Interactions of Evaporated Nickel and Silicon Thin Films
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In order to understand how Ni reacts with Si*, we carried out a systematic study of the phase sequence, the identity of the moving species and the stability of the phase NiSi 2 under various experimental conditions. EXPERIMENTAL Different types of samples were prepared on chemically clean Si or SiO substrates. All films were deposited in a dual electron-beam evaporator wit•i pressures prior to deposition of about 2 x 10-9 torr, rising to a maximum of 1 x 10torr during the evaporation process. Desired layered structures In were prepared by sequential evaporation of the materials of interest. alloyed samples were made by simultaneous electron-beam some cases evaporation. The Ni and Si evaporation rates were monitored independently through a feedback system which kept the rates constant. The deposition The rates for rates for Ni 0Si 0 were 5.5 A/sec of Ni and 10 A/Sec of Si. were 2.ý A/sec of Ni and 10 A/sec of Si. Ni 3 4 Si S 1ver was chosen as a marker in determining the diffusing species during Ni Si formation, because it was successfully used to study NiSi formd it broadened at relatively high However, on Si(100) substrates [111.
Mat. Res. Soc. Symp. Proc. Vol. 54. • 1986 Materials Research Society
46
temperatures, thus a thin Ta marker was used in NiSi and NiSi 2 formation. Annealing was carried out in a vacuum furnace at pressures below 3 x 8 10- torr. The compositional depth profiles were measured by Rutherford The crystal structure and microstructure backscattering spectrometry (RBS). of the growing phase were investigated by transmission electron microscopy
(TEM). RESULTS Phase Sequence The formation of nickel silicide between Ni and SiO in the structure A)/Ni(875 A) exhibits a sequential growth of three phases (Fig. 1). The phase Ni Si was initiated at temperatures of 250-300 0C and transformed to NiMi after the consumption of the entire Ni film. At 450 0 C NiSi was formed at the interface between NiSi and Si*. Prolonged annealing resulted in the completion of NiSi 2 formation and segregation of the unreacted Si in the NiSi 2 matrix. Si0 2/Si(32OO
Energy (MeV) 1.0
1.5
251
20
2.0
2.5
I
-Si02/Si(o)/Ni
AS-DEPOSITED
3MeV He
-" -
350C
45'
4OOC 450C
.....
30min
30mrin 30min
Tlt
E10 10
I
Ir
z
I
o'-
01 200
250
300
350
400
450
500
550
Channel Fig.l RBS spectra of Si0 2/Si/Ni before and after annealing at various temperatures. Diffusing Species A
Ni Si
The
initial
samples
consisted
of
5ooo /Si(2200 A)/Ag(7 A)
2 .i2 the backscattering /Si(l00 A. A)/Ni(1300 A). Fig. 2 shows spectra of the samples before and after thermal annealing. After heat treatments at 30000 for 30 m, a layer of vi was formed with a configuration SiO2/Si(1600 A)/Ni 2 Si (940 A)/Ag(7 A) /Ni 2 Si(220 A)/Ni(550 A). Annealing at 325 0C for 30 min completed the formation of Ni 2Si. The maker position had shifted to high energies, corresponding to a position 250 A deep in the silicide. As the marker position did not concide with the phase boundaries, the displacement of the marker can only be described as being
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