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In Abb. 32 sind die wesentlichen Ergebnisse der elektrischen
Messungen zusammengestellt. Die dielektrischen
Konstanten der untersuchten Dielektrika werden in
Abb. 32(a) miteinander verglichen. Der k-Wert von monoklinem
HfO 2 ist ungefähr 19 und somit in guter Übereinstimmung
mit veröffentlichten Daten. Durch Hinzumischen
von Ba kommt es zu einer leichten Erhöhung
der Dielektrizitätskonstante, so dass ein Wert von ~ 23
für amorphes BaHfO 3 erhalten wird. Die Kristallisation
in die c-BaHfO 3 -Phase, nachgewiesen durch XRD, wird
durch einen abrupten Anstieg der Dielektrizitätskonstante
auf 38 begleitet.
In Abb. 32(b) ist der Einfluss der RTA-Behandlung auf
die Leckströme in BaHfO 3 -Proben dargestellt. Amorphe
BaHfO 3 -Schichten erfüllen die DRAM-Leckstromerfordernisse
(J < 10 -8 A / cm 2 @ 1 V) für CET-Werte herunter
bis zu ~ 2 nm. Die RTA-induzierte Kristallisation
dieser Schichten ergibt eine signifikante Verringerung
von CET infolge einer verbesserten Dielektrizitätskonstante
und einer Verdichtung der dielektrischen Schicht.
Abb. 32: Vergleich zwischen m-HfO 2 , a-BaHfO 3 und c-BaHfO 3 .
Fig. 32: Comparison between m-Hfo 2 , a-BaHfo 3 , and c-BaHfo 3 .
A U S G E w ä H L T E P R O J E K T E – S E L E C T E d P R O J E C T S
In Fig. 32, the main results of the electrical measurements
are summarized. the dielectric constants of
the investigated dielectrics are compared in Fig.
32(a). the k-value of the monoclinic Hfo 2 is approx.
19, which is in good agreement with published data.
Admixture of Ba results in a slight increase of the
permittivity yielding a value of approx. 23 for amorphous
BaHfo 3 . Crystallization in the c-BaHfo 3 phase
detected by XRD is accompanied by an abrupt increase
of the dielectric constant to 38.
In Fig. 32(b), the influence of the RtA treatment on
leakage currents in BaHfo 3 samples is shown. Amorphous
BaHfo 3 layers meet the DRAM leakage current
requirement (J < 10 -8 A / cm 2 @ 1 V) for Cet values
down to approx. 2 nm. RtA induced crystallization of
these films results in a significant reduction of the
Cet due to improved dielectric constant and densification
of the dielectric film. At the same time, however,
a substantial increase in the leakage current density
is observed. leakage current characteristics of
thin c-BaHfo 3 layers were further investigated using
temperature dependent measurements summarized
in Fig. 33 showing leakage JV curves measured for
an about 8 nm thick film at different temperatures
under tin substrate injection. the currents detected
at lower voltages are noisy and show only weak temperature
dependence. Given the voltage dependence
and the magnitude of these currents, we suppose that
they are associated with macroscopic defects (“hot
spots”), but any specific characterization of these defects
is difficult at this stage of research. on the other
hand, it seems to be clear that leakage currents in the
higher voltage range are dominated by point defects
presumably also associated with some hot spot areas.
In this strongly temperature dependent leakage regime,
the concentration of carriers is determined by
carrier trapping and detrapping, with voltage dependence
resembling a poole-Frenkel process.
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