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DEPENDENCE OF SATURATION
MAGNETIZATION OF Fe-Ti SPUTTERED FILMS
ON Ar GAS PRESSURE, SUBSTRATE
TEMPERATURE AND BIAS VOLTAGE
Satoshi Ono, Makoto Sumide, Masahiko Naoe
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C8, Supplkment au no 12, Tome 49, dkcembre 1988
DEPENDENCE OF SATURATION MAGNETIZATION
OF
Fe-Ti SPUTTERED FILMS ON Ar GAS PRESSURE, SUBSTRATE TEMPERATURE AND BIAS VOLTAGESatoshi Ono, Makoto Sumide and Masahiko Naoe
Tokyo Institute of Technology, 2-12-1, 0-okayama, Meguro-ku, Tokyo 152, Japan
Abstract. -The dependences of saturation magnetization M, of Fe-Ti sputtered films on Ti content and typical sputtering conditions were studied. The substrate temperature Ts had the most remarkable effect on Ms. Ti content of the films deposited at Ts above 300 OC was higher for M, to become zero at room temperature.
1. Introduction
It is well known that the Fe-Ti sputtered films with Ti content above about 20 at.% are amorphous and paramagnetic at room temperature [l N 31. Since the
sputtering conditions have a great influence on the morphology and crystal structure of the films, their structure and magnetic properties can be changed to some extent by controlling them.
The purpose of this study is, therefore, to clarify the relationship between saturation magnetization M, of Fe-Ti films and several sputtering conditions, us- ing a Facing Targets Sputtering (FTS) method which can precisely and independently control the sputtering conditions.
2. Experiment
The principle of FTS method is schematically shown in figure 1. Two 99.99 % pure Fe Pisks and several 99.9 % pure Ti tips were used as targets to control Ti content CT; of the films. About 7 000
A
Fel-xTix (05
X<
30 at.%) films were deposited on the ther- mally oxidized Si-wafer substrates located outside theSUBSTRATE
Fig. 1. - Principle of FTS method.
plasma which is confined between the targets by the magnetic field applied normal t o the target plane. This sputtering method can, therefore, deposit films on the plasma-free substrates.
The dependences of magnetic properties on Ar gas pressure PA, of 0.8 N 7 m Torr, substrate temperature
Ts of 25 N 400 O C and bias voltage to substrate
VB
of0 N 150 V were studied. Magnetic properties at room
temperature were determined on the hysteresis loops observed with VSM. Microstructure was observed with SEM and TEM and crystal structure was analyzed by X-ray diffractometry.
3. Results and discussion
Figure 2 shows the dependence of saturation magne- tization M, of the films deposited at various PA, on Ti content CTi. The Ms depended little on PA,, decreased gradually with an increase of C T ~ from 0 to 17 at.% and abruptly vanished at CT~ of about 20 at.% . The films with C T ~ in the range of 17 20 at.% may be com- posed of Ti-poor bcc Fe crystallites and Ti-rich amor- phous matrix. X-ray diffractometry indicated that the (110) plane of the crystallites was preferentially ori- ented parallel to film plane and disappeared also at CT~ of about 20 at.%
. These results suggest that all
the films with CTi of about 20 at.% deposited at var- ious PA, are amorphous and paramagnetic at roomTi content (at. %I
Fig. 2. - Relationship between Ti content and M, of the films deposited at various PA,
C8
-
1748 JOURNAL DE PHYSIQUEtemperature, being in accordance with the results in other works [I
-
31.On the other hand, the M, depended much on T,,
as shown in figure 3. The M, of the film deposited at
T, of 200 OC became zero a t lower CT; than that at
T, of 25 OC. It may be attributed to the good mix-
ing of Fe and Ti atoms due to the higher mobility of adatoms at higher T,. The further increase of T, to
300 and 400 OC lowered the M, of the films with CTi
in the range from 5 to 20 at.% and shifted the C T ~ for zero M, to a higher side. Too high T, may promote
the mixing of Fe and Ti atoms in the films with low CTi, but cause the crystallization of amorphous ma- trix and the precipitation of intermetallic compounds in the films with high CTi. These results could be use- ful for explaining the dependence of M, on CTi at T,
above 300 OC.
Ti content (at .'I. f
Fig. 3. - Relationship between Ti content and M, of the films deposited at various T,.
Figure 4 shows the dependence of M, on CT; as a parameter of VB. The dependence of M, on C T ~ was similar to that on T,. The biasing of substrate can
cause the ~ r + ion bombardment onto the growing film. Consequently, Arf ions assist the adatoms to move at a high mobility on the surface of substrate and film. The films deposited at VB of
-
30 and - 90 V may be, therefore, given the good mixing of Fe and Ti atoms to the same extent in the films at T, of 200 OC. However, X-ray diffractometry indicated that too high VB of the order of-
150 V could cause the segregation of TiTi content ( at%
Fig. 4. - Relationship between Ti content and M, of the films deposited at various VB.
atoms in the amorphous matrix, resulting in a small shift of C T ~ for zero M, to a higher side.
4. Conclusions
The dependences of saturation magnetization M, of
Fe-Ti sputtered films on Ti content and several sput- tering conditions were studied. The following results were obtained:
(1) M, depends little on Ar gas pressure PA, in
the range from 0.8 to 7 mTorr. All the films with Ti content CT; of about 20 at.% become amorphous and paramagnetic at room temperature.
( 2 ) M, depends much on substrate temperature
T,
and bias voltage VB. The films deposited at T, of
200 OC and VB of
-
30 and-
90 V have lower CT~ for zero Ms. On the contrary, the further increase ofT, and VB shifts the C T ~ for zero M. to a higher side.
These could be explained by the mobility of adatoms in the amorphous matrix, and the precipitation of in- termetallic compounds seems to also affect the depen- dence of M, on CT~.
[l] Sumiyama, K., Hashimoto, Y. and Nakamura, Y.,
Trans.
J I M
(1983) 61.[2] Liou, S.
B.
and Chien, C. L., J. Appl. Phys. 55 (1984) 1820.[3] Tamai, H. and Tagarni, K., IEEE Trans. Magn.
