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Aluminum Oxide ALD with Hydrogen Peroxide: Comparative Study of Growth and Film Characteristics for Anhydrous H2O2‚ H2O2/H2O Mixtures‚ H2O and Ozone

Jeffrey Spiegelman‚ Dan Alvarez (RASIRC); Keisuke Andachi‚ Gaku Tsuchibuchi‚ Katsumasa Suzuki (Taiyo Nippon Sanso Corporation‚ Japan)

Thermal low temperature ALD has seen a resurgence in activity due to difficulties found with plasma approaches on 3D surfaces. Hydrogen peroxide reactivity may benefit low temperature growth rates and achieve improved film properties. We studied:

· Gas-phase hydrogen peroxide‚ delivered from an anhydrous‚ ampoule-based formulation by use of a membrane delivery system.

· High concentration H2O2/H2O delivery by in situ concentration methods and use of a membrane vaporizer as a gas generator.

ALD studies on Al2O3 films have been conducted with the use of Trimethyl Aluminum (TMA). Growth rates of H2O2/H2O‚ H2O‚ H2O2 and O3 have been observed at 100-350°C. As has been reported‚ growth rates drop with increased temperature. Previous works have explained that surface de-hydroxylation occurs with increasing temperature‚ and the slope of this decrease is significantly less for anhydrous hydrogen peroxide. This can be attributed to surface re-hydroxylation with the use of dry H2O2‚ where this oxidant can easily split into hydroxy radicals HO. The overall higher growth rates for H2O2/H2O and H2O may be attributed to the increased vapor pressure of these oxidants which provides added reactant material to the substrate surface. The H2O2/H2O combination leads to the highest overall growth rate‚ where the effects of H2O2 augment the fast growth rate of water.

Initial FT-IR study was performed on films grown with H2O2/H2O and H2O; the measured signal for the hydrogen peroxide films is approximately 20% stronger. Though this measurement is somewhat qualitative‚ it implies that films grown with hydrogen peroxide have higher film density.

Composition of films grown by all four oxidant methods was measured by XPS; all films have near stoichiometric Al2O3 composition‚ within the experimental error of the instrument.

Initial wet etch rate studies (7.14% buffered HF) were performed on H2O2/H2O and H2O films grown at 200°C. In this instance‚ H2O2/H2O film has an etch rate of 69.9nm/min vs 81.5nm/min for water: a 15% improvement in etch resistance.

Electrical properties of resultant Al2O3 films have been examined. For films grown at 300C‚ Dielectric Breakdown Strength was measured. Here‚ film grown with H2O2/H2O was significantly greater than both water and ozone grown films; anhydrous hydrogen peroxide was similarly improved‚ but to a lesser degree. An analogous result was obtained when measuring leakage current.

An extensive film property data set with all oxidants will be presented in the temperature range of 100-350C. Correlations to surface chemistry will made along with suggestions on how to tailor film properties for specific applications.

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