ClQwla-ku,
Tokyo
101 (Japan)
21, 1992)
Abstract Hydrogenated hard carbon films, deposited in a CH, r.f. parallel plate discharge, have been evaluated by means of internal film stress and friction coefficient measurements. The internal stresses were estimated using a round silicon substrate made of both convex and concave Si wafers, combined with electrical capacitance measurements. The typical internal stress of the hard carbon film was compressive and was in the range 0.5-l .5 GPa. The variation in the film stress depending on the CH, gas pressure during the film deposition was associated with the d.c. self-bias voltage on the cathode electrode. The friction coefficient between the hard carbon film deposited on a 3.5 in hard disk and a magnetic head was also examined.
hr
1. Introduction Diamond-like hard carbon (DLC) films, deposited by ion beam deposition [l-3] and plasma decomposition of hydrocarbon gases [4-61, have numerous useful properties such as extreme mechanical hardness, good IR transparency, high electrical resistivity and chemical inertness. These carbon films have been applied particularly as antireflection coatings and wear-resistant coatings. The hard carbon films normally have high internal stresses caused by ion bombardment with relatively high kinetic energy during the deposition. The film’s internal stress sometimes induces cracks and/or peeling off of the deposited films. It is therefore very important to evaluate this film stress in the progress of potential applications of hard carbon films. In this study we have developed a convenient technique for the measurement of this film stress, and measurements of the internal stress in hard carbon films prepared by an r.f. plasma deposition method were carried out using this novel technique. The friction coefficients of the hard carbon films were also measured in applications on wear-resistant coatings.
2. Experimental
details
The hydrogenated amorphous carbon films were deposited in a conventional plasma chamber made of a stainless steel (SUS) cylinder (40 cm in diameter and 20 cm in height) with a parallel electrode configuration, as shown in Fig. 1. The lower cathodic electrode (SUS disk 30 cm in diameter) is capacitively coupled to a 13.56 MHz r.f. generator through a tunable matching network. Both an upper SUS cover and a cylindrical
source
gas water
---I
ge&tor
Fig. I. Experimental r.f. discharge.
apparatus
I
for carbon
film deposition
in a CH,
envelope acting as an anodic electrode are connected to the ground. The spacing between the upper cover and the lower cathode electrode is about 15 cm. The source gas used is CH, gas of 99.9999% purity. The internal stress in amorphous films can generally be estimated by measuring the elastic deformation of the substrate. For the use of a strip-shaped substrate, the internal stress cr is calculated from the formula Ests2d
(1)
0 = 3( 1 - v)L”t,
where ES is Young’s modulus of the substrate, v is Poisson’s ratio of the substrate, t, and t, are the thicknesses of the film and the substrate respectively, L is the length of the scanned substrate, and 6 is the bending of the substrate. When a round substrate is used, and the
(’ 1992 ~
Elsevier Sequoia.
All rights
reserved
N. Mutsukura et al.
thin
59
I Mechanical properties of hydrogenated C
film
ire
(a)
(b)
Fig. 2. A cross-section of a round silicon substrate measurement of internal film stress: (a) before and deposition.
used for the (b) after film
internal stress is assumed to be isotropic in the film plane, the film stress is then calculated from ’ = 6( 1 - v)t,-R
l/2
s
27t:EoX (R2-x’)“2-[R2-(/,2)2]ii2+ddX
50 (Pa)
Fig. 3. The deposition rate of carbon function of CH, gas pressure.
