Atomic Layer Deposition of Metal Oxide Films on GaAs (100) surfaces

Abstract

Atomic Layer Deposition is used to deposit HfO2 and TiO2 films on GaAs (100) native oxides and etched surfaces. For the deposition of HfO2 films two different but similar ALD chemistries are used: i) tetrakis dimethyl amido hafnium (TDMAHf) and H2O at 275°C and ii) tetrakis ethylmethyl amido hafnium (TEMAHf) and H2O at 250°C. TiO2 films are deposited from tetrakis dimethyl amido titanium (TDMATi) and H2O at 200°C. Rutherford Back Scattering shows linear film growth for all processes. The film/substrate interface is examined using x-ray Photoelectron Spectroscopy and confirms the presence of an “interfacial cleaning” mechanism.

Decomposition of Metal Alkylamides, Alkyls, and Halides at Reducible Oxide Surfaces: Mechanism of ‘Clean-up’ During Atomic Layer Deposition of Dielectrics onto III–V Substrates

“…Indeed, this ligand transfer mechanism has been proposed by others , to explain the clean-up effect. Experimental study clearly shows enhancement of the clean-up process with increasing temperature when metal alkylamides are used. , Even though the first step of the ligand exchange reaction is extremely facile, both thermodynamically and kinetically, significant kinetic requirements may originate from steric effects in subsequent steps. There was evidence for this in our previous study for TMA, where we showed that the rate limiting step for the ligand transfer process could be crowding of methyl ligands at one surface site .…”

“…First reports on the clean-up effect documented an effective passivation of GaAs-based substrates with trimethylaluminium (TMA or AlMe 3 ; where Me = CH 3 ) when depositing Al 2 O 3 . For HfO 2 ALD, the clean-up effect was observed mainly when using hafnium alkylamides, with similar behavior shown by tetrakis(ethylmethylamido)hafnium (TEMAH or Hf(NEtMe) 4 ; where Et = C 2 H 5 ) or tetrakis(dimethylamido)hafnium (TDMAH, Hf(NMe 2 ) 4 ). ,, A recent study shows that ALD processes utilizing alkylamide precursors featuring Ti (tetrakis(dimethylamido)titanium, TDMAT, Ti(NMe 2 ) 4 ) or Ta (pentakis(dimethylamido)tantalum, PDMAT, Ta(NMe 2 ) 5 ) also result in the same interfacial cleaning effect while depositing TiO 2 or Ta 2 O 5 , respectively. , These observations indicate that the common requirement for self-cleaning is the use of organometallic or metalorganic precursors. However, the examples of the purely inorganic HfCl 4 and TiCl 4 ALD processes contradict this assumption.…”

“…The early stages of ALD growth determine the interface properties and therefore careful optimization of deposition conditions helps with improving device performance. An interfacial cleaning mechanism that results in consumption of semiconductor native oxides and in practically sharp dielectric/semiconductor interfaces has been observed during ALD of Al 2 O 3 , HfO 2 , TiO 2 , and Ta 2 O 5 on GaAs and InGaAs. This has been called ‘clean-up’ or ‘self-cleaning’.…”

“…Accumulation of metallic arsenic–arsenic suboxide at the interface has been observed for TMA based ALD and alkylamide based ALD . It seems that elevating the temperature of the process significantly enhances the clean-up abilities of alkylamides, and this differentiates these processes from TMA-based clean-up. , Granados-Alpizar and Muscat show differences in surface reactions during GaAs exposure to TMA and TiCl 4 pulses: both precursors remove the native oxide layer, but the mechanisms underlying this process seem to be fundamentally different. TMA deposits an Al 2 O 3 layer and removes a portion of As from the surface, whereas TiCl 4 removes O and leaves the surface passivated with Cl atoms.…”

Hybridization and localized flat band in the WSe2/MoSe2 heterobilayer

“…Similarly, to the Mo 3d peak, the W 4f peak (Figure 2(e)) presents two doublets (W 4f7/2 and W 4f5/2 with a SO splitting = 2.15 eV): the first one is related to stoichiometric WSe2 44 with the W 4f7/2 component at a BE of 32.7 eV; the second one at lower BEs (-0.40 eV) corresponds to defective/substoichiometric WSe2 52 . In all spectra, we find no signature of any additional component (e.g., carbon or oxygen bounds) [53][54][55] , indicating that our samples are not contaminated. Moreover, the absence of extra peaks indicates that there is no covalent bond between MoSe2 and WSe2.…”