Dielectric ALD with Hydrogen Peroxide: Comparative Study of Growth and Film Characteristics for Anhydrous H2O2, H2O2/H2o Mixtures, H2o and Ozone
Authors: Alvarez Daniel , Spiegelman Jeffrey , Andachi Keisuke , Tsuchibuchi Gaku , Suzuki Katsumasa 
Published: February 2020

ALD of dielectrics requires new precursor chemistries. Recent development efforts have focused on new Organometallic, Organosilicon and Organoaluminum precursors. Our research focus has been on oxidants, and specifically hydrogen peroxide reactivity. Due to this reactivity, hydrogen peroxide use may allow lower deposition temperatures and achieve distinct properties in the resulting film when compared to other oxidants. Our research study uses:

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.

Initial results for ALD growth of ZrO2 from anhydrous H2O2 and CpZr(N(CH3)3) exhibit high quality growth of film at 260° C. Minimal saturation delay and a linear growth curve were observed. XPS and XRR were used to characterize ZrO2 composition, showing significant similarities to films grown using ozone. Subsequently, films grown using ALD and H2O2 were placed into MIMCAP structures, which had high k values measured at 35. This was a slight improvement over films grown with 20% ozone concentration which had high k values of 32.

Novel Gas Generator

Our approach involved development of a novel gas generator that delivers H2O2/H2O mixtures. A carrier gas is connected to this generator, which delivers up to 5% H2O2/21% H2O gas by volume from 30wt% H2O2 liquid solution (H2O/H2O2=4.2). This gas mixture enables SiO2 films to be grown at highly reduced temperature compared to water. Initial testing was done with tris(dimethylaminosilane) (N(CH3) 2) 3SiH and H2O2/H2O. SiO2 was deposited at temperatures at least 200° C lower with the hydrogen peroxide mixture than with water.

Titanium dioxide ALD is of interest for several applications. The unique properties of this material make it an attractive candidate for advanced patterning applications. Here, low temperature deposition is required (100-250° C). Key required properties of the resultant film include film density and wet etch rate, where low wet etch rates are needed for selective etching of SiO2 vs TiO2. Moreover, high growth per ald cycle (GPC) is needed for increased manufacturing throughput.

For TiO2 ALD, we began our study with tetrakis(dimethylamino)titanium (TDMAT) precursor. Our initial goal was to compare the growth and film properties of Ozone (O3) vs Water (H2O) vs H2O2/H2O mixtures. Initial results show that H2O2/H2O mixtures can be grown at growth rates (GPC) 10-20% higher than H2O and 20-50% higher than O3. More significantly, the H2O2/H2O mixtures generate films with wet etch rates (WER) much lower than the traditional oxidants. At 125° C , over 50% reduction in WER was observed for H2O2/H2O vs H2O and over 70% reduction was observed for H2O2/H2O vs O3. Additional comparision data will be reported on wet etch rates, refractive index and composition. Initial composition results by XPS show that residual carbon and nitrogen for the H2O2/H2O film grown at 125° C are non-detectable vs 1.1% carbon and 1.1% nitrogen for Ozone at 125° C. Compositional correlations will be made with respect to wet etch rates.

Figure 1