100 films in CH,
r.f. plasma
as a
(2)
where R is the radius of curvature due to the film. In this work a round silicon wafer is used as the substrate. Figure 2 shows a cross-section of the silicon substrate used to measure the internal film stress. This silicon substrate consists of two kinds of silicon wafers: one is convex, and the other is concave. These two silicon wafers were connected together. Gold electrodes were evaporated on the surfaces of both silicon wafers in order to form parallel electrodes inside the silicon substrate, as shown in Fig. 2. Figures 2(a) and 2(b) show the silicon substrates respectively before and after film depositon. The convex and concave silicon wafers were made by chemical anisotropic etching of Si( 100) wafers using a KOH solution. The radius of curvature on the concave substrate after film deposition can be determined from the electrical capacitance between the two gold electrodes. The relationship between the radius R of curvature and the capacitance C is
‘=
5 10 PRESSURE
(3)
0
where a0 is the dielectric constant in vacuum, and x is a variable indicating position from the center of the round gold electrode. In practice, the R value was calculated by a microcomputer using the measured C value. The film stress was then estimated from eqn. (2). In the measurement of the electrical capacitance, a YHP 4280A 1 MHz C meter/C- V plotter was utilized. In order to evaluate the capability of this measuring technique, measurements using strip-shaped silicon substrates were also carried out simultaneously. In the study of the wear-resistant properties of the hard carbon film, the friction coefficient between the film deposited on a hard disk (3.5 in diameter) and a magnetic head (Mn-Zn mini monolithic head) was measured.
3. Results and discussion 3.1. Deposition rate of carbon film Figure 3 shows the deposition rates of the carbon films as a function of CH, source gas pressure for various r.f. input powers. The deposition rates depend strongly on both gas pressure and r.f. power. The deposition rate increases with increasing pressure and then exhibits a maximum (except that for 200 W). The pressure condition giving this maximum value exists at a higher pressure for a larger input r.f. power. In addition, at further high pressure conditions the mechanical properties deteriorate: the films become soft (for 50 and 100 W). The increase in deposition rate with increasing pressure in lower pressure region is associated with the increase in the number density of source gas molecules. The decrease with increasing pressure in the higher pressure region may be due to the decrease in d.c. self-bias voltage on the cathodic electrode, because the deposition rate depends on the cathode self-bias voltage, as reported previously [6]. The deposition mechanism for hard carbon film deposition will be discussed in detail elsewhere [7]. 3.2. Internal film stress measurements The internal stresses in the hard carbon films were measured using both strip-shaped and round (Fig. 2) silicon substrates, as mentioned previously. When the thicknesses of the substrate and the film are the same for both of the substrates, the following relationship can be obtained from eqns. ( 1) and (2): 6 1 2=$R
(4)
Figure 4 shows the 1/2R US. d/L2 relationship for compressive stress of the hard carbon films of different
60
N. Mutsukura
et al. I Mechanical
proprrtirs
of izydrogenared C
1.5 +/f
1oow
kc
1.0 -
P-P
: _
%
p
2oow
.
!
iii 0.5
i c,
. 0
I
G/~21(io-zcm-‘)
I
2
Fig. 4. The relationship between 1/2R and (5/L* values on diamondlike films. measured using both round and strip-shaped silicon substrates.
film thicknesses deposited under the conditions of 13 and 40 Pa of CH, and 200 W r.f. power. The result obtained indicates a relationship of the form of eqn. (4). Above 1 x 1O-2 cm-‘, however, the 1/2R value tends to saturate. This is due to the limitation of the expansion in concave substrate, so this round substrate will be suitable for measurements with a relatively large radius of curvature on the substrate. In this experiment, the dimensions of the round substrate are as follows: diameter I of the substrate, 3 cm; thickness of the substrate t,, 80 urn; distance d between the two gold electrodes, 7.7 urn (see Fig. 2). The strip-shaped substrate has a thickness t, = 80 urn and a length L = 2 cm. The capability of our silicon substrate depends on the values of I, t and d. The sensitivity of the film stress measurement increases with the decrease in the d value. The type of the stress, tensile or compressive, can be easily recognized by a change in the electrical capacitance after deposition. In the measurements on the carbon films this silicon substrate was used repeatedly, because the deposited carbon films can be removed quite easily in an 0, discharge plasma. The greatest advantage of our round substrate is that in situ measurement is possible without any modifications to the film deposition chamber. Figure 5 shows the compressive stresses of carbon films deposited under various CH, gas pressures for two r.f. input powers (100 W and 200 W). The film thickness is about 100 nm for all the films. In the calculation of the stress, a value of 1.8 x 10” Pa is used for the E/( 1 - v) value of the silicon substrate [8]. For the 100 W input r.f. power, the stress increases with the decrease in the pressure. The films deposited at pressures above 40 Pa were polymer-like soft films, and others obtained below 40 Pa were hard films. The formation of the hard films depends strongly on the kinetic energy of ions bombarding the substrate on the cathodic electrode during film deposition. Zou et al. [6] have reported that the hard carbon films were obtained
0
’
I
L”ll’l’
PRSESSURE 10
50
101
(Pa)
Fig. 5. The internal gas pressure during
stress in diamond-like the deposition.
