Optimization of Sputtering Parameters of Co2FeSi Thin
Films by Taguchi Design of Experiments.
K. Srinivas1*, L. Sarvanan2, M. Manivel Raja1, S. Arumugam2, S.V. Kamat1
1
Defence Metallurgical Research Laboratory, Hyderabad - 500059, India.
2
School of Physics, Bharthidasan University, Tiruchy- 605014, India
*
Corresponding author’s e-mail:kuchanasrinivas@gmail.com.
Abstract
Results and discussion
Taguchi design of experiments was used to determine
and optimize the largest influencing sputtering parameters
on the surface roughness and magnetic properties of asdeposited Co2FeSi thin films. A new process recipe yielded
a desired film with a minimum surface roughness of ~ 1
nm, saturation magnetization of 1190 emu/cc and
coercivity of 7 Oe.
In the present investigation, Taguchi-L9 (34)
design was employed .The experimental data was
subjected to ANOVA for each specific film to select the
significant level of the process parameter and to
understand the magnitude of the influence of each
variable had on the properties mainly surface roughness,
coercivity, saturation magnetization and grain size of
the films. Table 1 shows a typical ANOVA result for
surface roughness of the films for which smaller – thebetter is the desired characteristic.
Keywords: Heusler thin films, Sputtering, Design of
Experiments.
Introduction
Recently, Co2FeSi based alloys have evinced
much interest due to their high Currie temperature (T C
~1100 K) and high magnetic moment (~6 μB/f.u) along
with its half-metallic ferromagnetic nature for magnetic
tunnel junction (MTJ) applications. However, an
extremely high value of tunneling magneto-resistance
(TMR) can be achieved only if the Co2FeSi films have
stable L21 ordered structure which shows halfmetallicity. In addition to these, low surface roughness,
low switching fields and fine crystallite size for a given
thickness also play a crucial role. All these film
characteristics mainly depend on the film deposition
conditions and stoichiometry. Since the optimization of
sputtering processes typically involves a large number
of factors, design of experiments (DOE) technique is
well-suited to obtain desired properties with less
experimental runs [1]. Therefore, a systematic study of
DOE for the optimization of sputtering parameters of
the Co2FeSi thin films has been undertaken.
Experimental
Co2FeSi thin films were deposited on Si (100)
substrate by using UHV magnetron DC sputtering. To
perform Taguchi design of experiments [1], four factors
viz. sputtering power (50-150 W), sputtering pressure (3
-15 mTorr), deposition time (5- 20 min) and substrate
temperature (30-450 0C) with three different levels were
chosen (L9 - (34)). Thickness, surface roughness,
composition, crystal structure and field dependent
magnetization measurements were undertaken for the
films obtained from each experimental run. The validity
of optimum conditions was verified by regression
analysis and by experimental test.
Table 1: ANOVA results for surface roughness of thin
films (smaller is best).
Sputtering df
Sum of Mean
%
Condition
Square Square Contribution
(SS)
Power
2
38.0
19.0
31.43
Pressure
2
31.6
15.8
26.12
Deposition
Time
TS
2
24.5
12.3
20.24
2
43.5
21.8
35.97
Error
Total
0
8
-17
121
The most important parameters influencing surface
roughness are found to be substrate temperature and
sputtering power. From the complete analysis of all
ANOVA results, the optimum parameters to obtain
stoichiometric films with low coercivity and low surface
roughness with high saturation magnetization were
found to be 150 W and 3 mTorr at 100 0C substrate
temperature.
Conclusion
DOE study on the optimization of the DC
magnetron sputtering conditions for fabricating Co2FeSi
thin films showed that the lowest coercivity (7 Oe ) and
highest saturation magnetization (1190 emu/cc) at
surface roughness 1nm were obtained
for films
deposited on Si substrate at 100°C using 150 W power
and 3 mTorr pressure.
References
[1] G. Taguchi, S. Chowdhury, and Y. Wu, Taguchi’s
quality engineering handbook, John Wiley & Sons
(2004).