Plasma-Assisted Atomic Layer Deposition of Conductive Hafnium Nitride Using Tetrakis(ethylmethylamino)hafnium for CMOS Gate Electrode Applications

Abstract

Conductive hafnium nitride films were deposited from a plasma-assisted atomic layer deposition ͑PA-ALD͒ process using a metallorganic hafnium precursor, tetrakis͑ethylmethylamino͒hafnium ͑TEMAH͒, using H 2 plasma as a reducing agent, at a substrate temperature of 250°C. The effects of radio frequency plasma pulse time and power on film resistivity, composition, and microstructure were investigated. The deposited films consisted of cubic HfN phase as shown by X-ray diffraction analysis, and the resistivity ranged from ϳ2300 to 8200 ⍀ cm depending on the plasma conditions. The most conductive films were observed to result from conditions of higher plasma power, which is attributed to microstructural modifications as well as a decrease in N:Hf ratio, which approached unity at the highest plasma powers employed. Carbon incorporation in the form of HfC x phase was shown to be beneficial in terms of improving both post-rapid-thermal-anneal stability and electrical conductivity. A midgap work function ͑4.63 eV͒ was obtained for a HfN x electrode structure integrated into a metal-oxide-semiconductor capacitor featuring a SiO 2 dielectric.

Plasma-assisted atomic layer deposition of HfNx: Tailoring the film properties by the plasma gas composition

“…19 Note that thermal decomposition of TEMAH was observed at a stage temperature above 250 C. 19 On the other hand, low resistivity d-HfN x films (2.3 Â 10 À3 X cm) were obtained by Consiglio et al using Ar-H 2 mixed plasma and the same precursor (TEMAH) in a plasma-assisted ALD processes. 20 Using TDMAH, similar results were also reported by Kim et al with a N 2 -H 2 mixed plasma yielding a resistivity of 6.7 Â 10 À3 X cm for 14 nm film. 21 These studies demonstrate the requirement of highly reducing H 2 plasma species to achieve the conductive fcc d-HfN phase.…”

“…In the case HfN x films reported earlier, 20,21 very low O at. % can justify the realization of conductive d-HfN films with low resistivity.…”

“…-10 À3 X cm), either the O should be reduced which would therefore promote the presence of the Hf 3þ fraction 20,21 and/or the grain size has to be increased.…”

“…Supreme thickness controllability and conformality achieved by atomic layer deposition (ALD) has been demonstrated on high surface area materials such as silica gel [12][13][14][15] and nanopowders. [16][17][18] Some works on ALD of HfN x have already been reported in the literature [19][20][21] and are summarized in Table I. Becker et al reported the growth of insulating Hf 3 N 4 films by employing tetrakis(ethylmethylamino)hafnium (TEMAH) as the precursor and NH 3 as the coreactant in a thermal ALD process, demonstrating the low reduction potential of NH 3 .…”

“…21 These studies demonstrate the requirement of highly reducing H 2 plasma species to achieve the conductive fcc d-HfN phase. 20,21 The extent of Hf 4þ reduction (in the precursor) to Hf 3þ (in the film) by H 2 plasma species was not specifically addressed, and thus far, a comprehensive study of the influence of variable plasma conditions and gas composition on In such heteroleptic precursors, the Cp functional group imparts high thermal stability to the precursor, thus enabling a larger temperature window while minimizing precursor decomposition.…”