films as a function
of CH,
o.61
05
50 PRESSURE
100
(Pa)
Fig. 6. The d.c. self-bias voltage on the cathodic function of CH, gas pressure during the deposition.
electrode
as a
in the range lOOV
N. Mutsukura et al. 1 Mechanical properties of hydrogenated C
---DLC
(400A)
-Cr(2000A) :.:.:.:.
‘.:.;.~~~~.~..;.~?~~
. . . ..
cwyluruuyu
.:
$$$-Ni_P(lO_2Oym) z:::::::. (textured
-Al
or polished)
alloy
Fig. 7. The structures of 3.5 in hard disks with diamond-like films used for the measurements of the friction coefficients of the diamondlike films.
3.3. Friction coeficient measurements The friction coefficients of the hard carbon films on the hard disks were measured in two kinds of conditions at which the disk rotation speeds were 1 and 100 rev min’. The measurements were carried out using two kinds of hard disks having textured or polished surfaces, shown in Fig. 7. In the measurements for a rotation speed of 1 rev min-‘, the magnetic head (9.5 gf weight) contacts the disk surface at regular intervals during the 60 min measurement. For the 100 rev min’ rotation speed, the magnetic head touches continuously for 60 min. Figure 8 shows the behavior of the friction coefficient during the measurement using the textured surface disk. The friction coefficient increases with the
Initial
Fig. 8. The behaviors measurement period.
of the friction
61
elapsed time. This may be caused by the generation of microscopic cracks and/or the peeling off of the hard carbon films as a result of a lower adhesive strength between the film and the hard disk surface. Table 1 indicates the friction coefficients of the films initially and at the end of the 60 min measurement for both 1 and 100 rev min’ disk rotation speeds. The measurements were carried out for both the textured and the polished disks. The hard carbon films were deposited at 4 Pa CH, pressure and 100 W r.f. power, and the film thickness was about 40 nm. The friction coefficients of these films are very low compared with those of the r.f. sputtered film, as indicated in Table 1.
4. Summary The hydrogenated hard carbon films prepared by plasma deposition in a CH, r.f. discharge were examined in terms of the internal film stress and the friction coefficient. The film stress was measured using a specific round silicon substrate developed in this work. The substrate is fabricated with both convex and concave silicon wafers, and the stress was estimated from the change in the electrical capacitance between two parallel electrodes formed inside the silicon substrate.
60 mins passed
coefficients
of the diamond-like
films for
1 and 100 re:V min- ’ disk rotation
speeds,
during
a 60 min
62
N. Mutsukura
TABLE I. Friction coefficients of hard carbon both I and 100 rev min-’ disk rotation speeds Substrate
Friction
et al. / Mechanical
films measured
at
coefficient
properties
qf‘hydrogenatcd
C
of the measurement. This was thought to be associated with less adhesive strength between the hard carbon film and the disk surface.
100 rev min-’
I rev min-’
Acknowledgments Initial
After 60 min
Initial
After 60 min
Textured Polished Textured“
0.09 0.17 0.38
0.39 0.53 I .33
0.13 0.20 0.44
0.43 0.80 I .45
“r.f. sputtered
hard carbon
This work was partially supported by a research grant of Nippon Tylan Co. Ltd. The authors wish to thank Dr. Yamagata of Denki Kagaku Kogyo Co. Ltd. for the measurements of the friction coefficients.
film.
