Metals Atomic Layer Deposition Using Hydrogen Radicals
Many binary oxide and nitride materials
can be deposited using ALD techniques. In contrast, the deposition
of single-element metals is less compatible with the binary
reaction sequence chemistry that defines the ALD process.
To develop metal ALD procedures, a binary sequence can be
defined using hydrogen radicals as one of the two reactants.
The hydrogen radicals serve to strip the ligand from the metal
precursor according to the general overall reaction scheme:
MXn + nH -> M + nHX.
Our research is developing hydrogen radical
plasma sources and optimizing hydrogen radical transport for
efficient metal ALD. Hydrogen recombination to form H2 is
a significant hydrogen radical loss mechanism. The accompanying
figure shows the rapid reduction of hydrogen radicals with
transmission through a tube composed of pyrex, quartz, aluminum
or stainless steel.
Based on these results, a reactor for metal ALD has been constructed
to minimize hydrogen radical recombination. This reactor has
been employed recently to deposit various metals such as Ti
using TiCl4 + 4H ->Ti + 4HCl.
