Atomic layer deposited high-k gate dielectrics for III-V based metal-oxide-semiconductor field effect devices [electronic resource]
Keywords: Materials Science and Engineering.

III-V compound semiconductor channels coated by high-k dielectrics are the subject of intense interest for high performance metal-oxide-semiconductor (MOS) devices beyond the 11nm technology node. In0.53Ga0.47As and atomic layer deposited (ALD) Al2O3 are among the leading candidates for high-[kappa]/III-V n-channel MOS devices because of their high electron mobility and relatively low interface defect density compared to other deposited dielectrics. However, preventing formation of native oxides and developing a stable interface with a lower density of electrically active defects have been a long-standing challenge for III-V based MOS field-effect devices. In0.53Ga0.47As(100) channel surfaces that were initially covered with a protective As2-layer are thermally decapped in situ in the high vacuum ALD reactor at the substrate temperature of 360 ~ 390°C. The end point of decapping is determined by observation of a completed chamber pressure pulse during As2 desorption and confirmed by the binding energy shift (−0.7 eV) of As 3d peaks measured in x-ray photoelectron spectroscopy. A substantial fraction of the initially-present interface defects and border traps can be passivated by post-metallization forming gas anneal. The gate electrode deposited by thermal evaporation appears to result in a lower metal oxide/InGaAs interface defect density than does of electron beam evaporation of the same gate metals. Thermal desorption conditions for a protective As2 layer on the surface of the as-grown InGaAs channels and dosing of trimethylaluminum (TMA) prior to Al2O3 ALD are varied to alter the interface trap densities (Dit). The InGaAs(100) decapped at 460°C shows a higher density of interface defects in the InGaAs bandgap compared to the decapping at 370°C. TMA pre-dosing (large dose of TMA prior to the start of ALD-Al2O3) reduces the Dit distribution across the bandgap of InGaAs. It is suggested that TMA needs to be dosed at low temperatures (200°C or below) when the As2 cap is desorbed at 460°C, whereas temperature independence of TMA pre-dosing is observed on the InGaAs surfaces decapped at 370°C, consistent with previously reported scanning tunneling spectroscopy results. Water vapor pre-dosing in addition to the TMA pre-dosing can suppress the conduction band edge states by removing In-Ga bonds on the InGaAs (100) surface. Gate dielectric deposition and post-dielectric thermal processing during III-V MOS device fabrication can result in undesirable chemical reactions at the dielectric/channel interface. The oxidation of an In0.53Ga0.47As (100) surface through overlying ultrathin ALD-Al2O3 layers is investigated using x-ray photoelectron spectroscopy (XPS). A strong gallium oxide (Ga2O3) feature is observed in the Ga 3p core level of the InGaAs surface after the Al2O3/InGaAs is annealed at 500°C for 20 min in oxygen. The peak intensity of Ga-oxide component is reduced as the Al2O3 thickness increases from 1 nm to 2 nm and no Ga-oxide is detected in XPS when the oxide layer is 2.5 nm thick. The InGaAs surface oxidation also occurs through a 1.2 nm Al2O3 when H2O vapor is pulsed for 10 seconds at 300°C, increasing the interface defect density across the InGaAs bandgap. ALD-HfO2 deposition on ~1 nm Al2O3/InGaAs layer can produce XPS detectable signatures of InGaAs surface oxidation. TMA pre-dosing prior to ALD-HfO2 deposition is capable of suppressing InGaAs surface oxidation. The electrical properties of ALD-TiO2/Al2O3 bilayer gate oxides which simultaneously achieve high gate capacitance density and low gate leakage current density are discussed in the last part of this dissertation. The maximum accumulation capacitance of the bilayer gate stack increases by 33 % after the FGA at 400°C for 30 min, which can be attributed to the crystallization of the initially-amorphous TiO2 film. The bilayer dielectrics reduce gate leakage current density by approximately one order of magnitude at flatband compared to Al2O3 single layer of comparable capacitance equivalent thickness. The conduction band offset of TiO2 relative to InGaAs is 0.6 eV, contributing to the ability of the stacked dielectric to suppress gate leakage conduction. TMA pre-dosing or ultrathin (~5 ALD cycles) Al2O3 layer deposition prior to ALD-TiO2 and oxygen anneal at relatively low temperature can be beneficial for reduction of the gate leakage current of the TiO2 layer.