References The internal film stress was compressive for all the films deposited in the examined 4-70 Pa CH, pressure region. The film stress depends strongly on the d.c. self-bias voltage on the cathodic electrode in the CH, discharge during film deposition. This increases with the increase in the self-bias voltage, and then tends to saturate at around 1 GPa of internal stress. At very large self-bias voltages, the film stress decreases. This is due to the change in the film structure. The internal stress of the hard carbon film deposited in this work was in range 0.5-1.5 GPa. The friction coefficients between the hard carbon films deposited on hard disks and a magnetic head were measured for 1 and 100 rev min-’ disk rotation speeds. The friction coefficient became large at the end of the measurement for 60 min compared with that at the start
I S. Aisenberg and R. Chabot, J. Appl. Phys., 42 (1971) 2953. 2 C. Weissmantel, G. Reisse, H.-J. Erler, F. Henny, K. Bewilogua, U. Ebersbach and C. Schurer, Thin Solid Films, 63 ( 1979) 315. 3 P. Oelhafen, J. L. Freeouf, J. M. E. Harper and J. J. Cuomo. Thin Solid Films, 120 ( 1984) 231. 4 Y. Catherine and P. Couderc. Thin Solid Films, 144 (1986) 265. 5 K. Kobayashi, N. Mutsukura and Y. Machi, Thin Solid Films, 158 (1988) 233. 6 J. W. Zou, K. Reichelt, K. Schmidt and B. Dischler, .I. Appl. Phys., 65 (1989) 3914. 7 N. Mutsukura. S. Inoue and Y. Machi, J. Appl. Phy.‘., in the press. 8 W. A. Brantley, J. Appl. Phys., 44 (1973) 534. 9 X. Jiang, J. W. Zou, K. Reichelt and P. Grunberg, J. Appl. Phys., 66 ( 1989) 4729. 10 J. W. Zou, K. Schmidt, K. Reichelt and B. Dischler, J. Appl. Phys., 67 (1990) 487. 1 I P. Couderc and Y. Catherine, Thin Solid Films. 146 (1987) 93.
Mutsukura,
Departmenr
of Electronic
(Received
October
Shotare
Engineering,
2. 1991; accepted
Tomita
and Yoshie
Faculty of’ Enginerring. January
Tokyo
hard carbon films
Mizuma
Denki Unicersiiy,
ClQwla-ku,
Tokyo
101 (Japan)
21, 1992)
Abstract Hydrogenated hard carbon films, deposited in a CH, r.f. parallel plate discharge, have been evaluated by means of internal film stress and friction coefficient measurements. The internal stresses were estimated using a round silicon substrate made of both convex and concave Si wafers, combined with electrical capacitance measurements. The typical internal stress of the hard carbon film was compressive and was in the range 0.5-l .5 GPa. The variation in the film stress depending on the CH, gas pressure during the film deposition was associated with the d.c. self-bias voltage on the cathode electrode. The friction coefficient between the hard carbon film deposited on a 3.5 in hard disk and a magnetic head was also examined.
hr
1. Introduction Diamond-like hard carbon (DLC) films, deposited by ion beam deposition [l-3] and plasma decomposition of hydrocarbon gases [4-61, have numerous useful properties such as extreme mechanical hardness, good IR transparency, high electrical resistivity and chemical inertness. These carbon films have been applied particularly as antireflection coatings and wear-resistant coatings. The hard carbon films normally have high internal stresses caused by ion bombardment with relatively high kinetic energy during the deposition. The film’s internal stress sometimes induces cracks and/or peeling off of the deposited films. It is therefore very important to evaluate this film stress in the progress of potential applications of hard carbon films. In this study we have developed a convenient technique for the measurement of this film stress, and measurements of the internal stress in hard carbon films prepared by an r.f. plasma deposition method were carried out using this novel technique. The friction coefficients of the hard carbon films were also measured in applications on wear-resistant coatings.
