A bottom-up process from precursor
development for tin to plasma-enhanced
atomic layer deposition (PEALD) for tin(IV) oxide and its successful
implementation in a working thin-film transistor device is reported.
PEALD of tin(IV) oxide thin films at low temperatures down to 60 °C
employing tetrakis-(dimethylamino)propyl tin(IV) [Sn(DMP)4] and oxygen plasma
is demonstrated. The liquid precursor has been synthesized and thoroughly
characterized with thermogravimetric analyses, revealing sufficient
volatility and long-term thermal stability. [Sn(DMP)4]
demonstrates typical saturation behavior and constant growth rates
of 0.27 or 0.42 Å cycle–1 at 150 and 60 °C,
respectively, in PEALD experiments. Within the ALD regime, the films
are smooth, uniform, and of high purity. On the basis of these promising
features, the PEALD process was optimized wherein a 6 nm thick tin
oxide channel material layer deposited at 60 °C was applied in
bottom-contact bottom-gate thin-film transistors, showing a remarkable
on/off ratio of 107 and field-effect mobility of μFE ≈ 12 cm2 V–1 s–1 for the as-deposited thin films deposited at such low temperatures.
A bottom-up
approach starting with the development of new Hf precursors for plasma-enhanced
atomic layer deposition (PEALD) processes for HfO2 followed
by in situ thin-film surface characterization of HfO2 upon
exposure to reactive gases via near-ambient-pressure X-ray photoelectron
spectroscopy (NAP-XPS) is reported. The stability of thin films under
simulated operational conditions is assessed, and the successful implementation
of HfO2 dielectric layers in metal–insulator–semiconductor
(MIS) capacitors is demonstrated. Among the series of newly synthesized
mono-guanidinato-tris-dialkyl-amido class of Hf precursors, one of
them, namely, [Hf{η2-(
i
PrN)2CNEtMe}(NEtMe)3], was representatively
utilized with oxygen plasma, resulting in a highly promising low-temperature
PEALD process at 60 °C. The new precursors were synthesized in
the multigram scale and thoroughly characterized by thermogravimetric
analyses, revealing high and tunable volatility reflected by appreciable
vapor pressures and accompanied by thermal stability. Typical ALD
growth characteristics in terms of linearity, saturation, and a broad
ALD window with constant growth of 1.06 Å cycle–1 in the temperature range of 60–240 °C render this process
very promising for fabricating high-purity smooth HfO2 layers.
For the first time, NAP-XPS surface studies on selected HfO2 layers are reported upon exposure to reactive H2, O2, and H2O atmospheres at temperatures of up to
500 °C revealing remarkable stability against degradation. This
can be attributed to the absence of surface defects and vacancies.
On the basis of these promising results, PEALD-grown HfO2 films were used as dielectric layers in the MIS capacitor device
fabrication exhibiting leakage current densities less than 10–7 A cm–2 at 2 MV cm–1 and permittivities of up to 13.9 without postannealing.
Email address: kasischke@lat.rub.de (Maren Kasischke) The aim of this study is to assess femtosecond laser patterning of graphene in air and in vacuum for the application as source and drain electrodes in thin-film transistors (TFTs). The analysis of the laser-patterned graphene with scanning electron microscopy, atomic force microscopy and Raman spectroscopy showed that processing in vacuum leads to less debris formation and thus re-deposited carbonaceous material on the sample compared to laser processing in air. It was found that the debris reduction due to patterning in vacuum improves the TFT characteristics significantly. Hysteresis disappears, the mobility is enhanced by an order of magnitude and the subthreshold swing is reduced from S sub = 2.5 V/dec to S sub = 1.5 V/dec.
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