Abstract
Metal oxide semiconductor (MOS) capacitors that incorporated high κ materials of HfO2 and Al2O3 are fabricated by Molecular beam epitaxy (MBE) and Atomic layerdeposition (ALD) on Silicon and InGaAs substrates. The achievements in this work are to minimize the thickness of the interfacial layer at oxide/semiconductor and attainsub-nanometer equivalent oxide thickness (EOT) value in the MOS diodes. In Silicon phase, MBE grown high κ dielectrics of Al2O3 and HfO2 are employed as templates to suppress effectively the oxide/Si interfacial layer formation during the subsequent ALD Al2O3 and HfO2 growth. The nearly absence of the interfacial layer was confirmed using angle-resolved x-ray photoelectron spectroscopy (AR-XPS) andhigh resolution transmission electron microscopy (HR-TEM). The first two composite films consisting of ALD-Al2O3(1.9nm)/MBE-Al2O3(1.4nm) and ALD-Al2O3(3.0nm)/MBE-HfO2(2.0nm) showed overall dielectric constant (κ) of 9.1, 11.5; EOT of 1.41, 1.7nm; interface trap density (Dit) of 2.2, 2×1011 cm-2eV-1; and a leakage current density of 2.4×10-2 A/cm2 at VFB-1V and 1.1×10-4 A/cm2 at VFB+1V, respectively. In addition, to further enhance the dielectric constant and reduce the EOT value of gateoxide, the ultra-thin composite film with structure of ALD-HfO2(1.4nm)/MBE-HfO2(1.5nm) has been employed and demonstrated a κ value of 16.2, an EOT of 0.7 nm with a leakage current density of 5.3×10-1 A/cm2 at VFB-1V and Dit value of 3.6×1011 cm-2eV-1 at mid-gap calculated by conductance method. The attainment of high dielectric constants in these composite oxides suggests that no low κ capacitor in series near the oxide/Si interface.In III-V phase, ALD grown high κ dielectric HfO2 films on air-exposed In0.53Ga0.47As/InP (100), using Hf(NCH3C2H5)4 (TEMAH) and H2O as the precursors,were found to have an atomically sharp interface free of arsenic oxides, an important aspect for Fermi level un-pinning. A careful and thorough probing, using high-resolution AR-XPS with synchrotron radiation, however, observed the existenceof Ga2O3, In2O3, and In(OH)3 at the interface. The current transport of the metal-oxide-semiconductor capacitor for an oxide 7.8 nm thick follows the Fowler-Nordheim tunneling mechanism and shows a low leakage current density of~10-8 A/cm2 at VFB+1V. Well behaved frequency-varying capacitance-voltage curves were measured and an interfacial density of states of 2×1012 cm-2eV-1 was derived. Aconduction-band offset of 1.8±0.1 eV have been determined using the current transport data.A capacitive effective thickness value (CET) of 1.0 nm has been achieved in ALD high κ dielectrics HfO2 on In0.53Ga0.47As/InP. The key is a short air exposureunder 10 min between removal of the freshly grown semiconductor epi-layers and loading to the ALD reactor. This has led to minimal formation of the interfacial layerthickness, as confirmed using HR-XPS and HR-TEM. The measured electrical characteristics of metal-oxide-semiconductor diodes of Au/Ti/HfO2(4.5nm)/In0.53Ga0.47As showed a low leakage current density of 3.8x10-4 A/cm2 at VFB+1V,which is about 8 order of magnitudes lower than that of SiO2 with a same CET. The capacitance-voltage curves show an overall κ value of 17-18, a nearly zero flat bandshift, and an interfacial density of states Dit of 2×1012 cm-2eV-1 at mid-gap.