2. Experimental
details
The hydrogenated amorphous carbon films were deposited in a conventional plasma chamber made of a stainless steel (SUS) cylinder (40 cm in diameter and 20 cm in height) with a parallel electrode configuration, as shown in Fig. 1. The lower cathodic electrode (SUS disk 30 cm in diameter) is capacitively coupled to a 13.56 MHz r.f. generator through a tunable matching network. Both an upper SUS cover and a cylindrical
source
gas water
---I
ge&tor
Fig. I. Experimental r.f. discharge.
apparatus
I
for carbon
film deposition
in a CH,
envelope acting as an anodic electrode are connected to the ground. The spacing between the upper cover and the lower cathode electrode is about 15 cm. The source gas used is CH, gas of 99.9999% purity. The internal stress in amorphous films can generally be estimated by measuring the elastic deformation of the substrate. For the use of a strip-shaped substrate, the internal stress cr is calculated from the formula Ests2d
(1)
0 = 3( 1 - v)L”t,
where ES is Young’s modulus of the substrate, v is Poisson’s ratio of the substrate, t, and t, are the thicknesses of the film and the substrate respectively, L is the length of the scanned substrate, and 6 is the bending of the substrate. When a round substrate is used, and the
(’ 1992 ~
Elsevier Sequoia.
All rights
reserved
N. Mutsukura et al.
thin
59
I Mechanical properties of hydrogenated C
film
ire
(a)
(b)
Fig. 2. A cross-section of a round silicon substrate measurement of internal film stress: (a) before and deposition.
used for the (b) after film
internal stress is assumed to be isotropic in the film plane, the film stress is then calculated from ’ = 6( 1 - v)t,-R
l/2
s
27t:EoX (R2-x’)“2-[R2-(/,2)2]ii2+ddX
50 (Pa)
Fig. 3. The deposition rate of carbon function of CH, gas pressure.
100 films in CH,
r.f. plasma
as a
(2)
where R is the radius of curvature due to the film. In this work a round silicon wafer is used as the substrate. Figure 2 shows a cross-section of the silicon substrate used to measure the internal film stress. This silicon substrate consists of two kinds of silicon wafers: one is convex, and the other is concave. These two silicon wafers were connected together. Gold electrodes were evaporated on the surfaces of both silicon wafers in order to form parallel electrodes inside the silicon substrate, as shown in Fig. 2. Figures 2(a) and 2(b) show the silicon substrates respectively before and after film depositon. The convex and concave silicon wafers were made by chemical anisotropic etching of Si( 100) wafers using a KOH solution. The radius of curvature on the concave substrate after film deposition can be determined from the electrical capacitance between the two gold electrodes. The relationship between the radius R of curvature and the capacitance C is
‘=
5 10 PRESSURE
(3)
0
where a0 is the dielectric constant in vacuum, and x is a variable indicating position from the center of the round gold electrode. In practice, the R value was calculated by a microcomputer using the measured C value. The film stress was then estimated from eqn. (2). In the measurement of the electrical capacitance, a YHP 4280A 1 MHz C meter/C- V plotter was utilized. In order to evaluate the capability of this measuring technique, measurements using strip-shaped silicon substrates were also carried out simultaneously. In the study of the wear-resistant properties of the hard carbon film, the friction coefficient between the film deposited on a hard disk (3.5 in diameter) and a magnetic head (Mn-Zn mini monolithic head) was measured.
3. Results and discussion 3.1. Deposition rate of carbon film Figure 3 shows the deposition rates of the carbon films as a function of CH, source gas pressure for various r.f. input powers. The deposition rates depend strongly on both gas pressure and r.f. power. The deposition rate increases with increasing pressure and then exhibits a maximum (except that for 200 W). The pressure condition giving this maximum value exists at a higher pressure for a larger input r.f. power. In addition, at further high pressure conditions the mechanical properties deteriorate: the films become soft (for 50 and 100 W). The increase in deposition rate with increasing pressure in lower pressure region is associated with the increase in the number density of source gas molecules. The decrease with increasing pressure in the higher pressure region may be due to the decrease in d.c. self-bias voltage on the cathodic electrode, because the deposition rate depends on the cathode self-bias voltage, as reported previously [6]. The deposition mechanism for hard carbon film deposition will be discussed in detail elsewhere [7]. 3.2. Internal film stress measurements The internal stresses in the hard carbon films were measured using both strip-shaped and round (Fig. 2) silicon substrates, as mentioned previously. When the thicknesses of the substrate and the film are the same for both of the substrates, the following relationship can be obtained from eqns. ( 1) and (2): 6 1 2=$R
(4)
Figure 4 shows the 1/2R US. d/L2 relationship for compressive stress of the hard carbon films of different
60
N. Mutsukura
et al. I Mechanical
proprrtirs
of izydrogenared C
1.5 +/f
1oow
kc
1.0 -
P-P
: _
%
p
2oow
.
