CHEMICAL VAPOR DEPOSITION OF THIN FILM MATERIALS FOR ...

In a typical in-situ ATR-FTIR experiment, the bubbler with loaded TDMAH was kept in
an oil bath at 60˚C. Around 20 min of stabilization is needed before introduction of the gas phase
precursor into the ATR cell. No carrier gas was used in the experiments. The ATR cell, as shown
in the bottom of Fig.22, uses a trapezoidal shaped crystal for enhanced surface sensitivity via
multiple internal reflections of the IR beam along the long parallel faces of the crystal. The front
face of the crystal is exposed to the precursor, while the IR beam enters and exits from the
angled faces of the crystal from below. In the experiment, Si (100) crystals (Ge or ZnSe crystal
for liquid drop experiment) with 45 degree bevels were mounted in a custom built flow through
cell. With a crystal size of 50×10×2mm, the incident IR beam internally reflects 13 times off the
TDMAH-adsorbed face before it reaches the DTGS (deuterated triglycine sulfate) detector
(within Nicolet TM 4700 FTIR device). The sealing of the ATR cell uses a custom made Kalrez
gasket between the cell frame and the crystal surface edges. The cell was roughly pumped
(Rotary vane pump, Edwards RV3F) to a base pressure of about 5 mtorr. The crystal temperature
could be controlled up to 250 ºC, with the limitation from excited Si phonon modes resulting in
reduced transparency of the crystal. Before each experiment, the gas delivering lines and the
ATR cell were heated to around 100˚C and purged with ultra high purity N2 for 1 hour to
minimize the water vapor concentration in the system. Once the valve between the bubbler and
the ATR cell was opened, TDMAH started flowing into the ATR cell, the computer controlled
IR spectra taking was simultaneously started. In this flowing mode, the surface adsorption and
reaction behavior were instantaneously monitored. All the IR data were taken in the IR range of
400~4000 cm -1 and averaged over 16 scans with a resolution of 4 cm -1 , which took 22 seconds
for each spectrum. The IR spectra taking was preset into an automatic mode, in which the FTIR
will take one spectrum by one spectrum until the preset number (30) of spectra was reached. A
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