!
iii 0.5
i c,
. 0
I
G/~21(io-zcm-‘)
I
2
Fig. 4. The relationship between 1/2R and (5/L* values on diamondlike films. measured using both round and strip-shaped silicon substrates.
film thicknesses deposited under the conditions of 13 and 40 Pa of CH, and 200 W r.f. power. The result obtained indicates a relationship of the form of eqn. (4). Above 1 x 1O-2 cm-‘, however, the 1/2R value tends to saturate. This is due to the limitation of the expansion in concave substrate, so this round substrate will be suitable for measurements with a relatively large radius of curvature on the substrate. In this experiment, the dimensions of the round substrate are as follows: diameter I of the substrate, 3 cm; thickness of the substrate t,, 80 urn; distance d between the two gold electrodes, 7.7 urn (see Fig. 2). The strip-shaped substrate has a thickness t, = 80 urn and a length L = 2 cm. The capability of our silicon substrate depends on the values of I, t and d. The sensitivity of the film stress measurement increases with the decrease in the d value. The type of the stress, tensile or compressive, can be easily recognized by a change in the electrical capacitance after deposition. In the measurements on the carbon films this silicon substrate was used repeatedly, because the deposited carbon films can be removed quite easily in an 0, discharge plasma. The greatest advantage of our round substrate is that in situ measurement is possible without any modifications to the film deposition chamber. Figure 5 shows the compressive stresses of carbon films deposited under various CH, gas pressures for two r.f. input powers (100 W and 200 W). The film thickness is about 100 nm for all the films. In the calculation of the stress, a value of 1.8 x 10” Pa is used for the E/( 1 - v) value of the silicon substrate [8]. For the 100 W input r.f. power, the stress increases with the decrease in the pressure. The films deposited at pressures above 40 Pa were polymer-like soft films, and others obtained below 40 Pa were hard films. The formation of the hard films depends strongly on the kinetic energy of ions bombarding the substrate on the cathodic electrode during film deposition. Zou et al. [6] have reported that the hard carbon films were obtained
0
’
I
L”ll’l’
PRSESSURE 10
50
101
(Pa)
Fig. 5. The internal gas pressure during
stress in diamond-like the deposition.
films as a function
of CH,
o.61
05
50 PRESSURE
100
(Pa)
Fig. 6. The d.c. self-bias voltage on the cathodic function of CH, gas pressure during the deposition.
electrode
as a
in the range lOOV
N. Mutsukura et al. 1 Mechanical properties of hydrogenated C
---DLC
(400A)
-Cr(2000A) :.:.:.:.
‘.:.;.~~~~.~..;.~?~~
. . . ..
cwyluruuyu
.:
$$$-Ni_P(lO_2Oym) z:::::::. (textured
-Al
or polished)
alloy
Fig. 7. The structures of 3.5 in hard disks with diamond-like films used for the measurements of the friction coefficients of the diamondlike films.
3.3. Friction coeficient measurements The friction coefficients of the hard carbon films on the hard disks were measured in two kinds of conditions at which the disk rotation speeds were 1 and 100 rev min’. The measurements were carried out using two kinds of hard disks having textured or polished surfaces, shown in Fig. 7. In the measurements for a rotation speed of 1 rev min-‘, the magnetic head (9.5 gf weight) contacts the disk surface at regular intervals during the 60 min measurement. For the 100 rev min’ rotation speed, the magnetic head touches continuously for 60 min. Figure 8 shows the behavior of the friction coefficient during the measurement using the textured surface disk. The friction coefficient increases with the
Initial
Fig. 8. The behaviors measurement period.
of the friction
61
elapsed time. This may be caused by the generation of microscopic cracks and/or the peeling off of the hard carbon films as a result of a lower adhesive strength between the film and the hard disk surface. Table 1 indicates the friction coefficients of the films initially and at the end of the 60 min measurement for both 1 and 100 rev min’ disk rotation speeds. The measurements were carried out for both the textured and the polished disks. The hard carbon films were deposited at 4 Pa CH, pressure and 100 W r.f. power, and the film thickness was about 40 nm. The friction coefficients of these films are very low compared with those of the r.f. sputtered film, as indicated in Table 1.
4. Summary The hydrogenated hard carbon films prepared by plasma deposition in a CH, r.f. discharge were examined in terms of the internal film stress and the friction coefficient. The film stress was measured using a specific round silicon substrate developed in this work. The substrate is fabricated with both convex and concave silicon wafers, and the stress was estimated from the change in the electrical capacitance between two parallel electrodes formed inside the silicon substrate.
60 mins passed
coefficients
of the diamond-like
films for
1 and 100 re:V min- ’ disk rotation
speeds,
during
a 60 min
62
N. Mutsukura
TABLE I. Friction coefficients of hard carbon both I and 100 rev min-’ disk rotation speeds Substrate
Friction
et al. / Mechanical
films measured
at
coefficient
properties
qf‘hydrogenatcd
C
of the measurement. This was thought to be associated with less adhesive strength between the hard carbon film and the disk surface.
100 rev min-’
I rev min-’
Acknowledgments Initial
After 60 min
Initial
After 60 min
Textured Polished Textured“
0.09 0.17 0.38
0.39 0.53 I .33
0.13 0.20 0.44
0.43 0.80 I .45
“r.f. sputtered
hard carbon
This work was partially supported by a research grant of Nippon Tylan Co. Ltd. The authors wish to thank Dr. Yamagata of Denki Kagaku Kogyo Co. Ltd. for the measurements of the friction coefficients.
film.
References The internal film stress was compressive for all the films deposited in the examined 4-70 Pa CH, pressure region. The film stress depends strongly on the d.c. self-bias voltage on the cathodic electrode in the CH, discharge during film deposition. This increases with the increase in the self-bias voltage, and then tends to saturate at around 1 GPa of internal stress. At very large self-bias voltages, the film stress decreases. This is due to the change in the film structure. The internal stress of the hard carbon film deposited in this work was in range 0.5-1.5 GPa. The friction coefficients between the hard carbon films deposited on hard disks and a magnetic head were measured for 1 and 100 rev min-’ disk rotation speeds. The friction coefficient became large at the end of the measurement for 60 min compared with that at the start
I S. Aisenberg and R. Chabot, J. Appl. Phys., 42 (1971) 2953. 2 C. Weissmantel, G. Reisse, H.-J. Erler, F. Henny, K. Bewilogua, U. Ebersbach and C. Schurer, Thin Solid Films, 63 ( 1979) 315. 3 P. Oelhafen, J. L. Freeouf, J. M. E. Harper and J. J. Cuomo. Thin Solid Films, 120 ( 1984) 231. 4 Y. Catherine and P. Couderc. Thin Solid Films, 144 (1986) 265. 5 K. Kobayashi, N. Mutsukura and Y. Machi, Thin Solid Films, 158 (1988) 233. 6 J. W. Zou, K. Reichelt, K. Schmidt and B. Dischler, .I. Appl. Phys., 65 (1989) 3914. 7 N. Mutsukura. S. Inoue and Y. Machi, J. Appl. Phy.‘., in the press. 8 W. A. Brantley, J. Appl. Phys., 44 (1973) 534. 9 X. Jiang, J. W. Zou, K. Reichelt and P. Grunberg, J. Appl. Phys., 66 ( 1989) 4729. 10 J. W. Zou, K. Schmidt, K. Reichelt and B. Dischler, J. Appl. Phys., 67 (1990) 487. 1 I P. Couderc and Y. Catherine, Thin Solid Films. 146 (1987) 93.